側壁反射を用いて角水槽内に発生させた方向スペクトル波の特性

概要

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Directional irregular waves were generated in a square seakeeping basin by using 80 element wave maker. The basin is 60 metre in long, 25 metre in wide, 3.2 metre in deep, and has a X-Y towing carriage. Each element of wave maker is only 0.31 metre in wide to realize shorter component waves. Side-wall reflections were positively utilized in order to obtain uniform directional spectra in any regions of the basin. Because, uniform directional spectra in position are prerequisite for model experiments of ships running in directional waves. However, the technique generating uniform directional waves with side-wall reflections has not yet been examined at a square basin, although limited results by Takezawa were obtained at a long towing tank. Therefore, the directional spectra were analyzed from wave height records measured by a wave gauge array at various positions of the square basin. As a result, it was confirmed that spectral parameters, such as mean wave period, band width parameter, mean wave direction, mean spreading angle, are almost uniform in any position of the basin, although variance of water surface is not so uniform in position. Further, these parameters are not significantly varied when wave height increases even up to wave breaking or when directional spreading of wave energy changes. These results prove that model experiments in desired directional irregular waves can be carried out for a ship running with any heading angle.