Basic Research on Long-Period Waves at Fishery Harbors Facing to Open-Sea

Abstract

At fishery harbors facing to open-sea, we carried out a questionnaire survey which concerns the actual condition on long-period waves. Then a numerical calculation was performed on the basis of the received answers. The obtained results are summarized as follows : (1) As wave group causes the harbor oscillation of high order modes, long-period waves are not amplified so much, and in the harbor the height of long-period waves is about 1/10 times as high as offshore waves. (2) Even at the innermost point of harbor, the energy of long-period waves is not attenuated so much. (3) At fishery harbors facing to Open-sea, a water current and a vortex caused by long-period waves are easy to occur near the harbor entrance. (4) On the area of north side of the Pacific Ocean, ship entering into harbors is hard under a strong seasonal wind and a typhoon. (5) Even if the fishery harbor is facing to Open-sea, it is easy to enter the harbor and moored ships are safe, if the harbor is surrounded by natural geographical features. (6) In the Tohoku region of the Pacific Ocean and west side of Shikoku, most harbors are natural good harbors, and are not affected by long-period waves.