Directional Wave Characteristics of Multi-Directional Wave Generator based on Numerical Simulation

Abstract

Many experiments had been carried out in the long experimental towing tank in Yokohama National University (YNU) with generating directional spectrum waves by segmented and independent wave makers and using side-wall reflections positively. It is important to make more accurate generation of the directional spectrum waves considering the increasing demands for experiments among such waves.To accomplish these subjects, present paper investigates the characteristics of directional distribution by carrying out numerical generation of directional spectrum waves and its analysis for the case of without and with side-wall reflection. This calculation is based on the superposition of ring waves generated by the periodic line source distributions representing each wave maker unit. Mirror images are also introduced for considering reflections of side-wall including the ratio of reflection (reflection coefficient) because directional waves will not be reflected perfectly from real side-wall. In addition to this, directivity (Dd) and tapering effect for the distribution of source strength will be evaluated to generate more accurate directional spectrum waves. Especially, influence of spurious waves generated by the combined effect of finite width of segmented wave maker, wave length and main wave propagating direction will be investigated.To analyze directional spectrum waves, we use MLM (Maximum Likelihood Method) from calculated time series of wave elevation and two component wave slopes at the arbitrary spatial point. This corresponds to the Laser Beam Type Surface Wave Probe developed in Y. N. U, and reliability of this method was examined already.