Calibration of a roughness function model for ship simulations in the transitionally rough regime

In this paper, the impact of different equivalent sand-grain roughness sizes on the KRISO Container Ship (KCS) is quantitatively evaluated. Numerical uncertainty was assessed using the least squares method and the Grid Convergence Index. Subsequently, validation was performed against experimental data to demonstrate the accuracy of the simulations in reproducing hydrodynamic phenomena around the ship. Compared to previous studies, this research evaluates and analyzes a greater number of data points. The focus of this paper is on the transitional roughness regime to address the existing gap in prior research. Since ship coatings may fall within the transitional roughness regime, and given that previous calibrations have been primarily focused on the fully rough regime, lacking sufficient accuracy in the transitional range, this study performs renewed calibration based on a genetic algorithm to derive new, validated model coefficients specifically for the transitional regime. The newly calibrated model was then applied to the KCS and its predictions were compared against those of previous models to quantify improvements in the transitional roughness range.