Blockage effects in wave and current: 2D planar simulations of combined regular oscillations and steady flow through porous blocks

Abstract

This paper provides numerical evidence for reduced fluid loading on space-frame structures exposed to ocean waves and in-line current. Comparisons are made between the current blockage model presented previously (Taylor et al., 2013), Computational Fluid Dynamics (CFD) simulation and experimental data. Three different flow models are considered: steady flow, time-averaged mean flow and fully unsteady flow both for regular oscillations with an in-line steady flow. A porous block is used to model an obstacle array of cylinders. This is appropriate because of the global nature of current blockage, which has significant effects over distances of the order of the frontal width of the obstacle array. We find good agreement among the numerical simulation, the experimental data and the previously published current blockage model, which lends support to the validity and applicability of the theoretical model in predicting the blockage effects. We also demonstrate that, in general, the 2D porous block model simulates the reduced flow better than the simple 1D analytical current blockage model.