This paper presents experimental and numerical approaches to systematically investigate the aerodynamic characteristics of streamlined box girder at angles of attack (AoA) of up to 12°. The effects of AoA on the pressure characteristics and total forces are first studied through wind tunnel experiments. Based on three-dimensional large-eddy simulations (3D LES), the flow topology is investigated to study the influence mechanism of AoAs. The results show that the flow topology around the section can be divided into three types: (i) completely attached flow pattern as |α| ≤ 4°; (ii) separated-reattached flow pattern as 6°≤|α|≤8°; (iii) fully separated flow pattern as |α| ≥ 10°. The combination of experimental and numerical results presents a deep understanding of the aerodynamic characteristics of a streamlined box girder and reveals the relationships between the pressure features and flow topology. The pressure characteristics and total forces are very sensitive to the flow separation and reattachment. At small AoAs, the flow attaches to the bridge section, the mean and RMS pressure, total force, as well as streamwise correlations change slightly with AoAs. Besides, the shear layer is a laminar pattern and has less impact on the span-wise correlations. Moreover, the vortices in the wake remain successive in the span-wise direction, and the Strouhal numbers are larger. On the other hand, with the increase of AoAs, large separation bubbles can be observed around the bridge section. Especially for fully separated flow pattern as |α| ≥ 10°, the shear layer no longer attaches to the bridge section and the separation bubble is longer than the section width. Accordingly, the mean and RMS pressure, total force, as well as streamwise correlations increase significantly. Besides, the shear layer is a turbulent pattern, and the turbulent fluctuations in wake become complex and less organized in the span-wise direction, then the S _t is lower than others.

This study investigates the aerodynamic admittances of a closed-box girder in both streamwise (u-) and vertical (w-) sinusoidal flow fields. A series of sinusoidal flows with discrete oscillation frequencies (f_u = 00.2–1.2 Hz) and different oscillation amplitudes (Δu = 0.5 – 2.0 m/s) are experimentally generated, which are fully coherent in the span-wise direction. Meanwhile, the Computational Fluid Dynamics (CFD) method is utilized to simulate streamwise sinusoidal flows with higher frequencies (f_u = 0.2–14 Hz). The u-turbulence-related two-dimensional aerodynamic admittance functions (2D AAFs) of the closed-box girder are identified frequency by frequency. On the other hand, the vertical sinusoidal flows are numerically simulated (f_w = 0.2–14 Hz, Δw = 1.2 m/s), and the w-turbulence-related 2D AAFs are identified. Finally, the differences between u-, w- admittances and the equivalent ones are compared. The results indicate that u- and w-turbulence-related AAFs have different trends with the reduced frequency, and thus it is inaccurate to treat the contributions of u- and w-turbulence to admittances as equivalent in previous studies.

The field measurements, wind tunnel tests, and numerical calculations are utilized to conduct refined time‐domain buffeting analysis of a long‐span suspension bridge. The wind characteristics in the mountainous urban terrain are obtained through long‐term field measurements. The aerostatic force coefficients (AFCs) and aerodynamic admittance functions (AAFs) are experimentally tested in a wind tunnel. The fluctuating wind fields on the bridge are simulated by the spectral representation method. Finally, the buffeting responses are calculated in ANSYS. The influences of AAF, turbulence power spectrum, and angle of attack (AoA) on the buffeting responses are evaluated, which highlight the inaccuracies caused by empirical simplifications. To improve the buffeting performance without a considerable extra budget, minor modifications are introduced to the original design configuration. The buffeting responses are slightly reduced by increasing the ventilation rate of guardrails, and the control efficiency is better when concurrently moving the inspection rails inward. Besides, the buffeting responses are increased when considering the roughness on the girder surface. The influence mechanism of the countermeasure is analyzed using the Computational Fluid Dynamics (CFD) method, which mainly lies in the dissipation of turbulence energy around the girder. The findings can contribute to the wind‐resistant analysis and optimization design for similar bridges.

On the preliminary designing of a wide flat box girder with the slenderness ratio 12, vertical and torsional vortex-induced vibrations (VIV) are observed in wind tunnel tests. More than one lock-in region, which are defined as“multi-lock-in regions,”are recorded. Therefore, suspicions should be aroused regarding the viewpoint that wide box girders are aerodynamic friendly. As the three nascent vortexes originating at the pedestrian guardrails and inspection rails shed to near-wake through different pathways with different frequencies, the mechanisms of VIVs and multi-lock-in regions are analyzed to be determined by the inappropriate subsidiary structures. A hybrid method combiningLarge Eddy Simulation(LES) with experimental results is introduced to study the flow-structure interactions (FSI) when undergoing VIVs; the vortex mode of torsional VIV on wide flat box girders is defined as “4/2S,” which is different from any other known ones. Based on the mechanism of VIV, a new approach by increasing ventilation rate of the pedestrian guardrails is proved to be effective in suppressing vertical and torsional VIVs, and it is more feasible than other control schemes. Then, the control mechanisms are deeper investigated by analyzing the evolution of vortex mode and FSI using Hybrid-LES method.

In the present study, multiple-fan active control wind tunnel tests are conducted to investigate the aerodynamic forces on a 5:1 rectangular cylinder in sinusoidal streamwise winds with different angles of attack (AoA). The effects of the frequency, amplitude, and AoA of the sinusoidal flow on the statistical parameters, spectral characteristics, and spanwise distributions of drag, lift, and moment coefficients are analyzed. Results show that each force has two components: the one induced by the approaching velocity oscillation and the one induced by wake vortex-shedding—this is quite different from that in the smooth flows, where the fluctuating forces are totally due to wake vortex-shedding. For each force, changes of the two components and their relationship with the frequency, amplitude, and AoA are presented. The drag fluctuations are generally dominated by the approaching velocity oscillations, whereas the lift and moment are more sensitive to wake vortex-shedding. Therefore, the drag force has better spanwise correlations than the lift and moment forces. Meanwhile, at a non-zero AoA, the inflow amplitude has different effects on the vortex-shedding-induced component as that at a zero AoA. The differences of spanwise distributions between the sinusoidal flow cases and the smooth flow cases are analyzed.

With the increasingly dense distribution of urban subway network, line crossing will inevitably occur. The phenomenon of new tunnels passing through existing tunnels is becoming more and more common. Shield tunneling will inevitably disturb the surrounding soil and redistribute the stress and displacement fields, resulting in the deformation and additional stress of existing subway tunnels. The new tunnel should have strict requirements for the deformation control of existing tunnels and surrounding rocks. The spacing effect of new tunnels under existing tunnels can ensure the safety of new tunnels and the operation safety of existing shield tunnels, which has become an important problem to be solved urgently. On the basis of theoretical analysis, this paper takes a new shield tunnel under the existing tunnel in Xuzhou City as the backing, carries out numerical simulation of the new and old tunnel under different clearance by finite element software, and studies the influence of the new tunnel on the existing tunnel when the tunnel is constructed with different spacing of 1.5m, 0.5D, 1D, 1.5D, 2D and 3D. It is concluded that the reasonable distance between the new tunnel and the existing tunnel should be controlled between 1D and 1.5D under the circumstance of the surrounding environment, the permission of the new tunnel line and the economical and reasonable conditions.