Physics-based control of virtual characters in low frequency simulations

International audienceUsing a lower simulation frequency for physics-based control of virtual characters frees computation time that can be used for more complex environment. However, using low simulation frequency may introduce instabilities inside the simulation. In this paper, we demonstrate that even a simple control strategy can be used at a low simulation frequency by adapting the control parameters. Indeed we show that lower frequencies hold a more restrictive space of possible control parameters than higher ones. We propose a method to find optimized control parameters for frequencies as low as 200Hz. As using such low frequencies may introduce foot-ground contact instabilities, we also introduce an additional control feedback on the stance leg. Our controller shows similar robustness as high frequency controller while using 0.8ms per simulation step

Physics-based control of virtual character in complex environment

Cette thèse traite de l’animation de personnages virtuels composés de corps rigides reliés par des articulations et contrôlés par des interactions physiques (forces et moments). Le contrôleur est le système qui calcule dynamiquement ces interactions. Notre objectif est d’étudier et de réaliser un contrôleur pour la simulation de mouvements d’un personnage en interaction avec un fluide. La complexité du comportement de tels milieux ne permet pas de prédire les interactions entre le personnage et le fluide. Il en découle que le contrôleur proposé doit être capable de réagir à celles-ci. Nous avons focalisé nos travaux sur la conception d’un contrôleur de type SIMBICON capable de s’adapter aux perturbations apportées par la présence d’un fluide simulé physiquement. Ce choix est motivé par notre contrôleur précédent qui proposait un contrôleur en interaction avec un fluide représenté à travers l’utilisation de formule de dynamique des fluides simples. L’utilisation d’une véritable simulation physique du fluide nous permettrait d’améliorer le réalisme physique de la simulation en prenant en compte l’impact du déplacement du personnage sur le fluide. Ayant pour objectif un contrôleur interactif nous nous sommes focalisés sur deux axes principaux. Le premier est la conception d’un contrôleur capable de supporter des fréquences de simulation faibles tout en conservant la vitesse de calcul apporté par l’utilisation du modèle SIMBICON. Nous proposons de réduire les instabilités introduites par l’utilisation de fréquences de simulation faibles par un système de feedback utilisant une optimisation en ligne permettant d’obtenir une meilleure stabilité des contacts. Ce système, associé à une étude des paramètres du système en fonction de la fréquence de simulation, nous a permis de proposer un contrôleur capable de supporter des fréquences de simulation allant jusqu’à 225Hz. Le second axe de recherche visait à proposer une implémentation entièrement GPU et interactive d’une simulation lagrangienne de fluide. Nous avons étudié l’impact sur les performances de notre implémentation GPU de plusieurs optimisations proposé par des travaux proposant des implémentations parallèles CPU. Nous proposons également une solution permettant de déplacer la zone de fluide simulé en cours de simulation pour limiter l’espace de simulation du fluide à la proximité immédiate du personnage au cours de son déplacement pour assurer une simulation du fluide en temps interactif.This thesis deals with the animation of virtual characters composed of rigid bodies linked by joints and controlled by physic interactions (forces and torques). The controller is the system that dynamically calculates these interactions. Our goal is to study and create a controller that is able to control the character interacting with a fluid. The complexity of the behavior of such environment renders predicting the interactions between the fluid and the character impossible. Therefore, the controller must be able to react to such interactions. We have focused our works on the conception of a SIMBICON typed controller that is able to handle the perturbations caused by the physically simulated fluid. This choice is motivated by our previous controller that was able to handle the interactions with a simplified fluid based on simplified fluid dynamics equations. The use of the complete fluid dynamic equations should allow for a higher realism by taking into account to impact of the character motion on the fluid. Since our objective is to obtain an interactive controller, we focus our works on two main axes. The first one is the conception of a controller able to handle low simulation frequencies while keeping the high computation speed brought by the use of the SIMBICON framework. We propose to use a feedback system using an online optimization to reduce the instabilities caused by the of the low simulation frequencies. On top of this system, we study the evolution of the value of the PD-controllers depending on the simulation frequency to be able to propose a controller able to handle simulation frequencies as low as 225Hz. The second research axis aims to conceive a fully GPU implementation of a Lagrangian fluid simulation. We study the impact of various optimization proposed by previous work on our GPU implementation. We also present a system allowing us to move the simulation area of the fluid to be able to keep the character centered in the fluid simulation. This system allows us to only use a small area for the fluid simulation allowing us to propose a system showing interactive execution times

