ABSTRACT:

A systematic series of bench and/or towing tank test results of antirolling tanks are briefly described in this paper. The effects of damping plates in the duct of U-tube tank on the oscillating period of the moving fluid and of swash plates on roll damping moment of the tank are studied experimentally. A brief summary of the development of active U-tube tanks using air blower to control the flow in the tank by simple control algorithm is given. Towing tank tests are carried out in the irregular beam waves to show the effectiveness of the active tanks.

INTRODUCTION

The U-tube anti-rolling tanks (ART) used as stabilizers are called passive when they are left alone on board except for the infrequent tuning needed for a change in the loading conditions. And the tanks are called active when they use additional power such as air-blower to move water from one wing tank to the other using developed automatic control algorithm. The effect of the passive ART decreases when the roll period of the vessel does not match the designed oscillating period of the fluid in the tank. In order to improve the effect of the passive ART, the damping plates are installed in the lower duct of the ART to adjust the oscillating period of the fluid. The optimum damping due to the U-tube tank is possible when there is a phase difference of 90o between the motion of the vessel and that of the water in the tank. Passive U-tube tanks with optimum damping show the best stabilizing effect near the resonance frequency with the minimum adverse effect at the high and low frequency ranges. The internal structural members of the passive tanks should be carefully designed to have the optimum tank damping moments.

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