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.

Wind-tunnel study of wake galloping of parallel cables on cable-stayed bridges and its suppression

Yongle Li,Mengxue Wu,Xinzhong Chen,Tao Wang,Haili Liao 한국풍공학회 2013 Wind and Structures, An International Journal (WAS Vol.16 No.3

Flexible stay cables on cable-stayed bridges are three-dimensional. They sag and flex in the complex wind environment, which is a different situation to ideal rigid cylinders in two-dimensional wind flow. Aerodynamic interference and the response characteristics of wake galloping of full-scale parallel cables are potentially different due to three-dimensional flows around cables. This study presents a comprehensive wind tunnel investigation of wake galloping of parallel stay cables using three-dimensional aeroelastic cable models. The wind tunnel study focuses on the large spacing instability range, addressing the effects of cable separation, wind yaw angle, and wind angle of attack on wake galloping response. To investigate the effectiveness of vibration suppression measures, wind tunnel studies on the transversely connected cable systems for two types of connections (flexibility and rigidity) at two positions (mid-span and quarter-span) were also conducted. This experimental study provides useful insights for better understanding the characteristics of wake galloping that will help in establishing a guideline for the wind-resistant design of the cable system on cable-stayed bridges.

Wind-tunnel study of wake galloping of parallel cables on cable-stayed bridges and its suppression

Li, Yongle,Wu, Mengxue,Chen, Xinzhong,Wang, Tao,Liao, Haili Techno-Press 2013 Wind and Structures, An International Journal (WAS Vol.16 No.3

Flexible stay cables on cable-stayed bridges are three-dimensional. They sag and flex in the complex wind environment, which is a different situation to ideal rigid cylinders in two-dimensional wind flow. Aerodynamic interference and the response characteristics of wake galloping of full-scale parallel cables are potentially different due to three-dimensional flows around cables. This study presents a comprehensive wind tunnel investigation of wake galloping of parallel stay cables using three-dimensional aeroelastic cable models. The wind tunnel study focuses on the large spacing instability range, addressing the effects of cable separation, wind yaw angle, and wind angle of attack on wake galloping response. To investigate the effectiveness of vibration suppression measures, wind tunnel studies on the transversely connected cable systems for two types of connections (flexibility and rigidity) at two positions (mid-span and quarter-span) were also conducted. This experimental study provides useful insights for better understanding the characteristics of wake galloping that will help in establishing a guideline for the wind-resistant design of the cable system on cable-stayed bridges.

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.

The appropriate shape of the boundary transition section for a mountain-gorge terrain model in a wind tunnel test

Peng Hu,Yongle Li,Rui Kang,Haili Liao 한국풍공학회 2015 Wind and Structures, An International Journal (WAS Vol.20 No.1

Characterization of wind flows over a complex terrain, especially mountain-gorge terrain (referred to as the very complex terrain with rolling mountains and deep narrow gorges), is an important issue for design and operation of long-span bridges constructed in this area. In both wind tunnel testing and numerical simulation, a transition section is often used to connect the wind tunnel floor or computational domain bottom and the boundary top of the terrain model in order to generate a smooth flow transition over the edge of the terrain model. Although the transition section plays an important role in simulation of wind field over complex terrain, an appropriate shape needs investigation. In this study, two principles for selecting an appropriate shape of boundary transition section were proposed, and a theoretical curve serving for the mountain-gorge terrain model was derived based on potential flow theory around a circular cylinder. Then a two-dimensional (2-D) simulation was used to compare the flow transition performance between the proposed curved transition section and the traditional ramp transition section in a wind tunnel. Furthermore, the wind velocity field induced by the curved transition section with an equivalent slope of 30 was investigated in detail, and a parameter called the \'velocity stability factor\' was defined; an analytical model for predicting the velocity stability factor was also proposed. The results show that the proposed curved transition section has a better flow transition performance compared with the traditional ramp transition section. The proposed analytical model can also adequately predict the velocity stability factor of the wind field.

Flutter performance of central-slotted plate at large angles of attack

Haojun Tang,Yongle Li,Xinzhong Chen,K.M. Shum,Haili Liao 한국풍공학회 2017 Wind and Structures, An International Journal (WAS Vol.24 No.5

The flutter instability is one of the most important themes need to be carefully investigated in the design of long-span bridges. This study takes the central-slotted ideal thin flat plate as an object, and examines the characteristics of unsteady surface pressures of stationary and vibrating cross sections based on computational fluid dynamics (CFD) simulations. The flutter derivatives are extracted from the surface pressure distribution and the critical flutter wind speed of a long span suspension bridge is then calculated. The influences of angle of attack and the slot ratio on the flutter performance of central-slotted plate are investigated. The results show that the critical flutter wind speed reduces with increase in angle of attack. At lower angles of attack where the plate shows the characteristics of a streamlined cross-section, the existence of central slot can improve the critical flutter wind speed. On the other hand, at larger angles of attack, where the plate becomes a bluff body, the existence of central slot further reduces the flutter performance.

