Simulating mixed sea state waves for marine design

This paper concerns the calculation of the wave statistics in nonlinear mixed sea states (i.e. sea states of combined wind waves and swell). The calculations have been carried out by incorporating a 2nd order nonlinear wave model into a random phase deterministic spectral amplitude (DSA) simulation method. To demonstrate the effectiveness of this approach, the calculation results from a linear simulation method and a random phase non-deterministic spectral amplitude (NSA) simulation method and from using some empirical formulas have also been presented for comparison purpose. In order to validate the approach proposed in this article, the wave characteristics directly calculated from the wave data measured at an oil field in the North Sea were utilized. It has been shown, contrary to the usual belief, that the nonlinear DSA simulation method used in this study can predict slightly more accurate wave characteristics than the nonlinear NSA simulation method does. The calculation results in this paper are analyzed, and some findings valuable for marine structural design have been pointed out.