Numerical investigation of generic submarine self-propulsion in free-surface waves with an autopilot controller

Abstract

This study employs computational fluid dynamics (CFD) to investigate the attitude-keeping self-propulsion of a generic submarine in free-surface and wave environments under autopilot control. The Joubert BB2 hull form and Marine 7371R propeller are adopted as the reference models. Turbulent flow is resolved by solving the incompressible Reynolds averaged Navier-Stokes (RANS) equations in combination with the shear stress transport (SST) k-ω turbulence model, while free-surface dynamics are captured using the volume of fluid (VOF) method. To ensure numerical reliability, mesh-convergence studies are carried out with four levels of mesh resolution. An overset mesh technique is applied to the submarine hull and X-rudders, whereas a sliding mesh is used to represent propeller rotation. The autopilot is implemented as a proportional-derivative (PD) controller that adjusts attitude variables to maintain attitude-keeping self-propulsion. The influence of submergence depth and wave conditions on hydrodynamic characteristics is systematically examined: The presence of the free surface significantly alters the hydrodynamic loads, surface pressure distribution, and associated wave patterns during the self-propulsion process. Meanwhile, the wave action induces significant variations in the pitch angle, leading to distinct periodic oscillations in the submarine’s attitude.