Prediction of the behaviour of a submarine when operating close to the free surface is important to be able to assess the merits of competing designs; determine safe operating envelopes; and hence to develop procedures and limitations for safe operation when close to the free surface. In the past, manoeuvring prediction simulation tools used for such studies have neglected the effect of the free surface on the submarine. In this study, to better understand the behaviour of a submarine when operating in this environment, the standard coefficient based manoeuvring model has been modified to incorporate the effects of the free surface. Using results obtained from Computational Fluid Dynamics (CFD) modelling, validated experimentally using captive scale model tests, equations for these forces have been formulated for a high speed case, as previously presented by the authors. The extended manoeuvring model, including the equations for the additional coefficients, has been incorporated into a Time Domain Simulation. The effect of the presence of the free surface on the hydroplane angles required to achieve equilibrium when the boat is operating close to the surface are presented for two different configurations: one where the forward planes are located on the hull (bow planes); and one where they are located on the sail (sail planes). The additional hydroplane angles required due to the presence of the free surface when approaching periscope depth are also presented.
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