A Strip Theory and CFD Informed Lumped Parameter Model for Near-Surface Underwater Vehicle Maneuvering

Recent efforts at Virginia Tech have produced a 6-degree of freedom (6DOF) lumped parameter maneuvering model (LPM) that is able to accurately predict the deeply submerged maneuvering motions for a variety of underwater vehicles, including the VT 690 AUV. This model consists of 50 non-negligible hydrodynamic derivatives that are estimated through a series of unsteady and quasi-steady computational fluid dynamics (CFD) based maneuvers. To improve the applicability of this model to a broader range of operating conditions, free surface proximity effects are introduced into the model. The consideration of free surface effects influences the total system in many ways including changes in hydrodynamic derivatives with respect to depth (fluid asymmetry), radiation of surface waves (past motion memory forces), and incident wave excitation forces. This study incorporates the former two of these effects by correcting the hydrodynamic derivatives using near-surface data gathered from a frequency domain strip theory code. Simulations of the VT 690 AUV performing a series of near-surface maneuvers reveal the relevance of free surface effects as identical maneuvering inputs result in different motion histories near the surface than in deep water.