Wind characteristics in the high-altitude difference at bridge site by wind tunnel tests

Mingjin Zhang,Jinxiang Zhang,Yong-Le Li,Jisheng Yu,Jingyu Zhang,Lianhuo Wu 한국풍공학회 2020 Wind and Structures, An International Journal (WAS Vol.30 No.6

With the development of economy and construction technology, more and more bridges are built in complex mountainous areas. Accurate assessment of wind parameters is important in bridge construction at complex terrain. In order to investigate the wind characteristics in the high-altitude difference area, a complex mountain terrain model with the scale of 1:2000 was built. By using the method of wind tunnel tests, the study of wind characteristics including mean wind characteristics and turbulence characteristics was carried out. The results show: The wind direction is affected significant by the topography, the dominant wind direction is usually parallel to the river. Due to the sheltering effect of the mountain near the bridge, the wind speed and wind attack angle along the bridge are both uneven which is different from that at flat terrain. In addition, different from flat terrain, the wind attack angle is mostly negative. The wind profiles obey exponential law and logarithmic law. And the fitting coefficient is consistent with the code which means that it is feasible to use the method of wind tunnel test to simulate complex terrain. As for turbulence characteristics, the turbulence intensity is also related to the topography. Increases sheltering effect of mountain increases the degree of breaking up the large-scale vortices, thereby increasing the turbulence intensity. Also, the value of turbulence intensity ratio is different from the recommended values in the code. The conclusions of this study can provide basis for further wind resistance design of the bridge.

Wind field numerical simulation of a cable-stayed bridge in a mountainous area using improved inlet boundary by CIRFG method

Mingjin Zhang,Yiyan Dai,Bo Hu,Xu Xin,Lianhuo Wu,Yongle Li 대한토목학회 2023 KSCE Journal of Civil Engineering Vol.27 No.9

Bridges in mountainous areas are indispensable nodes in transportation networks, and wind resistance capabilities have become a controlling factor of long-span bridges built in mountain areas. Therefore, it is necessary to study the characteristics of wind fields under complex terrain. An improved inlet boundary by fitting the boundary curve was proposed in this study. The inlet fluctuating wind field was generated by the Correlation Improved Random Flow Generation method (CIRFG). The results of the numerical simulations show that the fluctuating wind input generated by CIRFG tallies with the target wind field, which proves the reliability of the proposed method. The method of fitting boundary curves to give inlet wind speed profiles can achieve non-uniform wind profile inputs. The results show the wind direction of the gorge varies significantly by height. The wind speed at the summit will accelerate affected by the terrain. Also influenced by the terrain, the turbulence intensity profiles in the simulated area show an S-shape. The transverse wind and angle of attack are uneven along the main girder, especially near slopes. The conclusions obtained in the study can provide references for the wind resistance of bridges built in mountainous areas.

CFD Numerical Simulation of Wind Field and Vehicle Aerodynamic Characteristics on Truss Bridge Deck under Crosswind

Mingjin Zhang,Jinxiang Zhang,Junting Long,Yongle Li,Yulin Zou,Dianguo Yin 대한토목학회 2022 KSCE Journal of Civil Engineering Vol.26 No.12

Due to the complexity and changeability of the wind field in deep-cut gorges, the vehicles on the bridge deck are easily affected by a strong crosswind. Thus, to accurately evaluate the wind field characteristics of a suspension bridge deck, the wind profiles of wind speed and angle of attack (AoA) and the vehicle aerodynamic parameters were investigated by the CFD. The results show that the shape of wind speed profile is mainly controlled by the AoA but less affected by the Reynolds number. The main girder's shielding effect can accelerate the local wind field, and the closer to the windward lane, the less the interference; thus, a suitable location of measuring points to represent the incoming flow is found. Furthermore, the equivalent wind speed based on the equivalent side force is generally larger than the value based on the rolling moment, and the responding value is greatly affected by the AoA. In addition, the vortex is a time-dependent phenomenon, the averaged flow field produced less force in the wake, but the high local wind speed variations may affect the traffic unfavorably. The results provide an essential reference significance for studying the local wind field characteristics of the bridge deck.

