Numerical Analysis of Wind Effect on Wave Overtopping on a Vertical Seawall

Abstract

Onshore wind significantly affects wave run-up and overtopping, thereby representing a major variable to account for in the design process. The aim of this study is to analyze the ability of numerical models to properly reproduce the wind effect on the overtopping at vertical seawall and to use them to understand how the wind influences the overtopping process as well. We use the RANS model, FLOW-3D, and the NLSW model, SWASH; both model the action of wind through the shear stress that it exerts on the sea surface. Although a simplified modelling of wind has been adopted, the CFD model has led to physically consistent results. On the other hand, SWASH seems to be unsuitable for reproducing the enhancement of the overtopping rate due to wind. CFD numerical results show that the wind affects only the lower overtopping regime (i.e., q < 1 l/s/m); as the mean overtopping discharge decreases, the influence of wind increases. Specifically, wind plays a key role in pure “white overtopping”, where the advection of spray is the predominant mechanism of the overtopping process. The effects of wind thus seem to be important in the design of seawalls, but are difficult to quantify through hydraulic models because of the unknown scaling laws. Therefore, we have found that a full-scale numerical approach is suitable to study the influence of wind on wave overtopping and to evaluate the wind factor to take into account in the design process.

Keywords

• wind stress
• wave overtopping
• computational fluid dynamics
• SWASH