Category: Uncategorized

• Anisotropic Elasticity for Inversion-Safety and Element Rehabilitation
• CD-MPM: Continuum Damage Material Point Methods for Dynamic Fracture Animation
• Silly Rubber: An Implicit Material Point Method for Simulating Non-equilibrated Viscoelastic and Elastoplastic Solids
• Decomposed Optimization Time Integrator for Large-Step Elastodynamics
• Efficient and Conservative Fluids Using Bidirectional Mapping
• On Bubble Rings and Ink Chandeliers
• Mixing Sauces: A Viscosity Blending Model for Shear Thinning Fluids
• On the Accurate Large-scale Simulation of Ferrofluids
• An Adaptive Variational Finite Difference Framework for Efficient Symmetric Octree Viscosity
• REDMAX: Efficient and Flexible Approach for Articulated Dynamics
• Fundamental solutions for water wave animation
• Implicit Untangling: A Robust Solution for Modeling Layered Clothing
• Harmonic Triangulations
• Hand Modeling and Simulation Using Stabilized Magnetic Resonance Imaging

TOG:

• Analytic Eigensystems for Isotropic Distortion Energies
• Editing Fluid Animation using Flow Interpolation
• Interlinked SPH Pressure Solvers for Strong Rigid-Fluid Coupling
• Efficient and Accurate Collision Response for Elastically Deformable Models
• Poly-Spline Finite Element Method

Tetsuya Takahashi, Ming C. Lin.

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.

A Geometrically Consistent Viscous Fluid Solver with Two-Way Fluid-Solid Coupling

Andreas Enzenhoefer, Nicolas Lefebvre, Sheldon Andrews

Simulating stiff physical systems is a requirement for numerous computer graphics applications, such as VR training for heavy equipment operation. However, iterative linear solvers often perform poorly in such cases, and direct methods involving a factorization of the system matrix are typically preferred for accurate and stable simulations. This can have a detrimental impact on performance, since factorization of the system matrix is costly for complex simulations. In this paper, we present a method for efficiently solving linear systems of stiff physical systems involving contact, where the dynamics are modeled as a mixed linear complementarity problem (MLCP). Our approach is based on a block Bard-type algorithm that applies low-rank downdates to a Cholesky factorization of the system matrix at each pivoting step. Further performance improvements are realized by exploiting low bandwidth characteristics of the factorization. Our method gives up to 3.5 times speed-up versus recomputing the factorization based on the index set. Various challenging scenarios are used to demonstrate the advantages of our approach.

Efficient block pivoting for multibody simulations with contact

Alexander Brown, Gary Ushaw, Graham Morgan

In this paper we propose a solution to delivering scalable real-time physics simulations. Although high performance computing simulations of physics related problems do exist, these are not real-time and do not model the real-time intricate interactions of rigid bodies for visual effect common in video games (favouring accuracy over real-time). As such, this paper presents the first approach to real-time delivery of scalable, commercial grade, video game quality physics. This is achieved by taking the physics engine out of the player’s machine and deploying it across standard cloud based infrastructures. The simulation world is then divided into sections that are then allocated to servers. A server maintains the physics for all simulated objects in its section. Our contribution is the ability to maintain a scalable simulation by allowing object interaction across section boundaries using predictive migration techniques. We allow each object to project an aura that is used to determine object migration across servers to ensure seamless physics interactions between objects. The validity of our results is demonstrated through experimentation and benchmarking. Our approach allows player interaction at any point in real-time (influencing the simulation) in the same manner as any video game. We believe that this is the first successful demonstration of scalable real-time physics

Aura Projection for Scalable Real-Time Physics

Ounan Ding, Craig Schroeder

We propose a novel penalty force to enforce contacts with accurate Coulomb friction. The force is compatible with fully-implicit time integration and the use of optimization-based integration. The contact force is quite general. In addition to processing collisions between deformable objects, the force can be used to couple rigid bodies to deformable objects or the material point method.The force naturally leads to stable stacking without drift over time, even when solvers are not run to convergence. The force leads to an asymmetrical system, and we provide a practical solution for handling these.

