||In the last few years, internal waves have been extensively studied by many scholars, mostly focused on the physical property and the effect on ecology and geochemistry. The geological influence, however, was rarely discussed. By EK500 and 3.5 kHz sub-bottom sonar system, it is reported that many sand waves exist in the South China Sea at 600 meter water depth. Internal waves are a very important driving mechanism in the South China Sea. Its movement over the marine bed causes unsteady flow field disturbance. In order to clarify whether the internal wave is the main factor to form sand wave, we conduct a series of numerical simulations.|
Most studies on the formation of sand waves are mainly in the nearshore area. Due to the difficulty in observation, only very few special discussions consider depth of 500 meters or deeper. First of all, in this thesis, we use the Korteweg de Vries (KdV) equation to derive wave and current in an internal soliton. Then, the flow field is substituted into the Regional Ocean Modeling System (ROMS) numerical model to simulate the three-dimensional movement of internal waves and the associated movement of suspended sediment in order to discuss the mechanism of sand wave formation. Finally, the variation of wavelengths of sand wave is analyzed and compared with in-situ measurement.
From the simulation result, the internal wave causes the formation of sand waves. After the passage of dozens of internal waves, a flat sea floor will gradually form sand wave topography. Different depth and slope of the sea bottom will affect the sand wave wavelength also.