NEES - Offshore Wind Turbines by Oliver Baldock

NATIONAL ENGINEERING EDUCATION SCHEME OFFSHORE WIND TURBINES OLIVER BALDOCK. JANUARY 2012.

CONTENTS Contents ......................................................................................................................................................................... 2 Our Team ....................................................................................................................................................................... 3 Engineering Education Scheme (Background) .............................................................................................. 4

The Possible Projects Available............................................................................................................................ 5

The Potential Solution .............................................................................................................................................. 7 Our Visit to BAE Systems ........................................................................................................................................ 8 Meeting Our Engineer............................................................................................................................................... 9

Our Planning.............................................................................................................................................................. 10

Initial Specification ................................................................................................................................................. 11 Research & Development ..................................................................................................................................... 13

Materials’ Properties.............................................................................................................................................. 14

Environmental Conditions................................................................................................................................... 15

Launch Strategies & Transport .......................................................................................................................... 17

Towing & Stabilisation .......................................................................................................................................... 18

Residential Trip to Canterbury .......................................................................................................................... 19

The Designs................................................................................................................................................................ 22

Development of Floatation Device ................................................................................................................... 23

Evaluation of Initial Design Ideas ..................................................................................................................... 25

Chosen Design For Floatation Device ............................................................................................................. 30

Exploded Isometric & Orthographic Designs .............................................................................................. 33

Mathematics Behind the Design........................................................................................................................ 35

Flooding & Sinking .................................................................................................................................................. 41

Points for Consideration (Includes Further Intense Maths & Physics) ............................................ 42 Testing ......................................................................................................................................................................... 45

Conclusion .................................................................................................................................................................. 49

Our Process Journal ................................................................................................................................................ 51

Evaluation................................................................................................................................................................... 52

Bibliography .............................................................................................................................................................. 60

Engineering Education Scheme: The Report | Contents

OUR TEAM Team Members: •

Josh Abrahams Having always had an interest in maths, physics, and just generally being creative with his thinking, engineering has always been of interest to him and is a field he wishes to pursue at Cambridge University, and indeed into a career afterwards in aviation and aeronautical engineering with ambitions towards the RAF. • Oliver Baldock With interests in design and particularly architecture since a young age, his passions have widened to include engineering in almost all circumstances, from civil to aeronautical, with aims to further this education at Cambridge, his mind is always open to new ventures. • Owen Clarridge Interested in automotive and aeronautical engineering since a young age, his granddad’s and uncles vintage cars began a journey through civil biomedical and material engineering which will lead to a profession in this realm. • Adam Skinner With aims to enter the engineering world, after a degree, he feels his competence in the engineering workplace is best suited to mechanical or automotive engineering as these are where his interests lie. Teacher •

Mr M. S. Pentecost, B.Ed. (Thames Polytechnic)

Engineer •

Richard Tomkins, Project Engineer, Laing O’Rourke

Engineering Education Scheme: The Report | Our Team

ENGINEERING EDUCATION SCHEME The Engineering Education Scheme is a 6 month programme run by the Engineering Development Trust which involves four Year 12 students and their teacher working with local companies to solve engineering problems. The aims of the scheme are to allow the students to experience; • part of a team • Use of a university’s engineering workshops to develop, build and test solutions to the problem • Professional skills lectures on communications and project management • The opportunity to develop technical skills and see applications of school subjects • An opportunity to meet professional and graduate engineers, scientists and technologists • Experience in presenting their solution, in a formal verbal presentation and formal written technical report, to a panel of senior professional engineers. •

However, more importantly, the programme is designed to allow students interested in engineering and related subjects to gain valuable experience which will further their knowledge and help them to decide on future careers.

Engineering Education Scheme: The Report | Engineering Education Scheme

THE POSSIBLE PROJECTS AVAILABLE Our project involved working with Laing O’Rourke, a company whom our school had previously worked with, to solve a real engineering problem within their organisation.

Laing O’Rourke is one of the largest global private construction businesses, consisting of a variety of engineering, construction, manufacturing and other services companies, working throughout the world in many different sectors of industry. The fact that the company’s head office is situated in Dartford, and therefore within minutes of our school, provided not only a close link between us, but also an opportunity to gain an insight into the industry by working with one of its leading companies. In terms of the project itself, after meeting with our engineer from Laing O’Rourke, Richard Tomkins, he gave us two choices: Option 1: Wind Turbine Base The Aim To model a conceptual design for a wind turbine base in order to assess its properties for use in the construction of an off-shore wind farm.

Key Facts/Features:

• A design is already in place from our team but it is very much at the concept stage. It has not been built, tested or finalised as yet.

• The turbine base will be constructed on shore and towed to location at sea where it will be filled with water and sunk to the ocean bed.

• For testing to be successful, the model must be to scale and have similar buoyancy/weight distribution properties. Testing Required: • • • • • • •

Assessment of buoyancy

Assessment of capability to be towed and optimum towing attachment location

Assessment of ability to resist inclement weather, i.e. wind loadings, waves and currents etc. Assessment of ability to push down and spring back. Rate of sinking of the unit once flooded.

Ability to bed down in sand, silt and ripples, etc. Any other issues or problems you can think of.

Engineering Education Scheme: The Report | The Possible Projects Available

He also presented us with a sketch of the concept, in order for us to gain a visual idea of the problem and potential solution. However, due to potential copyright issues, the sketch was a simplified version of the design already created by his team. Option 2: Conveyor Belt for Top-Down Muck Away The Aim: To design and model a conveyor belt for removing clay and gravel from a top-down environment. Key Facts/Features: •

• •

Top down construction is where you in effect cast the ground floor slab before the substructure underneath. Once the ground floor slab is constructed you undermine it and cast the slabs beneath. Due to a slab over your head working room is therefore cramped and all materials are taken out/in through holes in the already cast ground floor slab.

We therefore need a conveyor belt configuration which can operate in these cramped conditions.

Testing Required: • • • • •

Conveyor angle as suitability for use

Conveyor materials for optimum removal Conveyor speed

Conveyor hopper size/design Safety features required

He had also prepared a PowerPoint showing the top down construction method, as well as a sketch of the top down working environment, including hole sizes, etc. The Decision After reviewing both of the problems carefully, we chose unanimously to develop the wind turbine design idea, as we felt that it seemed more challenging and closely linked to the prominent issue of sustainability in engineering currently facing the industry.

Engineering Education Scheme: The Report | The Possible Projects Available

THE POTENTIAL SOLUTION As stated in the previous section, we chose unanimously to develop the wind turbine design idea. As a result, our project would therefore have to involve developing the design idea, building a model of the wind turbine base, and then testing it to ascertain its potential effectiveness. Consequently, we constructed a plan for how to solve the problem: • Primarily we will need to research into wind turbines to gain knowledge on the environment, materials, and mathematics related to constructing a base. This needs to cover a wide variety of topics to enable us to consider all potential solutions • The next critical step is putting our heads together to create some initial ideas for the model of the wind turbine base, developing on the original idea given to us by our engineer. • We then need to develop our ideas for the design to make sure all possibilities and solutions are covered before we move into the next major task. • Following smoothly on to the more kinaesthetic side of this project where we will make a model of the wind turbine base during the three day residential visit to the University of Kent, in Canterbury. • We will then complete this model back at school where the need for facilities is not as great, so will allow us to work in more familiar territories. • This model will need to be tested to measure how well it fits the criteria set out at the start of the project. • We will then conclude after we evaluate the project and make any suggestions for further improvement if the model is to be used in future full-scale production.

Engineering Education Scheme: The Report | The Potential Solution

OUR VISIT TO BAE SY STEMS

On Thursday the 13th of October, we visited BAE systems in Rochester to meet our designated engineer and to be introduced to the project. This is where the project would really start for us all.

We began the day by watching a presentation aimed at introducing us to BAE SYSTEMS the scheme by Matt Fox. He told us about Source: www.rochesteravionarchives.co.uk the background of the scheme and what its aims are. We then had a chance to Retrieved: March 2012 demonstrate our engineering abilities and were tasked with building a tower as tall as possible to support a golf ball. Unfortunately we didn’t win. However, we did demonstrate our ability to design and build a tower which supported the weight with ease. We were all rather happy with the outcome. Richard Tomkins, our engineer, left us to our own devices at the beginning and helped to strengthen our design at the end with supporting braces. We then had some much needed tea and biscuits.

The next presentation introduced us more thoroughly to the project. We were told in detail what exactly we were to produce. We needed to solve a problem set by our engineer and produce a presentation that would last 10-15 minutes and a portfolio outlining the whole project. To help plan this, we were advised to create a Gantt chart to help schedule our project. This would include various dates for completion of each section such as the portfolio, the model, and the presentation. Obviously there were many more things that would need to be allotted time.

We had learnt a lot from these presentations such as the importance to plan everything. If one part of the project fell behind, it could delay the whole project and this could be detrimental to the finished project. We also learnt the importance of details and how our research should be thorough. If not, small assumptions could lead us astray from our project and cause bigger problems later on. We would like to thank everyone involved in the presentations in BAE Systems, Rochester.

Throughout the day we also had a chance to meet our engineer, Richard Tomkins from Laing O’Rourke who are one of the biggest concrete fabrication companies in England who specify in pre-manufactured concrete components.

Engineering Education Scheme: The Report | Our Visit to BAE Systems

MEETING OUR ENGIN EER We first met Richard Tomkins at BAE Systems, Rochester where we had discussed various aspects of engineering we would like to deal with in the project. At this point we discussed our interests, as he spoke about the part he played within Laing O’Rourke’s concrete department. The next time that we met him was when he visited our school for a meeting to discuss possible problems for us to tackle. He had come up with two very different projects.

The first idea was to solve a problem that he currently has within his job. It involved excavating soil and hard-core from a building that was being built below ground level. This would have focused a lot on mechanical engineering. We briefly talked about possible solutions such as a conveyor belt system which would allow for constant flow of debris to be removed. We all thought that this would be an interesting project but didn’t want to decide on a particular one until both had been heard.

The second idea was to build a model of an engineering innovation: a wind turbine base. The was revolutionary as it is still in the idea stages and Laing O’Rourke are trying to get a patent on a design that they have mimicked from another company but made some alterations to. After building the model we would be required to test the model to see how it would behave on the water. The idea is that it would be built as a unit and then towed out to sea when it would be filled with water and sunk to the sea bed where it would remain until it needs to be re-sited. This would focus a lot more on maths and physics as buoyancy issues would undoubtedly arise. We decided on the second idea as it would be more of a challenge. Richard then gave us a plan for the wind turbine base that Laing O’Rourke had come up with and explained the orthographic drawing to us. It was detailed with various measurements and densities for concrete that would be used for its construction. He said that we would be able to make slight alterations to the design if we needed to accommodate any additional features such as towing points or flotation devices etc. The visit from Richard was extremely helpful as he was able to shed much more light on the two problems than were detailed. We were also able to ask him questions about the project such as the different types of concretes that would be used etc. These basic questions helped us to have an informed view on the project right from the start.

Engineering Education Scheme: The Report | Meeting Our Engineer

OUR PLANNING Gantt Chart

Points for Consideration • • • •

Although this is our initial plan we assume that timings will change as we find more efficient methods of production. Our final plan and journal can be seen at the end of this project with the appropriate adjustments. We have considered each week to equate to 5 hours of our time, thus the entire project equates to 125 hours of our time. Although within the residential trip we spent three whole days working on the project, we have counted that as the equivalent to one week.

Engineering Education Scheme: The Report | Our Planning

INITIAL SPECIFICATION • The tower will measure 50 metres in height and 36 metres in maximum diameter. Our design solution for launching this tower must keep modifications and alterations to its design to an absolute minimum. As such, our design must simply comprise a basic structure that can be fitted to the tower externally once it has been fabricated. • Due to the implications of the tower’s sheer size, it must not be sunk in waters deeper than 40 to 45 metres, so as to provide sufficient clearance above the surface of the water on which the turbine may later be built.

• In order for the tower to remain stable, level and therefore safe to build upon, it must also be sunk in an area of sea bed whose relief is relatively flat.

• The tower must feature a stabilisation device with which it can be towed safely and comfortably from dry dock to location. This device must fit around the base of the tower, and control its rocking and tilting motions sufficiently so as to prevent the structure from toppling. This is an essential design feature, because in its absence, the tower would be next to defenceless against the risk of falling over. This eventuality in itself would be catastrophic, because lifting it back up again would be a near-impossible task.

