An enhanced nonstationary buffeting force model for calculating tropical storm (i.e., typhoon/hurricane)–induced buffeting response of long-span bridges is presented. The evolutionary power spectral density (EPSD) in the existing nonstationary tropical storm wind model is first revisited and enhanced by taking into consideration the recently-proposed typhoon turbulence spectra. A coherence transfer function matrix and time-dependent aerodynamic admittance function are introduced to eliminate the strip and quasi-steady theory assumptions by way of implementing wind tunnel measured span-wise and chord-wise coherence of aerodynamic forces. Finally, the nonlinearity in the buffeting forces resulting from the variations in the instant effective angle of attack and the nonuniform span-wise profile of the mean wind speed are considered in the enhanced model. The influence of the aforementioned enhancements in the nonstationary buffeting force model on the tropical storm-induced buffeting response of long-span bridges is assessed through the example of the Stonecutters Bridge subjected to Typhoon Dujuan. The results suggest that the enhanced EPSD model of tropical storm winds, nonlinearity due to the instant effective angle of attack, and the variations in the velocity span-wise profile slightly change the buffeting responses. However, introduction of the span-wise coherence of buffeting forces increases nonstationary extreme responses by 25–40%, and the time-dependent admittance function reduces the extreme responses by as much as 70%.

Recent installation of many wind turbines in earthquake‐prone areas worldwide has increased concerns regarding their seismic performance. This study introduces a multiobjective optimization design method using a modified Sigmoid satisfaction function to efficiently minimize the seismic response by installing tuned mass dampers (TMDs) on wind turbines. Inspired by the human decision‐making process, the modified Sigmoid function was utilized to improve the satisfaction function and balance the optimization objectives. Incorporating the particle swarm optimization algorithm resulted in lower sensitivity to the combination weighting factors and significantly reduced the effort required to calibrate the weighting factors for any practical multiobjective optimization problem. To verify the efficacy of the proposed methodology, a TMD was designed on a National Renewable Energy Laboratory (NREL) 5‐MW benchmark wind turbine, with constraints on both the top displacement and TMD stroke as design objectives. The results were compared to those obtained using the conventional linear weighted sum method, thereby highlighting the advantages of the proposed method. The scope of application of the proposed method is further demonstrated by a more complex TMD design problem involving 13 design objectives with typical seismic excitations.

In this study, wind tunnel experiments were carried out in smooth flow to examine the nexus between flow patterns around a flat-box section and its aerodynamics with the variation of the wind angle of incidence (α). The model cross section closely represents the overall asymmetric geometry and attendant aerodynamics of a class of flat-box decks frequently employed in long-span bridges. To explore the flow around and associated aerodynamic properties of this model that are distinct from a typical symmetric section (e.g., rectangular), detailed wind tunnel tests involving smoke-wire based flow visualizations and synchronous multipoint pressure measurements were carried out. Experimental results were analyzed to identify flow patterns, pressure distributions and associated Strouhal numbers, power spectral densities, aerodynamic force coefficients, proper orthogonal decomposition (POD) analyses, and span-wise correlation. Three typical flow patterns previously observed around symmetric bluff bodies with varying α were also observed in the asymmetric cross section, i.e., the trailing-edge vortex shedding (TEVS), the impinging leading-edge vortices (ILEV), and the alternate-edge vortex shedding (AEVS). However, due to the chordwise asymmetry of the section, the three flow patterns identified are distinct from the classical ones associated with symmetric sections in terms of flow separation points, the static “stall” angle of the section, and characteristics of leading-edge vortices. The roles played by these flow patterns in the aerodynamics of the flat-box section have been identified. It is observed that, if the ILEV or AEVS governs the flow topology, the aerodynamic force coefficients vary nonlinearly with the increase in α, in contrast with the linear variation in the TEVS-dominant case. For cases in which the TEVS dominates, the POD mode participation factors of the fluctuating pressure field display energy in higher modes. In this case, the reconstruction process requires that higher POD modes are retained. Finally, in the TEVS flow pattern, a weaker spanwise correlation of the fluctuating forces is noted as compared to the ILEV and AEVS-type flows. This study is limited to the fundamental examination of asymmetric section aerodynamics in smooth flows, which should be extended in case the influences of turbulence and aeroelastic effect are of interest.