Control of underwater suspended vehicle to avoid 'falling deep' under the influence of internal solitary waves

The interaction between the underwater suspended vehicle and the ISWs at different submergence depth is investigated. When the vehicle is above the pycnocline, the surge motion is dominant. While under the pycnocline, the heave displacement will become more significant. The closer it is to the pycnocline, the more drastic the variations of heave displacement and pitch angle will be. As the heave displacement continues to increase, the vehicle will experience the serious 'falling deep' accident. To reduce the occurrence of such situations, different control strategies are applied to the vehicle. The control effect, motion response and hydrodynamic characteristics of the vehicle are explored. The results of the study show that the deflection of the vehicle can be effectively reduced with control. The influences differ significantly when different control parameters are applied. If the control is suitable, the heave displacement of the underwater vehicle can be reduced to nearly zero.