Design optimization of ocean renewable energy converter using a combined Bi-level metaheuristic approach

•Investigating the impact of geometric and hydrodynamic factors on wave converters' performance.•Developing a Ribbed-surface design of the converter's flap for improved performance.•Introducing a Bi-level Hill Climbing Multi-Verse Optimization method for this application.•Showing that greater wave heights and flap freeboard heights lead to better performance.•Optimum values for all parameters were achieved by the newly developed optimization algorithm.