Surface signature characteristics of the internal wave generated by a submerged body in the South China

The fluid density commonly stratifies in the ocean due to the vertical distribution of temperature and salinity. Coupled with a certain source of excitation, the surface wave and internal wave will be generated simultaneously. Compared with the surface wave, the internal wave has the characteristics of a long period and large amplitude. The emission of internal waves by submerged bodies in a stratified fluid is an important phenomenon in the ocean. It is possible to detect the submerged body through the internal waves. To study the surface signature in full scale generated by a submerged body, taking the Dongsha Sea area of the South China Sea as the research object, the vertical distribution of ocean salinity, temperature, density and Brunt–Vaisala (BV) in the Dongsha sea area is introduced in detail. Based on the actual sea conditions in Dongsha sea area, the surface wave excited by a slender volume source with 100m long and 10m diameter sailing at different depths and speeds is simulated by using the theoretical model with free surface boudary condition. The characteristics of the surface wave elevation field, velocity field and surface divergence field are studied. The results show that the amplitude of internal wave mode deceases if the BV frequency becomes smaller, the pycnocline is getting further away from the surface, or the submerged body is getting further away from the pycnocline. The pycnocline of the South China Sea is thinner and closer to the surface in summer, resulting in the bigger amplitude of internal wave mode. The pycnocline of the South China Sea is thicker and getting further away from the surface in winter, resulting in the smaller amplitude of internal wave mode.