Mechanika 2007

Indian Institute Of Technology Guwahati

Mechanical Engineering Students’ Association

Mechanika

2007

Encouraging scientific spirit by spreading scientific knowledge

MESA

MECHANIKA 2007 Edition

MESA Faculty adviser Dr. Niranjan Sahoo President Deepak Kumar Vice President Vijay Kumar Verma

EXECUTIVE MEMBERS Deepak Kumar Vijay Kumar Verma Alok Verma Rohit Mittal Palle Raghavendra Prasad Priyesh Sinha Sourabh Agarwal Neeraj Carpenter D. N. Vadiraja Atul Kumar Soti

COMMITTEES IN MESA Publication Committee Alok Verma (Secretary) Nishant Prakhar Adarsh Bikash Saikia Debendra Bahadur Singh Dharua Govind Mohan Activity Group Rohit Mittal (Secretary) Lokesh saini Naveen Tanwar Ballari Sagarkumar Satyanarayan G.Sairam Siddhart Mehta K.Prashanth Chauhan Sponsorship Committee Palle Raghavendra Prasad (Secretary) Aditya Mushyam Adarsh Bikash Saikia Sheshank Verma Website Committee Priyesh Sinha (Secretary) Atanu Bhuyan Bibekananda Murmu Deepak Shilpi Treasurer Sourabh Agarwal

FROM MECHANIKA 2007 TEAM Things are not gonna be as simple as they appear from the surface. The bird’s eye view reveals the pain and effort involved in each and every aspect of this Magazine. Maximum effort has been made to include disparate topics and ideas to content each and every individual.

Dwelling on any topic leads to many unanswered questions.

The skeptic mind of ours drives us to clarify them. In course of making MECHANIKA-2007, efforts were made to ensure that MECHANIKA-2007 lights an inquisitive flame in the mind of every iitgian.

“From its ashes, rises a phoenix” The statement holds true here. From the ashes of MECHANIKA-2006, MECHANIKA-2007 has risen. There has been a sincere effort on our part that all the features of MECHANIKA -2006, which were not well recieved; be either changed or modified.

“Perfection is somthing one can always tend to, and can never actually achieve it” In spirit of this statement we do expect some shortcomings in this issue.

By this time, we feel that you must have gone through entire magazine. So, you have had some thoughts about MECHANIKA-2007. What we would request you is - to stop for a moment, grab a piece of paper and write down these thoughts and send them to us. This feedback would be helpful in making sure that MECHANIKA-2008 lands at a higher padestal.

Finally, our special thanks goes to the faculty, staff and MESA members and all those authors who have contributed in MECHANIKA-2007.

MECHANIKA 2007 TEAM Editors

Alok Verma Palle Raghavendra Prasad Deepak kumar

Articles Collection Team

Nishant Prakhar Adarsh Bikash Saikia Govind Mohan Debendra Bahadur Singh Dharua

Batch Representatives Final Year Third Year Second Year First Year M.Tech Batch PhD Batch

: Deepak Kumar : Vijay Kumar Verma : Atul Kumar Soti : Shushant Kumar : Neeraj Carpenter : D. N. Vadiraja

-Overall layout & design by Alok Verma

MESSAGE FROM HOD

I express my sincere thanks to Dr. U.S. Dixit (HOD) and my colleagues of the department for their valuable suggestions.

I congratulate all the members of MESA, especially the publication committee for this great success.

Dr. Niranjan Sahoo Faculty Adviser, MESA It gives me immense pleasure that the students of Mechanical Engineering Department are bringing out the second issue of the annual magazine Mechanika. The magazine is published by the students through Mechanical Engineering Students’ Association (MESA) of Indian Institute of Technology Guwahati and provides a forum for expressing technical ideas for students and faculty members of the Department.

MESSAGE FROM THE PRESIDENT

This year a number of articles have been published and it is a matter of great satisfaction to see the contributions from B.Tech., M.Tech., and Ph.D. students as well as a few faculty members. There are some articles of general interest, providing valuable technical information to readers. On the other hand, there are a number of articles based on the projects carried out by the students.

I congratulate the editors, authors and members of MESA team for bringing out the second issue of Mechanika with added flavour. I expect that in years to come, MESA will play a more active role and the quality of Mechanika will keep on increasing.

Prof. Uday Shankar Dixit HOD, Mechanical Engineering

MESSAGE FROM FACULTY ADVISER

It is a matter of great pleasure to me that Mechanical Engineering Students’ Association (MESA), IIT-Guwahati is going to publish the 2nd edition of its annual magazine. At this stage, I would rather recall George Bernard Shaw’s statement, “If you have an idea, and I have an idea, and we exchange these ideas, then each of us will have two ideas”. The articles presented in this magazine has drawn upon a diverge range of skills and experiences from faculties and students of Mechanical Engineering (ME) Department. In this way, it is an endeavor to share the knowledge about the updates in various fields of engineering and technology through meaningful articles. It also covers the research contributions from the students of ME-Department at UG and PG levels.

MESA, a spirit embarked few years ago, with the aim to strengthen the integrity among future mechanical engineers, is now turning into a big success. With all the enthusiasm and hard work delivered by its members, MESA has a very bright future.

I am pleased that the 2nd edition of MESA’s annual magazine, Mechanika-2007, is out in the Campus. I am glad to see the various authors from B.Tech, M.Tech, Ph.D. as well as a few faculty members. This magazine provides an overview to different fields of mechanical engineering through its meaningful articles alongwith technical papers based on the current research work going on at IIT Guwahati. Apart from this, certain things of common interest have also been incorporated in this edition.

I congratulate all the members of MESA, especially the publication committee for this great achievement. Definitely, there has been a lot of improvement in terms of content, design and participation from the community in Mechanika2007 as compared to the previous edition. My message is to work even harder in the future and not to stop at such laurels. I would like to thank our faculty advisor, Dr. Niranjan Sahoo for his valuable advice. Further, I appreciate the faculty involvement in the activities of MESA which has been a great achievement for our association. Last but not the least, I would like to thank our HOD, Dr. U.S. Dixit, for his valuable suggestions. Finally, I am grateful to the department for the financial support.

I wish MESA all the very best for its future endeavors. Suggestions for improvement of this magazine are most welcome and would be incorporated in the next edition with a view to make this magazine more useful.

Deepak Kumar President, MESA

MECHANIKA

courtesy: Airbus

2007 Edition

SIZE MATTERS... : A glimpse of some of the biggest mechanical wonders. A380 and 5M Project...

ICE HEAT ENGINE: Water trapped in rocks is known to split them open upon freezing.

The intense pressure it exerts, and the fact that water expands when it freezes, suggests that the freezing of water may be utilized to do work....

A Brief History of Rotor Dynamics and Recent Trends: It all started when Rankine performed the first analysis of a spining shaft....

1

A-380 6

5M 8

1 4

TECHWATCH: Some of the latest innovations around the world

THE ROBOT THAT KNEW JUST ENOUGH:

A robot that can work itself, find its own way around......

HYDROGEN AGE: what does future has in store...

3D RECONSTRUCTION FROM POINTS TO FREEFORM SHAPES: A brief introduction of the Reverse Engineering (RE) and Rapid Prototyping (RP) technologies .....

23 courtesy RE Power

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SURVEY: Before you go on to this section, we would like you to keep a quote in mind “Stastics are like mini skirts, they show more than they hide”

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JUST FOR FUN.......................................................................................................................................22 GET YOUR PRIORITIES RIGHT........................................................................................................22 ADVICE FOR MS...................................................................................................................................35 BELL THE CAT......................................................................................................................................13 CAMPUS PLACEMENT 2006-07: A REPORT...................................................................................16

MECHANIKA 2007 Edition

THE ENERGY CRUNCH: Have you ever thought about the things that made our life so luxurious as compared to the primitive human races? What is the prime constituent in human controlled sophisticated goods like ACs, room heaters, various locomotives like trains, cars, aeroplanes etc.?......

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CURVES OBTAINED BY PARMANENT MAGNET DC MOTORS

BY Atul Kumar Soti.........................................................................................................................

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CONTROL OF SPACE MANIPULATOR FOR TRAJECTORY PLANNING AND OPERATION IN AN UNSTRUCTURED ENVIRONMENT

By Saurabh Garg, Deepak Kumar, G. Rajkumar..............................................................................

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MODELING ATMOSPHERIC RADIATIVE TRANSFER - SHDOM

By Rajpreet Singh............................................................................................................................

JOB SHOP SCHEDULING (JSP) THROUGH PARTICLE SWARM OPTIMIZATION (PSO)

By Deepankar Garg, Jaspreet Singh, Sudhanshu Kumar.................................................................

TERM PROJECTS BY 3rd YEAR STUDENTS Oral simulator- A review Automobile Leaf Springs- A Review Computer Aided Design of a Knee Simulator Mechanical Model of Rigid Axle Suspension System Expert System for Cam Design Design of gear test rig for kinematic analysis Test Rig for Wheel and Brake Assembly Performance Study

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HYBRID CARS – FUTURE OF AUTOMOBILE

By Vijaya Kumar Pantangi...............................................................................................................

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Engineering Design Methodology Projects: Creative Engagement for Learning

By Dr. G. Saravana Kumar...............................................................................................................

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BTPs ALLOTTED FOR 2006-07 SESSION...............................................................................

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MTPs ALLOTTED FOR 2006-07 SESSION..............................................................................

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SIZE matters....

They are the biggest...

Size matters... is an attempt to bring you the glimpse of these mechanical wonders, which continues to awe us,which stands against the time and nature like stalwarts.They represent the times, man locked horns with nature and came out victoriously.

By Alok Verma

It’s bigger than a hot air balloon, it’s bigger than a helicopter, and it’s bigger than an airplane….. wait, I went too far, it is an airplane.They call it A380.

D

courtesy: Airbus

Airbus A380 ecades of fierce competition has resulted in evermore efficient aircraft and flying has never been so cheap.

But there is one plane that since it flew back in 1969 has not been superceded, it is called “The Jumbo Jet”or “Boing 747”. The 747 has survived because in all that time no-one ever had the nerve and the money needed to take on this aircraft with an all new design. Until 27th April 2005-Airbus A380 flew for the first time, it replaced 747 from the position of “world’s biggest airliner”. It all started 10years back, when the European planemaker Airbus decided to take on Boing head-on. Airbus put everything on stake for a machine that would dominate the market for years. The company pumped in 10.7 billion dollars in building of what they call “The flagship of 21st century”. The stakes were so large that failure of A380 would have run the company bankrupt.

The building process of the plane called for the building of new factories, as no place on the face of earth was big enough to accomodate anything of this magnitude. The factories are spread allover Europe. Main centers being France, Spain, UK, Germany. Main asembly was done in Toulouse(France).

I can go on writing about it, but let me have the pictures do the “talking”. It is said “A picture speaks 1000 words”.

AIRCRAFT DIMENSIONS Overall length Height Fuselage Diameter Maximum Cabin Width Cabin Length Wingspan (geometric) Wing area (reference) Wing sweep (25% chord) Wheel base Wheel track Mechanika, April 2007

metric

73m 24.1m 7.14m Main deck:6.58 m/Upper deck:9.52 m 49.90m 78.9m 845m 233.5deg 30.4m 14.3m 1

BASIC OPERATING DATA Engines (4) Engine thrust range Typical passenger seating Range (w/maximum passengers) Max. operating Mach number (Mmo) Bulk hold volume - Standard/option

metric

Trent 900 or GP 7000 311 kN 555 15,000 km 0.89 Ma 18.4 m3

DESIGN WEIGHTS Maximum ramp weight Maximum takeoff weight Maximum landing weight Maximum zero fuel weight Maximum fuel capacity Typical operating weight empty Typical volumetric payload

metric

562 tonnes 560 tonnes 386 tonnes 361 tonnes 310000 litres 276.8 tonnes 66.4 tonnes The data shown above has been taken from Airbus A380 website

A size comparison between four of the largest aircraft

courtesy :Wikipedia

*another launch model, the A380-800F, will be one of the largest frei ght aircraft and will have a payload capacity exceeded only by the Antonov An-225.

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Mechanika, April 2007

A380 in the making... courtesy: Airbus

courtesy: Airbus

courtesy: Airbus

Huge parts of the aircraft were brought from all over the Europe for the final assembly at Toulouse, France

courtesy: Wikipedia

“The A380 structure incorporates a range of new materials, including a new material, Glare, that is highly resistant to fatigue.”

“The A380 is equipped with four 70,000lb thrust engines.”

27th April, 2005-The first flight of A380

Mechanika, April 2007

The information here has been taken from Airbus A380 website

courtesy: Airbus

courtesy: Airbus

The main assembly line at Toulouse. The complex on the right itself costs 240million Euros.

“The A380’s maximum operating speed is Mach 0.89 and the range is 15,000km.”

“The Airbus A380 is the world’s first twindeck, twin-aisle airliner.”

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5M project Ever heard about ‘brunsbuttel’. No, I guess; geographically speaking it is a port at river Elbe in Schleswig-Holstein (don’t try to pronounce this...), located in Germany(at last, something familiar). For years this place wandered in oblivion just like zillions of other townships scattered all around the globe. But all this changed when it was catapulted on the world map by the 5M project. The name might send you in deja-vu (think of Y2K). But like Y2K, 5M is not a problem that has arisen due to some misalignment in our system of representing dates in computer systems, in fact 5M is the one of the biggest endeavour of mankind to tap the vast potentials of wind. 5M project is the biggest wind turbine ever made. Let’s get technical....

Technical Data

Design Rated power Cut in wind speed Rated wind speed Cut out wind speed Off shore version On shore version

5000 kW 35 m/s 3 m/s 30 m/s 25 m/s

Rotor Diameter Speed range Control principle

126 m 6.9- 12.1 rpm Blade Angle and speed control, Electrical pitch

System 3 Individual Fail-Safe Blade Pitch Systems Rotor Locking Brake Fully integrated lightening protection system with multiple receptor principle in rotor blades

Gearbox Design Transmission Ratio

Combined planetary/Spur wheel gears i=97(approx)

Generator Design Speed Range

Doubly Fed Asynchronous Generator, 6 poles Approx. 670 - 1,170 rpm courtesy: RE power

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Mechanika, April 2007

5M in pictures... courtesy: RE power

Naclle At 6 m high, 6m wide and 18m long. Naclle alone is of the size of a single family home.

courtesy: RE power

61.5 m long, each blade of 5M is seperately brought to Burnsbuttel after an eleven hour journey thruogh land and water.

Look closely on the left side of the photo, you can see two men standing.

courtesy: RE power

courtesy: RE power

5M stands on steel and a concrete structure. 40 concrete piles - each 24m in length- support the foundation, of which only 23m wide plate is visible.

Around 1,300 cubic mtrs of concrete and 180 tons of steel are used in the foundation. The photo of 5M is at page 38

The data and photos shown here has been taken from RE power website

Blades

Alok Verma is a B.Tech 3rd Year student in the Department of Mechanical Engineering, Indian Institute of Technology Guwahati Mechanika, April 2007

5

The Ice Heat Engine Karthik C, B.Tech 3rd year

W

work for us.

ater trapped in rocks is known to split them open upon freezing– this is infact, one of the many methods through which soil forms. The intense pressure it exerts, and that fact that water expands when it freezes, suggests that the freezing of water may be utilized to do

The simplest device that uses this property is a heat engine, a bucket of water at zero degrees celsius (and atmospheric pressure). Such a mixture will usually contain both ice and water. If done very carefully however, all the water can be made to solidify at the same temperature- by maintaining the quintessential “infinitesimal” temperature difference between our bucket and a sink. Water expands when it solidifies, which means that with a piston like lid, the solidification of water at zero degrees can be used to raise a weight by a small height. Now the weight is removed, (moved horizontally, so we can neglect the energy used in doing so) and the ice is melted, again at zero degrees.

We have, in effect, created a heat engine that works at a single temperature. And Viola! There we have it the simplest perpetual motion machine ever built .

Of course, nature doesn’t work that way, and this is where the second law of thermodynamics steps in.

Clearly, atleast one of the processes in the cycle must be impossible - but which one?

1. With the weight on top, water at zero degrees solidifies to ice at zero degrees, and expands during the process.

2. With no weight on top, ice melts at zero degrees to give water at zero degrees, and contracts during the process.

This charming little thought experiment lends insight into the true utility of the second law of thermodynamics: By stating that at least two temperatures are required for cyclic operation, it tells us very little about heat engines - it does, however, tell us a lot about the properties of substances by imposing limits on their behaviour. In this case, it follows that water will not- it cannot- solidify at zero degrees celcius with a weight on top (or equivalently, at a positive gage pressure). The result of this ‘gedanken’ is information on the thermodynamic behaviour of water! At positive gage pressures, water must solidify at temperatures lower than zero degrees, and vice versa– a nice little snippet of information that comes right out of the second law.

The second law also provides an estimate of the pressure needed for water to solidify at, say, -5 degrees celcius. Assume that we run the heat engine reversibly (Among other conditions, this requires that it is run very, very slowly, with all heat transfer occuring across infinitesimal temperature differences), so that the thermal efficiency, that is, the ratio of the work done during the entire cycle to the heat absorbed at zero degrees, is the carnot efficiency of a heat engine operating between 0 and -5 degrees celcius.

Denoting the temperatures and (absolute) pressures at 0 and -5 degrees celcius by T1, P1 and T2, P2 respectively, and the specific volumes (the volume per unit mass) of liquid water and ice at these two temperatures by v1l, v1s and v2l, v2s:

(The Carnot Efficiency, evaluated between 0 and −5 degrees) This also explains why a ”solidification engine” is not economically viable - for a temperature difference of twenty five degrees, the maximum possible efficiency comes to 9.15%.

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Mechanika, April 2007

Our cycle now works like this: 1. The cycle begins with liquid water at -5 degrees and pressure P2. The system loses heat at -5 degrees and freezes, thereby raising the weight.

2. The weight is slid off, and the system undergoes an isentropic process until it reaches 0 degrees celcius, now at pressure P1.

3. The system gains heat at 0 degrees, and the ice melts to give water at pressure P1.

4. Another weight is slid onto the cylinder, and the cylinder is compressed isentropically until it reaches -5 degrees, now at pressure P2.

The net work done is :

that is, the difference between the work done as it freezes at -5 degrees celcius, and the work that the ambient atmosphere does on it as it liquifies at 0 degrees. Over small temperature ranges, the difference between v1sl and v2sl is negligible (for any pure substance), so the work done during the other two processes is neglected. (That is, v1sl≈ v2sl = δv).

And hence

The volume change per kg of water during solidification, δv is:

and the heat gained is δH = 334kJ/kg (The latent heat of fusion for water) Setting up the balance gives: The gage pressure obtained here is within 15% of the actual gage pressure - quite acceptable, since we neglected changes in density and latent heat over a span of 5 degrees. (This also explains why water develops enough pressure to break rocks).

Incidentally, writing out the expression for the gage pressure (δP) as obtained above gives:

or

Since the above analysis makes no use of the properties of water (in fact, it predicts them), it follows that this relation holds for any thermodynamically pure substance. We have derived what is called the Clausius -Clapeyron equation, a very commonly used relation in thermodynamics.

This exercise seems futile at first glance - as evidenced by the low efficiencies and the myriad practical hurdles, using ice/water as the working substance is certainly not feasible. However, it revleals the profound significance of the second law of thermodynamics in all its glory. The second law is a statement that tells us little about heat engines, but a lot about matter!

Reviewed by: Dr. Manmohan Pandey

Mechanika, April 2007

7

A Brief History of

Rotor Dynamics

and Recent Trends

magnitude. A critical speed occurs when the excitation frequency coincides with a natural frequency, and can lead to excessive vibration amplitudes. Rankine’s neglect of Coriolis acceleration led to erroneous conclusions that confused engineers for one-half century.

