vriphys: Workshop in Virtual Reality Interactions and Physical Simulations

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3D Mobility Learning and Regression of Articulated, Tracked Robotic Vehicles by Physics-based Optimization
(The Eurographics Association, 2012) Papadakis, Panagiotis; Pirri, Fiora; Jan Bender and Arjan Kuijper and Dieter W. Fellner and Eric Guerin
Motion planning for robots operating on 3D rough terrain requires the synergy of various robotic capabilities, from sensing and perception to simulation, planning and prediction. In this paper, we focus on the higher level of this pipeline where by means of physics-based simulation and geometric processing we extract the information that is semantically required for an articulated, tracked robot to optimally traverse 3D terrain. We propose a model that quantifies 3D traversability by accounting for intrinsic robot characteristics and articulating capabilities together with terrain characteristics. By building upon a set of generic cost criteria for a given robot state and 3D terrain patch, we augment the traversability cost estimation by: (i) unifying pose stabilization with traversability cost estimation, (ii) introducing new parameters into the problem that have been previously overlooked and (iii) adapting geometric computations to account for the complete 3D robot body and terrain surface. We apply the proposed model on a state-of-the-art Search and Rescue robot by performing a plurality of tests under varying conditions and demonstrate its efficiency and applicability in real-time.
3D Sketch Recognition for Interaction in Virtual Environments
(The Eurographics Association, 2010) Rausch, Dominik; Assenmacher, Ingo; Kuhlen, Torsten; Kenny Erleben and Jan Bender and Matthias Teschner
We present a comprehensive 3D sketch recognition framework for interaction within Virtual Environments that allows to trigger commands by drawing symbols, which are recognized by a multi-level analysis. It proceeds in three steps: The segmentation partitions each input line into meaningful segments, which are then recognized as a primitive shape, and finally analyzed as a whole sketch by a symbol matching step. The whole framework is configurable over well-defined interfaces, utilizing a fuzzy logic algorithm for primitive shape learning and a textual description language to define compound symbols. It allows an individualized interaction approach that can be used without much training and provides a good balance between abstraction and intuition. We show the real-time applicability of our approach by performance measurements.
Accelerated Hierarchical Collision Detection for Simulation using CUDA
(The Eurographics Association, 2010) Jorgensen, Jimmy A.; Fugl, Andreas Rune; Petersen, Henrik Gordon; Kenny Erleben and Jan Bender and Matthias Teschner
In this article we present a GPU accelerated, hybrid, narrow phase collision detection algorithm for simulation purposes. The algorithm is based on hierarchical bounding volume tree structures of oriented bounding boxes (OBB) that in the past has shown to be efficient for collision detection. The hierarchical nature of the bounding volume structure complicates an efficient implementation on massively parallel architectures such as modern graphics cards and we therefore propose a hybrid method where only box and triangle overlap tests and transformations are offloaded to the graphics card. When exploiting coarse-grained parallelism in grasping and stacking simulations, requiring all-contacts resolution, a performance gain of up to 7x compared to the collision detection package PQP is obtained.
Accurate Contact Modeling for Multi-rate Single-point Haptic Rendering of Static and Deformable Environments
(The Eurographics Association, 2015) Knott, Thomas C.; Kuhlen, Torsten W.; Fabrice Jaillet and Florence Zara and Gabriel Zachmann
Common approaches for the haptic rendering of complex scenarios employ multi-rate simulation schemes. Here, the collision queries or the simulation of a complex deformable object are often performed asynchronously on a lower frequency, while some kind of intermediate contact representation is used to simulate interactions on the haptic rate. However, this can produce artifacts in the haptic rendering when the contact situation quickly changes and the intermediate representation is not able to reflect the changes due to the lower update rate. We address this problem utilizing a novel contact model. It facilitates the creation of contact representations that are accurate for a large range of motions and multiple simulation time-steps.We handle problematic convex contact regions using a local convex decomposition and special constraints for convex areas.We combine our accurate contact model with an implicit temporal integration scheme to create an intermediate mechanical contact representation, which reflects the dynamic behavior of the simulated objects. Moreover, we propose a new iterative solving scheme for the involved constrained dynamics problems.We increase the robustness of our method using techniques from trust region-based optimization. Our approach can be combined with standard methods for the modeling of deformable objects or constraint-based approaches for the modeling of, for instance, friction or joints. We demonstrate its benefits with respect to the simulation accuracy and the quality of the rendered haptic forces in multiple scenarios.
