vriphys13

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https://diglib.eg.org/handle/10.2312/4332

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    Rethinking Shortest Path: An Energy Expenditure Approach
    (The Eurographics Association, 2013) Mousas, Christos; Newbury, Paul; Anagnostopoulos, Christos-Nikolaos; Jan Bender and Jeremie Dequidt and Christian Duriez and Gabriel Zachmann
    Considering that humans acting in constrained environments do not always plan according to shortest path criteria. rather, they conceptually measure the path which minimises the amount of expended energy. Hence, virtual characters should be able to execute their paths according to planning methods based not on path length but on the minimisation of actual expended energy. Thus, in this paper, we introduce a simple method that uses a formula for computing vanadium dioxide (VO2) levels, which is a proxy for the energy expended by humans during various activities.
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    Initial Steps for the Coupling of JavaScript Physics Engines with X3DOM
    (The Eurographics Association, 2013) Huber, Linda; Jan Bender and Jeremie Dequidt and Christian Duriez and Gabriel Zachmann
    During the past years, first physics engines based on JavaScript have been developed for web applications. These are capable of displaying virtual scenes much more realistically. Thus, new application areas can be opened up, particularly with regard to the coupling of X3DOM-based 3D models. The advantage is that web-based applications are easily accessible to all users. Furthermore, such engines allow popularizing and presenting simulation results without having to compile large simulation software. This paper provides an overview and a comparison of existing JavaScript physics engines. It also introduces a guideline for the derivation of a physical model based on a 3D model in X3DOM. The aim of using JavaScript physics engines is not only to virtually visualize designed products but to simulate them as well. The user is able to check and test an individual product virtually and interactively in a browser according to physically correct behavior regarding gravity, friction or collision. It can be used for verification in the design phase or web-based training purposes.
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    Parallel Collision Detection in Constant Time
    (The Eurographics Association, 2013) Weller, Rene; Frese, Udo; Zachmann, Gabriel; Jan Bender and Jeremie Dequidt and Christian Duriez and Gabriel Zachmann
    We prove that the maximum number of intersecting pairs spheres between two sets of polydisperse sphere packings is linear in the worst case. This observation is the basis for a new collision detection algorithm. Our new approach guarantees a linear worst case running time for arbitrary 3D objects. Additionally, we present a parallelization of our new algorithm that runs in constant time, even in the worst case. Consequently, it is perfectly suited for all time-critical environments that allow only a fixed time budget for finding collision. Our implementation using CUDA shows collision detection at haptic rates for complex objects.
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    Tridiagonal Matrix Formulation for Inextensible Hair Strand Simulation
    (The Eurographics Association, 2013) Han, Dongsoo; Harada, Takahiro; Jan Bender and Jeremie Dequidt and Christian Duriez and Gabriel Zachmann
    This paper proposes a method to simulate inextensible hair strands using tridiagonal matrix formulation in which distance constraints are formulated as a linear system. The proposed method avoids constructing a full matrix explicitly. Instead, it takes advantage of the chain topology and serial indexing to formulate symmetric tridiagonal matrix. Furthermore, we use a linear distance constraint so that the constraint gradient can be easily formulated. With this matrix-free formulation, memory usage can be extremely lowered. Since the formulated matrix is diagonally dominant, we can solve it by an efficient direct solver. Comparing error (i.e., stretch of constraints) of the proposed constraint solver to ones of the position-based solver with different number of iterations, we show that error of the proposed method is much smaller than those of position-based solver. Also the simulation result shows mush less numerical damping compared to Dynamic Follow-The-Leader method. By implementing in GPU, we demonstrate that our proposed method is simple and efficient.
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    RPI-MATLAB-Simulator: A Tool for Efficient Research and Practical Teaching in Multibody Dynamics
    (The Eurographics Association, 2013) Williams, Jedediyah; Lu, Ying; Niebe, Sarah; Andersen, Michael; Erleben, Kenny; Trinkle, Jeffrey C.; Jan Bender and Jeremie Dequidt and Christian Duriez and Gabriel Zachmann
    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.
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    Physics-based Human Neck Simulation
    (The Eurographics Association, 2013) Luo, Zhiping; Pronost, Nicolas; Egges, Arjan; Jan Bender and Jeremie Dequidt and Christian Duriez and Gabriel Zachmann
    In deformable character animation, the skin deformation of the neck is important to reproduce believable facial animation. The neck also plays an important role in supporting the head in balance while generating the controlled head movements that are essential to many aspects of human behavior. However, neck animation is largely overlooked both in computer graphics and animation due to the complexity of the cervical anatomy. This paper presents a physical human neck model based on biomechanical modeling. Relevant anatomical structures part of a 3D model of the human musculoskeletal system are modeled as deformable or linked rigid bodies. We couple the soft-hard bodies using soft constraints via elastic springs and form a Lagrangian dynamic system. The simulation of dynamic skin deformation is achieved by automatically binding the skin vertices to underlying bodies in an anatomically correct manner. Experimental results are provided and show the high level of realism that our model offers. In addition, the simulation runs at interactive rates on a modern computer.
