Submarine surfacing in currents is three-dimensional unsteady motion and includes complex coupling between force and movement. This paper uses computational fluid dynamics (CFD) to solve RANS equation coupled with six degrees of freedom solid body motion equations. The CFD code used is an in-house developed code. RANS equations are solved by finite difference method and PISO arithmetic. Level-set method is used to simulate the free surface. Computations were performed for the standard DARPA SUBOFF model. The structured dynamic overset grid is applied to the numerical simulation of submarine surfacing in regular currents and computation cases include surfacing in the static water, and steady, uniform flows with different speed (v=0.2, 0.4, 0.6 m/s) and surfacing with different value between gravity and buoyancy(n=2%, 4%). The asymmetric vortices in the process of submarine surfacing can be captured. It is shown that roll instability is caused by the destabilizing hydrodynamic rolling moment overcoming the static righting moment. Relations among maximum roll angle, surfacing velocity fluctuation and current parameters are concluded by comparison with variation trend of submarine motion attitude and velocity of surfacing in different current conditions. Simulation results confirm that current speed has a significant effect on surfacing velocity fluctuation. Maximum pitch angle decreases with the increase of current speed. Especially the law of pitch angle decreasing with the currents speed presents approximate linear relationship. Maximum pitch angle with current speed at 0.2m/s can reach to 12.89° while 3.07°at 0.6m/s. According to the above conclusions, maneuverability can be guided in the process of submarine surfacing in currents in order to avoid potential safety hazard.
Safety is a very important consideration in the design and operation of submarines. To reduce risk at depth, submarines are usually equipped with emergency systems designed to rapidly blow the ballast tanks rising to free surface quickly. In the case of emergency maneuvers, this requires simulating extreme and unsteady motions. In the process of submarine surfacing, motion, force, moment and free surface have complex coupling with each other. Especially in currents with high speed, submarine maneuvering conditions become more unpredicted and roll angle will be negatively affected while surfacing.
