Numerical investigation of solitary wave attenuation and resistance induced by rigid vegetation based on a 3-D RANS model

Abstract

Mangrove forests can significantly attenuate tsunami waves and thus play an important role in coastal protection. As a first approximation, the problem is modeled utilizing solitary waves impinging on emergent/submerged rigid cylinders. A three-dimensional (3-D) numerical model using cyclic boundary conditions was developed based on the IHFOAM solver to investigate the effects of wave nonlinearity and vegetation configuration on the solitary wave attenuation. The numerical model was established based on the Reynolds Averaged Navier-Stokes (RANS) equations combined with the standard k – ω shear stress transport (SST) turbulence model and the volume of fluid (VOF) surface capturing schemes. The results indicate that different patterns are found in terms of flow field characteristics (velocity and turbulent kinetic energy) and forces exerted on the cylinders for various wave nonlinearity and vegetation configuration, which helps to better understand wave dissipation mechanism induced by vegetation. Different from the bulk drag coefficient derived by the conventional wave dissipation models, the direct force method was applied to quantify the time-varying and period-averaged drag coefficients (CD) of individual cylinders. The time-varying CD associated with maximum force and local velocity is defined as the representative CD, for comparison with the period-averaged CD in detail. Besides, by considering the submergence ratio, new generic CD formulas are proposed as functions of the modified Reynolds number (Re) and Keulegan-Carpenter number (KC) for illustrating the CD dynamics under solitary wave conditions. Finally, a preliminary comparison between the proposed CD formulas and existing formulas are given to reveal the intrinsic CD law, which may lead to improved understanding and modeling concerning wave-vegetation interaction.