• The device must be competent of withstanding high intensity wave attack, and absorb the shock of high force and high amplitude oscillations. Repetitive strains must be resisted up to 15 times every minute and stability must be maintained for upward shifts due to wave heights of up to 2.5 m (as disclosed by research). • However, these shocks must be absorbed gradually, rather than completely obstructed by a sudden impact, as this would inflict tremendous damage upon the pistons and structure as a whole. The system must therefore feature mechanical pistons that can compress and expand slowly, with a good degree of control in order to work around unwanted oscillations due to wave attack. That said, these movements must also be slowed down with some form of critical damping, such that the tower does not continue to rock back and forth continually.

• The device must provide stability uniformly in all directions in order for the tower to be fully supported against all possible directions of toppling, but must also be hydro-dynamically streamlined, so that it can move through the water with relative ease and a good degree of manoeuvrability and controllability. • The floatation device must be easy to fit to the base of the tower, but at the same time must be capable of supporting its full weight during the course of the launch procedure as well. It must therefore be highly buoyant so as to achieve this effectively. In turn, it must also feature a robust, high-strength fixing with which it may hold the tower comfortably until it is ready to be sunk.

• When it comes to launching, the jacket must be easily deployable as well so as to avoid complications during the final stage (sinking). The tower will have to be dropped out through the centre of the jacket, sliding out downwards under its own weight as it fills with water. Engineering Education Scheme: The Report | Initial Specification

• In order to sink the tower on location, the outer shell must feature a number of holes through which the water can enter. There must also be pressure relief holes through which the air already inside the tower can escape, and hence prevent air locks. The diameter of these holes must be selected carefully in order to control the rate of fill.

< SCHEMATIC SHOWING DIMENSIONAL CONSTRAINTS OF THE TOWER Source: Primary

Created: December 2011

PROCEDURE DIAGRAM FOR CONVEYANCE OF TOWER Source: Primary Image

Created: 14th December 2011 V

Engineering Education Scheme: The Report | Initial Specification

RESEARCH & DEVELOPMENT Research is a crucial, even fundamental component of any design process. The purpose of this preliminary aspect is to provide us with an insight into how things are done in the real world, from which we can obviously derive our own ideas. It also aids our comprehension of certain constraints, as well as available strategies with which to implement our design solutions. More specifically, when it came to carrying out our own research, the process was facilitated by way of fragmenting the required information into four appropriate sub-topics, with each one assigned to a different member of the team. The primary goals for our research included:

1. Owen: To investigate physical and mechanical properties of concrete (in addition to those of any other materials we may consider utilising), in order to make well-informed and sensible decisions regarding the specifications of our design. Essentially, we needed to know which materials would provide the best performance results possible, whilst serving its purpose within our final project design, and what sort of pre-requisites come with the use of such materials, so that they can be adequately catered for. 2. Josh: To study the environmental conditions experienced on the North Sea, such as relief, weather, wave height, wave frequency, depth, tides, salinity and sediment composition, and hence understand the constraints within which the project must be made capable of working. 3. Oliver: Look into potential strategies for transporting large concrete panels around the country, as well as methods for the launch of structures from dry-dock, which would enable us to make suitable decisions as to how to construct the tower and convey it out to sea. 4. Adam: Obtain an understanding of tug-boats, common towing processes used at sea, and conventional methods of stabilising buoyant structures on turbulent waters. This would place us in a good position to maintain the safety and effectiveness of our tower whilst being towed to location, alongside upholding that of the people involved in the launch process as well. With these targets in mind, the questions were addressed, and a wealth of helpful information was obtained, as follows:

Engineering Education Scheme: The Report | Research & Development

MATERIALS’ PROPERTIES • Concrete is a composite material, comprising a fibre (in the form of aggregate), and a matrix resin (in the form of a cement and water paste). • Inherently, this produces an extremely resilient and hard-wearing material: one that is very resistant to water, wind and chemical erosion, and also has a high Compressive Strength. That said, its relatively low Tensile Strength means that steel Reinforcement Bar (Rebar) may be a beneficial and worthwhile addition. • Concrete is, however, slightly porous, so the steel would be vulnerable to corrosion from the sea water. This may lead to spalling, whereby small fragments of concrete are gradually disintegrated from the rest of the structure by the corrosion of the Rebar inside. • Moreover, freeze-thaw action will prove a major issue if water becomes trapped within the structure, because it will have the effect of breaking the material apart as the ice expands. • This information will prove extremely useful indeed, as it provides us with a vital insight into exactly what we are dealing with, and what complications must be allowed for in the use of concrete. For example, we know now that the concrete alone is not enough to protect the steel Rebar (needed to overcome the concrete’s lack of SPALLING OF CONCRETE Tensile Resilience) from corrosion, and some Source: upload.wikimedia.org form of Galvanisation is therefore imperative so as to evade spalling. Retrieved: April 3rd 2012 • We were aware from the beginning that Laing O’Rourke’s concrete is a highly-specialist material, whose performance characteristics are not only closely-guarded, but also are such that very specific manufacturing conditions are required. This would obviously influence us in our decision as to how and where the concrete should be manufactured, and whether the best option would be to cast the tower in dry dock, or to pre-fabricate structural panels and assemble these in the dock instead.

Engineering Education Scheme: The Report | Materials’ Properties

ENVIRONMENTAL CONDITIONS • The North Sea, characteristically, is a particularly rough and treacherous area of water, adjacent to the east coast of the UK, with wind speeds of up to 30 mph 1, and powerful waves of around 2.5 metres in height, that break between 10 and 15 times per minute. This information was extremely useful to us, because it proved very beneficial in aiding our understanding of the conditions in which the tower would have to be NORTH SEA CONDITIONS capable of working. For example, we learned that Source: www.freefoto.com the tower must be stable enough so as not be toppled by vertical displacements of up to 2.5 m Retrieved: April 1st 2012 due the oscillation of passing water waves. It was therefore clear to us that some sort of stabilisation device was mandatory. This device would provide our tower with the adequate degree of stability required in order for it to remain up right whilst being buffeted by the relentless wind and wave action. This device would have to be easily attachable, without requiring drastic alterations to the existing structure and design of the tower. It would also need to be quickly and easily deployable, such that the tower could be dropped from it and sunk at sea without difficulty. • Tides vary by around 6 metres 2, with high water marks occurring in the early morning and late afternoon, and low tides mid-morning and late at night. This piece of information is also of particular use to us, because it will enable us to time the launch procedure of the tower in accordance with the most appropriate conditions. For example, our launch procedure must be timed to coincide with these high tides, so as to provide sufficient water-depth, and therefore clearance, for the tower to get out of the dock and not scrape on the sea floor. Now we know exactly when this occurs. • The North Sea floor is largely composed of soft and easily-compacted Glacial Till. This is very fine silt, which poses the risk of the tower sinking into it or listing to one side unless treated properly. It is therefore necessary that the base of the tower is kept as wide as possible to prevent this eventuality, but also that the base is provided with resilient support structures. From this piece of information, the importance of ensuring that the tower does not come down too quickly is clear. If the tower does collide with the sea-floor with too high a velocity, the excessively high impulse force that this would instigate would in effect cause the tower to embed in the silt during the collision, possibly in such a position that it can neither be built upon safely, nor corrected at a later stage. That said, the softness of the till may help to soften the blow caused during the tower’s collision with the sea floor, and hence reduce stresses exerted on the concrete by the impact.

Engineering Education Scheme: The Report | Environmental Conditions

• As also revealed by our research, Open-Ended Steel Tubes are by far the most common form of foundation for off-shore structures, which involve a form of steel tube driven down vertically into the sea floor, and filled with concrete, providing a solid base on the bed, onto which the structure can be built. This process is relatively easy to implement, and is actually quite effective as the steel tubes offer rigid containment of the concrete while it is setting. This technique therefore seemed like a highly probable option for laying our tower down on the sea floor.

OPEN-ENDED STEEL TUBULAR PILES Source: www.maritimejournal.com Retrieved: April 1st 2012

Engineering Education Scheme: The Report | Environmental Conditions

LAUNCH STRATEGIES & TRANSPORT Dry Docks Dry-docks allow sea-bound structures to be built feasibly on-land, with the sea close-by. This obviously reduces the cost of transporting the finished product from the place of manufacture to the point of launch, but does impinge on access to vital manufacturing conditions and specialist equipment that may not be available outside of the factory, in a dry-dock. In this case, the concrete would be composed in the factory and transported to the dock via a convoy of cement-mixers, so to speak, and then cast into shape in the dock itself before the final launch. The largest cement mixers available for use in the UK have a capacity of around 14 m3, meaning that, with a total structural volume of 1662.65 m3, the total concrete requirement for the construction of this tower would demand as many as 120 individual loads. The Alexandra Dock in Hull, East Yorkshire, is one example of where this could be done. Factory Construction The other option that our research disclosed involves constructing the tower in separate panels inside the factory (so that the concrete can be fabricated to the optimum quality in the requisite conditions), and subsequently transporting them by lorry to the dock, where they would be assembled ready for launch. Imagine an enormous, 50 metre tall Lego-set, if you can! Such that we may work within the constraints of a conventional engineering context, this would limit us to 7m x 7m panels, as this is the largest that could feasibly be transported in view of their exceptional thickness (0.3m). This would give a total mass of 37 tonnes for the denser panels, and 26 tonnes for the lighter ones, which can just be handled within the normal operating capacity of a heavy-duty crane.

Engineering Education Scheme: The Report | Launch Strategies & Transport

TOWING & STABILIS ATION • When towing large buoyant objects out to sea, it is very common for a large ocean-going tug to provide the pulling power, with two or more complementary harbour tugs to provide the directional control and stability. • When stabilising large, heavy objects that have a tendency to move drastically, it is often necessary to absorb the force of that motion gradually, rather than trying to stop it abruptly, as this would incur tremendous impact forces and hence fracture the support structures involved. This movement must of course also be dampened so as to reduce the effect of repeated oscillation. • This information will of course influence HARBOUR TUG our thought-process when it comes to integrating Source: www.maritiemjournal.com certain features into the design of our solution, with particular relevance to the floatation device Retrieved: April 1st 2012 and how we go about towing it out to location. For example, our attention has now been drawn to the need for substantial damping pistons with which to control the articulation of the pontoon, as well as the need for providing three separate towing points, by the information gained in this section.

So, after a long week of internet-browsing and perusing through various books, needless to say we were beginning to feel a little like sponges! On the plus side, we certainly benefited from a significantly better understanding of our direction within this project, and armed with all this technical information we had managed to obtain, we were then able to clarify what exactly our initial specification wanted of us.

Engineering Education Scheme: The Report | Towing & Stabilisation

RESIDENTIAL TRIP T O CANTERBURY The residential trip was a three day trip designed to get us started with the making of the project. However, there was also a lecture in the morning to explain the layout of the university and who we would be able to ask for assistance with any machines or specific needs. Before we left for Canterbury, we already had a clear idea of what we wanted to do. Our main aims were:

1. 2. 3. 4. 5.

Calculate the mass distribution, centre of mass and buoyancy Research into suitable modelling materials for the construction of the scale model Construct the scale model as accurate as we could Test materials for a buoyancy aids CAD Drawings of the tower

However, as we tackled these, the testing of the flotation devices was not completed as we didn’t have enough materials to test and so decided to leave this until we returned home and had completed the model.

The calculations for the mass distribution, centre of mass and buoyancy were obviously our major priority and little other than the structure could be produced before these were done, so half of our team set off and spent the majority of the first day working on these tasks. For further details into the exact methods and numbers involved in this please view the ‘Mathematics Behind the Design,’ which works through all the calculations involved in this and the rest of the design process. Research into Suitable Materials for the Model:

As we began to plan the model, quick attention was drawn to the fact that it would have to replicate the real thing in the water. This would mean that we should try to replicate the thicknesses and densities of each section. Upon research, it was found that aluminium had a density of 2700kg.𝑚𝑚−3 3 and so would suit our needs for the high density concrete that was

2500kg.𝑚𝑚−3 4. Similarly we found that PVC had a density of 1400kg.𝑚𝑚−3 5 which was relatively close to the lower density concrete at 1800kg.𝑚𝑚−3 6. This at the time seemed like a good idea until we realised that although these had similar densities, the thickness of each would be hard to match. We decided then to use these materials but to also used added masses internally which would help reproduce the same centre of mass.

