Effects of Homogeneous and Inhomogeneous Roughness on the Ship Resistance

Ship hull roughness can significantly increase the ship resistance. The roughness caused by biofouling attached to the ship hull is not uniform but has a random distribution. The purpose of this study is to investigate how the inhomogeneous surface roughness distribution affects the ship resistance and the various resistance components. The KRISO container ship (KCS) is considered as a case study. To model the inhomogeneous surface roughness, the ship hull is divided into three segments with equal wetted surface area. Combinations of three roughness heights, denoted as P, Q, and R with k_s values of 125 μm, 269 μm, and 425 μm, respectively, are considered to obtain homogeneous and inhomogeneous roughness arrangements (PPP, QQQ, RRR, PQR, PRQ, QPR, QRP, RPQ, and RQP). CFD method is utilized in this study, utilizing RANS equations and k-ω SST turbulence model. A VoF method is used to model the free surface. CFD simulation results show that for the homogeneous roughness, the total resistance coefficient C_T increases with increasing k_s (PPP < QQQ < RRR), as expected. For the inhomogeneous roughness, the friction resistance coefficient C_F increases in the order PQR < PRQ < QPR < QRP < RPQ < RQP, consistent with results from earlier studies. In all the cases, the friction resistance (C_F) is the dominant component of the total resistance. As Re increases from 2.2 x 10⁹ to 2.7 x 10⁹, the percentage of the friction resistance decreases, while the percentage of the wave resistance increases. The viscous-pressure resistance decreases slightly as Re increases from 2.2 x 10⁹ to 2.7 x 10⁹.