Simulation of Wind and Waves with Complex Land Topography

Water wave dynamics in nearshore regions are mostly dominated by the topographical complexity of the terrain, leading to complex processes, such as wave shoaling, wave breaking, and current shears. Most previous simulated-based studies of coastal waves are unable to capture these land-air-sea interaction processes. The goal of our study is to address this limitation by using an advanced numerical framework developed in our research group. In the near field of coast, we employ the Curvilinear Immersed boundary method (CURVIB) of Calderer et al. (J. Comp. Physics 2014), which is able to perform large-eddy simulation (LES) of two-phase free-surface flows over complex topographies, such as dunes, beaches, and cliffs. The method can incorporate realistic wind and wave conditions, obtained with a far-field precursor simulation. The wind is transferred to the near-field domain by feeding the velocity at the inlet plane; and the waves are incorporated using the technique of Guo and Shen (J. Comp. Physics 2009) consisting of applying a distributed force on the air-water interface. In the far field, we adopt the two-fluid method of Yang and Shen (J. Comp. Physics 2011) and Yang, Meneveau and Shen (J. Fluid Mech. 2013), which couples an efficient phase-resolved nonlinear wave modelling technique based on the high-order spectral (HOS) method with a LES solver for the air field. We demonstrate the validity of the numerical methods by simulating benchmark test cases of monochromatic and broadband waves reaching a sloping beach, showing comparisons with available numerical and experimental data. Then, we apply the methods to simulate nearshore land-air-sea interactions, and illustrate the physical processes of the flow induced by the presence of a complex topography.