DIGITAL DESIGN + FABRICATION SM1, 2017 M4 JOURNAL
Zhiyin Wang
736938 Matthew Greenwood Seminar 4
0.0 Introduction 1.0 Ideation 1.1 Object 1.2 Object + System Analysis 1.3 Volume 1.4 Sketch design proposal 1.5 Reflection 2.0 Design 2.1 Personal Space Analysis 2.2 Design Development Intro 2.3 Second Skin Design Proposal V1 2.4 Precedent Research 2.5 Design Development V1 2.6 Design Development V2 2.7 Prototype V1 + Testing Effects 2.8 Reflection 3.0 Fabrication 3.1 Fabrication intro 3.2 Design Development 3.3 Fabrication of prototype 3.4 Final Prototype development + optimisation 3.5 Final Digital model 3.6 Fabrication Sequence 3.7 Assembly drawing 3.8 Completed 2nd Skin 3.9 Reflection 4.0 Reflection 4.1 Final Second Skin optimisation 4.2 Final Digital model 4.3 Fabrication Sequence 4.4 Week 10 Show 4.5 Reflection 5.0 Appendix 5.1 Credit 5.2 Bibliography
0.0 INTRODUCTION In this subject, there are 3 systems: skin and bone, panel and folding, section and profiling. The system I choose to focus on is panel and folding. Sudent are requested to create the second skin using digital method. To achieve this goal, we fiestly need to decide the personal space of aimed people. Then we need to try to explore, analyse, design and fabricate in 4 modules. The second skin need to have volume and accommodate with the surface of body. For the design, function is the key factor, which means structure and form both should follow function. To achieve these factors, digital method is the main method in the whole process. This journal will document the process of my work before we get our final physical model.
1.0 IDEATION 1.1 Object 1.2 Object + System Analysis 1.3 Volume 1.4 Sketch design proposal 1.5 Reflection In Modlue 1, I explored “panel and folding � system and try to extract design ideas from the object I choose. Through a series of observation, analysis and measurement on the expanding file, the design process of this system has been accurately experienced. Based on analysis and digital model making, a sketch model has been made as the start and reconfiguration for material in this system, acting as a very conceptual idea for the first series of sletch designs.
1.1 Object
u EXPANDING FILE My choosen object is an expanding file. Because it can not stay open without holding, Scanning seems to be not a good way to draw it. Therefore, I just took different pictures of it using one hand to hold its shape while the other hand to take photos. When I did the drawings, I put the expanding file on the paper and used pencil to follow its edge. I measured its size and recorded numbers when I was drawing. After scaned, I used InDesign to m a rk its dimension.
1.1 Object
30mm
260mm
SECTION / SCALE 1:2
30mm
ELEVATION / SCALE 1:2
260mm
PLAN / SCALE 1:2
140mm
140mm
u Measured Drawings
BEFORE OPEN 20
40
60
80
100
1.1 Object
145mm
220mm
90mm
u Measured Drawings
145mm
260mm
PLAN / SCALE 1:4
ELEVATION / SCALE 1:4
The expanding file was measured by two steps. Firstly, I put the expanding file on the paper and draw carefully along its edge to get a shape. Then I used a ruler to remaesure the size of the expanding file to avoid errors which maight be caused by hand darwing.
AFTER OPEN 40
80
120
160
200
1.2 Object + System Analysis u Digital model
PLAN
PERSPECTIVE
ELEVATION
1.2 Object + System Analysis u Analysis
ELEVATION / CLOSED
ELEVATION / PARTLY OPEN
ELEVATION / FULLY OPEN
( MAX 170° )
Movement and folding: l CLOSED: All the panels stay together. l PARTLY OPEN: Side sheets open like a fan. They keep stay together at the bottom while sheets on the top become wide. l FULLY OPEN: When the expanding file is entirely opened, the maximum degree that it can reach is 170°, not 180°, as the top part of side sheets has length limitation.
1.2 Object + System Analysis u Analysis ELEVATION / PARTLY OPEN
Element
Twist
Connect
DIGITAL MODEL OF SIDE SHEETS
PLAN / PARTLY OPEN Element
Twist
Connect
In summary, the elements of expanding file has two kinds of ways to connect each other. Not only folding, but also twisting.
