SCA: Eurographics/SIGGRAPH Symposium on Computer Animation

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Browsing SCA: Eurographics/SIGGRAPH Symposium on Computer Animation by Author "Batty, Christopher"

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    Divergence-Free and Boundary-Respecting Velocity Interpolation Using Stream Functions
    (ACM, 2019) Chang, Jumyung; Azevedo, Vinicius C.; Batty, Christopher; Batty, Christopher and Huang, Jin
    In grid-based fluid simulation, discrete incompressibility of each cell is enforced by the pressure projection. However, pointwise velocities constructed by interpolating the discrete velocity samples from the staggered grid are not truly divergence-free, resulting in unphysical local volume changes that manifests as particle spreading and clustering.We present a new velocity interpolation method that produces analytically divergence-free velocity fields in 2D using a stream function. The resulting fields are guaranteed to be divergence-free by a simple calculus identity: the curl of any vector field yields a divergence-free vector field. Furthermore, our method works on cut cell grids to produce fields that strictly obey solid boundary conditions. Therefore, no artificial gaps are created between fluid particles and solids, and fluid particles do not trespass into solid regions.
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    A Multilevel Active-Set Preconditioner for Box-Constrained Pressure Poisson Solvers
    (ACM Association for Computing Machinery, 2023) Takahashi, Tetsuya; Batty, Christopher; Wang, Huamin; Ye, Yuting; Victor Zordan
    Efficiently solving large-scale box-constrained convex quadratic programs (QPs) is an important computational challenge in physical simulation.We propose a new multilevel preconditioning scheme based on the active-set method and combine it with modified proportioning with reduced gradient projections (MPRGP) to efficiently solve such QPs arising from pressure Poisson equations with non-negative pressure constraints in fluid animation. Our method employs a purely algebraic multigrid method to ensure the solvability of the coarser level systems and to merge only algebraically-connected components, thereby avoiding performance degradation of the preconditioner. We present a filtering scheme to efficiently apply our multilevel preconditioning only to unconstrained subsystems of the pressure Poisson system while reusing the hierarchy constructed per simulation step. We demonstrate the effectiveness of our method over previous approaches in various examples.
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    Surface-Only Dynamic Deformables using a Boundary Element Method
    (The Eurographics Association and John Wiley & Sons Ltd., 2022) Sugimoto, Ryusuke; Batty, Christopher; Hachisuka, Toshiya; Dominik L. Michels; Soeren Pirk
    We propose a novel surface-only method for simulating dynamic deformables without the need for volumetric meshing or volumetric integral evaluations. While based upon a boundary element method (BEM) for linear elastodynamics, our method goes beyond simple adoption of BEM by addressing several of its key limitations. We alleviate large displacement artifacts due to linear elasticity by extending BEM with a moving reference frame and surface-only fictitious forces, so that it only needs to handle deformations. To reduce memory and computational costs, we present a simple and practical method to compress the series of dense matrices required to simulate propagation of elastic waves over time. Furthermore, we explore a constraint enforcement mechanism and demonstrate the applicability of our method to general computer animation problems, such as frictional contact.