| Internal waves are generated by disturbances to a stratified ocean at frequencies between the inertial and the buoyancy frequency. A primary source is the oscillating barotropic tidal flow over varying topography, which gives rise to the disturbance of the pycnocline. Under certain circumstances, this disturbance can transform into a set of high frequency, non-linear internal waves. This thesis mainly focuses on the evolution of internal solitary wave (hearafter"ISW"), which is a special kind internal wave. Internal solitary waves (hereafter"ISWs") are typically observed as propagating in packets with the longer and larger amplitude waves leading, indicating that both nonlinear and dispersive (nonhydrostatic) effects may play a significant role in the evolution process. As ISWs propagate in the ocean, they carry considerable momentum and energy, resulting in significant transient hydrodynamic loading on any offshore structures, undersea navigation vehicles and subsurface storage facilities that they may encounterIn the Northern South China Sea (SCS), ISW has been found to be active and frequently happened phenomenon. Observations have revealed the existence of large amplitude ISWs with amplitude more than 100m and wave crest more than 200km, which propagated out from the Luzon Straits and disappeared on the continental shelf in the Northern South China Sea. Combined with the in situ observation data on ISWs during ASIAEX, this thesis studied the evolution characteristics of ISW on variable topography, and can be resolved into three aspects.First, the weakly nonlinear variable coefficients KdV theory for ISWs was reviewed and the application of the slowly varying solitary wave theory was discussed, the fission characteristic of ISW was studied numerically. Even further, the two dimensional KP equation for ISWs in continuously stratified fluid was derived, which can be used for the simulation of the two dimensional characteristics of ISWSecond, a nonhydrostatic numerical model for density stratified flow was developed. With this model, we studied the local generation of ISW trains around the continental shelf break; it revealed that the interaction of barotropic tide with the continental shelf break can promote the generation of ISW trains with amplitude of several meters propagating towards the continental shelf. The pycnocline depth and the intensity of the tidal current were two main factors controlling the generation process. After that, we numerically studied the evolution characteristics of large amplitude ISWs on the continental shelf. The simulation captured the depression to elevation conversion the large amplitude ISWs, the effect of topography on the ISW propagation. The nonhydrostatic pressure was quantified. Empirical Orthogonal Function (EOF) method was employed on the analysis of the mode evolution characteristics during this whole process. Results revealed the generation of higher mode during the interaction of the first mode ISW with the shelf break.Finally, we report the recently developed PIV (Particle Image Velocity) systems for the laboratory experiment on density stratified flow and internal wave research. Experiments were carried out on the run-up of ISW on a slope. Different polarity ISW with different amplitude has been considered. The main focus is on the complex velocity and vorticity field during the strong breaking process, development of vortices structure were analyzed. Furthermore, a typical numerical experiment has been accomplished, results were compared with the laboratory experiment, numerical results provided a clearer picture on the whole breaking process, and revealed the strong mixing process during the ISW run-up and breaking process.
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