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Indexed by:期刊论文

Date of Publication:2016-05-15

Journal:OCEAN ENGINEERING

Included Journals:SCIE、EI

Volume:118

Page Number:138-151

ISSN No.:0029-8018

Key Words:Twice expansion; Second-order time-domain method; Wavelet transform; Drift motion

Abstract:A twice expansion method in the time-domain was proposed for computing wave interaction with a body experiencing large amplitude drift motion. The body displacement was divided into two components, a low frequency and a high frequency oscillations. The low frequency oscillation was computed by a wavelet transform method with time matching in the computation, and was called as the instantaneous mean position. Then the first and the second order boundary conditions were established at the instantaneous mean position and the still free surface by a perturbation expansion method which would guarantee that the expansion factors are always small. The velocity potential was separated into the incident, the scattering and the steady disturbance potentials. The scattering and the steady disturbance potentials were computed by solving integral equations respectively. Numerical examinations were carried out for a forced moving truncated cylinder in waves and wave interaction with a spar platform with mooring system in deep water. The comparisons were made between the results from the present twice expansion method and the direct expansion method. The comparisons show that the present method can consider the changes in the phase and the encounter frequency of wave loads due to body drift motion at low frequency. The body response at the natural frequency of the spar platform from the twice expansion method is smaller than that from the direct expansion method, but is larger at lower frequency. The peak frequency of the response amplitude from the present method moves to lower frequency, as the influence of wave drift damping is included in the model. (C) 2016 Elsevier Ltd. All rights reserved.