Comparative study of the effects of hull roughness on full-scale ship resistance using different numerical models

• A CFD-based investigation was performed to evaluate the impact of hull surface roughness on ship resistance. • Three different roughness wall function formulations are implemented and systematically compared. • Uncertainty quantification was conducted in accordance with ITTC guidelines to ensure numerical reliability. • The resistance was analyzed both in terms of total and local sectional contributions to clarify the influence of roughness. • The effect of roughness on the log-law velocity shift was examined through low of wall. Hull surface roughness, caused by coating degradation and marine biofouling, increases ship resistance, leading to higher fuel consumption and greenhouse gas emissions. However, most studies based on computational fluid dynamics (CFD) often assume smooth hulls, which underestimates real performance losses. In this study, the effects of realistic roughness on resistance were investigated using the full-scale MV-Regal, a medium-sized vessel from the JoRes project. The JoRes project provides a rich reference database for this vessel, including sea-trial measurements and numerical simulation results from multiple institutions, enabling a robust validation and benchmarking of the present CFD approach. Numerical simulations were performed using snuMHLFoam, an in-house solver based on OpenFOAM. The k–ω SST turbulence model was applied with the mesh design satisfying wall-function requirements. Grid and temporal uncertainties were assessed in accordance with the ITTC guidelines to ensure reliability. Resistance was decomposed into frictional and pressure components and further analyzed by hull sections (fore, mid, aft, and rudder). The results showed that roughness primarily increased frictional resistance, with the greatest increase at the forebody and a gradual reduction toward the stern. Pressure resistance exhibited minor variations, including a slight increase at the rudder. These results highlight the importance of incorporating roughness models into full-scale CFD analyses and offer valuable insights into hull maintenance strategies and regulatory compliance with energy efficiency standards, such as EEXI and CII.