Submarine Motions in Confined Waters. INSEAN Technical Report No. 6

This technical report concerns the work element WE-5.1 within the WEAO EUCLID RTP 10.17 project "Submarine Motions in Confined Waters". The CFD solver developed at INSEAN to analyse unsteady water/waves interactions with a manoeuvring submarine has been applied to investigate the fluid-induced body loads during the passage of the vessel across a vertical step separating an initial deep (open) water region from a final shallow (close-to-bottom) area. The submarine is assumed to follow a straight path at a constant speed and is fully appended and propelled, consistently with the INSEAN unsteady experiments. The results are presented in terms of global forces and moments and validated against the corresponding INSEAN model tests. The comparison shows a quite promising agreement. The vertical-plane loads are consistent with the experimental results and capture correctly the transient phase due to the passage across the step. When the submarine is in the close-to-bottom region, the numerical loads show a low-frequency behaviour similar to the one observed experimentally. This supports the physical explanation given in chapter 3 of the INSEAN technical report EUCLID/RTP 10.17/INSEAN/WE-3.3/TR/3/1. The numerical method is also used to analyse the local flow features, i.e. the velocity and pressure field evolutions during the transient phase. Concluding remarks are made in terms of challenges and capabilities of the developed solver as aimed within the Project for the examined Work Element.