Numerical investigation on performance of submerged porous breakwater to mitigate hydrodynamic loads of coastal bridge deck under solitary wave

Abstract

Coastal bridges are vulnerable to extreme surges and waves generated during hurricanes and tsunamis. Over the past few decades, extensive research works were conducted to study the damage mechanisms of coastal bridges under the impact of extreme surges and waves. However, these research efforts mainly focused on the hydrodynamic characteristics involved in surge waves impinging bridges. However, there has been little research on mitigation measures to protect coastal bridges. This study examines the installation of a submerged porous breakwater to protect coastal bridge decks from the impacts of solitary waves. As an environmentally friendly wave-reduction device, submerged porous breakwater structures have been widely implemented in coastal regions due to their ease of installation and cost effectiveness. To investigate the performance of the submerged porous breakwater on the hydrodynamic loads of a coastal bridge deck under the impact of a solitary wave, a high-resolution numerical wave tank is established based on an open-source flow solver REEF3D, which numerically solves the governing equations of incompressible two-phase flow on a staggered mesh arrangement and captures the interface between air and water using a high-resolution level-set method. The hydrodynamic characteristics of coastal bridge decks with the installations of submerged porous breakwater are systematically investigated by considering the effects of six prominent factors, i.e. wave height, submersion depth, water depth, permeability, spacing distance between breakwater and bridge, and aspect ratios of breakwaters. Results show that the submerged porous breakwater is effective in reducing the hydrodynamic loads applied to the coastal bridge decks under most of the situations. Therefore, it is believed that the findings drawn from this paper can further enhance our understanding on the damage mechanism of coastal bridges under extreme waves and should be instructive for future bridge designs.