On the Estimation of Virtual Mass of Stiffened Plates Vibrating in Water

Abstract

The proper design estimate of stiffened plates is very important because they are one of the most basic structural elements of a ship hull. Since stiffened plates such as walls in a tank are immersed in water or other kinds of liquid, their natural frequencies tend to decrease and often become resonant with the exciting force due to a propeller or a main engine. In many cases, the scantlings of stiffened plates are increased to avoid resonant vibrations. In the previous paper, we developed a computer program for the vibration analysis of rectangular stiffened plates in water, and we obtained a good agreement between calculations and experiments. According to those results and adding some other calculations, we are discussing here a simple method to estimate the virtual mass of immersed stiffened plates. We performed a vibration analysis of aft-peak tank floor using NASTRAN as an example. The result showed a possibility of large reduction in natural frequency for the floor vibrating in water.