vriphys15

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https://diglib.eg.org/handle/10.2312/13862

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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.
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.
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.
Evaluation of Surface Tension Models for SPH-Based Fluid Animations Using a Benchmark Test
(The Eurographics Association, 2015) Huber, Markus; Reinhardt, Stefan; Weiskopf, Daniel; Eberhardt, Bernhard; Fabrice Jaillet and Florence Zara and Gabriel Zachmann
We evaluate surface tension models in particle-based fluid simulation systems using smoothed particle hydrodynamics (SPH) with a benchmark test. Our benchmark consists of three experiments and a set of analysis methods that are useful for the comparison of surface tension models. Although visual quality is of major interest and is considered as well, we suggest quantification methods for the properties of these models. The goal is to identify if a certain model is suitable for a given scenario and to be able to control the results in the creation of animations. We apply the proposed evaluation methods to three existing surface tension models in combination with different SPH techniques (WCSPH, PCISPH, and IISPH) and perform systematic tests to show the influence of different settings and parameter choices. The surface tension models are chosen from different classes: a pure inter-particle force model, a model based on surface curvature, and a model using a combination of these. Additionally, we present a simple modification to improve the quality of inter-particle force models.
Frontmatter: Workshop on Virtual Reality Interactions and Physical Simulations
(The Eurographics Association, 2015) Jaillet, Fabrice; Zara, Florence; Zachmann, Gabriel; Fabrice Jaillet and Florence Zara and Gabriel Zachmann
Grid-Free Surface Tracking on the GPU
(The Eurographics Association, 2015) Chentanez, Nuttapong; Müller, Matthias; Macklin, Miles; Kim, Tae-Yong; Fabrice Jaillet and Florence Zara and Gabriel Zachmann
We present the first mesh-based surface tracker that runs entirely on the GPU. The surface tracker is both completely grid-free and fast which makes it suitable for the use in a large, unbounded domain. The key idea for handling topological changes is to detect and delete overlapping triangles as well as triangles that lie inside the volume. The holes are then joined or closed in a robust and efficient manner. Good mesh quality is maintained by a mesh improvement algorithm. In this paper we describe how all these steps can be parallelized to run efficiently on a GPU. The surface tracker is guaranteed to produce a manifold mesh without boundary. Our results show the quality and efficiency of the method in both Eulerian and Lagrangian liquid simulations. Our parallel implementation runs more than an order of magnitude faster than the CPU version.
Implicit Incompressible SPH on the GPU
(The Eurographics Association, 2015) Goswami, Prashant; Eliasson, André; Franzén, Pontus; Fabrice Jaillet and Florence Zara and Gabriel Zachmann
This paper presents CUDA-based parallelization of implicit incompressible SPH (IISPH) on the GPU. Along with the detailed exposition of our implementation, we analyze various components involved for their costs. We show that our CUDA version achieves near linear scaling with the number of particles and is faster than the multi-core parallelized IISPH on the CPU. We also present a basic comparison of IISPH with the standard SPH on GPU.
Interleaved Cloth Simulation
(The Eurographics Association, 2015) Han, Dongsoo; Fabrice Jaillet and Florence Zara and Gabriel Zachmann
Implicit integration is a standard for stiff spring-based cloth simulation because of its stability. However constraints are useful to simulate various physical behaviors such as contact collisions or interaction with rigid bodies. Modified Conjugate Gradient (MCG) could support constraints as a part of implicit integration but constraints could not be added or removed during integration and they were limited to vertex nodes. Normally, a contact constraint has one or two frictional constraints and act inside of triangle or edge rather than vertex node. Also its inequality property makes it harder to be included in MCG. For this reason, constraints are typically applied after implicit integration as a separate step or replaced with springs. In this paper, we propose a novel method to interleave various constraints with stiff springs so that we can take advantages from both sides. Also our Jacobian-free and matrix-free implicit integration allows us to use various nonlinear forces such as pressure or none vertex-centered forces. Interleaving collision constraints into integration step can eliminate unpleasant local deformation.
Level-of-Detail Modal Analysis for Real-time Sound Synthesis
(The Eurographics Association, 2015) Rausch, Dominik; Hentschel, Bernd; Kuhlen, Torsten W.; Fabrice Jaillet and Florence Zara and Gabriel Zachmann
Modal sound synthesis is a promising approach for real-time physically-based sound synthesis. A modal analysis is used to compute characteristic vibration modes from the geometry and material properties of scene objects. These modes allow an efficient sound synthesis at run-time, but the analysis is computationally expensive and thus typically computed in a pre-processing step. In interactive applications, however, objects may be created or modified at run-time. Unless the new shapes are known upfront, the modal data cannot be pre-computed and thus a modal analysis has to be performed at run-time. In this paper, we present a system to compute modal sound data at run-time for interactive applications. We evaluate the computational requirements of the modal analysis to determine the computation time for objects of different complexity. Based on these limits, we propose using different levels-of-detail for the modal analysis, using different geometric approximations that trade speed for accuracy, and evaluate the errors introduced by lower-resolution results. Additionally, we present an asynchronous architecture to distribute and prioritize modal analysis computations.
