____________

Frequency domain analysis. The wave trace shown in Figure 8.20(a) can also be analysed in the frequency domain. This is made possible by application of the Fourier series representation. In essence, any sea state can be described mathematically as being composed of an infinite series of sine waves of varying amplitude and frequency. Thus the surface excursion ll(t) at any time (defined in Figure 8.3) may be represented as

ll(t) = L [an cos (J)nt + b n sin omt ] (8.55) n=l

0.3", 6.3 (n)

0.18", 3.8 (n)

Figure 8.22 Histogram and superimposed Rayleigh pdf.