Numerical simulation of the neutral equilibrium atmospheric boundary layer using the SST k-ω turbulence model

Peng Hu,Yongle Li,C.S. Cai,Haili Liao,G.J. Xu 한국풍공학회 2013 한국풍공학회지 Vol.17 No.1

Modeling an equilibrium atmospheric boundary layer (ABL) in an empty computational domain has routinely been performed with the k-ε turbulence model. However, the research objects of structural wind engineering are bluff bodies, and the SST k-ω turbulence model is more widely used in the numerical simulation of flow around bluff bodies than the k-ε turbulence model. Therefore, to simulate an equilibrium ABL based on the SST k-ω turbulence model, the inlet profiles of the mean wind speed U, turbulence kinetic energy k, and specific dissipation rate ω are proposed, and the source terms for the U, k and ω are derived by satisfying their corresponding transport equations. Based on the proposed inlet profiles, numerical comparative studies with and without considering the source terms are carried out in an empty computational domain, and an actual numerical simulation with a trapezoidal hill is further conducted. It shows that when the source terms are considered, the profiles of U, k and ω are all maintained well along the empty computational domain and the accuracy of the actual numerical simulation is greatly improved. The present study could provide a new methodology for modeling the equilibrium ABL problem and for further CFD simulations with practical value.

Stability of suspension bridge catwalks under a wind load

Zheng, Shixiong,Liao, Haili,Li, Yongle Techno-Press 2007 Wind and Structures, An International Journal (WAS Vol.10 No.4

A nonlinear numerical method was developed to assess the stability of suspension bridge catwalks under a wind load. A section model wind tunnel test was used to obtain a catwalk's aerostatic coefficients, from which the displacement-dependent wind loads were subsequently derived. The stability of a suspension bridge catwalk was analyzed on the basis of the geometric nonlinear behavior of the structure. In addition, a full model test was conducted on the catwalk, which spanned 960 m. A comparison of the displacement values between the test and the numerical simulation shows that a numerical method based on a section model test can be used to effectively and accurately evaluate the stability of a catwalk. A case study features the stability of the catwalk of the Runyang Yangtze suspension bridge, the main span of which is 1490 m. Wind can generally attack the structure from any direction. Whenever the wind comes at a yaw angle, there are six wind load components that act on the catwalk. If the yaw angle is equal to zero, the wind is normal to the catwalk (called normal wind) and the six load components are reduced to three components. Three aerostatic coefficients of the catwalk can be obtained through a section model test with traditional test equipment. However, six aerostatic coefficients of the catwalk must be acquired with the aid of special section model test equipment. A nonlinear numerical method was used study the stability of a catwalk under a yaw wind, while taking into account the six components of the displacement-dependent wind load and the geometric nonlinearity of the catwalk. The results show that when wind attacks with a slight yaw angle, the critical velocity that induces static instability of the catwalk may be lower than the critical velocity of normal wind. However, as the yaw angle of the wind becomes larger, the critical velocity increases. In the atmospheric boundary layer, the wind is turbulent and the velocity history is a random time history. The effects of turbulent wind on the stability of a catwalk are also assessed. The wind velocity fields are regarded as stationary Gaussian stochastic processes, which can be simulated by a spectral representation method. A nonlinear finite-element model set forepart and the Newmark integration method was used to calculate the wind-induced buffeting responses. The results confirm that the turbulent character of wind has little influence on the stability of the catwalk.

Flutter performance of central-slotted plate at large angles of attack

Tang, Haojun,Li, Yongle,Chen, Xinzhong,Shum, K.M.,Liao, Haili Techno-Press 2017 Wind and Structures, An International Journal (WAS Vol.24 No.5

The flutter instability is one of the most important themes need to be carefully investigated in the design of long-span bridges. This study takes the central-slotted ideal thin flat plate as an object, and examines the characteristics of unsteady surface pressures of stationary and vibrating cross sections based on computational fluid dynamics (CFD) simulations. The flutter derivatives are extracted from the surface pressure distribution and the critical flutter wind speed of a long span suspension bridge is then calculated. The influences of angle of attack and the slot ratio on the flutter performance of central-slotted plate are investigated. The results show that the critical flutter wind speed reduces with increase in angle of attack. At lower angles of attack where the plate shows the characteristics of a streamlined cross-section, the existence of central slot can improve the critical flutter wind speed. On the other hand, at larger angles of attack, where the plate becomes a bluff body, the existence of central slot further reduces the flutter performance.

Numerical simulation of the neutral equilibrium atmospheric boundary layer using the SST k-ω turbulence model

Hu, Peng,Li, Yongle,Cai, C.S.,Liao, Haili,Xu, G.J. Techno-Press 2013 Wind and Structures, An International Journal (WAS Vol.17 No.1

Modeling an equilibrium atmospheric boundary layer (ABL) in an empty computational domain has routinely been performed with the k-${\varepsilon}$ turbulence model. However, the research objects of structural wind engineering are bluff bodies, and the SST k-${\omega}$ turbulence model is more widely used in the numerical simulation of flow around bluff bodies than the k-${\varepsilon}$ turbulence model. Therefore, to simulate an equilibrium ABL based on the SST k-${\omega}$ turbulence model, the inlet profiles of the mean wind speed U, turbulence kinetic energy k, and specific dissipation rate ${\omega}$ are proposed, and the source terms for the U, k and ${\omega}$ are derived by satisfying their corresponding transport equations. Based on the proposed inlet profiles, numerical comparative studies with and without considering the source terms are carried out in an empty computational domain, and an actual numerical simulation with a trapezoidal hill is further conducted. It shows that when the source terms are considered, the profiles of U, k and ${\omega}$ are all maintained well along the empty computational domain and the accuracy of the actual numerical simulation is greatly improved. The present study could provide a new methodology for modeling the equilibrium ABL problem and for further CFD simulations with practical value.