65 research outputs found

    Animated surfaces in physically-based simulation

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    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 große Herausforderung und die Ähnlichkeit 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, Ähnlichkeiten 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 großen planaren Deformation erfordern und die StĂ€rke des Textils wĂ€re an die PartikelgrĂ¶ĂŸe 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

    Development of the Distributed Points Method with Application to Cavitating Flow

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    A mesh-less method for solving incompressible, multi-phase flow problems has been developed and is discussed along with the presentation of benchmark results showing good agreement with theoretical and experimental results. Results of a systematic, parametric study of the single phase flow around a 2D circular cylinder at Reynolds numbers up to 1000 are presented and discussed. Simulation results show good agreement with experimental results. Extension of the method to deal with multiphase flow including liquid-to-vapor phase transition along with applications to cavitating flow are discussed. Insight gleaned from numerical experiments of the cavity closure problem are discussed along with recommendations for additional research. Several conclusions regarding the use of the method are made

    Development of the Distributed Points Method with Application to Cavitating Flow

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    A mesh-less method for solving incompressible, multi-phase flow problems has been developed and is discussed along with the presentation of benchmark results showing good agreement with theoretical and experimental results. Results of a systematic, parametric study of the single phase flow around a 2D circular cylinder at Reynolds numbers up to 1000 are presented and discussed. Simulation results show good agreement with experimental results. Extension of the method to deal with multiphase flow including liquid-to-vapor phase transition along with applications to cavitating flow are discussed. Insight gleaned from numerical experiments of the cavity closure problem are discussed along with recommendations for additional research. Several conclusions regarding the use of the method are made

    Parallel fluid dynamics for the film and animation industries

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    Includes bibliographical references (leaves 142-149).The creation of automated fluid effects for film and media using computer simulations is popular, as artist time is reduced and greater realism can be achieved through the use of numerical simulation of physical equations. The fluid effects in today’s films and animations have large scenes with high detail requirements. With these requirements, the time taken by such automated approaches is large. To solve this, cluster environments making use of hundreds or more CPUs have been used. This overcomes the processing power and memory limitations of a single computer and allows very large scenes to be created. One of the newer methods for fluid simulation is the Lattice Boltzmann Method (LBM). This is a cellular automata type of algorithm, which parallelizes easily. An important part of the process of parallelization is load balancing; the distribution of computation amongst the available computing resources in the cluster. To date, the parallelization of the Lattice Boltzmann method only makes use of static load balancing. Instead, it is possible to make use of dynamic load balancing, which adjusts the computation distribution as the simulation progresses. Here, we investigate the use of the LBM in conjunction with a Volume of Fluid (VOF) surface representation in a parallel environment with the aim of producing large scale scenes for the film and animation industries. The VOF method tracks mass exchange between cells of the LBM. In particular, we implement the new dynamic load balancing algorithm to improve the efficiency of the fluid simulation using this method. Fluid scenes from films and animations have two important requirements: the amount of detail and the spatial resolution of the fluid. These aspects of the VOF LBM are explored by considering the time for scene creation using a single and multi-CPU implementation of the method. The scalability of the method is studied by plotting the run time, speedup and efficiency of scene creation against the number of CPUs. From such plots, an estimate is obtained of the feasibility of creating scenes of a giving level of detail. Such estimates enable the recommendation of architectures for creation of specific scenes. Using a parallel implementation of the VOF LBM method we successfully create large scenes with great detail. In general, considering the significant amounts of communication required for the parallel method, it is shown to scale well, favouring scenes with greater detail. The scalability studies show that the new dynamic load balancing algorithm improves the efficiency of the parallel implementation, but only when using lower number of CPUs. In fact, for larger number of CPUs, the dynamic algorithm reduces the efficiency. We hypothesise the latter effect can be removed by making using of centralized load balancing decision instead of the current decentralized approach. The use of a cluster comprising of 200 CPUs is recommended for the production of large scenes of a grid size 6003 in a reasonable time frame

    Knitted architecture and wind: Designing loosely fitted architectural textiles for interaction with wind

