SIGGRAPH 2015

It’s my favourite time of the year. Stay tuned for more simulation paper links as they appear. As usual, see Ke-Sen Huang’s page for the full list.

  • A Stream Function Solver for Liquid Simulations
  • Power Particles: An incompressible fluid solver based on power diagrams
  • Double Bubbles Sans Toil and Trouble: Discrete Circulation-Preserving Vortex Sheets for Soap Films and Foams
  • Air Meshes for Robust Collision Handling
  • Fast Grid-Free Surface Tracking
  • Deformation Capture and Modeling of Soft Objects
  • Simulating Rigid Body Fracture with Surface Meshes
  • Restoring the Missing Vortices in Advection Projection Fluid Solvers

 

TOG papers:

Water Wave Animation via Wavefront Parameter Interpolation

Stefan Jeschke, Chris Wojtan

We present an efficient wavefront tracking algorithm for animating bodies of water that interact with their environment. Our contributions include: a novel wavefront tracking technique that enables dispersion, refraction, reflection, and diffraction in the same simulation; a unique multi-valued function interpolation method that enables our simulations to elegantly sidestep the Nyquist limit; a dispersion approximation for efficiently amplifying the number of simulated waves by several orders of magnitude; and additional extensions that allow for time-dependent effects and interactive artistic editing of the resulting animation. Our contributions combine to give us multitudes more wave details than similar algorithms, while maintaining high frame rates and allowing close camera zooms.

Water Wave Animation via Wavefront Parameter Interpolation

Scalable Partitioning for Parallel Position Based Dynamics

Marco Fratarcangeli, Fabio Pellacini

We introduce a practical partitioning technique designed for parallelizing Position Based Dynamics, and exploit- ing the ubiquitous multi-core processors present in current commodity GPUs. The input is a set of particles whose dynamics is influenced by spatial constraints. In the initialization phase, we build a graph in which each node corresponds to a constraint and two constraints are connected by an edge if they influence at least one com- mon particle. We introduce a novel greedy algorithm for inserting additional constraints (phantoms) in the graph such that the resulting topology is qˆ-colourable, where qˆ ≥ 2 is an arbitrary number. We color the graph, and the constraints with the same color are assigned to the same partition. Then, the set of constraints belonging to each partition is solved in parallel during the animation phase. We demonstrate this by using our partitioning technique; the performance hit caused by the GPU kernel calls is significantly decreased, leaving unaffected the visual quality, robustness and speed of serial position based dynamics.

Scalable Partitioning for Parallel Position Based Dynamics

Implicit Formulation for SPH-Based Viscous Fluids

Tetsuya Takahashi, Yoshinori Dobashi, Issei Fujishiro, Tomoyuki Nishita, Ming C. Lin

We propose a stable and efficient particle-based method for simulating highly viscous fluids that can generate coiling and buckling phenomena and handle variable viscosity. In contrast to previous methods that use explicit integration, our method uses an implicit formulation to improve the robustness of viscosity integration, therefore enabling use of larger time steps and higher viscosities. We use Smoothed Particle Hydrodynamics to solve the full form of viscosity, constructing a sparse linear system with a symmetric positive definite matrix, while exploiting the variational principle that automatically enforces the boundary condition on free surfaces. We also propose a new method for extracting coefficients of the matrix contributed by second-ring neighbor particles to efficiently solve the linear system using a conjugate gradient solver. Several examples demonstrate the robustness and efficiency of our implicit formulation over previous methods and illustrate the versatility of our method.

Implicit Formulation for SPH-Based Viscous Fluids

Eurographics 2015

Physics-based animation papers at Eurographics 2015:

A Dimension-reduced Pressure Solver for Liquid Simulations

Ryoichi Ando, Nils Thuerey, Chris Wojtan

This work presents a method for efficiently simplifying the pressure projection step in a liquid simulation. We first devise a straightforward dimension reduction technique that dramatically reduces the cost of solving the pressure projection. Next, we introduce a novel change of basis that satisfies free-surface boundary conditions {\em exactly}, regardless of the accuracy of the pressure solve. When combined, these ideas greatly reduce the computational complexity of the pressure solve without compromising free surface boundary conditions at the highest level of detail. Our techniques are easy to parallelize, and they effectively eliminate the computational bottleneck for large liquid simulations.