After these conclusions were made, we decided to find the best matches that we could for the items that we needed. We realised that the university had an abundance of aluminium and we also found some PVC. However, the only PVC tube that we could find to make the central cylinder was 10.4cm instead of 8cm. This is the only area of the plan which was not accurately represented in the model.

Engineering Education Scheme: The Report | Residential Trip to Canterbury

The Making Process of the Model: Firstly we began by cutting a circle which was to be the base. This was done with relative ease on a band saw. The next stage was to mark on this the location for all of the components which would be attached such as the lower ring and the central column. This was done by using a piece of string and a score used as a compass to mark the centre by drawing small sectors as close to the middle as possible. We could then determine the centre by eye. Secondly we cut out a sheet of aluminium the same size as the lower ring. This was the correct height and the length of the circumference of the lower ring. We actually decided to cut it slightly larger in length so that when it is bent around, it fits flush end to end. This was later rolled into the correct curvature to create the correct sized ring. The central column was then cut to length of 49cm to allow for the 1cm thick base.

The next stage was the hardest: creating the conical shape between the lower ring and the central column. This was done by measuring the two circumferences; the top and bottom and then marking these from the same origin. This was cut out and then rolled using the same technique as the lower ring. However, because it is conical, you can’t simply feed it through the rollers in the same way we did for the lower ring, it had to be twisted at the same time. This was extremely time-consuming as it kept getting stuck in the rollers when it got close to the correct shape. Once this was completed, the first major problem occurred. We realised that the smaller circumference used in the marking out stage was 8cm as it should be instead of 10.4cm to fit the only available tube that we had for the central column. We decided to file it down as rolling it took a long time for which none of us were prepared to do again. The next stage was to attach the lower ring and the conical section. For this we decided to rivet the two piece together using brackets that we had to make ourselves. The brackets had to be cut out, drilled or hole-punched and then bent to the correct angle for the join. The two sections were then joined with the rivet gun. This was also a hard section of the build as we found it hard to create a flush fit between the two sections. We decided to test fit this complete module over the central column and onto the base disk to ensure that no other mistakes had been made. Much to our relief, there weren’t any. Engineering Education Scheme: The Report | Residential Trip to Canterbury

As I had previously stated, the base was to be 1 cm thick however, we had only managed to find aluminium that was 2 and 3mm thick. We decided to add feet to the design which could also help the unit to bed down into the silt and sand at the bottom of the ocean. These were created on the lathe and then a hole was cut in the middle of them. We then tapped out a thread in this hole to allow for them to be attached via a bolt through the base.

Having created all sections of the model, it was then time to assess its weight and how we should distribute this. Following on from the calculations of the centre of mass, we needed to add mass to the top and bottom sections and so the correct mass was created from a solid steel rod. This was turned on a lathe to remove rust and some weld deposits. The next stage was to drill a hole in the centre and then tap a thread into the block. This would allow us to move the weight to the correct height. Some stud bar was then cut down to length and attached through a hole in the base of the model. The weight was then attached and set to the desired height. We then turned our attention to the weight for the top section. This was created from a thick aluminium tube then had a hole drilled through it sideways. We then cut some smaller stud bar down to length and attached this through two holes halfway up the top section of the column. We were extremely lucky as the tapped holes in the aluminium lined up correctly so that the thread wasn’t half a turn out.

Lastly we decided to assemble the whole product. This did not just include assembly but also attaching the lower ring and conical section to the base. This was done in a similar fashion as with the lower ring and conical section. We simply created some brackets, this time at right angles, and then pop riveted the two together. Upon completion, it was decided that as the unit had to be watertight, we would need to seal it in some way. This is a problem that we hadn’t contemplated and so as a group decided to use some form of bathroom sealant. This would be done at a later date most probably back at school.

Engineering Education Scheme: The Report | Residential Trip to Canterbury

THE DESIGNS

NB: This is a simple CAD drawing created in Autodesk to represent our finished model, prior to the end of construction, and accurately represents our design.

Engineering Education Scheme: The Report | The Designs

DEVELOPMENT OF FLOATATION DEVICE In immediate response to our trip and the creation of this model, ideas soon turned to floatation devices and how we would be able to transport such a large load so it was not long at all before our note pads soon became inundated with ideas. With sketches here, annotations there, and crossings-out filling just about every other bit of free page-space, we had very quickly compiled a multitude of potential design solutions. Our initial sketches can be found in the Appendices section of this write-up. That said, having a number of design solutions is one thing, but having good solutions is another entirely! As such, a process of critical evaluation (and subsequently selecting the best design) is crucial. Initial Ideas and Designs for the Floatation Device

Design #1

Design #2

Engineering Education Scheme: The Report | Development of Floatation Device

Design #3

Design #4

Design #5

Design #6

Engineering Education Scheme: The Report | Development of Floatation Device

EVALUATION OF INIT IAL DESIGN IDEAS DESIGN IDEA # 1~ Features & Functional Description: The design features a central floatation jacket, which acts as the core foundation for the attachment of the stabilising pontoons. It also helps to add to the initial buoyancy of the tower, by providing a large increase in the volume of waterdisplacement for a relatively small gain in weight.

This is then surrounded by four individual floatation pods, which can move freely up and down with the movement of the waves, but can also rotate through a slight angle back and forth about their longitudinal axes. The further out these pods sit from the centre, the stronger the effect they have of stabilising the tower. An upper ring is also connected by pistons, the purpose of which is to stabilise tilting and rocking motions by way of restricting the movement of the top-half of the tower. Again, the higher up this sits, the greater its stabilising effect.

A Gas-Transfer System also features as a potential option, in which the compression of one piston forces gas out of it, and into the piston on the opposite side, hence causing it to simultaneously expand by the same length, and at the same time. The result is that as the piston on one side raises, the piston on the other side lowers by the same distance. This serves to keep the tower upright: it stops the raising of one pontoon pushing the tower over, by way of extending a support to the other side and hence holding it up. 2~ Features & Functional Description: This design provides stabilisation in a much more omniscient manner, in the sense that supporting forces can be exerted from all directions, all at once or at any one time, indeed in any way necessary depending on the action of the waves at a given point in time. This is provided by the

STRENGTHS (+)

WEAKNESSES (-)

The four floatation pods are independent of each other, and so can move freely and randomly, accommodating the sporadic chaos of wave action on the North Sea.

The weight of these pistons is going to be huge, impeding on the probable buoyancy of the whole system.

The inner floatation ring of this design allows the tower to be held high out of the water, and hence alleviates previous concerns over the tower sinking if the lower base became submerged. This also reduces the risk of the tower striking the sea floor.

However, holding the tower and its Centre of Mass so high out of the water in this way may in fact have its implications. For one, it may make the tower quite unstable, with so much mass at the top being free to move. It also increases the size of the gap between the base of the tower and the sea floor. With further to fall, the tower will eventually hit the floor at a greater velocity, and hence experience larger, potentially damaging impact forces. Four floatation pods provide universal, Omni-directional stability, as mandated by the Specification.

Uniform, Omni-directional stability is again provided by the circular ring. The inner ring and damping pistons allow the tower to move about freely inside, but help to absorb the shocks and dramatic movements of the

They will also be exhaustive and costly in manufacture, both in time and in raw materials. With this implication already existing on such a phenomenal scale due solely to the size of the tower itself, we should really be looking to minimise these extra costs. The articulated joints will also be complex, and will need to be substantial so as to stand up to the intense stresses of the moving pistons.

As the outer floatation ring is effectively split into 4 separate sections, it may be slightly flimsy, so to speak, and if these pods shift by different amounts at different times, which they inevitably will, then the tower may be forced into precarious positions on the water. The Gas-Transfer System assumes that opposing floatation pods will shift alternately and uniformly, which clearly may not be the case. It is also intrinsically complex, and is likely to be another point of potential failure. With the tower hanging so low in the water, there is the obvious collision-risk in shallow waters.

More pistons are used here, which, needless to say, is detrimental in weight and complexity, though it is not

Engineering Education Scheme: The Report | Evaluation of Initial Design Ideas

all-surrounding floatation ring, whose 8 pistons can absorb shocks from the tower’s motion in any direction. Furthermore, the pivotal pin-joints at either end of each piston, coupled with their extensibility, allow the tower to reciprocate up and down as needed as well as back and forth, and so on. Water-inlet valves are placed beneath the floatation jacket so as to make best use of the water pressure above in order to fill the tower effectively.

3~ Features & Functional Description: This design is essentially a collaboration of the previous two, in which the outer floatation ring has been coupled with an upper fixing ring, such that a compromise may be met between firmness of the base (through being a wide, solid unit) and catering for the tower being so high out of the water (through the upper fixing ring). The inherent instability derived from moving the Centre of Mass so high is compensated for by the height of the upper fixing, which helps the restrict the movement of the top part of the tower.

As before, the articulated pistons connecting the inner and outer rings allow the tower to move freely in any of the x (Side → Side), y (Front → Back) and z (Up → Down) axes, in variable magnitudes and at any time, be them simultaneous or individual. As in the previous design, the Gas-Transfer System suggested by the first design has been dispelled on account of is complexity, inappropriateness and lack of necessity.

outer ring (due to wave attack), and thus reducing the degree of movement transferred into the tower itself. As the tower sits lower in the ring, it will have less distance to drop when sunk, and this will hence reduce the impact on the tower when it hits the sea floor.

The pivot point of the tower (where it is fixed at the inner ring) is very close to the Centre of Mass of the tower, and consequently, Turning Moments exerted onto it as the Centre of Mass is displaced from the central point of pivot will be reduced, hence mitigating the effect of sway. This design still provides excellent all-round stability through the circular outer floatation ring. The reduction in the number of pistons is effective in reducing weight, complexity, consumption of raw materials and hence cost.

The tower sits higher in the water, and hence eliminates the implications met by design 2 in shallow waters. With the outer ring being taller, it will have more control over the top of the tower, as the upper pistons will be connected between the two at less of an angle and will hence be able to exert a greater force component onto, and in the direction of, the tower, hence confining its sway-motion more effectively.

The inner ring provides support to the base of the tower, and overcomes previous concerns over the tower sinking if the lower base became submerged. It also adds to its initial buoyancy, by significantly

essential to have quite that many.

Both the fixing points of the inner ring and the holes for filling the tower with water are submerged, which will make the process of sinking the tower extremely difficult.

As there are far fewer pistons involved, each one will effectively have to take a greater level of stress, and in turn, the articulated joints will also be stressed more severely as well. With the tower sitting higher in the ring, the centre of mass will be moved further from the point of fixing, and consequently, greater Turning Moments will be produced in the sway of the tower, though this is to an extent mitigated by the height of the outer ring, which will be effective in controlling the position of the top part of the tower.

In being a circular base, its hydro-dynamic stream-lining is somewhat limited, and as such will make towing a tricky process. The large cross-sectional area exposed to the flow of water will increase both the Drag CoEfficient, and indeed the thickness of the wake trailing behind it, hence increasing the overall Drag Force. This is a crucial point from the specification that this design

Engineering Education Scheme: The Report | Evaluation of Initial Design Ideas

increasing the volume of water displacement, without increasing the weight by any major amount.

4~ Features & Functional Description: This design works in much the same way as the previous one, except that the pistons have been replaced with high tension steel cables. These function in a very similar manner, and that is to slow the motion of the towertop during a sway, gradually, and hence prevent it from toppling whilst reducing sudden impact stress during such movements.

A drastic reduction in weight is obviously achieved through the use of cables in this manner, but sadly, that is about all that can be said for this design!

fails to meet.

With the outer ring being so much taller, it will of course be heavier and therefore more exhaustive and costly to manufacture, though this is of course compromised by the reduction in the number of pistons. The predominant issue here is the risk of the steel cables snapping, which would be extremely dangerous. The cables would go slack when the ring moves closer to the tower, rendering them useless, and when the ring moves the other way; they are pulled taut and hence become very dangerous.

Potential corrosion in the cable would exacerbate this danger. To reduce this slacking, the cables could be pre-stressed, but this would be extremely difficult, as the cables in this context would have to be highly substantial.

