係留船舶の長周期動揺に関する基礎的研究

概要

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Long-period motion of a moored ship in the harbor facing the open sea causes suspension of unloading and to break mooring lines. The long-period motion with large amplitude surging has been recognized as an incomplehensive phenomenon because the exciting waves can not be observed at all. It is considered that the exciting waves are shallow water waves with very long period, from 30s to 300s, and small wave height, 10 and several centimeters. As well known, the water particle of shallow water waves has a flat elliptic trajectory. In the case of 20m water depth, the length of waves with 300s period reaches 4,200m and it is possible to consider the shallow water waves as a kind of "flow". In this study, the model experiments are carried out for quantitative understanding of the surging exciting force produced by the shallow water waves from the view point of the "flow". The model experiments were conducted using the circulating water channel that the water level was lowered to make up the shallow water conditions. The measured value were compared with the theoretical value of frictional resistance and the Froude-Krylov force. The results concludes that the measured hydrodynamic forces are smaller than the Froude-Krylov force and it is no need to consider the "flow-like" aspects of the shallow water waves.
2010-03-25