The turbine built by Parsons in 1884 (Parsons, 1948) operated at speeds of around 18000 rpm, which was fifty times faster than the existing reciprocating engine. In 1883 Swedish engineer de Laval developed a singlestage steam impulse turbine (named after him) for marine applications and succeeded in its operation at 42000 rpm. He aimed at the selfcentering of the disc above the critical speed, a phenomenon which he intuitively recognized. He first used a rigid rotor, but latter used a flexible rotor and showed that it was possible to operate above critical speed by operating at a rotational speed about seven times the critical speed (Stodola, 1924).

It all started in 1869, when Rankine performed the first analysis of spinning shaft. Rotor Dynamics has come a long way now. A retrospect on the 140 year long history of Rotor Dynamics and an overview on the methods of analysis and recent trends in the field.

By Prof. Rajiv Tiwari

A

rotor is a body suspended through a set of cylindrical hinges or bearings that allow it to rotate freely about an axis fixed in space. Engineering components concerned with the subject of rotor dynamics are rotors of machines, especially of turbines, generators, motors, compressors, blowers and the like. The parts of the machine that do not rotate are referred to with general definition of stator. Rotors of machines have, while in operation, a great deal of rotational energy, and a small amount of vibrational energy. It is very evident from the fact that a relatively small turbine propels a huge aircraft. The purpose of rotor dynamics as a subject is to keep the vibrational energy as small as possible. In operation rotors undergoes the bending, axial and torsional vibrations.

FROM RANKINE TO JEFFCOTT ROTOR MODELS Rotor dynamics has a remarkable history of developments, largely due to the interplay between its theory and its practice.

Rotor dynamics has been driven more by its practice than by its theory. This statement is particularly relevant to the early history of rotor dynamics. Research on rotor dynamics spans at least a 140 year history.

Rankine (1869) performed the first analysis of a spinning shaft.

He predicted that beyond a certain spin speed “. . . the shaft is considerably bent and whirls around in this bent form.” He defined this certain speed as the whirling speed of the shaft. In fact, it can be shown that beyond this whirling speed the radial deflection of Rankine’s model increases without limit. However, Rankine did add the term whirling to the rotor dynamics vocabulary. Whirling refers to the movement of the center of mass of the rotor in a plane perpendicular to the shaft. The frequency of whirl depends on the stiffness and damping of the rotor and the amplitude is a function of the excitation force’s frequency and 8

In order to calculate the critical speeds of cylindrical shafts with several discs and bearings the general theory of Reynolds (Dunkerley, 1895) was applied. The gyroscopic effect was also considered, together with its dependence on speed. Dunkerley found, as a result of numerous measurements, the relationship known today by that of Southwell, by which the first critical speed can be calculated, even for complicated cases. The first sentence of Dunkerley’s paper reads, “It is well known that every shaft, however nearly balanced, when driven at a particular speed, bends, and, unless the amount of deflection be limited, might even break, although at higher speeds the shaft again runs true. This particular speed or critical speed depends on the manner in which the shaft is supported, its size and modulus of elasticity, and the sizes, weights, and positions of any pulleys it carries.” Föppl used an undamped model to show that an unbalanced disc would whirl synchronously with the heavy side flying out when the rotation was subcritical and with the heavy side flying in when the rotation was supercritical. Also the behaviour of Laval rotors at high speed was confirmed by his theory.

One can speculate that engineers of the day laboured under a confusion of concepts - equating Rankine’s whirling speed with Dunkerley’s critical speed. This was particularly unfortunate since Rankine was far more eminent than Dunkerley and, as a result, his dire predictions were widely accepted and became responsible for discouraging the development of high speed rotors for almost 50 years. It was in England in 1916 that things came to the end. Kerr published experimental evidence that a second Mechanika, April 2007

critical speed existed, and it was obvious to all that a second critical speed could only be attained by the safe traversal of the first critical speed.

The first recorded fundamental theory of rotor dynamics can be found in a classic paper of Jeffcott in 1919. Jeffcott confirmed Föppl’s prediction that a stable supercritical solution existed and he extended Foppl’s analysis by including external damping (i.e., damping to ground) and showed that the phase of the heavy spot varies continuously as the rotation rate passes through the critical speed. We can appreciate Jeffcott’s great contributions if we recall that a flexible shaft of negligible mass with a rigid disc at the midspan is called a Jeffcott rotor. The bearings are rigidly supported, and viscous damping acts to oppose absolute motion of the disc. This simplified model is also called the Laval rotor, named after de Laval.

ROTOR

DYNAMICS

PHE-

erated. This restriction was removed by Stodola.

About a decade latter, the study of asymmetrical shaft systems and asymmetrical rotor systems began. The former are systems with a directional in the shaft stiffness and the latter are those with a directional difference in rotor inertia. Two-pole generator rotors and propeller rotors are examples of such systems. As these directional differences rotate with the shaft, terms with time-varying coefficients appear in the governing equations.

These systems therefore fall into the category of parametrically excited systems. The most characteristic property of asymmetrical system is the appearance of unstable vibrations in some rotational speed ranges. In 1933 Smith obtained a pioneer work in the form of simple formulas that predicted the threshold spin speed for super-critical instability varied with bearing stiffness

“It is well known that

and with the ratio of external to internal viscous damping. To quote from Smith’s paper “ . . . [the] increase of dissymmetry of the bearing stiffness and in the intensity of [external] damping relative to [internal] damping raises the [threshold] speed . . . and [this threshold] speed is always higher than either critical speed.” The formula for damping was obtained independently by Crandall (1961) some 30 years later.

ries.”

ity of shaft motion and considering pressure forces due to oil films. The mechanism of vibrations due to the

every shaft, however nearly balanced, when Developments made in rotor dydriven at a particular namics up to the beginning of the twentieth century are detailed in the speed, bends, and, unmasterpiece book written by Stodola (1924). Among other things, this book includes the dynamics of elasless the amount of detic shaft with discs, the dynamics of In the early 1920s a supercritical continuous rotors without considerin built-up rotors was flection be limited, instability ing gyroscopic moment, the secondencountered and, shortly thereafary resonance phenomenon due to first shown by Newkirk (1924) might even break, al- ter, gravity effect, the balancing of roand Kimball (1924 to be a manitors, and methods of determining apfestation of rotor internal dampproximate values of critical speeds though at higher speeds ing (i.e., damping between rotor of rotors with variable cross seccomponents). Then, Newkirk and tions. He presented a graphical pro- the shaft again runs true. Taylor (1925) described an instabilcedure to calculate critical speeds, ity caused by the nonlinear action which was widely used. He showed of the oil wedge in a journal bearthat these supercritical solutions This particular speed or ing, which was named as oil whip. were stabilized by Coriolis accel(1933) described self-excited critical speed depends Baker erations. The unwitting constraint of vibrations due to contact between these accelerations was the defect in rotor and stator. The Soviet scientist Rankine’s model. It is interesting to on the manner in which Nikolai (1937) examined the stabilnote that Rankine’s model is a senity of transverse and torsional vibrasible one for a rotor whose stiffness in a shaft with a disc mounted the shaft is supported, tions in one direction is much greater than in the center and the stability of a its stiffness in the quadrature direcshaft with a disc attached to the free tion. Indeed, it is now well known its size and modulus of end. Kapitsa (1939) pointed out that that such a rotor will have regions of a flexible shaft could become unstadivergent instability. It is less well elasticity, and the sizes, ble due to friction conditions in its known that Prandtl (1918) was the sliding bearings. In the middle of first to study a Jeffcott rotor with a twentieth century, Hori (1959) weights, and positions the non-circular cross-section (i.e. elassucceeded in explaining various tic asymmetry in the rotor). In Jefcharacteristics of oil of any pulleys it car- fundamental fcott’s analytical model the disk did whip by investigating the stabil-

STUDIES STODOLA TO LUND NOMENA

FROM

not wobble. As a result, the angular velocity vector and the angular momentum vector were collinear and no gyroscopic moments were genMechanika, April 2007

9

steam whirl in turbines was explained by Thomas (1958) and that in compressors was explained by Alford (1965). The vibration of hollow rotor containing fluid was the problem of flowinduced vibrations. Instability due to liquids partially filling interior cavities of rotors was demonstrated by Kollmann (1962), and in 1967 Ehrich reported that fluid trapped in engine-shafts induced asynchronous vibration and also changed the shape of resonance curves. Kuipers (1964), and Wolf (1968) independently successed in explaining the appearance of an unstable speed range in a postcritical region of a rotor system containing inviscid fluid. In 1980s the rotor dynamic effects of seals in fluid handling machines received a great deal of attention. Rotor destabilization due to seals was predicted and demonstrated in an operational compressor by Jenny (1980).

As rotors became lighter and rotational speeds higher, the occurrence of nonlinear resonances such as subharmonics became a serious problem. Yamamoto (1955, 1957) studied various kinds of nonlinear resonances after he reported on subharmonic resonance due to ball bearings in 1955. He also investigated combination resonances. Tondl (1965) studied nonlinear resonances due to oil films in journal bearings. Ehrich (1966) reported subharmonic resonances observed in an aircraft gas turbine due to strong nonlinearity produced by the radial clearance of squeezefilm dampers.

Non-stationary phenomena during passage through critical speeds have been studied since, Lewis (1932) reported his investigation on the Jeffcott rotor. Non-stationary phenomena that occur are one in a process with a constant acceleration and another with variable acceleration (limited driving toque). Natanzon (1952) studied shaft vibrations at critical speeds and Grobov (1953, 1955) investigated in general form the shaft vibrations resulting from varying rotational speeds. The development of asymptotic method by Mitropol’skii (1965) considerably boosted the research on this subject.

Beginning in the early 1960s, most attention focused on hydrodynamic bearings, this was largely stimulated by Lund (1964).

Gunter’s work (1966) related to rotor dynamic stability problems, combined with Ruhl and Booker’s (1972), and Lund’s (1974) methods for calculating damped critical speeds, stimulated a great deal of interest in rotor-bearing stability problems.

Lund (1987) gave an overview of the field. In the mid 1970s, rotor dynamic instability experiences with various high-pressure compressors and the high-pressure fuel turbo-pump of the Space Shuttle main engine focused a great deal of attention on the influence of fluid-structure-interaction forces, particularly forces due to the liquid and gas seals, in pumps and turbines. Someya (1989), and Tiwari et al. (2004) complied extensive numerical and experimental results, and literatures; respectively. Shaft seals have similar effect as fluid-film bearings. They influence the critical speeds, can provide damping or on the other hand cause instability. Shaft seals have acquired a significant role in their effect on rotor dynamics.

Instability from fluid-film bearings and shaft seals arises from the fact that, during radial displacement of a rotor, a restoring force is produced, which has a component at right angles to this displacement. The phenomenon of instability was described in detail by Newkirk (1924), whose interest was in turbo machiner10

ies. The cause of this instability, in fact, lay in the oil-film bearings. Notwithstanding, in the following years it was established that in a few cases, internal friction or damping could indeed be a cause of instability. The designer must thus be aware of these possibilities.

DEVELOPMENT OF ROTOR DYNAMICS ANALYSIS TOOLS

In rotor dynamics a remarkable amount can be explained by the dynamics of a single mass Jeffcott rotor model. This model, introduced in 1895 by Föppl, was named after Jeffcott, because in 1919 he explained the science of rotor dynamics in a graphic and illuminating way. Gradually, the Jeffcott rotor model, in its many variations, came closer to the practical needs of the rotor dynamicists of the day.

Many practical rotors, especially those being designed for aircraft gas turbines, were not suitable for a Jeffcott model. For one thing, the distinction between disk and shaft is blurred in the typical aircraft gas turbine. In the practical design of rotating machinery, it is necessary to know accurately the natural frequencies, mode shapes and forced responses to unbalances in complex-shaped rotor systems. The technique for this was supplied by Prohl in the late 1930s and published in 1945 for critical speed evaluation of turbine shaft. It is similar to the method published about the same time by Myklestad (1944) for the natural frequencies of aircraft wings but was developed independently. Together, Prohl’s and Myklestad’s work led to a broader method, now called the Transfer Matrix Method (TMM). This method is particular useful for multirotor-bearing systems and has developed rapidly since 1960s by the contribution of many researchers such as Lund et al. (1965, 1967, 1974) and Rao (1996). The TMM for rotors remains viable; indeed, it seems still to be the method of choice for most industrial rotor dynamic analyses. Another representative technique used for this purpose is the finite element method. The name “Finite Element Method” first appeared in the title of a paper by Clough (1960).

The first application of the finite element method to a rotor system was made by Ruhl and Booker (1972). Then Nelson and McVaugh (1976) generalised it by considering the rotary inertia, gyroscopic moment, and axial force. It was soon recognised that the large number of nodes necessary to provide accurate stress distribution created dynamic systems too large for economical calculation. Condensation of the number of dynamic degrees of freedom by division into master and slave degrees of freedom was introduced by Guyan (1965). Other dynamic condensation techniques were described by Uhrig (1966), Friswell and Mottershead (1996), and Tiwari and Dharmaraju (2006). A related technique for the dynamic analysis of structure assembled from distinct components or substructures in the component mode synthesis introduced by Hurty (1960) and applied to rotor dynamics by Glasgow and Nelson (1980), Geradin and Kill (1984), and Crandall and Yeh (1986). Each substructure interacts only through their constraint modes.

DYNAMIC BALANCING OF ROTORS

The most important and fundamental procedure to reduce unfavourable vibrations is to eliminate geometric imbalance in the rotor. The balancing procedure for a rigid rotor was established relatively early. The arrival of high-speed rotating machines Mechanika, April 2007

made it necessary to develop a balancing technique for flexible rotors. Two representative theories were proposed. One was the modal balancing method proposed in the 1950s by Federn (1957), and Bishop and Gladwell (1959). The other is the influence coefficient method proposed in late 1930s by Rathbone (1929), and later by Thearle (1932) and developed mainly in the Unites States along with the progress of computers and instruments for vibration measurements (Wowk, 1995).

SOFTWARES FOR ROTOR DYNAMICS ANALYSIS World War II can be considered as the demarcation between the early stages of rotor dynamics and what might be called modern rotor dynamics. In the 1960s there was a coalescence of numerical methods applied to structural dynamics and of digital computer capacity that fostered the development of a series of general purpose computer codes. The initial application of these codes to rotor dynamics was based on the TMM method but in the 1970s another underlying algorithm, the FEM, became available for the solution of the prevailing beam-based models. Now, in the beginning of the 21st century, rotor dynamicists are combining the FEM and solid modeling techniques to generate simulations that accommodate the coupled behavior of flexible disks, flexible shafts and flexible support structures into a single, massive, multidimensional model. Crandall (1992) gave an overview of the rotor dynamic computer codes (e.g. ANSYS, CADENSE, MADYN, RODYN, ROMAC, SAMCEF, VT-FAST, etc.). He also concluded that with regards to quality and quantity of software the specialised area of rotor dynamics still lags behind the broader field of non-rotating structural dynamics.

CONDITION MONITORING OF ROTATING MACHINERIES

In the 1960s, cracks were found in rotors of some steam turbines. To prevent serious accidents and to develop a vibration diagnostics system for detecting cracks, research on vibrations of cracked shafts begun. In the 1970s, it was showed that an unstable region appeared or disappeared at the critical speed, depending on the direction of the unbalance.

Another area in which lot of development took place is on assessment of turbomachinery condition monitoring and failure prognosis technology. High-performance turbomachines are now extremely important elements of worldwide industry. The electric power, petrochemical, mining, marine, and aircraft industries are prime examples for which turbomachinery is crucial to business success. According to Eshleman (1990), over the past several years, instrumentation and monitoring capabilities have increased dramatically, but techniques for fault diagnosis have evolved slowly. The tools are therefore still more advanced than the techniques. Edward et al. (1998) provided a broad review of the state of the art in fault diagnosis techniques, with particular regard to rotating machinery. Special treatment was given to the areas of mass unbalance, bowed shafts and cracked shafts, these being amongst the most common rotor-dynamic faults. Vibration response measurements yield a great deal of information concerning any faults within a rotating machine. Cracks in shafts have long been identified as factors limiting the safe and reliable operation of turbomachines. They can sometimes result in catastrophic failure of equipment (rotor bursts) and, more often, in costly process upsets, repairs and premature scrapping and re-

Mechanika, April 2007

placement of equipment. In the past two decades, much research and many resources have gone into developing various on-line and off-line diagnostic techniques to effectively detect cracks before they cause serious damage. One of the earliest documented applications of acoustic emission technology (AET) to rotating machinery monitoring was in the late 1960s. Since then, there has been an explosion in research- and application-based studies covering bearings, pumps, gearboxes, engines, and rotating structures.

CONCLUSIONS & RECENT TRENDS

Research in rotor dynamics is aimed at improving the understanding of rotor dynamic phenomena and improving the performance of rotating machinery. In most rotordynamic systems the vibratory amplitudes are sufficiently small that the linear analysis of rotor and stator deformations is satisfactory. In rotor dynamics the structural modeling is generally adequate and most research is centered on fluid-structure interactions: bearings, seals, blade forces, squeeze-film dampers etc. It is here that the nonlinearities are concentrated. The equations of motion of such systems consist of a great many linear equations coupled to a small handful of nonlinear equations (Yamamoto and Ishida, 2001). The most promising area of the research for performance improvement is the active control. The latest topic in rotor dynamics is a study of magnetic bearings (a mechtronics product), which support a rotor without contacting it and active dampers (Schweitzer et al., 2003; Chiba, et al., 2005). This study has received considerable attention since Schweitzer reported his work in 1975. We are now a long way from the approaches of Jeffcott and Prohl, a journey that deserves its own history sometime.

REFERENCES

Alford, J.S.,1965, Protecting turbomachinery from self-excited rotor whirl, Trans ASME, J of Eng. Power, 86(2), 141-148.

Baker, J.G., 1933, Self-induced vibrations, Journal of Applied Mechanics, 1(1), 5-12.

Bishop, R.E.D. and Gladwell, G.M.L., 1959, The vibration and balancing of an unbalanced flexible rotor, J. Mech. Eng. Sci., 1(1), 66-77.

Chiba A., Fukao T., Ichikawa O., Oshima, M., Takemoto M. and Dorrell D.G. (2005): Magnetic Bearings & Bearingless Drives. Newnes, Elsevier.

Clough, R.W., 1960, The finite element method in plane stress analysis, Proc. 2nd ASCE Conf. on Electronic Computation, Pittsburgh, 345378.

Crandall, S.H., 1992, Rotordynamic Software. Rotating Machinery, Transport Phenomena, editors: J.H. Kim, W.J. Yang. Hemisphere Publishing Corporation, Washington, Philadelphia, London (1992), pp. 321.

Crandall, S.H. and Brosens, P.J., 1961, On the stability of rotation of a rotor with unsymmetric inertia and stiffness properties, J. Appl. Mechanics, 28, 567-570.

Crandall, S.H. and Yeh, N.A., 1986, Component mode synthesis of multi-rotor system. Refined Dynamical Theories of Beams, Plates and Shells and their Applicatrions, Proc. Euromech Colloquium 219, Springer, Berlin, 44-55.

Dunkerley, S., 1895, On the whirling and vibrations of shafts, Phil.

Trans. of the Royal Soc., A, 185, I, 279-360.

Edwards, S., Lees, A.W. and Friswell, M.I., 1998, Fault diagnosis of rotating machinery. Shock and Vibration Digest, 30(1), 4-13.

Ehrich, F.F., 1966, Subharmonic vibration of rotors in bearing clearance, ASME paper 66-MD-1, American Society of Mechanical Engineers, New York.

Ehrich, F.F., 1967, The influence of trapped fluids on high speed rotor 11

vibration, Trans ASME, J. Eng. Ind., 91(4), 806-812.

Eshleman, R.L., 1990, Detection, diagnosis and prognosis: An evaluation of current technology, in Proceedings of MFPG 44, Vibration Institute.

Federn, K., 1957, Grunlagen einer systematischen schwingungsentstörung Wellenelastischer rotoren, VDI Ber. Bd., pp 9-25.

Friswell, M.I. and Mottershead, J.E., 1996, Finite Element Model Updating in Structural Dynamics. Kluwer Academic Publishe.

Föppl, A., 1895, Das Problem der Lavalschen Turbinenwelle, Der Civillingerenieur, 4, 335-342.

