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CONTENTS
Volume 16, Number 3, March 2013
 

Abstract
The wind-induced vibrations of the mast arm of cantilever traffic signal structures can lead to the fatigue failure of these structures. Wind tunnel tests were conducted on an aeroelastic model of this type of structure. Results of these experiments indicated that when the signals have backplates, vortex shedding causes large-amplitude vibrations that could lead to fatigue failure. Vibrations caused by galloping were only observed for one particular angle of attack with the signals having backplates. No evidence for galloping, previously thought to be the dominant cause of fatigue failures in these structures, was observed.

Key Words
cantilevered traffic signal structures; fatigue; wind-induced vibrations; galloping; vortex shedding

Address
Hector J. Cruzado : Department of Civil and Environmental Engineering, Polytechnic University of Puerto Rico, San Juan, USA
Chris Letchford : Department of Civil and Environmental Engineering, Rensselaer Polytechnic Institute, Troy, NY, USA
Gregory A. Kopp : 3Boundary Layer Wind Tunnel Laboratory, Faculty of Engineering, University of Western Ontario
London, Ontario, Canada

Abstract
The wind turbine blade is a very important part of the rotor. Extraction of energy from wind depends on the design of blade. In this work, the analysis is done on a blade of length 38.95 m which is designed for V82-1.65 MW horizontal axis wind turbine (supplied by Vestas). The airfoil taken for the blade is NACA 634–221 which is same from root to tip. The analysis of designed blade is done in flap-wise loading. Two shapes of the spar are taken, one of them is of square shape and the other one is combination of square and cross shape. The blade and spar are of the same composite material. The Finite element analysis of designed blade is done in ANSYS. This work is focused on the two segments of blade, root segment and transition segment. Result obtained from ANSYS is compared with the experimental work.

Key Words
design; material; chord; twist; blade

Address
Nitin Tenguria and N.D. Mittal : Department of Applied Mechanics, Maulana Azad National Institute of Technology, Bhopal, India
Siraj Ahmed : Department of Mechanical Engineering, Maulana Azad National Institute of Technology, Bhopal, India

Abstract
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.

Key Words
cable-stayed bridge; parallel cables; wake galloping; wind tunnel test; cable dynamics; vibration suppressing measures

Address
Yongle Li, Mengxue Wu, Tao Wang and Haili Liao : 1Department of Bridge Engineering, Southwest Jiaotong University, Chengdu, Sichuan 610031, P. R. China
Xinzhong Chen: Wind Science and Engineering Research Center , Department of Civil and Environmental Engineering,
Texas Tech University, Lubbock, Texas 79409-1023, USA

Abstract
The fatigue load of a turbine blade has become more important because the size of commercial wind turbines has increased dramatically in the past 30 years. The reduction of the fatigue load can result in an increase in operational efficiency. This paper numerically investigates the load reduction of large wind turbine blades using active aerodynamic load control devices, namely trailing edge flaps. The PD and LQG controllers are used to determine the trailing edge flap angle; the difference between the root bending moment and its mean value during turbulent wind conditions is used as the error signal of the controllers. By numerically analyzing the effect of the trailing edge flaps on the wind turbines, a reduction of 30-50% in the standard deviation of the root bending moment was achieved. This result implies a reduction in the fatigue damage on the wind turbines, which allows the turbine blade lengths to be increased without exceeding the designed fatigue damage limit.

Key Words
wind turbine blade; load reduction; fatigue; smart control; trailing edge flap

Address
Jong-Won Lee, Joong-Kwan Kim and Jae-Hung Han : Department of Aerospace Engineering, KAIST, Daejeon, 305-600, Korea
Hyung-Kee Shin : Korea Institute of Energy Research, Daejeon, 305-343, Korea

Abstract
This paper presents a new analysis framework for predicting the internal buffeting forces in bridge components under skew wind. A linear regressive model between the internal buffeting force and deformation under normal wind is derived based on mathematical statistical theory. Applying this regression model under normal wind and the time history of buffeting displacement under skew wind with different yaw angles in wind tunnel tests, internal buffeting forces in bridge components can be obtained directly, without using the complex theory of buffeting analysis under skew wind. A self-anchored suspension bridge with a main span of 260 m and a steel arch bridge with a main span of 450 m are selected as case studies to illustrate the application of this linear regressive framework. The results show that the regressive model between internal buffeting force and displacement may be of high significance and can also be applied in the skew wind case with proper regressands, and the most unfavorable internal buffeting forces often occur under yaw wind.

Key Words
bridge; linear regression; skew wind; buffeting; internal force

Address
Zengwei Guo, Yaojun Ge, Lin Zhao and Yahui Shao : State Key Laboratory of Disaster Reduction in Civil Engineering, Department of Bridge Engineering, Tongji University, shanghai 200092, P. R. China


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