10 research outputs found
Finite element modelling in integral design strategies of form- and bending-active hybrid structures
This paper discusses form-finding and simulation strategies for form- and bending-active hybrid structures, with practical feedback from two realised projects. Next to some general aspects of computational form-finding approaches with focus on finite element methods (FEM), the influence of changing mechanical properties of elastic beams on the resultant form-found hybrid system will be discussed on an umbrella structure with integrated bendingactive beam elements. Alongside the question of simulation strategies comes the search for a practical design setup to establish an FEM environment that is cross integrating information from various other modelling environments. This is discussed through the case study project M1 where physical form-finding and vector-based spring methods are utilised to generate input data for the FEM simulation
Intuitive interactive form finding of optimised fabric-cast concrete
Producing organic shapes in concrete has been a challenging problem since complex freeform buildings became a major trend in contemporary architecture. Many different techniques for casting doubly-curved shapes have been proposed. Most of them produce elements which exactly match a preconceived design, but at a high cost in manufacture. Fabric formwork techniques (such as those pioneered at the Centre of Architectural Structures and Technology at the University of Manitoba (CAST)) are relatively economical, but require a form-finding approach which takes into account the physics of casting, as well as structural and functional requirements of the finished element. The research presented here involves a specialised methodology for the design and manufacture of optimised concrete elements cast in fabric formwork. Using a novel software tool, our approach lies in between the largely intuitive methods reported by CAST and the precise but expensive computer-controlled manufacturing methods normally used in practice. Combining topological optimisation with computational form-finding, the developed software guides the designer towards a shape that is economical in both material and manufacturability. By combining knowledge of computational structural analysis, optimisation algorithms, fabric simulation and the practical casting techniques of fabric formwork; the gap between structurally optimised forms, and those developed intuitively by fabric casting, can be bridged. This is demonstrated through a case study involving the computational design of a centrally supported slab, supplemented with design studies realised using plaster scale models
The application of three-dimensional mass-spring structures in the real-time simulation of sheet materials for computer generated imagery
Despite the resources devoted to computer graphics technology over the last 40 years,
there is still a need to increase the realism with which flexible materials are simulated.
However, to date reported methods are restricted in their application by their use of
two-dimensional structures and implicit integration methods that lend themselves to
modelling cloth-like sheets but not stiffer, thicker materials in which bending moments
play a significant role.
This thesis presents a real-time, computationally efficient environment for simulations
of sheet materials. The approach described differs from other techniques principally
through its novel use of multilayer sheet structures. In addition to more accurately
modelling bending moment effects, it also allows the effects of increased temperature
within the environment to be simulated. Limitations of this approach include the
increased difficulties of calibrating a realistic and stable simulation compared to
implicit based methods.
A series of experiments are conducted to establish the effectiveness of the technique,
evaluating the suitability of different integration methods, sheet structures, and
simulation parameters, before conducting a Human Computer Interaction (HCI) based
evaluation to establish the effectiveness with which the technique can produce credible
simulations. These results are also compared against a system that utilises an
established method for sheet simulation and a hybrid solution that combines the use of
3D (i.e. multilayer) lattice structures with the recognised sheet simulation approach.
The results suggest that the use of a three-dimensional structure does provide a level of
enhanced realism when simulating stiff laminar materials although the best overall
results were achieved through the use of the hybrid model
Real-time simulation and visualisation of cloth using edge-based adaptive meshes
Real-time rendering and the animation of realistic virtual environments and characters
has progressed at a great pace, following advances in computer graphics hardware
in the last decade. The role of cloth simulation is becoming ever more important in
the quest to improve the realism of virtual environments.
The real-time simulation of cloth and clothing is important for many applications
such as virtual reality, crowd simulation, games and software for online clothes shopping.
A large number of polygons are necessary to depict the highly
exible nature of
cloth with wrinkling and frequent changes in its curvature. In combination with the
physical calculations which model the deformations, the effort required to simulate
cloth in detail is very computationally expensive resulting in much diffculty for its
realistic simulation at interactive frame rates. Real-time cloth simulations can lack
quality and realism compared to their offline counterparts, since coarse meshes must
often be employed for performance reasons.
The focus of this thesis is to develop techniques to allow the real-time simulation of
realistic cloth and clothing. Adaptive meshes have previously been developed to act as
a bridge between low and high polygon meshes, aiming to adaptively exploit variations
in the shape of the cloth. The mesh complexity is dynamically increased or refined to
balance quality against computational cost during a simulation. A limitation of many
approaches is they do not often consider the decimation or coarsening of previously
refined areas, or otherwise are not fast enough for real-time applications.
A novel edge-based adaptive mesh is developed for the fast incremental refinement
and coarsening of a triangular mesh. A mass-spring network is integrated into
the mesh permitting the real-time adaptive simulation of cloth, and techniques are
developed for the simulation of clothing on an animated character
Animated surfaces in physically-based simulation
Physics-based animation has become a ubiquitous element in all application areas of computer animation, especially in the entertainment sector. Animation and feature films, video games, and advertisement contain visual effects using physically-based simulation that blend in seamlessly with animated or live-action productions. When simulating deformable materials and fluids, especially liquids, objects are usually represented by animated surfaces. The visual quality of these surfaces not only depends on the actual properties of the surface itself but also on its generation and relation to the underlying simulation. This thesis focuses on surfaces of cloth simulations and fluid simulations based on Smoothed Particle Hydrodynamics (SPH), and contributes to improving the creation of animations by specifying surface shapes, modeling contact of surfaces, and evaluating surface effects of fluids. In many applications, there is a reference given for a surface animation in terms of its shape. Matching a given reference with a simulation is a challenging task and similarity is often determined by visual inspection. The first part of this thesis presents a signature for cloth animations that captures characteristic shapes and their temporal evolution. It combines geometric features with physical properties to represent accurately the typical deformation behavior. The signature enables calculating similarities between animations and is applied to retrieve cloth animations from collections by example. Interactions between particle-based fluids and deformable objects are usually modeled by sampling the deformable objects with particles. When interacting with cloth, however, this would require resampling the surface at large planar deformations and the thickness of cloth would be bound to the particle size. This problem is addressed in this thesis by presenting a two-way coupling technique for cloth and fluids based on the simulation mesh of the textile. It allows robust contact handling and intuitive control of boundary conditions.