Geradin, M. and Kill, N., 1984, A new approach to finite element modeling of flexible rotors, Engng. Computation, 1, 52-64.

Glasgow, D.A. and Nelson, H.D., 1980, Stability analysis of rotor-bearing systems using component mode synthesis. J. Mechanical Design, Trans. ASME, 102, 352-359.

Grobov, V.A., 1953, O poperechnykh kolebaniyakh vraschchayushchegosya vala pri peremennoi skorosti vrashcheniya, Sbornik Voprosy dinamiki I dinamicheskoi prochnosti, Izdatel’stvo AN Latv. SSR, Vypusk 1. (Transverse vibrations of a shaft rotating with variable angular velocity, Symposium Problems of Dynamics and Dynamics Stability, Publishing House of the Latvian SSR, Academy of Sciences, No. 1).

Grobov, V.A., 1955, Poperechnye kolebaniya rotora s raspredelennoi po dline massoi pri peremennoi skorosti vrashcheniya, Izvestiya AN Latv.

SSR, Vypusk 5. (Transverse vibrations at variable speed of a rotor carrying an axial distributed mass, Journal of the Latvian SSR Academy of Sciences, No. 5).

Gunter, E., 1966, Dynamic stability of rotor bearing systems, NASA paper No. SP-113, 29.

Guyan, R.J., 1965, Reduction of stiffness and mass matrices, AIAA Journal, 3, p. 380.

Hori, Y., 1959, A theory of oil whip, Trans. ASME, Journal of Applied Mechanics, 26(2), 189-198.

Hurty, W.C., 1960, Vibrations of structural systems by component mode synthesis, J. Engrg. Mechs. Div. Proc. ASCE, 86, EM4, 51-69.

Jeffcott, H.H., 1919, The lateral vibration of loaded shafts in neighbourhood of a whirling speed: the effect of want of balance. Philosophical Magazine, Ser. 6, 37, 304-314.

Jenny, R., 1980, Labyrinths as a cause of self-excited rotor oscillations in centrifugal compressors. Sulzer Technical Review, 4, 149-156.

Kapitsa, P.L., 1939, Ustoichivost I perekhod cherez kriticheskie oboroty bistro vrash-chayushchikhsya rotorov pri nalichii treniya, Zhurnal Technicheskoi fiziki, IX, Vypusk 2. (Stability and transition through critical speeds of high-speed rotors sunject to friction, J. Tech. Phys., IX, No. 2.

Kimball, A. L., 1924, Internal friction theory of shaft whirling, General Electric Review, 27(4), 244-251.

Kollmann, F.G., 1962, Experimentelle und theoretische Untersuchen über die Kritischen drezahlen flüssigkeits-gefullter Hohlkörper, Forschung auf dem Gebiete des Ingerieurwesens, 28(4), 115-123 and (5), 147-153.

Kuipers, M., 1964, On the stability of a flexibly mounted rotating cylinder partially filled with liquid. Applied Scientific Research, A13, 121137.

Lewis, F. M., 1932, Vibrations during acceleration through a critical speed, Trans. ASME, 54(3), 253-261.

Lund, J.W., 1964, Spring and damping coefficients for the tilting pad journal bearing, ASLE Transations, 7, 342-352.

Lund, J.W., 1974, Stability and damped critical speed of a flexible rotor in fluid-film bearings, Trans. ASME, J. Eng. Ind., 96(2), 509-517.

Lund, J.W., 1987, Review of the concept of dynamic coefficients for fluid film journal bearings. Journal of Tribology, 109, 37-41.

Lund, J.W. and Orcutt, F.K., 1967, Calculation and experiments on the unbalance response of a flexible rotor, Trans. ASME, J. Eng. Ind., 89(4), 785-795.

Mitropol’skii, Y.A., 1965, Problems of Asymptotic Theory of Nonstationary Vibrations, Israel Program for Science Translation, Jerusalem.

Myklestad, N. O., 1944, A new method of calculating natural modes of uncoupled bending vibrations. Journal of. Aeronautical Science, 11(2), 12

153-162.

Natanzon, V.Ya., 1952, Dvizhenie gibkogo vala na kriticheskoi skotosti, Sbornik Dinamika aviadvigatelei, Oborongiz, No. 8. (Movement of a flexible shaft at critical speed, Symposium on Aircraft Engine Dynamics, Oborongiz, No. 8.

Nelson, H.D. and McVaugh J.M., 1976, The dynamics of rotor bearing systems using finite elements, Trans. ASME, J. Eng. Ind., 98(2), 593-600.

Newkirk, B.L., 1924, Shaft whipping, General Electric Review, 27(3), 169-178.

Newkirk, B.L., and Taylor, H.D., 1925, Shaft whirling due to oil action in journal bearings, Gen. Electric Rev., 28(7),559-568.

Nikolai, E.L., 1937, K teorii gibkogo vala, Trud Leningr. Ind. Inst., No. 6, Razdelenie Fiziko-Matematicheskikh Nauk, Vypusk 3. (The theory of a flexible shaft, Trans. Leningr. Industr. Inst., No. 6, Department of Physico-Mathematical Sciences, No.3.

Parsons, R.H., 1948, The Steam Turbine and other Inventions of Sir Charles Parsons, OM. Lomgman, Green and Co. Prandtl, L., 1918, Beitrage zur Frage der Kritischen Drehzahlen, Dinglers Polytechn. Journal, 333, 179-182.

Prohl, M.A., 1945, A general method for calculating the critical speeds of flexible rotors, J. Appl. Mech., 12(3), 142-148.

Rankine, W. J. M., 1869, On the centrifugal force of rotating shaft. The Engineer, 27, p. 249.

Rao J.S., 1996, Rotor Dynamics, Third edition, New Age, New Delhi.

Rathbone, T.C., 1929, Turbine vibration and balancing, ASME Trans., 51, Paper APM-51-23.

Ruhl, R.L. and Booker, J.F., 1972, A finite element model for distributed paramter turbogenerator system, Trans. ASME, J. Eng. Ind., 94(1), 126-132.

Schweitzer, G., 1975, Stabilization of self-excited rotor vibrations by an active damper, in Dynamics of Rotors, Springer-Verlag, New York, pp. 472-493.

Schweitzer G., Bleuler H. and Traxler A. (2003): Active Magnetic Bearings: Basics, Properties and Applications of Active Magnetic Bearings.

Authors Reprint: Zürich.

Smith, D. M., 1933, The motion of a rotor carried by a flexible shaft in flexible bearings, Proc. R. Soc. London, Ser. A, vol 142, pp. 92-118.

Someya, T., 1989, Journal Bearing Hand Book. Berlin … Tokyo: Springer.

Stodola, A., 1924, Dampf- und Gasturbinen, 4, Aufl., Berlin: Springer.

English translation (1927), Steam and Gas Turbines, McGraw-Hill, New York.

Thearle, E.L., 1932, Dynamic balancing of rotating machinery in the field, ASME Trans., Paper APM-56-19.

Tiwari, R. and Dharmaraju, N., 2006, Mechanical Systems and Signal Processing, Development of a condensation scheme for transverse rotational degrees of freedom elimination in identification of beam crack parameters (In press).

Tiwari, R., Lees, A.W. and Friswell, M.I., 2004, Identification of dynamic bearing parameters: a review, The Shock & Vibration Digest, 36(2), 99-124.

Thomas, J.J., 1958, Instabile eigenschwingungen von turbinenlaufern, Angefacht durch die spaltstromungen, in stopfbuchsen and beschauflungen, AEG-Sonderdruck, pp. 1039-1063.

Tondl, A., 1965, Some Problems of Rotor Dynamics, Czechoslovak Academy of Sciences, Prague, Czechoslovakia.

Uhrig, R., 1966, Reduction of the number of unknown in the displace Wolf, J.A., 1968, Whirl dynamics of a rotor partially filled with liquid, Trans. ASME, J. Appl. Mech., 35(4), 676-682.

Wowk, V., 1995, Machinery Vibration: Balancing, McGraw-Hill.

Yamamoto, T., 1955, On the critical speed of a shaft of sub-harmonic oscillation, Trans JSME, 21(111), 853-858 (in Japanese).

Yamamoto, T., 1957, On the vibrations of a rotating shaft, Mem. Fac. Eng. Nagoya Univ., 9(1), 25-40.

Yamamoto, T., and Ishida, Y., Linear and Nonlinear Rotordynamics, Wiley & Sons, 2001.

Mechanika, April 2007

BELL THE CAT An MBA (Master of Business Administration) is a post graduate degree recognized internationally and widely accepted as a passport to a successful career. An MBA offers a range of benefits, including: �

Business Knowledge: The MBA program and the business schools give you valuable knowledge about business and all its related aspects.

�

Leadership Abilities: An MBA helps to set you apart from those who do not have such expertise and can make you a leader in your chosen field.

�

Networking: The alliances that you form with your classmates and the network that you create is deemed as one of the most important and valuable things that an MBA program can give you.

Traditionally the tenure of full-time MBA programs has been two years. However the majority of MBAs abroad tend to follow the twelve month model. Now to the question how will it impact one’s career?

An MBA opens up newer avenues and provides the modern manager with tools and skills needed to identify new opportunities for organizational success. The broad based understanding of business dynamics gained from the MBA helps in making the transition from roles hitherto limited by knowledge gained from the primary degree (engineering, arts, life sciences etc) to a management role. It is also useful to those who seek a change of career. The key here is obtaining the qualification from a reputable institute. The fact that it leads to well-paid jobs and a more secure future has made it one of the most popular postgraduate programs. Once one has his mind fixed, the next task is - how to get an MBA? In India we have number of reputed management institutes like IIM’s , XLRI , FMS, IIFT, NITIE etc. To secure an admission into these, candidates have to face a stiff competition in the entrance tests. The fact that as many as 1.9 lakh students appeared in CAT this year should be an eyeopener in this regard. Other exams include XAT, JMET and IIFT. To pursue an MBA abroad one needs to write GMAT. These scores are accepted in most colleges.

Focusing on CAT for now lets see how the test is structured. One of the prime reasons why CAT is known to be the toughest exams to crack is its unpredictability. There is no pattern to how the test will be so one needs to keep a cool head throughout the exam. It generally is a 2- 2.5 hrs exam which tests the candidate in three sections broadly – Quantitative ability, Verbal Ability, and Reasoning ability.

Quant tests the numerical aptitude in topics like numbers, algebra, alligation problems, geometry, permutations and probability etc. The portion though basically at 10+2 level will require speed and accuracy. Verbal ability checks one’s grammar, sentence structuring and vocabulary. Also tested are the reading abilities and ability to draw inferences. Vocabulary tested is more application based hence rote learning is not of much help as in GRE. The ability to read passages on abstruse topics with the same zeal and summarize efficiently is critical as these questions carry more weightage. This is one area we generally lag behind in and it is better to work on this beforehand.

Reasoning section has questions on arrangements, conditional groupings and logic. Here one needs to sound logic and some skill in permutations and combinations. Questions could vary from simple linear arrangements to making an itenary of tournaments. Also tested are the Data Interpretation skills. Here one needs strong calculating skills and ability to discern data shown in any presentation – pie chart, histogram, frequency polygon, tables etc. Also needed is the clarity in deciding whether the data is sufficient in various cases. Other exams tend to have extra sections maybe on G.K. or a writing section (XAT). These also play an important part and should be stressed upon sufficiently during preparation for the exam.

Other salient point is that these exams have –ve marking i.e. a penalty for answering wrongly. So one should be cautious while answering and pick questions wisely. Generally a low attempt rate with desirable accuracy is sufficient to secure a seat. This shows that answering what little you know correctly will increase your chances. The written test is a filtering process – once the test is completed the final candidates are selected after a series of Group discussion and/or interview. Having a good academic track record and all round profile stands one in good stead. Moreover here many things are tested from communication skills to academics, current affairs to opinions on various topics. In short candidate has to prove his mettle in both the test and interview to make the final call. When to do an mba?

The best time to do an MBA depends upon why you want to do an MBA. You can do an MBA immediately after graduation if you want to kick start your career with a managerial profile with the best MNCs in India or abroad.

You can also do an MBA after gaining industry experience, as a MBA is about training you in business management, where industry experience would prove beneficial to further sharpen your skills and propel your career faster. Students with work experience have an added advantage in pursuing MBA abroad as international B-schools consider work experience as major criterion for selecting candidates.

In response to the current global economic scenario, companies are increasingly becoming diversified and multifaceted, thereby augmenting the scope and need for an MBA. The fruits of this qualification are being reaped by fresh graduates as well as practicing managers both in India and Abroad.

G Sasi Sekhar B.Tech Final year Mechanika, April 2007

13

Curves Obtained by driven Parmanent Magnet DC Motors Atul Kumar Soti, B.Tech 2nd year

S

mall permanent magnet DC motors are used in many places like in tape records, in toys, in automotive applications like wiper etc. Another important application of permanent magnet DC motors is in speed control and R.P.M. measurements where these motors are used as small generators. Motors when used as generators are called driven motors. DC driven motors produce DC voltage but the waveform of the EMF induced is time varying. While looking at the waveforms obtained by a number of same types of this small permanent magnet DC motors we find some differences in the waveforms. The Objective here is to explain those waveforms and why there are some differences?

Motors under consideration have a ring shaped permanent magnet stator and a rotor. The rotor consists of three poles which are 120 degrees apart and made of thin metal plates stacked together with thin copper wire coiled around each of the three poles. The two ends of each wire are soldered onto a terminal and then each of the three terminals is wired to one plate of the commutator.

The waveforms are almost similar but the difference between them is the time after which each curve repeats. We call this time as time period of the waveform and it is represent by Δt. Table-A shows some experimental values obtained for figure1 at different R.P.M.. An important thing to observe is that Δt is equal to the time required for the rotor to rotate by an angle of 60 degrees. This observation itself is sufficient to understand what is happening. Consider the top view of an open motor shown in figure 3. Windings on each rotor pole are replaces by a sinusoidal voltage source which are shown as time varying DC source. The line joining north and south poles of the stator is called pole axis and the line joining the points where brushes make contact with the commutator bars is called brush axis. Angle between the pole axis and the brush axis is represented by Θb. where as Θc is the maximum angle by which rotor can rotate without changing the contact of brushes from one pair of commutator bars to another. For a three rotor pole motor Θc is equal to 60 degrees.

In figure 3 commutator bars 1 and 3 are in contact with the brushes and Θb= 0°. ε1 and ε2 are in series whose sum is equal to ε3 in magnitude and is in parallel with it therefore EMF generated (E) is equal to -ε3. When rotor is rotated by an angle of Θc i.e. 60 degrees in anticlockwise direction brush contact changes from cummutator bars 1, 3 to 1, 2 and E becomes equal to ε1. During this period, When E = -ε3 ε3 = sine (Θ) When E = ε1 ε1 =sine (Θ)

where -120° < Θ < -60° where 60° < Θ <120°

Above discussion can be extended for a P number of rotor pole machine. To make the net EMF in rotor circuit equal to zero, sum of EMFs induced in all rotor poles should be zero. Therefore the EMF obtained across the two brushes is equal to sum of the EMFs induced in P/2 rotor poles which lie between the brushes, when P is even, or is equal to sum of the EMFs induced in (P+1)/2 rotor poles or rest (P-1)/2 rotor poles which lie between the brushes when P is odd. Therefore, 14

courtesy: Electrical Machines Lab, IITG

Therefore the value of E is always equal to sine (Θ) where 60° < Θ < 120°. Hence waveform of E will be a curve, repeating after time Δt, which is obtained by cutting the sine wave with two vertical lines passing through the points (60°, 0) and (120°, 0). This is similar to what is shown in figure1. Now if the value of Θb is non-zero.

Let us rotate the pole axis by an angle Θb in anticlockwise direction.

From the similar discussion we can say that the value of E is now equal to sine (Θ-Θb) where 60° < Θ < 120°. And waveform of E will be a curve, repeating after time Δt, which is obtained by cutting the sine wave with the two same previous lines but shifted towards negative x-axis by a distance of Θb. This explains the figure2 in which Θb is nearly equal to 20°.

Figure 1 and 2 waveforms obtained from two motors Mechanika, April 2007

When P is even,

Θc = 2π/P

and Δt = 60/N*P

P/2-1

E (t) =Σ Nε0sin [2nπ/P+ (Θc) {N*P*t/60} +Θb] n=0

P/2-1

= Nε0 Im Σ exp [i(2nπ/P+ (Θc) {N*P*t/60} +Θb)] n=0

E (t) = (Nε0/ sin (π/P)) sin [(Θc) {N*P*t/60} + Θb+ cos-1sin (π/P)] E (t) = (Nε0/ sin (π/P)) cos [(Θc) {N*P*t/60} + Θb- π/P]

for P>1

Figure 3

When P is odd,

Θc = π/P

and Δt = 30/N*P

(P-1)/2

E (t) =Σn=0Nε0sin [2nπ/P+ (Θc) {N*P*t/30} +Θb] E (t) = (Nε0/2sin (π/2P)) sin [(Θc) {N*P*t/30} + Θb+ cos-1sin (π/P) + π/2P] E (t) = (Nε0/2sin (π/2P)) cos [(Θc) {N*P*t/30} + Θb- π/2P]

for P>1

Where N stands for R.P.M, t for time and -π/2 < Θb < π/2.

And {x} denotes the fractional part of x.

This graph shows the net EMF generated in three rotor pole machine with Θb =0° (solid lines). Dotted curve is the EMF in individual rotor pole.

Mechanika, April 2007

15

Campus Placement 2006-07: A Report (Only for Mechanical Engineering)

This year IIT Guwahati has drawn the attention of a wide spectrum of companies for campus recruitment. As compared to the previous years the job scenario has been exceptionally good. The placement session for this academic year was held over two phases. The first phase started from 1st Dec 2006 and continued till 10th Dec 2006. Then there was a break for inter IIT sports meet followed by the second phase, which started from 25th Dec 2006 and is still going on. Out of around 76 companies that visited the campus this year, around 42 were interested in Mechanical Engineering students including B.Tech and M.Tech. Out of all these companies we had 16 core companies, 16 software companies, 1 consultancy, 2 finance, 2 from IPR and 6 other companies.

21. Covansys+

Table 1 Name of the Company

Interested in

No. of offers

Core Oil and Gas 1. Schlumberger

B.Tech + M.Tech

0

2. Shell

22. Bentley Systems+ 23. OnMobile

B.Tech

2

24. Niksun+

B.Tech

1

25. Flextronics+

B.Tech + M.Tech

0

26. IBM

B.Tech + M.Tech

6 +6

27. Accenture+

B.Tech + M.Tech

0

B.Tech + M.Tech

5+0

B.Tech

1

4. IOCL

B.Tech

1

28. Wipro

B.Tech + M.Tech

2+2

5. BPCL

B.Tech

3

29. TCS

B.Tech + M.Tech

0+3

B.Tech

3

30. Patni

B.Tech + M.Tech

0

31. Infosys

B.Tech + M.Tech

1+0

B.Tech + M.Tech

1+ 2

6. Reliance

+

7. Ashok Leyland+

M.Tech

3

8. Tata Motors

M.Tech

8

B.Tech + M.Tech

3+4

9. M&M

32. Cognizant

Consultancy B.Tech + M.Tech

33. PWC+

4+1

Finance

Others B.Tech

10. HLL+

0

34. Byte Consulting 35. Future First+

B.Tech

1

12. GE+

B.Tech + M.Tech

2+6

13. L&T

B.Tech + M.Tech

1+0

36. Pangea3

14. Fluent

B.Tech + M.Tech

1+0

37. Evalueserve

15. Tata Technologies

B.Tech

5

16. DRDO

B.Tech

2

11. NTPC

+

B.Tech

1

B.Tech + M.Tech

1+0

IPR +

B.Tech + M.Tech

1+0

B.Tech + M.Tech

2+1

Others 38. Fands Infotech+

B.Tech + M.Tech

0

39. TIME

B.Tech + M.Tech

0

17. Oracle

B.Tech + M.Tech

0

40. Global Analytics+

B.Tech + M.Tech

0

18. DE Shaw

B.Tech + M.Tech

0

41. Absolute Data+

B.Tech

0

42. CADOPIA+

M.Tech

1

Software

19. Techspan

B.Tech

0

20. Manhattan

B.Tech

2

+

courtesy: Placement Cell intranet Website

2 4+1

3. NRL+

+

Automobile

16

B.Tech B.Tech + M.Tech

The companies who visited the campus for the first time Table 2 B.Tech No. of students registered: 39 Actual No. of students placed: 38 No. of Job offer: 58 Average Annual Salary (lpa): 5.37 Highest Pay Package (lpa): 10.53 As on April 22, 2007

M.Tech No. of students registered: 31 Actual No. of students placed: 28 No. of Job offer: 38 Average Annual Salary (lpa): 4.39 Highest Pay Package (lpa): 6.2 Deepak Kumar B.Tech Final Year

Mechanika, April 2007

CONTROL OF SPACE MANIPULATOR FOR TRAJECTORY PLANNING AND OPERATION IN AN UNSTRUCTURED ENVIRONMENT Saurabh Garg, Deepak Kumar, G. Rajkumar B.Tech Final Year (2003-2007 Batch), Department of Mechanical Engineering Indian Institute of Technology Guwahati Abstract: Various factors should be taken into account when we choose the mechanism and size of a robot manipulator at the design stage, or when we determine the posture of the manipulator in the work space for performing a given task during operation. An important factor among theses is the ease of arbitrarily changing the position and orientation of the end-factor at the tip of the manipulator. For a total evaluation of manipulators, of course we should consider many other factors including size of workspace, positioning accuracy, load capacity, speed, reliability, safety, cost, ease of operation, and settling time.