DETAIL OF SIDE SHEETS
1.3 VOLUME
u How to get volume
1.cut the parallel sheets along the edge of cover panel.
2. hold one side of the parallel sheets and try to twist it.
3. fix the twisted side so it has svolume.
1.3 VOLUME u How is the volume like
FRONT
TOP
LEFT
BACK
1.4 Sketch design proposal u Sketch Design #1
TWIST / CURVE / GROW / WEMEN / TOW SIDES I am interested in curves and want to use the method of twisting. In order to create second skin of people. The body could be regarded as a column. And a line grow from the bottom to the top.
1.4 Sketch design proposal u Sketch Design #2
FAN/ BUTTERFLY / FREEDOM / THIN I was inspirated by the fan. And when I saw arms, they just like the side of fan. But a single fan is no changable, so I considered the shape of butterfly. When lifting arms, the person is just like a butterfly. It could give me a sense of freedom.
1.4 Sketch design proposal u Sketch Design #3
SPIRAL/ CONCH / SECRET SPACE/ THINKING According to sketch model, the back view of the moel is just like a conch. The space in conch gives people a personal space to stay with themselves. It is designed for people who feels stressful to communicate with aothers or do not hope to be pay attentioned.
1.5 Reflection
Through the study of module 1, I have learned how to analyze an object after doing mea su red dra wing a nd dig ita l making. To treat it as a whole, observation and analysis are both important methods to extract designing ideas from a specific object. I understood the working principles of expanding file and the detailed process from folding to unfolding. However, when I look back, I realize that my sketch designs were very similar to dress designing. And just like designing a dress, I paid too much attention to the form rather than the function, which resulted in formism. To be more specific, I wrongly understood “ the second skin� as clothes. When I was drawing my sketch designs, I even adopted the style of dress designer for the female model. They seemed to be beautiful, but nothing else can be found except the beauty. My excessive pursuit of aesthetics leads to the deficiency of functionality, which still effected the later work in group.
2.0 Design 2.1 Personal Space Analysis 2.2 Design Development Intro 2.3 Second Skin Design Proposal V1 2.4 Precedent Research 2.5 Design Development V1 2.6 Design Development V2 2.7 Prototype V1 + Testing Effects 2.8 Reflection Based on the the ideas of second skin in module 1, Huiyuan Koh and I worked as a group to continue exploring panel and folding system on the visual and emotional effects. We combined our two sketch design ideas and produced a new design. The combined one was ba sed on the hood element from huiyuan and the fan folding element from mine. To improve its functionality, we defined the character of its user and made personal space analysis to decide the form of the design.
TEAM NUMBER Zhiyin Wang 736038 & Huiyuan Koh 799168
2.1 Personal Space Analysis u Information of user & Personal space l Physical: Female, young girl, 165cm l Personality: Shy, introvert, antisocial l Background: Victim of domestic violence, school bully l Personal space: By creating a barrier around head and upper body parts. Users are able to block off any interactions with other people because socializing drainher energy. Besides, the user will be able to gain a sense of security.
extreme personal personal stages
very personal personal safe distance
2.2 Design Development Intro u Concept combination
combination
l Fan structure from Zhiyin Wang'
l Hood from Huiyuan Koh
l New sketch design
Personal space is a boundaries around a person’s body which intruders may not come in ( Sommer, 2008) . From the reading Personal Space, we also understand that personal space varies from person to person and have different stages. Therefore, we have made a design which aims to protect female users who are uncomfortable around people because of their unfortunate past. The design we came out with at the beginning is the combination of 2 chosen designs from our M1 journal. The key characteristics from each design are integrated together based on the personal space analysis. It consists of an expandable hood structure that covers area around the head and a fan structure that ties to the arm. The hood and fan can be expanded when the user feels insecure around strangers or crowd to block out any contacts with them. As the user raises her arm, the upper body and the sides of the body which is more sensitive will be covered by the fan structure.
2.2 Design Development Intro u Design development
can be made
not realistic optimization
too long
easy to move
In the process of design developing, we have taken the fan element from the document file and researched about various kind of folds. Fan structure is interesting in a sense where they can unfold at different degree and we have implemented this mechanism in our following designs. By folding at different angle and pattern, the fan structure will expand and bend into different shapes which occupy different amount of volume. Making sketch paper models made us realise that an exact curve on the hood is not feasible so several angle folds are made to produce the similar curve around the neck. Furthermore, instead of covering the whole arm with the fan structure we focus down to just the forearm as that will be more correspond to the personal space analysis we did.
