Ocean wave nonlinearity and phase couplings

The bispectrum of a swell dominated sea state is computed using Fourier coefficients from an original record and from simulated Fourier coefficients using pseudorandom (uniform) phase spectrum. The differences in the bispectra clearly show the effect of phase couplings or phase relationships in forming nonlinear characteristics of the sea state. Even in the very mildly nonlinear sea state, the phase spectral values are related as in Stokes waves. Nonlinear activity in a sea state depends also on presence and intensity of nonlinear component waves.