Contrôle physique de mouvement de personnages virtuels en environnement complexe

This thesis deals with the animation of virtual characters composed of rigid bodies linked by joints and controlled by physic interactions (forces and torques). The controller is the system that dynamically calculates these interactions. Our goal is to study and create a controller that is able to control the character interacting with a fluid. The complexity of the behavior of such environment renders predicting the interactions between the fluid and the character impossible. Therefore, the controller must be able to react to such interactions. We have focused our works on the conception of a SIMBICON typed controller that is able to handle the perturbations caused by the physically simulated fluid. This choice is motivated by our previous controller that was able to handle the interactions with a simplified fluid based on simplified fluid dynamics equations. The use of the complete fluid dynamic equations should allow for a higher realism by taking into account to impact of the character motion on the fluid. Since our objective is to obtain an interactive controller, we focus our works on two main axes. The first one is the conception of a controller able to handle low simulation frequencies while keeping the high computation speed brought by the use of the SIMBICON framework. We propose to use a feedback system using an online optimization to reduce the instabilities caused by the of the low simulation frequencies. On top of this system, we study the evolution of the value of the PD-controllers depending on the simulation frequency to be able to propose a controller able to handle simulation frequencies as low as 225Hz. The second research axis aims to conceive a fully GPU implementation of a Lagrangian fluid simulation. We study the impact of various optimization proposed by previous work on our GPU implementation. We also present a system allowing us to move the simulation area of the fluid to be able to keep the character centered in the fluid simulation. This system allows us to only use a small area for the fluid simulation allowing us to propose a system showing interactive execution times.Cette thèse traite de l’animation de personnages virtuels composés de corps rigides reliés par des articulations et contrôlés par des interactions physiques (forces et moments). Le contrôleur est le système qui calcule dynamiquement ces interactions. Notre objectif est d’étudier et de réaliser un contrôleur pour la simulation de mouvements d’un personnage en interaction avec un fluide. La complexité du comportement de tels milieux ne permet pas de prédire les interactions entre le personnage et le fluide. Il en découle que le contrôleur proposé doit être capable de réagir à celles-ci. Nous avons focalisé nos travaux sur la conception d’un contrôleur de type SIMBICON capable de s’adapter aux perturbations apportées par la présence d’un fluide simulé physiquement. Ce choix est motivé par notre contrôleur précédent qui proposait un contrôleur en interaction avec un fluide représenté à travers l’utilisation de formule de dynamique des fluides simples. L’utilisation d’une véritable simulation physique du fluide nous permettrait d’améliorer le réalisme physique de la simulation en prenant en compte l’impact du déplacement du personnage sur le fluide. Ayant pour objectif un contrôleur interactif nous nous sommes focalisés sur deux axes principaux. Le premier est la conception d’un contrôleur capable de supporter des fréquences de simulation faibles tout en conservant la vitesse de calcul apporté par l’utilisation du modèle SIMBICON. Nous proposons de réduire les instabilités introduites par l’utilisation de fréquences de simulation faibles par un système de feedback utilisant une optimisation en ligne permettant d’obtenir une meilleure stabilité des contacts. Ce système, associé à une étude des paramètres du système en fonction de la fréquence de simulation, nous a permis de proposer un contrôleur capable de supporter des fréquences de simulation allant jusqu’à 225Hz. Le second axe de recherche visait à proposer une implémentation entièrement GPU et interactive d’une simulation lagrangienne de fluide. Nous avons étudié l’impact sur les performances de notre implémentation GPU de plusieurs optimisations proposé par des travaux proposant des implémentations parallèles CPU. Nous proposons également une solution permettant de déplacer la zone de fluide simulé en cours de simulation pour limiter l’espace de simulation du fluide à la proximité immédiate du personnage au cours de son déplacement pour assurer une simulation du fluide en temps interactif