SPRING DAMPING FOR TENSILE CABLES This helps to offer the tensile cables a little give when tensile stresses are applied to them, such that they do not snap or having the unwanted effect of stopping the tower too abruptly.

The spring allows tensile give, hence absorbing the shock of the movement in the outer ring. This would also alleviate the issue of the cable going slack as the tower approaches the ring, at least to an extent. The oil provides very effective critical damping, and would hence slow these motions down very well. The oil also allows dissipation of heat from the stressed spring.

Complications would also arise in deploying the rings, and sinking the tower. For example, when the upper ring is detached, the cables will go slack, and the ring will hence plummet, leading to inevitable damage below. This is quite a complex system, and just adds more and more weight to the overall system. It is also something else to look after, and another aspect to break or go wrong.

Significant implications would arise in the event of an oil leak. The spring would, however, filter the oil, but in doing so, would get clogged up with debris. This would hinder it

Engineering Education Scheme: The Report | Evaluation of Initial Design Ideas

5~ Features & Functional Description: As a completely radical divergence form the previously circular design ideas seen so far, this design features a double Catamaran pontoon layout, so as to afford the tower good hydro-dynamic proficiency, directional control and ease of glide whilst in tow.

The two pontoons run parallel to each other, either side of the tower, and are independently articulated on damping pistons such that they can absorb the chaotic motion of the waves and hence keep the tower from toppling. If the tower leans to one side, the upper section of the tower will push down, through its support structure and upper linkage strut, onto the pontoon below. Met by resistance from the pontoon’s Buoyant Force, the pontoon will therefore displace outwards to the side, hence extending the piston beneath. Once the piston reaches its maximum extension, it begins to pull the pontoon down. This submerges it slightly, and the increased Buoyant Force that arises from this acts upwards, and therefore begins to resist the downward force of the leaning tower. This both pulls up on the extended piston and pushes up on the linkage strut above, thereby raising the tower back into its upright position. 6~ Features & Functional Description:

This is a much simpler version of design five, and yet serves no fewer functions. Again, in being suspended from the structure above by a pair of pistons, each pontoon is free to oscillate vertically, independently of the other, and of course they both move up and down with the movement of the waves so as to absorb their motion and minimise its translation into movement of the tower. As the tower leans to one side, the top of the tower will of course push down on the pontoon on that side, hence compressing the pistons supporting it as resistance is met with its Buoyant Force. In response, the gas inside these pistons will pressurise, and this increased pressure will eventually serve to push back up against the structure

Unlike the previously circular pontoon designs, this style provides greater directionality to the structure, meaning that it will glide through the water more efficiently, and also that the process of manoeuvring it will be much easier and indeed safer.

The size of the pontoons will provide very large buoyant forces, hence resisting the unwanted motion of the top of the tower (due to sway) very powerfully indeed, proving effective at preventing a complete topple.

The independent movement of each of the pontoons allows for the sporadic irregularity of wave action on the North Sea. The reduction in the number of component parts of this system (pontoons, pistons and articulated joints) is effective in minimising the complexity of the design, and hence reducing consumption of time, money, raw materials and energy in manufacture. The straight, streamlined, narrow pontoons will, as before, offer this design far superior directionality and ease of tow in comparison to previous designs. The pistons act as struts, clearly, holding the pontoons onto the structure, but help to slow the movement of the tower down as they are compressed by the upward motion of the waves below. The tower is attached to its support structure by a single point of fixing at the very top. This means that the tower can simply be dropped out from this position, straight down

in carrying out its primary function, as it would not be able to stretch or recoils as efficiently. Deployment of the tower will be extremely difficult, because the fixings of the lower pistons are in fact submerged. The tower does actually hang quite low in the water in this design, which will be a major implication in shallow waters, certainly. Also, with so much of the tower hanging below the fixing point on the upper ring, the tower may be quite susceptible to the lower half swinging like a pendulum. This will of course inflict major sheer stresses on the pin-joint fixings featured both on top of and underneath the floatation pontoon.

The length of the pontoons may make it difficult to implement a change in the tower’s course of direction. With the two pontoons being so far apart, it will be difficult to fix a single tow point from which the tugs can pull the structure through the water. In being one single unit, with the tower very much rigidly fixed to its pontoons, there is little or no allowance for maintaining the tower’s upright position in the event of a very large wave tilting the whole structure over to one side. Although this is not likely to tip the whole thing over (due to its great width and indeed weight), it will certainly put immense stresses on whichever pontoon the base happens to be pivoting on, and of course its respective pistons. Again, the length of this system’s pontoons may make steering tricky.

Engineering Education Scheme: The Report | Evaluation of Initial Design Ideas

above, and in turn against the top part of the tower, finally restoring it into its original position. Any submersion that the pontoon experiences during this process will simply add to this effect, because the increased Buoyant Force will also push back up against the tilted tower and hence move back into its upright position.

The piston on the far side, meanwhile, will extend, as the tower lifts away from the water on that side, and the pontoon drops away under its own weight. That pontoon therefore stays in relatively close contact with the surface of the water, in readiness to hold the tower up when it rights itself again.

into the water below by way of unfastening a single set of clamps. This means that attachment and deployment of the floatation device from the tower is in fact incredibly easy. This design has far fewer articulated pin joints than any of the other designs. This is an extremely important attribute that this design exhibits, because such joints are not only complex, but also points of weakness, so by virtue of minimising them here, the overall strength and structural integrity of this pontoon is optimised.

As with design five, the positioning of a fixed towpoint may prove to be difficult on account of the large gap between the two pontoons. As the entire weight of the tower and support structure combined will inevitably be supported by just the four vertical pistons, these will have to be incredibly strong so as to support such great loads.

They will also require some form of triangulated support structure, like slanted struts, ties or triangular webs. Otherwise, they will simply stand as basic, unsupported columns. Being so tall, yet having such a narrow base, this will make them vulnerable to collapsing, bending or toppling.

Engineering Education Scheme: The Report | Evaluation of Initial Design Ideas

CHOSEN DESIGN FOR FLOATATION DEVICE

PROCEDURE DIAGRAM FOR CONVEYANCE OF TOWER Source: Primary Image

Created: 14th December 2011

After much deliberation, our final decision was that the sixth design idea transpired as the strongest competitor, and indeed the one with the greatest prospects for functional effectiveness and success. The design works such that the tower may be built in a dry dock, and that dock is then flooded upon completion of the tower so as to float it, in readiness for being moved out to the required location. Once the water has lifted the tower off the ground to a satisfactory level, and the water level inside the dock is equivocal to that of the sea on the far side of the dock-gates, they are opened, and the tower’s journey begins. This launch procedure would have to take place in the mid- to late afternoon, because this is high tide on the North Sea, and this is essential for ensuring that there is adequate depth in order for the tower to leave the dock without scraping on the sea floor.

The pulling power comes, in the main, from a leading ocean-going tug, whose purpose is rudimentarily to tow the tower out of the dock. The actual tow-line arrangement, in terms of number of cables and their optimum fixing positions, is to be ascertained during the testing process. Engineering Education Scheme: The Report | Chosen Design For Floatation Device

In the meantime, two harbour tugs (one on either side) are there to manoeuvre the tower on a finer level, steering, pushing or pulling it here and there as required, so as to control both its direction and its position relative to the ocean-going tug in front. This is an essential part of the process, because the ocean-going tug in front will simply not be capable of preventing the tower from drifting from side to side as it trundles along behind it, and the harbour tugs are therefore play a crucial part in keeping the tower on course and preventing unwanted strains on the tow-ropes and the manifestation of health and safety risks to the personnel involved.

In all three of the tugs, the cables must feature a quick release system, in which the cables can quickly and instantly be released in the event of the tower falling over. By disconnecting the tugs from the structure in this circumstance, the safety of the crew can be maximised. Otherwise, the tower would pull on the tow-lines and hence pull the tugs over if it were to fall completely, hence putting the crew at risk. ORTHOGRAPHIC VIEWS OF DESIGN #6 Source: Primary Sketch

Created: November 29th 2012

Once the tower reaches its location, it is then released from the floatation jacket, and the water inlet valves are opened in that same instance, such that the tower may begin to flood and consequently sink under the weight of the water it is taking on [this is all depicted in the previous diagram]. The tower will be sunk in waters of depth 45 m, such that 5 metres’ worth of tower protrudes above the surface, with which to build the wind turbine.

In regards to stabilising the tower whilst being moved, design six was selected as being the most effective design choice, on account largely of its simplicity and relative ease of construction. Nonetheless, not only is it a very simplistic design, but it is also the one that conformed most closely to the Specification, and it is for this reason also that design six was selected. As per the requirements laid down in the Specification, the device provides the structure with an all-round stability, making use of the Buoyant Forces produced by intermittent submersions of the floatation pontoons during tilt of the tower. It is designed to resist the tilt of the tower gently, but with a firm, underlying control, and provides effective shock absorbency of the tower’s more sudden movements, via the piston arrangement that suspends the floats beneath the framework. It also makes provision for damping of these movements, through the very same system just mentioned, such that the tower can be brought to a halt as quickly as possible. This comes from the effect of pressurising the gas inside the piston by compressing its volume. Engineering Education Scheme: The Report | Chosen Design For Floatation Device

Therefore, this design was considered to be one of the very successful options for selection. To add to this, the single, out-of-water point of attachment, with which the pontoon support structure is fitted onto the tower, will help in making the process of both attaching it, and subsequently deploying it, very easy indeed, unlike design five, which would require an entire sub-aqua team just to access the detachment point. The structure can simply be set up adjacent to the tower and clamped on, and once out at sea, the tower can then simply be dropped out from inside, meaning these are also key Specification points that this design is successful in meeting. Again, the actual height at which this structure should be fitted is to be determined during the testing process. That said, as a provisional requirement, it should be mounted such that that tower’s Centre of Mass is as close to the pivot point on the surface of the water as possible, so as to minimise the Turning Moments produced by the tower's weight during a tilt. Another aspect in which design six has the upper hand over design five is that it does not require any alterations to the existing tower (another Specification point that has been successfully adhered to by this design). Moreover, unlike the first four designs, this one in particular utilises directional, hydro-dynamically-streamlined pontoons in order to ensure ease of directional control and a smooth, efficient glide through the water. By reducing the cross sectional area of the pontoons that is exposed to the flow of water, the Drag Co-efficient, wake thickness and overall Drag Forces exerted onto them may be minimised. This, as said, helps too facilitate smooth and easy movement through the water. More detailed discussion of this design may be found in the table seen previously.

That said, the strengths and performance characteristics that we were able to discuss at this stage were of course hypothetical, as the design was then only based upon the drawings we had. Therefore, testing was to form part of the next crucial stage so as to obtain an insight into how effective this design actually was in the flesh.

Engineering Education Scheme: The Report | Chosen Design For Floatation Device

EXPLODED ISOMETRIC & ORTHOGRAPHIC DESIGNS

Engineering Education Scheme: The Report | Exploded Isometric & Orthographic Designs

MATHEMATICS BEHIND THE DESIGN Introductory Theories: Possessing a rudimentary diagram that depicts a particular concept, or even a more elaborate one for that matter, is a far cry from being able to appreciate exactly how that design is likely to perform. A bit of ‘number-crunching’ is therefore an essential leg of the journey towards being able to accomplish this.

The fundamental principle behind the floatation of this tower is that of the Buoyant Force, which states that the force of upthrust (the Buoyant Force) in a particular submersion is equal to the total weight of all the water that the tower displaces in that submersion. 7

Moreover, in order for the tower to stand any chance of floating, it must produce a Buoyant Force whose magnitude is equal to its own weight. In this circumstance, the tower’s weight will continue to act downwards, but the equal-magnitude Buoyant Force acting upwards in the opposite direction will effectively cancel it out (and vice versa), hence establishing an equilibrium of balanced forces, in which the tower will consequently stay afloat.

