The Impulse Response Function and Motions of Floating Body

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In order to obtain the precise results of the motions of a moored ocean structure under the combined action of waves and/or stepwise wind force, the convolution integral equation with the memory effect function in the time domain simulation are frequently used. Therefore, in this study, the following subjects are investigated.1) Approximate evaluation method for the impulse response function (memory effect function) which is involved in the convolution integral equation.2) Validity of the time domain simulation for the motions of a moored marine structures in waves with the memory effect function evaluated by the method of 1).3) Estimation method of the memory effect function from the forced oscillationtests.From the present study, the following results are found. 1) An approximation of the integrand at high frequency region by a triangle is to be applicable for the evaluation of the memory effect function.2) Time domain simulations using the convolution integral equation for motions of a moored semi-submersible platform show a good agreement with the measurements.3) The memory effect function evaluated from the measured data in the forced oscillation test show somewhat good agreement with the one obtained by the method of 1). In order to more accurate results, further investigations are needed.