Time-domain numerical modelling of the connector forces in a modular pontoon floating breakwater under regular and irregular oblique waves

Abstract

Floating breakwaters are an interesting alternative to bottom-fixed structures due to their lower cost and environmental impact. Nonetheless, structural failures in the module connections are frequent. Accurate analysis of the hydrodynamic response is therefore crucial to their structural design. This article reports on numerical modelling of the forces on the module connectors in a modular pontoon breakwater. The study case was an array of five pontoons with elastic mooring lines under regular and irregular oblique waves. A 3D Boundary Element Method (BEM) solver was applied to find the velocity potentials and to characterize the frequency-domain response. The time-domain response of the floating breakwater is calculated along with the forces in the elastic mooring lines and module joints. Nonlinear hydrodynamic effects were reproduced by calculating the Froude-Krylov and hydrostatic forces over the instantaneous wetted surface at each time step. The response of the modular array under regular waves was then compared with previous experiments. After calibrating connector stiffness, the numerical and experimental results were in good agreement. Finally, the floating structure's response to regular and irregular waves was compared. The results revealed that simulation of only regular waves underestimates maximum connection forces by one order of magnitude.