Numerical and experimental study on the hydrodynamic characteristics of submersibles under the internal solitary waves

Based on OpenFOAM and the DJL theory, a numerical flume is established to simulate the interaction between an internal solitary wave (ISW) and a submersible. The experiments are carried out in a large gravity stratified flume, and the accuracy of the numerical model is validated by comparing with experiments. The motion characteristics of the submersible under different ISW amplitudes, diving depths, and pycnocline thicknesses are further investigated numerically. Four key kinematic parameters affecting submersible safety are proposed to provide guidance for safe navigation. The results show that the average error between the numerical results and experiments is less than 20 %, indicating that the numerical model can accurately describe the interaction between the ISW and the submersible. The motion characteristics of the submersible are the same under different ISW amplitudes, and the motion amplitude increases with increasing ISW amplitude. The motion characteristics of the submersible vary significantly with diving depth, and the difference between positions above and below the pycnocline is pronounced. In contrast, the motion law of the submersible exhibits no obvious difference under varying pycnocline thicknesses. The maximum horizontal relative velocity, maximum depth, maximum drop depth speed and maximum positive pitch angle are important kinematic parameters that affect the navigation safety of the submersible. A large ISW amplitude increases the horizontal relative velocity of the submersible and enhances its rudder effect, but it also accelerates the submersible’s depth drop and pitch angle variation. The ISW is less harmful to the submersible above the pycnocline center, but becomes harmful when the submersible is completely below the pycnocline center. When the submersible is located below the center of the pycnocline but partly within it, the largest depth drop rate also poses a threat to the navigation safety of the submersible.