## 2 Methods
### Simulation Approach
Six other wind speeds are of relevance at this stage and they are explained in Table 4. The abbreviations in Tables 3 and 4 will be used herein after to refer to the respective table item. The wind shear is described according to the appropriate formula in the standard with a height exponent of 0.2 for all DLCs. In addition, no dynamic yawing has been included in the simulations as it is not required by the standard. The values in Table 4 are specific to the WT at hand, which is a Vestas V52 in this case belonging to the wind class Ia. The reference wind speed, or Vref, is defined by the IEC 61400-1 standard depending on the wind class of the WT under investigation. The standard also provides formulas to calculate the 50-year and 1-year return period wind speeds, respectively, based on Vref and the WT hub height. For a more in depth explanation of the design conditions, design load cases, and the wind conditions outlined in Table 3, see [43]. Generally, DLCs can be grouped into two categories, those requiring a turbulent wind field model and those requiring a laminar wind field model. To realize a turbulent wind field model, the standard specifies that six wind fields should be generated per wind speed with the turbulence model in each field simulated using a different random seed. The \begin{table}
\begin{tabular}{c c c} \hline \hline
**ID** & **Explanation** & **Value/Source** \\ \hline V\({}_{\text{hub}}\) & Speed at hub of WT & Depends on DLC \\ \hline V\({}_{\text{in}}\) & Cut-in wind speed & 4 m/s \\ \hline V\({}_{\text{out}}\) & Cut-out wind speed & 25 m/s \\ \hline V\({}_{\text{r}}\) & Rated wind speed & 14 m/s \\ \hline V\({}_{\text{ref}}\) & Reference wind speed & 50 m/s \\ \hline - & 50-year return period & For formula, see [43] \\ \hline - & 1-year return period & For formula, see [43] \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Relevant wind speeds specified using the IEC 61400-1 [38] and Vestas V52 datasheet [46]. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Design Condition** & **DLC** & **Ambient Wind Condition** & **Wind Speed(s) 1** \\ \hline \multirow{4}{*}{1. Production} & 1.1 & \multirow{4}{*}{Normal Turbulence Model} & \multirow{4}{*}{V\({}_{\text{in}}\) \(<\) V\({}_{\text{hub}}\)\(<\) V\({}_{\text{out}}\)} \\ \cline{2-3}  & 1.2 & & \\ \cline{2-3}  & 1.3 & & \\ \cline{2-3}  & 1.4 & & \\ \cline{2-3}  & 1.5 & & \\ \hline \multirow{4}{*}{3. Startup} & 3.1 & Normal Wind Profile & V\({}_{\text{in}}\) \(<\) V\({}_{\text{hub}}\)\(<\) V\({}_{\text{out}}\) \\ \cline{2-3}  & 3.2 & & \\ \cline{2-3}  & 3.3 & & \\ \cline{2-3}  & 4.1 & & \\ \cline{2-3}  & 4.2 & & \\ \hline \multirow{2}{*}{4. Normal shutdown} & 4.1 & Normal Wind Profile & V\({}_{\text{in}}\) \(<\) V\({}_{\text{hub}}\)\(<\) V\({}_{\text{out}}\) \\ \cline{2-3}  & 4.2 & & \\ \cline{2-3}  & 4.2 & & \\ \hline \multirow{2}{*}{5. Emergency stop} & 5.1 & Normal Turbulence Model & V\({}_{\text{hub}}\) \(=\) V\({}_{\text{out}}\) and V\({}_{\text{r}}\)\(\pm\) 2 m/s \\ \hline \multirow{4}{*}{6. Parked (idling)} & 6.1 & \multirow{4}{*}{Extreme Wind speed Model} & \multirow{4}{*}{50-year return period} \\ \cline{2-3}  & 6.2 & & \\ \cline{1-1} \cline{2-3}  & 6.3 & & \\ \cline{1-1} \cline{2-3}  & 6.4 & Normal Turbulence Model & V\({}_{\text{hub}}\)\(>\) 0.7*V\({}_{\text{ref}}\) \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Design conditions, design load cases, and implied wind conditions [43]. standard also defines the turbulence model according to the wind class of the WT under investigation. Wind speed ranges, such as the one required for DLC 1.1 from Table 3, are covered in this investigation with increments of 1 m/s. Therefore, as an example, 132 wind fields (22 wind speeds multiplied by six random seeds per wind speed) were generated to cover DLC 1.1 as it requires a turbulent wind field model, normal turbulence model.