Open Access

ARTICLE

Aerodynamic Response and Data-Driven Modal Analysis of a Wide Streamlined Box Girder under Harmonic Wind Excitation

Jian Zhan^1,2, Shiping Li^1,2, Hongfu Zhang^3,*
1 Municipal and Transportation Planning, Design & Research Institute of CISPDR Corporation, Wuhan, China
2 Key Technology Innovation Center for Bridge and Aqueduct Engineering of CISPDR Corporation, Wuhan, China
3 Department of Mechanical Engineering, Hong Kong Polytechnic University, Hong Kong, China
* Corresponding Author: Hongfu Zhang. Email:

Structural Durability & Health Monitoring https://doi.org/10.32604/sdhm.2026.085669

Received 15 May 2026; Accepted 19 August 2026; Published online 01 September 2026

Abstract

Wind-induced vibrations and aeroelastic risks of long-span bridges are conventionally assessed using aerodynamic models that assume uniform inflow, despite the inherently unsteady and non-uniform nature of natural wind fields at bridge sites. This study numerically investigates the unsteady aerodynamic response and flow field characteristics of a wide streamlined box girder section (width-to-depth ratio B/D ≈ 15) subjected to harmonic inflow excitation, which serves as an idealized representation of gust-like streamwise fluctuations. Two-dimensional CFD simulations are performed for a baseline uniform inflow at a Reynolds number of 2.27 × 10⁶ based on the girder width B, and for nine harmonic pulsating inflows with excitation frequencies ranging from 0.1f₀ to 2f₀, where f₀ denotes the dominant vortex shedding frequency identified under uniform inflow. Aerodynamic force coefficients, spectral characteristics, and flow features are systematically examined. Dynamic mode decomposition (DMD) is further employed to quantify the dominant coherent structures and the redistribution of modal energy. The results reveal that when the excitation frequency coincides with integer multiples of f₀ (notably f/f₀ = 1 and 2), both the mean drag coefficient and the magnitude of the mean lift coefficient increase relative to the uniform inflow case. The fluctuating lift is substantially amplified by the harmonic excitation, with the most pronounced enhancement occurring in the low-frequency regime (f/f₀ = 0.1~0.5). The lift response exhibits a consistent phase lag of approximately half an excitation period with respect to the inflow velocity. Flow visualizations further demonstrate that bridge railings are highly sensitive to inflow pulsation, promoting localized flow separation and intensified small-scale vortex activity. DMD analysis indicates that harmonic inflow excitation strengthens the dominant coherent mode and energizes secondary modes. Notably, the coherent structures are not confined to the near wake but extend upstream into the deck region, with pronounced coherent regions emerging behind the railings.

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Keywords

Streamlined box girder; harmonic inflow excitation; dynamic mode decomposition (DMD); unsteady aerodynamic force; flow field characteristics

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