On the Wave-Making or Wave-Absorbing Property of a Symmetric Cylinder

Abstract

This is a theoretical and experimental study on the wave-absorbing problem of a floating cylinder of symmetric section which oscillates vertically around a point of off-centerline. If we consider the time-reversed motion of this problem when the wave energy is completely absorbed, we have the radiation problem in which the radiating waves vanish on the one side of the cylinder. Hence, we study only the radiation problem which is simpler than the wave absorption problem. Then, we consider a symmetric cylinder which oscillates vertically and rotates freely around an arbitrary point and seek points such that the radiating waves vanish on the one side by the oscillation around them. The wave amplitudes radiating toward both sides of the cylinder are calculated on the basis of the linear water-wave theory and such points are found easily. Moreover, the maximum efficiency which could be achieved in the wave absorption problem is obtained by the wave amplitudes radiated to both sides. Experiments on a simple cylinder show the validity of the theoretical Predictions.