Comparisons between seabed and free surface effects on underwater vehicle hydrodynamics

This paper presents a numerical study on the hydrodynamic coefficients of the DARPA SUBOFF hull when deeply submerged and near the seabed. The CFD-based model was validated with experimental data, namely experiments involving the SUBOFF and BB2 undergoing straight-ahead motion near the free surface and the SUBOFF only when deeply submerged at drift angles without the influence of either the free surface or the seabed. The validated model was used to investigate the effects of the seabed's effect on the hydrodynamic behaviour of the SUBOFF across a range of speeds, drift angles, and submergence depths. The results were then compared to operations near the free surface. The results show that the seabed has a smaller influence on the hydrodynamic coefficients compared to the free surface. Also, the hydrodynamic coefficients do not vary with Froude number when near the seabed but do vary with Froude number when near the free surface.