A simplified version of the double peak spectral model for ocean waves (Torsethaugen, 1993, 1994, 1996) is described. For the locally fully developed sea, the spectral peak period Tpf is a function of the significant wave height, Hs, Tpf=af*Hs 1/3 with af slightly dependent on fetch. This classifies sea states as wind sea Tp <=Tpf and swell Tp>Tpf each consisting of two wave systems. Empirical parameters given by significant wave height and spectral peak period define the spectral form parameters and energy distribution between the two wave systems in the model. The adequacy of the model is indicated by comparing the model with measured wave spectra from the Norwegian Continental shelf.
For a number of years, the Torsethaugen double peak spectral model has frequently been used for design purposes at the Norwegian Continental Shelf, both in connection with numerical analyses and model tests. The original Torsethaugen model was established by fitting two JONSWAP shaped models to average measured spectra from the Norwegian Continental Shelf. The observed sea states were grouped with respect to significant wave height, Hs, and spectral peak period, Tp. This means that average spectra were established from a broad range of combinations of Hs and Tp. Regarding the adequacy of the original fit to the average spectra, reference is made to Torsethaugen (1993, 1994, 1996). Over the years, users of the spectral model have often raised the question if the model can be simplified without a significant loss of validity. The final use of the model has always been rather simple, since the spectrum is defined as the total significant wave height and the period of the dominating spectral peak are given. The complexity lies in the number of parameters involved in parameterize the spectral model in merely two parameters.