Adding Physics to Animated Characters with Oriented Particles
(The Eurographics Association, 2011) Müller, Matthias; Chentanez, Nuttapong; Jan Bender and Kenny Erleben and Eric Galin
We present a method to enhance the realism of animated characters by adding physically based secondary motion to deformable parts such as cloth, skin or hair. To this end, we extend the oriented particles approach to incorporate animation information. In addition, we introduce techniques to increase the stability of the original method in order to make it suitable for the fast and sudden motions that typically occur in computer games. We also propose a method for the semi-automatic creation of particle representations from arbitrary visual meshes. This way, our technique allows us to simulate complex geometry such as hair, thick cloth with ornaments and multi-layered clothing, all interacting with each other and the animated character.
Animating Shapes at Arbitrary Resolution with Non-Uniform Stiffness
(The Eurographics Association, 2006) Nesme, Matthieu; Payan, Yohan; Faure, François; Cesar Mendoza and Isabel Navazo
We present a new method for physically animating deformable shapes using finite element models (FEM). Contrary to commonly used methods based on tetrahedra, our finite elements are the bounding voxels of a given shape at arbitrary resolution. This alleviates the complexities and limitations of tetrahedral volume meshing and results in regular, well-conditionned meshes. We show how to build the voxels and how to set the masses and stiffnesses in order to model the physical properties as accurately as possible at any given resolution. Additionally, we extend a fast and robust tetrahedron-FEM approach to the case of hexahedral elements. This permits simulation of arbitrarily complex shapes at interactive rates in a manner that takes into account the distribution of material within the elements.
An Application of Photo RealisticWater Surface Interaction Using Mixed Reality
(The Eurographics Association, 2009) Tawara, Takehiro; Ono, Kenji; Hartmut Prautzsch and Alfred Schmitt and Jan Bender and Matthias Teschner
The Reality of Virtual Reality is affected by many research areas. Therefore, individual researches must be combined to achieve the extreme goal of Virtual Reality. In this paper, we present an application of the novel and clever combination of height field wave simulation, photo realistic rendering, and a 6DOF manipulator exploiting Augmented Reality. In our system, a user can touch a virtual water surface with a real pen attached a tracking cube in natural manners. We also take into account rendering optical effects like shadows and caustics, which give users a great deal of reality. We show how such a combination is important to achieve reality in the videos of our real time demonstrations.
Approximate Air-Fluid Interactions for SPH
(The Eurographics Association, 2017) Gissler, Christoph; Band, Stefan; Peer, Andreas; Ihmsen, Markus; Teschner, Matthias; Fabrice Jaillet and Florence Zara
Computing the forces acting from a surrounding air phase onto an SPH free-surface fluid is challenging. For full multiphase simulations the computational overhead is significant and stability issues due to the high density ratio may arise. In contrast, the air-fluid interactions can be approximated efficiently by employing a drag equation. Here, for plausible effects, the parameterization is important but challenging. We present an approach to calculate the parameters of the used drag equation in a physically motivated way. We approximate the deformation and occlusion of particles to determine their drag coefficient and exposed surface area. The resulting effects are validated by comparing them to the results of a multiphase SPH simulation. We further show the practicality of our approach by combining it with different types of SPH solvers and by simulating multiple, complex scenes.
Area Preserving Strain Limiting
(The Eurographics Association, 2015) Han, Dongsoo; Fabrice Jaillet and Florence Zara and Gabriel Zachmann
In this paper we present a novel fast strain-limiting method that allows cloth to preserve its surface area efficiently. By preserving triangle area rather than edge length as other approaches do, this method does not remove the degrees of freedom of triangles and does not suffer from locking. Borrowing ideas from fluid simulation, we define pressures in each triangle and solve the global linear equation which shows a faster convergence over prior approaches which use Gauss-Seidel-like iterations. The linear equation is easy to build by using edge and normal vectors and can be solved using Conjugate Gradient solver with regularization which not only helps the solver converge fast but also allows users to have a control over the stretchiness of cloth materials. Our area preserving strain limiting (APSL) can be also used as stand-alone cloth solver with linear bending springs.