BUOYANT FORCE DIAGRAM Source: askphysics.com

Therefore, by combining this with the theory of Retrieved: April 7th 2012 Buoyant Forces, it can be deduced that the tower must displace a quantity of water with such a volume that the weight of that water collectively is equal to the weight of the tower. Step 1

This leads us to the first step of this process: calculating the weight of the tower. This was an inevitably arduous process, and one that involved breaking the structure down into separate, individual sections, and subsequently calculating the mass of each one in turn, with regards to their volumes and respective densities. Particular care had to be taken in view of the fact that the bottom two sections have a different density (2500 kg.m-3) to the rest of the tower (1800 kg.m-3). Incidentally, this did transpire as quite a major source of error in our first attempt at working this out, which we resolved in the only way we could: starting again! The cone-shaped section of the tower proved to be a particular mathematical challenge, which we tackled by way of treating the situation much as if we were looking to calculate the volume of a torus. In doing this, we were successful in taking a seemingly complex and somewhat daunting calculation, and converting it into something more familiar and therefore something we felt more comfortable in addressing, The only difference was of course that, Engineering Education Scheme: The Report | Mathematics Behind the Design

instead of the cross section being circular, it was more of a trapezium, as this is the shape obtained when a cross-section is taken through the wall of the cone at one side. Eventually, we arrived at an answer: the total mass of the tower is equal to 3,814,688.4 kg, giving a total weight of 37,422,093.2 N (found by multiplying this mass by the Earth’s surface Gravitational Field Strength, 9.81 N.kg-1). 8

From our previous discussion, it is possible to deduce that this is in actual fact the weight of the water that the tower must be capable of displacing during a particular submersion, if it is to stay afloat. 3,814,688.4 kg of water must therefore be displaced, and with a density of 1000 kg.m-3, this equates to 3,814.7 m3.

By comparing this to the total volume of the tower, it is possible to infer what proportion of the tower’s complete body must be immersed in order to displace this much water. Eventually, this works out such that the very bottom edge of the tower’s base sits at 7.2 m below the surface of the water, assuming that the tower floats in an upright position as it would on dry land.

Incidentally, the tower will in fact pivot about the point at which its vertical centre line intersects the surface of the water. This will therefore be 7.2 m above the base of the tower. Step 2

So, we know now that the tower has the ability to float, but in the grand scheme of things, does this really tell us very much? Well, no, not really. For example, being able to float is all well and good, but what use would this be if the tower kept flipping up-side down? The assumption just mentioned is therefore an extremely important one, but what would be more use to us is obtaining a mathematical feel for the tower’s stability. One way in which this may be done is to pin point the tower’s Centre of Mass. We did this using a Plumb-Line Method and a simple 2-Dimensional Model, which we fabricated carefully in the engineering workshop at the University of Kent, Canterbury, whilst on the Residential Visit.

The major difficulty we had, which we stumbled across almost immediately, was that, whilst the real tower has varying densities and mass distributions throughout different sections of its structure, those of the 2-D Model were consistent throughout, and so could not hope to provide an accurate representation. This we resolved by simply looking at the whole mass of the tower, in more holistic terms. We essentially split the tower into two separate halves (the divide being at the top of the coned section), and hence observed that the masses of the two halves (top and bottom), were bound by the ratio 1:8.74 respectively. This we endeavoured to emulate by cladding the bottom half of our 2-D Model with MDF blocks, until it too was as close as possible to being 8.74 times as massive as the top half.

The major hindrances we experienced at this point were a combination of time constraints, and the somewhat limited availability of MDF sheets of an appropriate thickness. Nevertheless, this task was completed fairly successfully, all things considered, and it actually turned out that the bottom half was in fact around 8.8 times heavier than the top half. Engineering Education Scheme: The Report | Mathematics Behind the Design

Once the model was finally completed, testing could then begin. The following method was employed:

• Drill a small hole (no more than 2mm in diameter) in each of the four corners of the model

• Suspend the model from one of these corners by passing a pin, rod or nail through the hole and clamping it firmly to the desk using a G-Clamp (NB: the model MUST not be obstructed from swinging freely) • Suspend also from the pin, a Plumb-Line (in this test, we used a heavy M12 Stainless Steel Bolt on a string)

• Allow both to come to rest. At this point, the Centres of Mass of both objects will be directly beneath the point of pivot, so it stands to reason that any straight lines that connect the point of pivot and the Centre of Mass will be vertical. As such, if we could just copy such lines onto our model, we would effectively produce a linear locus: a straight line, somewhere along which the Centre of Mass must lie. This we achieved by ‘tracing’ the line made by the string of the Plumb-Line, knowing that this too hung vertically, onto the model.

• Repeating the experiment for the other corners of the model produces four separate lines, along all of which the Centre of Mass has to lie. Of course, the only place where a single point can be on all four of the lines at once is where these lines cross, and indeed, it is here that the Centre of Mass is found.

PLUMB-LINE EXPERIMENT

Source: Primary Photograph Taken: December 13th 2011

When we completed the experiment, we discovered that the lines did not so much cross each other all at the same point, as they did cross in pairs, at four different places. This uncertainty was alleviated by way of placing the Centre of Mass in a relatively central position inside the small area enclosed by these four lines.

This resulted in finding the Centre of Mass of the tower at a height of 10.6 m above the base. As predicted, this is quite low down within the tower’s structure: we were anticipating this, because here is where the vast majority of the tower’s mass is concentrated

Engineering Education Scheme: The Report | Mathematics Behind the Design

Step 3 So, having established the position of the Centre of Mass, and that of the pivot point, the resulting gap that lies between the two (a vertical height of 3.4 m) can now allow us to build up a picture of the tower’s stability. The implication of this height difference is that the tower structure, when floating on its own, is Inherently Unstable. This means that the tower has no capability of righting itself if it tilts over, and any slight tilt to one side will therefore mean that the tower is doomed to fall over completely. This is because of the effect of Turning Moments. The weight of the tower is a force, which acts vertically and originates from the tower’s Centre of Mass. Moreover, the tower’s motion will always pivot more or less about the central point fixed on the surface of the water, 7.2 m vertically above the base of the tower. As soon as the tower is tilted to one side, by the action of a wave, say, the Centre of Mass, and indeed the line of action of the Weight Force acting from it, are instantly displaced from their central position above the pivot point, and a horizontal displacement is therefore immediately established between them. This enables the weight force to produce a Turning Moment, which again acts about the central pivot point on the surface of the water and works to topple the tower completely. This Moment can be expressed using the following formula: 𝜏𝜏 = 𝐹𝐹 𝑑𝑑

𝑑𝑑 = 𝑟𝑟 𝑠𝑠𝑠𝑠𝑠𝑠(𝜃𝜃°)

𝜏𝜏 = 𝐹𝐹 𝑟𝑟 𝑠𝑠𝑠𝑠𝑠𝑠(𝜃𝜃°) Where:

𝜏𝜏

= Torque due to Weight Force (N.m)

𝑟𝑟

= Straight line distance between the two red dots (Centre of Mass and Pivot Point, 3.4 m)

𝐹𝐹 𝑑𝑑 𝜃𝜃

= Weight Force (37,422,093.2 N)

= Perpendicular distance between line of action of weight force and pivot point (m) = Angle of tilt (°)

Engineering Education Scheme: The Report | Mathematics Behind the Design

As the tower leans further and further, the angle is increased, and the Centre of Mass is hence displaced further from the central position. The consequence of this is such that the magnitude of the Turning Moment produced by the Weight Force is increased, meaning the effect is precipitous, because it becomes more and more severe as the tower leans further. Once tilted, the effect is therefore completely irreversible, unless some immense force is applied to counter it. This highlights the importance of the floatation pontoons that have been designed so far. In view of this information, they have become an extremely important, even vital piece of equipment, crucial for the safe and effective conveyance of the tower structure through the water and for preventing it from toppling over completely. Without it, the tower will be completely unstable, and as such, completely unable to support itself in choppy waters. The pontoons used in such a support structure must function in such a way that they can directly and fully oppose the Turning Moments produced by the weight of the tower. As the tower leans over to one side, its weight is obviously exerting an incredibly strong Turning Moment downwards, in the direction of the water. In doing so, it presses the floatation pontoon on that side down into the water, hence culminating in a Buoyant Force that acts upwards, in response to the submersion of the pontoon. In order to stop the tower from leaning further, and even push it back up again, that Buoyant Force would have to be of such a magnitude, and applied at such a distance from the pivotal point, that the Turning Moment it leads to is equal to, or even greater than, that produced by the tower’s weight initially.

Research conducted previously had disclosed that the average wave height on the North Sea is around 2.5 metres. A combination of sequential trigonometric processes and meticulous visual analysis of the tower structure enabled us to determine the sorts of torque loadings that Engineering Education Scheme: The Report | Mathematics Behind the Design

the tower would be likely to experience as a result of its instability in a lean, in a normal North Sea environment. Assuming that a single wave of 2.5 metres in height acts on the very outer edge of the tower’s base, pushing this part of the structure up by that height, we came to the conclusion that the tower structure would tilt accordingly about its pivot, through an angle of 7.8°. This would consequently displace the Centre of Mass by 0.46 m from the centre, instigating a Turning Moment of 17245785.2 N.m. If the pontoon is to be able to hold the tower there, and prevent it from leaning over any further, it must therefore also exert a Turning Moment of this magnitude, but back in the opposite direction so as to counteract the lean of the tower. This Turning Moment is of course provided by the Buoyant Force that acts upwards in response to the submersion of the pontoon. With a slanted radius between the centre of the tower and the Centre of Pressure at which this Buoyant Force is exerted on the pontoon, of 21 m, and an angle of tilt again equal to 7.8° (leading to a perpendicular distance of 20.8 m), this would require a Buoyant Force of 828897.0 N. In addition to this, the tower will of course have to withstand buffeting from North Sea winds as well. Fundamentally, forces are exerted onto an object by the passage of a high-speed airflow (like wind) because of the Drag that that object makes with the air passing over it. So, assuming that:

• The air has a Drag Co-Efficient (CD) of 0.9 • The air has a density (ρ) of 1.225 kg.m-3 at 15°C and 1 ATM (NASA Lewis Research Centre; April 6th 2012) • As disclosed by our research, average North Sea wind speed (v) falls around the value of 30 mph, equalling 13.4 m.s-1 • The airflow exerts its associated drag force onto the top section of the tower (assuming that below this level, the wind will be too turbulent to exert any such forces), giving a crosssectional area exposed to the airflow (A) of 240 m3 (height 30 m, diameter 8 m) • Using the formula D = ½CD ρv2A The total force exerted by the wind in these conditions is equal to 23,785.3 N. Again making an assumption, this time that the force is exerted and distributed evenly across the entirety of this area, there will be a Centre of Pressure (located in the Geometric Centre of the area), at which point all the drag forces appear to act together. Due to the dimensions of the tower, and its position in the water, this Centre of Pressure works out at being 27.8 m directly above the tower’s pivotal point on the surface of the water, hence producing a Turning Moment of 661,232.6 N.m.

As before, this Moment will have the undesirable effect of toppling the tower, and once it does, the precipitous effect will again kick in.

Engineering Education Scheme: The Report | Mathematics Behind the Design

FLOODING & SINKING • The intake of the water during the flooding phase is powered by the pressure exerted by the weight of all the water directly above the valve. Therefore, as the tower sinks deeper, this pressure will increase, due simply to there being an increasing weight of water above it. The rate of fill will therefore increase as well.

• The inlet valves will have to be placed below the surface of the water, so as to make the best possible use of this pressure. They must, however, not be too deep, as that would make it difficult to operate them whilst out at sea.

• Moreover, as the pressure forces acting on the inlet valve do increase, both the speed of the water and its Dynamic Pressure (pressure exerted by the water in its direction of travel) will do the same. The flow of water will therefore exert substantial frictional forces on the concrete material surrounding the edge of the valve as it passes through, making it susceptible to wear. As such, the need to line the inside of the valves with a hard, wear-resistant material, such as Tungsten-Carbide becomes apparent, in order to mitigate this.

• However, whilst all this is going on, the Static Pressure of the water (the pressure exerted outwards against the insides of the valve) will in fact decrease. This is because, in moving faster through the valve, each individual water molecule effectively spends less time in contact with its inside faces, and so less pressure overall is exerted in this direction. Intrinsically, this has the effect of leading to the implosion of any bubbles that may exist in the water, in turn leading to a process called Cavitation, whereby material is gradually ripped away from the sides of the valve. Again, lining is therefore necessary so as to prevent this.

