5 research outputs found

    Robust interactive simulation of deformable solids with detailed geometry using corotational FEM

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    This thesis focuses on the interactive simulation of highly detailed deformable solids modelled with the Corotational Finite Element Method. Starting from continuum mechanics we derive the discrete equations of motion and present a simulation scheme with support for user-in-the-loop interaction, geometric constraints and contact treatment. The interplay between accuracy and computational cost is discussed in depth, and practical approximations are analyzed with an emphasis on robustness and efficiency, as required by interactive simulation. The first part of the thesis focuses on deformable material discretization using the Finite Element Method with simplex elements and a corotational linear constitutive model, and presents our contributions to the solution of widely reported robustness problems in case of large stretch deformations and finite element degeneration. First,we introduce a stress differential approximation for quasi-implicit corotational linear FEM that improves its results for large deformations and closely matches the fullyimplicit solution with minor computational overhead. Next, we address the problem ofrobustness and realism in simulations involving element degeneration, and show that existing methods have previously unreported flaws that seriously threaten robustness and physical plausibility in interactive applications. We propose a new continuous-time approach, degeneration-aware polar decomposition, that avoids such flaws and yields robust degeneration recovery. In the second part we focus on geometry representation and contact determination for deformable solids with highly detailed surfaces. Given a high resolution closed surface mesh we automatically build a coarse embedding tetrahedralization and a partitioned representation of the collision geometry in a preprocess. During simulation, our proposed contact determination algorithm finds all intersecting pairs of deformed triangles using a memory-efficient barycentric bounding volume hierarchy, connects them into potentially disjoint intersection curves and performs a topological flood process on the exact intersection surfaces to discover a minimal set of contact points. A novel contact normal definition is used to find contact point correspondences suitable for contact treatment.Aquesta tesi tracta sobre la simulaci贸 interactiva de s貌lids deformables amb superf铆cies detallades, modelats amb el M猫tode dels Elements Finits (FEM) Corotacionals. A partir de la mec脿nica del continuu derivem les equacions del moviment discretes i presentem un esquema de simulaci贸 amb suport per a interacci贸 d'usuari, restriccions geom猫triques i tractament de contactes. Aprofundim en la interrelaci贸 entre precisi贸 i cost de computaci贸, i analitzem aproximacions pr脿ctiques fent 猫mfasi en la robustesa i l'efici猫ncia necess脿ries per a la simulaci贸 interactiva. La primera part de la tesi es centra en la discretitzaci贸 del material deformable mitjan莽ant el M猫tode dels Elements Finits amb elements de tipus s'implex i un model constituent basat en elasticitat linial corotacional, i presenta les nostres contribucions a la soluci贸 de problemes de robustesa 脿mpliament coneguts que apareixen en cas de sobreelongament i degeneraci贸 dels elements finits. Primer introdu茂m una aproximaci贸 dels diferencials d'estress per a FEM linial corotacional amb integraci贸 quasi-impl铆cita que en millora els resultats per a deformacions grans i s'apropa a la soluci贸 impl铆cita amb un baix cost computacional. A continuaci贸 tractem el problema de la robustesa i el realisme en simulacions que inclouen degeneraci贸 d'elements finits, i mostrem que els m猫todes existents presenten inconvenients que posen en perill la robustesa plausibilitat de la simulaci贸 en aplicacions interactives. Proposem un enfocament nou basat en temps continuu, la descomposici贸 polar amb coneixement de degeneraci贸, que evita els inconvenients esmentats i permet corregir la degeneraci贸 de forma robusta. A la segona part de la tesi ens centrem en la representaci贸 de geometria i la determinaci贸 de contactes per a s貌lids deformables amb superf铆cies detallades. A partir d'una malla de superf铆cie tancada constru铆m una tetraedralitzaci贸 englobant de forma autom脿tica en un preproc茅s, i particionem la geometria de colisi贸. Proposem un algorisme de detecci贸 de contactes que troba tots els parells de triangles deformats que intersecten mitjan莽ant una jerarquia de volums englobants en coordenades baric猫ntriques, els connecta en corbes d'intersecci贸 potencialment disjuntes i realitza un proc茅s d'inundaci贸 topol貌gica sobre les superf铆cies d'intersecci贸 exactes per tal de descobrir un conjunt m铆nim de punts de contacte. Usem una definici贸 nova de la normal de contacte per tal de calcular correspond猫ncies entre punts de contacte 煤tils per al seu tractament.Postprint (published version

    Doctor of Philosophy

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    dissertationPhysical simulation has become an essential tool in computer animation. As the use of visual effects increases, the need for simulating real-world materials increases. In this dissertation, we consider three problems in physics-based animation: large-scale splashing liquids, elastoplastic material simulation, and dimensionality reduction techniques for fluid simulation. Fluid simulation has been one of the greatest successes of physics-based animation, generating hundreds of research papers and a great many special effects over the last fifteen years. However, the animation of large-scale, splashing liquids remains challenging. We show that a novel combination of unilateral incompressibility, mass-full FLIP, and blurred boundaries is extremely well-suited to the animation of large-scale, violent, splashing liquids. Materials that incorporate both plastic and elastic deformations, also referred to as elastioplastic materials, are frequently encountered in everyday life. Methods for animating such common real-world materials are useful for effects practitioners and have been successfully employed in films. We describe a point-based method for animating elastoplastic materials. Our primary contribution is a simple method for computing the deformation gradient for each particle in the simulation. Given the deformation gradient, we can apply arbitrary constitutive models and compute the resulting elastic forces. Our method has two primary advantages: we do not store or compare to an initial rest configuration and we work directly with the deformation gradient. The first advantage avoids poor numerical conditioning and the second naturally leads to a multiplicative model of deformation appropriate for finite deformations. One of the most significant drawbacks of physics-based animation is that ever-higher fidelity leads to an explosion in the number of degrees of freedom

    OGO program summary

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    An overview of the OGO program is presented. Brief descriptions of the six OGO spacecraft, and the experiments on each are included

    Large space structures and systems in the space station era: A bibliography with indexes (supplement 05)

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    Bibliographies and abstracts are listed for 1363 reports, articles, and other documents introduced into the NASA scientific and technical information system between January 1, 1991 and July 31, 1992. Topics covered include technology development and mission design according to system, interactive analysis and design, structural and thermal analysis and design, structural concepts and control systems, electronics, advanced materials, assembly concepts, propulsion and solar power satellite systems
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