Efficient modelling and accurate knowledge of the mechanical behaviour of the reactorcore are needed to estimate the effects of seismic excitation on a nuclear power plant. Thepresence of cooling water flow (in PWRs) gives rise to fluid structure interaction phenomena.Modelling of fluid structure interactions on fuel assemblies is thus of fundamentalimportance in order to assure the safety of nuclear reactors. The main objective of thePhD project which is presented in this document is to investigate fluid structure interactionsin order to have a better understanding of the involved phenomena. Both modellingand experimental approach are considered. A new simplified linear model for fluid structureinteractions is developed by using the potential flow theory for fluid force modellingwhile the Euler-Bernoulli beam model is used for the structural part. The model, is firstdeveloped for a single cylinder and it is validated with reference works in literature. Theeffects of the confinement size and of the wavenumber are investigated. The potential flowmodel developed for a single cylinder, is thus extended to a multi cylinders geometry. Theexperimental approach is thus needed in order to validate the developed model. A newexperimental facility, ICARE, is designed in order to investigate fluid structure interactionphenomena on half scale fuel assemblies. In this document, the results provided bydisplacement and LDV measurements are widely analysed. The dynamical behaviour ofthe fuel assembly and coupling effects are investigated. Calculations are compared to theexperimental results in order to validate the model and to analyse its limits. The model isin agreement with experimental results regarding the added mass effect. In addition, themodel qualitatively predicts couplings effects on different directions. As a drawback, thepotential flow model cannot predict added damping effects, which are mainly due to viscousforces. Finally in this document another application of the developed model is described.The model is used in order to simulate experiments performed on a surrogate fuel assemblyin the experimental facility installed at George Washington University (GWU). The modelis able to predict and to provide a valid interpretation for the water flow perturbation dueto the motion of the excited assembly. The thesis concludes with perspectives for furtherimprovements of the model, by integrating viscous terms in the equations. Work needs tobe carried out on the analysis of Particle Image Velocimetry (PIV) data collected duringICARE experimental campaigns.

Publishing papers presented at the Fourth International Conference on Fluid Structure Interactions, this book features contributions from experts specialising in this field on new ideas and the latest techniques. A valuable addition to this successful series and will be of great interest to mechanical and structural engineers, offshore engineers, earthquake engineers, naval engineers and any other experts involved in topics related to fluid structure interaction. Topics covered include: Hydrodynamic Forces; Response of Structures including Fluid Dynamic; Offshore Structure and Ship Dynamics; Fluid Pipeline Interactions; Structure Response to Serve Shock and Blast Loading; Vortex Shedding and Flow Induced Vibrations; Cavitations Effects in Turbo Machines and Pumps; Wind Effects on Bridges and Tall Structures; Mechanics of Cables, Rivers and Moorings; Building Biofluids and Biological Tissue Interaction Problems in CFD; Experimental Studies and Validation; Vibrations and Noise; Free Surface Flows and Moving Boundary Problems.

This paper describes a seismic analysis which includes fluid-structure interactions for a large LMFBR reactor with many internal components and structures. Two mathematical models were employed. An axisymmetrical model was used for the vertical excitation analysis whereas a three-dimensional model was used for the horizontal excitation analysis. In both analyses, the sodium coolant was treated by continuum fluid elements. Thus, important seismic effects such as fluid-structure interaction, free-surface sloshing, fluid coupling, etc. are included in the analysis. This study is useful to the design of future LMFBR reactors. The results of this study can be used to improve the margin of safety of LMFBR plants under seismic conditions.

A formulation which accounts for fluid-structure interaction of piping system under seismic excitation is presented. The governing equations of the fluid and the structure to model the pipe are stated. Using the finite element method the discretized equations are obtained. A transformation procedure for proper assembly of matrices is introduced. A solution algorithm is described. 9 refs., 2 figs.

This book provides a comprehensive overview of the numerical simulation of fluid–structure interaction (FSI) for application in marine engineering. Fluid–Structure Interaction details a wide range of modeling methods (numerical, semi-analytical, empirical), calculation methods (finite element, boundary element, finite volume, lattice Boltzmann method) and numerical approaches (reduced order models and coupling strategy, among others). Written by a group of experts and researchers from the naval sector, this book is intended for those involved in research or design who are looking to gain an overall picture of hydrodynamics, seakeeping and performance under extreme loads, noise and vibration. Using a concise, didactic approach, the book describes the ways in which numerical simulation contributes to modeling and understanding fluid–structure interaction for designing and optimizing the ships of the future.

Soil-structure interaction (SSI) is an important phenomenon in the seismic response analysis. As seismologists describe seismic excitation in terms of the seismic motion of certain control point at the free surface of the initial site, the question is whether the same point of the structure (after structure appears) will have the same seismic response motion in case of the same seismic event. If yes, then seismic motion from seismologists is directly applied to the base of the structure (it is called “fixed-base analysis”), and they say that “no SSI occurs”’ (though literally speaking soil is forcing structure to move, so interaction is always present). This is a conventional approach in the field of civil engineering. However, if heavy and rigid structure (sometimes embedded) is erected on medium or soft soil site, this structure changes the seismic response motion of the soil as compared to the initial free-field picture. Such a situation is typical for Nuclear Power Plants (NPPs), deeply embedded structures, etc. The book describes different approaches to SSI analysis and different SSI effects. Special attention is paid to the Combined Asymptotic Method (CAM) developed by the author and used for the design of NPPs in seismic regions. Nowadays, some civil structures have parameters comparable to those of NPPs (e.g., masses and embedment), so these approaches become useful for the civil structural engineers as well.