The most used methods of numerical simulation of linear irregular sea waves are studied, including the Wave Superposition Method and inversions of FFT"s. An alternative method applying Walsh functions is also used. The generated wave records are analyzed applying the well known FFT Method and the Maximum Entropy Method. Results of the simulations are presented for the Deterministic (DSA) and for the Non-deterministic (NSA) models. The results of the simulations are compared under the point of view of computational efficiency, estimated spectra and statistical properties of the generated records. Finally, the wave records are used in the motion analyses of a semi-submersible platform in time domain.
In the study of the dynamic behavior of floating structures in irregular waves, two steps are of great importance: the digital simulations of the sea surface elevations, and the spectral analyses of the generated signals. And recently, great effort has been spent to successfully represent the ocean waves through computational programs, and several methods of spectral analysis and statistical calculations have been developed to analyze the wave records. In the present work, some of these methods of wave simulation and spectral analysis are shown and applied in the study of the motions of floating structures. These methods are largely used in the simulation of irregular sea waves, and are known as the Wave Superposition or the Summation models, and were applied by Morooka and Yokoo (1992) for the simulations of directional waves. Borgman (1969) applied these models and introduced the simulation through white noise filtering in time domain. Later, Wittig and Sinha (1975) presented a method of synthesis of random processes using Fast Fourier Transforms (FFT) of the spectrum in frequency domain. This method was improved by Hudspeth and Borgman (1979) with the application ofFFT routines for real numbers.
