Wave interactions with 2D structures on/inside porous seabed by a two-domain boundary element method
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The interaction of water waves with porous seabed or partially/fully buried porous/rigid structures is studied based on the potential theory and Darcy's law. A two-domain boundary element method (BEM) based on a desingularized integral equation is developed to fully account for the interactions at the soil-water interface and other structural boundaries. The numerical solutions are obtained by using two different methods, iteration method and global-matrix method. Both are shown to be accurate compared to the analytic solution in the case of flat porous seabed of finite thickness. The developed computer program was utilized to study various ocean-engineering applications, such as wave propagation over flat porous seabed, wave scattering by a series of rigid/porous submerged mounds, and wave induced seepage force on a fully/partially buried pipeline. In the case of fully buried pipeline, the exact numerical solution was compared with the so-called no interaction (NI) approximation, which was previously used by many authors. The limitation of the NI approximation is discussed. A long-wave (LW) approximation analogous to the inertia-force expression in Morison's formula is newly developed and proven to be practically very useful in predicting wave induced seepage forces on arbitrarily shaped, fully submerged slender structures. Based on the NI-LW approximation, analytic expressions for the second-order difference-frequency seepage force by bichromatic incident waves are developed. (C) 2000 Elsevier Science Ltd. All rights reserved.