2.3 Second Skin Design Proposal V1 u Digital model making
PLAN
ELEVATION
This design is inspired by ruff, a fashion item in Europe during Renaissance period. It was a symbol of status and wealth, as it is a highly luxurious item. Therefore, this design of the second skin does not only act as a firm barrier between people, it also encourage the user to be more proud of themselves and confident to face the society. Furthermore, the curve in the structure preserve the elegancy of the female user. The angle of the fold is made in such a way that the structure fits the body shape of the user.
2.3 Second Skin Design Proposal V1
u Personal space stages
safe distance
STAGE I
personal
STAGE II
very personal
extreme personal
STAGE III
STAGE IV
The diagrams above show the stages of personal space and how the second skin varies in each stage. Instead of attaching an external system to fix the expandable hood at each stage, we tried to use the panel and fold system. That is applied by pushing out the edge of the panels which folds inward as shown in stage II to IV. The tension of the panels pushed against each other, hence support the whole structure.
2.4 Precedent Research u Precedent research
Veasyble, 2010
Isolation / Collapsibility / Intimacy / Wearable This project is about isolation, intimacy and ornamentation. It has the folding system much like the one we are working on. The ability of fold make them transform and collapse. The aim of Veasyble is emphases on the change of mood in people, the search of both separation and companionship at different situation. This is because the project remind us to always look for the beauty within ourselves and share connection with others in the surrounding. We have notice Veasyble has this 3 forms we called them: ‘the bag’, ‘the hood’ and the mask. All of them can expand to different extend. The big volume of ‘the bag’ can even fits 2 person.
Veasyble by GAIA
2.4 Precedent Research u Precedent applied to design
After evaluating our present designs, we found out that even though the second skin execute different stages depending on the situation, we did not explore the volume that project out of the body to show the different distance of each personal space stages away of the body. l without safety distance
l Lack of volume
l Not stable strucutre
By implementing some key ideas such as complete isolation and wearable characteristics from the precedent, we develop our design into an enlarged hood structure that sits across our body with its end hook to a support system. The expanding hood indicates the personal space user needed at different situation such as day and night. The support system holds the hood structure so that the second skin is wore stably on the user’s body. The length of the rod on the su pport system a lso define the personal space distance away from the user body. This changes then solves our problem of personal space not thoroughly explored and shown.
Optimization
Safety distace
Isoluation
2.5 Design Development V1 u Digital model
PLAN
ELEVATION
The keywords we have taken from the the precedents into this design is isolation and wearable. They have evolved our design into 2 big hood structure hanging of the center of the user’s chest from the support system. As the user become insecure and nervous in the crowd, she will expand the hoods and it will narrow her vision down until complete isolation when the both hood is closed. In the previous design, we did not consider how the second skin is fixed to the user’s body. Therefore, the design is improved by adding a support system into it. The support system model is made by a few commands we learned in the rhinoceros intensive workshop such as MeshtoNurb and BooleanDifference.
2.5 Design Development V1 u Personal space stages
personal
safe distance
very personal
extreme personal
2.6 Design Development V2 u Digital model
PLAN
ELEVATION
As we develop the last design while referring back to our personal space analysis, we discovered that by varying the size of the hood, the boundary of each stages can be shown more clearly. The pictures of the Veasyable project showing the models at different environment had give us the idea of camouflage. Since our user is an introvert person who dislike socializing, she would like to blend in the crowd and camouflage when she is in an unfamiliar places. Therefore the colour of the hood is black and white in colour. The white and smaller one is to be used during the day time; the black and the smaller one is to be used during the night time when most of the dangerous situations happen.
2.6 Design Development V2 u Personal space stages
personal
safe distance
very personal
extreme personal
2.7 Prototype V1 + Testing Effects u Prototype We have tried different types of paper such as tracing paper, cartridge paper and watercolour paper during the sketch model making and decided that thicker paper is more suitable in making the hood structure of the second skin as it will be more rigid. W e ha ve selected the 240gsm heavyweight coloured card which has both white and black colour. As we made our full sized prototype, we encountered the problem of paper size. Single A1 sheet is not enough to made the whole structure so we have to fold a few hood elements and connect them together using double sided tape and cellophane tape. Folder rings is then insert into the holes which are punched at the end of the hood structures to connect them to the support system. Our attempt to make the support system is not very successful because the material we have chosen to use. We used aluminium wire as it is malleable and easy to shape but without sufficient material to support itself, the wire frame support system collapsed under the weight of the paper hood structure. This brings us to the conclusion of using increase the amount of wire in the wireframe support system or use another material for the support system.
