Statistical Characteristics Of Crest Lengths And Their Influence On VLFS

The dimension of the very large floating structures (VLFS) is usually more than 1km. The design of such giant structures must consider the spatial coherence of waves. Crest length is one of the main parameters in wave coherence. In this dissertation, the progress in the researches of spatial coherence of random waves is reviewed. Based on this, studies have been carried out for the statistical characteristics of crest lengths and their influence on VLFS. The main points of the dissertation are as follow:â—‡ A clear definition of 3-D wave crest and a description of the procedures to detect the boundary of wave crest are presented based on Goda's definition. By using random wave theory and directional wave spectrum, a MATLAB-platformed program is designed to simulate random wave crests for various directional spectral conditions in deep water.â—‡ Statistics of wave crests with different directional spreading parameters and different directional functions are obtained and discussed. JONSWAP spectrum and the directional function suggested by Mitsuyasu, Donelan and Wen respectively are employed in the analyses.â—‡ Statistical distribution of wave crest characteristics such as crest length, crest height, and directional angles based on the above-mensioned numerical simulation of 3-D random waves are analyzed. The result shows the distributions of wave crests are no longer uniform and continuous but have different distributions after considering the directional information. The distribution of crest length is greatly influenced by the directional function. The wider range of the directional distribution of wave energy, the shorter of the mean crest lengths and the wider range of the distribution of crest directional angles. The crest height and crest length show a high relativity while the crest heights are low and become independence at very high crest height.â—‡ A brief introduction of Synthetic Aperture Radar(SAR) and the application of SAR image data in the research of crest length distribution is introduced. The method to compute the action of random waves with different crest lengths on VLFS. is also reviewed. Both can be served as a basis for further study in the related fields.