On Wave-Free Forms in Swaying Oscillation

Abstract

This paper deals with the wave-free forms of a two-dimensional body in swaying oscillation. The wave-free body generates no radiating waves when oscillating horizontally on the free surface of a fluid at a wave-free frequency. By Haskind relations, the body experiences no sway exciting force in incident waves of the frequency.A method of the tracing of stream lines of the wave-free potentials which satisfy the conditions of the free surface and no radiating waves at infinity is used to investigate the features of the wave-free forms. The numerical approach gives two kinds of wave-free forms. One is a floating body, the sides of which are not vertical and inclined inwardly beneath the free water surface, and another is a submerged body. Numerical calculations of hydrodynamic forces are carried out for the floating bodies derived from the stream line tracing. Hydrodynamic characteristics of the bodies are discussed.Measurements of wave exciting forces are performed on the models of floating bodies and a submerged body with the various amplitudes of incident waves. The results reveal that the effect of wave height on sway exciting forces is significant. A tendency is observed that the measured exciting forces for smaller wave height are closer to the calculated ones, so that the existence of wave-free frequency in swaying oscillation can be verified experimentally.