Author(s): Anastasia Fragkou; Athanasios Angeloudis; Vengatesan Venugopal; Christopher Old

Linked Author(s): Anastasia Fragkou, Athanasios Angeloudis

Keywords: Wave-current interactions; Wave-induced breaking and setup; Shallow-water equations; Spectral wave modelling; Coupled model

Abstract: A parallelised coupled two-dimensional model is developed to capture wave-current interactions at regional scales. The model is comprised of the spectral wave model Simulating WAves Nearshore (SWAN; Booij et al., 1999) and the coastal hydrodynamics shallow-water equations model Thetis (Kärnä et al., 2018). The two models are coupled through the Basic Model Interface (BMI; Hutton et al., 2020) employing a set of standard functions. They run iteratively and exchange information at prescribed time-intervals. SWAN provides the necessary parameters for the calculation of radiation stress, performed by Thetis, upon solving the action density equation encompassing multiple source terms accounting for deep- and shallow-water phenomena. In turn, Thetis returns water elevation and velocity information by considering the 2-D depth-averaged formulation of the shallow water equations. The coupled model's capability to account for wave-induced breaking and wave set-up, as well as friction is examined using the experiment of Boers (1997) on the behaviour of waves acting upon a barred beach. The model domain consists of two domains with maximum still water depth at 0.80 m: an outer domain with dimensions 45 m x 15 m; and a nested domain with the same length and 5 m width. The width and length used in the numerical domains are larger than those of the experimental tank to avoid introducing errors generated at the boundaries in the area of interest. During the coupled model’s validation, all three experimental wave conditions are applied. These conditions are parameterised by the following significant wave heights, Hs, and peak wave periods, Tp: (i) Hs = 0.16 m and Tp = 2.1 s; (ii) Hs = 0.22 m and Tp = 2.1 s; and (iii) Hs = 0.10 m and Tp = 3.4 s, for each experiment respectively. The model's results exhibit good correlation with the experimental data, which consists of derived wave spectra and water elevation measurements. Additionally, the model’s performance is compared against other coupled models whose circulation model is 3-D. The proposed model’s results showcase the same level of accuracy as other coupled models and could be extensible to 3-D modelling applications. References [1] Boers M. Simulation of a surf zone with a barred beach; Part 1: wave heights and wave breaking. Oceanographic Literature Review 1997;4(44):292. [2] Booij N, Ris RC, Holthuijsen LH. A third-generation wave model for coastal regions: 1. Model description and validation. Journal of geophysical research: Oceans 1999;104(C4):7649-7666. [3] Hutton EW, Piper MD, Tucker GE. The Basic Model Interface 2.0: A standard interface for coupling numerical models in the geosciences. Journal of Open Source Software 2020;5(51):2317. [4] Kärnä T, Kramer SC, Mitchell L, Ham DA, Piggott MD, Baptista AM. Thetis coastal ocean model: discontinuous Galerkin discretization for the three-dimensional hydrostatic equations. Geoscientific Model Development 2018;11(11):4359-4382.

DOI: https://doi.org/10.3850/IAHR-39WC252171192022865

Year: 2022