1. INTRODUCTION

This work basically presents a simplified analysis of the working of a 3-D space manipulator by regulating its end-effector to move along a particular trajectory only. A control system is intended to serve this purpose of regulating this trajectory motion. The “Control” is not obtained by conventional techniques like linear feedback control or a two-stage control by linearization and servo-compensation, but through a simplified mathematical model of a multi-layer perceptron feed forward Backpropagation Neural Network. This model has the typical characteristics of a control system - e.g.: use of transfer functions, feed-back, comparator performing the comparison between actual and desired outputs etc. The network is trained for information about a particular trajectory within a given error bound say x%, which is then used to predict its response to unknown and previously unseen coordinates.

Although there are many smoother functions that satisfy these conditions, we select polynomials of time t because of their case of computation and simplicity of expression. We express ζ (t) as a fifth-order polynomial: ζ( t ) = ao + a1t + a2t2 + a3t3 + a4t4 + a5t5 Then, the unknown coefficients a0 – a5 are:a o = ζo a1 = ζo a2 = ζo / 2

2. LITERATURE SURVEY

Xu et al. [1] have developed a self mobile space manipulator, a laboratory version of a robot designed to work on the trusswork and other exterior surfaces of space station freedom. Mavroidis et al. [2] have proposed the end-point control of a long reach manipulator systems (LRMS) to perform tasks in different and difficult to reach systems . T. Yoshikawa [3] in his book ‘Foundation of Robotics’ describes position control and end-effect control as elements of robotic control.

3. FORMULATION OF THE PROBLEM: GENERATING A DESIRED TRAJECTORY: We first choose an arbitrary joint variable qi , and represent it by ζ . We assume that the value of ζ at the initial time (0) is ζo and that the value at the final time ζf .

Boundary Conditions:1.ζ(0) = ζo 2.ζ( tf ) = ζf 3.ζ‘(0) = ζo‘ 4.ζ‘‘(tf) = ζf‘ 5.ζ‘‘(0) = ζo‘‘ 6.ζ‘(tf) = ζf‘‘ Mechanika, April 2007

Formulation of the problem involves discussing two cases:A) Two Link manipulator moving from an initial to a final position (Fig. 1) B) Generalized case of 3-D end-effector control The case for Two Link Manipulator is described below: Applying the above method as described previously, θ1(t) = 90 – 80 t3 + 80 t4, = 85 – 20 (t – 0.5), = 65 – 20 (t – 1.5) + 80 (t –1.5)4, And the second joint angle θ2 is given by:θ2 (t) = - 60 – 160 t3 + 160 t4, = - 70 – 40 (t – 0.5),

17

= - 110 – 40 (t - 1.5) + 160 (t – 1.5)3 -160

(t – 1.5)4,

4. NEURAL NETWORK MODELING

The backpropagation neural network (BPNN) as used in this work is shown in Fig. 2 and utilizes the generalized delta rule algorithm for the network training. The most general structure of the network consists of an input layer, a variable number of hidden layers each containing any number of nodes and an output layer. The input layer receives the information from an external source, which is subsequently modified by the interconnection weights between it, and the adjacent hidden layer.

The sum of the modified signals (total activation) is then operated upon by a suitable transfer function, and these activated values in turn become the starting signals for the next adjacent layer. In this way, the modified signal finally reaches the output layer where it is communicated to the external receptor(s).

The supervised learning used here is of batch mode type in which the input-output patterns are sequentially presented to the network undergoing a training phase and depending upon the deviation of the predicted output from the desired output, the various interconnections are adjusted using average gradient information. The process is repeated iteratively until the mean square error falls below a prescribed limiting value Mean Square Error ‘MSE’ is calculated as

where, P is the number of patterns, M is the number of nodes in the output layer, dkp is the desired output of the kth node of pth pattern, ckp is the calculated output of the kth node of pth pattern.

5. NUMERICAL RESULTS AND DISCUSSION: Case A: 2-Link Manipulator The training data set (input file for the source code) was prepared consisting of around 120 inputs corresponding to the ‘θ1’ values of the driver link of the manipulator. The ‘θ2’ value corresponding to the angular position of the end-effector link was fixed by the constraint to move along a particular trajectory in order to reach the desired final location.

Various BPNN architectures (corresponding to different number of hidden nodes) were selected by hit and trial and the best optimized network i.e. the one which minimized the mean square error was found by trial and error to be Input - (5-7-7-1) - Output. The learning rate was set to be 0.0025 while the momentum coefficient was around 0.25.

• Typical set of training and testing error curves are obtained.

• In this way, the end-effector of the manipulator can be pro vided information about the desired trajectory and ‘trained’ control system can move the end-effector within a particular error-domain.

• Here the training error domain was found around 12% and this can be reduced with a larger training data-set. This is shown in Fig.2.

• The level of error domain is determined by the requirement for the precision and accuracy in application.

Case B: General case Similar results are obtained for this general 3-D case, but the input data-set here consisted of randomly selected (x, y, z) coordinates in 3-D space. To make the problem simpler and easy to visualize, the y-coordinate was kept zero, and the z fixed at 1, so that the point moves along the line z = 1 in the x-z plane. The corresponding ‘y’values are noted to form a curve by assuming a function of the form f (x,z) = x . The training and testing data-set was

Fig.1 Schematic diagram of a two link manipulator

Fig.2 Schematic diagram of the BPNN architecture 18

Mechanika, April 2007

formed out of this function’s values, and similar curves for MSE were obtained, justifying the validity of the method used. The error prediction by the network is shown in Fig.3.

Fig. 4 shows how the neural network architecture performs the trajectory control operation. The solid line curve is the desired trajectory for the end-effector. By training the network with some random intermediate trajectory points, we can provide artificial intelligence (AI) to the network to be able to predict (within certain error domain, e.g. x% as indicated), the path of the trajectory for any other points.

x% error bound around the desired trajectory

Fig.5: Generalized 3-D case error prediction for trajectory control by the BPNN Fig. 3 Trajectory control for the space manipulator

6. CONCLUSION

The present work aims at giving a simplified analysis of a neural network approach to trajectory planning and control. It shows how the end-effector path can be traced within certain error limits for a multi-input and multi-output system and in general for any number of degrees of freedom for the manipulator. The method may not be exactly suitable for high precision applications such as fault diagnosis of unmanned space vehicles or satellites but offers a useful insight into the application of artificial intelligence techniques in robotic manipulations where some degree of error is tolerable.

REFERENCES [1]Yangsheng Xu, Ben Brown, Mark Friedman, Takeo Kanade “Control Systems of Self-Mobile Space Manipulator”, IEEE Trans. on Control Systems Technology, Vol.2, No.3, pp.207-219, 1999.

[2] Mavroidis C, Dubowsky S, Raju V “End point control of long reach manipulator systems” Proceedings of the Ninth World Congress on the theory of machines and mechanisms, September 1-3, 1995, Milan, Italy.

Fig. 4: 2-Link manipulator error prediction for trajectory control by the BPNN

Mechanika, April 2007

[3] Yoshikawa T. “Foundations of robotics: analysis and control.” Cambridge, Massachusetts: MIT Press; 1990.

19

Modeling Atmospheric Radiative Transfer SHDOM Rajpreet Singh, B.Tech Final Year

Abstract: All life on earth exists because of the sun’s energy available in the form of solar radiation. To reach the surface of the earth the solar radiation must travel past the earth’s atmosphere. It is known fact that only 5% of the total radiation that should have reached the earth reaches it. Rays only in the infra-red spectrum are able to penetrate to the surface while high energy radiation like ultraviolet are mostly blocked by the atmosphere. Except the blocking of UV radiation there is another prime factor which considerably reduces radiation from reaching the earth’s surface and that is intervention of the incoming radiation with the clouds.

NEED TO MODEL Observations confirm that clouds have a large impact on the radiative energy flows in the atmosphere. The measure of this energy serves the basis of the climate predictions and remote sensing in many cases. Besides the problem of predicting the distribution of cloud properties, one difficulty is modeling the radiative transfer in clouds because of the ubiquitous in-homogeneity of clouds. Almost no cloud fields on Earth are horizontally uniform, which is the assumption of plane-parallel models that are the mainstay of atmospheric radiative transfer.Modeling studies show that in-homogeneity effects are significant in overcast clouds and potentially large in broken cloud fields. Thus there is a need for 3D radiative transfer models to serve as numerical tools for understanding these in-homogeneity effects, parameterizing their effects in climate models, and correcting for their effects in remote sensing inversions. The atmospheric science community has been developing 3D radiative transfer models for over two decades. The reason that this area of modeling is still the subject of ongoing research is because it is so computationally demanding. Solving the radiative transfer equation in a 3D medium is a 5D (three space co-ordinates, two angles) boundary value problem. There are still needs for computationally efficient, accurate, and flexible 3D models.

need to be computed. For example, to compute the domain average reflected and transmitted solar flux, a Monte Carlo calculation with 100 000 photons will often suffice, which would be faster than an explicit radiative transfer method for a 3D medium. On the other hand, if many quantities, such as an image of upwelling radiances from the domain top or the 3D distribution of heating rate, are needed, then an explicit method can be much faster than Monte Carlo methods. For explicit methods, since the whole radiance field is computed, any desired radiative quantity may be computed at little extra cost. For Monte Carlo methods, either many more photons or successive calculations are required for more output quantities but the Monte Carlo methods will always use much less memory. The exact cross-over point in computational speed between Monte Carlo and explicit methods depends on the particular problem being solved and the models used.

SHDOM – A NEW TECHNIQUE There are many hopelessly inefficient ways to compute 3D radiative transfer. Focusing on the general, computationally efficient methods, we find that they all represent the spatial variation of the radiance field with a grid, rather than spectrally. There are methods with discrete

COMPARISON OF MODELS Research on modeling the atmospheric radiative transfer is quite recent. In fact the first and the most common type of radiative transfer model used to study 3D cloud effects has been the Monte Carlo method which was proposed by Marchuk in 1980. This method, which can be thought of as simulating photon paths in the medium, has a reputation as being rather slow for results with good accuracy. The alternatives to Monte Carlo methods are those methods that explicitly represent the radiance field in the computational domain. This class of model is the standard for plane-parallel transfer. Monte Carlo methods are generally more efficient than explicit methods when relatively few quantities 20

Figure 1 Homogenous Cloud box surrounding the earth Mechanika, April 2007

ordinate representation of the angular aspects of the radiance field, such as the discrete ordinates method (DOM) or SN methods.Other methods use a spectral approach for the angular part of the field, such as the spherical harmonic spatial grid (SHSG) method. And the latest one being used widely is the spherical harmonics discrete ordinate method (SHDOM) which is an outgrowth of SHSG with combined aspects ofdiscrete ordinate methods using a new solution method and it has been successfully implemented in 3D. The SHDOM uses both spherical harmonics and discrete ordinates to represent the radiance field during different parts of the solution algorithm. In it the spherical harmonics are employed for computing the source functions including the scattering integral whereas the discrete ordinates are used to integrate the radiative transfer equation spatially. The one innovation is the discrete adaptive grid, which helps in providing that extra resolution wherever needed. The ability to specify the angular and spatial resolution allows the trade-off between calculation speed and accuracy to be explored. The method works well for both monochromatic or broadband (with a k distribution) collimated solar and/or thermal emission radiation.For better climate prediction and remote sensing all over the world, more research is being carried out and efforts are being made to improve the computation efficiency of the methods and subsequently reduce the computational costs associated. The major research centers are the top US universities like university of California Los Angles (UCLA), university of Wisconsin-Madison, university of Colorado at Boulder etc.

Figure 2(b) The algorithm followed by the SHDOM

Figure 2(a) The adaptive nature of the spatial grid enabling us to make the grid more intense where cloud density is more basically taking in account for the in-homogeneity.

Mechanika, April 2007

21

Just for FUN One mechie boy is deeply in love with a mechi girl (though the girls in mech are rare). Think how this poor boy will propose the girl. It would be somewhat this way...

Boy: I want to propose you.

Girl: Propose!!! But what for??

Boy: I want you to be a part of my closed system.

Girl: Unless all the failure criteria is checked, you cannot enter in my heart.

Boy: You know, when I saw you my heart behaved like a unit step function.

Girl: Thank God!! It didn’t cross the ultimate strength.

Boy: How much iteration would be required to open up the valves of your heart?

Girl: It depends on your load bearing capacity.

Boy: Reply me soon; else I will cross my endurance limit.

Girl: Don’t worry, I will not apply cyclic load.

Boy: See, I will not let any stress enter in your life.

Girl: Ok!! But what about the residual stress.

Boy: We will do heat treatment and will release all those stresses.

Girl: But, I have low boiling point.

Boy: No Problem. I will increase the pressure.

Girl: I want composites of my relationship to be perfectly bonded and there should be no room for delamination.

Boy: Our properties are exactly similar so there is no chance of any failure.

Girl: OK!! With an appropriate factor of safety, I allow you to ignite the spark of my love life.

Sudhanshu kumar Final year Mechanical 22

Get your priorities right!

A professor stood before his philosophy class and had some items in front of him. When the class began, wordlessly, he picked up a very large and empty mayonnaise jar and proceeded to fill it with golf balls. He then asked the students if the jar was full. They agreed that it was. The professor then picked up a box of pebbles and poured them into the jar. He shook the jar lightly. The pebbles rolled into the open spaces between the golf balls. He then asked the students again if the jar was full.

They agreed it was. The professor next picked up a box of sand and poured it into the jar. Of course, the sand filled up everything else. He asked once more if the jar was full. The students responded with an unanimous “yes”.

The prof. then produced two cups of coffee from under the table and poured the entire contents into the jar, effectively filling the empty space between the sand. The students laughed. “Now”, said the prof., as the laughter subsided, “I want you to recognize that this jar represents your life. The golf balls are the important things - your God, family, your children, your health, your friends, and your favorite passions- things that if everything else was lost and only they remained, your life would still be full. The pebbles are the other things that matter like your job, your house, and your car. The sand is everything else- the small stuff. If you put the sand into the jar first,” he continued, “there is no room for pebbles or the golf balls. The same goes for life.

If you spend all your time and energy on the small stuff, you will never have room for the things that are important to you. Pay attention to the things that are critical to your happiness. Play with your children. Take time to get medical checkups. Take your partner out to dinner. There will always be time to clean the house and fix the disposal. Take care of the golf balls first, the things that really matter. Set your priorities. The rest is just sand.”

One of the students raised her hand and inquired what the coffee represented. The prof. smiled, “I’m glad you asked. It just goes to show you no matter how full your life may seem, there’s always room for a couple of cups of coffee with a friend.”

Mechanika, April 2007

By Deepak Shilpi, B. Tech 1st Year

T

he robot learns how to move in its environment and reacts to physical changes. When it’s damaged, it relearns how to walk.

The most remarkable thing about this robot, however, is what it lacks - a preprogrammed map of its environment. As described in the November 17 edition of the journal Science, the machine uses stored sensory input and a computer algorithm to figure out where it is and how it’s oriented. This self-reflexive ability may some day help other robots perform tasks as wide-ranging as exploring Mars or repairing complex machines.

This robot, built in a Cornell University laboratory, can figure out on its own how to crawl across a table.

The Cornell robot, created in the lab of Hod Lipson, an assistant professor of mechanical engineering, is programmed only with the knowledge of what its parts are, not where they are on its body or how to use them to crawl forward. But much like a newborn learns from trial and error, the robot sends commands to various actuators and notes the results.

The key step comes next: The results are compiled and a model is created that best explains them. For instance, commands to separate motors on the same leg will cause the leg to stretch out.

After many cycles of model building, the robot tries to move forward. The results weren’t exactly pretty, Mechanika, April 2007

It’s still too soon to begin building self-awareness into machines in the field, but in time, model-based algorithms could instill a real autonomy into robots tasked with performing in extreme conditions. Someday, for example, submersible robots may be able to automaticourtesy: Wikipedia

Tech Watch

Four Legged Freak

usually involving pulling itself across a table. Next, the researchers broke a bit off one of the legs and the robot had to figure out how to move all over again. But using the model-driven algorithm, the robot found a new way to ooch itself across the surface.

cally compensate for ocean currents as they work on oil pipelines.

Hydrogen Age

By Govind Mohan, B.Tech 1st Year

E

ven after the record-setting run-up in oil prices last year, many people refuse to face the facts.

But the truth is clearly visible to those who are willing to look at the situation: Our society’s dependence on petroleum is indeed unsustainable.

The vast majority of geologists and others who study energy resources have developed a more pessimistic view of energy in the future. Statistics demonstrate that the supply of petroleum is certainly diminishing.

Energy needs are expanding rapidly as developing nations continue to demand a larger quantity of resources. World energy consumption rose forty-nine 23

car would go into low volume production in 2008.

courtesy: Wikipedia

Honda FCX is a hydrogen fuel cell automobile manufactured

by Honda. It is said to be entirely silent in operation. percent between 1973 and 1993. Scientists estimate that the population of the world will double during the next fifty years and the demand for energy will quadruple.

Just what that alternative should be, however, is not so clear-cut. The main contenders for the title of emission-free, safe energy are wind power and nuclear power, and the division between the two camps is stark. Nuclear advocates often pooh-pooh wind as too intermittent to rely on and too diffuse to harvest profitably. Wind enthusiasts generally deride nuclear energy as a technological nightmare that can only compete if many costs-for insurance, cleanup, and waste disposal, for example-are borne by taxpayers.

The natural gas is being tried as a source of fuel for motor vehicles. Large companies use it for their fleet cars. LPG is another alternative already in use too. As for being produced in a lab, that’s only for research. Large-scale production occurs in big factories. Unlimited supply is pushing it too. It seems like no matter how much resources we have, they are going to run out sooner or later.

The new global, strategic, and market analyses show that the impact of climate change can be mitigated by introducing non-carbon hydrogen as a fuel in transportation; that nuclear electricity based on current advanced designs can supply the hydrogen fuel that is needed, plus the electricity, in a distributed system; that a potential synergism exists between wind and nuclear hybrid energy systems, when a balanced portfolio of electricity and hydrogen production is introduced that is market driven; and as a result, advanced designs and fuel cycles provide an economical, secure, and safe energy future.

The future could well become the Hydrogen Age. A major reduction in greenhouse gases worldwide can be obtained by nuclear electric production of hydrogen. No more smelly fumes at the gas station. No more polluting C02 emissions. Far less dependence on uneven supplies of fossil fuels.