Aerodynamic effects of subgrade-tunnel transition on high-speed railway by wind tunnel tests

Jingyu Zhang,Mingjin Zhang,Yongle Li,Chen Fang 한국풍공학회 2019 Wind and Structures, An International Journal (WAS Vol.28 No.4

The topography and geomorphology are complex and changeable in western China, so the railway transition section is common. To investigate the aerodynamic effect of the subgrade-tunnel transition section, including a cutting-tunnel transition section, an embankment-tunnel transition section and two typical scenarios for rail infrastructures, is selected as research objects. In this paper, models of standard cutting, embankment and CRH2 high-speed train with the scale of 1:20 were established in wind tunnel tests. The wind speed profiles above the railway and the aerodynamic forces of the vehicles at different positions along the railway were measured by using Cobra probe and dynamometric balance respectively. The test results show: The influence range of cutting-tunnel transition section is larger than that of the embankment-tunnel transition section, and the maximum impact height exceeds 320mm (corresponding to 6.4m in full scale). The wind speed profile at the railway junction is greatly affected by the tunnel. Under the condition of the double track, the side force coefficient on the leeward side is negative. For embankment-tunnel transition section, the lift force coefficient of the vehicle is positive which is unsafe for operation when the vehicle is at the railway line junction.

The enhancement of humidity sensing performance based on Eu-doped ZnO

Shuguo Yu,Hongyan Zhang,Cunchong Lin,Mingjin Bian 한국물리학회 2019 Current Applied Physics Vol.19 No.2

In this work, a high performance impedance-type humidity sensor based on Europium-doped ZnO with abundant surface oxygen vacancy defects was synthesized by sol-gel method. Response of the Eu-doped ZnO with different molar ratio were investigated by exposing them to humidity environments in wide range of 11–95% RH at room temperature. The Eu-doped ZnO (2 mol%) exhibits a three orders impedance change, along with short response/ recovery time (5 s/19 s), low hysteresis and best linearity. Complex impedance spectra indicates that dopant Eu can enhance humidity sensing performance of ZnO, which is resulted from the introduction of Eu3+ ions into ZnO structure to produce more defects of surface oxygen vacancy and more active sites on the surface of ZnO. The results show that this is a feasible method to achieve high humidity sensing performance by Eu doped ZnO, which make it a promising candidate for humidity sensing materials and broaden the use of ZnO materials.

Wind loads on a moving vehicle-bridge deck system by wind-tunnel model test

Li, Yongle,Hu, Peng,Xu, You-Lin,Zhang, Mingjin,Liao, Haili Techno-Press 2014 Wind and Structures, An International Journal (WAS Vol.19 No.2

Wind-vehicle-bridge (WVB) interaction can be regarded as a coupled vibration system. Aerodynamic forces and moment on vehicles and bridge decks play an important role in the vibration analysis of the coupled WVB system. High-speed vehicle motion has certain effects on the aerodynamic characteristics of a vehicle-bridge system under crosswinds, but it is not taken into account in most previous studies. In this study, a new testing system with a moving vehicle model was developed to directly measure the aerodynamic forces and moment on the vehicle and bridge deck when the vehicle model moved on the bridge deck under crosswinds in a large wind tunnel. The testing system, with a total length of 18.0 m, consisted of three main parts: vehicle-bridge model system, motion system and signal measuring system. The wind speed, vehicle speed, test objects and relative position of the vehicle to the bridge deck could be easily altered for different test cases. The aerodynamic forces and moment on the moving vehicle and bridge deck were measured utilizing the new testing system. The effects of the vehicle speed, wind yaw angle, rail track position and vehicle type on the aerodynamic characteristics of the vehicle and bridge deck were investigated. In addition, a data processing method was proposed according to the characteristics of the dynamic testing signals to determine the variations of aerodynamic forces and moment on the moving vehicle and bridge deck. Three-car and single-car models were employed as the moving rail vehicle model and road vehicle model, respectively. The results indicate that the drag and lift coefficients of the vehicle tend to increase with the increase of the vehicle speed and the decrease of the resultant wind yaw angle and that the vehicle speed has more significant effect on the aerodynamic coefficients of the single-car model than on those of the three-car model. This study also reveals that the aerodynamic coefficients of the vehicle and bridge deck are strongly influenced by the rail track positions, while the aerodynamic coefficients of the bridge deck are insensitive to the vehicle speed or resultant wind yaw angle.

