Advancement of CFD Analysis Techniques for the Resistance Performance of High-Speed Planing Craft

High-speed planing craft generate complex local flows, including spray, free-surface deformation, and air ventilation behind steps, which complicate CFD-based resistance prediction. This study investigates three factors affecting resistance estimation: free-surface numerical diffusion, computational-domain confinement, and local-flow resolution. Numerical diffusion is governed by the convection scheme rather than the time step; with the scheme fixed, a 160-fold change in time step altered the resistance by only a few percent. By restricting the flow around the hull, towing-tank boundaries induce coupled changes in the free-surface profile, pressure field, and wetted area, which are reflected in the resistance. Therefore, a computational domain matching the tank dimensions is required when comparing CFD results with model tests. Adaptive mesh refinement was applied to spray and air ventilation behind the step. Resolving spray detached from the hull had negligible influence on resistance, whereas resolving the ventilated region improved pressure-resistance prediction and reduced the resistance error relative to the model test from about 10% to within a few percent. These results show that grid refinement is warranted by whether a local flow contributes to the forces on the hull, not by its apparent complexity. All simulations were validated against high-speed towing-tank measurements from the Research Institute of Medium & Small Shipbuilding.