Browsing by Author "Jeschke, Stefan"

Now showing 1 - 7 of 7
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    Cloth and Skin Deformation with a Triangle Mesh Based Convolutional Neural Network
    (The Eurographics Association and John Wiley & Sons Ltd., 2020) Chentanez, Nuttapong; Macklin, Miles; Müller, Matthias; Jeschke, Stefan; Kim, Tae-Yong; Bender, Jan and Popa, Tiberiu
    We introduce a triangle mesh based convolutional neural network. The proposed network structure can be used for problems where input and/or output are defined on a manifold triangle mesh with or without boundary. We demonstrate its applications in cloth upsampling, adding back details to Principal Component Analysis (PCA) compressed cloth, regressing clothing deformation from character poses, and regressing hand skin deformation from bones' joint angles. The data used for training in this work are generated from high resolution extended position based dynamics (XPBD) physics simulations with small time steps and high iteration counts and from an offline FEM simulator, but it can come from other sources. The inference time of our prototype implementation, depending on the mesh resolution and the network size, can provide between 4 to 134 times faster than a GPU based simulator. The inference also only needs to be done for meshes currently visible by the camera.
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    Detailed Rigid Body Simulation with Extended Position Based Dynamics
    (The Eurographics Association and John Wiley & Sons Ltd., 2020) Müller, Matthias; Macklin, Miles; Chentanez, Nuttapong; Jeschke, Stefan; Kim, Tae-Yong; Bender, Jan and Popa, Tiberiu
    We present a rigid body simulation method that can resolve small temporal and spatial details by using a quasi explicit integration scheme that is unconditionally stable. Traditional rigid body simulators linearize constraints because they operate on the velocity level or solve the equations of motion implicitly thereby freezing the constraint directions for multiple iterations. Our method always works with the most recent constraint directions. This allows us to trace high speed motion of objects colliding against curved geometry, to reduce the number of constraints, to increase the robustness of the simulation, and to simplify the formulation of the solver. In this paper we provide all the details to implement a fully fledged rigid body solver that handles contacts, a variety of joint types and the interaction with soft objects.
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    Learning Physics with a Hierarchical Graph Network
    (The Eurographics Association and John Wiley & Sons Ltd., 2022) Chentanez, Nuttapong; Jeschke, Stefan; Müller, Matthias; Macklin, Miles; Dominik L. Michels; Soeren Pirk
    We propose a hierarchical graph for learning physics and a novel way to handle obstacles. The finest level of the graph consist of the particles itself. Coarser levels consist of the cells of sparse grids with successively doubling cell sizes covering the volume occupied by the particles. The hierarchical structure allows for the information to propagate at great distance in a single message passing iteration. The novel obstacle handling allows the simulation to be obstacle aware without the need for ghost particles. We train the network to predict effective acceleration produced by multiple sub-steps of 3D multi-material material point method (MPM) simulation consisting of water, sand and snow with complex obstacles. Our network produces lower error, trains up to 7.0X faster and inferences up to 11.3X faster than [SGGP*20]. It is also, on average, about 3.7X faster compared to Taichi Elements simulation running on the same hardware in our tests.
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    Making Procedural Water Waves Boundary-aware
    (The Eurographics Association and John Wiley & Sons Ltd., 2020) Jeschke, Stefan; Hafner, Christian; Chentanez, Nuttapong; Macklin, Miles; Müller-Fischer, Matthias; Wojtan, Chris; Bender, Jan and Popa, Tiberiu
    The ''procedural'' approach to animating ocean waves is the dominant algorithm for animating larger bodies of water in interactive applications as well as in off-line productions - it provides high visual quality with a low computational demand. In this paper, we widen the applicability of procedural water wave animation with an extension that guarantees the satisfaction of boundary conditions imposed by terrain while still approximating physical wave behavior. In combination with a particle system that models wave breaking, foam, and spray, this allows us to naturally model waves interacting with beaches and rocks. Our system is able to animate waves at large scales at interactive frame rates on a commodity PC.
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    Physically Based Shape Matching
    (The Eurographics Association and John Wiley & Sons Ltd., 2022) Müller, Matthias; Macklin, Miles; Chentanez, Nuttapong; Jeschke, Stefan; Dominik L. Michels; Soeren Pirk
    The shape matching method is a popular approach to simulate deformable objects in interactive applications due to its stability and simplicity. An important feature is that there is no need for a mesh since the method works on arbitrary local groups within a set of particles. A major drawback of shape matching is the fact that it is geometrically motivated and not derived from physical principles which makes calibration difficult. The fact that the method does not conserve volume can yield visual artifacts, e.g. when a tire is compressed but does not bulge. In this paper we present a new meshless simulation method that is related to shape matching but derived from continuous constitutive models. Volume conservation and stiffness can be specified with physical parameters. Further, if the elements of a tetrahedral mesh are used as groups, our method perfectly reproduces FEM based simulations.
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    Primal/Dual Descent Methods for Dynamics
    (The Eurographics Association and John Wiley & Sons Ltd., 2020) Macklin, Miles; Erleben, Kenny; Müller, Matthias; Chentanez, Nuttapong; Jeschke, Stefan; Kim, Tae-Yong; Bender, Jan and Popa, Tiberiu
    We examine the relationship between primal, or force-based, and dual, or constraint-based formulations of dynamics. Variational frameworks such as Projective Dynamics have proved popular for deformable simulation, however they have not been adopted for contact-rich scenarios such as rigid body simulation. We propose a new preconditioned frictional contact solver that is compatible with existing primal optimization methods, and competitive with complementarity-based approaches. Our relaxed primal model generates improved contact force distributions when compared to dual methods, and has the advantage of being differentiable, making it well-suited for trajectory optimization. We derive both primal and dual methods from a common variational point of view, and present a comprehensive numerical analysis of both methods with respect to conditioning. We demonstrate our method on scenarios including rigid body contact, deformable simulation, and robotic manipulation.
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    Small Steps in Physics Simulation
    (ACM, 2019) Macklin, Miles; Storey, Kier; Lu, Michelle; Terdiman, Pierre; Chentanez, Nuttapong; Jeschke, Stefan; Müller, Matthias; Batty, Christopher and Huang, Jin
    In this paper we re-examine the idea that implicit integrators with large time steps offer the best stability/performance trade-off for stiff systems. We make the surprising observation that performing a single large time step with n constraint solver iterations is less effective than computing n smaller time steps, each with a single constraint solver iteration. Based on this observation, our approach is to split every visual time step into n substeps of length Δt/n and to perform a single iteration of extended position-based dynamics (XPBD) in each such substep. When compared to a traditional implicit integrator with large time stepswe find constraint error and damping are significantly reduced. When compared to an explicit integrator we find that our method is more stable and robust for a wider range of stiffness parameters. This result holds even when compared against more sophisticated implicit solvers based on Krylov methods. Our method is straightforward to implement, and is not sensitive to matrix conditioning nor is it to overconstrained problems.