ISO 19901-1 wind spectrum

The ISO spectrum is also referred to as the NPD spectrum and is defined as follows:

\[S(f, z)=\frac{\displaystyle 320\cdot (\frac{\bar{u}_r}{10})^2\cdot (\frac{z}{10})^{0.45}}{\displaystyle (1+f_m^n)^{5/(3n)}}\\\\\]

where

\[f_m=172\cdot f\cdot (\frac{z}{10})^{2/3}\cdot (\frac{\bar{u}_r}{10})^{-0.75}\]
\[n = 0.468\]

According to the ISO 19901-1 document, the spectrum formula is defined on the domain \([1/600,~0.5]~\mathrm {Hz}\). In the SIMO implementation, the spectrum is set to zero above \(0.5~\mathrm {Hz}\) and limited in magnitude below \(1/600~\mathrm {Hz}\).

ISO 19901-1 wind spectrum for a mean wind speed of 20 m/s. In the SIMO implementation, the magnitude is limited for frequencies between 0 and 1/600 Hz as shown in Figure 1.

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Figure 1. ISO 19901-1 wind spectrum for a mean wind speed of 20 m/s