Internal waves generated by a submarine during ultra-low speed navigation in stratified fluids

When navigating in a stratified fluid, submarines generate internal wave wakes, which can be non-acoustically detected. These internal wave wakes are caused by the propagation and diffusion of the submarine kinetic energy within the stratified fluid. The greater the navigation speed, the more energy is imparted to the internal wave wakes. Thus, is it still possible for the non-acoustic method to detect the submarine at ultra-low speeds? To help answer the question, a numerical model is built to simulate the evolution of internal waves generated by a moving submerged body in stratified fluids, which is validated by a comparison between experimental data and simulated results. Later, internal wave characteristics induced by a geometrically simplified submarine model navigating at four speeds (0.5, 1.0, 1.5, and 2.0 m/s) are studied. It is shown the internal wave wake varies with both the speed and water depth, and a transition from multi-mode to one-mode wave characteristics is observed when the speed increases from 0.5to 2.0 m/s. Within the observed water depth range of [50, 70] m, the internal wave amplitude is in the range of [0.144, 2.679] m, and the wake width and length change with the critical amplitude. For a critical amplitude of 0.2 m, the wake width and length ranges are [0, 481] m and [0, 1054] m, respectively. When the critical amplitude reduces to 0.1 m, the internal wave wake width and length increase to [95, 780] m and [123, 1521] m, respectively.