In this paper numerical simulations are utilized to study the transformation of internal solitary waves (ISWs) of depression type propagation on an underwater slope in a two-layer fluid system. Gravity collapse method is used to generate the depression type of internal solitary waves. The flow evolution of a depression ISW in different physical conditions (i.e. lock length x0, step depth η0 and upper/lower layer depth ratio h1h2) is considered in an incompressible free-surface flow problem. The continuity equation and Navier-Stokes equations are utilized to simulate the flow problem. In order to simulate the deforming and breaking effect of wave and flow during the interaction between internal solitary waves and the slope, the Renormalization-Group (RNG) k-ε model is chosen as the turbulence model. The generation, propagation, breaking phases and reflecting energy of large amplitude internal solitary waves interaction with a uniform slope have been investigated in a numerical flume. ISWs main features depend on the geometrical parameters that define the initial experimental setting. The relations between ISWs geometric and kinematic features and the initial setting parameters are analyzed and compared with the existing empirical relations. The energy dissipation during wave propagation is investigated. We find that the attenuation rate of amplitude and energy of ISWs decrease as η0 increases, however, this trend tends to flatten as the internal wave amplitude increasing. The investigated slope values range from 7.2° to 43.5°. Based on both wave properties and slope values, different breaking types have been found. We also find that different slope values and breaking types cause different reflected wave amplitudes, which means different energy dissipation during the interaction between ISWs and the uniform slope. The energy dissipation during the interaction between the internal wave and the slope decreases with the slope value increasing, and the energy dissipation rate is between 64.6% and 96.2%. Such an energy dissipation during the interaction between internal solitary waves and the slope may cause mixing of the two-layer fluid.
Over the past four decades, the combination of in situ and remote sensing observations has demonstrated that long nonlinear internal solitary-like waves are ubiquitous features of coastal oceans. In a continuously stratified fluid, the interface between warm and cold fluid or between fresh and salt water can oscillate forming an internal solitary wave. Ocean internal waves typically have wavelengths ranging from hundreds of meters to tens of kilometers and periods from several minutes to several hours (Massel, 2016). Internal waves in the ocean are primarily important as they affect mixing through the transport of energy. ISWs may also affect nutrients transport towards the surface, in particular when mixing occurs (Lai, 2010), and also may cause lateral transport of nutrients (Lamb, 1997).
