NUMERICAL SIMULATION OF BREAKING WAVE IMPACT ON STRUCTURES

Abstract

The breaking of ocean waves is a common occurrence and an important element in oceanographic and coastal engineering. When waves break on coastal or offshore structures, the wave impingement forces can be tremendous and may cause significant damages to the structures. An enhanced Smoothed Particles Hydrodynamics (SPH) method has been developed to study the breaking wave impacts. The key parameters of the SPH model are calibrated through benchmark studies. A first order density smooth procedure and the addition of a density diffusion term in the continuity equation are introduced to smooth the pressure field and to improve the computation of pressures. A pressure post-process procedure based on the moving average and FFT method is introduced to filter off erroneous pressure oscillations after the occurrence of peak pressures. An improved two-step free surface identification method is introduced to improve the free surface identification. The ghost particle method is introduced to simulate the free slip wall boundary. A sponge layer method is introduced to dissipate the reflected wave energy at the far end of the numerical wave flume. A hybrid Verlet-linked-list technique is introduced to improve the efficiency of search neighbour particles. The code is paralleled with the Parallel Particle Mesh (PPM) library, which can simplify the parallelization, improve the computational capacity and speed up the parallel computations. The developed SPH model is validated through a series of benchmark case studies, including the dam break problem, sloshing problems, sloshing impact problems and impact problems characterized by flip-through. The developed SPH model has been successfully employed to simulate plunging wave impact on suspended vertical walls and horizontal decks. Different scenarios of wave impact on vertical walls are studied systematically by suspending the wall at different prescribed locations relative to the plunging wave. Three broad categories of wave impact have been identified, those associated with impact before wave plunging, those associated with impact during wave plunging and those associated with impact after wave plunging. The kinematics and dynamics of the different impact scenarios are carefully examined and key features of the impacts are identified. The impingement of an extreme wave onto a horizontal deck is also simulated to study the green water problem. Impact pressures at the underside and topside of the deck are carefully correlated to the kinematics of the wave-structure interactions.