It stands the longstanding reflexes of the environmental movement on its head. But embracing nuclear power is an extraordinarily green idea. It is the first necessary step toward saving modern society, familiar ecosystems, and indeed the planet itself.

Reference: Honda website and Wikipedia

In June of 2005 Honda became the first car company in the world to lease a hydrogen fuel cell powered car to Jon Spallino, of Redondo Beach,California. During the 2005-6 auto show season, they showed off a concept version of their first purpose-built fuel cell powered car. Earlier this year they announced that the 24

Mechanika, April 2007

Freshers 1.Which of the following career options would you prefer after your B.tech ?

5. Which of the following areas are you interested in?

8 7 6 5 4 3 2 1 0

10 8

CFD

6 4

0

Software

Core

Entrepenurship

Higher Studies

Heat & Mass Transfer

2 Other

Civil Services

Solid Mechanics Robotics

8 7 6 5 4 3 2 1 0

Thermodymics

2.Where would you like to do MS?

U.S.

Canada

Australia

UK

Germany

France

M.S.

M.S.+Phd

Mettalurgy

MBA

No

Material Science

Yes

Aerospace

4.Would you like to get settled in India later on in life?

Not sure right now

Biomechanics

M.Tech

Mechatronics

Other

MEMS

3.What would be your option in higher studies?

Other

Others

Mechanika, April 2007

25

Sophomores 1.Which of the following career options would you prefer after your B.tech ?

5. Which of the following areas are you interested in?

8 7 6 5 4 3 2 1 0

8 7 6 5

CFD

4 3 2 0

Software

Core

Higher Entrepenurship Studies

Civil Services

Heat & Mass Transfer

1 Other

Thermodymics

2.Where would you like to do MS?

10

Solid Mechanics

8 6 4

Robotics

2 0

U.S.

Canada

Australia

UK

Germany

France

M.S.

M.S.+Phd

Mettalurgy

MBA

No

Material Science

Yes

Aerospace

4.Would you like to get settled in India later on in life?

Not sure right now

Biomechanics

M.Tech

Mechatronics

Other

MEMS

3.What would be your option in higher studies?

Other

Others

26

Mechanika, April 2007

3rd Year 1.Which of the following career options would you prefer after your B.tech ?

5. Which of the following areas are you interested in?

8 7 6 5 4 3 2 1 0

8 7 6 5

CFD

4 3 2

Heat & Mass Transfer

1 0

Software

Core

Entrepenurship

Higher Studies

Other

Civil Services

Thermodymics

2.Where would you like to do MS?

10

Solid Mechanics

8 6 4

Robotics

2 0

U.S.

Canada

Australia

UK

Germany

France

M.S.

M.S.+Phd

Mettalurgy

MBA

No

Material Science

Yes

Aerospace

4.Would you like to get settled in India later on in life?

Not sure right now

Biomechanics

M.Tech

Mechatronics

Other

MEMS

3.What would be your option in higher studies?

Other

Others

Mechanika, April 2007

27

Final Year 1.Which of the following career options would you prefer after your B.tech ?

5. Which of the following areas are you interested in?

8 7 6 5 4 3 2 1 0

10 8

CFD

6 4

0

Software

Core

Higher Entrepenurship Studies

Civil Services

Heat & Mass Transfer

2 Other

Thermodymics

2.Where would you like to do MS?

10

Solid Mechanics

8 6 4

Robotics

2 0

U.S.

Canada

Australia

UK

Germany

France

M.S.

M.S.+Phd

Mettalurgy

MBA

No

Material Science

Yes

Aerospace

4.Would you like to get settled in India later on in life?

Not sure right now

Biomechanics

M.Tech

Mechatronics

Other

MEMS

3.What would be your option in higher studies?

Other

Others

28

Mechanika, April 2007

3D Reconstruction from Points to Freeform Shapes

By Dr. G. Saravana Kumar

R

everse engineering (RE) and rapid prototyping (RP) are emerging technologies that have been accepted to play a promising role in reducing the product development time.

RE refers to the process of creating engineering design data from existing parts [1-3]. It recreates an existing part by acquiring the surface data of the part using a scanning or measurement device.

RE helps a designer to create, using conceptual clay or wood model, a CAD model for further use in analysis and manufacturing. The existence of a CAD model provides enormous gains in improving the quality and efficiency of design, manufacture and analysis by exploiting the CAD/CAM technologies. Coordinate measuring machines have been used to extract surface data but their data capturing operation is very slow for parts having complex free-form surfaces. In recent years, laser scanning has become a powerful tool in capturing the geometry of complicated models. The CAD model developed by an RE process can be converted into a physical prototype using an RP technique. Generally, in RP, prototypes are fabricated layer by layer. It uses additive manufacturing processes, which do not require any tools or setups compared to the subtractive techniques used in the traditional machining. Different fabrication methods exist for RP, but nearly all use the same input geometry format, called STL (Stereo Lithography), which consists of a list of triangular facet data. The STL format has advantages due to its simple structure, ease of use and availability of robust computational algorithms.

The application of these new technologies is very encouraging. A few of the many application areas include;  Aesthetic design particularly in automobile industry where a scaled wooden or clay model is first conceptualized and from the same the CAD definition is to be evolved  Produce a copy of part when its original design data is unavailable  Re-engineer an existing part when analysis and modification are required  Inspection and Quality control  Generate custom fits to a human surface for designing helmets, shoes, and space suits  Bio modeling for preoperative surgical studies and for custom prosthetics  Areas other than engineering such as sculpting, archeology etc.

A good introduction of RE technology is given by Varady et. al..

[1]. Bisson [2], describes various types of scanners to digitize the objects. The point clouds obtained through these scanners are processed to fit curves and surfaces by different techniques to obtain CAD models [3-6]. Pham and Gault [7] present a detailed study as well as comparison of various RP process. Part orientation Mechanika, April 2007

has to be selected in RP in order to get quality parts with minimum error. A recent work by Feng lin, et. al. [8] discusses on developing a mathematical model for optimal orientation for minimum error in RP. Smith [9] and Kochan [10] discuss the recent trends and business of RP. Research on integrating RE and RP [11, 12 and 13] though at an infant stage is a promising way to reduce the development time.

In India the automobile and aerospace industries are using RE and RP for research and development. New application areas are being pursued in using RE and RP for rapid product development and other non-engineering applications like bio modeling and sculpting etc. The article serves as an information source about the latest technology available at the disposal of designers, bio medics and sculptors to enhance the products and services and also provides prospects for research and development.

REVERSE ENGINEERING (RE) Point Cloud Acquisition There are many different methods for acquiring shape data. A broader classification and listing is given in Figure 1. Essentially, each method uses some mechanism or phenomenon for interacting with the surface or the volume of the object of interest. The noncontact methods use light, sound or magnetic fields, while in contact methods the surface in touched by mechanical probes. In each case an appropriate analysis of the data acquired has to be done to locate the positions of points on the surface. As an example, in laser range finders, the time of flight is used to determine the distance traveled and subsequently the point location. There are many practical problems with acquiring usable data, the major ones being calibration, accuracy, accessibility, occlusion, fixturing, multiple views, noise and incomplete data and surface finish.

Despite the practical problems, it is possible to obtain sufficient data in reasonable short period of time using appropriate methods as per the application area. Once the measured data is available, the process of modeling from the same can begin.

Modeling Global shape characterization from the measured point data is a key step in the process of converting discrete data set into a piecewise continuous model. The organization of data and neighborhood information are important issues at this stage. Modeling from point samples thus is essentially to compute a mathematical definition that stores this topological information from point cloud. The procedure for construction of models thus depends not only on the type of data but also the type of model required. The kind of 29

Figure 1. Data acquisition methods created depends on the intended use. Some applications just need generation of set of planar surfaces that store topology implicitly.

While others need connected higher order surface patches with or without enforcing smooth continuity. Figure 2 illustrates the kinds of models that are constructed from point cloud data for various applications.

Faceted models (refer Figure 2 (b)) are the simpler ones to construct with very less intervention on the part of the user. The models are a set of planar faces largely triangular in nature but other polygonal faces are also possible. A rectangular faceted model is used in Geographical Information System. Images of geographical regions are produced from photographs taken from airplanes or satellites. A series of digitized photographs of a region taken from several angles and at different times of the day are combined and processed to form a Digital Elevation Model (DEM format). This model gives the terrain surface as a mesh of rectangular grids with each grid point having latitude, longitude and altitude information.

Triangular faceted models can be generated from point clouds produced by digitizers for modeling for graphics, animation, CAD, CAM as well as prototyping to name a few. A triangular facet data model called an STL file is extensively used in CAD data transfer for downstream applications like tooling for manufacturing and prototyping.

Computed Tomography (CT) and Magnetic Resonance Imaging (MRI) readily yield object boundary information as data points lying in parallel planes, or slices, which can be arranged into polygonal contours to represent a 3D object. In the medical field, CT is used to scan the interior of the body. It is effective for capturing images of bones and dense organs such as the brain and abdominal region. CT scanners produce images by firing X-rays at the region of interest and measuring the intensity of the rays after they have passed through the body. Industrial CT scanners can be used to image engineering artifacts in order to detect cracks or holes. MRI is effective for producing images of soft tissues and is especially useful for detecting tumors in the human body. A series of 2D CT or MRI scans is treated as a single 3D image. Usually the images produced by CT and MRI scanners are noisy, and in medical applications they capture densities for more organs than are needed for the study. Thus the images must be filtered to reduce noise, and they must be threshold and segmented to isolate regions or organs of interest. CT and MRI scans come in a variety of vendor-specific formats. For medical images, the American College of Radiology and the National Electronics Manufacturers Association have set a standard called Digital Imaging and Communications in Medicine 30

(a) Point cloud acquired

(b)Triangulated model

(c) Contour model

(d) Surface model Figure 2. Geometrical models from point cloud data Mechanika, April 2007

(DICOM). For displaying, manufacturing of these medical models one has to develop mesh of facets from contours to represent the boundary of the object. Some applications like RP need only contours representing the boundary of the object to build the same.

In this case the contour data obtained from processing CT or MRI images can be directly used without further processing. Optical scanners give partially connected point data in multiple views when scanning wrap around objects. These raw point data are processed to yield triangular or surface models depending on the need of application. Some researchers have suggested direct-RP from point samples [11, 12 and 13]. Here contour information that represents the object boundary has to be extracted after merging cloud from multiple views (refer Figure 2 (c)). In establishing a direct link between point sampled geometry and RP, an major challenge is to handle the huge amount of point data generated by scanning devices.

Surface models (refer Figure 2 (d)) are B-rep models, which represent an object boundary as a set of surfaces. In majority of CAD/CAM applications such surface models are required.

Particularly in mechanical engineering, a plane or a cylindrical hole cannot be approximated by set of faces or by a series of contours, since these are functional faces to be manufactured by grinding or drilling. Moreover aesthetic parts such as car body panels require at least (curvature) continuity between surface elements, which requires a mathematical surface model. The order and degree of surfaces and the continuity between the surface patches vary depending on the nature of objects. Prismatic parts can generally be represented by simple algebraic surfaces (planes, quadrics) with (position) continuity or in some cases with (tangential) continuity. In the design of exterior of automobiles,

household appliances, cellular phones, aerospace components etc., curved surfaces are widely used to enhance the design features and functionality. The design of such freeform parts needs the shape to be represented by freeform surfaces (parametric surfaces continuity between the like B’eziers and B-splines with surface elements. Although ideally one would like to have a fully automatic surface patching system on to a cloud of points, which can make decision and classification without user interaction, this is not still realized. The information that specifies what sort of surface elements occurs in the object and its location has to be still supplied through user interaction. Hierarchies of surfaces (planes, quadrics, sweep surfaces, B-splines) that are in the order of geometric complexity have to be defined at this stage, which a human can recognize and specify to the computer, which shall determine the final model.

RAPID PROTOTYPING (RP) The RP technology is based on the principle of converting a 3Dimensional solid model into a series of 2 Dimensional crosssectional layers stacked on top of each other. Each layer is generated by one of the several techniques available, such as photo curing, fusing and deposition, cutting, sintering or binding with binding material (some processes are shown in Figure 3 (a)-(c)). The layers are created bottom up and are joined to each other during the progressing of the process itself. The dimensional accuracy of the model depends on the thickness of the layer (accuracy may be different in horizontal (X-Y) and vertical directions (Z)) the layer formation techniques and post curing operations if any. The essential components of a RP system are

(a) Selective Laser Sintering

(b) Stereolithography

(c) Fused Deposition Modeling

(d) Prototype of a complex mold

Figure 3. Rapid prototyping processes and prototypes Mechanika, April 2007

31

  

Software for solid modeling or accepting solid models created by other software packages, Software to convert the solid model into instructions for RP machine and RP machine itself.

A number of software packages are available today to assist in creating a 3D model of a part. Almost every modeling package currently available translates the model into STL format. The initial step in the process involves ‘slicing’ the solid model into a number of 2D layers. This is achieved by using an algorithm which computes the sequential points of intersection of horizontal plane with the faces and edges of the solid model. The cutting plane is positioned at different elevations, based on the layer thickness or number of layers specified by the user, to compute the various cross-section of the model. For each layer, instructions are generated for the movement of the RP machine elements (head and /or table movement) and stored in a machine language file (referred to as SML in some systems.) In many RP machines, each layer is obtained by a raster movement of the head to cover the area enclosed within the boundary of the layer cross-section.

One of the main problems in a few RP techniques is related to the creation of layers in the vicinity of an undercut or an overhanging portion of the component. This is taken care by providing support structure. Later once the model is constructed the same is removed by many processes including heating, washing in a solvent solution or simply breaking it off. The surface in contact with the support structure is generally impaired. Another inherent limitation is poor surface finish due to stair case effect. This can be minimized by using very thin layers but again limited by the hardware. Size limitation of RP machines have largely been taken care off. Large size prototypes can be build in parts and later glued together. Currently larger machines are also available. Owing to the novelty of the technology and non standardization, the technology is currently priced high. A sample prototype produced by a commercial machine is shown in Figure 3(d).

HARDWARE AND SOFTWARE FOR RE AND RP Current state of art of RE and RP hardware and software offers fairly very good point cloud processing and surface fitting, creation of CAD model and prototyping with interactive help. The section discusses the characteristics of certain hardware and software with which the author is familiar. The section is not exhaustive or biased.

The motive is to introduce some of the hardware and software and the reader is advised to evaluate all the available systems in the market as per one’s need.

3-D Coordinate Measuring Machine, make: Carl Zeiss [14] shown in Figure 4(b) is a contact type of digitizer. Though this is primarily used for metrology and quality control, the same can be used for reverse engineering. The other equipment is PICZA from Roland [15]. It works on the principle of range sensing. The equipments measure distances by sensing the time of flight of the laser beams.

Before digitizing any part, the fixtures are prepared keeping in view the geometry, so as to protect positional accuracy and prevention of any form of vibrations. It is necessary to scan in multiple views and merge the same to obtain the complete point cloud model of an object. The output of the digitizing is a high-density point cloud in ASCII format. Further the associated software polygonizes the point cloud and delivers a optimized polygon mesh in STL format.

Other scanners include a Silver Series FARO Arm [16] and ATOS II [17] an optical scanner.

Scanned point cloud file can be imported into software like Imageware’s Surfacer [18] for point cloud processing. First of all the existing flaws and noise is to be reduced from the point cloud.

Later data is reduced as per the requirement of geometric modeling.

Cloud characteristics like straightness, flatness, circularity, cylindricity, concentricity, coaxiality etc. help to recognize the shape properties of the cloud and aid in modeling. Geometric modeling of the objects can be done in Surfacer and IDEAS [18].

Imageware Surfacer, is a powerful and intuitive surface

Figure 4.

RE and RP facilities available in IITG (a) EOS RP machine

(b) Carl Ziess 3D CMM

(c) Rolland Laser scanner

Figure 5. Flexible surface creation and real time surface diagnostics with Rhino [32] 32

Mechanika, April 2007

creation tool for direct creation of freeform surfaces from curves, surfaces, or measured point data. The flexible design environment supports both Bezier and NURBS surface patch layout. Dynamic surface modification tools allow design changes to be explored interactively to immediately visualize the aesthetic and engineering implications of the design. The creation tools (refer Figure 5) offer a mechanism for developing anything from rapid to high-quality surfaces including surfaces with the high accuracy and smoothness required of automotive Class A. Efficient continuity and constraint management tools maintain surface-to-surface transitions up to curvature continuity. Real-time diagnostics provide a complete suite of quality analysis tools. These tools are instrumental in identifying surface curvature and highlights used to detect surface flaws, deviations and imperfections. Additionally, Imageware digital validation tools include checking for machining capability, parting lines and surface gaps, to identify design flaws before data is released to downstream processes. Surface model file of the objects can later be imported in solid modeling packages such as Autodesk [19], IDEAS modeling software for converting the geometry to watertight solid geometry. MIMICS [20] commercially available software is dedicated to bio modeling application from CT and MRI. The data in STL format are converted to machine language for machining using DELCAM [21], FDM using Quick-

(a) Digitized point cloud of mock

Deposition Modeling system (FDM) RP system [23]. The system is equipped for prototyping with ABS plastic. Another RP machine is Solid Ground Curing (SGC) system [24]. The system is Cubital Solider 5600 and is an industry class machine. Vacuum casting system, epoxy tooling, arc spray gun and low melting alloy furnace all from HEK [25] are some Rapid Tooling (RT) facilities that are commercially available for users.

RAPID PRODUCT DEVELOPMENT The motive behind this work (the author was involved with this project during his tenure at CAD P Lab, IIT Kanpur) was to use CAD-CAM technology, to automate the design and development process of a saddletree. Saddletree is the basic skeleton structure of the saddle and is designed in a way to fit both the rider and the back of the horse. Saddletrees are traditionally hand made in India with various wooden elements in it. The traditional manufacturing lacks in strength, symmetry, standardization and accuracy and its time to market is long. Hence the proposed technology, which is feature-based development of polymer saddletrees with total mass manufacturing solution integrating CAD, CAM and reverse engineering, was evolved. A contact type of digitizer (FARO Arm) was used to acquire shape data. In the present case the object was

(b) CAD model of Saddletree

(c) Prototype of Saddletree

(d) Steel molds for injection molding Figure 6. Rapid product development of Saddletree. Courtesy CAD P Lab, IITK Slice [23] and for SGC using Data Front End [24]. Computing facilities capable of handling large amount of data with powerful processing and graphic display are needed. Some typical computer configurations are Silicon Graphics on Irix platform, several PC with 2 GB RAM and 120 GB local disks.

Selective Laser Sintering system [22] (shown in Figure 4(a)) uses polymer powder for prototyping using a laser for sintering the area required as per design. The maximum build size is 340mm × 340mm × 620mm (Depth × Breadth × Height). Polymer powders that can be used in this machine are polyamide, polyester, glass fibre filled polymers and polymer metal alloy called aluminide.

Polyamide popularly called as nylon and glass fibre filled polyamide is used for functional prototypes and polyester is used for making rapid prototyped parts to be used as sacrificial pattern in casting. Another popular system commercially available is Fused Mechanika, April 2007

rigid and also had gross features, which were accessible by the digitizing probe and thus did not pose any problem for contact type of scanning. This stage of manual operation involved in RE required a great amount of time and operator skill and is also subject to error. The construction of CAD model was essential for doing analysis and shape modification. The task of creating surfaces from the point clouds, however, is difficult and time-consuming even with the help of surface modeling programs (Surfacer, Rhino [32]) and this task took approximately 60% of the overall project time. The availability of literature on saddletree shapes and feature definitions lead the design team to choose a feature based reverse engineering approach. Optimal orientation was discarded in this case and the criterion for part orientation was to utilize maximum part built area so as to reduce number of segments in the prototype. Figure 5 illustrates the various phases carried out in the project work. After three cycles of design modification 33

and two prototype evaluation the design was freezed and molds for injection molding made. Part CAD model and mold design were done in IDEAS and g-code for mold generated in DELCAM. The project was completed in eight months time at an approximate cost of 120,0000 Indian Rupees. Table 1 presents approximate break up of time and cost involved in the project.

