DETERMINATION OF VIRTUAL MASS EFFECT OF WATER ON SUBMERGED PLATES

Abstract

This investigation deals with determination of virtual mass effect of water on vibrating submerged plates. Free vibration tests are carried out on Perspex models of circular and rectangular plates of different sizes and thicknesses. The fundamental frogaency of models are measured in air and water at different depths of submergence. The free vibration tests are also conducted on plates with different sizes and shapes of o~)enings. In all eighteen models of fixed circular plates and seven models of rectangular cantilever plates are tested to determine the effect of size and flexibility of the plate on the virtual mass under water. It has been found that .t added mass of water' depends on diameter of plate, diameter-thickness ratio of circular plates and their frequency in air. Added mass also depends on the depth of submergence but it becomes constant beyond a certain depth which depends on the diameter of the plate and diameter-thickness ratio. :,dried mass of water is found to be fifteen to fifty six times the weight of the plate. By a single test ii forced vibration, it is seen th.:,t added mass effect of water on the plate is same as in free vibration in fundamental mode. For rectangular cantilever plates, it is found that added mass depends on size of plate, aspect ratio and thickness of plate. vii It is observed that the shape of opening in fixed circular plate affects the added mass considerably but the size of opening has no definite relation with added mass. It changes with change . in thickness of Plate.. For rectangular cantilever plates, it Is found that added mass reduces to about 25% due. to openings of +O to 60%.