2.7 Prototype V1 + Testing Effects u Testing effects
l DAY TIME
l NIGHT TIME
As we develop the last design while referring back to our personal space analysis, we discovered that by varying the size of the hood, the boundary of each stages can be shown more clearly. The pictures of the Veasyable project showing the models at different environment had give us the idea of camouflage. Since our user is an introvert person who dislike socializing, she would like to blend in the crowd and camouflage when she is in an unfamiliar places. Therefore the colour of the hood is black and white in colour. The white and smaller one is to be used during the day time; the black and the smaller one is to be used during the night time when most of the dangerous situations happen.
2.8 Reflection In module 2, we worked as a group. As the second skin project is comprehensively related to the user's personality and requirements, we defined the user's character and did personal space analysis on her. We tried to create a defensive mechanism and help her feel safe when get in touch with others. Before exploring our concept digitally, we firstly made physical model on body doll. As Scheurer and Stehling (2007) have argued that “ Architecture is a process of communication”, it is a long way for the designers to make their initial idea to achieve the physical reality. We really struggled, but we realized that we went a wrong way after we got the feedback. There are some serious mistakes we ignored about digital designing. As this course is about digital design and fabrication, the designing process should be in digital method, not just make a digital model after design finishes. We did not apply the key digital method “panelling tools” in rhino entirely and paid no attention to the concept of developable surface in reading Architectural Geometry by Pottmann( 2007). Using panelling tools, we could easily produce 3D model which has developable surface, then we are able to get unrolled 2D drawings to make physical model through laser cutting or 3D printing. We wrongly made the physical model without digital method and wasted plenty of time. Another mistake was that there is only “folding” element in our design, so we need to add “panel” element to achieve the goal of system. We ever tried to make a supporting structure for our prototype so that it can be wore, but now we realized that the prototype structure should support itself without any other added thing. On top of that, our design were too similar to the precedent. As a result, we will redesign the second skin using digital designing method in next module.
3.0 Fabrication 3.1 Fabrication intro 3.2 Design Development 3.3 Fabrication of prototype 3.4 Final Prototype development + optimisation 3.5 Final Digital model 3.6 Fabrication Sequence 3.7 Assembly drawing 3.8 Completed 2nd Skin 3.9 Reflection In module 3, we were mainly redesigning the second skin and solving the problems in the progress of the digital fabrication. Because of the serious mistake in module 2, it was very urgent for us to fix our design and make the fianl second skin model. The fan structure on the body was discarded and we just remained the hood part on the head. The new “panel� element become the main part of design and we adopted panelling tools to explore the best form to combine with its fucntion.
TEAM NUMBER Zhiyin Wang 736038 & Huiyuan Koh 799168
3.1 Fabrication intro u Review
In response to our feedback for M2 final design, we have some problems to be solved. l Our design lack of the use of digital design method “panelling tools�. l No variation of the panel and fold system as it only has one consistent fold. l The design needs to sit structurally on the user’s body without additional elements outside our selected material system. l The design is too similar to the precedent and does not have its own character.
3.2 Design Development u Sketch Design development
Sketch is made to explore the posiible designs.
Variation of panels in response to the digital model making method.
3.2 Design Development u Digital design development
Digital design to fabrication
3.2 Design Development u Design proposal
PLAN
Prototype digital model
PLAN
PLAN
3.3 Fabrication of prototype u Fabricaction analysis
l Pyramid element with hollow surface and doubly curved
l Pyramid element as a group
l Triangulation
l Unroll surface and explode
l Unrolled surface. 2D shape becomes very complex and it is difficult to add tabs for folding.
