The present paper deals with numerical analysis of fluid-structure interaction problems with commercial finite element codes. The various fluid-structure formulations are today well known from a theoretical point of view, but their application to the dynamic analysis of industrial problems with spectral methods can not be performed with all available codes. The present study exposes a developing process currently undertaken in order to integrate symmetric FSI formulation within the commercial finite element code Ansys. This process is carried out in several steps which are detailed here: first, on overview of the existing fluid-structure formulations is exposed with the view to comparing various finite element codes. Then, coupled symmetric and non-symmetric formulations are recalled on two general FSI problems (elasto-acoustic and hydro-elastic problems) and applied on a generic reference test case. Numerical integration of the presented methods is performed on the Ansys code in the following direction: free surface condition for sloshing mode in pressure formulation, harmonic axi-symmetric pressure fluid formulation for coupled axi-symmetric calculations, general symmetric coupled formulation in u,p,φ (for elasto-acoustic problems with fluid free surface without sloshing) and u,p,η (hydro-elastic problems with fluid free surface with sloshing) formulations. Elementary validations of the implemented methods are proposed by comparing Ansys numerical results to calculations results obtained with a finite element code developed by DCN Propulsion, and presented in the paper. All the developments will be available in future release of the Ansys code in the coming years for the benefit of the Ansys users’ community.
The present paper deals with the numerical simulation of a non-linear coupled fluid-structure problem with finite element/finite volume coupled technique and mainly focus on the time coupling algorithm: the coupling procedure lies on a staggered explicit or implicit strategy. A simple coupled case is studied; namely a non-linear elastic beam coupled with an incompressible fluid with free surface effects. The structure problem is solved with a finite element approach. The nonlinear discrete structure problem is integrated in time with the non-linear Newmark scheme with a fixed-point procedure. The fluid problem is solved with a finite volume approach. The non-linear discrete fluid problem is solved with the PISO (Pressure Implicit by Splitting Operator) algorithm. The coupled problem is solved with two different approaches. At first, an explicit approach is proposed, based on a step by step alternate integration of the structure and fluid non-linear problems. As expected the method is found to be numerically dissipative and potentially unstable. An implicit approach is then proposed, using inner coupling iterations. The proposed algorithm is proved to be stable and less dissipative. Implicit and explicit approaches are presented. Numerical calculations are performed on the elementary studied case. Results are presented and compared for the two time-integration procedures, highlighting the numerical qualities of each procedure in terms of numerical damping, stability and precision.
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.
The present paper deals with the modal analysis of a nuclear with fluid-structure interaction effects. In a previous study, added mass and added stiffness effects due to fluid-structure interaction were modeled and studied. A dynamic analysis was performed for a seismic excitation, i.e. in the low frequency range. The present study deals with high frequency analysis, i.e. taking into account compressibility effects in the fluid problem. Elasto-acoustic coupling phenomena are studied and described in the industrial case. The elasto-acoustic coupled problem is formulated using the displacement/pressure-displacement potential coupled formulation which yields symmetric matrices. A modal analysis is first performed on the fluid problem alone, with a calculation of acoustic eigenfrequencies and the corresponding modal masses. A modal analysis is then performed for the coupled fluid-structure problem in the case of an incompressible fluid and a compressible fluid at standard pressure and temperature conditions and for a compressible fluid at the operating pressure and temperature conditions. Elasto-coupling effects are then highlighted and discussed.
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