Development of an unsteady indicial response model for horizontal submarine maneuvers
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Date
2025-11
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University of New Brunswick
Abstract
The safe operating envelope of a submarine is designed by careful analysis of a series of recovery maneuvering simulations. To ensure the accuracy of the design limits, hydrodynamicists rely on estimation models that predict the maneuvering loads on the vehicle. Traditional reduced order modeling methods neglect the history of the wake using a quasi-steady assumption, but previous research suggests that these effects may be significant for a submarine in operationally relevant conditions.
This work used an unsteady Reynolds Averaged Navier-Stokes simulation method to study the hydrodynamic phenomena affecting a generic submarine vehicle in horizontal plane maneuvers. The simulation method was validated in comparison to model scale experimental wind tunnel and towing tank tests. An analysis of an unsteady oscillation maneuver database showed that, although the in-plane hydrodynamics are dominated by quasi-steady phenomena, the out-of-plane hydrodynamic loads in horizontal plane maneuvers are highly unsteady.
Indicial responses, which describe the time evolution of the viscous wake, were used to model the unsteady hydrodynamic loads. The indicial responses for the fully appended submarine were found to exhibit non-linear history dependence and cross-coupling characteristics, which a baseline modelling approach could not account for. A rate correction coefficient was introduced to approximate the history dependence of the out-of-plane indicial responses, and it is shown that a simple linear fitting can significantly improve the qualitative behavior of the out-of-plane hydrodynamic model. Subsequently, a constant pivot point approach was adopted to limit the achievable kinematic range of the vehicle, where the cross-coupling effects could be studied directly.
With these additional contributions the unsteady indicial response model significantly improved the hydrodynamic predictions for oscillation maneuvers in comparison to a traditional quasi-steady model. Specifically, it was found that the rolling moment experiences substantial interference effects due to the convection of the sail tip vortex. Furthermore, the indicial model captures a complex stern-rising phenomenon that occurs when the vehicle changes direction, which the standard quasi-steady model has no mechanism to predict.