Numerical simulation of the turbulent wind field on long-span bridges is an important task in structural buffeting analysis when it comes to the system non-linearity. As for non-stationary extreme wind events, some efforts have been paid to update the classic spectral representation method (SRM) and the fast Fourier transform (FFT) has been introduced to improve the computational efficiency. Here, the non-negative matrix factorization-based FFT-aided SRM has been updated to generate not only the horizontal non-stationary turbulent wind field, but also the vertical one. Specifically, the evolutionary power spectral density (EPSD) is estimated to characterize the non-stationary feature of the field-measured wind data during Typhoon Wipha at the Runyang Suspension Bridge (RSB) site. The coherence function considering the phase angles is utilized to generate the turbulent wind fields for towers. The simulation accuracy is validated by comparing the simulated and target auto-/cross-correlation functions. Results show that the updated method performs well in generating the non-stationary turbulent wind field. The obtained wind fields will provide the research basis for analyzing the non-stationary buffeting behavior of the RSB and other wind-sensitive structures in adjacent regions.

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Fluctuating velocity plays an essential role in tornadic winds and the induced transient loads, while its characteristics are rarely considered in existing tornado models. Based on the coherent structure extraction technology, this study investigates the characteristics of the fluctuating velocity in a single-cell tornado-like vortex (TLV) and proposes a unified wind spectrum formula accordingly. Firstly, the performance of proper orthogonal decomposition (POD) and dynamic mode decomposition (DMD) is compared and validated using synthetic vortices. A single-cell TLV is then generated by large eddy simulation (LES). The relationship between the fluctuating velocity and the coherent structures is analyzed. Finally, a wind spectrum formula is obtained from the fluctuating velocity reconstructed by the first two POD modes that are almost unchanged with height. It is thus a unified formula suitable for different heights. The results show that at a lower height in the single-cell TLV, more than 90% of the velocity fluctuation is induced by vortex wandering and size variation. The first two POD modes can accurately reconstruct the fluctuating velocity with an error of less than 8%. The power spectral density of the reconstructed fluctuating velocity agrees well with the Kaimal wind spectrum in the low-frequency subrange and the proposed formula in the high-frequency subrange.

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