l Laser cutting and glue these exploded surfaces according to label
3.3 Fabrication of prototype u Fabrication process
In our second skin design, digital fabrication is implemented when we were producing our 3-dimensional pyramid elements that are join together to form a self-supporting form. The design we made in Rhinoceros is unrolled into 2-dimensional form, which then cut and scored using laser-beam cutting. This fabrication method can produce accurate 3-dimensional measure for each of the pyramid element that we design in Rhinoceros. Digitally manipulated building skins brought new aesthetic qualities, tectonic and geometric complexities in architecture. Using a geometrically complex envelope, the structure of the building is then incorporated into the skin as it absorbs all or most of the stresses. Hence, the concept of combining two elements in one create a self-supporting form that open up more possibilities in the material and design aspect of architecture. This reading made us realise that by manipulating the surface of the second skin design, we actually able to make the skin self-support itself without using any external support system such as wireframe. Using NURBS isoparms the curvilinear surfaces on the structural skin are produced by triangulation or by the conversion of doubledcurve into ruled surface. During our redesign process, we faced the problem of fabricating doubly-curved surfaces. We tried using this method but the triangulation of a single pyramid element, especially those with hollowed surfaces are too complex when we unroll them in Rhinoceros. The previous non self-supporting and overly complex design leads us to slight change of design and also the sequence of adding hollow surfaces in our pyramid elements.Another fabrication process that affect our second skin project is the length of the tabs attached to each panel. We found out that the longer the tabs, the more rigid the structure will be.
3.4 Final Prototype development + optimisation u Final design development
Hood
Not enough proctection
American football equipment
HOOD-BODY SKIN CONNECTION In this development, we considered about the American football equipment to achieve better protection. The structure at back part of the body skin is made of rectangular panel with side connected to the triangular edge of the pyramid so that the size of the modular elements have similar height. The hood is then join together at the top part of the rectangular panel near the neck. The hood which is also made of rectangular panel then could be blend with the body skin structure. Heart form - Symmetrical
3.4 Final Prototype development + optimisation u Final design development u Design effect
Hood
Heart Form - Asymmetrical
PYRAMID ELEMENTS SIZE VARIATION
PERFORATION VARIATION
Comparing the digital model version 1 and version 2, in version 2 we made size variotion of pyramid at different area. The size of the pyramid can be compare clearly at the shoulder area, where the right shoulder has taller pyramids compare to the left shoulder ones.
Our personal map analysis had improve over the period of designing. We think that personal space can be varies in 2 different ways, distance and sight. This is because some body parts, for example the shoulder are less sensitive when other people look at it but very sensitive when people touch it. A bigger shoulder can also helps the introvert and mentally weak user to be more confident and stronger.
3.4 Final Prototype development + optimisation u Final prototype optimisation
HOOD-BACK CONNECTION While making our second prototype, we faced the problem of not able to connect the hood with the second skin around the body. We thought of many solution but they did not work because they seems to be forced together instead of being one integrated structure. Therefore, we change our design once again, this time, thinking how to connect them together with gradual change of shape and size. In this design, the structure at back part of the body skin is made of rectangular panel with side connected to the triangular edge of the pyramid so that the size of the modular elements have similar height. The hood is then join together at the top part of the rectangular panel near the neck. The hood which is also made of rectangular panel then could be blend with the body skin structure.