The funding for the project came through a central agency aimed at technology development and transfer for the saddletree industry.

Many saddletree manufactures on realizing the advantage offered by the developed technology for saddletree manufacture have gone for the same but many are still to follow. The project was realized due to the initiative taken by the agency and this is the case with many small-scale industries in India. Many industries in India are not competent to face the global market because of slow paced or non-existent product development. Awareness on the need and justification of funding for research on product development is the key constraint and some form of modality has to emerge through a combined effort both from the industry and government. A detailed paper on this project has been published [26].

BIO MODELING AND PROSTHETIC DESIGN Recently RP models are being used in non-engineering application such as medicine. A preliminary study has been conducted by Bal Sanghera et. al. [27]. The study was conducted in London and reveals that the technology is in a very infant stage as for as the application in the medical field is concerned. The study also reveals that though the medical community highly regards the technology the financial cost is of concern. RP can be used for

(a) CT Scan of the skull

the CT data to STL. The STL was then used to make a full-scale RP model in FDM. The model was used to visualize as well as create silicon rubber casts for assessing forces and strains caused by the designed corrective fixture for the club foot, later clinical assessment was also done by orthopedic surgeons. The qualitative assessment in terms of usability is favorable nevertheless cost is a primary concern and a detail study on the economic feasibility is desired. Another study by Object Geometries [31] illustrates (Figure 7) using RP models for surgical treatment of skull defects.

The patient met with a road accident and had a major head injury and following a surgery he had a right front temporal cranial defect (a big hole in the scull cap). This necessitated the fixation of the missing skull part. A geometrically as well as materially similar prosthetic was fabricated by using CT scan, bio modeling and 3D printing of the missing part for mold casting of the part in dental lab acrylic. The fabricated part was used in the operation, where it was mildly trimmed and fixed using titanium plates and screws.

DISCUSSION AND CLOSURE Reverse Engineering of physical objects to obtain threedimensional geometrical models and physical realization of these models through rapid prototyping for CAD/CAM/CAE is a fast developing technology in which interest is currently high.

These rapid product development technologies are having a visible impact in the automobile and aerospace sector. The case studies discussed demonstrated the significant role of RE and RP as a design development and advanced manufacturing tool. The case studies also demonstrated the far-reaching applications of these technologies. The critical issues involved such as selection

(b) Reconstructed defect skull

(c) Acrylic prosthetic fixed during operation

Figure 7. Case study of skull defect surgery using RP prosthetic. Courtesy Object Geometries [31]. treatment planning/visualization instead of 2D X-ray, CT or MRI data, which are prone to problems in visualization. RP can also play a vital role in custom prosthetic design and implants. RP has also been investigated in bio modeling of fossil specimens [28]. Another interesting study by Guangming Zhang et. al., [29] presents using RP for reconstructing fossil of Homunculus skull.

A study of feasibility and implications of using RP for orthopedic application was carried out by the author [30]. The study proposed methods to correct club foot deformity is new born babies by studying and experimenting with the RP medical models of club foot of subjects. CT scan data (2mm slice thickness without gantry tilting) of 6 new born subjects with various degree of club foot was obtained for the case study. MIMICS software dedicated to bio modeling application from CT and MRI data was used to convert 34

of hardware, software and possible implications in terms of technology, economics and time have been discussed with respect to different application. The scope of the RE and RP in nonengineering applications is promising particularly in the domain of small-scale artisan product development, biomedical engineering and heritage preservation. Economics of the process is of primary concern. The author hopes that with reduced technological cost and global competition, RE and RP will be economically viable in the near future to designers, artisans and bio medics to enhance the products and service.

Mechanika, April 2007

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REFERENCES Varaday T., Martin R.R. and Cox J., Reverse Engineering of geometric Models – an introduction, Computer Aided Design, 1997, Vol. 29, No.4, pp.255-268.

Bisson J., High Speed, High Density Inspection to Offload CMM, SME Reverse Engineering Seminar, December 10, 1998.

Keytack O.H. et. al., CMM Application in Reverse Engineering – Integrating CMM with CAD/CAM for Existing Parts Without Drawings, Society of Manufacturing Engineers, Paper No. MS890529, 1989.

Steinberg B., Razdan A., and Farin G., Reverse Engineering Trimmed NURB Surafces From Laser Scanned Data, 1st International Conference on RP and Manufacturing, 1998, Beijing China.

Guo B., Surface Reconstruction from Points to Splines, Computer Aided Design, 1997 Vol. 29, No. 4, pp. 269-277.

Sarkar B. and Menq C.H., Smooth Surface Approximation and Reverse Engineering, Computer Aided Design, 1991, Vol. 23, No. 9, pp. 623-628.

Pham D.T. and Gault R.S., A Comparison of Rapid Prototyping Technologies, International Journal of Machine Tools & Manufacture, 1998, Vol. 38, 1257-1287.

Feng Lin, Wei Sun and Yongnian Yan, Optimization with minimum process error for layered manufacturing fabrication, Rapid Prototyping Journal, 2001, Vol. 7, No. 2, pp. 73-81.

Preston G. Smith, The Business of Rapid Prototyping, Rapid Prototyping Journal, 1999, Vol. 5, No. 4, pp. 179-185.

Anna Kochan, Rapid Prototyping Trends, Rapid Prototyping Journal, 1997, Vol. 3, No. 4, pp. 150-152.

Pralay Pal, An Easy Rapid Prototyping Technique with Point cloud Data, Rapid Prototyping Journal, 2001, Vol. 7, No. 2, pp. 82-89.

Kwan H. Lee, Woo H., Direct Integration of Reverse Engineering and Rapid Prototyping, Computers & Industrial Engineering, 2000, Vol. 38, pp. 21-38.

Saravana Kumar G., Kalra P. K. and Dhande S. G., Direct Layered Manufacturing of Point Sampled Geometry, Int. J. Manufacturing Technology & Management, Vol. 6, No. 6, 2004, pp. 534 - 549.

Carl Zeiss Inc., http://www.zeiss.com.

Roland DG Corporation, Japan. http://www.rolanddg.co.jp.

FARO Technologies Inc., http://www.faro.com.

GOM mbH, Braunschweig, Germany, http://www.gom.com.

Structural Dynamics Research Corporation., http://www.sdrc.com.

Autodesk Inc., http://www.autodesk.com.

Materialise, Belgium, http://www.materialise.be/mimics/ DELCAM, UK, http://www.delcam.com.

EOS GmbH, DTM corp.

Stratasys Inc., http://www.stratasys.com.

Cubital GmbH, Ringstrasse 132, 55543 Bad Kreuznach, Germany.

HEK-GmbH, Germany, http://www.mcp-group.de.

Puneet Tandon, Mukul Shukla, K. Siva Prasad, Saravana Kumar G., Sanjay G. Dhande, Feature Based Design and Rapid Product Development of Saddletree, International Journal of Agile Manufacturing, Vol. 4, Issue 2, 2001.

Bal Sanghera, Satyajit Naique, Yannis Papaharilaou and Andrew Amis, Preliminary Study of Rapid Prototype Medical Models, Rapid Prototyping Journal, 2001, Vol. 7, No. 5, pp. 275-284.

D’Urso P.S. Thompson R.G. and Earwaker W.J., Stereolithographic (SL) Biomodelling in Palaeontology: A Technical Note, Rapid Prototyping Journal, 2000, Vol. 6, No. 3, pp. 212-215.

Guangming Zhang, Yi-Chien Tsou and Alfred Rosenberge L., Reconstruction of the Homunculus Skull using a Combined Scanning and Sterolithography Process, Rapid Prototyping Journal, 2000, Vol. 6, No. 4, pp. 267-275.

M L Jain, S G Dhande, Saravana Kumar G., Sanjay Rastogi, Mukul Shukla, T.V.K. Gupta, Preliminary Study of Clubfoot Deformity in New Born Baby by Rapid Prototype Models, International Congress on Biological and Medical Engineering, Singapore, December 4-7, 2002.

Mechanika, April 2007

Advice For MS This article serves to highlight that students of Mechanical Engineering at IIT Guwahati are now consistently making inroads into the most prestigious graduate schools of US which is a testimony to the quality of our undergraduate education and the motivation and opportunities for some meaningful research provided to us by our experienced faculty. This year too we have two of the B-Tech Final year students, Saurabh Garg and Puneet Chhabra, making it to the Ivy-League Universities: University of California-Berkeley and Stanford University respectively. Saurabh has been admitted for the MS/PhD program of Mechanical Engineering with a specialization in manufacturing technology, while Puneet will be joining the Computational and Mathematical Engineering Department for his MS. Both of them attribute their success to their persistence with research along with an academic understanding of the nuances of the overall discipline of mechanical engineering, together with a motivation for graduate studies from the very beginning.

In a significant initiative, the two have built a combined App-File that discusses their experiences in applying to various universities, a document that is now with MESA. In a departmental talk given by them, Saurabh emphasized that “Mechanical Engineering students have a number of fields at their disposal in which they can contribute significantly through their research endeavors, some of them being manufacturing, CFD, Mems, Biomechanics, Industrial Engineering and Operations Research.

It is very essential to begin working in an area early in order to crystallize your research interests, if one wants to enter into a graduate school immediately after B-tech, so that one has a considerable build up leading to the time of application.” Puneet added that, “One should always set ones targets higher. He acknowledged that both he and Saurabh may not be academically the best scholars of their batch, as seen by their DRs, but the strength of their applications was a balanced profile marked by a significant research experience highlighting their passion for research and the joy of finding a solution to a problem.”

Both of them believe that all serious aspirants from coming batches, who want to make it to the ivy-league, should have a clear focus of what research means and demands and to identify your liking or passion for it. If you discover this inclination at any stage, work on it through your summer projects and interns and by taking up meaningful and ‘doable’ projects under the faculties at IIT Guwahati. Working seriously on one’s BTP would also be a great experience in the same direction.

In the end, the MESA team would like to congratulate both of them for their success in achieving their dreams and hope that they continue doing the same in future.

-Mechanika Team

35

The Energy Crunch

By Palle Raghavendra Prasad

H

is converted into useful energy in conventional power plants and transporting to the sites in underground porous media mainly in depleted oil or gas fields or saline formation in order to boost oil production. Present existing power generation technique can capture from 85-95% of carbon in coal as CO2 and rest is released to atmosphere. The main drawback of this method is effort involved in extracting CO2 from flue gas is considerably high because it contains substantial amount of other compounds such as nitrogen, sulphur etc.

FOSSIL FUELS

Second is the gasification technology. It is the replacement of primitive coal steam power plants by a newer integrated gasification combined cycle (IGCC) which is an effective and least expensive than CCS technology. In an IGCC system coal is partially oxidized at high pressure in gasifier. The resultant is called Syngas or synthesis gas and is composed of CO+H2 undiluted with nitrogen. IGCC removes most of the conventional pollutants from syngas and then burn it to turn both gas and steam turbine generator in what is called a combined cycle. Syngas reacted with steam to produce gaseous mixture of mainly CO2+H2. CO2 is then extracted, dried, compressed and transported to a storage site. There

80% of energy comes from carbon emitting fossil fuels like coal, oil and natural gas. Though they have wide variety of usages in electricity, transportation and house hold purposes they do have detrimental effects of polluting the environment. Annually around 7billion tons of carbon is released to the atmosphere which is main constituent in green house gases.

COAL Coal is cheaper to other fossil fuels.

Coal is primarily used in coal power plants for generating electricity and in transportation purposes. Though coal is ample and cheaper all across the world the major problem is it produces considerably more CO2 per unit electricity generated rather than burning oil and natural gas.

courtesy: www.worldenergy.org

ave you ever thought about the things that made our life so luxurious as compared to the primitive human races? What is the prime constituent in human controlled sophisticated goods like ACs, room heaters, various locomotives like trains, cars, aero planes etc.? For all these one of the major contributors is energy. Energy is required for electricity, transportation, industrial usage etc. so let us glance over various sources of energy, their impact on the globe, recent developments, future plans, scope for research works and so on…

RESEARCH AND TECHNIQUES Reading previous passage the first and foremost question that arises in our mind is can’t we eradicate the seepage of CO2 going to the atmosphere? Researches are going on this point.

Techniques that provide to store CO2 from entering atmosphere are called CO2 capture storage (CCS) or Geological carbon sequestration.

First is simple combustion technology and the process involved is separation of CO2 that is generated after carbon

36

IGCC plant diagram

Mechanika, April 2007

are 5 IGCC plants that are currently operating in the world. Two are in U.S and one each in Indiana, Tampa and Florida.

One thing that is understandable from above study is adding CCS or IGCC technology will significantly increase the cost of electricity in order to compensate the expenses made for installing equipment.

NUCLEAR ENERGY It is carbon free energy and provides 1/6th of world’s electricity. Many of the countries became lackadaisical and ceased the construction of new power plants mainly due to three reasons. First, they require high capital investment. Second, lack of proper nuclear waste disposal system. Third, development of a nation’s nuclear power plants may encourage them to have nuclear armaments.

There are generally two types of fuel cycles are implemented. One is open cycle in which uranium is burned in a reactor and the spent fuel is sent to geological repositories for storage. Second is closed cycle in which the spent fuels like plutonium is chemically extracted and made as a fuel for another nuclear plant. Doing this we can reduce the nuclear waste by a great amount but it is bounded with three main problems.

First, recycled fuel becomes much costlier than original uranium.

Second, we have ample uranium resources for the present and future considerations which make the investors to incline towards open cycles than closed cycles. Third, reprocessing of spent fuel into a fuel form is complex and highly dangerous. Accidents may lead to catastrophic effects.

The Chernobyl accident in 1986 was the result of a flawed reactor design that was operated with inadequately trained personnel and without proper regard for safety. 28 people died within four months from radiation or thermal burns, 19 have subsequently died, and there have been around nine deaths from thyroid cancer apparently due to the accident: total 56 fatalities as of 2004.

The first permanent disposal is expected to occur about 2010. Most countries intend to introduce final disposal sometime after about 2010, when the quantities to be disposed of will be sufficient to make it economically justifiable.

RECENT DEVELOPMENTS Now days a pebble bed modular reactor is implemented which are the modular nuclear plants. Instead of building 1000 MW plant, modules each producing around 100 MW can be built which yields low capital costs and it will flagrantly entice the parsimonious investors.

The above technical tasks with the daunting economic and social problems hustled us to raise the production of renewable sources of energy. One thing that seems apparent is either we can have effective CO2 removal methods to use fossil fuels or we can develop Mechanika, April 2007

the effective methods to produce the renewable sources of energy in large amounts.

RENEWABLE SOURCES OF ENERGY These are the most inconspicuous sources of energy for the last few decades. Solar cells, wind turbines, Fuel cells and biofuels come under renewable sources of energy. They emit very negligible or no carbon to the atmosphere. These sources are explored several decades ago but remained under shade due to excess usage of fossil fuels. Recent studies on these areas have enhanced their capacity by a very large amount.

SOLAR ENERGY Total generating capacity of solar energy is 5000 MW and is only 0.15% of the total generating capacity from all sources but it has the surfeit of potential to increase its production to several thousand times. This is the main source of energy at the remote areas where the accessibility to normal electricity is not available.

Two often used solar cells are multi crystalline silicon wafers and thin film silicon cells. First kind is cheaper to the other but is less efficient around the maximum of 30%. An investment of Rs 5000 for the panel and wiring, one can use to charge a car battery, which can then produce enough power to run a fluorescent lamp or black and white TV for several hours.

Apart from solar cells we have solar thermal systems which absorb sunlight and convert heat to generate electricity. One such device is Stirling engine in which working fluid operates between hot and cold chambers. The required heat is absorbed from the system as many mirrors focus the light on Stirling engine. The fluid expands as the sunlight heats it, pushing the piston, in turn drives a turbine.

The only obstacle for solar energy is high cost of electricity and less efficiency of solar cells.

37

Lessons from the past 3 mile

Chernobyl

The data shown above has been taken from Wikipedia

•The Chernobyl accident in 1986 was the result of a flawed reactor design that was operated with inadequately trained personnel and without proper regard for safety.

•The resulting steam explosion and fire released at least five percent of the radioactive reactor core into the atmosphere and downwind.

•28 people died within four months from radiation or thermal burns, 19 have subsequently died, and there have been around nine deaths from thyroid cancer apparently due to the accident: total 56 fatalities as of 2004.

•An authoritative UN report in 2000 concluded that there is no scientific evidence of any significant radiation-related health effects to most people exposed. This was confirmed in a very thorough 2005 study.

courtesy: Wikipedia

courtesy :Wikipedia

• In 1979 a cooling malfunction caused part of the core to melt in the # 2 reactor at Three Mile Island in USA. The reactor was destroyed.

• Some radioactive gas was released a couple of days after the accident, but not enough to cause any dose above background levels to local residents.

• The Three Mile Island accident was the worst accident in American commercial power generating history,even though there were no injuries or adverse health effects from the accident

courtesy: RE Power

WIND ENERGY

5M

The largest wind turbine 38

This energy is highly consumed in European countries since of great assistance from nature. The generating capacity is around 60,000 MW in the world. Germany is the country that is leading in this technology and installed around 18000 MW of wind power plants. 0.5% of US energy comes from wind turbines. At present no other renewable source of energy produces more electricity than wind energy. Suitable location plays an important role in installing wind turbines.

GREEEN FUELS These less carbon emitting sources are a great hope of future energy and have the capacity to replace the fossil fuels.

The most common biofuel is corn based ethanol. The problem with Mechanika, April 2007

this type is much energy is consumed in extraction ethanol from corn. Producing corn in a large amount makes way to enhance the corn. Producing corn in a large amount makes way to enhance the utility of fertilizers and this in turn causes lot of pollution. This ultimately makes less effective in terms of reducing carbon emissions.

Another recent development is cellulosed based ethanol that is extracted from like grass or poplar. The process involved is burning lignin, an unfermented part of organic material to heat plant sugars. The green house gases emitted are nullified by absorption of CO2 by growing plants which are used to produce ethanol. Hence the process can slash green house emissions by around 90%.

transportation, building and industrial usage would give people more services they need without having to build as many power plants, refineries or gas pipelines.

The shocking thing is that 35% of green house gas emissions come from buildings. So beings engineers why don’t we construct energy effective buildings? It is possible to build energy efficient buildings without affecting economic efficiency. 65% of primary energy that is the natural sources we harness for power is lost during conversion to the useful energy.

Using effective insulation, refrigeration, energy conscious design, industrial processes, aerodynamic cars, using fluorescent light will add to increase in efficiency. So why don’t we work on these challenging tasks to make human life more peaceful?

One more primary biofuel is green diesel. The steps involved are gasifying biomass, heating organic material enough that they release CO+H2 and then converting these compounds into long chain hydrocarbons using the Fischer-Tropsch process. This technology almost adds no green house gases to atmosphere.

BIOGAS

Biogas can be used in cooking purpose, lighting purpose, electricity generation and running engines. Few uses are there will be no smoke in the kitchen, health of woman and children are protected, It produces organic manure as by product and no need of firewood hence free from deforestation.

courtesy :Wikipedia

It is a clean, non polluting and low cost fuel. Its composition is methane 55%, carbon dioxide 35%, hydrogen 7.4%, nitrogen 2.6% and water in traces. Its calorific value is 21.5 kJ/ltr. It is a source of energy that can be pretty useful in rural areas where agricultural wastage is expected.

Bjarnarflag Geothermal Station in northeast Iceland

Biogas development and training center (BDTC) for northeastern region states, sponsored by the ministry of non conventional energy sources, New Delhi was established at center for energy, Indian institute of technology Guwahati, during February 2006. In our campus at present we have four Deenbandhu model biogas plants which are producing biogas at good efficiency. Deenbandhu model of biogas plant is mostly preferred because of advantages like low construction cost, local availability of needed building materials, reduced maintenances cost and its hidden underground structure.

