Scientific papers

Journal Ocean Engineering 2022

Title : Investigation of blade-mast fluid-structure interaction of a tidal turbine

Autors :
Corentin Lothode (a,b), Jules Poncin (b), Didier Lemosse (c), David Gross (b), Eduardo Souza de Cursi (c)
(a) LMR, UMR 6085 (CNRS, Université de Rouen)
(b) Société K-Epsilon
(c) LMN, INSA Rouen

In this article, we investigate the movement and vibrations of a blade due to the presence of the mast. When the blade passes in front of the mast, a sudden pressure spike induces vibrations in the blade. To study the influence of stiffness, two different structures were studied. We present our numerical schemes concerning the resolution of the flow, the behavior of the structure and the coupling of the two systems. Then, we validate two methods against an experiment (Bahaj et al., 2007). In a third section, we present cases of fluid-structure interaction. Several structures are setup by modifying the stiffness of the material. Their steady open-water (without a mast) behaviors are compared. And finally, two dynamic fluid-structure computations are performed to compare the behavior of an elastic blade passing next to a mast. For all the cases, we use K–FSI developed by K-Epsilon to solve the fluid-structure interaction (FSI).

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25iéme Congrès Français de mécanique 2022

Title : Determination of the equivalent structural properties of a composite hydrofoil

Autors :
A. Faye*, N. Carrere**, M. Sacher**, F. Hauville***, A. Neme**
*K-EPSILON, ** ENSTA Bretagne, *** IREnav

Journal of Fluids and Structures 2019

Title : Curvature-based, time delayed feedback as a means for self-propelled swimming

Autors :
David Gross (a,b), Yann Roux (a), Médéric Argentina (b)
(a) K-Epsilon S.A.R.L., 1300 Route des Cretes, 06560 Valbonne, France
(b) Université Côte d’Azur, CNRS, INPHYNI, France

The development of bio-inspired robotics has led to an increasing need to understand the strongly coupled fluid–structure and control problem presented by swimming. Usually, the mechanical forcing of muscles is modeled with an imposed distribution of bending moments along the swimmer’s body. A simple way to exploit this idea is to define a central pattern forcing for this active driving, but this approach is not completely satisfactory because locomotion results from the interaction of the organism and its surroundings. Gazzola et al. (2015) have proposed that a curvature-based feedback with a time delay can trigger self-propulsion for a swimmer without necessitating such a pre-defined forcing. In the present work, we implement this feedback within a numerical model. We represent the swimmer as a thin elastic beam using a finite element representation which is coupled to an unsteady boundary element method for the resolution of the fluid domain. The model is first benchmarked on a flexible foil in forced leading edge heave.

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Title : Flexible hydrofoil optimization for the 35th America’s Cup with constrained EGO method

Autors :
M. Sacher
M. Durand
E. Berrini
F. Hauville
R. Duvigneau
O. Le Maître
J. A. Astolfi.

This paper investigates the use of constrained surrogate models to solve the multi-design optimization problem of a flexible hydrofoil. The surrogate-based optimization (EGO) substitutes the complex objective function of the problem by an easily evaluable model, constructed from a limited number of computations at carefully selected design points. Associated with ad-hoc statistical strategies to propose optimum candidates within the estimated feasible domain, EGO enables the resolution of complex optimization problems. In this work, we rely on Gaussian processes (GP) to model the objective function and adopt a probabilistic classification method to treat non-explicit inequality constraints and non-explicit representation of the feasible domain. This procedure is applied to the design of the shape and the elastic characteristics of a hydrofoil equipped with deformable elements providing flexibility to the trailing edge. The optimization concerns the minimization of the hydrofoil drag while ensuring a non-cavitating flow, at selected sailing conditions (boat speed and lifting force). The drag value and cavitation criterion are determined by solving a two-dimensional nonlinear fluid-structure interaction problem, based on a static vortex lattice method with viscous boundary layer equations, for the flow, and a nonlinear elasticity solver for the deformations of the elastic components of the foil. We compare the optimized flexible hydrofoil with a rigid foil geometrically optimized for the same sailing conditions. This comparison highlights the hydrodynamical advantages brought by the flexibility: a reduction of the drag over a large range of boat speeds, less susceptibility to cavitation and a smaller angle of attack tuning range.

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Marine 2017

Title : Geometric model for automated multi-objective optimization of foils

Autors :
E. Berrini*, B. Mourrain**, R. Duvigneau**, M. Sacher***, Y. Roux****
* MyCFD, ** INRIA Sophia Antipolis, *** IRENAV, **** K-Epsilon

This paper describes a new generic parametric modeller integrated into an auto-mated optimization loop for shape optimization. The modeller enables the generation of shapes by selecting a set of design parameters that controls a twofold parameterization: geometrical- based on a skeleton approach - and architectural - based on the experience of practitioners - to impact the system performance. The resulting forms are relevant and effective, thanks to a smoothing procedure that ensures the consistency of the shapes produced.
As an application, we propose to perform a multi-objective shape optimization of a AC45 foil. The modeller is linked to the fluid solver AVANTI, coupled with Xfoil, and to the optimization toolbox FAMOSA.

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Marine 2015

Title : Numerical study of VIV over a flexible riser

Autors :
C. Lothode*, G. Fontaine*, E. Guilmineau*, A. Wang**, F. Vertallier***, M. Minguez***, A. Cinello*** and D. Gross*
* K-Epsilon, ** LHEAA, Ecole Centrale de Nantes, *** CITEPH 

Ce papier décrit les problématique de VIV d'un riser lorsque celui -ci est placé dans un courant. Les simulations ont été réalisé avec les outils d'interactiuon fluide structure développé par K-epsilon et validé à travers des essais en tunnel hydrodynamique.

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