Jean-François Sigrist

Modal analysis of fluid-structure interaction problems with pressure-based fluid finite elements for industrial applications

The present paper deals with numerical developments performed in the finite element code ANSYS in order to carry out coupled fluid-structure analysis with pressure-based formulation. As a result, enhancement of the modeling possibilities within ANSYS is carried out for the following fluid and fluid structure modes: i) fluid sloshing modes, ii) fluid and fluid-structure modes with pressure-displacement formulation in axi-symmetric geometry with non axi-symmetric loading, iii) fluid-structure modes with symmetric formulations for elasto-acoustic and hydro-elastic problems, using the so-called symmetric (u, p, φ) and (u, η, φ) formulations. The paper also aims at providing finite element code users with test cases to refer to, for application of the new FSI formulations. The paper also serves as an introduction to the numerical calculation of eigenvalue problems with FSI. Theoretical bases of the formulations are first exposed; test-cases and industrial applications are then proposed. It is shown in particul...

Numerical simulation of an elementary Vortex-Induced-Vibration problem by using fully-coupled fluid solid system computation

Numerical simulation of Vortex-Induced-Vibrations (VIV) of a rigid circular elastically-mounted cylinder submitted to a fluid cross-flow has been extensively studied over the past decades, both experimentally and numerically, because of its theoretical and practical interest for understanding Flow-Induced-Vibrations (FIV) problems. In this context, the present article aims to expose a numerical study based on fully-coupled fluid-solid computations compared to previously published work [34], [36]. The computational procedure relies on a partitioned method ensuring the coupling between fluid and structure solvers. The fluid solver involves a moving mesh formulation for simulation of the fluid structure interface motion. Energy exchanges between fluid and solid models are ensured through convenient numerical schemes. The present study is devoted to a low Reynolds number configuration. Cylinder motion magnitude, hydrodynamic forces, oscillation frequency and fluid vortex shedding modes are investigated and the “lock-in” phenomenon is reproduced numerically. These numerical results are proposed for code validation purposes before investigating larger industrial applications such as configurations involving tube arrays under cross-flows [4].

A Fully Elastic Model for Studying Submerged Circular Cylindrical Shells Subjected to a Weak Shock Wave

The transient dynamics of evacuated and fluid-filled circular elastic shells, submerged in an infinite fluid medium and subjected to an external weak shock wave, is considered in this paper. This circular shell/acoustic medium interaction problem has already been tackled with simplified thin shell models, based on the Love-Kirchhoff hypotheses for the structural dynamics. In this case, the resulting radiated pressure field displays some discrepancies related to the A0 /S0 waves when compared to the experimental data available in the literature for the evacuated case. These drawbacks are overcome here by the use of an isotropic elastic model for the structural dynamics and an inviscid acoustic flow for the fluid dynamics, in a two-dimensional framework. It is assumed that the shell displacements are small compared to both its radius and thickness. The approach is based on the methods of Laplace transform in time, Fourier series expansions and separation of variables in space. For the fluid-filled case, the transient thick shell-weak shock wave interaction problem is explored and the radiated acoustic field described.Copyright

Implementation of a Stuctural-Acoustic Homogenized Method for the Dynamic Analysis of a Tube Bundle With Fluid Structure Interaction Modeling in ABAQUS: Formulation and Applications

The present paper deals with the dynamic analysis of a tube bundle with Fluid Structure Interaction (FSI) modeling using a structural acoustic homogenized method. Such a coupled problem leads to many degrees of freedom [a system of very large matrices] to compute tube displacements and pressure in the acoustic domain, it is therefore irrelevant to use standard coupled methods in industrial cases. Instead, specific modelings have to be used, such as structural acoustic homogenized method. Implementation and applications of such a technique within the general finite element code ABAQUS are performed using the so-called UEL Fortran subroutine. Firstly, general theoretical aspects on the homogenized method proposed by Broc & Sigrist are revisited. Then, subroutines developments are validated comparing results from the homogenized method to those of a standard approach on the representative case of a 10×10 tube bundle in two-dimensional and three-dimensional configurations subjected to seismic loadings. Results show that: (i) homogenized elements can easily be used as standard elements from the ABAQUS elements library, (ii) the homogenized approach is accurate on a physical point of view and (iii) considerably reduces modeling effort and computational time compared to a standard structural acoustic method.© 2014 ASME

Study of a Fluid-Structure Interaction Instability Mechanism in a Tube Bundle With Multiphase-POD Approach

Multiphase-Proper Orthogonal Decomposition Reduced-Order Method has been proven to be efficient for the low-cost study of fluid-structure interaction mechanisms. Applications to a single tube under cross-flow, then to a tube bundle system revealed good behaviours of this method, which was shown to be able to accurately reproduce the velocity flow field as well as the solid displacement, even in the case of large magnitudes. The goal here is to go further by studying an instability mechanism with the Multiphase-POD technique, involving a tube array configuration because of its high interest in the nuclear domain. We first want to know if this method can reproduce critical to unstable cases and finally, we are interested in the possibility of leading a parametric study coupled with the Multiphase-POD Method in order to evaluate the instability threshold. Indeed, parametric studies coupled with a reduced-order method could lead to a CPU time additional gain, since only one basis calculation could cover several configurations with low computational cost.Copyright

