A Frequency-Time domain Method for the Calculation of the Dynamics of Mooring Line

概要

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Dynamics of an oscillating mooring line are commonly calculated by using the traditional numerical method as FEM and FDM. In this paper another approach is proposed which is based on the linearization of the dynamic equations of the mooring line, and the method of the inversion from frequency domain to time domain. By using the perturbation method, the nonlinear dynamic equations of an oscillating mooring line were linearized, and transformed into frequency domain. This Frequency domain equations were solved by using Goodman-Lance method. The impulse response functions were then obtained by the inverse Fourier transform of such frequency domain solutions. The time history of the tension induced by the oscillation of upper end of a mooring line then can be calculated by a convolution integral along the time axis with the corresponding impulse function and the oscillation velocity. This method has the merits of less time required and more stable compared with other numerical methods as FEM and FDM. In order to verify the validity of the proposed method an oscillating experiment of a model mooring line was conducted in a water flume by an oscillating apparatus. Comparison between the calculated results and measured results show that in the frequency of interesting this method gives good coincidence with measured results.
社団法人日本船舶海洋工学会の論文
1992-09-25