Further, a solution for intersection-free fluid surface reconstruction at contact with thin flexible objects is presented. The visual quality of particle-based fluid animation highly depends on the properties of the reconstructed surface. An important aspect of the reconstruction method is that it accurately represents the underlying simulation. This thesis presents an evaluation of surfaces at interfaces of SPH simulations incorporating the connection to the simulation model. A typical approach in computer graphics is compared to surface reconstruction used in material sciences. The behavior of free surfaces in fluid animations is highly influenced by surface tension. This thesis presents an evaluation of three types of surface tension models in combination with different pressure force models for SPH to identify the individual characteristics of these models. Systematic tests using a set of benchmark scenes are performed to reveal strengths and weaknesses, and possible areas of applications.Physikalisch basierte Animationen sind ein allgegenwĂ€rtiger Teil in jeglichen Anwendungsbereichen der Computeranimation, insbesondere dem Unterhaltungssektor. Animations- und Spielfilme, Videospiele und Werbung enthalten visuelle Effekte unter Verwendung von physikalisch basierter Simulation, die sich nahtlos in Animations- oder Realfilme einfĂŒgen. Bei der Simulation von deformierbaren Materialien und Fluiden, insbesondere FlĂŒssigkeiten, werden die Objekte gewöhnlich durch animierte OberflĂ€chen dargestellt. Die visuelle QualitĂ€t dieser OberflĂ€chen hĂ€ngt nicht nur von den Eigenschaften der FlĂ€che selbst ab, sondern auch von deren Erstellung und der Verbindung zu der zugrundeliegenden Simulation. Diese Dissertation widmet sich OberflĂ€chen von Textil- und Fluidsimulationen mit der Methode der Smoothed Particle Hydrodynamics (SPH) und leistet einen Beitrag zur Verbesserung der Erstellung von Animationen durch die Beschreibung von OberflĂ€chenformen, der Modellierung von Kontakt von OberflĂ€chen und der Evaluierung von OberflĂ€cheneffekten von Fluiden. In vielen Anwendungen gibt es eine Referenz fĂŒr eine OberflĂ€chenanimation, die ihre Form beschreibt. Das Abgleichen einer Referenz mit einer Simulation ist eine groĂe Herausforderung und die Ăhnlichkeit wird hĂ€ufig visuell ĂŒberprĂŒft. Im ersten Teil der Dissertation wird eine Signatur fĂŒr Textilanimationen vorgestellt, die charakteristische Formen und ihre zeitliche VerĂ€nderung erfasst. Sie ist eine Kombination aus geometrischen Merkmalen und physikalischen Eigenschaften, um das typische Deformationsverhalten genau zu reprĂ€sentieren. Die Signatur erlaubt es, Ăhnlichkeiten zwischen Animationen zu berechnen, und wird angewendet, um Textilanimationen aus Kollektionen anhand eines Beispiels aufzufinden. Interaktionen zwischen partikelbasierten Fluiden und deformierbaren Objekten werden gewöhnlich durch das Abtasten des deformierbaren Objekts mit Partikeln modelliert. Bei der Interaktion mit Textilien wĂŒrde dies jedoch ein neues Abtasten bei groĂen planaren Deformation erfordern und die StĂ€rke des Textils wĂ€re an die PartikelgröĂe gebunden. Mit diesem Problem befasst sich diese Dissertation und stellt eine Technik fĂŒr die wechselseitige Kopplung zwischen Textilien und Fluiden vor, die auf dem Simulationsnetz des Textils beruht. Diese erlaubt eine robuste Kontaktbehandlung und intuitive Kontrolle von Randbedingungen. Des Weiteren wird ein Lösungsansatz fĂŒr eine durchdringungsfreie OberflĂ€chenrekonstruktion beim Kontakt mit dĂŒnnen flexiblen Objekten prĂ€sentiert. Die visuelle QualitĂ€t von partikelbasierten Fluidanimationen hĂ€ngt stark von den Eigenschaften der rekonstruierten OberflĂ€che ab. Wichtig bei Rekonstruktionsmethoden ist, dass sie die zugrundeliegende Simulation genau reprĂ€sentieren. Die Dissertation prĂ€sentiert eine Evaluierung von OberflĂ€chen an GrenzflĂ€chen, die den Zusammenhang zum Simulationsmodell miteinbezieht. Ein typischer Ansatz aus der Computergrafik wird mit der OberflĂ€chenrekonstruktion in der Werkstoffkunde verglichen. Das Verhalten von freien OberflĂ€chen in Fluidanimationen wird stark von der OberflĂ€chenspannung beeinflusst. In dieser Dissertation wird eine Evaluierung von drei OberflĂ€chenspannungsmodellen in Kombination mit verschiedenen Druckmodellen fĂŒr SPH prĂ€sentiert, um die Charakteristika der jeweiligen Modelle zu identifizieren. Es werden systematische Tests mit Hilfe von Benchmark-Tests durchgefĂŒhrt, um StĂ€rken, SchwĂ€chen und mögliche Anwendungsbereiche deutlich zu machen