The Numerical And Experimental Studying On The Multi-directional Focusing And Exteme Waves

The extreme wave is one kind of limited wave, which imposes large or extreme forces on ship and offshore structures. Recently, it has been paid a considerable attention to. A lot of research indicated that wave focusing is one of the most important mechanisms that contributed to the extreme wave. In this paper, the extreme waves generated by wave focusing method are studied by physical experiment and numerical simulation.At the beginning of this paper, the method of focusing wave generation was introduced. The influencing factors are discussed through linear theory, such as, assumed amplitude, central frequency, frequency band, spectral distribution, directional distributional band and water depth.In the third chapter, the extreme and breaking waves were generated using focusing wave method in three-dimensional wave basin, considering effects of different assumed amplitudes, spectral distributions, water depth and directional distributions. The focusing wave surface characteristics, breaking criteria, the change of spectrum and energy loss are discussed. The results show that wave focusing and breaking are strongly affected by assumed focusing amplitude, frequency spectra, water depth and directional distribution. The waves with larger amplitude and shallower water depth are easier to break. For the same water depth, the waves with constant wave amplitude are easier to break than those of constant wave steepness.In the following chapters, the numerical model was developed based on the high-order spectral (HOS) method. The method has the properties of fast convergence and low computational costs, owing to using the fast Fourier transformation (FFT) method to solve the differential equations. It permits the fully-nonlinear simulation of gravity-wave evolution within periodic unbounded 3-D domains. But the original surface and velocity potential should be given.. In order to simulate the generation of focusing waves, the model is developed by introducing wave maker boundary.In the sixth chapter, the 2-Dand 3-D focusing waves were numerically studied using the developed numerical model, considering different parameters. The characteristics of the focusing wave including surface elevations, maximum crest, the shift of focusing point, surface parameters and the change of frequency spectra are discussed. The results indicate that the nonlinearity of the focusing wave becomes obviously with the increase of assumed focusing amplitude and central frequency, the decrease of directional distribution and water depth.Finally, the numerical model was developed to simulate the wave propagation over regular bottom. The numerical results were compared with experimental results. The comparisons show that the model is available.The extreme waves are studied through experimental and numerical method. The results lay the foundation for the study of interaction between wave and structures.