2.0 Form-Finding

 

K E Y   C O N C E P T S

Viscosity:

 is basically a property of liquid materials. It is a measure of the resistance of a fluid to deform under shear stress In other words, is the liquid’s internal resistance to flow. It is commonly perceived as ‘thickness’ as a measure of fluid friction and measured in centipoise (CPS). vismorph.jpg 

 Surface Tension:  

 

Because the molecules in the surface of a liquid have no neighbouring molecules above, they exhibit attractive force to their nearest molecules forming a ‘film’ in a behaviour called Surface Tension. The surface tension is measured in Dynes/cm and can change under different temperatures. D’Arcy Thompson highlighted the importance of surface tension in the generation of specific forms, from a simple rain drop, to a more complex system. D’Arcy Thompson regarded all systems as diagrams of forces that acted over them, and a characteristic of fluids which can also be explained in viscous materials, is that most of the forces act in a molecular level, hence, self organisation and overall behaviour is generated at a micro level. For example, in the case of surface tension dependant forms he explains:

“fluid surfaces that are under the influence of surface tension are limited to conditions under which other forces are relatively unimportant, that is to say where the surface energy is a considerably fraction of the whole energy of the system, and in general this will be the case when we are dealing with portions of liquid so small that their come within or near to what we call the molecular range” (D’Arcy W. Thompson, On Growth and Form; 1961)

P H Y S I C A L   F O R M   F I N D I N G :  O V E R V I E W

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Assumption:The resulting forms would not only depended on the intrinsic properties of every viscous substance like their density or viscosity and their surface tension, but also on external factors like temperature, time, and other components (like hardeners), where despite an isotropic inherent behaviour, an anysotropic material system can be created.

 

Strategy overview:The whole set of experiments was divided into two processes: Vertical Manipulation (uniaxial stress), and Horizontal Manipulation (bi-axial stress) which were discarded for the final research presentation. Each set of experiments resulted in different morphological and behavioural outputs that where subsequently analysed.

“We intend to do an exhaustive material research and explore on production and manufacturing logics that would lead to the development of a first prototype that will define the development and design strategies for the final project.

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structural test

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In a Series of experiments conducted by Prof. Emma Johnson at the Centre for Biomimetics at Reding University, BiResin’s Y Modulus was calculated and also the material’s behaviour under compression and strain.

Bi-Resin is a polymer (a polyurethane resin) which hardens in 3 minutes. Due to the short time in hardening and the availability of the material; BiResin was chosen to perform the physical experimentation.

A s a complement to the Resin analysis we did a series of analysis using a filler, based on sand,  in order to compare the results with the previous experiments and to have a broader view of the structural properties of the resin. Almost every test we did using the filler, the samples of resin cracked and split after a few seconds. We concluded that the use of sand or dry fillers in the basic mix of resin, decreases the elasticity of the resin. The Y modulus of Resin+Filler is 0.08345 GPa compared to the 1.375 GPa of the resin alone.

Resin’s Tensile Strtain and Compressive Strain is very similar to Bone’s Tensile and Compressive Strain, meaning that Resin, when hardened, can bear similar loads and behave in a similar structural way. On the other hand, the modulus of elasticity of Resin is lower than than Concrete and the tensile and compressive strain properties are different as well. While Concrete can bear higher loads without collapsing, Resin can undergo to higher tensile forces before collapsing.

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Structural Analysis was developed using Ansys Multiphysics (TM) using the “Y” Modulus as an imput and digitizing the spine patterns (self-formed formations).

A series of small scale analysis were done in order to investigate the morphology – structure relation of the selfoptimised formations.

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Multiple minimal hole

The structure was tested under the ‘safety factor’ criteria both in an Elastic Strain scenario and a Stress Analysis. In the case of the Elastic Strain analysis, the areas that tend towards a red colour, are the ones that can resit a lower degree of pressure, hence, are the ones that would collapse in first place when exposed to strain forces. The branch or fibre-like areas are the ones that show a ‘safer’ degree, meaning that they can resit a higher degree of pressure (tend to blue or green in the images). A similar case occurs on the Stress Analysis, where the safest areas, highlighted in blue, are the ones that are less exposed to strain forces, while the whole force-flow is concentrated in the branch or fible-like areas and the minimal holes surroundings. The Assumption mentioned before is corroborated by these series of analysis, showing that the minimal holes highlight the less dense, hence, the weaker areas, while the branch or fibre-like areas can resist higher pressures, because they are the areas where a higher distribution of material occurs.

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When a system of ‘spines’ undergoes structural tests, it is clear how the components distribute the forces both along each member, that act as a whole in collaboration with other spine formations, and along the upper and lower layers  or membranes. Despite Resin’s intrinsic  isotropic behaviour, the overall behaviour induced by the viscous morphologies is Anisotropic, depending basically on the orientation of the ‘spines’ and their distribution along the surface or system. Deformation occurs mainly on the membranes as the ‘spines’ distribute the compressive load in  an uniaxial direction which determines the ‘strength’ and stiffness of the whole system.  The system’s behaviour under shear, stress and strain forces is also optimised by these spine formation as the critic areas are located mainly on the borders of the membranes, where the spines’ influence is reduced.The analysis clearly show how geometry affects the structural behaviour in a system, where the material’s intrinsic properties is less relevant (only determines the system’s elasticity -using resin’s Y modulus- and the overall behaviour depends on the orientation and direction of the “components’

 

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Digital Form-Finding based on Evolutionary algorithms and parametric design was developed in parallel to the physical form finding, is an opportunistic use of available software to have a wider design research range on self-forming patterns, that would be informed by the

Physical form-finding experiments. On a first instance, we experimented with Real Flow, a software that uses Python scripting language, to study viscous behaviour in a digital environment. Our main goal was to reproduce viscosity in a digital environment, as close to reality as possible. We were able to develop a porous system based on the rules of viscosity, density control, and surface tension. Unfortunately spine formations were not possible to reproduce through this media, hence, a new software was used: Generative Components.

 On our final project design, a more complex use of GC was developed and viscosity and self-organisation were translated into Mathematical equations in order to reproduce the physical experiments in a digital environment and also inform the design process.

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Parametric Modeling:

Viscous behaviour was translated into mathematical equations in order to reproduce the physics and logics behind the self-forming and self optimising patterns and viscous structures

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A viscous pattern was used as a ‘component’ in order to generate a  material system and each single component was par of a parametric  mesh, where the component interacts with the rest of the components and with the surface itself.

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Viscous Behaviour represented in a digital-parametric environment