A More Efficient Parallel Method For Neighbour Search Using CUDA
(The Eurographics Association, 2015) Morillo, Daniel; Carmona, Ricardo; Perea, Juan J.; Cordero, Juan M.; Fabrice Jaillet and Florence Zara and Gabriel Zachmann
In particle systems simulation, the procedure of neighbour searching is usually a bottleneck in terms of computational cost. Several techniques have been developed to solve this problem; one of particular interest is the cell-based spatial division, where each cell is tagged by a hash function. One of the most useful features of this technique is that it can be easily parallelized to reduce computational costs. However, the parallelizing process has some drawbacks associated to data memory management. Also, when parallelizing neighbour search, the location of neighbouring particles between adjacent cells is also costly. To solve these shortcomings we have developed a method that reduces the search space by considering the relative position of each particles in its own cell. This method, parallelized using CUDA, shows improvements in processing time and memory management over other ''standard'' spatial division techniques.
A New Force Model for Controllable Breaking Waves
(The Eurographics Association, 2015) Brousset, Mathias; Darles, Emmanuelle; Meneveaux, Daniel; Poulin, Pierre; Crespin, Benoît; Fabrice Jaillet and Florence Zara and Gabriel Zachmann
This paper presents a new method for controlling swells and breaking waves using fluid solvers. With conventional approaches that generate waves by pushing particles with oscillating planes, the resulting waves cannot be controlled easily, and breaking waves are even more difficult to obtain in practice. Instead, we propose to use a new wave model that physically describes the behavior of wave forces. We show that mapping those forces to particles produces various types of waves that can be controlled by the user with only a few parameters. Our method is based on a 2D representation that describes wave speed, width, and height. It handles many swell and wave configurations, with various breaking situations.
Quaternion Fourier Transform for Character Motions
(The Eurographics Association, 2015) Kenwright, Ben; Fabrice Jaillet and Florence Zara and Gabriel Zachmann
The Fourier transform plays a crucial role in a broad range of signal processing applications, including enhancement, restoration, analysis, and compression. Since animated motions comprise of signals, it is no surprise that the Fourier transform has been used to filter animations by transforming joint signals from the spatial domain to the frequency domain and then applying filtering masks. However, in this paper, we filter motion signals by means of a new approach implemented using hyper-complex numbers, often referred to as Quaternions, to represent angular joint displacements. We use the novel quaternion Fourier transform (QFT) to perform filtering by allowing joint motions to be transformed as a 'whole', rather than as individual components. We propose a holistic Fourier transform of the joints to yield a single frequency-domain representation based on the quaternion Fourier coefficients. This opens the door to new types of motion filtering techniques. We apply the concept to the frequency domain for noise reduction of 3-dimensional motions. The approach is based on obtaining the QFT of the joint signals and applying Gaussian filters in the frequency domain. The filtered signals are then reconstructed using the inverse quaternion Fourier transform (IQFT).
Using Personalized Finger Gestures for Navigating Virtual Characters
(The Eurographics Association, 2015) Ouzounis, Christos; Mousas, Christos; Anagnostopoulos, Christos-Nikolaos; Newbury, Paul; Fabrice Jaillet and Florence Zara and Gabriel Zachmann
In this paper, we present and evaluate a method to navigate a character into a virtual environment based on personalized finger gestures. The methodology that has been developed allows a user to generate his/her own finger gestures that are associated with the actions of a character. Specifically, in a pre-processing stage, the user wishes to perform specific gestures for specific actions of a character creating a dataset of gestures. During the runtime of the application, Dynamic Time Warping (DTW) and template matching methods were used to compute the similarity of the input and examples of gestures. The system recognizes the input gesture of a user and generates the motion required to navigate a character into the virtual environment. To demonstrate the efficiency and possible use of such a character navigation method, a number of users participated in an evaluation process. The results of the evaluation process indicate the possible use of personalized finger gestures for navigating a character into a virtual environment.
Vascular Neurosurgery Simulation with Bimanual Haptic Feedback
(The Eurographics Association, 2015) Dequidt, Jeremie; Coevoet, Eulalie; Thinès, Laurent; Duriez, Christian; Fabrice Jaillet and Florence Zara and Gabriel Zachmann
Virtual surgical simulators face many computational challenges: they need to provide biophysical accuracy, realistic feed-backs and high-rate responses. Better biophysical accuracy and more realistic feed-backs (be they visual, haptic. . . ) induce more computational footprint. State-of-the-art approaches use high-performance hardware or find an acceptable trade-off between performance and accuracy to deliver interactive yet pedagogically relevant simulators. In this paper, we propose an interactive vascular neurosurgery simulator that provides bi-manual interaction with haptic feedback. The simulator is an original combination of states-of-the-art techniques that allows visual realism, bio-physical realism, complex interactions with the anatomical structures and the instruments and haptic feedback. Training exercises are also proposed to learn and to perform the different steps of intracranial aneurysm surgery (IAS). We assess the performance of our simulator with quantitative performance benchmarks and qualitative assessments of junior and senior clinicians.

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