In the present study, the effect of bottom undulations on the performance of a trapezoidal shaped oscillating water column (OWC) in the presence of a shore-fixed wall is investigated numerically using the boundary element method (BEM). The BEM is used to generate a solution, and the results are compared with existing analytical, and experiment results available in the literature. The results show that the Bragg resonance effects due to the bottom undulation topography significantly increases the efficiency of the OWC. Various parameters relevant to the behavior of the trapezoidal OWC-WEC, such as radiation susceptibility, conductance coefficients, and hydrodynamic efficiency, are addressed for diverse wave conditions and OWC geometry variations.
Ocean wave energy is a ubiquitous resource in many regions/countries worldwide and is among the renewable energies with the greatest potential (Westwood (2004)) but it is still almost entirely untapped. With rational exploitation and effective utilization, wave energy might afford a reliable alternative renewable energy resource to mitigate concerns about environmental issues. In the last decades, the hydrodynamic performance of OWC devices has been extensively investigated by many researchers by means of theoretical analysis, experimental tests, and numerical simulations. A comprehensive review of OWC devices is reported by Heath (2012). Investigations regarding wave power extraction from water waves have been published since the 1970s. These studies mainly concentrated on rigid body models. The theoretical design criteria of tethered-float breakwater for maximum power extraction from a general floating cylinder was reported by Mei (1976). Evans (1978) analytically studied the efficiency of a two-dimensional OWC device with a plane internal water surface in the frequency domain using the Galerkin approximation method.
The early studies were mostly theoretical, and in the later stages, more experimental as well as numerical studies have been conducted by several researchers. Renewable energy resources play a central role in the world's ever-increasing energy demand. The propagation of water waves in the presence of bottom undulation is important in several circumstances, including wave transformations over continental shelves and wave scattering by submerged breakwaters and trenches of various designs. The bottom effects have a substantial influence on the incident wave energy. This is significant as the waves propagate toward coastal locations. Many physical processes, such as breaking, wave refraction, and shoaling, occur because of bottom friction. As a result, it is essential to include the bottom undulation while analyzing the hydrodynamic efficacy of an OWC device mounted on a steep cliff in coastal locations. The influence of stepped sea bottom topography on the efficiency of a nearshore oscillating water column device was carried out using both theoretical and numerical approaches by Rezanejad et al. (2013). Experimental and numerical investigations on the hydrodynamic performance of an oscillating water column wave energy converter over stepped bottom in an appropriate 2D model was reported by Rezanejad et al. (2017). The numerical study was conducted by implementation of the multi-domain boundary integral equation method (BIEM). A theoretical analysis of an asymmetric offshore stationary oscillating water column device with bottom plate was reported by Deng et al. (2020). The operating principle of an OWC device is well known, and it provides many benefits over other ocean-energy devices. The role of dual breakwaters and trenches on the efficiency of an oscillating water column was studied by Naik et al. (2023a). Furthermore, the study was extended to wave power extraction by a dual chamber OWC in the presence of a bottom undulation by Naik et al. (2023b). Recently, Naik et al. (2024) investigated the impact of a sloping porous seabed on the efficiency of an OWC in oblique waves. A 3D boundary element method for analyzing the hydrodynamic performance of a land-fixed oscillating water column device was investigated by Rodriguez et al. (2022).