Wind–train–bridge coupled dynamics modeling of aerodynamic responses and ride comfort in straddle-type monorail systems

Straddle-type monorail systems (STMSs) are gaining global traction as medium-capacity urban transit solutions due to their rapid construction, modular prefabrication, alignment flexibility, and low noise emissions. However, their slender structures are particularly susceptible to crosswinds, posing potential risks to ride comfort and operational safety—an area that remains largely underexplored. This study develops a coupled wind–train–bridge interaction framework that integrates computational fluid dynamics (CFD) and multibody dynamics to investigate aerodynamic responses of STMSs under different wind field modeling approaches and train speeds. A comparative analysis of uniform inflow and spectral decomposition methods reveals asymmetric wind-induced behavior, where vertical vibrations remain largely governed by train speed, while lateral displacements and rolling motions are significantly amplified by wind loads. The CFD-based spectral decomposition method for wind field modeling leads to a 56.65% degradation in lateral ride indices, compared to only 7.43% in the vertical direction, with comparison to the no wind condition, underscoring the dominance of wind-driven lateral dynamics in comfort deterioration. Additionally, vertical train accelerations increase by approximately 70% as speed rises from 60 to 120 km/h, indicating a notable speed sensitivity. Despite amplified responses, aerodynamic performance remains within acceptable safety limits. The findings offer critical insights into wind–STMS interaction mechanisms and provide a robust computational tool for aerodynamic design, performance evaluation, and safe operation of monorail systems under crosswind conditions.