Aerostatic pressure of streamlined box girder based on conformal mapping method and its application

Lianhuo Wu,J. Woody Ju,Mingjin Zhang,Yong-Le Li,Jingxi Qin 한국풍공학회 2022 Wind and Structures, An International Journal (WAS Vol.35 No.4

The conformal mapping method (CMM) has been broadly exploited in the study of fluid flows over airfoils and other research areas, yet it’s hard to find relevant research in bridge engineering. This paper explores the feasibility of CMM in streamlined box girder bridges. Firstly, the mapping function transforming a unit circle to the streamlined box girder was solved by CMM. Subsequently, the potential flow solution of aerostatic pressure on the streamlined box girder was obtained and was compared with numerical simulation results. Finally, the aerostatic pressure attained by CMM was utilized to estimate the aerostatic coefficient and flutter performance of the streamlined box girder. The results indicate that the solution of the aerostatic pressure by CMM on the windward side is satisfactory within a small angle of attack. Considering the windward aerostatic pressure and coefficient of correction, CMM can be employed to estimate the rate of change of the lift and moment coefficients with angle of attack and the influence of the geometric shape of the streamlined box girder on flutter performance.

Wind loads on a moving vehicle–bridge deck system by wind-tunnel model test

Yongle Li,Peng Hu,You-Lin Xu,Mingjin Zhang,Haili Liao 한국풍공학회 2014 Wind and Structures, An International Journal (WAS Vol.19 No.2

Wind-vehicle-bridge (WVB) interaction can be regarded as a coupled vibration system. Aerodynamic forces and moment on vehicles and bridge decks play an important role in the vibration analysis of the coupled WVB system. High-speed vehicle motion has certain effects on the aerodynamic characteristics of a vehicle-bridge system under crosswinds, but it is not taken into account in most previous studies. In this study, a new testing system with a moving vehicle model was developed to directly measure the aerodynamic forces and moment on the vehicle and bridge deck when the vehicle model moved on the bridge deck under crosswinds in a large wind tunnel. The testing system, with a total length of 18.0 m, consisted of three main parts: vehicle-bridge model system, motion system and signal measuring system. The wind speed, vehicle speed, test objects and relative position of the vehicle to the bridge deck could be easily altered for different test cases. The aerodynamic forces and moment on the moving vehicle and bridge deck were measured utilizing the new testing system. The effects of the vehicle speed, wind yaw angle, rail track position and vehicle type on the aerodynamic characteristics of the vehicle and bridge deck were investigated. In addition, a data processing method was proposed according to the characteristics of the dynamic testing signals to determine the variations of aerodynamic forces and moment on the moving vehicle and bridge deck. Three-car and single-car models were employed as the moving rail vehicle model and road vehicle model, respectively. The results indicate that the drag and lift coefficients of the vehicle tend to increase with the increase of the vehicle speed and the decrease of the resultant wind yaw angle and that the vehicle speed has more significant effect on the aerodynamic coefficients of the single-car model than on those of the three-car model. This study also reveals that the aerodynamic coefficients of the vehicle and bridge deck are strongly influenced by the rail track positions, while the aerodynamic coefficients of the bridge deck are insensitive to the vehicle speed or resultant wind yaw angle.

Experimental and Numerical Investigation of Local Scour for Suspended Square Caisson under Steady Flow

Qiqi Xiang,Kai Wei,Yadong Li,Mingjin Zhang,Shunquan Qin 대한토목학회 2020 KSCE JOURNAL OF CIVIL ENGINEERING Vol.24 No.9

A caisson can be suspended in the river during its settlement construction. The water flows induces the local scour of sediments under the caisson, which increases the settlement difficulty and threatens the safety of construction. A numerical model using computational fluid dynamics (CFD) was introduced to simulate the local scour process around the caisson. The numerical model was validated with a set of experimental tests, which were conducted to investigate the local scour for a square caisson model with different clearances under steady flow. The evolutions and characteristics of local scour pits as a function of clearance were investigated based on the experimental and numerical results. The effect of grain size of sediment and the scour mechanism for suspended caisson were discussed as well. The main findings include: 1) the minimum inflow velocity for the scour of sediment depends on the clearance between the caisson bottom and sediment; 2) the numerical model provides reasonable evolution of local scour pit and flow field around the caisson; and 3) the scour depth of suspended caisson can be as high as 70% of that for the settled caisson and deserves attention for the safe settlement of caisson.