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    Utilising the textile’s ability to adapt to external forces such as the wind could lead to the creation of new design expressions and functional features within architecture. Prompted by architectural potentials of textiles deliberately designed to move and flex, this thesis aims to explore and demonstrate how such knitted textiles could contribute to enriched aesthetic expression and improved performance of\ua0architectural elements placed in windy environments. A key part of the research is the interaction of textile and wind, viewing it as a source of energy or force that could be used, diffused, or directed - to enrich and create a more comfortable urban environment. As such, this work is positioned at the intersection of three knowledge areas: architectural design, knitted textile design, and wind engineering. A research by design approach is used to conduct quantitative and qualitative investigations with design prototypes as main vehicles of inquiry. Specifically, a hybrid method of design-based research is applied, involving artistic making and qualitative evaluations of the design prototypes as well as scientific methods featuring quantitative textile performance measurements. Both physical and digital prototypes are utilised to probe the geometric expressions of knitted textiles and investigate the performative features of different knitted textile designs in relation to their wind reduction capacity. The main finding from the quantitative part of the study, encompassing wind tunnel experiments, is that loosely fitted knitted structures efficiently reduce wind velocities and high-energy eddies. Along with this, the qualitative investigations, involving a series of diversely designed knitted architectural prototypes, show that knitted textiles can be applied to design three-dimensional architectural structures that are aesthetically diverse and have a dynamic, ever-changing expression. Finally, the developed framework for designing loosely fitted textiles for interaction with wind seeks to provide architects with guidance concerning important aspects of such design, including the workflows, tools, and evaluation methods

    Development of design criteria for novel 3D-printed quadric-surfaced sludge digesters for wastewater infrastructure

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    The quadric-surfaced sludge digester (QSD), also known as the egg-shaped sludge digester, has proven its advantages over traditional cylindrical digesters recently. A reduction in operational cost is the dominant factor. Its shell can be described as a revolution of a parabola with the apex and base being either tapered or spherical. This shape provides a surface free of discontinuities, which is advantageous regarding the efficiency during mixing. Since the shape does not produce areas of inactive fluid motion within the tank, sludge settlement and an eventual grit build-up are avoided. The stresses developed in the shell of the sludge digester, vary along the meridian and equatorial diameters. A non-dimensional parameter, Ο, defines the height-to-diameter aspect ratio which is used to delineate the parametric boundary conditions of the shell’s surface. Three groups of analyses were conducted to determine the orthogonal stresses in the shell of the QSD. The first-principles numerical models ran reasonably quickly, and many iterations were made during the study. The results showed that they were in within the range 5.34% to 7.2% to 2D FEA simulations. The 3D FEA simulations were within the range of 8.3% to 9.2% to the MATLAB time-history models. This is a good indicator that the first principles numerical models are an excellent time-saving method to predict the behaviour of the QSD under seismic excitation. Upon examining the criteria for the design, analysing the results for the 2D FEA simulations showed that the fill height is not a significant variable with sloshing however the 3D FEA showed that the hydrostatic pressure is a significant variable. With the maximum tensile stress of the 3D-printed ABS being 24.4 MPa, the overall maximum stress of 5.45 MPa, the material can be a viable option for the use of QSD construction in small island developing states (SIDS)

    Adaptive Modeling of Details for Physically-based Sound Synthesis and Propagation

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    In order to create an immersive virtual world, it is crucial to incorporate a realistic aural experience that complements the visual sense. Physically-based sound simulation is a method to achieve this goal and automatically provides audio-visual correspondence. It simulates the physical process of sound: the pressure variations of a medium originated from some vibrating surface (sound synthesis), propagating as waves in space and reaching human ears (sound propagation). The perceived realism of simulated sounds depends on the accuracy of the computation methods and the computational resource available, and oftentimes it is not feasible to use the most accurate technique for all simulation targets. I propose techniques that model the general sense of sounds and their details separately and adaptively to balance the realism and computational costs of sound simulations. For synthesizing liquid sounds, I present a novel approach that generate sounds due to the vibration of resonating bubbles. My approach uses three levels of bubble modeling to control the trade-offs between quality and efficiency: statistical generation from liquid surface configuration,explicitly tracking of spherical bubbles, and decomposition of non-spherical bubbles to spherical harmonics. For synthesizing rigid-body contact sounds, I propose to improve the realism in two levels using example recordings: first, material parameters that preserve the inherent quality of the recorded material are estimated; then extra details from the example recording that are not fully captured by the material parameters are computed and added. For simulating sound propagation in large, complex scenes, I present a novel hybrid approach that couples numerical and geometric acoustic techniques. By decomposing the spatial domain of a scene and applying the more accurate and expensive numerical acoustic techniques only in limited regions, a user is able to allocate computation resources on where it matters most.Doctor of Philosoph
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