A spectral description for extreme sea states offshore Denmark Part I: Power spectrum

Abstract

A power spectral density function that describes extreme sea states in the Danish sector of the North Sea is developed. The power spectrum is specified in terms of the parameters: significant wave height, spectral peak period, and spectral second-moment period. The power spectral density function is a modified Torsethaugen spectrum, involving an expression for the peak enhancement factor that is dependent on the inverse of the square root of wave steepness and a high-frequency tail that decays at a rate which is dependent on the significant wave height and the ratio of the peak and second-moment periods. The new function was developed from Directional Waverider data measured at two sites in the Danish sector of the North Sea and validated with data from other sites offshore Denmark, primarily recorded with Saab WaveRadars. A companion paper describes a new directional spreading function, which together with the power spectral density function, provides a description of the complete frequency-direction spectrum of extreme sea states in the Danish sector of the North Sea.