vriphys17

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https://diglib.eg.org/handle/10.2312/2631244

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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.
Real-time Landscape-size Convective Clouds Simulation and Rendering
(The Eurographics Association, 2017) Goswami, Prashant; Neyret, Fabrice; Fabrice Jaillet and Florence Zara
This paper presents an efficient, physics-based procedural model for the real-time animation and visualization of cumulus clouds at landscape size. We couple a coarse Lagrangian model of air parcels with a procedural amplification using volumetric noise. Our Lagrangian model draws an aerology i.e., the atmospheric physics of hydrostatic atmosphere with thermodynamics transforms, augmented by a model of mixing between parcels and environment. In addition to the particle-particle interactions, we introduce particle-implicit environment interactions. In contrast to the usual fluid simulation, we thus do not need to sample the transparent environment, a key property for real-time efficiency and scalability to large domains. Inheriting from the highlevel physics of aerology, we also validate our simulation by comparing it to predictive diagrams, and we show how the user can easily control key aspects of the result such as the cloud base and top altitude. Our model is thus fast, physical and controllable.
Elasticity-based Clustering for Haptic Interaction with Heterogeneous Deformable Objects
(The Eurographics Association, 2017) Gouis, Benoît Le; Marchal, Maud; Lécuyer, Anatole; Arnaldi, Bruno; Fabrice Jaillet and Florence Zara
Physically-based simulation of heterogeneous objects remains computationally-demanding for many applications, especially when involving haptic interaction with virtual environments. In this paper, we introduce a novel multiresolution approach for haptic interaction with heterogeneous deformable objects. Our method called "Elasticity-based Clustering" is based on the clustering and aggregation of elasticity inside an object, in order to create large homogeneous volumes preserving important features of the initial distribution. The design of such large and homogeneous volumes improves the attribution of elasticity to the elements of the coarser geometry. We could successfully implement and test our approach within a complete and real-time haptic interaction pipeline compatible with consumer-grade haptic devices. We evaluated the performance of our approach on a large set of elasticity configurations using a perception-based quality criterion. Our results show that for 90% of studied cases our method can achieve a 6 times speedup in the simulation time with no theoretical perceptual difference.
A Fast Linear Complementarity Problem (LCP) Solver for Separating Fluid-Solid Wall Boundary Conditions
(The Eurographics Association, 2017) Andersen, Michael; Niebe, Sarah; Erleben, Kenny; Fabrice Jaillet and Florence Zara
We address the task of computing solutions for a separating fluid-solid wall boundary condition model. We present an embarrassingly parallel, easy to implement, fluid LCP solver.We are able to use greater domain sizes than previous works have shown, due to our new solver. The solver exploits matrix-vector products as computational building blocks. We block the matrix-vector products in a way that allows us to evaluate the products, without having to assemble the full systems. Any iterative sub-solver can be used. Our work shows speedup factors ranging up to 500 for larger grid sizes.
See-through Visualisation for Training and Assessing Unsighted Physical Examinations
(The Eurographics Association, 2017) Granados, Alejandro; Perhac, Jan; Rosby, Lucy Victoria; Lee, Yee Mun; Tan, Glenn Wei Leong; Tan, Tai Chi; Higham, Jenny; Thalmann, Nadia; Low-Beer, Naomi; Bello, Fernando; Fabrice Jaillet and Florence Zara
Objective: Motivated by the limitations of being unable to provide feedback and adequately assess technical skills whilst training unsighted physical examinations, such as Digital Rectal Examinations (DRE), we present a see-through visualisation system that can be used with benchtop models widely available in medical schools. Methods: We use position and pressure sensors located on the examining finger and have implemented a Virtual Reality (VR) simulation learning tool consisting of registered 3D models of the benchtop, augmented with relevant surrounding pelvic anatomy. The proposed system was evaluated with six medical students and eleven consultants. Results: The system is stable, runs in real time, uses unobtrusive sensor coils and pads, is able to capture data from sensors at 40Hz and adequately translates and rotates the position of the examining finger aligned to the 3D models of the benchtop and surrounding anatomy. Both medical students and consultants recognised the educational value of being able to see-through and visualise surrounding relevant anatomy. Although novices are reported to be the group that could benefit the most from our system, it is crucial not to be over reliant on visual cues for too long and to develop a strategy for the adequate use of the see-through system. Conclusions: The proposed VR simulation system is intended to improve the experience of novices learning unsighted examinations by providing real-time feedback and visualisation, allowing trainees to reflect on their performance and permitting more adequate assessment of technical skills.
Unified Simulation of Rigid and Flexible Bodies Using Position Based Dynamics
(The Eurographics Association, 2017) Frâncu, Mihai; Moldoveanu, Florica; Fabrice Jaillet and Florence Zara
In this paper we present a new position based approach for simulating rigid and flexible bodies with two-way coupling. This is achieved by expressing all the dynamics as constraints and running them in the same solver. Our main contribution is an accurate contact and Coulomb friction model based on a fixed point iteration of a cone complementarity problem. We formulate the problem as a nonlinear convex minimization at position level and solve it using a new accelerated form of projected Jacobi. We add elasticity to the constraints by means of regularization and show how to add more damping in a credible manner. We also use this viscoelastic model to build an accurate position-based finite element solver for soft bodies. The novelty of this solver is that it is no longer an approximation and it is based directly on the elasticity theory of continuous media.
