This paper presents a large-scale 2-D numerical simulation of wave-structure interactions using IH2VOF which is one of the most advanced RANS models. A non-conventional seawall structure was deployed on Vietnam's coastline as a case study. The value of mean wave overtopping discharge is used to evaluate the hydraulic performance of such construction. It is one of the most significant factors to consider while assessing the feasibility of proposed designs. For novel structure design with complex shape, it is inconvenient to adopt the traditional methods like empirical formulae, or the current approaches using machine leaning algorithms due to the geometrical difference. Therefore, numerical modelling is considered for analyzing such types of structure as a supplement to the experimental study. The reliability of numerical model initially is validated by experimental data, and theoretical results as well. Thereafter, the large-scale numerical model of wave-structure interaction is conducted with various wave conditions. The simulation results are compared to empirical solution and prediction methods using neural networks. Hence, the numerical set-up model and calibration for this problem are proposed.