## 3 Determination of the Wind Load
### CFD Simulation  
The CFD simulation was carried out to capture the characteristics of the wind field along the structure, aiming to find the root cause of the IE effect on wind loads. Meanwhile, the wind force of each member of each case was obtained, serving as an important supplement for the investigation of wind loads and the preparation of dynamic response calculation. The CFD simulation was conducted using the Fluent 17.0 software platform. The 3D steady Reynolds stress model (RSM) was adopted in the computation, as it was shown to be appropriate by [PERSON] [15]. The coupling of pressure and velocity was computed using the SIMPLE method. The first-order dispersion scheme was applied for the moment equation, turbulent kinetic energy, and turbulent dissipation rate. According to the convergence standard, all the variables must remain below 10\({}^{-4}\). The same scale and test cases were adopted as those in the wind tunnel tests. As shown in Table 3, the CFD model is divided into 15 parts according to the category of the members in the code. Because of the complicated geometry of the model, the computational domain is divided into a cylindrical interior field and an exterior field. Unstructured tetrahedral meshes are applied in the interior area, and structured hexahedral meshes are used in the outer area (Figure 6). The interior mesh is denser to better capture \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multirow{2}{*}{**Items**} & \multicolumn{3}{c}{**Boom Down**} & \multicolumn{3}{c}{**Boom Up**} \\ \cline{2-9}  & **Azimuth** & **Mean** & **RMS** & **Peak** & **Azimuth** & **Mean** & **RMS** & **Peak** \\ \hline \(C_{\text{Fx}}\) & 15/165\({}^{\circ}\) & 0.80 & 0.13 & 1.15 & 30/150\({}^{\circ}\) & 0.94 & 0.19 & 1.30 \\ \(C_{\text{Fy}}\) & 75/105\({}^{\circ}\) & 1.24 & 0.16 & 1.65 & 60/120\({}^{\circ}\) & 1.40 & 0.25 & 1.82 \\ \(C_{\text{Mx}}\) & 75/105\({}^{\circ}\) & 0.76 & 0.10 & 1.05 & 60/120\({}^{\circ}\) & 1.08 & 0.10 & 1.45 \\ \(C_{\text{My}}\) & 15/165\({}^{\circ}\) & 0.47 & 0.08 & 0.62 & 30/150\({}^{\circ}\) & 0.63 & 0.06 & 0.88 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: The most unfavorable azimuths and values for each wind force/moment coefficient. the airflow characteristics around the model. The grids are merged in nodes on the surface between two fields, so the boundary condition of the surface is set as 'Interior'. The area around the main and diagonal members is encrypted by constructing a 10-layer boundary layer grid with an equal growth ratio of 1.1. The total number of meshes reaches 7 million. The mesh outside the interior domain is constant. So only the interior part is changed according to the model (isolated or group-arranged ones), spacing, and azimuth. The dimensions and the boundary condition of the computation domain are demonstrated in Figure 7. The computational domain is configuated as a simple rectangular box. It has dimensions of 3.33 \(\times\) 6.67 \(\times\) 10 m\({}^{3}\) (500 \(\times\) 1000 \(\times\) 1500 m\({}^{3}\) for prototype model) to ensure the magnitude is larger than 5, 40, and 15 times of the height, width, and length of the crane model. The maximum the blockage ratio is less than 1%. The mesh independency analysis is performed in this study. The trial test of the \(C_{\text{Fy}}\) is performed by varying the number of meshes, and the results obtained are shown in Table 4. Despite the number of meshes varying widely, the calculated \(C_{\text{Fy}}\) are similar, with an error of 3.2%, and 5.38 million meshes satisfied the calculation requirements and could guarantee high calculation efficiency. After comprehensive consideration, the 7.58 million mesh scheme was conservatively used in the subsequent analysis.