EFFECT OF ADDED MASS ON SUBMERGED VIBRATED PLATES V.H. Vu 1 , M. Thomas 1 , A.A. Lakis 2 and L. Marcouiller 3 1 Department of mechanical engineering, École de technologie supérieure, Montréal, QC, Canada marc.thomas@etsmtl.ca 2 Department of mechanical engineering, École Polytechnique, Montréal, QC, Canada 3 Hydro-Québec’s research institute, Varennes, QC, Canada ABSTRACT Vibration of solid-fluid interaction systems requires a deterministic knowledge of vibration analysis and structures coupling. It is evident that a structure vibrating in a fluid has to support an interactive inertial effect caused by the fluid which changes the dynamic behavior of the solid itself. This paper presents an experimental study on the effect of added mass on submerged plate structures which are subjected to vibration. Different plates vibrating in water at different depths with various geometry ratios are studied using a number of boundary conditions. Dynamic testing is conducted in time domains to identify the modal parameters of the structures. The modal added mass value and added mass coefficient are then derived from the change of modal frequencies from air to water. This is followed by a comparison of experimental results with several numerical analyses found in the literature. 1. INTRODUCTION In solid-fluid interaction study, plate structures have often been considered for two major reasons. Firstly, plates are widely used in common structures for ships, heat exchangers, aerospace and civil engineering. Secondly, the plate has an advantage in terms of structural convenience in modeling, analysis and testing. From a theoretical point of view, there are many published articles describing developments for dynamic analysis of plate structures. Lamb [1] conducted what is considered the first study on frequency analysis of a plate-fluid contact system using the Rayleigh method. Fu and Price [2] studied vibration responses of cantilevered vertical and horizontal plates partially or totally immersed in fluid. They assumed that the plates vibrated in a semi-infinite fluid medium. A finite element method and a singularity distribution panel approach were used to analyze the dynamic responses of plates in air and also to determine the hydrodynamic coefficients for each element in contact with fluid. Haddara and Cao [3] investigated dynamic responses of plates in air and submerged in fluid under various boundary conditions. They presented an approximate solution for the equation of motion of a plate coupled with fluid and provided an analytical added-mass factor depending on the height of the free surface and the depth of fluid under the plate. An approximate expression for the evaluation of the modal added mass was derived. Their results were in agreement with Fu and Price; when the plate depth attains 25% of its length, first frequency bending starts to change. Liang [4] took an alternative approach, using the Rayleigh Ritz method to derive the added mass factor for each mode of cantilever plate vibration with a correction coefficient for the aspect ratio. These added mass factors were then used to calculate free vibration of the plate. Use of the finite element method for structural analysis is well known, however the problem of solid-fluid interaction is so complicated that, to date, no coupled element has been developed to model this situation in commercial software. Recently, a research group at Polytechnique de Montreal developed a hybrid finite element model using the Sanders’ thin plate method to analyze the vibration of a variety of classes of plates in fluid. The interactive effects are distinctly derived and include