Browsing by Author "Takahashi, Tetsuya"

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    An Efficient Hybrid Incompressible SPH Solver with Interface Handling for Boundary Conditions
    (© 2018 The Eurographics Association and John Wiley & Sons Ltd., 2018) Takahashi, Tetsuya; Dobashi, Yoshinori; Nishita, Tomoyuki; Lin, Ming C.; Chen, Min and Benes, Bedrich
    We propose a hybrid smoothed particle hydrodynamics solver for efficientlysimulating incompressible fluids using an interface handling method for boundary conditions in the pressure Poisson equation. We blend particle density computed with one smooth and one spiky kernel to improve the robustness against both fluid–fluid and fluid–solid collisions. To further improve the robustness and efficiency, we present a new interface handling method consisting of two components: free surface handling for Dirichlet boundary conditions and solid boundary handling for Neumann boundary conditions. Our free surface handling appropriately determines particles for Dirichlet boundary conditions using Jacobi‐based pressure prediction while our solid boundary handling introduces a new term to ensure the solvability of the linear system. We demonstrate that our method outperforms the state‐of‐the‐art particle‐based fluid solvers.We propose a hybrid smoothed particle hydrodynamics solver for efficiently simulating incompressible fluids using an interface handling method for boundary conditions in the pressure Poisson equation. We blend particle density computed with one smooth and one spiky kernel to improve the robustness against both fluid–fluid and fluid–solid collisions.To further improve the robustness and efficiency, we present a new interface handling method consisting of two components: free surface handling for Dirichlet boundary conditions and solid boundary handling for Neumann boundary conditions.
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    A Geometrically Consistent Viscous Fluid Solver with Two-Way Fluid-Solid Coupling
    (The Eurographics Association and John Wiley & Sons Ltd., 2019) Takahashi, Tetsuya; Lin, Ming C.; Alliez, Pierre and Pellacini, Fabio
    We present a grid-based fluid solver for simulating viscous materials and their interactions with solid objects. Our method formulates the implicit viscosity integration as a minimization problem with consistently estimated volume fractions to account for the sub-grid details of free surfaces and solid boundaries. To handle the interplay between fluids and solid objects with viscosity forces, we also formulate the two-way fluid-solid coupling as a unified minimization problem based on the variational principle, which naturally enforces the boundary conditions. Our formulation leads to a symmetric positive definite linear system with a sparse matrix regardless of the monolithically coupled solid objects. Additionally, we present a position-correction method using density constraints to enforce the uniform distributions of fluid particles and thus prevent the loss of fluid volumes. We demonstrate the effectiveness of our method in a wide range of viscous fluid scenarios.
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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.