Engineering Education Scheme: The Report | Flooding & Sinking

POINTS FOR CONSIDERATION

• In all designs, in which a fundamental aspect is formed of mechanical pistons, Gas Pressure Laws are a core principle. In any of the example designs featured, the compression of a piston is utilised so as to hinder the initial force implementing that compression, and hence bring it to a stop, before finally returning the system to its original state. • In the context of these designs, the tilting motion of the tower will exert a considerable downward force, thereby compressing the pistons on the side to which the tower is leaning. This compression leads to a reduction in the volume of the gas inside the piston, in turn leading to an increase in the frequency with which the gas molecules collide with the walls of the cylinder. • In addition, the exertion of the forces causing the compression will of course transfer a quantity of Mechanical Energy into the gas, raising its Internal Energy and in turn, therefore, its temperature. • This is because, as the gas absorbs this Mechanical Energy, its molecules each up-take a certain fraction of it, and so their average individual Kinetic Energy will increase (remembering that gas molecules are forever in a state of random motion, while ever they possess Kinetic Energy). • The combined effect of the increased temperature (Pressure Law) and the decreased volume (Boyle’s Law) will therefore lead to a drastic increase in pressure. • This is an Adiabatic Change, in which all of the gas’ gain in Internal Energy comes from the Mechanical Work originally done upon it, and no additional thermal energy is supplied or removed. • To add to this, bearing in mind that the gas stored inside the piston will not behave entirely like an Ideal Gas, the compression of its volume will eventually begin to strain the elastic intermolecular forces of the gas, and the Potential Energy of these forces will therefore increase as well. • This will add to the pressure of the gas as it pushes back out from the inside. Referring back to the context of these designs, this will have the effect of pushing back against the leaning of the tower, therefore beginning to convey it back into its original position. PISTON COMPRESSION

Source: wikipremed.com Retrieved: April 9th 2012

Engineering Education Scheme: The Report | Points for Consideration

• Indeed, the pontoon on that same side will inevitably undergo some degree of submersion as well, meaning a greater volume of water will have been displaced in the process. The increased Buoyant Force that consequently arises from this will therefore add to the aforementioned effect of righting the tower back up. Incidentally, attention must be drawn to one particular point raised in relation to the Internal Energy and Temperature:

• As a certain force acts to compress the gas inside the piston cylinder, it will do work upon that gas, and consequently cause it to absorb a certain quantity of Mechanical Energy equal to: Where:

𝑊𝑊 = 𝑃𝑃 ∆𝑉𝑉

𝑊𝑊 = Mechanical Energy transferred into the system by external forces (Joules, J) 𝑃𝑃 = Pressure exerted (Pascals, Pa) ∆𝑉𝑉 = Resulting Volume Change due to compression (m3)

As aforementioned, this energy will lead to an increase in the gas’ temperature, due to the increase in average Kinetic Energy of the molecules, as follows: 𝑊𝑊 = 𝑚𝑚 𝑐𝑐 ∆𝑇𝑇

Where:

Therefore: ∆𝑇𝑇 = 𝑊𝑊 / (𝑚𝑚 𝑐𝑐) ∆𝑉𝑉 (𝑚𝑚 𝑐𝑐) = 𝑃𝑃 ∆𝑇𝑇

𝑊𝑊 = Total energy absorbed by the gas, equalling the Mechanical Energy (P ∆V) in the previous formula (J) 𝑚𝑚 = Mass of the gas inside the piston cylinder (kg) 𝑐𝑐 = Specific Heat Capacity of the gas (J.kg-1.K-1) ∆𝑇𝑇 = Arising Temperature rise (K) In view of this, it therefore becomes essential that the pistons are in some way kept cool, so as to prevent structural damage to these pistons in the form of thermal expansion or even hardening.

• One way in which this may be achieved is to use a heat-dissipating lubricant, which would of course simultaneously help to reduce friction as well, hence reducing the effect of over heating further. This does, however, lead us directly into the second detriment that is attributable to the use of pistons. Any lubricants used will be vulnerable to getting washed away or chemically-corroded by the salt water.

• Moreover, the seals on these pistons may also leak, and water droplets or vapour contaminating the gas inside the piston will of course impinge upon its performance, and subsequently damage the piston itself by causing corrosion, hence rendering the device useless for later applications. Engineering Education Scheme: The Report | Points for Consideration

Tensile Steel Cables: • Having a very high Young’s Modulus (Stiffness Co-Efficient in Tension and Compression in an elastic material) of 206GPa 9, steel is far from ductile: though not necessarily brittle, it is certainly extremely stiff. Effectively, Young’s Modulus is the ratio, or constant of proportionality, between a material’s Strain, and the Stress causing it (which, due to Hooke’s Law, are directly proportional to one another). As such, with this ratio being so high, it is clear that a large degree of Stress will result in a small degree of Strain. That is, even very large forces will only stretch the steel by very small amounts. • The Young’s Modulus can be calculated using: Where:

𝐸𝐸 = 𝜎𝜎 / 𝜉𝜉

𝐸𝐸 = Young’s Modulus (Pa) 𝜎𝜎 = Stress (Applied Force per unit of cross sectional area perpendicular to the axis in the direction of the Applied Force, Pa) 𝜉𝜉 = Strain (Change in length due per unit of original length: deformation due to applied stress, along the axis in the direction of the Applied Force) 10

• As such, when stressed by the relative movement between tower and base, the cables will not afford any sort of give, and instead will come to an abrupt stop. Apart from failing an essential Specification point, on account of not slowing down the tower’s movements gradually, this will produce a sudden, sharp and hence intense impact force known as ‘Snatch’, the consequence of which is the frightening likelihood of the cable snapping. • More to the point, in having such a high Modulus of Resilience (the quantity of Strain Energy absorbed by the steel per unit volume, for a given Stress Force acting upon it), a substantial quantity of energy will be absorbed by the steel cable before it finally snaps. This means that, when it does eventually go, all that energy is released, and the event is therefore highly dangerous. It is usually characterised by a high-speed recoil of the cable, capable of inflicting serious, even fatal injury to anyone in the way.

EFFECTS OF A CABLE-SNAP Source: cache.gizmodo.com

• Furthermore, the weight of the steel cable will Retrieved: April 4th 2012 unfortunately make it susceptible to sinking; in turn making recovery of the cable difficult once the tower has been sunk.

Engineering Education Scheme: The Report | Points for Consideration

TESTING

All our work and time spent on the project so far was in aim of testing this scale model in similar conditions that the construction would face in the North Sea. However, before we could begin this level of experiment, we had to first test our completed and sealed model on a smaller scale to see whether it would float unaided. There was much dispute among the team’s hypothesis as to the result of this experiment, and after all the bets were taken, we set to work in testing the buoyancy of the model in our very ‘elegantly sourced’ rubbish bin. The aim of this test was to simply find the level at which the base would float and so allow us to know where and how we would have to construct the flotation device which would improve the stability of the base, and would be needed irrespective of the buoyancy. Therefore, this fairly simple test was a major part of the rest of our testing, and fortunately for us, the next parts of our project were made simpler when we discovered that the model, and thus the scaled up construction, would float at a reasonable level. Quite conveniently we found that the model alone floats so that the water level is 16cm above the base, which is 8m on the real construction, and lies right on a seal, meaning that positioning the floatation device was relatively easier than previously thought. However, the model was unstable and would always topple over unless held upright. This proved the need for a stabilising device as we had already anticipated.

This meant our plans for a floatation device could then be implemented and suited to our model to enable stability in the water. The process of construction of this floatation device meant that we would have to create and estimate the size of the floats before we could work out their effectiveness. A decision was made and the size and material of these floats (Styrofoam) were decided and therefore remained through to the end of the project. This meant we proceeded into the testing phase with a limited number of variables. • •

The height of the floatation device The mass (of water) that the model held so to influence the position that it sat in the water.

The location of the experiments we had chosen to undertake had been decided on the basis of ease of access and to some extent, similarity to the conditions that the real construction would undergo. This meant that a handily located private swimming pool became our experimental ground and site of all further testing on our completed model. Having attached a suitable length of rope to act as our tug, completed a few preliminary runs to adjust the force needed to pull the model and then set up our recording equipment in the form of both camera and video we were ready to proceed. Aiming for a valid set of results, we implemented our knowledge of the sciences to conduct a reasoned experiment where only one variable changed at a time. This meant that throughout the experiments we tested different masses of water at one height, before changing the height and then repeating said experiment. This order was very much chosen due to the accessibility of the floatation device. Changing the height of such a major component took ill-afforded time, Engineering Education Scheme: The Report | Testing

and would be a greater cause of human error than the regular change in mass. Each variable and interval was tested three times to make sure our findings were reliable. However, we cannot quantify our results for we were not testing against a known scale for stability, thus these results are only our perception of what occurred in the experiment. Although, the outcome is reliable and our preferred choice of variables we remain the same, the perception of the experiment will change for all who participate in it. So, we can qualify our results, and judge them to have met a certain criteria, in this case, stability throughout the experiment, but we cannot quantify our results and set a pattern to them, for as you will see, there are some surprising outcomes. Moreover, this means that the results you see are very limited in their response as there is little more you can perceive about the experiment than whether the model was stable or the rate at which it falls and so once again qualified data is a limiting factor to further analysis.

It must be mentioned though that through this experimental period our ideas of the model developed and we further improved our methods in positioning our ’tug’ to gain the maximum stability from constant variables. These and such other small adjustments can only be made once the model had been completed and used in experimentation for we lacked the experience with such projects to pick up on these details from the start. There are a few assumptions we have made within our results, since we measured the amount of water added at each interval in millilitres, we then converted this number into grams. Here, we assumed the water we were using was pure and did not hold any minerals or such materials so that the conversion would mean 1litre = 1kilogram. However, within a realistic situation, salt water would be used, as it is the major source for the construction, so the conversion rate would differ considerably such that 1litre could weight as much as 1.027kilograms 11, meaning a reduction in the amount of water needed to create a stable base. We also started our experimentation where the floatation device was level with the models’ buoyancy level, assuming that moving the floats beneath this would reduce stability and so would be impractical and ill use of time to test. Therefore the results that follow begin where the floatation device is clamped around the central tubing at a height of 50cm from the base (25m on the real model) so that the floats would sit at 16cm (8m) above the base, which is the level at which the model floats. Waves were simulated both by the movement of the model and by the use of a rugby ball in one corner of the pool so as to keep the wave height small in relation to the model considering Engineering Education Scheme: The Report | Testing

our previous research of such conditions, this allowed us to monitor how well the model moved through these factors and thus assess the stability of motion.

The intervals for our variables were chosen with the precision of our instruments in mind. For example, our measuring jug could only record at a minimum level of 250g so the interval was set by this. Moreover, due to our time constraints we decided to increase the height of the floats by 5cm every time, and by changing this as little as possible we reduced the error in our results. It’s also important to note for our first two tests we had out tugs first attached above the floats then below, and both achieved the same results. This arrangement later changed as mentioned further on. AT A HEIGHT OF 16CM ABOVE THE BASE Mass of Water Added (grams) Stability 0 Unstable but moves easily through waves. 250 More stable however the floats are low in the water so the waves affect the motion of the model. 500 Unstable as the floats are too low in the water and the model begins to topple. 750 Unstable and the model falls on entry into the water. 1000 Unstable and the model falls on entry into the water.

AT A HEIGHT OF 21CM ABOVE THE BASE Mass of Water Added (grams) Stability 0 Unstable and falls immediately upon entry into the water. 250 Not tested as interval was changed after seeing the previous result(s). 500 Unstable and falls immediately upon entry into the water. 1000 Unstable and falls immediately upon entry into the water. 1500 Unstable and begins to fall after a force is applied. 2000 Unstable and begins to fall after more force is applied. 2500 Stable and floats well under minimal surface conditions. Any sudden movements cause unbalancing and possible sinking. 2750 Stable but falls under small force but deals well with surface conditions. 3000 Unstable and falls under small force. Engineering Education Scheme: The Report | Testing

Changes to the Positioning of the Tug At this point we began to see the affect that the position of the tug was having on the model, so the ropes were adjusted so that two line were attached to each float, one above and one below, so that the force was distributed evenly and provided a more stable tug. AT A HEIGHT OF 21CM ABOVE THE BASE Mass of Water Added (grams) Stability 500 Not tested as previous results showed ideal mass. 1000 Unstable and falls immediately upon entry into the water. 2000 Unstable and begins to fall after more force is applied. 2500 Unstable and falls after movement. 2750 Stable and floats well at both a constant velocity and whilst still under rougher surface conditions. 3000 Unstable and falls under small force. 4000 Sinks immediately Disaster! At this point the seal on our construction broke and the model would not hold any water, thus the experiment could not continue for the model had to completely dry before being resealed. However, we believe that we have found from three separated experiments that the model is most stable with an added mass of 2750g with the floats positioned 21cm above the base. However, it would be ridiculous for us to say that this is the only solution. For we have not tested all possibilities and entertained all strands of thought about this model but for the variables we have tested, I think we can conclusively say that the model can float with a stable position.