A Dimension-reduced Pressure Solver for Liquid Simulations

 

Yarn-Level Simulation of Woven Cloth

Gabriel Cirio, Jorge Lopez-Moreno, David Miraut, Miguel A. Otaduy

The large-scale mechanical behavior of woven cloth is determined by the mechanical properties of the yarns, the weave pattern, and frictional contact between yarns. Using standard simulation methods for elastic rod models and yarn-yarn contact handling, the simulation of woven garments at realistic yarn densities is deemed intractable. This paper introduces an efficient solution for simulating woven cloth at the yarn level. Central to our solution is a novel discretization of interlaced yarns based on yarn crossings and yarn sliding, which allows modeling yarn-yarn contact implicitly, avoiding contact handling at yarn crossings altogether. Combined with models for internal yarn forces and inter-yarn frictional contact, as well as a massively parallel solver, we are able to simulate garments with hundreds of thousands of yarn crossings at practical framerates on a desktop machine, showing combinations of large-scale and fine-scale effects induced by yarn-level mechanics.

Yarn-Level Simulation of Woven Cloth

Interactive Material Design Using Model Reduction

Hongyi Xu, Yijing Li, Yong Chen, Jernej Barbic

We demonstrate an interactive method to create heterogeneous continuous deformable materials on complex three-dimensional meshes. The user specifies displacements and internal elastic forces at a chosen set of mesh vertices. Our system then rapidly solves an optimization problem to compute a corresponding heterogeneous spatial distribution of material properties, using the Finite Element Method (FEM) analysis. We apply our method to linear and nonlinear isotropic deformable materials. We demonstrate that solving the problem interactively in the full-dimensional space of individual tetrahedron material values is not practical. Instead, we propose a new model reduction method that projects the material space to a low dimensional space of material modes. Our model reduction accelerates optimization by two orders of magnitude, and makes the convergence much
more robust, making it possible to interactively design material distributions on complex meshes.We apply our method to precise control of contact forces and control of pressure over large contact areas between rigid and deformable objects for ergonomics. Our tetrahedron-based dithering method can efficiently convert continuous material distributions into discrete ones and we demonstrate its precision via FEM simulation. We physically display our distributions using haptics, as well as demonstrate how haptics can aid in the material design. The produced heterogeneous material distributions can also be used in computer animation applications.

Interactive Material Design Using Model Reduction

Realistic Biomechanical Simulation and Control of Human Swimming

Weiguang Si, Sung-Hee Lee, Eftychios Sifakis, Demetri Terzopoulos

We address the challenging problem of controlling a complex biomechanical model of the human body to synthesize realistic swimming animation. Our human model includes all of the relevant articular bones and muscles, including 103 bones (comprising 163 articular degrees of freedom) plus a total of 823 muscle actuators embedded in a finite element model of the musculotendinous soft tissues of the body that produces realistic deformations. To coordinate the numerous muscle actuators in order to produce natural swimming movements, we develop a biomimetically motivated motor control system based on Central Pattern Generators (CPG), which learns to produce activation signals that drive the numerous muscle actuators.

Realistic Biomechanical Simulation and Control of Human Swimming

Strain Limiting for Clustered Shape Matching

Adam W. Bargteil, Ben Jones

In this paper, we advocate explicit symplectic Euler integration and strain limiting in a shape matching simulation framework. The resulting approach resembles not only previous work on shape matching and strain limiting, but also the recently popular position-based dynamics.However, unlike this previous work, our approach reduces to explicit integration under small strains, but remains stable in the presence of non-linearities.

Strain Limiting for Clustered Shape Matching