During the early design stage of an underwater vehicle, the correct assessment of its manoeuvrability is a crucial task. Conducting experimental tests still has high costs, especially when dealing with small vehicles characterized by low available budget. In the current investigation, virtual towing tank tests are simulated using the open-source OpenFOAM library in order to assess the reliability of CFD methods for the prediction of hydrodynamic forces and moments. A well-known case study, the Defence Advanced Research Projects Agency (DARPA) SUB-OFF model, is used, and the outcomes are compared to the experimental results available in the literature. Five different configurations are investigated for pure drift tests, rudder tests and pure rotation in both vertical and horizontal plane. The results show an overall good agreement with the experimental data with a quite low demanding mesh arrangement of 3M cells, a favourable balance between accuracy and computational time. In more detail, the expected error in the most significant forces during manoeuvres is less than 2% for the fully appended configuration (the submarine real operative condition), whereas the accuracy is moderately reduced for the barehull configuration (a case not representative of a real hull) with an expected error of 15%. A possible reason for the differences observed could be attributed to the description of the two streamwise vortices generated when manoeuvring. Apart from the lateral force and yaw moment, the results of the longitudinal force are also presented, having a greater disparity when compared to the experimental data. Nevertheless, the longitudinal force has no important role for the purpose of making stability and control predictions. The study contributes to the validation and consolidation of CFD methods, offering insights into their accuracy and limitations for practical applications in underwater vehicles.

The hydrodynamic interaction between two or more ships in harbours or inland waterways is a classical maritime engineering research area. In ship manoeuvring practice, ship masters try to determine the speed and gap limit when a ship is passing or encountering others, particularly in confined water ways. This requires an accurate prediction of the interaction force acting on both ships. The pioneer experimental studies showed that the interaction could lead to a very large yaw moment and this moment is strongly time-dependent, which could make the ships veer from their original courses, leading to collisions. Based on the findings on experimental measurements, some empirical formulas are proposed in the literature to predict such interaction forces. However, these formulas could provide a satisfactory estimation only when the ship speed is quite high, and the water depth is shallow and constant. Numerical simulation overcomes this issue by simulating the ship-to-ship problem by considering the effect of the 3D ship hull, variable water depth and ship speed. Numerical simulation has now become the most widely adopted method to investigate the ship-to-ship problem. In the present study, the development of the methodologies of ship-to-ship problems will be reviewed, and the research gap and challenges will be summarized.