Efficient Semi-Analytical Methodology for the Pre-Design Analysis of the Shock Response of Marine Structures

We introduce a robust and computationally efficient methodology for numerical simulation of shock-structure interaction. The methodology is based on the use of some of the classical methods of mathematical physics, with the subsequent coupling between the fluid dynamics and structural parts using the finite-difference methodology. In order to demonstrate the versatility of the approach, we apply it to two rather different practically important problems of the interaction between shock waves and submerged cylindrical structures, aiming at providing insights that would be useful to engineers at the pre-design stage.We first consider a submerged cylindrical shell subjected to two consecutive shock waves, and analyze the effect of such loading in the context of both hydrodynamic fields and the structural stresses it induces. The most important result of this analysis is the observation, for certain values of the distance between the wavefronts, of a very significant increase of the maximum stress observed in the structure.Then, we consider a submerged cylindrical shell subjected to a single shock wave, but employ a more advanced shell theory than the one traditionally used, namely, the Reissner-Mindlin theory instead of the Kirchhoff-Love one. We demonstrate that such an advancement of the model not only leads to a very significant improvement of the accuracy of the respective simulations, but also allows for modeling relatively thick shells.Copyright

Numerical Study of Fluid-Structure Interactions in Tube Bundles With Multiphase-POD Reduced-Order Approach

Fluid-Structure Interactions are present in a large number of systems of nuclear power plants and nuclear on-board stoke-holds. Particularly in steam generators, where tube bundles are submitted to cross-flow which can lead to structure vibrations. We know that numerical studies of such a complex mechanism is very costly, that is why we propose the use of reduced-order methods in order to reduce calculation times and to make easier parametric studies for such problems.We use the multiphase-POD approach, initially proposed by Liberge (E. Liberge; POD-Galerkin Reduction Models for Fluid-Structure Interaction Problems, PhD Thesis, Universite de La Rochelle, 2008). This method is an adaptation of the classical POD approach to the case of a moving structure in a flow, considering the whole system (fluid and structure) as a multiphase domain. We are interested in the case of large displacements of a structure moving in a fluid, in order to observe the ability of the multiphase-POD technique to give a satisfying solution reconstruction. We obtain very interesting results for the case of a single circular cylinder in cross-flow (lock-in phenomenon). Then we present the application of the method to a case of confined cylinders in large displacements too. Here again, results are encouraging.Finally, we propose to go further presenting a first step in parametric studies with POD-Galerkin approach. We only consider a flowing-fluid around a fixed structure and the Burgers’ equation. A future work will consist in applications to fluid-structure interactions.Copyright

Analytical and numerical study of validation test-cases for multi-physic problems: application to magneto-hydro-dynamic

The present paper is concerned with the numerical simulation of Magneto-Hydro-Dynamic (MHD) problems with industrial tools. MHD has receivedattention some twenty to thirty years ago as a possible alternative inpropulsion applications; MHD propelled ships have even been designed forthat purpose. However, such propulsion systems have been proved of lowefficiency and fundamental researches in the area have progressivelyreceived much less attention over the past decades. Numerical simulationof MHD problem could however provide interesting solutions in the field ofturbulent flow control. The development of recent efficient numericaltechniques for multi-physic applications provide promising tool for theengineer for that purpose. In the present paper, some elementary testcases in laminar flow with magnetic forcing terms are analysed; equationsof the coupled problem are exposed, analytical solutions are derived ineach case and are compared to numerical solutions obtained with anumerical tool for multi-physic applications. The present work can be seenas a validation of numerical tools (based on the finite element method) foracademic as well as industrial application purposes.

Etude dynamique linéaire et non linéaire d’une poutre couplée avec un fluide

Nous proposons dans cet article une étude dynamique d’une pouter élastique couplée avec un fluide incompressible, contenu dans une cavité cylindrique et présentant une surface libre. Dans un premier temps, nous conduisons une analyse modale du système couplé, en mettant en oeuvre une technique éléments finis basée sur une description en déplacement de la structure et en pression du fluide. Une étude numérique permet de décrire les effets du couplage fluide/structure. Dans un second temps, on s’intéresse au problème temporel en formulant les équations dynamiques au second ordre de la poutre couplée avec le fluide, l’ensemble du système étant soumis à une accélération donnée. L’intégration en temps du problème utilise un algorithme implicite, nécessitant le calcul de la matrice tangente du problème. Une étude numérique est ensuite exposée et met en évidence l’apparition des nonlinéarités avec l’augmentation de l’amplitude de la sollicitation dynamique appliquée à l’ensemble. Une étude de l’influence respective des non-linéarités et des interactions fluide/structure sur la dynamique du problème est exposée.