Fluid structure interaction between a pendulum and focused breaking waves

Abstract

To study how an extreme wave load on a maritime structure causes structural deformation, an experiment is conducted to measure the response of a one degree-of-freedom pendulum in a focused, breaking wave. The tube that makes up the base of the pendulum covers almost the entire width of the tank so that three-dimensional effects can be considered small. The experiment varies the focus location with respect to the position of the pendulum as well as the vertical clearance between pendulum and mean free surface. Although the energy of the wave input was the same for all experiments, the response of the pendulum varied greatly with small variations of initial vertical clearance and wave focus location, with the wave breaking farthest away from the pendulum causing the largest response. A reduced-order model for the response of the pendulum shows the same behavior when initial clearance and focus location are varied. Even when initial clearance and focus location were kept the same between tests, large variability of the pendulum response was observed, meaning that the impulse exerted by the wave must have been different. This is different from the literature on breaking waves against rigid walls that found that local pressures show variability between experiments but that the impulse typically is the same. The experimental data and a description have been made available.