Study On The Evolution Law Of Internal Solitary Waves Over Topography

The 21st century is the century of the ocean,on the one hand,with the continuous exploitation of natural resources on land,they are dwindling,On the other hand,Ocean development technologies are constantly evolving,so people will put eyes to the ocean.Internal waves are a kind of movement occurring in the ocean interior.At present,internal waves have been observed in many sea areas in the world.As a kind of internal waves,the amplitude of the internal solitary wave is large,the period is short,the wavelength range is from a few hundred meters to several thousand kilometers.It can transmit in the ocean in the long distance but maintains the waveform and the wave speed invariable.Internal solitary waves carry a huge amount of energy.Marine structures and Marine vehicles have a major safety hazards because of shear flow that formed by its opposite rate of upper and lower flow.Therefore,scholars at home and abroad have done a lot of research on internal solitary waves.On the basis of summarizing the previous work,the paper investigated the applicability of the theoretical model of the internal solitary waves experimentally,and the propagation and evolution rules of the internal solitary wave passing up the steps at the laboratory scale and passing over the submarine terrain in the South China Sea was calculated.Scholars have put forward many theoretical models based on different hypotheses.In this paper,the applicability of eKdV model,KdV model and MCC model based on the rigid cover hypothesis,and KdV model and MCC model based on the free surface hypothesis are investigated experimentally.The experiment adopted a strong stratified fluid system where the upper and lower fluids were dimethyl silicone oil and water respectively.The experimental data were collected by taking photos with a camera,and the program of image processing was written to process the data.The applicable conditions of several theoretical models were obtained.The CFD business software Fluent was used to calculate the propagation process of the internal solitary wave when it went up the steps,the reliability of the numerical calculation method was verified by comparing with the experimental results,and the evolution law of the internal solitary wave when it went up the steps was summarized.A section of submarine topography in Xisha sea area of South China Sea was selected to build a model,and the evolution law of internal solitary waves passing through this section of submarine topography was calculated by using the same numerical method where Wave generation method was the velocity inlet.The results show that the free surface solution is narrower than the rigid cover solution in both KdV model and MCC model.The nonlinear parameters e are defined based on the water depth.The KdV theory and eKdV are mainly applicable to the case e ?0.1.When the amplitude exceeds the maximum amplitude of eKdV,the experimental waveform is in good agreement with the theoretical solution of MCC free surface.The MCC theoretical wave velocity based on the free surface hypothesis is the closest to the experimental wave velocity.When the internal solitary wave passes through the terrains of the steps,the waveform,amplitude,velocity and energy of the upper and lower layers will change.As the amplitude of the incident internal solitary wave increases,the variation degree of these physical quantities also increases.When the internal solitary wave passes through a section of the actual submarine topography in the South China Sea,the waveform changes are complicated,and K-H waves appear at the same time.The velocity of the upper layer of the internal solitary wave decreases,while the velocity of the lower layer increases when the amplitude of the incident wave is small.When the amplitude of the incident wave is large,the velocity of the lower layer decreases.Among the six positions for monitoring the velocity changes,the velocity field changes are the most drastic below the surface of the inner solitary wave in the shallow water depth of the second segment.When the amplitude of incident wave is large,a counterclockwise vortex will be generated at the upward slope of the left end of the terrain.Based on the definition of nonlinear parameters and dispersion parameters,this paper quantitatively provides several applicable standards of theoretical models,which can be used by scholars to develop and improve the theoretical models.The numerical results of the evolution law of internal solitary waves passing through the topography in Xisha sea area of South China Sea are of great reference value for Marine engineering construction.