Environment: Data for Ochi-Hubble spectrum

The Ochi-Hubble formulation allows double peaked spectra to be set up, enabling you to represent sea states that include both a remotely generated swell and local wind-generated waves.

H_s and T_z

$\Hs$ is the significant wave height, $\Tz$ the zero crossing period. The behaviour of these data items is governed by the option for setting the spectral parameters: with the automatic option you define $\Hs$ only, and appropriate spectral parameters and the resulting $\Tz$ value are calculated by OrcaFlex; while the specified option allows you define all the spectral parameters explicitly, and have OrcaFlex calculate the resulting $\Hs\text{ and }\Tz$.

H_s1, f_m1, λ₁, H_s2, f_m2 and λ₂

The Ochi-Hubble spectrum is the sum of two component spectra, each of which is specified by a set of three parameters: $\HsL,\fmL,\lambda_1$ for the lower frequency component and $\HsH,\fmH,\lambda_2$ for the higher frequency component.

Parameters $\HsL\text{ and }\HsH$ are the significant wave heights of the component spectra; the overall significant wave height is then $\Hs = (\HsL^2+\HsH^2)^{1/2}$. Parameters $\fmL\text{ and }\fmH$ are the modal frequencies of the two spectra. Finally, $\lambda_1\text{ and }\lambda_2$ are shape parameters that, in each case, control the extent to which the spectral energy is concentrated around the modal frequency – larger values give more sharply-peaked spectra.

These spectral parameters can be given in two ways.

• Automatic. You define $\Hs$, and OrcaFlex determines the most probable spectral parameters for that value of $\Hs$ and the resulting $\Tz$ value, based on the Ochi-Hubble paper, table 2b.
• Specified. You define all the spectral parameters explicitly, and OrcaFlex calculates the resulting $\Hs\text{ and }\Tz$.