Engineering Education Scheme: The Report | Testing

CONCLUSION The testing stage wasn’t as successful as we had hoped as we only managed to ascertain one true position of the floats and a volume of water added at which the model was stable. After the seal broke around the bottom, we couldn’t test further. However, the results that we did obtain have led us to the following conclusions in relation to our specification. Assessment of Buoyancy

The model itself is very buoyant. It floats much higher in the water than was initially expected. This has helped as we have not needed to add any means of flotation. Instead, we have had to stabilise it. However, left to its own devices, its buoyancy is ambiguous as it isn’t buoyant once it has fallen over and began to sink. If anything, the buoyancy has also caused problems as we have had to add mass, in the form of water, to help in sit lower in the water to make it more stable. The real tower will therefore fall victim to the same flaws in the design. It will sit high in the water with a strong chance of toppling over. Assessment of Capability to be Towed

Towing the unit will require incredible skill. The pontoons that we have added have helped somewhat in stabilising the unit but have not been totally effective. The pontoons added, were streamlined and so would create little drag compared to some of our previous ideas for stability. The pontoons are also very easy to steer. They would naturally follow the tow rope and so could be manoeuvred easily. We had 2 tow ropes initially but then decided to have 4, 2 on each pontoon. One of these was positioned above the water’s surface, and the other was below. This helped to stabilise the two moments created and caused equilibrium at the towing force. This made the towing process much easier. However, the pontoons didn’t prevent forward and back swaying motion and so we believe that for the real construction, the pontoons will have to be at least 25% longer. They already seem to stop sideways swaying but when the ropes are pulled with anything other than a small force, the model topples forward in the direction it is being pulled. Also for the full size base, towing would need to be completed by at least two vessels as the construction would need to be pushed and pulled into place at the site that it will be sunk. If only one boat is used, then there would be no control over pushing the model away from the boat. Assessment of Resistance to Inclement Weather

This was hard to accurately replicate for our model. For example, in a scale model situation, a small wind to humans is almost gale force winds to the model. The small natural ripples in the water were relatively large waves. We did however, use a rugby ball to simulate larger waves and to some degree, the model did remain stable. The stability would be improved considerably once the pontoons have been made larger. We would advise however, that when the real base is launched, it should not be done in bad weather conditions as this would add to the unstable nature of the tower. The pontoons are essential in minimising the risk but if the risk factor is raised, even more strain is placed on the tower. Engineering Education Scheme: The Report | Conclusion

Assessment of Self-Righting Ability Vertically this has excellent results. Even though the large base creates large disturbance in the water, the spring back buoyancy of the tower exceeds this. Thus the vessel can absorb extensive vertical movement. However, the stability issue arises here as well. The model did not return back vertically after being pushed down. It came back at an angle and so this created a turning moment which collects momentum and causes the tower to topple. This would be helped a lot by the longer pontoons as they should keep the model level whilst it is low in the water. This current instability has led us to conclude that our design has failed on this account. Assessment of Rate of Sinking

Due to the seal breaking under stress, we were unable to test this. However, the amount of water that is placed into the tower will equal the amount of water displaced from its original height in the water. If the amount of water is monitored, then you can determine the rate of sinking and predict how long it will take. However, this will depend entirely on the size of the pump, the thickness of the hose used and the weather conditions. If it is raining, then the unit will take in water in the top. This will lead to an inaccurate prediction of the timings.

Engineering Education Scheme: The Report | Conclusion

OUR PROCESS JOURN AL Gantt Chart

Points for Consideration •

•

• •

•

Initial designs finished a week in advance due to concerns over time lost in Research & Feedback. One of us began preparation for workshop in advance of plan, because time was left free whilst some were finalising research notes, and one of us made a start on design work. Manufacture of the model delayed the design of the floats by a week. The contingency time for the model manufacture was left until after completion of the floats, because this was time set aside for painting and stylising, but by that stage the floats were our priority. Contingency time was also used to work on the model while others were compiling report. The manufacture of floats was brought forward a week due to concerns over time lost in manufacturing model and the testing conducted before completion of the floats was done on the tower on its own, purely to test buoyancy without stability. This was done due to concerns over time lost in manufacturing, and concerns over having to wait until full testing could be done. Final Testing had to be delayed further to 6th April due to limited availability of pool. In the meantime, we started on the report and made final touches to the floats and model.

Engineering Education Scheme: The Report | Our Process Journal

EVALUATION The success of the project may be assessed from two perspectives: the design itself, and the actual process of getting there. Technical Evaluation of the Design: Strengths: Largely, the strengths of the design have been made clear from the outset: they were discussed in depth in the table of initial ideas, and were therefore the very attributes that led us to the selection of this design in the first place. However, the physical testing process of our representative model has of course confirmed some of these strengths, whilst negating others. To summarise, the revised appraisal is as follows: • •

• • • •

•

The structure is effective in holding the tower in the upright position It provides a degree of spring-back stability (self-righting) when the tower is tilted to the left or to the right, but is not quite as effective when tilting the tower forwards or backwards The hydro-dynamically-streamlined pontoons make towing and manoeuvring the tower a relatively easy task The framework can be both attached to and removed from the tower very quickly and easily The design makes provision for adjusting the height of the framework relative to the tower, as per requirement, depending on the conditions of the North Sea at the time of launch The structure is simplistic, and therefore quick and easy to construct, making it ideal for the production and deployment of large numbers of towers to various locations on the North Sea The testing process incidentally gave us the opportunity to devise an effective tow-point strategy, which had of course not been determined prior to this. It works such that the stability of the tower during the towing process may be maximised. The tug is attached to the tower by four individual tow-lines: one to each side of the very top part of the pontoon structure, and one to the bottom of each of the pontoons. With this arrangement, tension in the tow-lines therefore acts both above and below the pivot point on the surface of the water, hence culminating in both clockwise and anti-clockwise moments. These effectively cancel each other out, meaning the tower has the inclination to neither lean backwards, nor forwards.

DIAGRAM DEPICTING TOWING

Source: Primary Creation Created: April 7th 2012

Engineering Education Scheme: The Report | Evaluation

Weaknesses: •

Instability of the Tower:

As much as the floatation device is successful in keeping the tower upright, it is an extremely delicate system, and the slightest bit of turbulence has the potential to knock the whole thing over. This instability was most profound when acting forwards and backwards, as the tower was most prone to toppling this way (though the system was, in fairness, actually quite stable when moved from side to side, as aforementioned). In leaning back or forth like this, one end of the pontoon would be submerged, while the other would lift out of the water, and once tilted, even by a small angle, the tower would topple completely. Contrary to this, we were really hoping more for it to be able right itself automatically if tilted by a wave, rather than simply keep falling until it hit the surface. This brings our attention to the fact that the floatation device may not be as successful as it may have at first seemed: if this were the real thing, it would stand next to no chance at all of being able to handle the brutal action of the North Sea’s waves and 30 mph winds. One improvement that was put forward to this end, with the view to alleviating this shortcoming, was to lengthen the pontoons by at least 25% at each end (though this would of course require essential testing before this figure can be quoted for certain). This suggestion was made, because we knew it would help not only to increase the magnitude of the Buoyant Forces produced by the pontoons (simply because they would displace more water), but also mean forces these being exerted further away from the central pivot, hence amplifying the Turning Moment created in a double sense, and in turn maximising the effect they have of pushing the tower back into its upright position. True enough, this would be an effective solution, at least to some extent, but what would be equally as effective, albeit for different reasons, would be to provide the tower with an all-round stability, such as that provided by the circular pontoon structures featured in the first three designs. Although hydro-dynamic streamlining was a key requirement for this project, equally so is the provision of stability in all directions, but what we wish to achieve is both. Therefore, in order to evade such implications as drag, bow waves and difficulty of steering, which are intrinsic to circular pontoon designs, it may be worth developing the parallel pontoons from before to such a point where they can provide this omni-directional stability themselves. To this end, a number of pontoon shapes could be tested:

POTENTIAL PONTOON SHAPES

Source: Primary Sketch

Created: March 29th 2012 Engineering Education Scheme: The Report | Evaluation

•

Rigidity of the Unified Structure:

The tower and floatation device, collectively as a single unit, together form a very rigid structure. Therefore, the slightest movement in one part of the system will manifest in a similar movement in every other part of the structure as well. This will surely pose a significant problem, in so much as there is no provision whatsoever for keeping the tower upright in the event of the pontoon being tilted by a large wave. If we take a moment to consider a point accentuated previously, in relation to the Turning Moments produced by the tilting of the tower, this attribute will prove to be extremely problematic. Therefore, such that this implication may be resolved, one possible solution may be to fix the pontoon’s support structure with more of a loose fitting, in which the tower is held in place, but is free to swing, on a single pin joint, in any direction within the structure’s enclosure. If supported in this manner, the tower will be free to adopt an upright vertical position, even if the pontoon support structure is forced to contort into a different angle. This will help the tower to maintain its stability by keeping the Centre of Mass within as close a proximity to the central pivot point as possible, and hence reducing the magnitude of Turning Moments produced by the tower’s weight during a tilt. Having said that, this would inevitably lead to some fairly prominent complications, particularly from a structural point of view. Needless to say, there would certainly be significant difficulties transpiring in the design of a pin joint that can not only handle gargantuan sheer stresses, in excess of 37 MN, but also stand up to enormous torsional stresses at the same time, and still maintain freedom in the joint’s movement. The pin would also need to resist intense wear from high-magnitude frictional forces. •

General Solution Through Suggested Design Change:

Instead, therefore, it would certainly be an appropriate solution to build a more robust, effective articulation system into the existing parallel pontoon design we already have in place. This would be useful, because it would remain in keeping with the design features we already have in place, whilst building upon its as yet decidedly limited effectiveness, by affording it the degree of flexibility just mentioned. Moreover, by virtue of adhering to the use of parallel, hydro-dynamically-streamlined pontoons, this solution would also maintain the previous design’s directionality, minimal drag and ease of steering. One way in which this could be achieved would in fact be quite similar to the first design idea put forward, as shown. ALTERNATIVE PONTOON DESIGN Source: Primary Sketch

Created: March 28th 2012

Engineering Education Scheme: The Report | Evaluation

As can be seen from the diagram, the use of two parallel pontoons is continued, but connected at the ends (to the central tower) by four very strong, robust pneumatic pistons, with two of them to each pontoon. The system of articulation that this provides is therefore much more reliable than the minimal number of tenuous pin joints mentioned before. In addition, the compressibility of these pistons, apart from enabling the tower to uphold its vertical standing position as required, also helps to absorb the shocks and impacts of persistent wind and wave attack whilst out on the North Sea.

Alternatively, design idea 2 could well be used to much the same effect. However, the major drawback with this design is the use of the circular pontoon. Whilst this does certainly offer excellent all-round stability, perhaps in such a way that cannot really be beaten, the width of the design poses tremendous difficulties to the towing process, due to high levels of drag, considerable wake (bow waves) and difficulties in steering the thing!

