Ocean Wave Rendering Using Wave Number Spectra In The Visual System Of Maritime Simlator

Realistic ocean wave rendering contributes to improving the environmental reality of the visual system of maritime simulator. In the dissertation, the algorithm using wave number spectrum is selected to render ocean waves in the visual system of maritime simulator. The author of the dissertation does detailed study on the algorithm.The Phillips spectrum is a wave number spectrum widely used in rendering, but the value of its spectral constrant is not provided in concerned references. The author of the dissertation analyses the structure of the Phillips spectrum, finding that the frequency spectrum of the Phillips spectrum is similar to the P-M spectrum in form. Assuming that the P-M and Phillips spectra share the same potential, the author of the dissertation computes the value of the spectral constant. This solves the problem that the value of the spectral constant lacks of theoretical support. When the computed value is applied in rendering, the amplitude of the rendered sea surface is malformed. When other wave number spectra are tried, the amplitude of the rendered wave is also malformed. To solve the problem, a method of correcting the amplitude malformation is presented. The algorithm of using wave number spectrum is initianlly provided by Tessendorf without complete derivation. The algorithm is re-derived in the dissertation. The derivation indicates that both the Fourier coefficients of the height field and the Choppy wave vector contain the wave number spectrum and the area of the discrete integral domain of wave number vector. Comparison studies show that the Fourier coefficient provided by Tessendorf omits the area of the discrete integral domain. It leads to the amplitude malformation. According to the derivation of the dissertation, the Fourier coefficient is corrected, and the amplitude malformation is corrected. Some open source codes, including osgOcean, directly apply Tessendorf's algorithm in rendering. These open source codes use some factitious methods to reduce the over large amplitude of the rendered sea surface. The factitious methods are useful, but lack of theoretical support. The ocean wave potential of the open source codes is close to that of the method presented by the dissertation. This confirms the method presented by the dissertation.The vertical acceleration on the wave crest is taken as criterion of whitecap generation in rendering, and a continuous mathematical whitecap coverage model is provided. The inverse fast Fourier transform form of the vertical acceleration is given. The model uses the vertical acceleration to compute the whitecap coverage, the parameter of the model is determined by Standard Genetic Algorithm, and the life time of whitecap existing is controlled by the parameter of the model. The mean of the computed whitecap coverage equals to the whitecap coverage computed by the stochastic model. The whitecap coverage is used as the blending factor to blend the pixel color of the sea surface and that of the whitecap texture, and the whitecap is real-time rendered. The shape and size of the rendered whitecap can accurately reflect the wind influence on the whitecap, are similar to the whitecap in photoes of the actural sea surface, and accord to the description of the Beaufort scale.