Study On The Added Mass For The Vibration Of The Liquid Tank’s Bulkheads

Liquid tanks are common in naval architecture and ocean engineering. Local vibration caused by them will bring great harm to ships, thus it is important to ensure the dynamic safety of these liquid tanks. The crucial part in the study on the dynamic behavior of liquid tanks is the calculation of the structural added mass caused by fluid.In the second chapter of this paper, the added mass coefficient formula for the same phase and anti phase vibration of rectangular tanks was developed based on the idea of dry mode method. The solution of potential function in fluid was attained by method of separation of variables. The formula is related to vibration wave numbers and its solution corresponds to the modal added mass for each set. Water depth index was derived with the consideration of water level and has been applied to get natural frequency of lateral vibration of bulkheads with full tanks.In the third chapter, three numerical methods for fluid-structure interaction vibration problems were used in this case and the methods are ANSYS/Fluid30, ANSYS/Fluid80and NASTRAN Virtual Mass method. The former two methods are based on structure-fluid finite element method and the last method is based on structure finite element and fluid boundary element method. The comparison of numerical results and theoretical results by the present method shows that ANSYS/Fluid80is more credible in solving this sort of problem and the results by the present method are in close agreement with the numerical ones in solving the same phase vibration.Finally, a series of more detailed numerical analysis was carried out by ANSYS/Fluid80. The water level, the gravitational effects of the free surface and bulkheads’ stiffeners were considered, and the results were compared with the ones by the present method. According to the comparison, the added mass coefficient and water depth index developed by this paper can be applied more suitable for the water tank model with the elastic support boundary conditions, and they have a certain accuracy in solving the same phase vibration.