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CONTENTS
Volume 29, Number 4, October 2019
 


Abstract
Conductor galloping is a common disaster for the transmission lines. Among the existing analytical methods, the wind tunnel test is highlighted as the most effective approach to obtain the aerodynamic coefficients. In this paper, the aerodynamic coefficients of 12 conductor models covered with the crescent-shaped ice, which were fabricated considering the surface roughness of the iced conductor, were obtained based on the wind tunnel test. The influence of the Reynolds number and the shape parameter B, defined as the ratio of ice thickness to the diameter, were investigated. In addition, the effect of surface roughness of the iced conductor was discussed. Subsequently, unsteady areas of conductor galloping were calculated according to the Den Hartog criterion and the Nigol criterion. The results indicate that the aerodynamic coefficients of iced conductors change sharply at the attack angles of 20 and 170 with the increase of B. The surface roughness of iced conductors changed the range of attack angle, which was influenced by the increase of the Reynolds number. The experimental results can provide insights for preventing and controlling galloping.

Key Words
conductor with crescent-shaped ice; wind tunnel test; shape parameter; Reynolds number; galloping instability

Address
Jia-xiang Li: Department of Civil Engineering, Northeastern University, Shenyang, Liaoning Province, China
Xing Fu and Hong-nan Li: State Key Laboratory of Coastal and Offshore Engineering, Dalian University of Technology, Dalian, Liaoning Province, China

Abstract
Wind loading is one of important loadings that should be considered in the design of large hyperbolic natural-draught cooling towers. Both external and internal surfaces of cooling tower are under the action of wind loading for cooling circulating water. In the previous studies, the wind loads on the external surface attracted concernedly attention, while the study on the internal surface was relatively ware. In the present study, the wind pressure on the internal surface of a 220 m high cooling tower is measured through wind tunnel testing, and the effect of ventilation rate of the packing layer on internal pressure is a major concern. The characteristics of internal wind pressure distribution and its effect on wind-induced responses calculated by finite element method are investigated. The results indicate that the wind loading on internal surface of the cooling tower behaves remarkable three-dimensional effect, and the pressure coefficient varies along both of height and circumferential directions. The non-uniformity is particularly strong during the construction stage. Analysis results of the effect of internal pressure on wind-induced responses show that the size and distribution characteristics of internal pressure will have some influence on wind-induced response, however, the outer pressure plays a dominant role in the wind-induced response of cooling tower, and the contribution of internal pressure to the response is small.

Key Words
cooling tower; internal wind pressure; wind loading; wind tunnel test; wind-induced response

Address
Yun-feng Zou, Zheng-yi Fu, Xu-hui He, Hai-quan Jing and Ling-yao Li: School of Civil Engineering, Central South University, Changsha, 410075, China;
National Engineering Laboratory for High Speed Railway Construction, Changsha, 410075, China
Hua-wei Niu and Zheng-qing Chen: Wind Engineering Research Center, Hunan University, Changsha, 410082, China


Abstract
Wind-resistant design of existing cooling tower structures overlooks the impacts of rainfall. However, rainstorm will influence aerodynamic force on the tower surface directly. Under this circumstance, the structural response of the super-large cooling tower (SLCT) will become more complicated, and then the stability and safety of SLCT will receive significant impact. In this paper, surrounding wind fields of the world highest (210 m) cooling tower in Northwest China under three typical wind velocities were simulated based on the wind-rain two-way coupling algorithm. Next, wind-rain coupling synchronous iteration calculations were conducted under 9 different wind speed-rainfall intensity combinations by adding the discrete phase model (DPM). On this basis, the influencing laws of different wind speed-rainfall intensity combinations on wind-driving rain, adhesive force of rain drops and rain pressure coefficients were discussed. The acting mechanisms of speed line, turbulence energy strength as well as running speed and trajectory of rain drops on structural surface in the wind-rain coupling field were disclosed. Moreover, the fitting formula of wind-rain coupling equivalent pressure coefficient of the cooling tower was proposed. A systematic contrast analysis on its 3D distribution pattern was carried out. Finally, coupling model of SLCT under different working conditions was constructed by combining the finite element method. Structural response, buckling stability and local stability of SLCT under different wind velocities and wind speed-rainfall intensity combinations were compared and analyzed. Major research conclusions can provide references to determine loads of similar SLCT accurately under extremely complicated working conditions.

Key Words
super-large cooling tower; wind speed-rainfall intensity combination; numerical simulation; wind-rain coupling; aerodynamic force; mechanical property

Address
Shitang Ke: Department of Civil Engineering, Nanjing University of Aeronautics and Astronautics, Nanjing 210016, China
Wenlin Yu: Jiangsu Power Design Institute Co., LTD, China Energy Engineering Group, Nanjing 211102, China
Yaojun Ge: State Key Laboratory for Disaster Reduction in Civil Engineering, Tongji University, Shanghai 200092, China

Abstract
The optimum damping and tuning frequency ratio of the tuned mass damper-inerter (TMDI) for the base-isolated structure is obtained using the numerical searching technique under stationary white-noise and filtered white-noise earthquake excitation. The minimization of the isolated structure's mean-square relative displacement and absolute acceleration, as well as the maximization of the energy dissipation index, were chosen as the criteria for optimality. Using a curve-fitting technique, explicit formulae for TMDI damping and tuning frequency for white-noise excitation are then derived. The proposed empirical expressions for TMDI parameters are found to have a negligible error, making them useful for the effective design of baseisolated structures. The effectiveness of TMDI and its optimum parameters are influenced by the soil condition and isolation frequency, according to the comparison made of the optimized parameters and response with different soil profiles. The effectiveness of an optimally designed TMDI in controlling the displacement and acceleration response of the flexible isolated structure under real and pulse-type earthquakes is also observed and found to be increased as the inertance mass ratio increases.

