浮体係留システムの運動応答と係留力の予測(浮遊式海洋構造物の実海域実験その2 研究報告)

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Methods of modelling (statistically) and simulating the response and the mooring force of moored floating offshore systems excited by irregular seas and winds, including the effects of both nonlinear wave forces and nonlinearity in system dynamics, are investigated in this paper on a basis of at-sea data of a full scale floating offshore structure "POSEIDON". The characteristics of waves and wind at the test field is studied from a viewpoint of external forces. Volterra series and the Quadratic Transfer Function are introduced to describe the nonlinear wave forces. Cross bi-spectral analysis is applied to estimate the Quadratic Transfer Functions. A linear force model is introduced to describe the slowly varying forces due to wind fluctuations. Multi-input analysis is applied to study the contribution rate of slowly varying wind and wave forces to slow drift motion. In order to estimate the nonlinear viscous and mooring forces in the system dynamics from full scale free decaying test data, a new analysis method, which is based on time series fitting method using a nonlinear optimization technique, is developed. On a basis of these investigations, a comparison between a measured time histories of the motion and mooring force and their simulations is carried out. Relating to estimates of the PDF (Probability density function) and the extreme response of the motion and mooring force, two statistical models are introduced newly. The one is a nonlinear statistical method based on two term Volterra series theory for taking effects of both nonlinear wave forces and varying wind loads into account and the other is a modified version of the Hermite moment model introduced by Winterstein. At-sea measured sample data, the statistical prediction based on the Rayleigh distribution, i.e. the so-called Cartwright-Longuet-Higgins estimates and the results obtained from the present methods are compared. It is concluded that the present statistical models and simulation procedures provide useful tools for estimating the behaviour of nonlinear moored floating offshore systems and for predicting the extreme values of the motion response and mooring forces.
独立行政法人海上技術安全研究所の論文
1994-12-28

浮体係留システムの運動応答と係留力の予測(浮遊式海洋構造物の実海域実験その2 研究報告)

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浮体係留システムの運動応答と係留力の予測(浮遊式海洋構造物の実海域実験 その2 研究報告)

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浮体係留システムの運動応答と係留力の予測(浮遊式海洋構造物の実海域実験その2 研究報告)