GEOTHERMAL ENERGY Around 99% of earth mass consists of temperature more than 1000OC. So transforming this energy into useful form of energy such as electricity and heat is the main idea. Process involves extraction of heat energy by means of geothermal probes which can go deep into the earth. They contain a liquid that can absorb the heat deep in the earth and transfers into a heat pump. This technology is at infant stage and installation is quite expensive for the time being.

EFFICIENCY MATTERS One thing that is to be clear is increasing efficiency doesn’t mean reducing comforts. Programs to implement efficient systems in Mechanika, April 2007

Biogas Plant at IITG Palle Raghavendra Prasad is a B.Tech 3rd Year student in the Department of Mechanical Engineering, Indian Institute of technology Guwahati 39

Job Shop Scheduling (JSP) through Particle Swarm Optimization (PSO)

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Deepankar Garg Jaspreet Singh Sudhanshu Kumar Guide: Dr. Sankha Deb B.Tech Final Year, Indian Institute of Technology Guwahati

cheduling of jobs and activities is an important area of research for maintaining a firm’s competitive market position.

In a job shop, jobs may follow different machine sequences and may use the same machine more than once. The problem is to find the order in which a given number of jobs must be processed on a specified set of machines so that one or more decision objectives are optimized, e.g. minimization of the total makespan time, minimization of the penalty incurred by not delivering on time, etc.

PSO is an iterative algorithm that was first proposed by Eberhart and Kennedy, where the population dynamics simulate the behavior of a “birds flock”, where social sharing of information takes place and individuals profit from the discoveries and previous experiences of all other companions during the search for food. This is modeled by particles in multidimensional space that have a position and a velocity. These particles fly through search space and have two essential reasoning capabilities: their memory of their own best position and knowledge of the swarm’s best; the best being defined by the value of the objective function at that position.

interesting fundamental area of study.

In JSP, it may so happen that a schedule determined by the PSO might not be feasible because of the precedence constraints. As a simplistic case, consider an iteration which resulted in a schedule where, on each machine, the scheduled first operation needs some other operation to be completed first, due to precedence constraints of jobs. Hence in this case, no machine can start its operation; so this schedule is infeasible. Outrightly rejecting an infeasible schedule is a wasteful option because the probability of arriving at an infeasible schedule is much larger than a feasible solution (the ratio of unconstrained to constrained permutations). Hence a method needs to be devised to convert an infeasible schedule into a feasible one. This offers another important aspect of study as it affects the

For a particular dimension, let the position be defined by x, pb be the personal best position, gb be the global best position and velocity by v. Then, the new position and velocity are obtained as follows: vi+1 = wvi + c1r1(pb – xi) + c2r2(gb – xi), xi+1 = xi + χ vi+1 where χ ,w, c1, c2 and are the weights (which may be varied) and r1 and r2 are random numbers within the range [0, 1].

In Multi Objective (MO) problems, a particular solution may not be able to optimize all the objectives; e.g. a schedule with low penalty cost may have high machine idle time. In such cases, the aim is to find the set of pareto-optimal solutions i.e. the set of particles in which one objective cannot be further optimized without compromising the other objective functions. Therefore, in MO problems, the concept of a single best solution also needs to be revised.

The local/global best used to evaluate the new velocity and position of a particle is essentially the search direction in which the probability of finding an optimum solution is high. Therefore, various methods may be used to define the search direction in case of MO, e.g. the swarm may be divided into subgroups and different subgroups may be assigned different objective functions to determine the ‘bests’, or alternatively, multiple ‘bests’ corresponding to each objective function may be used, or the neighborhood pareto-optimal solutions may be used to define the search direction. Hence, the determining factor affecting the velocity in MOPSO offers an 40

efficiency of the algorithm.

PSO is a relatively newer optimization technique and has not been extensively applied to JSP; hence this field offers a wide scope for novel experimentation. Existing heuristic algorithms may be interpreted in the context of MOPSO and PSO techniques used in other fields and can also be interpreted in the context of JSP to arrive at interesting results.

Bibliography

[1] Tapan P. Bagchi , Jatinder N.D. Gupta , Chelliah Sriskandarajah [2006], “A review of TSP based approaches for flowshop scheduling”, European Journal of Operational Research 169 (2006) 816–854 [2] http://en.wikipedia.org/wiki/Particle_swarm_optimisation [3] Swarm Intelligence. James Kennedy, Russell C. Eberhart and Yuhui Shi, Morgan Kaufmann Publishers, 2001 Mechanika, April 2007

Oral Simulator - A Review Aditya taneja Alok Verma Reviewed by: Dr. S. Senthilvelan Kunal kumar Palle raghavendra prasad B.Tech 3rd Year, Indian Institute of Technology Guwahati

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ral Simulator is a mechanical device that replicates the basic human jaw movement using mechatronic actuators.

It replicates all the forces and kinematic parameters involved in this process. Mastication systems/robots finds its use in many areas of research which concern with facial movements.

mandibular joint (TMJ) despite of its complexity is one of the most frequently used joint in the human body. This joint is responsible for most problems pertaining to the jaw. Its susceptibility to injuries is largely influenced by the regular usage during mastication and by the strong forces applied by the muscles and wide range of movements.

BIOLOGICAL ASPECTS OF THE ORAL SIMULATOR

ROBOTICS

The human skull basically consists of two parts : the mandibular and the maxilla. One of the most essential jaw motions occurs while mastication (which is basically the process of chewing food to a proper form suitable for swallowing). The human mandibular has two processus (processus coronoideus and processus condylaris). The top of processus condylaris is caput mandibulae, and the joint between this and fossa mandibularis is the temporomandibular joint.

MANDIBULAR MOVEMENTS During the opening and closing of the mandibular the paths of most points on the condyle are infinite or loop shaped, but there is one special point that traces a linear path (point K). The mandibular rotates around a virtual axis linking point K on the right condyle and point K on the left condyle, and at the same time this virtual axis (kinematic axis) moves forward and backward.

DENTAL STUDIES The understanding of mastication system is essential for maxillofacial surgeons and dentists in procedures concerning jaws and teeth correction. Oral simulators are being extensively used in dental institutions and colleges for training purposes. The temporo-

Mandibular model Mechanika, April 2007

Humanoid robotics is one of the most interesting topics of research in recent years. Providing machines with the ability to produce sound just like we humans do is the main challenge researchers are facing. It is not difficult to understand why research on oral simulators is being pressed on, considering the fact that jaw movement is an integral part of human speech system and mastication.

Many speaking robots have been built till now. But none of them have come even close to speak fluently as we still have not found the technology and the mechanism to duplicate the mechanical elements of human speech-making. A lot of research is being carried out to produce cellular phones that can compress data by transmitting human vocal movement instead of human voices. For this there is a need to clarify a human vocal mechanism from engineering viewpoints and to create the dynamic model.

ERGONOMICS Ergonomics by definition is the application of scientific information concerning human in designing of objects, products, systems and environment of human usage. Oral simulators can provide us with data pertaining to the facial movements which can be helpful in developing better systems and environments. As a particular emotion is associated with a particular set of muscle movement, oral simulation also finds its usage in research dealing with computer modeling of human emotions.

Point path on condyle

Mastication Robot 41

Automobile Leaf Springs-A Review Antriksh Singh Priyesh Sinha Reviewed by: Dr S. Senthilvelan Rohit Mittal Satish Mittal B.Tech 3rd Year, Indian Institute of Technology Guwahati

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eaf spring finds their greatest application within the automotive industry. Most leaf spring applications are comprised of a multi-leaf system found primarily in rear suspensions.

They usually take the form of a slender arc-shaped length of rectangular cross-section. The center of the arc provides location for the axle, while tie holes are provided at either end for attaching to the vehicle body. For very heavy vehicles, a leaf spring can be made from several leaves stacked on top of each other in several layers, often with systematically shorter leaves. Leaf springs can serve locating and to some extent damping as well as springing functions.

The optimum design of the leaf spring has evolved over the years.

In recent years the primitive steel leaf springs have been replaced by its several new derivatives like composite leaf springs, coil springs etc. However, leaf springs are still used in heavy commercial vehicles such as vans and trucks, and railway carriages.

For heavy vehicles, they have the advantage of spreading the load more widely over the vehicle’s chassis.

Since the stiffness-to-strength relationship within a multi-leaf system, along with weight are important considerations in spring design, hence leaf springs made of different materials such as com-

Typical leaf spring in a automobile Leaf springs, during its service life, are subjected to high bending forces and axial stresses. Lifetime of a spring is of the order of million cycles of vibration. Thus this calls for a pre-manufacture simulation of a spring system as it gives near correct estimation of desired system parameters, is highly economical and takes a little time(as compared to millions of test cycles!).

Finite element analysis of a leaf spring posite materials to offer significant advantages, for e.g. primary reason for their usage being high specific strain energy capacity, low weight, high stiffness-to-strength, fatigue resistance and low noise during operation. The commonly used composites, called glass-fiber reinforced plastics, are materials made from woven fabric fiberglass/epoxy.

Forces and moments acting on a leaf spring With the use of finite element analysis softwares like Ansys, Nastron, design and analysis of a graduated multi-leaf spring system can be easily done, the results of which reflect spring rate, stresses, and strains. The main objective remains the desire for obtaining a design with minimum weight and high strength and flexibility that is capable of carrying given static and dynamic forces without failure.

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Single leaf composite leaf spring Mechanika, April 2007

Computer Aided Design of a Knee Simulator Bikram Bhatia Sulabh Kakkar Reviewed by: Dr S. Senthilvelan Varun Choudhary Yambem Volga Singh B.Tech 3rd Year, Indian Institute of Technology Guwahati

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he use of artificial joints for the treatment of degenerative diseases of the knee is becoming more widespread as life expectancy increases, and with it, the need of accurate experimental evaluation of the total knee replacements (TKR). Once in vivo, the accurate and reproducible assessment of TKR design mechanics is exceedingly difficult, with the secondary variables of the patient and the surgical technique hindering the research, thus the need of a machine that simulates the knee joint, a Knee Simulator.

A knee simulating machine is a machine that is capable of simulating the motion of a knee joint. It is capable of applying loads across the joint similar to the loads during deep knee bend, walking or stair climbing. It is required for the design and evaluation of TKRs, especially the kinematic aspects and the long-term wear of the prosthetic joint.

Knee: Not just another Hinge Joint The knee is the lower extremity joint connecting the femur and the tibia, supporting nearly the entire weight of the body. The knee permits the following movements: flexion, extension, as well as slight medial and lateral rotation. The ligaments and menisci, along with the muscles which traverse the joint, prevent movement beyond the knee’s intended range of motion.

A study has analyzed classified the failure of the TKRs in five modes: Tilt and Sink, Compression mode, Torsion mode, Toggle mode and Combination mode. As a general principle, the mechanism of a knee simulator should include the six degrees of freedom (three translational and three rotational), with appropriate constraints and capable of applying loads, normally experienced by a knee joint

Primary Knee Movements and Loads The Proposed Model A model for the knee simulator has been chosen as shown if the figure (with some modifications). The mechanism is capable of simulating six degrees of freedom of the knee joint (however the medial-lateral (M-L) displacement of the femur is assumed negligible). The flexion is kept fixed at a particular angle (through the use of a DC stepper motor) while a time-varying anterior-posterior (A-P) force is applied to the tibia (using a hydraulic cylinder) to simulate normal gait. Another couple of hydraulic cylinders are used to apply the compressive load (the largest force acting on the knee joint) and varus-valgus rotation to the femur, through two load beams. The femoral and tibial components of a knee joint (TKR) is fixed to the femoral and tibial shafts respectively, by means of two pneumatic grippers. Elastomeric bumpers are provided to simulate the soft tissues surrounding the knee joint. With the specifications of all the components determined, the modeling of this mechanism shall be done using ProE.

The Proposed Knee Simulator Model Mechanika, April 2007

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Mechanical Model of Rigid Axle Suspension System Anup Raj Aseem Bansal Reviewed by: Dr. Sankha Deb Gaurav Kumar Sourabh Agarwal B.Tech 3rd Year, Indian Institute of Technology Guwahati

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uspension is the term given to the system of springs, shock absorbers and linkages that connects a vehicle to its wheels. Suspension systems serve dual purpose – contributing to the car’s handling and braking for good active safety and driving pleasure, and keeping vehicle occupants comfortable and reasonably well isolated from bumps and vibrations. The suspension also protects the vehicle itself and any cargo or luggage from damage and wear. The figure shows the front suspension components of a ford model.

Suspension Types Suspension systems can be broadly classified into two subgroups - dependent and independent. These terms refer to the ability of opposite wheels to move independently of each other.

A dependent suspension normally has a live axle (a simple beam or ‘cart’ axle) that holds wheels parallel to each other and perpendicular to the axle. When the camber of one wheel changes, the camber of the opposite wheel changes in the same way (by convention, on one side this is a positive change in camber, and on the other side, this a negative change).

An independent suspension allows wheels to rise and fall on their own without affecting the opposite wheel. Suspensions with other devices, such as anti-roll bars that link the wheels in some way are still classed as independent.

A third type is a semi-dependent suspension. In this case, jointed axles are used, on drive wheels, but the wheels are connected with a solid member, most often a deDion axle. This differs from “dependent” suspension mainly in unsprung weight.

Axles Axles are an important structural component of a wheeled vehicle. The axles maintain the position of the wheels relative to each other and to the vehicle body. Since for most vehicles the wheels are the only part touching the ground, the axles must bear the weight of the vehicle plus any cargo, and also any acceleration forces between the vehicle and the ground.

Roll Analysis Model Assuming that the body is rigid, a roll is a rotary motion about a roll axis that is determined by the mechanism of suspension. We assume two planes, one which intersects the ground point of front and rear tires and second which is still perpendicular to the front and aft axis of body. The two points where the roll axis intersects these two planes are the roll center (RC) of each front and rear suspension.

The figure shows the suspension model for analysis. This rigid axle suspension has a point RC at which the sprung mass and unsprung mass are connected. This connecting point moves upward and downward along the slide guide of sprung mass. The weight of sprung mass is shared by both right and left suspension springs, and that of unsprung mass is ignored. The roll center of this model is the connecting point RC and is integrated with unsprung mass.

Inward roll is realized when the roll axis is higher than CG, without harmful influence over the driving stability. Only the four-wheel vehicle produces outward roll in a turn, although other vehicles and creatures produce inward roll.

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Mechanika, April 2007

Expert System for Cam Design B.Varun Kshitij Maheshwari Reviewed by: Dr S. Senthilvelan Shamit Srivastava B.Tech 3rd Year, Indian Institute of Technology Guwahati

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am is a machine element having a curved outline or a curved groove, which, by its oscillation or rotation motion, gives a predetermined specified motion to another element called the follower. By rotating the cams we get different kinds of motion for followers varying from continuous motion to oscillatory motion to intermittent discontinuous motion. Most common application of cams is in IC engines of vehicles where cam shafts are required to control valve timings of intake and exhaust valves.

Design Methodology In the solving program user has to provide either one of displacement or velocity or acceleration profile of the motion of follower as a function of θ (As other two parameters can be calculated by integration or differetiation) inverse method has been used, in which problem can be solved by assuming cam as fixed and rotating the folllower in opposite direction along the cam profile.The basic logic behind the program is to find the co-ordinates of the contact point of follower as it traces the shape of the cam.

For doing so we use the Meshing Equation given as follows V.nc = 0 where V is a vector of relative velocity of a follower with respect to

the cam; and nc is a unit vector of the common normal line.

Using this equation the contact point on cam can be determined.

If the contact point is found, the profile and pressure angle of the cam will become known.

From kinematics of a particle, when a particle moves along a space path, its centripetal acceleration an in the world coordinate system can be calculated by an = where is the radius of curvature at that point and V is the velocity of follower at that point.

The code of program involves transformation matrices which calculate the normal acceleration and velocity of the point from the profiles inputted by user. This calculated data is stored and used to calculate the radius of curvature at each point using the above mentioned equation and its postion is determined using the meshing equation.

Once radius vector of each point (magnitude of radius of curvature and its direction) is known, co-ordinate plotting can be done with to obtain the cam shape.

References

1. Tsay, D. M., and Wei, H. M., 1996, ‘A General Approach to the Determination of Planar and Spatial Cam Profiles’, ASME J. Mech. Des., 118, pp. 259–265.

2. A Computational Approach to Profile Generation of Planar Cam Mechanisms JANUARY 2004, Vol. 126 pp. 183-188

Hope This makes you Smile :) EVER WONDER...

...why the sun lightens our hair, but darkens our skin? ...why “abbreviated” is such a long word? ...why you have to click on “Start” to stop Windows XP? ...why they call the airport “the terminal” if flying is so safe? ...why they are called apartments when they are all stuck together?

AND...

In case you need further proof that the human race is doomed because of stupidity, here are some actual label instructions on consumer goods..

On a bag of Fritos: You could be a winner! No purchase necessary. Details inside. (the shoplifter special?)

On most brands of Dewali lights: “For indoor or outdoor use only.” (as opposed to...what?)

On a Japanese food processor: “Not to be used for the other use.” (Now, somebody out there, help me on this.

I’m a bit curious.)

Mechanika, April 2007

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Design of gear test rig for kinematic analysis Sanjeev Kumar Saurabh Garg Reviewed by: Dr S. Senthilvelan Anjan jyoti hira B.Tech 3rd Year, Indian Institute of Technology Guwahati

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inematic analysis determines the configurations (positions and orientations) at which two parts contact and the velocities at which they maintain contact. Mechanical systems perform functions by transforming motions via part contacts. The shapes of the interacting parts impose constraints on their motions that largely determine the system function. Designers perform kinematic analysis to derive the evolving sequence of contacts and motion constraints. The results help them simulate the system function, find and correct design flaws, measure performance, and compare design alternatives. Estimation of kinematic performance of geared system is based on transmission error of meshing teeth.To assess the validity of gear simulation models the transmission error of a gear set are measured under a variety of operating positions and applied loads.To accurately evaluate transmission error at the design stage is essential in optimizing the tooth profile geometry.

Transmission error Transmission error is the difference between theoretical and actual angular position of gear. Source of vibration and noise in a gear system is the transmission error.It is due to manufacturing inaccuracy, mounting errors, and elastic deflections under load. Gear designers often attempt to compensate for transmission error by modifying gear teeth. Different load will cause a different transmission error.During operation, Transmission error at different loads can cause the gear system components to deflect such that the relative position and orientation between the gear elements change. Accurate transmission error data will help researchers better understand the mechanisms that cause gear noise and vibration

Experimental setup The test rig designed for measuring transmission error has various components: 1. Pinion rotated by a servo controlled electric motor going through a speed reducer to increase the input torque.

2. Disk brake attached to gear member to apply torque and a load cell to measure the same.

3. Multiple operating positions to incorporate gear sets of different sizes.

4. Measurement sets connected to gear/pinion shafts. The encoder can be Analog or Optical.

5. Encoder solver and filter for analyzing and filtering data.

6. Data Acquisition System for error measurement calculations.

Results

1. The transmission error is maximum around mid tooth height and minimum at entry and exit.

2. As applied torque increases, the transmission error curve deepens and its amplitude increases.

3. The effects of minor surface deviations progressively disappear and the shape of the graph approaches that of a convex parabola.

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Mechanika, April 2007

Test Rig for Wheel and Brake Assembly Performance Study M.Nelson A.Vijay Anand Reviewed by: Dr S. Senthilvelan V.Uma Maheshwar N.Bharath Reddy B.Tech 3rd Year, Indian Institute of Technology Guwahati

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rake systems and wheel/hub assemblies are critical safety-relevant components of the vehicle chassis which are exposed to severe loads. Their reliability can only be safeguarded by performing tests in the laboratory under conditions which resemble actual loading conditions as closely as possible. Fundamental design aspects and subsequent development of an laboratory test rig for the accurate measurement of braking and wheel system performance of a truck is described in this article.

Applications

1. Fatigue testing of wheels as part of a design validation process before production.

2. Rim roll accelerated durability testing, vertical input of high dynamic loads caused by road roughness and vehicle maneuvering, superimposed on the truck weight component acting on a wheel.

3. Estimation of wear and Coefficient of friction on brake pads and tyre due to series of high lateral inbound and outbound loads superimposed on the corresponding vertical loads.

