| As the world population grows, the land-based resource is under demand, Therefore, the ocean is becoming a secondary human resource and living space, exploiting marine resources relied on marine Engineering facilities. However,with the scale is becoming more complex and larger, the offshore exploration extend to deep water. This facility may be impact by strongly nonlinear waves in actual sea conditions. Extreme wave is one of the most dangerous waves that could course big disaster and great damage,the wave heights are tall and huge, wave peak is sharp and narrow, the energy is very concentrative, the speed of this wave crest is faster then other waves with the same height, the destructive force is huge.Therefore, It is very important to study the basic characteristics, evolutionary changes, generation mechanism, internal and external structure of the extreme wave.It will benefit to marine engineering structure, the safety of navigation of ships, reduce or avoid the potential risk and so on.In this dissertation,firstly,we introduced the definition and the basic characteristics, currently research of the extreme in the first, and then introduced the generation mechanism of the extreme wave in several aspect,such as spatial focusing, dispersion focusing, wave-current interaction, nonlinear modulation, wave-wave interaction and so on. In oceanography, one of the main way to study the sea wave is that using by the means of stochastic processes to describe the sea wave by spectrum. we introduce several sea spectrum and then present a numerical method for study of nonlinear interactions between a long wave and multiple short harmonic waves in infinite depth water. Specifically, this method is applied to the calculation of the temporal and spatial evolution of the surface elevations in which a given long wave interacts with several short harmonic waves. Another important application of our method is to quantitatively analyze the nonlinear interactions between an arbitrary short wave train and another short wave train.A numerical method to extract parameters of extreme sea wave and to calculate its dispersion relation is presented in this disertation. The nonlinear sea surface can be regarded as waves whose wave numbers and frequencies change with temporal and spatial points. At every point, the height of sea surface can be interpolated by the value of an extending sine wave whose parameters (such as wave numbers, frequencies et al.) are constant. With the first order and the second order derivative of extreme wave, one can extract wave numbers, frequencies, and amplitudes of the extreme wave. The numerical amplitude results show that this method is valid.according to the method presented and the relevant formula,for example in analytic extreme wave function, we give the ratiocinate and numerical calculation of the parameters such as wave number, angular frequency, amplitude and other parameters about the actual extreme wave. Our method has two advantages compared to wavelet and Hilbert transform analysis method.In the end, we summarized the work, given some ideas and advices for further research. |
