Aeroelastic modeling and flutter-derivative identification of a streamlined box girder under a moving wave boundary

The aeroelastic behavior of sea-crossing bridge girders may be affected by wave-induced motion of the air–water interface, which alters the near-surface airflow and consequently modifies the aerodynamic forces acting on the bridge deck. To characterize this mechanism, a deformable wave boundary based on Stokes wave theory is implemented together with dynamic mesh updating and two-way fluid–structure interaction to simulate the bending–torsional coupled response of a streamlined box girder. The time- and frequency-domain characteristics of the displacement and aerodynamic force responses are first examined. Subsequently, wave-induced periodic lift and aerodynamic moment are incorporated into Scanlan's self-excited force formulation, leading to a semi-empirical time-domain flutter model under a prescribed moving-wave boundary. A hierarchical iterative search algorithm (HISA) is further developed to identify aerodynamic frequencies, aerodynamic damping ratios, and flutter derivatives from free-vibration responses. The results indicate that the girder response comprises a transient self-excited component and a steady wave-induced periodic component, with the fundamental wave frequency and its low-order harmonics dominating the response spectra. The reconstructed displacement and aerodynamic force histories agree well with the numerical results, demonstrating the accuracy of the proposed flutter model and the reliability of the identification method. Bridge clearance exerts a more pronounced influence on the aeroelastic response than wave height, particularly at high wind speeds, where reduced clearance leads to larger vibration amplitudes and lower torsional aerodynamic damping. In contrast, wave height primarily affects the higher-order spectral components and has a comparatively limited influence on the overall aeroelastic behavior. These findings provide a theoretical and methodological basis for flutter modeling, aerodynamic parameter identification, and stability assessment of sea-crossing bridges under moving-wave-boundary conditions.