Validity of the one-dimensional limp model for porous materials

A straightforward criterion to determine the limp model validity for porous materials is addressed here. The limp model is an "equivalent fluid" model which gives a better description of the porous behavior than the well known "rigid frame" model. It is derived from the poroelastic Biot model assuming that the frame has no bulk stiffness. A criterion is proposed to identify the porous materials for which the limp model can be used. It relies on a new parameter, the Frame Stiffness Influence FSI based on porous material properties. The critical values of FSI under which the limp model can be used, are determined using a 1D analytical modeling for a specific boundary set: radiation of a vibrating plate covered by a porous layer.Comment: 12th International Student Conference on Electrical Engineering, Prague : Tch\`eque, R\'epublique (2008

A Positive-definite Cut-cell Method for Strong Two-way Coupling Between Fluids and Deformable Bodies

© ACM, 2017. This is the author's version of the work. It is posted here by permission of ACM for your personal use. Not for redistribution. The definitive version was published in Zarifi, O., & Batty, C. (2017). A Positive-definite Cut-cell Method for Strong Two-way Coupling Between Fluids and Deformable Bodies. In Proceedings of the ACM SIGGRAPH / Eurographics Symposium on Computer Animation (p. 7:1–7:11). New York, NY, USA: ACM. https://doi.org/10.1145/3099564.3099572We present a new approach to simulation of two-way coupling between inviscid free surface fluids and deformable bodies that exhibits several notable advantages over previous techniques. By fully incorporating the dynamics of the solid into pressure projection, we simultaneously handle fluid incompressibility and solid elasticity and damping. Thanks to this strong coupling, our method does not suffer from instability, even in very taxing scenarios. Furthermore, use of a cut-cell discretization methodology allows us to accurately apply proper free-slip boundary conditions at the exact solid-fluid interface. Consequently, our method is capable of correctly simulating inviscid tangential flow, devoid of grid artefacts or artificial sticking. Lastly, we present an efficient algebraic transformation to convert the indefinite coupled pressure projection system into a positive-definite form. We demonstrate the efficacy of our proposed method by simulating several interesting scenarios, including a light bath toy colliding with a collapsing column of water, liquid being dropped onto a deformable platform, and a partially liquid-filled deformable elastic sphere bouncing.Natural Sciences and Engineering Research Council of Canad

Porous layer impedance applied to a moving wall: Application to the radiation of a covered piston

International audienceModelling a porous layer mounted on a vibrating wall by mean of an acoustic impedance is investigated in this paper. It is shown that the use of the surface impedance usually measured with the impedance tube method can provide erroneous estimation of the acoustic pressure radiated by the coated structure. The paper focuses on the derivation of an impedance, denoted the ”transfer impedance”, which describes accurately the dynamic movement of the porous layer. Biot's theory is used in the model to account for deformations in the thickness of the layer. Experimental validation is performed using a circular piston covered by a foam or a fibrous layer and radiating in a infinite halfspace. The radiation model including the transfer impedance shows good agreement with experimental data

Rayonnement acoustique de structures de type ossature bois : comparaison entre méthode éléments finis et formulation intégrale

Un des points délicats de la construction bois se situe au niveau de l'isolation acoustique des planchers bois. L'objectif de cette article est de déterminer le rayonnement acoustique de ce type de structures (légères et nervurées). Deux méthodes sont présentés, l'une modélisant, par éléments finis, le domaine global (structure in-vivo) et son couplage, l'autre exploitant une méthode combinée (élément finis et formulation intégrale) sur la structure in-vacuo. Un code éléments finis sous licence libre (FreeFem++) est employé dans cette étude en comparaison avec un des codes commerciaux

Adaptive Neural Network-Based Approximation to Accelerate Eulerian Fluid Simulation

The Eulerian fluid simulation is an important HPC application. The neural network has been applied to accelerate it. The current methods that accelerate the fluid simulation with neural networks lack flexibility and generalization. In this paper, we tackle the above limitation and aim to enhance the applicability of neural networks in the Eulerian fluid simulation. We introduce Smartfluidnet, a framework that automates model generation and application. Given an existing neural network as input, Smartfluidnet generates multiple neural networks before the simulation to meet the execution time and simulation quality requirement. During the simulation, Smartfluidnet dynamically switches the neural networks to make the best efforts to reach the user requirement on simulation quality. Evaluating with 20,480 input problems, we show that Smartfluidnet achieves 1.46x and 590x speedup comparing with a state-of-the-art neural network model and the original fluid simulation respectively on an NVIDIA Titan X Pascal GPU, while providing better simulation quality than the state-of-the-art model

