## 4 Typhoon-Induced Wind and Wave Loading  
### Typhoon-Induced Wind Loading  
To advance theoretical research and engineering practices on stress concentration phenomena in fixed offshore platforms, this study focuses on a nearshore wind farm in Zhejiang Province as a case study, systematically reconstructing the historical typhoon process of the severe typhoon \"Muifa\". Leveraging the WRF mesoscale meteorological model, a high-resolution numerical simulation framework was developed to investigate typhoon-induced dynamic impacts on wind fields [29]. As shown in Figure 6, spatiotemporal coupling analysis reveals three-dimensional wind speed and direction profiles in the target wind farm area. Results indicate that during Typhoon \"Muifa\", the wind farm experienced significant dynamic meteorological changes, with the peak measured wind speed at the platform top (\(V_{top}\)) exceeding 45 m/s, consistent with regional meteorological monitoring data. Through multi-scenario comparative analysis and uncertainty quantification, the wind speed profile at 04:00 UTC on 14 September 2022, was selected as the extreme design scenario, providing reliable boundary conditions and load input parameters for subsequent structural stress response analysis of the platform. Figure 6 illustrates the wind profile at the most critical moment. A customized wind profile, derived by fitting an exponential function to WRF simulation results, is input into the typhoon module to generate turbulent wind speeds. Importantly, the application of WRF in this study was validated against available field measurements. Specifically, the exponential wind profile fit applied to the WRF output (as shown in Figure 6) was calibrated using measured wind data from the target site in Taizhou. Furthermore, the key spectral model (Equation (12)) used within the Zwind typhoon module to characterize turbulence was itself derived from and fitted to field-measured data at the site. Additionally, the turbulence intensity values utilized in the analysis (0.1023, 0.0665, and 0.0665) were directly obtained from these field measurements. This multi-faceted approach--calibrating the mean wind profile shape, employing a site-fitted turbulence spectrum, and incorporating measured turbulence intensities--provides a robust validation foundation for the WRF-simulated wind conditions used in this specific engineering scenario. When a struc  
Figure 6: Wind speed and direction profiles at a wind farm site in Taizhou. (**a**) Wind speed profile; (**b**) Wind direction profile. ture obstructs the airflow path, it induces stagnation or deflection of the airflow, converting the wind's kinetic energy into static pressure either partially or entirely. Consequently, the wind load on the structure originates from the pressure differential caused by airflow obstruction, with its magnitude determined by parameters such as wind speed, inflow direction, wind-exposed area of structural components, and aerodynamic shape. The aerodynamic excitation mechanism follows the principle of the Strouhal number (\(St\)) for cylindrical components, where the calculated \(St=0.2\) in this paper is consistent with the vortex shedding model of offshore structures [30]. This approach replicates wind-structure interaction dynamics observed in field studies of slender marine infrastructure. Although wind loading is inherently a dynamic force action, it is typically simplified as equivalent static pressure in engineering design. The typhoon module in Zwind [31], a software previously developed by our team, supports user-defined spectral models. Therefore, this study adopts a spectral model fitted to field-measured data (Equation (16)) as the computational basis for this specific scenario.