Photon Differential Splatting for Rendering Caustics

Jeppe Revall Frisvad, Lars Schjøth, Kenny Erleben, and Jon Sporring

We present a photon splatting technique which reduces noise and blur in the rendering of caustics. Blurring of illumination edges is an inherent problem in photon splatting, as each photon is unaware of its neighbours when being splatted. This means that the splat size is usually based on heuristics rather than knowledge of the local flux density. We use photon differentials to determine the size and shape of the splats such that we achieve adaptive anisotropic flux density estimation in photon splatting. As compared to previous work that uses photon differentials, we present the first method where no photons or beams or differentials need to be stored in a map. We also present improvements in the theory of photon differentials, which give more accurate results and a faster implementation. Our technique has good potential for GPU acceleration, and we limit the number of parameters requiring user adjustment to an overall smoothing parameter and the number of photons to be traced.

Computer Graphics Forum early view

Moving Conforming Contact Manifolds and related Numerical Problems

Kenny Erleben

Talk at BIRS workshop on “Computational Contact Mechanics: Advances and Frontiers in Modeling Contact”

Slides download

Workshop link

Conforming Contact Manifolds for Multibody Simulations

Vincent Visseq, Ulrik Bonde, Marek K. Misztal and Kenny Erleben

Computer simulation of physical phenomena involving contact mechanics is of great in- terest to many fields of research and industries. New applications, such as biomedical simulations, are appealing for the modelling of soft materials and sliding contact. Several different approaches have been developed over the last four decades to formulate con- tact constraints for numerical simulation methods. In the finite element method, mortar meshes, Lagrange multipliers and penalty approaches are widely used to handle con- tact constraints. We propose to develop a new simulation framework providing conform- ing contact manifolds for deformable multibody dynamics, based on the Moving Meshes framework.

Abstract download

Disjoint Domains Interactions Framework for Hyperelastic Simulations

Ulrik Bonde, Marek K. Misztal, Vincent Visseq and Kenny Erleben

Contact interactions in the modeling of biomechanical systems are often simplified as Dirichlet or Neumann boundary conditions. The aim of this work is to propose a generic framework for the simulation of biomechanical disjoint domains and large transformations.

Abstract download



RPI-MATLAB-Simulator: A tool for efficient research and practical teaching in multibody dynamics

Jedediyah Williams, Ying Lu, Sarah Niebe, Michael Andersen, Kenny Erleben, and Jeff C. Trinkle

We present the RPI-MATLAB-Simulator (RPIsim) as an open source tool for research and education in multibody dynamics. RPIsim is designed and organized to be extended. Its modular design allows users to edit or add new components without worrying about extra implementation details. RPIsim has two main goals: 1. Provide an intuitive and easily extendable platform for research and education in multibody dynamics; 2. Maintain an evolving code base of useful algorithms and analysis tools for multibody dynamics problems. Although research often focuses on a specific subset of problems, work too often begins with developing software in a broader scope simply to realize a test bed for research to begin. It is our hope that RPIsim alleviates some of this burden by decreasing development time, thusly increasing efficiency in research. Further, we aim to provide a practical teaching tool. Because it is a fully working simulator, and since it offers the instant gratification of visualized contact dynamics, RPIsim offers students the opportunity to experiment and explore dynamics in the powerful environment of MATLAB. With multiple built-in simulation methods, and support for a simulation data convention, RPIsim facilitates the fair comparison of methods, including those being developed with RPIsim.

Paper download
RPI MATLAB Simulator here

Multiphase Flow of Immiscible Fluids on Unstructured Moving Meshes

Marek. K. Misztal, Kenny Erleben, Adam Bargteil, Jens Fursund, Brian Bunch Christensen, J. Andreas. Bærentzen and Robert Bridson

In this paper, we present a method for animating multiphase flow of immiscible fluids using unstructured moving meshes. Our underlying discretization is an unstructured tetrahedral mesh, the deformable simplicial complex (DSC), that moves with the flow in a Lagrangian manner. Mesh optimization operations improve element quality and avoid element inversion. In the context of multiphase flow, we guarantee that every element is occupied by a single fluid and, consequently, the interface between fluids is represented by a set of faces in the simplicial complex. This approach ensures that the underlying discretization matches the physics and avoids the additional book-keeping required in grid-based methods where multiple fluids may occupy the same cell. Our Lagrangian approach naturally leads us to adopt a finite element approach to simulation, in contrast to the finite volume approaches adopted by a majority of fluid simulation techniques that use tetrahedral meshes. We characterize fluid simulation as an optimization problem allowing for full coupling of the pressure and velocity fields and the incorporation of a second-order surface energy. We introduce a preconditioner based on the diagonal Schur complement and solve our optimization on the GPU. We provide the results of parameter studies as well as a performance analysis of our method, together with suggestions for performance optimization.

Authors Copy here
CS Digital Library go
Extended Journal Version of SCA ’12 best paper

Numerical Methods for Linear Complementarity Problems in Physics-Based Animation

Authors Kenny Erleben ( 2013 )

This course provides an introduction to the definition of linear complementarity problems (LCPs) and outlines the derivation of a toolbox of numerical methods. It also presents a small convergence study on the methods to illustrate their numerical properties. The course is a good introduction to implementing numerical methods, because it includes tips and tricks for implementation based on considerable practical experience.

SIGGRAPH Course Webpage here
Software here
Course Notes here
Course slides and rigid ball simulator exercise here

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