# Wind Load Distribution in Float Photovoltaic System
## 4 Modeling Description
### Model Evaluation Strategy  
The numerical analysis was performed by CFD analysis using ABAQUS [21]. The analysis model used a hexahedron-shaped trimmed mesh and consisted of a total of 81,758,581 grids. As the boundary condition, the velocity of the fluid was entered as the velocity condition in the air inlet. In the other air outlet, fluid flow was applied without back pressure under the pressure outlet condition. The pressure applied to the PV panel was extracted under the assumption that the airflow remains steady without considering the change over time as a steady state. For the CFD analysis, it was assumed that about 189 solar modules would be installed, considering the efficiency of the analysis program. The CFD analysis was performed for the forward and backward directions of the PV module with the largest wind pressure area. The structural shape was first modeled considering the dimensions of the PV module, and the CFD model was constructed after setting the analysis conditions, including wind \begin{table}
\begin{tabular}{c c c c} \hline
**Direction** & **Installed Angle (Deg.)** & **Wind Speed (m/s)** & **Etc.** \\ \hline \multirow{4}{*}{Forward} & & 36.16 & Basic wind speed 32 m/s \\  & & 51.74 & Basic wind speed 45 m/s \\  & & 70.00 & Recorded maximum \\  & & 36.16 & Basic wind speed 32 m/s \\ Backward & & 51.74 & Basic wind speed 45 m/s \\  & & 70.00 & Recorded maximum \\ \hline \end{tabular}
\end{table} 
Table 2: Design parameters to determine wind load. Figure 4: Power generation and losses depending on the tilt angle of PV module. Figure 5: Designation of applied wind load direction. speeds. The analysis was divided into wind direction from the forward and backward of the PV modules. Unlike the structural analysis, the number of finite elements in the analysis model is very large because the flow analysis must separately model the flow area where the fluid flow is induced in addition to the structural analysis model of the target structure. Therefore, considering the limitations of the program and the efficiency of the analysis, the flow analysis was performed on a power plant with 189 PV modules to evaluate the flow behavior caused by wind, as shown in Figure 6. The installation angle of the solar modules is assumed to be 12\({}^{\circ}\), and the solar modules are 450 W modules from Company H, which are currently widely used in South Korea. Considering the dimensions of these modules and the altitude of the sun, the spacing between the PV module arrays was calculated as the following Equation (1), and the spacing in the direction of the solar module arrays was assumed to be about 30 mm apart, considering the dimensions of the clamps to fix the modules in Figure 7.  
\[d=l\times\bigg{[}\frac{\sin\alpha\cos\beta+\cos\alpha\sin\beta}{\sin(\beta)} \bigg{]}, \tag{1}\]  
where \(d\) is the allowable separation between the arrays (mm), \(l\) is the length of the longer side of the photovoltaic module (mm), \(\alpha\) is the installation angle of the photovoltaic module, and \(\beta\) is the solar azimuth angle. Figure 8 shows a schematic illustration of the structural geometry of the solar power plant, and the flow-influenced boundary induced by the fluid flow around the plant is modeled. Figure 6: Exemplary PV power plant. Figure 7: Spacing PV module arrays. In Figure 9, the most dominant load on the PV power plant is the wind load, and since the structural form is very simple, the wind load on the power plant is transferred to the foundation, so the bottom of the PV module is assumed to be an arbitrary boundary condition. In general, the load transmitted to the foundation is derived through the reaction force of the boundary condition through structural analysis, but in flow analysis, the pressure applied to the solar module is directly derived by the behavior of the fluid, so an arbitrary boundary condition is assumed at the bottom of the solar module.