DYNAMIC BEHAVIOUR OF SUBMERGED TOWER STRUCTURES

Abstract

An effective method for calculating hydrodynamic pressures and added mass for submerged tower structures has been developed. Finite Element Method is. employed for evaluating the hydrodynamic effects and the beam analysis is adopted for the evaluation of the response of the structure. The effect of the extent of the reservoir on hydrodynamic pressures has been studied. It has been found that a reservoir length equal to three times the height of the structure gives a reasonably accurate estimate of the hydrodynamic pressures. Hydrodynamic pressures have been calculated for the towers with different radius to height ratios. I,t has been found that the pressure in case of very slender towers (i.e., the towers having radius to height ratio upto 0.10) is almost uniform upto about 80 % of their height above the base. However, it is not so for non-slender towers. The effect of the inclination of the face of the tower an hydrodynamic pressures has also been studied. Towers of different radius- to height ratios were ,taken and it. was found that the effect of the inclination of the face with respect to vertical is to reduce the hydrodynamic pressures. As the inclination of the face increases, the hydrodynamic pressure- reduces. e, Tbts ductin in pressures is more in case c. slender • towers than for squatty towers.. The analysis of the structure is carried out treating it as a cantilever bead fixed at the bàse. For this purpose, a 58.28 m high intake tower has been • -t.ken. The effect of the presence of the surrounding water is o.und. to elongate the. natural period of vbra-tion of the tower. 'The increase in the natural period is o the order of 50 %. Dynamic moments and shears in the bower are. also found to increase due to Rub — mergence, and the increase is of the order of 70 % at the base of the tower. The maximum response of the tower is seen to occur in the fundamental mode only.