Computer graphics liquids simulation using the Navier-Stokes equations, and visualization

L'inclusion réaliste de phénomènes naturels est l'un des objectifs de l'infographie. Les travaux exposés dans cette thèse découlent de cette problématique pour le cas des liquides, et s'intéressent à la simulation de leurs mouvements ainsi qu'à la visualisation des résultats de ces simulations.Dans le contexte de la simulation, a été proposé un mode d'interaction automatique du liquide, simulé grâce à la méthode Markers And Cells appliquée aux équations de Navier-Stokes, avec des objets déformables représentés à l'aide une modélisation masses-ressorts. L'interaction étudiée, de nature empirique mais traitée en cohérence avec la physique, autorise une interaction vraisemblable. Constituant la première étape d'une meilleure résolution de ce problème d'interaction, une méthode de simulation de liquides fondée sur une résolution des équations de Navier-Stokes par la méthode des éléments finis a ensuite été développée.Les aspects de visualisation ont été étudiés selon deux axes. Dans le premier, des travaux ont été menés pour exploiter sans reconstruction de surface les données issues des simulateurs MAC, qui sont constituées de nuages de points volumiques. L'intégration efficace de cette forme de données dans un algorithme de lancé de rayons a été étudiée, tout comme un mode de visualisation rapide de ces données, à l'aide d'une technique de visualisation volumique. Le second axe a concerné la mise au point d'une méthode de rendu interactif du phénomène visuel prépondérant en présence d'objets transparents comme les liquides, c'est-à-dire la réfraction. Une méthode pour en autoriser un affichage interactif, dans le cas d'objets de géométrie arbitraire, a été proposée. Elle s'appuie sur une capture de la distorsion visuelle induite par l'objet durant un précalcul, puis sur une synthèse interactive de la distorsion à partir des données précalculées, qui sont compressées à l'aide d'une représentation en harmoniques sphériques.Realistic inclusion of natural phenomena is a major issue in computer graphics. The work done in this PhD is related to this topic, for fluids. It is connected to both the simulation of motion and to the visualization of these simulation results.Regarding motion simulation, a fully automatic interaction scheme between liquid and deformable solids has been suggested, for the case of a Markers And Cells fluid simulation of the Navier-Stokes equations and spring-mass solids simulation. While empirical, the suggested interaction scheme gets a physically coherent treatment, in order to provide realistic behavior. Next, a solver using the Finite Elements Method applied to the Navier-Stokes equations has been developed, as a first step toward more realistic interaction with solids.Concerning visualization, two different ways have been followed. The first one deals with the direct use of the results of MAC simulation, that is volumetric marker clouds, without surface reconstruction. Efficient integration of this kind of data in ray-tracing and fast visualization using volume rendering of these data have both been studied. The second way explored in visualization deals with interactive rendering of the most prominent visual effect induced by transparent objects like liquids: refraction. A method able to provide interactive refraction on arbitrary geometry has been suggested. It relies on a preprocessing step in which the visual distortion induced by the object is captured and compressed using spherical harmonics. Then, distortion can be synthesized interactively for arbitrary viewpoints using these data

Computer graphics liquids simulation using the Navier-Stokes equations, and visualization

L'inclusion réaliste de phénomènes naturels est l'un des objectifs de l'infographie. Les travaux exposés dans cette thèse découlent de cette problématique pour le cas des liquides, et s'intéressent à la simulation de leurs mouvements ainsi qu'à la visualiRealistic inclusion of natural phenomena is a major issue in computer graphics. The work done in this PhD is related to this topic, for fluids. It is connected to both the simulation of motion and to the visualization of these simulation results.Regardin

Derivation of a frequency independent criterion to determine the limp model validity for highly porous sound absorbing materials

A frequency independent criterion to determine the limp model validity for highly porous sound absorbing materials is investigated. Although limp model is derived from the Biot theory assuming that the porous frame has no bulk stiffness, it is shown that this model can be used for highly porous materials since the criterion is respected. Abacus giving the criterion limit as function of the porous layer thickness are given for two configurations: sound absorption of a porous layer backed by a rigid backing and sound radiation of a plate covered by a porous layer. Its is shown that the derived criterion matches Beranek criterion but it is less restrictive

Hybrid Rendering of Dynamic Heightfields using Ray-Casting and Mesh Rasterization

International audienc