To investigate the spanwise correlation of vortex‐induced forces (VIF) of a typical section of a streamlined box girder, wind tunnel tests of simultaneous measurement of force and displacement responses of a sectional model were conducted in a smooth flow. The spanwise correlation of VIF and pressure coefficients on the measurement points of an oscillating main deck were analyzed in both the time domain and frequency domain, respectively. The research results indicated that the spanwise correlation of VIF and pressure coefficients on the measurement points were related to the amplitudes of vortex‐induced vibration (VIV), both of them weakened with the increase of spanwise distance; the maximum value of spanwise correlation coefficient is situated at the ascending stage of the lock‐in region, rather than at the extreme amplitude point. The amplitudes of VIV showed different impacts on the spanwise correlation of pressure coefficients on the measurement points of the upper and lower surfaces, for which the maximum value of the spanwise correlation coefficients is located at the extreme amplitude point and the ascending stage of the lock‐in region, respectively. Furthermore, the spanwise correlation of the pressure coefficients decreases continually from the upstream to downstream of the main deck; large coherence of vortex‐induced forces and pressure appears around the frequency of vortex shedding, and the coherence of VIF and pressure becomes smaller with the increase in the spanwise distance.
To study the influence of maintenance track on the vortex-induced vibration (VIV) performance of main girder, the VIV response and time history of surface pressure data of a section model were obtained by wind tunnel vibration and pressure measurements for a large-span steel box girder suspension bridge. The VIV performance of the main girder was tested at ±5° attack angles of various maintenance track positions, including 1, 2.5, and 5 m away from the outer edge of the girder bottom plate. The mean values, root variances and amplitude spectra of vortex-induced force and the correlation and contribution coefficients of local aerodynamic force to overall aerodynamic force were analyzed. The results show that when the maintenance track is 1 m away from the outer edge of the bottom plate, the main girder exhibits the worst VIV performance with a maximum amplitude of 0.457 m, far beyond the allowable value of the specification. The VIV performance of the main girder was greatly improved by moving the maintenance track inward. The pressure analysis indicates that the large pressure fluctuation at the front and rear parts of the upper surface is attributed to the strong VIV of the main girder. In this sense, the improved VIV performance is mainly contributed by the weakening of pressure fluctuation in these two areas and the reduced local aerodynamic force. When the distance between the maintenance track and bottom plate is adjusted to 2.5 m, a 3.5 m wind barrier with a ventilation rate of 30% effectively inhibits the VIV of the box girder. The main reason for the suppression is that the elimination of pressure fluctuation on the upper surface of the girder disturbs the correlation between local aerodynamic force and overall aerodynamic force, consequently diminishing the contribution of local aerodynamic force to the vortex-induced force.
Abstract The primary air stem wire separation device employed in the ZJ-17 machine features a single gas inlet, resulting in airflow instability upon entry into the cavity, leading to vortex formation and backflow. This instability adversely affects the separation efficiency of the primary air stem wire, causing significant weight discrepancies in individual cigarette production. By analyzing the stem separation device using Computational Fluid Dynamics (CFD) and conducting test verifications, the design of the primary air separator cavity is optimized, with the double arc guide rectifier identified as the final design solution. The results demonstrate that the optimized double arc-oriented rectifier device boasts a straightforward structure, ensuring stable and dependable operation. It effectively reduces the number of substandard products, enhances the neutrality and stability of cigarette weight, yields substantial economic benefits, and enhances the consistency of cigarette internal flavor absorption.
With the continuous increase of span lengths, modern bridges are becoming much more flexible and more prone to flutter under wind excitations. A reasonable probabilistic flutter analysis of long-span bridges involving random and uncertain variables may have to be taken into consideration. This paper presents a method for estimating the reliability index and failure probability due to flutter, which considers the very important variables including the extreme wind velocity at bridge site, damping ratio, mathematical modeling, and flutter derivatives. The Aizhai Bridge in China is selected as an example to demonstrate the numerical procedure for the flutter reliability analysis. In the presented method, the joint probability density function of wind speed and wind direction at the deck level of the bridge is first established. Then, based on the fundamental theories of structural reliability, the reliability index and failure probability due to flutter of the Aizhai Bridge is investigated by applying the Monte Carlo method and the first order reliability method (FORM). The probabilistic flutter analysis can provide a guideline in the design of long-span bridges and the results show that the structural damping and flutter derivatives have significant effects on the flutter reliability, more accurate and reliable data of which is needed.
An accurate identification of the aerodynamic characteristics of vehicles and the bridge is the premise for the coupled vibration analysis of a wind-vehicle-bridge system. At present, the interaction of aerodynamic forces between the road vehicles and bridge is ignored in most previous studies. In the present study, an experimental setup was developed to measure the aerodynamic characteristics of vehicles and the bridge for different cases in a wind tunnel considering the aerodynamic interference. The influence of the wind turbulence, the wind speed, the vehicle interference, and the vehicle position on the aerodynamic coefficients of vehicles, and the influence of vehicles on the static coefficients of the bridge were investigated, based on the experimental results. The variations in the aerodynamic characteristics of vehicles and the bridge were studied and the measured results were validated according to the results of surface pressure measurements on the vehicle and the bridge. The measured results were further validated by comparing the measured results with values derived numerically. The measured results showed that the wind turbulence, the vehicle interference, and the vehicle position significantly affected the aerodynamic coefficients of vehicles. However, the influence of the wind speed on the aerodynamic coefficients of the studied vehicle is small. The static coefficients of the bridge were also significantly influenced by the presence of vehicles.
Wind tunnel tests were conducted to investigate the wind pressure characteristics of sawtooth roofs in a simulated open country wind field with relatively low turbulence intensity. Models of monosloped and sawtooth roof (two to four spans) buildings that were 1∶200 scale were constructed with intense pressure taps installed on the 15° sloped roofs. Both local and area-average pressure coefficients were determined under different wind directions. Preliminary results indicated that the local peak negative pressure coefficients were slightly lower than the literature results. The increase of roof slope led to higher peak design pressure coefficients for sawtooth roofs, especially in the interior and edge regions of roofs. The peak values of negative pressure captured in high corner regions of monosloped roofs were similar to the corresponding data measured on the windward span of sawtooth roofs, which indicated that the American standard provisions for wind pressure design of monosloped roof structures and the Chinese local wind pressure provisions for sawtooth roofs may underestimate the critical wind suction on high corner regions of monosloped roofs. Generally, the area-average pressures heavily depend on the size of tributary area and the region concerned, and higher roof slope led to faster reduction.
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