## 4 Results and Discussions  
The simulation results of wind fields were collected at various town and street sites of Taizhou. The wind speed contour plots across the computational domain are shown for five simulation cases in Figure 7, respectively. It can be seen that the wind speed results varied from case to case. When the Tiantai, Xianju, and Linhai stations were used as the references, the maximum wind speed at the surface was about 40 m/s, while when the Wenling and Hongjia stations were used as references, the maximum wind speed could reach more than 70 m/s. Because of the large difference in elevation of the mountains in the computational domain, the uneven spatial distribution of mean wind speed was observed for each simulation case. Thus, it was necessary to carry out such a mesoscale CFD simulation study to determine the extreme wind speed and in turn the reference wind pressure for a specific site without a long history of observation data. The wind speed and wind direction simulation data of each location (latitude, longitude and elevation) are summarized in Table 7. The 50-year return period maximum wind speeds in Table 7 were calculated according to the extreme type I probability distribution model based on the measured data collected from the five meteorological station of M1 to M5. \begin{table}
\begin{tabular}{c c c c c} \hline Case & Reference Weather & Maximum Wind Speed & Wind Angle & Elevation of the Wind \\  & Station Name & in 50-Year Return & Corresponding to & Speed Acquisition \\  & & Period (m/s) & Maximum Speed & Point (m) \\ \hline Case 1 & Tiantai Station (M1) & 21.53 & ESE & 108.6 \\ Case 2 & Xianju Station (M2) & 21.69 & NE & 79.1 \\ Case 3 & Linhai Station (M3) & 23.74 & WNW & 6.8 \\ Case 4 & Wenling Station (M4) & 26.40 & N & 33.6 \\ Case 5 & Hongjia Station (M5) & 27.22 & NNE & 5.3 \\ \hline \end{tabular}
\end{table} 
Table 7: The cases of CFD simulation. Figure 7: _Cont._  
According to the extreme type I probability distribution model, the distribution function of extreme wind speed was:  
\[F(x)=e^{-e^{[-\alpha(x-u)]}} \tag{6}\]  
To find the extreme wind speed once in 50 years, it means the probability of \(x\leq x_{\max}\) is 49/50, then:  
\[\exp\{-\exp[-\alpha(x-u)]\}=98\% \tag{7}\]  
Take two natural logarithms from both sides of Equation (5) and simplify it as:  
\[x_{50}=u+3.90194\frac{1}{\alpha} \tag{8}\]  
where \(u\) and \(\alpha\) are the position parameter and scale parameter, respectively, corresponding to the extreme type I probability distribution, which could be estimated statistically with the observed extreme wind speed data from the five main stations of M1 to M5. A comparison of the simulated and measured wind speeds at 17 meteorological stations in Taizhou City was reported in Table 8. The difference between the simulated maximum wind speed and the 50-year return period wind speed calculated from the observation data was small for stations with a long history, but the discrepancies became large for relatively new meteorological stations with a short history. For the 51-year-old station in Hongjia (Jiaojiang district), the discrepancy between the simulation and reference wind speed was only about 0.11%. The difference between \(v_{50}\) and \(v_{8}\) in Table 8 was smaller when the observation duration was more than 19 years, and the maximum was 36.4% at Haimen station. However, the difference will be larger when the observation duration of a station is less than 19 years, and the largest discrepancy of 360.47% was found at Fuxi station in Tiantai district with a 9-year observation history. Figure 8 presents a scatter plot of the simulated wind speed data for the 17 meteorological stations in Taizhou. The dotted line in the plot is the envelope of the maximum wind speed at each station. According to the meteorological records, in the past 19 years, only in 2019 did Typhoon Lekima land in Taizhou directly. A large number of new meteorological stations have since been built with a relatively short history, but few data have been collected due to typhoon.