An initial evaluation of the free surface effect on the maneuverability of underwater vehicles

The present study aims to evaluate the free surface effect on the maneuverability of an axisymmetric underwater vehicle (UV) in the horizontal plane. Therefore, the hydrodynamic captive tests, including the straight-ahead resistance, drift and rotating arm tests, are performed over various submergence depths by using URANS equations with a Reynolds stress turbulence model available in the commercial code STARCCM+. To assess the maneuverability, the forces and moments generated by the velocity components, which are obtained from captive tests, are implemented in the maneuvering equations. Moreover, analytical equations are used to calculate the loads arising from the UV accelerations, thrust and rudder, which are all assumed to remain constant with respect to depth. The results show that the behavior of the lateral force and yaw moment generated by the UV stern region reduces significantly the UV stability over the entire range of depths. The results further show that, as the UV approaches the free surface, the behavior of the lateral force and yaw moment induced by the region between the UV midlength and aft shoulder increases the UV stability, which consequently decreases the maneuverability.