ABSTRACT
Internal solitary waves (ISWs) are a huge threat to submarines. In order to investigate the influence of internal solitary waves on submarine, a numerical method based on Reynolds-Averaged Navier-Stokes (RANS) equations was adopted in the paper. Besides, KdV internal solitary theory was used to modeling ISW-induced currents. Captive submarine model was simulated and analyzed. And simulation for submarine free motion with the interaction of ISWs was realized by Dynamic Fluid Body Interaction method. It indicates that flow fields become very complex when a submarine goes through solitary waves, resulting an extremely considerable loads and motion. Thus it is necessary to pay special attention to safe operation of submarine in ISWs.
Internal solitary waves (ISWs) appeared frequently in South China Sea (Lien, et al., 2014). Temperature and salinity are important factors affecting the density stratification of seawater. The density difference is much smaller compared with that between water and air. It is equivalent to placing in the microgravity field. So the restoring force of ISW is smaller, only 0.1% of water wave. And because amplitude is inversely proportional to the square root of gravity, the amplitude of internal wave can be 20-30 times of water wave under the same energy condition (Li, 2015). This is the essential difference between internal waves and water waves.
Internal solitary wave is a kind of non-linear large amplitude internal wave in nature, which is generally generated when strong current passing through the steep slope or ridge of seabed. There are strong amplitude dispersion and sudden strong current in internal wave. The wave length can be hundreds of meters to hundreds of kilometers, and the amplitude can be larger than one hundred meters. The maximum velocity of flow field induced by internal wave may be 2m/s or higher (Cai, et al., 2011). Therefore, the influence of internal waves on submarines should not be ignored.
Nowadays, computations of viscous turbulence flow around constrained submarine has been widely adopted to study the hydrodynamic loads exerted by ISWs (Chen, You, et al., 2010). And experiments are also carried out by using constraint models (Du, et al., 2016). But influence of ISWs to free motion submarine is an important and interesting problem, while there is no condition to carry out relevant tests so far. So numerical simulation method is used to investigate the problem here. We investigate the influence of internal solitary waves, focusing on movements of SUBOFF model (Groves NC, et al., 1989) as well as hydrodynamic loads. The research work in the paper were based on own codes combining with software.
