AN ADDED MASS THEORY FOR THE BASE PLATE IN A PARTIALLY FILLED RECTANGULAR TANK FOR USE WITH FEA

Undertaking a dynamic finite element analysis on a tank containing a fluid either requires both the fluid and tank to be modelled or the mass of the vesselʹs walls and base to be adjusted to account for the presence of the fluid. The former generally requires specialized solid elements to model the fluid, which are not available in all finite element software packages. This paper details a set of properties for structural solid elements that allow these elements to accurately emulate water within a vessel. Two fully welded rectangular steel tanks, constructed from plate of different thicknesses, were partially filled with water and dynamically excited. Excellent agreement was found between the dynamic measurements taken from the base of the tanks and the predictions from a finite element model with the fluid modelled using structural solid elements and the derived property set. These experiments show that the fundamental mode of dynamic behaviour of the base of these tanks is primarily dependent on both the depth of fluid in the tank and the thickness of its base. The added mass principle of Greenspon (Journal of Acoustical Society of America33, 1485–1497 [1]), derived mainly for plates exposed to essentially an infinite body of fluid, could not be used to accurately calculate the adjustment in mass of the base plate to account for the presence of a finite volume of fluid. A modification to the added mass principle of Greenspon has been proposed that fully accounts for this depth and base thickness dependency.