Key Words
cycloidal pulses; filtered white-noise; floor accelerations; optimum parameters; seismic base isolation; stationary excitation; tuned mass damper-inerter

Address
Department of Civil Engineering, Indian Institute of Technology Bombay, Powai, Mumbai - 400 076, India.


Abstract
This work deals with designing the aircraft wing and simulating the flow behavior on it to determine the aerodynamically efficient wing design. A NACA 4412 airfoil is used to design the base wing model. A wing with a rectangular planform and the one with curved leading edge planform was designed such that their surface areas are the same. Then, a comprehensive flow analysis is carried out at various velocities and angle of attacks using computational fluid dynamics (CFD) and the results were interpreted and compared with the experimental values. This study shows that there is a significant improvement in the aerodynamic performance of the curved leading edge wing over the wing with rectangular planform.

Key Words
coefficient of lift; coefficient of drag; L/D ratio; NACA; CFD; ansys fluent

Address
B. Ravi Kumar: School of Mechanical Engineering, SASTRA Deemed University, Thanjavur, Tamilnadu, India

Abstract
Strong winds threaten the safety of vehicles on long-span bridges considerably, which could force traffic authorities to reduce speed limits or even close these bridges to traffic. In order to maintain the safe and economic operation of a bridge, a reasonable evaluation of the driving safety on that bridge is needed. This paper aims at carrying outdriving safety analyses for three types of vehicles on a long-span bridge in crosswinds by considering the aerodynamic interference between the bridge and the vehicles based on the wind-vehicle-bridge coupling vibration analysis. Firstly, CFD numerical simulations along with previously obtained wind tunnel testing results were used to determine the aerodynamic force coefficients of the three types of vehicles on the bridge. Secondly, the dynamic responses of the bridge and the vehicles under crosswinds were simulated, and based on those, the driving safety analyses for the three types of vehicles on the bridge were carried out for both cases considering and not considering the aerodynamic interference between the vehicles and the bridge. Finally, the effect of the aerodynamic interference on the safety of the vehicles was investigated. The results show that the aerodynamic interference between the bridge and the vehicles not only affects the accident critical wind speed but also the accident type for all three types of vehicles. Such effects are also different for each of the three types of vehicles being studied.

Key Words
long-span bridges; driving safety analyses; crosswinds; aerodynamic interference; accident critical wind speed

Address
Yan Han and Jingwen Huang: School of Civil Engineering, Changsha University of Science & Technology, Changsha, China, 410004
C.S. Cai: Department of Civil and Environmental Engineering, Louisiana State University, Baton Rouge, LA 70803, USA
Suren Chen: Department of Civil and Environmental Engineering, Colorado State University, Fort Collins, CO 80523, USA
Xuhui He: School of Civil Engineering, Central South University, Changsha, China, 410075

Abstract
Heritage timber structures represent the history and culture of a nation. These structures have been inherited from previous generations; however, they inevitably exhibit deterioration over time, potentially leading to structural deficiencies. Structural Health Monitoring (SHM) offers the potential to assess operational anomalies, deterioration, and damage through processing and analysis of data collected from transducers and sensors mounted on the structure. This paper reports on the design and implementation of a long-term SHM system on the Feiyun Wooden Pavilion in China, a three-story timber building built more than 500 years ago. The principles and features of the design and implementation of SHM systems for heritage timber buildings are systematically discussed. In total, 104 sensors of 6 different types are deployed on the structure to monitor the environmental effects and structural responses, including air temperature and humidity, wind speed and direction, structural temperatures, strain, inclination, and acceleration. In addition, integrated data acquisition and transmission subsystem using a newly developed software platform are implemented. Selected preliminary statistical and correlation analysis using one year of monitoring data are presented to demonstrate the condition assessment capability of the system based on the monitoring data.

Key Words
heritage timber structure; heritage timber structure; monitoring system integration; structural health monitoring; structural response monitoring

Address
(1) Qingshan Yang:
School of Civil Engineering, Chongqing University, Chongqing 400044, China;
(2) Juan Wang, Huihui Chen:
School of Civil Engineering, Beijing Jiaotong University, Beijing 100044, China;
(3) Qingshan Yang, Juan Wang, Huihui Chen:
Beijing's Key Laboratory of Structural Wind Engineering and Urban Wind Environment, Beijing Jiaotong University, Beijing 100044, China;
(4) Sunjoong Kim:
Department of Civil and Environmental Engineering, Seoul National University, Seoul 08826, Korea;
(5) Billie F. Spencer Jr.:
Department of Civil and Environmental Engineering, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA.


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