Second-order hydroelastic analysis of a flexible floating structure under spatially inhomogeneous waves

Abstract

In this study, a second-order hydroelastic analysis method for moored flexible floating structures under spatially inhomogeneous, long-crested waves is developed, based on the beam-connected-discrete-modules (BCDM) hydroelastic method. The continuous structure is first discretized into rigid modules connected by elastic beams to evaluate the first-order hydroelastic responses. The inhomogeneous wave field is spatially discretized by different isolated homogeneous waves. Based on the first-order motions, the mean drift force on each module is obtained in the frequency-domain. According to the discrete inhomogeneous wave field, the second-order slowly-varying wave drift forces by Newman’s approximation with the drift forces are calculated using the corresponding wave spectra. Finally, the second-order hydroelastic equation in inhomogeneous waves is established in the time-domain using Cummins’ equation. The mean drift force of flexible structures and the nonlinear time histories of motions under homogeneous waves using the proposed method are verified against the results obtained by general commercial software. Then, a limited case study using the proposed method is conducted by a flexible barge and an inhomogeneous wave condition, both of which are exaggerated. The results show that slowly-varying drift forces dominate the horizontal displacements and mooring forces, and the spatial inhomogeneity of waves has a significant effect on the second-order hydroelastic responses, especially in beam seas.