Effect of viscosity on seismic response of waste storage tanks

A study of the effect of viscosity on the dynamic response of a liquid storage tank subjected to base excitations is presented. The tank is a typical high level waste storage tank which has a diameter of 50 ft. and liquid height of 20.4 ft. The liquid density is taken to be 93.6 lb/ft3. The tank is assumed to be rigid. Both harmonic and earthquake excitations are used in the study. The finite element method is employed to attack the problem. The response functions examined include the sloshing wave height and the impulsive and convective components of the hydrodynamic pressure. A small tank, about 1/15 the size of the typical waste storage tank, is also used in the study to understand the effect of viscosity on the response of liquid storage tanks and to investigate the dependency of the viscosity effect on the size of the tank. The results of this study show that the effect of viscosity depends strongly on the size of the liquid-tank system. For the typical waste storage tank considered, the effect of viscosity on the sloshing wave height and the impulsive and convective pressures is very small and can be neglected. For the viscosity effect to become noticeable in the response of the typical waste storage tank, the liquid viscosity must be greater than 10,000 cP. This value is far greater than the estimated viscosity value of the high level wastes, which may range from 60 to 200 cP