Impact pressure and void fraction due to plunging breaking wave impact on a 2D TLP structure

Violent impacts due to the plunging breaking wave impingement on a 2D tension-leg platform (TLP) structure were experimentally investigated in a laboratory. Simultaneous pressure, void fraction, fluid velocity, and structure motion measurements were performed on the multiphase, turbulent flow. The maximum mean impact pressure is 2.3 rho C-2 with C being the wave phase speed. The pressure maximum and its rise time are negatively correlated, and the rise time for impulsive-type impacts is less than 15 ms or 0.18H/C with H being the wave height. Different approaches show that impact coefficients vary from 0.6 to 9.7, including relating the impact pressure maxima to the wave phase speed, local velocity, and void fraction. By modeling the plunging breaking wave impact as a filling flow, a pressure-aeration relationship was investigated and compared with the approximate solution derived by Peregrine and Thais (J Fluid Mech 325: 377-397, 1996). The measured data show that a high aeration level tends to reduce the impact pressure maximum so the cushioning effect is significant for breaking wave impacts on a moving vertical wall.