Asynchronous Preconditioners for Efficient Solving of Non-linear Deformations
(The Eurographics Association, 2010) Courtecuisse, Hadrien; Allard, Jérémie; Duriez, Christian; Cotin, Stéphane; Kenny Erleben and Jan Bender and Matthias Teschner
In this paper, we present a set of methods to improve numerical solvers, as used in real-time non-linear deformable models based on implicit integration schemes. The proposed approach is particularly beneficial to simulate nonhomogeneous objects or ill-conditioned problem at high frequency. The first contribution is to desynchronize the computation of a preconditioner from the simulation loop.We also exploit today's heterogeneous parallel architectures: the graphic processor performs the mechanical computations whereas the CPU produces efficient preconditioners for the simulation. Moreover, we propose to take advantage of a warping method to limit the divergence of the preconditioner over time. Finally, we validate our work with several preconditioners on different deformable models. In typical scenarios, our method improves significantly the performances of the perconditioned version of the conjugate gradient.
Audio Texture Synthesis for Complex Contact Interactions
(The Eurographics Association, 2008) Picard, Cecile; Tsingos, Nicolas; Faure, Francois; Francois Faure and Matthias Teschner
This paper presents a new synthesis approach for generating contact sounds for interactive simulations. To address complex contact sounds, surface texturing is introduced. Visual textures of objects in the environment are reused as a discontinuity map to create audible position-dependent variations during continuous contacts. The resulting synthetic profiles are then used in real time to provide an excitation force to a modal resonance model of the sounding objects. Compared to previous sound synthesis for virtual environments, our approach has three major advantages: (1) complex contact interactions are addressed and a large variety of sounding events can be rendered, (2) it is fast due to the compact form of the solution which allows for synthesizing at interactive rates, (3) it provides several levels of detail which can be used depending on the desired precision.
Bézier Shell Finite Element for Interactive Surgical Simulation
(The Eurographics Association, 2012) Golembiovský, Tomá¹; Duriez, Christian; Jan Bender and Arjan Kuijper and Dieter W. Fellner and Eric Guerin
There is a strong need, in surgical simulations, for physically based deformable model of thin or hollow structures. The use of shell theory allows to have a well-founded formulation resulting from continuum mechanics of thin objects. However, this formulation asks for second order spatial derivatives so requires the use of complex elements. In this paper, we present a new way of building the interpolation: First, we use the trianular cubic Bézier shell to allow for a good continuity inside and between the elements and second, we build a kinematic mapping to reduce the degrees of freedom of the element from 10 control points with 3 Degrees of Freedom (
Boundary Handling and Adaptive Time-stepping for PCISPH
(The Eurographics Association, 2010) Ihmsen, Markus; Akinci, Nadir; Gissler, Marc; Teschner, Matthias; Kenny Erleben and Jan Bender and Matthias Teschner
We present a novel boundary handling scheme for incompressible fluids based on Smoothed Particle Hydrodynamics (SPH). In combination with the predictive-corrective incompressible SPH (PCISPH) method, the boundary handling scheme allows for larger time steps compared to existing solutions. Furthermore, an adaptive time-stepping approach is proposed. The approach automatically estimates appropriate time steps independent of the scenario. Due to its adaptivity, the overall computation time of dynamic scenarios is significantly reduced compared to simulations with constant time steps.
Brownian Dynamics Simulation on the GPU: Virtual Colloidal Suspensions
(The Eurographics Association, 2015) Tran, Công Tâm; Crespin, Benoît; Cerbelaud, Manuella; Videcoq, Arnaud; Fabrice Jaillet and Florence Zara and Gabriel Zachmann
Brownian Dynamics simulations are frequently used to describe and study the motion and aggregation of colloidal particles, in the field of soft matter and material science. In this paper, we focus on the problem of neighbourhood search to accelerate computations on a single GPU. Our approach for one kind of particle outperforms existing implementations by introducing a novel dynamic test. For bimodal size distributions we also introduce a new algorithm that separates computations for large and small particles, in order to avoid additional friction that is known to restrict diffusive displacements.