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    Exploring the Use of Adaptively Restrained Particles for Graphics Simulations
    (The Eurographics Association, 2013) Manteaux, Pierre-Luc; Faure, François; Redon, Stéphane; Cani, Marie-Paule; Jan Bender and Jeremie Dequidt and Christian Duriez and Gabriel Zachmann
    In this paper, we explore the use of Adaptively Restrained (AR) particles for graphics simulations. Contrary to previous methods, Adaptively Restrained Particle Simulations (ARPS) do not adapt time or space sampling, but rather switch the positional degrees of freedom of particles on and off, while letting their momenta evolve. Therefore, inter-particles forces do not have to be updated at each time step, in contrast with traditional methods that spend a lot of time there. We present the initial formulation of ARPS that was introduced for molecular dynamics simulations, and explore its potential for Computer Graphics applications: We first adapt ARPS to particle-based fluid simulations and propose an efficient incremental algorithm to update forces and scalar fields. We then introduce a new implicit integration scheme enabling to use ARPS for cloth simulation as well. Our experiments show that this new, simple strategy for adaptive simulations can provide significant speedups more easily than traditional adaptive models.
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    Physically-Based Character Skinning
    (The Eurographics Association, 2013) Deul, Crispin; Bender, Jan; Jan Bender and Jeremie Dequidt and Christian Duriez and Gabriel Zachmann
    In this paper we present a novel multi-layer model for physically-based character skinning. In contrast to geometric approaches which are commonly used in the field of character skinning, physically-based methods can simulate secondary motion effects. Furthermore, these methods can handle collisions and preserve the volume of the model without the need of an additional post-process. Physically-based approaches are computationally more expensive than geometric methods but they provide more realistic results. Recent works in this area use finite element simulations to model the elastic behavior of skin. These methods require the generation of a volumetric mesh for the skin shape in a pre-processing step. It is not easy for an artist to model the different elastic behaviors of muscles, fat and skin using a volumetric mesh since there is no clear assignment between volume elements and tissue types. For our novel multi-layer model the mesh generation is very simple and can be performed automatically. Furthermore, the model contains a layer for each kind of tissue. Therefore, the artist can easily control the elastic behavior by adjusting the stiffness parameters for muscles, fat and skin. We use shape matching with oriented particles and a fast summation technique to simulate the elastic behavior of our skin model and a position-based constraint enforcement to handle collisions, volume conservation and the coupling of the skeleton with the deformable model. Position-based methods have the advantage that they are fast, unconditionally stable, controllable and provide visually plausible results.
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    Connective Tissues Simulation on GPU
    (The Eurographics Association, 2013) Bosman, Julien; Duriez, Christian; Cotin, Stéphane; Jan Bender and Jeremie Dequidt and Christian Duriez and Gabriel Zachmann
    Recent work in the field of medical simulation have led to real advances in the mechanical simulation of organs. However, it is important to notice that, despite the major role they may have in the interaction between organs, the connective tissues are often left out of these simulations. In this paper, we propose a model which can rely on either a mesh based or a meshless methods. To provide a realistic simulation of these tissues, our work is based on the weak form of continuum mechanics equations for hyperelastic soft materials. Furthermore, the stability of deformable objects simulation is ensured by an implicit temporal integration scheme. Our method allows to model these tissues without prior assumption on the dimension of their of their geometry (curve, surface or volume), and enables mechanical coupling between organs. To obtain an interactive frame rate, we develop a parallel version suitable for to GPU computation. Finally we demonstrate the proper convergence of our finite element scheme.
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    Multilevel Cloth Simulation using GPU Surface Sampling
    (The Eurographics Association, 2013) Schmitt, Nikolas; Knuth, Martin; Bender, Jan; Kuijper, Arjan; Jan Bender and Jeremie Dequidt and Christian Duriez and Gabriel Zachmann
    Today most cloth simulation systems use triangular mesh models. However, regular grids allow many optimizations as connectivity is implicit, warp and weft directions of the cloth are aligned to grid edges and distances between particles are equal. In this paper we introduce a cloth simulation that combines both model types. All operations that are performed on the CPU use a low-resolution triangle mesh while GPU-based methods are performed efficiently on a high-resolution grid representation. Both models are coupled by a sampling operation which renders triangle vertex data into a texture and by a corresponding projection of texel data onto a mesh. The presented scheme is very flexible and allows individual components to be performed on different architectures, data representations and detail levels. The results are combined using shader programs which causes a negligible overhead. We have implemented CPU-based collision handling and a GPU-based hierarchical constraint solver to simulate systems with more than 230k particles in real-time.