Enabling the prediction of manoeuvring characteristics of a submarine operating near the free surface

Predicting the behaviour of a submarine operating close to the free surface is important in order to assess the merits of particular designs, identify the operational characteristics, and determine a safe operating envelope. To predict submarine behaviour near the free surface requires both a mathematical model that captures the dynamics of a submarine in motion, and an understanding of the additional forces and moments generated in the near surface region. In the past, submarine manoeuvring models in published literature have neglected the effect of the presence of the free surface, thus the authors are developing a coefficient based submarine manoeuvring model incorporating the effects of near surface operation. The hydrodynamic coefficients required for the model are obtained using Computational Fluid Dynamics (CFD) and validated against results from captive model experiments in the Australian Maritime College (AMC) towing tank. This paper describes hydrodynamic coefficients that can be added to existing submarine manoeuvring models to account for near surface effects in the vertical plane, for the SUBOFF geometry. Validated CFD predictions of the forces acting on a generic submarine operating near the free surface are presented along with empirically based equations to predict them.