Collision Detection between a Complex Solid and a Particle Cloud assisted by Programmable GPU
(The Eurographics Association, 2006) Jiménez, Juan J.; Ogáyar, Carlos J.; Segura, Rafael J.; Feito, Francisco R.; Cesar Mendoza and Isabel Navazo
In this work the problem of collision detection (CD) between a Complex Solid and a Particle cloud with autonomous movement is studied. In order to do this, some algorithms and data have been adapted to suit new extensions of the new generations of programmable graphics cards. These types of graphics cards allow more flexible programming in order to solve problems not-related to visualization process. We use a representation based on simplicial coverings as well as a structure named Tetra-Tree in order to represent and classify the simplices of complex objects. With this type of representation the operations carried out in CD are more robust and efficient than those used in classic algorithms, so it is not necessary to decompose the complex object into more simple pieces. We also propose some implementation alternatives and give a study of their performance.
Comparison of Mixed Linear Complementarity Problem Solvers for Multibody Simulations with Contact
(The Eurographics Association, 2018) Enzenhöfer, Andreas; Andrews, Sheldon; Teichmann, Marek; Kövecses, József; Andrews, Sheldon and Erleben, Kenny and Jaillet, Fabrice and Zachmann, Gabriel
The trade-off between accuracy and computational performance is one of the central conflicts in real-time multibody simulations, much of which can be attributed to the method used to solve the constrained multibody equations. This paper examines four mixed linear complementarity problem (MLCP) algorithms when they are applied to physical problems involving frictional contact. We consider several different, and challenging, test cases such as grasping, stability of static models, closed loops, and long chains of bodies. The solver parameters are tuned for these simulations and the results are evaluated in terms of numerical accuracy and computational performance. The objective of this paper is to determine the accuracy properties of each solver, find the appropriate method for a defined task, and thus draw conclusions regarding the applicability of each method.
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.
Constraint Sets for Topology-changing Finite Element Models
(The Eurographics Association, 2007) Gissler, Marc; Becker, Markus; Teschner, Matthias; John Dingliana and Fabio Ganovelli
We propose constraint sets as an efficient data structure for topology-changing deformable tetrahedral meshes. Using constraint sets, data structure updates in case of topology changes are simple and efficient. The consistency of the geometric representation is maintained and elasto-mechanical properties of the object are preserved. In combination with a Finite Element model for elasto-plastic objects and a geometric constraint approach, con- straint sets are applied to simulate the merging and breaking of conforming and non-conforming tetrahedral meshes. Experiments illustrate the efficiency of the data structure in interactive applications and its versatility.
Continuous Collision Detection Between Points and Signed Distance Fields
(The Eurographics Association, 2014) Xu, Hongyi; Barbic, Jernej; Jan Bender and Christian Duriez and Fabrice Jaillet and Gabriel Zachmann
We present an algorithm for fast continuous collision detection between points and signed distance fields. Such robust queries are often needed in computer animation, haptics and virtual reality applications, but have so far only been investigated for polygon (triangular) geometry representations. We demonstrate how to use an octree subdivision of the distance field for fast traversal of distance field cells. We also give a method to combine octree subdivision with points organized into a tree hierarchy, for efficient culling of continuous collision detection tests. We apply our method to multibody rigid simulations, and demonstrate that our method accelerates continuous collision detection between points and distance fields by an order of magnitude.
Controlling the Shape and Motion of Plumes in Explosion Simulations
(The Eurographics Association, 2014) Kawada, Genichi; Kanai, Takashi; Jan Bender and Christian Duriez and Fabrice Jaillet and Gabriel Zachmann
We propose a fluid simulation method with controlling the shape and motion of rising fire and smoke, called plumes, in the incompressible phase of explosion phenomenon. With our method, plumes are generated based on physical phenomenon called entrainment, which strongly characterizes plume behaviors such as rise and circulation. We consider to newly utilize properties characterizing these behavior (physical property). Then, control elements of plume such as rising velocity, size, and the magnitude and position of swirling motions are individually adjusted using these physical properties. With this method, each control element is adjusted by the velocity field which represents the corresponding behavior. By combining all velocity fields and applying those fields to grid-based simulation, plumes can be generated. Our method is unique in that it can both generate and control plumes based on one unified physical model, and this type of model is firstly proposed here. Consequently, our method realizes plumes in the incompressible phase which maintain their physical characteristics as much as possible while being controlled by the user.

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