Inverse Kinematic Solutions for Articulated Characters using Massively Parallel Architectures and Differential Evolutionary Algorithms
(The Eurographics Association, 2017) Kenwright, Ben; Fabrice Jaillet and Florence Zara
This paper presents a Differential Evolutionary (DE) algorithm for solving multi-objective kinematic problems (e.g., end-effector locations, centre-of-mass and comfort factors). Inverse kinematic problems in the context of character animation systems are one of the most challenging and important conundrums. The problems depend upon multiple geometric factors in addition to cosmetic and physical aspects. Further complications stem from the fact that there may be non or an infinite number of solutions to the problem (especially for highly redundant manipulator structures, such as, articulated characters). What is more, the problem is global and tightly coupled so small changes to individual link's impacts the overall solution. Our method focuses on generating approximate solutions for a range of inverse kinematic problems (for instance, positions, orientations and physical factors, like overall centre-of-mass location) using a Differential Evolutionary algorithm. The algorithm is flexible enough that it can be applied to a range of open ended problems including highly non-linear discontinuous systems with prioritisation. Importantly, evolutionary algorithms are typically renowned for taking considerable time to find a solution. We help reduce this burden by modifying the algorithm to run on a massively parallel architecture (like the GPU) using a CUDA-based framework. The computational model is evaluated using a variety of test cases to demonstrate the techniques viability (speed and ability to solve multi-objective problems). The modified parallel evolutionary solution helps reduce execution times compared to the serial DE, while also obtaining a solution within a specified margin of error (<1%).
VRIPHYS 2017: Frontmatter
(Eurographics Association, 2017) Jaillet, Fabrice; Zara, Florence;
Kernel Projection of Latent Structures Regression for Facial Animation Retargeting
(The Eurographics Association, 2017) Ouzounis, Christos; Kilias, Alex; Mousas, Christos; Fabrice Jaillet and Florence Zara
Inspired by kernel methods that have been used extensively in achieving efficient facial animation retargeting, this paper presents a solution to retargeting facial animation in virtual character's face model based on the kernel projection of latent structure (KPLS) regression between semantically similar facial expressions. Specifically, a given number of corresponding semantically similar facial expressions are projected into the latent space. By using the Nonlinear Iterative Partial Least Square method, decomposition of the latent variables is achieved. Finally, the KPLS is achieved by solving a kernalized version of the eigenvalue problem. By evaluating our methodology with other kernel-based solutions, the efficiency of the presented methodology in transferring facial animation to face models with different morphological variations is demonstrated.
Implicit Mesh Generation using Volumetric Subdivision
(The Eurographics Association, 2017) Altenhofen, Christian; Schuwirth, Felix; Stork, André; Fellner, Dieter W.; Fabrice Jaillet and Florence Zara
In this paper, we present a novel approach for a tighter integration of 3D modeling and physically-based simulation. Instead of modeling 3D objects as surface models, we use a volumetric subdivision representation. Volumetric modeling operations allow designing 3D objects in similar ways as with surface-based modeling tools. Encoding the volumetric information already in the design mesh drastically simplifies and speeds up the mesh generation process for simulation. The transition between design, simulation and back to design is consistent and computationally cheap. Since the subdivision and mesh generation can be expressed as a precomputable matrix-vector multiplication, iteration times can be greatly reduced compared to common modeling and simulation setups. Therefore, this approach is especially well suited for early-stage modeling or optimization use cases, where many geometric changes are made in a short time and their physical effect on the model has to be evaluated frequently. To test our approach, we created, simulated and adapted several 3D models. Additionally, we measured and evaluated the timings for generating and applying the matrices for different subdivision levels. For comparison, we also measured the tetrahedral meshing functionality offered by CGAL for similar numbers of elements. For changing topology, our implicit meshing approach proves to be up to 70 times faster than creating the tetrahedral mesh only based on the outer surface. Without changing the topology and by precomputing the matrices, we achieve a speed-up of up to 2800.
Moving Least Squares Boundaries for SPH Fluids
(The Eurographics Association, 2017) Band, Stefan; Gissler, Christoph; Teschner, Matthias; Fabrice Jaillet and Florence Zara
The paper shows that the SPH boundary handling of Akinci et al. [AIA 12] suffers from perceivable issues in planar regions due to deviations in the computed boundary normals and due to erroneous oscillations in the distance computation of fluid particles to the boundary. In order to resolve these issues, we propose a novel boundary handling that combines the SPH concept with Moving Least Squares. The proposed technique significantly improves the distance and normal computations in planar boundary regions, while its computational complexity is similar to Akinci's approach. We embed the proposed boundary handling into Implicit Incompressible SPH in a hybrid setting where it is applied at planar boundaries, while Akinci's technique is still being used for boundaries with complex shapes. Various benefits of the improved boundary handling are illustrated, in particular a reduced particle leakage and a reduced artificial boundary friction.

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