DESIGN #2, FEATURING CIRCULAR PONTOON Source: Primary Sketch

Created: November 29th 2011

•

Provision for Pistons Over-Heating:

Had we included the compressible pistons that were initially put in the design work to begin with, these would have enabled the model to absorb any shocks exerted by ripples during the testing, (hence reducing the likelihood of the structure toppling over when buffeted in this way), just as they are intended to in the context of the real tower. However, the very design of these pistons was incidentally another particular point of weakness in this project. As disclosed at a previous stage, pressurisation of the gas inside these pistons will, after repeated compressions, make them extremely hot. With no designed system with which to keep them cool, this will inevitably lead to physical and structural failure of the metals used in their construction. That said, the wind and sea water would certainly contribute to the cooling effect anyway, but to aid it, the simple solution would be to conceive a basic coolant system that would help to draw excessive heat away from the piston and hence optimise their function. For example, radiating fins could be made to shroud the outside of the outer piston-sleeves. The large surface area that these would provide would help to dissipate heat quickly, but could also be complemented by coating these in a smooth, shiny and therefore highly radiant surface. In addition, if these fins were made hollow, the cavity inside could be filled with Ammonia gas, whose high Specific Heat Capacity and Thermal Conductivity would enable it to conduct excess Engineering Education Scheme: The Report | Evaluation

thermal energy down the Temperature Gradient (from the surface of the hot piston to the cold adjacent air) very quickly and efficiently. This would be a suitable alternative to lubricants, hence evading the risk of them being washed away by the sea-water. That said, it may well be that, because of intense levels of friction in the pistons, a lubricant is not something that can be avoided anyway, and so, the Ammonia-storing fins may well have to simply accompany a lubricant, rather than replace it. Evaluation of the Team & Design Procedure: Strengths: One thing we felt was done particularly well throughout the project was the delegation and sharing of tasks. This had two main benefits. Firstly, it enabled us to manage time very successfully. Tasks could be done simultaneously, and so, with more than one thing getting done at once, tasks were completed much more quickly than they would have been had each one had to wait until the completion of the previous. This was in fact complemented by the individual, personal organisation of members of the team. By filling in the GANTT Chart regularly, and taking down minutes of each meeting in a permanent record, we were able to keep a constant eye on the project’s progress, as well as foresee that which had to be completed next. One example of where this was of particular benefit to us was in the few weeks leading up to the Residential Visit in December. Forward planning of what we were aiming to get done by the end of the trip meant that we were able to get straight on with it once we arrived, and also that no time was wasted at the start in thinking about what we were going to try and achieve.

Secondly, this principle of task delegation also made extremely effective and suitable use of different people’s skills, so as to ensure that each task was completed to the best quality it possibly could. For example, editorial and presentational tasks were given to Oliver, on account of his excellent graphical skills, while the practical skills offered by Adam and Owen meant that they both had a considerable part to play in the manufacture of the test model, the outcome of which was in consequence notably successful. If, on the other hand, we had attempted to get every single person directly involved in each and every single task, the whole project would have descended into anarchy. Many tasks only require one person to do them for example, and can in fact be hindered by the intervention of others. Completing the technical drawings is a good example of this.

That said, there are, on the other hand, numerous examples of tasks that cannot be completed by one person alone, and full team participation is therefore required. Whenever this came to be the case, we displayed good team-working skills, such that the task could be completed effectively. For example, when we went about testing the tower in a swimming pool, all four of us got stuck in from the word go, and maintained thorough participation throughout, until we had finished. Whilst I was in the pool handling the model, Adam and Owen set about towing it across the surface and providing external control via the tow-lines, and Oliver went about recording the results and taking photographs. So, in summary, the team performed well throughout the course of the project, collaborating well with a common goal, to accomplish which we all shared the same strive, which undoubtedly lead us to a successful outcome. Engineering Education Scheme: The Report | Evaluation

Weaknesses: To start off with, there were a number of things that we actually overlooked in the course of the project, and could certainly have paid more attention to if we were looking to improve the outcome of our project: • • • •

Rate of fill and rate of sinking Bedding the tower down on the sea floor Clamping the pontoon structure to the tower Design of the valves

That said, we felt as a team that, by overlooking these areas in this way, we did not necessarily have a detrimental impact on that outcome. We had a direction in our project, in which we chose to focus specifically on the stability of the tower during the towing process. Rather than briefly addressing everything, we opted instead to focus more specifically on one particular aspect, and assess the design’s capabilities within this area to a greater level of detail than would otherwise be feasible.

Nonetheless, if we had tested all aspects of the brief, we could certainly have obtained a broader and therefore (arguably) more insightful understanding of the capabilities of our design. For example, it is all well and good perfecting the tower’s capability of being towed, but if it hits the sea bed with such impact that it breaks, there is little use in this. As such, it is clear that one of the team’s most rudimentary shortcomings was the quantity of crucial information that we overlooked, which potentially hindered us in the quality of our proposal and write-up. However, if we had gone down this route, and tried to assess everything we possibly could, we inevitably would have sacrificed the level of detail with which we could address each one. Working in the way we did enabled us to ensure a very thorough scrutiny of the aspect we chose to study, and hence ensure that it was designed to work in the best way it possibly could be. Surely, this is more beneficial than having lots of features that only partially work, because it reduces the need for returning to certain areas at a later stage to iron out the flaws. We therefore believe, as a team, that this was not to detriment us very much at all in the grand scheme of things, and in fact seemed to have more positive effects than it did negative ones.

On the other hand, one prominent blow we did take to the ultimate quality of our outcome was related to the accuracy with which the physical aspects of the project (that is, construction and testing of the model) were actually realised. Whilst on the Residential Workshop, a decidedly limited availability of material resources had the unfortunate consequence that not every part of the model could be kept to the correct, required scale. For example, in being made on a 1:100 scale, the top part of the tower ought to have had a diameter of 80 mm, but in reality turned out to be over 100 mm, simply because we couldn’t find any 80 mm PVC pipe! The obvious effect of this was to have a detrimental impact on the accuracy with which the model emulated the weight distribution of the real thing. This we endeavoured to overcome, through use of the weight ratio seen previously, which mandated that the bottom half of the tower was to be 8.74 times the weight of the top half. In knowing that the linear scale factor of the model was ideally 1:100, we were able to determine that the volume scale factor was 1:1000000 (the Engineering Education Scheme: The Report | Evaluation

cube of the linear scale factor). As the mass, and in turn the weight, are both directly proportional to the volume, it was also possible to ascertain that the mass and weight scale factors were also 1:1000000, meaning that the model ought to be 1000000 times lighter than the model. This of course also applies individually to the two separate halves, and so by using the weight ratio and the weight scale factor in tandem, we used mass loadings of steel and aluminium to ensure that the accuracy of the weight distribution was restored. That said, a limited availability of resources once again made it extremely difficult to ensure that that was done accurately as well; after all, imagine trying to machine a block of steel to exactly 274.379…… g!

But our troubles of inaccuracy did not stop there. In being so much more voluminous than it should have been, the tower also had the problem of displacing too much water for a given submersion, when trying to represent that of the real thing. As such, it could be argued that the buoyancy of the model was too great, but again, the inaccurate weight distribution from before would make it hard to say for sure. As before, therefore, a simple matter of paying even more attention to details during the construction process would be effective in resolving this issue. Moreover, the actual process of testing could itself have been more accurate. For one, although we took repeats of the tests, time constraints limited this to less than we would have liked. This undoubtedly impinged on the range and reliability of the results attained, because the consequently limited sample range would have hindered our ability to spot continued trends, variations within these trends, or even identify anomalous results.

To add to this, our selection of numerical, quantifiable, or even comparable data, with which we could have drawn graphs or charts, was limited. Rather, we made visual observations of the tower’s behaviour in the water and passed qualified comments in response, exposing us to such issues as subjectivity and ambiguity in the data. The obvious effect that this would have inflicted is to impede us from having been able to make clear comparisons between different floatation and towing methods, as to which was the most effective. This also made it even more difficult for us to spot anomalies, or even take averages of repeated tests. As such, it is hard for us to be certain as to whether or not the decision we have made is truly the best: in essence, our results are incomplete, and potentially less accurate than would have been preferred. This was, of course, only exacerbated by the lack of precision in the equipment we used. For example, we had no way of determining: the angle to which the tower could be tilted before it toppled, the speed at which the tower could be feasibly towed in order for it to remain stable, or the time taken for the tower to fall from upright to horizontal. Furthermore, the precision of the ruler we used to measure the height of the floats and the submersion depth of the tower, and the jug used to determine the volume of water present inside the tower, also had a limited degree of precision.

It is also plausible to say that the validity of our experiments was hindered too, simply because we often changed more than one variable (including float-height, position of the tow-point and mass of the water inside the tower) at a time, based on what we had observed in previous tests, rather than testing the tower in all possible combinations these three variables. The consequence of this is that there are potentially very effective arrangements or solutions that we overlooked. For example, it could well be that, by positioning the floats right at the very top of the tower, with the tower itself filled with a much larger mass of water than previously tested Engineering Education Scheme: The Report | Evaluation

so as to submerge it very deeply, the system could have operated much more effectively. But then again, who knows? From this, it is therefore clear that essential improvements could, and in fact should, be made to the physical construction and testing aspects of the project by any or all of the following: •

• • • •

Fabricating a more accurate model, by sourcing materials that are more appropriate and suitable to our specific design requirements. This would help make both the tower’s buoyancy and its weight distribution more accurate, and also easier to keep it that way. Carry out a broader sample range of tests, with more repeats of each test so as to improve reliability and accuracy Plan the tests so as to obtain numerical, quantifiable data with which to enable clear comparisons, identification of anomalies, drawing of graphs and calculating of averages Enforce better control of appropriate variables in order to improve validity Employ a broader range of more sensitive equipment, hence improving precision, but also enabling testing of a greater range of trends and correlations.

Lastly, we did actually suffer quite a significant drawback when it came to completing all the tests we wanted, the effect of which was to hinder us from sinking the tower in a controlled manner. As such, we were unable to test the rate of fill or the rate of sinking for the tower. The actual problem was that the silicone acetate seal that lined the base of the model broke! This, we suspect, resulted from a combination of the weight of the water stored inside the tower at the time, and the stresses exerted whilst attempting to remove the framework from it, and consequently led to an uncontrollable leak of water from inside. In view of the time constraints, and the presence of other, more pressing priorities, such as completing the write-up, we decided as a team not to try and mend it so that we might have continued testing. By this point we felt we had just enough data from which to be drawing reasoned conclusions, so getting any more was not entirely necessary, although desirable. Summary:

To conclude, we feel as a team that we have been predominantly successful in our approach to the project as a whole, and certainly displayed a good level of teamwork when it came to getting things done. Although we did not conceive a design solution that was 100% successful at performing its intended role, we believe that our scientific methods, and approach to designing, predicting and testing outcomes was appropriate, and certainly helped bring our attention to the reality of that which we were intending to design (that is, the fact that it didn’t work!).

The four of us have certainly enjoyed partaking in the Engineering Education Scheme, and the principles it has taught us with regards to the world of engineering will certainly remain with us for years to come.

The success of the project may be assessed from two perspectives: the design itself, and the actual process of getting there.

Engineering Education Scheme: The Report | Evaluation

BIBLIOGRAPHY

NB: Please note that all images here, unless cited are primary and taken by one of our team throughout the process. All secondary sources used throughout the project have been cited appropriately. 1 2 3 4 5 6 7 8 9

Holderness Coast: http://databases.eucc-d.de/files/000164_EUROSION_Holderness_coast.pdf [Oct. 2011] Maritime Journal: www.maritimejournal.com [Oct. 2011]

Engineering Toolbox: http://www.engineeringtoolbox.com/material-properties-t_24.html [Oct. 2011] Specific to Laing O’Rourke [Oct. 2011]

Department of Physics: http://www.phy.ntnu.edu.tw [Apr. 2012] Physics Study: http://www.studyphhysics.ca [Apr. 2012] www.wikipedia.org [Oct. 2011]

10 11

Sim Science: http://simscience.org [Oct. 2011]

Mass of Sea Water: www.catsic.ucsc.edu/kudela/OS101/LectureNotes_07/OS101_012407/OS101_012407_notes.p df [Apr. 2012]

Engineering Education Scheme: The Report | Bibliography

NEES - Offshore Wind Turbines

Articles inside

Evaluation

Our Process Journal

Conclusion

Testing

Points for Consideration (Includes Further Intense Maths & Physics

Flooding & Sinking

Mathematics Behind the Design

Chosen Design For Floatation Device

Evaluation of Initial Design Ideas

The Designs

Towing & Stabilisation

Residential Trip to Canterbury

Launch Strategies & Transport

Materials’ Properties

Research & Development

Our Planning

Initial Specification

The Potential Solution

Meeting Our Engineer

Our Visit to BAE Systems

Our Team

The Possible Projects Available

Engineering Education Scheme (Background