International audienceThis paper gives an example of numerical methods with finite element coupling for the numerical study of an industrial fluid/structure coupled problem. The problem is solved by coupling a finite element discretization of both fluid and structure domain. The coupled system is described in terms of pressure and displacement for the fluid and structure problem. The unknown degrees of freedom are expanded in a Fourier serie. A numerical code is developed in Matlab in order to perform the modal analysis of the coupled problem. Numerical calculations are performed and compared with the Ansys code in order to validate our numerical developments.Nous présentons une analyse modale d'une structure industrielle couplée avec un fluide, en utilisant les techniques numériques de calculs couplés fluide/structure. Compte tenu de la nature axisymétrique de la géométrie et de la nature non axisymétrique des équations de couplage, la modélisation du problème est réalisée au moyen d'éléments finis axisymétriques développés en série de Fourier. Un code de calcul est implanté dans Matlab pour permettre l'analyse modale de la structure. Différentes formulations du problème sont comparées ; les résultats de calcul Matlab sont comparés avec les résultats de calculs obtenus avec le code généraliste Ansys. Les développements mis en œuvre pour cet exemple seront à terme intégrés dans le code Ansys pour l'étude de problèmes couplés en pression/déplacement avec développement en série de Fourier

This paper is related to the study of a nuclear propulsion reactor prototype for the French Navy. This prototype is built on ground and is to be dimensioned toward seismic loading. The dynamic analysis takes the coupled fluid structure analysis into account. The basic fluid models used by design engineers are inviscid incompressible or compressible. The fluid can be described in a bidimensional by slice or a three-dimensional approach. A numerical study is carried out on a generic problem for the linear FSI dynamic problem. The results of this study are presented and discussed. As a conclusion, the three-dimensional inviscid incompressible fluid appears to be the best compromise between the description of physical phenomena and the cost of modeling. The geometry of the reactor is such that large displacements of the structure in the fluid can occur. Therefore, the linearity hypothesis might not be longer valid. The case of large amplitude imposed oscillating motion of a cylinder in a confined fluid is numerically studied. A CFD code is used to investigate the fluid behavior solving the NAVIER-STOKES equations. The forces induced on the cylinder by the fluid are computed and compared to the linear solution. The limit of the linear model can then be exhibited.

The present paper deals with the numerical s imulation of a coupled non linear flu id-structure problem by explicit coupling between a finite element structure code and a fi nite volume fluid code. This numerical study is carried out in order to develop robust and general coupling with FE and CFD commercial code for industrial applications.A geometrically simple non linear coupled problem is presented in order to validate the numerical approach. The structure non linear problem is solved with a finite element technique, using a iterative implicit algorithm for time integration. The fluid problem is solved using standard numerical techniques (finite volume approach, implicit splitting operator scheme). The whole coupled problem is solved with a commercial CFD code: a dedicated FE structure code is developed in the CFD code together with coupling (in time, in space) procedures.The proposed method is validated in the case of a incompressible inviscid fluid. for which the coupled problem is solved with an analytical solution. The present study gives a reference test case for a full scale fluid-structure model. Industrial applications can now be considered by coupling commercial 1-'E and FV codes with general cou pling code.

The present paper is related to a seismic analysis of a naval propulsion ground prototype nuclear reactor with fluid-structure interaction modeling. Many numerical methods have been proposed over the past years to take fluid/structure phenomenon into account [14] in various engineering domains, among which nuclear engineering in seismic analysis [15]. The purpose of the present study is to apply general methods on a global approach of the nuclear reactor. A simplified design of the pressure vessel and the internal structure is presented; fluid-structure interaction is characterized by the following effects: • added mass effects are highlighted with the calculation of an added mass operator, obtained from a finite element discretisation of the coupled problem. The numerical model is developed within the CASTEM code using an axi-symmetric model of the industrial structure; • coupling effects between the external and internal structure via the confined inner fluid are also illustrated and numerically described with the added mass operator; • added stiffness effects are taken into account with an added stiffness matrix describing pre-stress effects due to a static pressure loading simulating the actual operating conditions of the reactor. The expected fluid-structure interaction effects on the nuclear pressure vessel and their numerical modeling leads to the definition of a global coupled model which can be used to perform a seismic analysis. A modal analysis is first performed and classical linear methods (static, spectral and temporal) are then applied on the studied structure with taking fluid-structure into account.

International audienceThis paper deals with fluid forces induced by an oscillating rigid circular cylinder in a fluid initially at rest. The amplitude of the imposed movement is assumed sufficiently small so that no wake is formed. The objective of the present paper is to review different theoretical methods to evaluate fluid forces. A wide variety of conditions is considered, from inviscid, compressible flows in infinite fluid domains, to viscous, incompressible and strongly confined ones. A special care is taken to underline the limits of the simplified models regarding real fluid effects, such as three-dimensional centrifugal instabilities. This review is related to a study whose ultimate aim is to predict dynamic fluid load during a typical shock encountered in the environment of a military ship