SCA 09: Eurographics/SIGGRAPH Symposium on Computer Animation

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https://diglib.eg.org/handle/10.2312/427

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Browsing SCA 09: Eurographics/SIGGRAPH Symposium on Computer Animation by Subject "Computational Geometry and Object Modeling"

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    Accurate Tangential Velocities For Solid Fluid Coupling
    (ACM SIGGRAPH / Eurographics Association, 2009) Robinson-Mosher, Avi; English, R. Elliot; Fedkiw, Ronald; Eitan Grinspun and Jessica Hodgins
    We propose a novel method for obtaining more accurate tangential velocities for solid fluid coupling. Our method works for both rigid and deformable objects as well as both volumetric objects and thin shells. The fluid can be either one phase such as smoke or two phase such as water with a free surface. The coupling between the solid and the fluid can either be one-way with kinematic solids or fully two-way coupled. The only previous scheme that was general enough to handle both two-way coupling and thin shells required a mass lumping strategy that did not allow for freely flowing tangential velocities. Similar to that previous work, our method prevents leaking of fluid across a thin shell, however unlike that work our method does not couple the tangential velocities in any fashion, allowing for the proper slip independently on each side of the body. Moreover, since it accurately and directly treats the tangential velocity, it does not rely on grid refinement to obtain a reasonable solution. Therefore, it gives a highly improved result on coarse meshes.
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    Energy Stability and Fracture for Frame Rate Rigid Body Simulations
    (ACM SIGGRAPH / Eurographics Association, 2009) Su, Jonathan; Schroeder, Craig; Fedkiw, Ronald; Eitan Grinspun and Jessica Hodgins
    Our goal is to design robust algorithms that can be used for building real-time systems, but rather than starting with overly simplistic particle-based methods, we aim to modify higher-end visual effects algorithms. A major stumbling block in utilizing these visual effects algorithms for real-time simulation is their computational intensity. Physics engines struggle to fully exploit available resources to handle high scene complexity due to their need to divide those resources among many smaller time steps, and thus to obtain the maximum spatial complexity we design our algorithms to take only one time step per frame. This requires addressing both accuracy and stability issues for collisions, contact, and evolution in a manner significantly different from a typical simulation in which one can rely on shrinking the time step to ameliorate accuracy and stability issues. In this paper we present a novel algorithm for conserving both energy and momentum when advancing rigid body orientations, as well as a novel technique for clamping energy gain during contact and collisions. We also introduce a technique for fast and realistic fracture of rigid bodies using a novel collision-centered prescoring algorithm.
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    Spatial Deformation Transfer
    (ACM SIGGRAPH / Eurographics Association, 2009) Ben-Chen, Mirela; Weber, Ofir; Gotsman, Craig; Eitan Grinspun and Jessica Hodgins
    Much effort is invested in generating natural deformations of three-dimensional shapes. Deformation transfer simplifies this process by allowing to infer deformations of a new shape from existing deformations of a similar shape. Current deformation transfer methods can be applied only to shapes which are represented as a single component manifold mesh, hence their applicability to real-life 3D models is somewhat limited. We propose a novel deformation transfer method, which can be applied to a variety of shape representations tet-meshes, polygon soups and multiple-component meshes. Our key technique is deformation of the space in which the shape is embedded. We approximate the given source deformation by a harmonic map using a set of harmonic basis functions. Then, given a sparse set of user-selected correspondence points between the source and target shapes, we generate a deformation of the target shape which has differential properties similar to those of the source deformation. Our method requires only the solution of linear systems of equations, and hence is very robust and efficient. We demonstrate its applicability on a wide range of deformations, for different shape representations.