Multi-disciplinary co-simulation of floating process induced by pneumatic inflatable collar for underwater vehicle recovery

The recovery of underwater vehicles using a pneumatic inflatable collar provides an economical approach to the re-use of the vehicles and/or collar. However, limited high-fidelity numerical studies have been conducted to examine this approach. Accordingly, in this study, a multi-disciplinary co-simulation is conducted. The results show helical floating processes exhibiting random rolling and yawing motions, with the mechanisms stated as follows: a) a symmetric flow around the vehicle/collar conjunction body is generated owing to a small incidence angle; b) symmetric vortex pairs are generated on the leeside of the conjunction body owing to the inflation of the collar acting as a ‘source’; c) an accelerated pitching angular rotation suppresses the detached vortices on the leeside of the airbag to be attached pairs, and asymmetric vortices are shed from the tail fins; d) the deceleration of the pitching motion induced by the damping of water results in the formation of a detached horse-shoe vortex, and the horse-shoe vortex forms two detached vortices, which flow downstream and interact with the asymmetric tail fin vortices; and e) the rolling and yawing motions of the conjunction body intensify the asymmetric characteristics of the collar and tail fin vortices, augmenting the pitching and rolling motions and inducing the helical floating process. In general, the pitching angular velocity induced by the collar inflation governs the mechanisms for the evolutionary processes of flow patterns and determines the floating process.