Penalty Force for Coupling Materials with Coulomb Friction

Teseo Schneider, Yixin Hu, Jeremie Dumas, Xifeng Gao, Daniele Panozzo, Denis Zorin

For a given PDE problem, three main factors affect the accuracy of FEM solutions: basis order, mesh resolution, and mesh element quality. The first two factors are easy to control, while controlling element shape quality is a challenge, with fundamental limitations on what can be achieved. We propose to use p-refinement (increasing element degree) to decouple the approximation error of the finite element method from the domain mesh quality for elliptic PDEs. Our technique produces an accurate solution even on meshes with badly shaped elements, with a slightly higher running time due to the higher cost of high-order elements. We demonstrate that it is able to automatically adapt the basis to badly shaped elements, ensuring an error consistent with high-quality meshing, without any per-mesh parameter tuning. Our construction reduces to traditional fixed-degree FEM methods on high-quality meshes with identical performance. Our construction decreases the burden on meshing algorithms, reducing the need for often expensive mesh optimization and automatically compensates for badly shaped elements, which are present due to boundary constraints or limitations of current meshing methods. By tackling mesh generation and finite element simulation jointly, we obtain a pipeline that is both more efficient and more robust than combinations of existing state of the art meshing and FEM algorithms.

Decoupling Simulation Accuracy from Mesh Quality

• GPU Optimization of Material Point Methods
• Hybrid Grains: Adaptive Coupling of Discrete and Continuum Simulations of Granular Media
• Decoupling Simulation Accuracy from Mesh Quality
• Real-Time Viscous Thin Films
• I-Cloth: Incremental Collision Handling for GPU-Based Interactive Cloth Simulation
• Accurate Dissipative Forces in Optimization Integrators
• Inverse Elastic Shell Design with Contact and Friction
• Inexact Descent Methods for Elastic Parameter Optimization

Christian Schumacher, Steve Marschner, Markus Gross, Bernhard Thomaszewski

We propose a comprehensive approach to characterizing the mechanical properties of structured sheet materials, i.e., planar rod networks whose mechanics and aesthetics are inextricably linked. We establish a connection between the complex mesoscopic deformation behavior of such structures and their macroscopic elastic properties through numerical homogenization. Our approach leverages 3D Kirchhoff rod simulation in order to capture nonlinear effects for both in-plane and bending deformations. We apply our method to different families of structures based on isohedral tilings— a simple yet extensive and aesthetically interesting group of space-filling patterns. We show that these tilings admit a wide range of material properties, and our homogenization approach allows us to create concise and intuitive descriptions of a material’s direction-dependent macromechanical behavior that are easy to communicate even to non-experts. We perform this characterization for an extensive set of structures and organize these data in a material browser to enable efficient forward exploration of the aesthetic-mechanical space of structured sheet materials. We also propose an inverse design method to automatically find structure parameters that best approximate a user-specified target behavior.

Mechanical Characterization of Structured Sheet Materials

• Liquid Splash Modeling with Neural Networks
• Collision-Aware and Online Compression of Rigid Body Simulations via Integrated Error Minimization
• An Efficient Solver for Two-way Coupling Rigid Bodies with Incompressible Flow
• A Temporally Adaptive Material Point Method with Regional Time Stepping
• Time-Domain Parallelization for Accelerating Cloth Simulation
• Cable Joints
• Distributing and Load Balancing Sparse Fluid Simulations
• Coupled Fluid Density and Motion from Single Views
• Cosserat Rods with Projective Dynamics
• Fast Corotated FEM using Stiffness Matrix Splitting
• Strain Rate Dissipation for Elastic Deformations
• MPM simulation of interactive and reactive fluids and solids
• HairControl: A Tracking Solution for Directable Hair Simulation
• Realtime Performance Driven Physical Simulation for Facial Animation (CGF)
• Real-time High-fidelity Surface Flow Simulation (TVCG)
• A Skinned Tetrahedral Mesh for Hair Animation and Hair-Water Interaction (TVCG)

Zherong Pan., Dinesh Manocha

We present an efficient spacetime optimization method to automatically generate animations for a general volumetric, elastically deformable body. Our approach can model the interactions between the body and the environment and automatically generate active animations. We model the frictional contact forces using contact invariant optimization and the fluid drag forces using a simplified model. To handle complex objects, we use a reduced deformable model and present a novel hybrid optimizer to search for the local minima efficiently. This allows us to use long-horizon motion planning to automatically generate animations such as walking, jumping, swimming, and rolling. We evaluate the approach on different shapes and animations, including deformable body navigation and combining with an open-loop controller for realtime forward simulation.

Active Animations of Reduced Deformable Models with Environment Interactions