Spectral and statistical properties of ocean waves
The fundamental property of surface waves induced by wind is their irregularity. The prediction of wave parameters can be achieved through stochastic analysis only. This analysis can be developed in two basic domains, i.e. frequency and probability domains. Frequency analysis mainly deals with an evaluation of the distribution of wave energy among various frequencies and directions. In this chapter we start with the basic properties of frequency analysis of the time series to interpret the frequency spectra of ocean surface waves. In general, the resulting shape of the frequency spectrum depends on the external wave generation conditions (wind speed, wind fetch and duration, water depth, swell presence, and storm stage) as well as on internal mechanisms in the wave field (nonlinear interaction between wave components, energy dissipation due to wave breaking or bottom friction). However, the spectrum shape is not arbitrary and some fundamental properties of energy distribution apply for all spectra. The wave spectral energy reaches its maximum at frequency ω = ωp and decreases for both lower and higher frequencies. Usually the reduction in the low-frequency range is faster than that for the high-frequency band. The lowest frequency for wind-induced gravity waves is estimated at approximately 0.03 Hz (0.2 rad/s). Energy at frequencies lower than this value is for surf beat, seiches or tides (Massel, 1996a).
KeywordsProbability Density Function Wave Height Wave Period Ocean Wave Rayleigh Distribution
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