Study On The Propagation Model For The Deep-sea Internal Waves And Its Numerical Simulation

Ocean internal wave is a kind of wave which occurs in the density stratificationsea water for thermohaline change. In-situ measurements and remote sensing haveshowed that internal waves are ubiquitous in the ocean. The development of theresearch of oceanic internal waves and the characteristics of internal waves wouldgreatly promote the developments of ocean acoustics, ocean engineering, militaryoceanography etc. The propagation of deep-sea internal waves will be affected bysome factors such as terrain and seamounts, because of which, the dispersion effectand nonlinear effect may be relatively complex. However, it is difficult to obtain theobservation and experiment data for the deep sea internal waves, so appropriate modelestablishment, and numerical simulation are used to study deep-sea internal waves inthe thesis. The deep-sea internal wave generalized nonlinear Schr dinger(NLS)equation of which the high-order dispersion effect and high-order nonlinear effect willlay the foundations for the further study on the variation mechanism of the internalwave propagation is obtained. The thesis are arranged as follows：Firstly, deep-sea internal wave generalized NLS equation is derived. From theassumption that the amplitude is small, the model equation that governs the evolutionof the deep-sea internal waves at the interface of incompressible, inviscid andirrotational two-layer fluid is studied. On the basis of the Laplace equation andBernoulli equation, we show that the generalized NLS equation includinghigher-order dispersion effect and higher-order nonlinear effect can be derived byperturbation analysis. By analyzing the higher-order dispersion coefficient andhigher-order nonlinear coefficient, we obtain two kinds of soliton solutions.Secondly, numerical simulation of the generalized NLS equation is studied. Theaffect of the high-order dispersion effect and high-order nonlinear effect to thevariation mechanism of the internal wave propagation are researched. The deep-seaarea which would be studied is selected, and its environmental parameters are analyzed. Internal wave propagation is simulated using generalized NLS equation inthis area. The results show that internal waves are constantly broadening, theiramplitudes gradually decreasing, turbulence, and self-steeping with crest frequencyshift. This is the manifestation of higher-order effects of the equation. Compared withinternal waves measured data and SAR image, the useful result is obtained. Bynumerical calculating the propagation of the internal waves with the different initialwaves pattern and the initial waves pattern with initial chirps，the effect of the initialwaves pattern is obtained and compared with internal waves measured data. Theinfluence of initial wave pattern and initial chirps for the propagation of the deep seainternal waves is researched.Finally, the mixed model is used to numerical simulate the spread of internalwaves from deep sea to shallow sea. The internal wave prone areas the South ChinaSea near Dongsha Island waters is selected as area of study. According to the changesof the terrain, the spread of waves in deep sea is simulated with the NLS equationfirstly, then, the spread of wave in shallow is simulated with the EKdV equation. Itcan be found that the results are in good agreement with the actual remote sensingimages, comparing single model which consists of the NLS equation or the EKdVequation. It shows that the mixed model is reasonable.