3.4 Final Prototype development + optimisation u Final prototype optimisation
MESH
NURB
UNROLL
GROUP UNROLL
The laser cutting files are the comparison of 2D shapes obtained after unrolling prototype 2 and final prototype. In prototype 2 because of the double curve we cannot use UnrollSrf command in Rhino so instead of that we used ptUnrollFaces. This command can only explode faces but it insert label automatically on each tab. Whereas, we were able to use UnrollSrf command because we solved the doubly curve problem using Mesh. UnrollSrf does not automatically insert labels so we have to use Text command to write down the label number one by one on the tab. This is time consuming compare to using ptUnrollFaces. On the other hand, we were able to save up lots of material, cutting time and printing money by unrolling surface into geometrical form as seen in the later version of laser cutting template. This is because the machine was able to cut lesser compare to cutting each of the exploded triangular shapes.During assembling the elements, the later version also save up significant of time
3.5 Final Digital model u Digital model
TOP
RIGHT
FRONT
LEFT
BACK
3.6 Fabrication Sequence u Fabrication sequence comparision
WASTE OF TIME AND MONEY
SAVE ENERGY AND LIFE
3.7 Assembly drawing
Colour coded by type of perforation Small perforation No perforation Small perforation Big perforation Samll perforation No perforation No perforation No perforation (hand made hood
3.8 Completed 2nd Skin
3.8 Completed 2nd Skin
3.9 Reflection In module 3, our second skin entered into CAM process that transformed digital design into physical, geometric edged model. Laser cutting could highly increase our efficiency and greatly reduce the difficulty brought by prototype's combination. As fabrication is digital, the accuracy and precision are improved to a new standard compared with the past time. Furthermore, digital fabrication frees designers, which means that designers could save more time on ideas and concepts rather than consider about the problems in the process of fabrication. Different from the struggling in physical model making by hand in module 2, in this module we adopted digital method in model making. As we discarded large part of design in module 2, new design had to be put forward. I drew a concept sketch which could be produced using panelling tools, and we successfully made the prototype after solving different kinds of probelms such as doubly curves. However, when the prototype was finished, we found that it was too flexible to keep its shape and sit on the body. Without wires supporting in it, the prototype even can not have the volume. We were both very upset facing this problem, because this outcome meant that our design was unsuccessful again. Luckily, Rosie gave us the advice of American football player, then we refined our design and got “heart protector�, which not only ensured the function to protect the girl but also had a beautiful form. Although it was still flexible, the second skin could sit on the shoulder without additional structure out of the system. Another problem we faced was that the hood part was still made by hand because of the difficulty in digital model making. The consistence of the whole model was not satisfying. As a result, before the week 12 show, our goal was to make the structure all digital fabricated and be rigid enough to keep its shape and volume .
4.0 Reflection 4.1 Final Second Skin optimisation 4.2 Final Digital model 4.3 Week 12 Show 4.4 Reflection
4.1 Final Second Skin optimisation
u Element optimisation
Pyramid
u Fabrication process
Box foundation
New element
Rigid structure
4.2 Final Digital model
TOP
BACK
FRONT
RIGHT
4.4 Reflection This subject Digital Design and Fabrication can be regarded as a start point of making the transformation from hand making to digital fabrication for me. Through the whole semester study, our design started from measured drawings of a relevant object and digital model making of this object, which helped me to get a better understand of object's working principles and detailed connection method. As for the concept modeling, I learned how to extract abstract ideas from a specific physical thing and develop my own concept. Then we were divided into groups to produce design sketch, combining different ideas with others. At the design stage, my partner and I did not on the right way. We misunderstood the true meaning of digital design which was the medium to achieve the production of prototypes and provide strong visual support of complex model. When it came to fabrication, we finally corrected our way in hand making and made the prototype using panelling tools. At this stage, laser cutting and 3D printing highly improved our efficiency, which gave us chance to catch up with the lack of digital designing in module 2. We tried several prototypes, and with Matt's help of doubly curves in Rhino and Rosie's advice of the form, we optimized our design and successfully made our second skin. After the presentation in week 10, we optimized our second skin again according to the feedback. Firstly we solved the problem of flexibility of the structure through adding a box foundation to the element, then every element connected surface by surface, so the prototype became rigid enough keep its own shape. Another optimization is the hood, this time we successfully built its digital model in Rhino and combined it with the main part just as a whole. Through the whole semester of making the second skin project, the most thing I learn is that the importance of optimizarion. It is not realistic to produce a perfect work in just one time. All we need to to is test and refinement, test and refinement, test and refinement......It is not shamed that we made mistakes or go to the wrong direction. As a designer, we need to have the courage to face problems. And just in this kind of process, we can learn something and grow up. Digital design and fabrication is a great subject to strenghth our ability, both mental and physical. Although it is hard and have huge work to do, I'm not regret to take this course at all.
5.0 Appendix Arzuaga, Amaya, 2011. Spring 2011 RTW, photograph, viewed 8 June 2017 http://orlandaspleasure.tumblr. com/post/38751305902/amaya-arzuaga-spring-2011-rtw GAIA, 2010, Veasyble, photograph, viewed 8 June 2017, https://www.yatzer.com/Veasyble-byGAIA Sommer, R. 1969. Personal space: the behavioral basis of design / Robert Sommer. Englewood Cliffs, N.J.: Prentice-Hall, c1969 Scheurer, F. and Stehling, H. _2011_: Lost in Parameter Space? IAD: Architectural Design, Wiley, 81 _4_, July, pp. 70-79