Underwater vehicle manoeuvring: performance prediction tool in constrained and shallow water

For naval submarines operations as well as for civilian underwater vehicles exploitation, navigation around obstacles and in shallow areas is becoming more frequent. Navigation in restricted water is historically managed through the definition of an appropriate margin to the seafloor. Nowadays, Naval Group provides submarine designs capable to operate closer to the seafloor, while maintaining a high level of navigation safety. To achieve this objective, an evolution in operating instructions, as well as in autopilot definition, is needed. This also requires performance prediction tools that are adapted to take into account the hydrodynamic interaction with the seafloor.This paper focuses on the performance prediction tools used in Naval Group design process to address constrained and shallow water (CSW) manoeuvring topics. Several tools can be used for performance prediction in shallow water: during a submarine design process, a range of complementary tools is necessary, for fast analysis and for more advanced verifications.Model tests in shallow water are possible, and have already been conducted on submarine projects. However, such tests can be long, complex and still insufficient: they do not allow optimising and verifying performance on the whole range of operational scenarios.Nowadays, computational fluid dynamics (CFD) is widely used for manoeuvring performance prediction, in infinite water situations as well as in shallow water. Such methods can be used on a wider range of configurations, with a reduced time and cost compared to model tests.In addition to CFD and model tests, lighter tools are needed for several applications:-Parametric studies on a wide range of configurations-Optimisation of submarine design and autopilot-Analysis of the submarine dynamic behaviour in complete scenariosNaval Group tool for submarine dynamic performance prediction already took into account various external environmental effects (swell, current...). For shallow water application, the tool has been improved to take into account more precisely the hydrodynamic interaction between the submarine and the boundaries (sea floor and sea surface). This evaluation is based on boundary element methods (BEM) calculation, which represents a fast and reliable calculation approach, adapted to the underlying physics. The results obtained with the developed method are compared with those from more complex methods, as well as with existing data from literature.Finally, this work shows how Naval Group integrated the appropriated tools in its submarine design process to take into account the shallow water effects on the submarine manoeuvrability. This allows reducing the necessary navigation margins on shallow waters condition.