4. Specific service strength tests of wheel fastening and braking elements (bolts and discs), hub units and truck twin wheel designs using supplementary rig equipment.

5. To compare Theoretical and Experimental performance paramerts like coefficient of friction and wear

Features Sailent features of proposed test rig are listed below 1. Simultaneous radial and lateral loading of wheels using an original tyre for load transfer from the rig to the test object.

2. Variable wheel rotation, speeds 3. Variable wheel camber positioning specimens or application of a static roughness and vehicle maneuvering, allows true in-service stress.

4. Compact sturdy design that requires a minimum of floor space and no special foundation.

Typical performance curves Mechanika, April 2007

Design In addition to the functional requirements, detail shaft, and bearing design has been done to design the proposed test rig and following major design details were arrived Shaft Diameter = 105 mm Length of Shaft = 500 mm Drum diameter = 920mm Breadth = 28mm Width of the Drum = 340mm Material = Plain Carbon Steel 40C8 hickness of the Drum = 20mm Maximum Vertical Load = 40KN Maximum Radial Load = 40KN Maximum Axial Load = 50KN Bearing Type SKF 3321 Vericom, VC3000, brakemeter to estimate frictional force and coefficient of friction on tyre. Gill Sensor to estimate wear in the brake pad. LVDT to estimate the tyre wear 47

HYBRID CARS – FUTURE OF AUTOMOBILE

By Vijaya Kumar Pantangi

to 25 miles an hour in a sizzling 10 seconds—three times faster than contemporary cars.

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From around 1890 to 1920, the peck of early hybrid revelation, there were more than 100 makers of electric cars in the U.S. and Canada. By 1920, the electric vehicle started to disappear, and consequently, so did the interest and development of hybrid powertrains. Up until 1960s, hybrid automobiles were relegated to the automaker and inventors.

Then, in the late 1960s, the serious public health effect from use of internal combustion engines became more concerned and public official reprehending the auto industry for it,

hen a vehicle uses multiple propulsion systems to provide motive power, it’s called a hybrid vehicle. Combination of propulsion systems may be many types but most commonly used system is gasolineelectric which known as gasoline-electric hybrid vehicles.

Electric hybrid vehicles use gasoline (petrol) to power internal-combustion engines (ICE’s), and electric batteries to power electric motors. Modern hybrid cars are driven by electric motors powered by both batteries and an ICE. They recharge MG1 their batteries by capturing kinetic Inverter energy via re generative braking. As well, when cruising or idling, some of the output of the combustion Gasoline engine is fed to a generator which engine produces electricity to charge the batteries. Thus the advantages of hybrid cars over the conventional vehicles, predictable by everyone, are reduced green gas emissions and fuel consumption. They even perform as well if not better than non-hybrids and are as safe, reliable and comfortable as any traditional Electric motor/ car. These cars also overcome the generator drawbacks of electric powered vehicles, like limited range due the size and weight limitation of the batteries, long charging hours and Axles exorbitant costs.

HISTORY OF HYBRID CARS

Power split device

Silent chain

Reduction gears

Electric motor/ generator

Front wheels

Most of us may think hybrid technology as recent idea but the revolution started at the end of 19th century itself. During 1897 to 1907 the Compagnie Parisienne des Voitures Electriques (the Paris Electric Car Company), an important early contributor to electric car technology, built a series of electric and hybrid vehicles, including the 1903 Krieger.

First official milestone of hybrid technology is a patent application filed by American engineer H. Piper for a gasoline engine-electric motor powertrain-a hybrid in November 23, 1905.Unlike today his hybrid design wasn’t to increase a vehicle’s fuel mileage and lower its emissions. According to the patent application, an electric motor would supplement a gasoline engine, allowing a vehicle to accelerate from zero 48

MG2 Inverter

Battery

Differential

which renewed interest in the electric vehicle. The oil crises of 1973 and 1979 prompted another flurry of activity during the mid 1970s and into the ‘80s. In mid-December 1997 Toyota began offering a hybrid automobile, “The Prius” for execution.

TYPES OF HYBRID VEHICLES There are many types of hybrids, differentiated by how the electric and fueled halves of the power train connect, and at what times each portion is in operation. Two major categories are series hybrids and parallel hybrids.

A series hybrid, the internal combustion engine is not directly Mechanika, April 2007

connected to the drive train at all, but powers an electrical generator instead. This is similar to the operation of dieselelectric train locomotives, but they do not store auxiliary power in batteries for later use, and in fact is similar to an electric car which is recharged by electricity from a stationary fossil fuel power plant, except that the power plant is carried on board.

Parallel systems connect both the electrical and internal combustion systems to the mechanical transmission. This is most common types of hybrid at present. They can be subcategorized depending upon how balanced the different portions are at providing motive power. Such as A full hybrid, sometimes also called a strong hybrid is a vehicle that can run on just the engine, just the batteries, or a combination of both.

An Assist hybrids use a battery and electric motors to accelerate the car in combination with an internal combustion engine. In a mild hybrid the gasoline engine provides the main drive power and an electric motor helps give the car additional power when needed. A plug-in hybrid electric vehicle (PHEV) is a full hybrid, able to run in electric-only mode, with larger batteries and the ability to recharge from the electric power grid. They are also called gas-optional, or gridable hybrids. A hydraulic hybrid vehicle uses hydraulic and mechanical components instead of electrical ones.

Finally Pneumatic hybrid which use compressed air to power a hybrid car with a gasoline compressor to provide

the power.

Nearly all hybrids still require gasoline as their sole fuel source though diesel and other fuels such as ethanol or seen in occasional plant based oils.

FUTURE FUEL SOURCES FOR HYBRID VEHICLES Hydrogen-powered fuel cells hold the promise as a clean source of power for electric motors, without the limitations of batteries. In a fuel cell, hydrogen is burned in a pollutionfree chemical reaction where the fuel cell combines hydrogen and oxygen to produce electricity, water and waste heat. Since hydrogen is the most abundant element in the universe, it seems like the best replacement for more limited resources like oil. However, due to production costs and refueling limitations, manufacturers estimate that roadready hydrogen-powered vehicles are at least a decade away.

In addition to hydrogen fuel cells, engineers continue to experiment with alternative fuels such as biodiesel, natural gas, ethanol, methanol and propane-as well as fuel made from corn, soybeans, grass and sugar beets. Concept vehicles are being tested and some are even being used in commercial situations, like buses and other commercial vehicles that run on diesel. These fuels may represent a new breed of hybrid beyond the still gas-polluting engines of the current crop of HEVâ&#x20AC;&#x2122;s.

Vijaya Kumar Pantangi is a Research Scholar in Department of Mechanical Engineering, Indian Institute of Technology Guwahati

Computer controlBattery ling both the power sources

Reviewed by: Dr. Niranjan Sahoo 4-cylinder internal combustion engine

References www.howstuffworks.com www.autozine.com www.hybrid.com www.hybridcar.org

Regenerative brakes to charge the battery Electric transaxle for combined functions of transmission and electric motor Mechanika, April 2007

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Engineering Design Methodology Projects: Creative Engagement for Learning

By Dr. G. Saravana Kumar Foreword As an inventor Leonardo was an astonishing genius. Although he lived over 450 years ago he foresaw the coming of advanced technology, and filled his notebooks with thousands of drawings for new machines and weapons, many of which anticipate twentieth century engineering techniques. We see him designing armoured tanks, steam guns, ballistic missiles, flying machines, parachutes, helicopters, underwater diving suits, water turbines, movable cranes, lifting jacks, gearboxes!! Each of his inventions is a source of wonder and excitement, displaying both Leonardo’s awesome intelligence and an incredible anticipation of the future. When it comes to inventors, the contributions of Thomas Edison demonstrate the value of systematic approach to invention, design and product development. Edison was meticulous and painstakingly through when it came to design. He tested hundreds of different materials in his search for perfect filament to use in his incandescent light bulb (including bamboo and sewing thread). His style had its advantages: He is still on record as one of the most prolific (and famous) inventors in US history with 1,100 patents!! This clearly emphasizes the fact that to succeed in a new venture, the design process must be planned carefully and executed systematically. In particular, an engineering design method must integrate the many different aspects of designing in such a way that the whole process becomes logical and comprehensible. To that end, the design process must be broken down, first into phases and then into distinct steps, each with its own working methods. A new PG course Engineering Design Methodology has been introduced in our department from this academic year 2006-07 and aims to present systematic engineering design process with latest information about general theory and practice. As part of this course the students undertake projects that will give hands on experience in design practices. This article is a compilation of these projects (in various stages of progress) that are being pursued by the present batch of students.

Subsonic Wind Tunnel

A Ravi Kumar, N Praveen Kumar and K Siva Sankar Reddy The project aims at designing an open loop wind tunnel that creates a low-turbulence air flow at maximum Mach No. 0.4 through the test section that shall allow researchers to measure the aerodynamic effects such as lift, drag, pressure, temperature and boundary layer on the model being tested. The wind tunnel design mainly consists of a centrifugal fan driven by a variable speed motor to control the air velocity. Before reaching the working section, the air will pass through an inlet zone with constant pressure diffuser and a settling chamber. The working section design includes tapered corner fillets to ensure uniform air velocity and transparent windows for clear observation. A versatile data acquisition system will enable accurate real-time data capture, monitoring, display, calculation and charting of all relevant parameters on a computer.

Vacuum Casting Machine

D J Bardoloi, K Acharyya and K Sunil Kumar The work involves designing and developing a casting machine that incorporates vacuum to get a better casting of intricate and complex objects by eliminating general casting defects such as, porosity, shrinkage defects, flow defects, oxidation etc. generally originating from lack of desired level of flowability of molten charge and reaction/ interaction of molten charge with atmosphere. The machine will be used for casting of small metal parts or jewellery having fine detail or for casting various plastic materials. We expect on completion of this work at least, a design framework for a vacuum casting machine that is feasible both technically and economically.

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Simulator and Test Rig for Complete Leg Prosthetic Ambati Apparao, K Veera Babu and Srinivas Madduri

The main objective of the test rig to be designed is to test for various motion and force bearing capacity of complete leg prosthetic. The complete leg prosthetic is made up of different components such as knee, ankle, foot, pylon, socket, etc.. The range of motions of every component as well as the corresponding forces and torques which will act while doing different tasks such standing, different gaits etc. is of interest. We limit our design scope to some kinematics and total torque measurement only. A preliminary model of the test rig is shown.

Test Rig for Straight Axle Fatigue Test

G R Santosh Kumar, Harjeet K Banjare and Lanjekar R Deorao The test rig being designed shall produce completely reversed, alternating and fluctuating reversed fatigue stresses on straight axle to determine fatigue life. The design objective is that the test rig should produce meaningful and reliable test results in a reasonable period of time. Test rig assembly mainly consists of fatigue test fixture, energy source, modification and control of the same so as to produce the desired loading at desired rates for determining fatigue life of axle. A function structure including various sub-functions and their working principles has been arrived at and some solution variants have been analyzed. We plan to do weak spot analysis of the variants before embodying the best solution.

A Machine for Crack Generation

L Praveen Kumar, P Venkateswara Choudari and Srinivasulu M This project addresses the design and development of equipment for generating different types of predefined cracks on metallic plates, so that further analysis on cracks and their potency under different loading conditions can been found. The system includes fixture for holding different geometry of plates, sub system for creating high stress concentration zones at desired location and crack detection system. In the layout design we intend to focus on reducing the space occupied by the equipment. A function structure including various sub-functions and their working principles has been arrived at and some solution variants have been analyzed.

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Thin Strip Casting Machine

Kamble Ajinath H, Manoj Kumar Sinha and Sunil B Deshpande The projectâ&#x20AC;&#x2122;s goal is to redesign & develop a thin strip casting machine to decrease the number of processes for production of thin metal strips with reduced production time, cost and energy.

These machines accept molten metal from the furnace and output stack of thin strips or rolls of desired thickness and width. Some commercial machines are available for mass production of thin strips of Aluminum, Copper, Zinc, Steel alloys and Lead. Initially we did a market survey for the available products and found out customer and technical requirements of the product. Later we have arrived at a function structure that will include automatic thin strip thickness and width adjustment system in the existing machine at IITG. We also intend to design auxiliary systems for strip ďŹ nishing purpose.

Test Rig for Rolling Contact Element Bearing Kaushik B, P Manikandan and W Ravi Kumar

A bearing is a device to permit constrained relative motion between two parts, typically rotation or linear movement. Failure of the rotor systems is associated mostly with failure of bearings. So predicting the accurate life of bearing is very important. In this project, we intend to design a test rig to investigate the life of bearing. The test rig shall be able to test the bearings of different material composition available in dimensions of range; outer diameter<150mm, inner diameter >45mm, supply an axial load of 10kN, radial load of 120kN and speed of 20 krpm. The test rig shall be facilitated to test 12 bearings at a time which are to be mounted on 4 test stations having 3 pulleys each. The life period that is obtained by carrying accelerated life test (high load and speed conditions) is then extrapolated to designed conditions.

Laser Assisted Metal Coating System Amit Rawal, Anil Kumar and Dependra Nath Mishra

The machine designed will take coating material in powdered form and the component to be coated as input and will perform suitable high performance metallic coating on the surface of the component, wherein the energy required for process will be obtained from Laser and would give coated component of desired dimensional accuracy and ďŹ nish as output. Studies have shown that metals deposited via Laser technology display fewer voids, better adhesion and superior hardness properties as compared to other existing processes like Electrolysis, Plasma arc, Electrochemical, Welding, Electron beam, etc. The process also has the potential for controlled deposition and removal of materials with Laser beam precision. It can operate with very small quantities, thereby preserving precious coating metal and minimizing wastes. In addition, the system can be designed as an automated closed loop process, thus increasing rate of coating with desired precision.

Acknowledgement

The students are thankful for useful discussions with faculty members of mechanical engineering department, IITG.

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B.Tech. Projects Allotted for 2006-07 Session 1

RAHUL KUMAR S. KUMAR MISHRA VIVEK KUMAR

Application of relaxation scheme and Lattice Boltzman method for compressible flows

2

PUNEET CHHABRA

3

ANAS VIQUAR GAURAV JINDAL

Computation of turbulent flow in a channel Prediction of heated turbulent round jet in a cold co-flowing ambient using different turbulence models

4

RAVI KUMAR PATNI SAURABH GARG

5

AZAD SUDHENDU

6

NIRDOSH KUMAR S. KUMAR NIRALA

7

C. KUMAR CHOLLETI

8

YOGESH YADAV

9

DANI RISSANG M. SANJEEV KUMAR G. RAJKUMAR LEKSAR MODI

10

DEEPAK KUMAR

11 MOHAMMAD SHADAN 12 13

K. VIDYA SAGAR NOOTHI RAVI KIRAN PRATEEK PRASAD N. SINGH SEKHAWAT NITISH KUMAR ROY RAJPREET SINGH ABHISHEK MISHRA

14 ATUL KUMAR GARG

N. CHANDRA BEHERA ANKUR PAHUJA

Applications of soft computing and machining 3D Geometrical Modeling of The Human Heart h-adaptive finite element analysis of 2D elasticity problems using ANSYS Mixed convection flow in a lid-driven enclosure filled with a fluidsaturated porous medium Design of Pneumatic Conveying System Analysis of thermoelectric generator Performance Evaluation of PEM type Fuel Cell Investigation of Segregation in Vertical Centrifugal Casting FEM Analysis of a composite hip prosthesis An insight into the modelling of short pulse laser transport through a participating medium Analysis of phase change of a 3D semi-transparent medium using LBM and FVM

15 SOHIL GARG

Application of the LBM to the Analysis of heat transfer in a porous radiant burner

16

Optimization of jobshop scheduling based on particle Swarm Optimization technique

KOLAN SREEKANTH DEEPANKAR GARG JASPREET SINGH SUDHANSHU KUMAR M.KOSURU VENKATA

17 G. SASI SEKHAR 18

KISHORE AGGARWAL RAVI GUPTA VENU YARAMSHETTI

Mechanika, April 2007

Optimization of set-up plans in Computer Aided Process planning systems for machining based on Ant colony Optimization technique Modeling and optimization of microextrusion process

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M.Tech. Projects Allotted for 2006-07 Session

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1 2 3

N. Mahendra Benarjee Tumma C. Naveen Kumar

4

Neeraj Carpenter

5

S. Swamy

6

Shounak Basak

7

Pasumarthy V.V.N. Prasad

8

Walsange Ganesh Dagadu

9

P. Naveen Kumar

10

Tammireddy Ramakrishna

11

Sreenivasaraju Chekur

12

N. L. Sairam Babu .K

13

K. Chaitanya Mummareddy

14 15 16

S Varun Sivaprasad Koralla Parashar Ketan Sharad

17

Devangre Rahul B

18

Gopal Kishor Gummadi

19

Bhaskar Agrawal

20

Kakularam Sailender Reddy

21

Harish Alugoju

22

Manvendra M. Umekar

23

Chopade Ramchandra Prabhakar

24

Srinivas Yannabathula

25

Kapil Gupta

Parametric instability of softcore sandwich beams.

Fatigue analysis of artificial hip joint using FEM Stability analysis of water cooled reactor Finite element analysis and optimisation of 2 link robotic manipulators Experimental determination of stress intensity factors of finite plates using strain gage technique Optimisation of hard turning process using neural networks Computer aided design and stress analysis of crowned cylindrical roller bearings Computer aided design and analysis of spur gear Performance of recovery by equilibrium(REP) method on meshes of quadratic triangular elements FEM modelling of smart composites Estimation of bearing dynamic parameters in rotor bearing system and seals.

Unstructured mesh generation over multiply connected arbitrary 2D domain by conventional Advancing FRON method An experimental investigation of the edge quality in sheet metal shearing process Force measurement in active magnetic bearings Optimization of pipe routing through arbitrary domain Large eddy simulation of heated and unheated coaxial jets Conjugate mixed convection heat transfer in plane laminar wall jet flow Modelling and simulation of natural circulation boiling water reactor Development of implicit compressible flow solver Euler’s equation for unstructured mesh Improved memory management and performance enhancement of a 2D cell centered finite volume CFD code on unstructured meshes.

Numerical analysis of Metal hydride based thermal energy storage device Numerical analysis of Metal hydride based thermal energy storage device An experimental study of long run performance and exhaust emission of CI engine fuelled with blends of jatrope oil and diesel Flow induced vibration in a penstock pipe of a hydro power station Vibration control of smart FRP composite structures Mechanika, April 2007

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Kapil Gupta

26

Chinige Sampath Kumar

27

Ohal Pravin Shridhar

28

Moode Ramamurthy Naik

29

Arun Difoe

30

Lonavath Dayanand

31

Uppugandla Madhava Krishna

32

Pavitra Singh

33

Ajoy Krishna Dutta

34

Prafulla Kumar Swain

Vibration control of smart FRP composite structures Experimental and numerical investigation for a laminar fully developed pulsating flow Study of natural convection heat transfer in a partially heated square cavity using nanofluids Prediction of surface roughness and cutting forces in micro end milling Characterisation of hybrid motion membrane for direct methanol fuel cell A comparison of different turbulence models on the effectiveness of pin fins arrays in a 3D flow in a rectangular duct with a heated bottom wall Numerical investigation of coupled heat and mass transfer in metal hydride based hydrogen storage device Design , development and performance evaluation of a batch type biodiesel oil processing system.

Acooustic charaterisation of of tool wear in machining Comparison between various displacement based stress intensity factor computation technique

What They Say “Obstacles are those frightful things you see when you take your eyes off your goal.”

-Henry Ford “The weak can never forgive. Forgiveness is the attribute of the strong.”

-Mahatma Gandhi “Success is the ability to go from one failure to another with no loss of enthusiasm.”

-Winston Churchill “Success usually comes to those who are too busy to be looking for it.”

-Henry David Thoreau “Anyone who has never made a mistake has never tried anything new.”

-Albert Einstein

“When everything seems to be going against you, remember that the airplane takes off against the wind, not with it.”

-Henry Ford

Mechanika, April 2007

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