Poincaré-Cosserat equations for Lighthill three-dimensional dynamic model of a self propelled eel devoted to Robotics

International audienceIn this article, we propose a dynamic model of the three-dimensional eel swim. This model is analytical and suited to the on-line control of eel-like robots. The proposed solution is based on the Large Amplitude Elongated Body Theory of Lighthill and a working frame recently proposed in [1] for the dynamic modeling of hyper-redundant robots. This working frame was named "macro-continuous" since at this macroscopic scale, the robot (or the animal) is considered as a Cosserat beam internally (and continuously) actuated. This article proposes new results in two directions. Firstly, it achieves an extension of the Lighthill theory to the case of a self propelled body swimming in three dimensions, while including a model of the internal control torque. Secondly, this generalization of the Lighthill model is achieved due to a new set of equations which is also derived in this article. These equations generalize the Poincaré equations of a Cosserat beam to the case of an open system containing a fluid stratified around the slender beam

Fast Dynamics of a three dimensional eel-like robot: comparisons with Navier-Stokes simulations

International audienceThis article proposes a dynamic model of the swim of elongated ﰣshes suited to the on-line control of bio-mimetic eel-like robots. The approach is analytic and can be considered as an extension of the original reactive "Large-Elongated-Body-Theory" of Lighthill to the three dimensional self propulsion augmented of a resistive empirical model. While all the mathematical fundamentals are detailed in [1], this article essentially focuses on the numerical validation and calibration of the model and the study of swimming gaits. The proposed model is coupled to an algorithm allowing us to compute the motion of the ﰣsh head and the ﰣeld of internal control torque from the knowledge of the imposed internal strain ﰣelds. Based on the Newton-Euler formalism of robots dynamics, this algorithm works faster than real time. As far as precision is concerned, many tests obtained with several planar and three dimensional gaits are reported and compared (in the planar case) with a Navier-Stokes solver, devoted until today to the planar swim. The comparisons obtained are very encouraging since in all the cases we tested, the diﰢerences between our simpliﰣed and reference simulations do not exceed ten per cent

Towards performance optimisation in kayak using CFD

International audienceThis article summarizes the major part of the research project SOKA ”Simulation et Optimisation de canoës-KAyaks”, in collaboration with INRIA Sophia-Antipolis and the French Canoe Federation, founded by INSEP (the French National Institute of Sport and Physical Education) and the French ministry ”Ministère de la Ville de la Jeunesse et des Sports”.The main goal was to develop a procedure which includes experimenal measurements and advanced numerical simulation of the flow around the hull to deduce an analytical model of the global loads of the kayaker on his hull. This model was thus used to ad- dress and test an optimisation procedure based on unsteady CFD simulations with solved motions and analyse the influence of some parameters on the forward velocity of the hull

Robot anguille sous-marin en 3D

L'objectif de ce projet soutenu par le programme ROBEA CNRS est de concevoir, étudier et réaliser un robot « anguille » capable de nager en trois dimensions. Pour cela nous étudions sur la base de modèles continus macroscopiques, les problèmes de la simulation, locomotion et commande. L'étude s'appuie sur une analyse biomécanique de la nage et se concrétise par la réalisation d'une plate-forme logicielle et d'un prototype. Pour atteindre ces objectifs un groupe pluridisciplinaire d'équipes et laboratoires a été formé : · Muséum National d'Histoire Naturelle (MNHN) : Laboratoire d'Ichtyologie · Laboratoire de Mécanique des Fluides (LMF) de Nantes : Divisions Modélisation Numérique (DMN) et Hydrodynamique Navale (DHN) · IRCCyN : Equipes Robotique, Méthodes de Conception Mécanique, Systèmes Temps Réel · LAG : Axe Commande et Observation · LIRMM : Equipe Robotique sous-Marin

Towards automated computation with uncertainty estimation for industrial simulation of ship flow

Adaptive grid refinement is tested for routine, automated simulations of ship resistance in calm water. A simulation protocol for these computations is fine-tuned on one test case and then applied unchanged to three different cases. The solutions are numerically accurate and compare well with experiments. Effective numerical uncertainty estimation increases the trustworthiness of the solutions

Interaction Fluide-Structure pour les corps élancés

Cet article présente le couplage du solveur fluide ISIS-CFD du LMF et d’un solveur structure de type poutre appliqué à des problèmes 3D complexes d’interaction fluide-structure des corps élancés en grand déplacement, comme les risers. Le couplage temporel s’appuie sur un algorithme itératif. Un soin tout particulier a été porté au couplage spatial, en particulier au processus de déformation de maillage. Afin de valider le code IFS, le cas-test 2D d’Hübner a été traité

Development of a CFD-based screening tool for VIV prediction

This paper presents an efficient screening tool, based on the 2D strip method and the CFD-based approach. The proposed method allows the study of the dynamics of the vortex-induced vibration (VIV) phenomenon with almost the same accuracy as a fully 3D Fluid-Structure interaction (FSI) model, but with a reduction in computational times by a factor of nearly 20 compared to the 3D approach. Such a large reduction makes the use of CFD-based analysis feasible on a workstation within a reasonable time frame and opens the possibility of CFD approaches in a subsea pipeline design process

Procédure de time-splitting pour la résolution de la fraction volumique dans le cas d'écoulements instationnaires

Les simulations numériques d'écoulements multifluides utilisant des schémas de capture d'interface souffrent de la contrainte sur le pas de temps imposée par la condition Courant-Friedrichs-Lewy (CFL). Nous proposons ici une méthode pour accélérer les calculs, appelée procédure time-splitting. L'équation de convection de la fraction volumique est résolue sur des pas de temps intermédiaires où la condition CFL est vérifiée. Elle permet ainsi l'utilisation d'un pas de temps global plus grand. Les développements ont été validés sur différents écoulements 2D. Nous présentons un cas test modélisant l'écoulement provoqué par une rupture de barrage suivie de l'impact sur un obstacle. Dans cet exemple, un facteur de réduction du temps de calcul allant jusqu'à 3 a été obtenu

The use of High-Performance Computing in nautical sports with a focus in hydrodynamics on rowing and kayaking

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