INFLUENCE OF DIVING DEPTH ON MOTION RESPONSE AND LOAD CHARACTERISTICS OF SUBMERGED BODY UNDER ACTION OF INTERNAL SOLITARY WAVE

Internal solitary waves frequently occur in ocean pycnocline. Because of its high crest, deep trough and huge energy, the seawater flow above and below the pycnocline will show a shear state and cause a sudden strong current. When hovering underwater, the submersible is likely to encounter internal solitary waves. Due to the flow field characteristics of internal solitary waves, the motion response and hydrodynamic load changes of the suspended submersible placed above and below the pycnocline are different, and even the phenomenon of falling deep will occur. This work aims to explore the influence of the submerged depth on the wave-body coupling based on mKdV theory and the CFD method. The velocity inlet boundary is used for wave generation. The overset grid and fluid-structure coupling methods are adopted to simulate the submerged body with multi-degree-of-freedoms. The motion response and hydrodynamic load of suspended submerged bodies at different depths are analyzed. The results show that under the action of internal solitary waves, the submerged body above and in the pycnocline move along the forward direction of the wave, sink at first and then rises, and the submerged body below the pycnocline will continue to sink against the current; The smaller the vertical distance between the submerged body and the wave surface, the more significant the influence on its surge, heave and velocity. However, the submerged body located in the pycnocline moves along the waveform at the interface, and its motion response and load changes are slightly affected; The directions of the horizontal force on the submerged body above and below the pycnocline are opposite. The peak value of the horizontal force is less than the peak value of the vertical force, and the submersible below the pycnocline always experiences a head-down moment, which eventually leads to falling deep.