Fluid initialization and dynamic window for SPH simulation

Fluid simulation is an essential tool to produce realistic looking animations. In particular, Lagrangian simulations offer interactive computation times with an easy integration of the two-way interaction with rigid bodies. However, the interactivity is lost for larger scenes even if only the areas around the bodies have any visual interest. In this software, a novel approach to quickly initialize additional fluid in a rest state in simulations with any 3D boundary shape is implemented and is able to preserve any already existing fluid. It only uses the density property of the particles to allow compatibility with any smoothed-particle hydrodynamics (SPH) simulation scheme and any boundaries model. This initialization method is fast enough to allow the initialization of new fluid volumes interactively while the simulation is running. The software also proposes the creation of a dynamic simulation window, allowing therestriction of simulating the fluid only around moving objects. The archive includes multiple experiments to demonstrate the capabilities and performance of the software

Fluid initialization and dynamic window for smoothed-particle hydrodynamics simulation

International audienceFluid simulation is an essential tool to produce realistic looking animations. In particular, Lagrangian simulations offer interactive computation times with an easy integration of the two-way interaction with rigid bodies. However, the interactivity is lost for larger scenes even if only the areas around the bodies have any visual interest. In this paper, we present a novel approach to quickly initialize additional fluid in a rest state in simulations with any 3D boundary shape and able to preserve any already existing fluid. Our approach only uses the density property of the particles to allow compatibility with any smoothed-particle hydrodynamics (SPH) simulation scheme and any boundaries model. This initialization method is fast enough to allow the initialization of new fluid volumes interactively while the simulation is running. We showcase our approach by proposing a method to create a dynamic simulation window, allowing the restriction of simulating the fluid only around moving objects. We propose multiple experiments to demonstrate the capabilities and performance of our approach

Physics-based control of walking virtual characters in low frequency simulations

International audiencePhysics-based control of virtual characters traditionally uses high simulation frequencies of 1 to 2 kHz. While lowering the simulation frequency frees computation time, it usually introduces instabilities within the simulation. In this paper, we propose a control strategy that can be used for high and low simulation frequencies, down to 225 Hz. The inherent instabilities were reduced by optimizing control parameters and by introducing a novel control feedback for the stance leg. We also show how lower frequencies hold a more restrictive space of possible control parameters than higher ones. Our controller shows equal robustness as high frequency controllers while requiring in average only 0.8 ms per simulation step

Physics-based control of virtual characters in low frequency simulations

International audienceUsing a lower simulation frequency for physics-based control of virtual characters frees computation time that can be used for more complex environment. However, using low simulation frequency may introduce instabilities inside the simulation. In this paper, we demonstrate that even a simple control strategy can be used at a low simulation frequency by adapting the control parameters. Indeed we show that lower frequencies hold a more restrictive space of possible control parameters than higher ones. We propose a method to find optimized control parameters for frequencies as low as 200Hz. As using such low frequencies may introduce foot-ground contact instabilities, we also introduce an additional control feedback on the stance leg. Our controller shows similar robustness as high frequency controller while using 0.8ms per simulation step

Real-time gait control for partially immersed bipeds

International audiencePhysics-based animation is an increasingly studied subject of computer animation because it allows natural interactions with the virtual environment. Though some existing motion controllers can handle the simulation of interactions between a character and a liquid, only few methods focus on the simulation of the locomotion of immersed bipeds. In this paper, we present a control strategy capable of simulating partially immersed gaits. The impact of the liquid on the character's motion is modeled through simple hydrodynamics. To produce natural looking animations, we design a controller allowing the combination of multiple gait styles, the conservation of balance through intelligent foot placement and precise control of the character's speed. We determine the optimal parameters for the controller by using an optimization process. This optimization is repeated for several scenarios where the character has to walk across a volume of liquid parametrized by its height. Our controller produces natural looking gaits while being capable of online adaptation to the variation of liquid height, to the modification of the liquid density and viscosity and to the variation of the required character's speed

Optimizations for predictive–corrective particle-based fluid simulation on GPU

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