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CONTENTS
Volume 18, Number 2, February 2014
 

Abstract
Aeroelasticity is the main source of instability in structures which are subjected to aerodynamic forces. One of the major reasons of instability is the coupling of bending and torsional vibration of the flexible bodies, which is known as flutter. The presented investigation aims to study the aeroelastic stability of composite blades of wind turbine. Geometry, layup, and loading of the turbine blades made of laminated composites were calculated and evaluated. To study the flutter phenomenon of the blades, two numerical and analytical methods were selected. The finite element method (FEM), and JAR-23 standard were used to perform the numerical studies. In the analytical method, two degree freedom flutter and Lagrange\'s equations were employed to study the flutter phenomena analytically and estimate the flutter speed.

Key Words
aeroelasticity; wind turbine; composite blade; flutter; finite element method

Address
Ahmad Reza Ghasemi and Mohammad Hassan Tarighat: Department of Mechanical Engineering, University of Kashan, Kashan, Iran
Arezu Jahanshir : Department of Physics, Buein ZahraTechnical University, Ghazvin, Iran

Abstract
It is believed that offshore wind farms may satisfy an increasing portion of the energy demand in the next years. This paper presents a comparative study of the fatigue performances of tripod and jacket steel support structures for offshore wind turbines in waters of intermediate depth (20-50 m). A reference site at a water depth of 45 m in the North Atlantic Ocean is considered. The tripod and jacket support structures are conceived according to typical current design. The fatigue behavior is assessed in the time domain under combined stochastic wind and wave loading and the results are compared in terms of a lifetime damage equivalent load.

Key Words
offshore wind turbine; support structure; tripod; jacket; fatigue analysis

Address
N. Alati, G. Failla, F. Arena and A. Santini: 1Department of Civil, Energy, Environmental and Materials Engineering (DICEAM),University \"Mediterranea\"of Reggio Calabria, 89122 Reggio Calabria, Italy
V. Nava: Tecnalia Research and Innovation, Parque Científico y Tecnológico de Bizkaia, C/ Geldo. Edificio 700,E-48160 Derio (Bizkaia)

Abstract
Aerodynamic characteristics of crescent and D-shape bundled conductors were measured by high frequency force balance technique in the wind tunnel. The drag and lift coefficients of each sub-conductor and the whole bundled conductors were presented under various attack angles of wind. The galloping possibility of bundled conductors is discussed based on the Den Hartog criterion. The influence of icing thickness, initial ice accretion angle and sub-conductor on the aerodynamic properties were investigated. Based on the measured aerodynamic force coefficients, a computationally efficient finite element method is also implemented to analyze galloping of iced bundled conductors. The analysis results show that each sub-conductor of the bundled conductor has its own galloping feature due to the use of aerodynamic forces measured separately for every single sub-conductors.

Key Words
iced bundled conductors; aerodynamic force coefficients; galloping analysis; wind tunnel tests

Address
Wenjuan Lou, Jiang Lv, M.F. Huang and Lun Yang : Institute of Structural Engineering, Zhejiang University, Hangzhou, 310058, Zhejiang, China
Dong Yan: Henan electric power testing and research institute, Zhenzhou, 450052, Henan, China

Abstract
The safety of road vehicles on the ground in crosswind has been investigated for many years. One of the most important fundamentals in the safety analysis is aerodynamic characteristics of a vehicle in crosswind. The most common way to study the aerodynamic characteristics of a vehicle in crosswind is wind tunnel tests to measure the aerodynamic coefficients and/or pressure coefficients of the vehicle. Due to the complexity of wind tunnel test equipment and procedure, the features of flow field around the vehicle are seldom explored in a wind tunnel, particularly for the vehicle moving on the ground. As a complementary to wind tunnel tests, the numerical method using computational fluid dynamics (CFD) can be employed as an effective tool to explore the aerodynamic characteristics of as well as flow features around the vehicle. This study explores crosswind effects on a high-sided lorry on the ground with and without movement through CFD simulations together with wind tunnel tests. Firstly, the aerodynamic forces on a stationary lorry model are measured in a wind tunnel, and the results are compared with the previous measurement results. The CFD with unsteady RANS method is then employed to simulate wind flow around and wind pressures on the stationary lorry. The numerical aerodynamic forces are compared with the wind tunnel test results. Furthermore, the same CFD method is extended to investigate the moving vehicle on the ground in crosswind. The results show that the CFD results match with wind tunnel test results and the current way using aerodynamic coefficients from a stationary vehicle in crosswind is acceptable. The CFD simulation can provide more insights on flow field and pressure distribution which are difficult to be obtained by wind tunnel tests.

Key Words
crosswind effects; road vehicles; aerodynamic characteristics; stationary and moving vehicle; wind tunnel tests; computational fluid dynamics simulation

Address
Bin Wang and You-Lin Xu: Department of Civil and Environmental Engineering, The Hong Kong Polytechnic University, Hong Kong, China
Le-Dong Zhu: State Key Laboratory of Disaster Reduction in Civil Engineering, Tongji University, Shanghai, China
Yong-Le Li: Department of Bridge Engineering, Southwest Jiaotong University, Chengdu, China

Abstract
A major problem with high-mast light poles is the effects that wind vortex shedding can have on the pole itself because of the lock-in phenomenon. It is desired that the coefficients in the AASHTO Standard Specifications (5th edition) for Structural Supports for Highway Signs, Luminaries, and Traffic Signals be analyzed and refined. This is for the belief that the span of the shapes of poles for which the coefficients are used is much too broad and a specific coefficient for each different shape is desired. The primary objective of this study is to develop wind vortex shedding coefficient for a multisided shape. To do that, an octagonal shape was used as the main focus since octagonal cross sectioned high-mast light poles are one of the most common shapes in service. For the needed data, many wind parameters, such as the static drag coefficient, the slope of aerodynamic lift coefficient, Strouhal number, the lock-in range of wind velocities producing vibrations, and variation of amplitude of vortex-induced vibration with Scruton number are needed. From wind tunnel experiments, aerodynamic parameterswere obtained for an octagonal shape structure. Even though aerodynamic coefficients are known from past test results, they need to be refined by conducting further wind tunnel tests.

Key Words
high mast light pole; fatigue design; vortex shedding; slender support structures; wind tunnel testing; simulation

Address
Byungik Chang: University of New Haven, WestHaven, Connecticut06516, USA
Michael Neill:Phillips 66 Borger Refinery, Borger, Texas 79007, USA
Roy Issa and Aaron Miller: West Texas A&M University, Canyon, Texas 79015, USA

Abstract
Recently, the horizontal axis rotor performance optimizer (HARP_Opt) tool was developed in the National Renewable Energy Laboratory, USA. This innovative tool is becoming more popular in the wind turbine industry and in the field of academic research. HARP_Optwas developed on the basis of two fundamental modules, namely, WT_Perf, a performance evaluator computer code using the blade element momentum theory; and a genetic algorithm module, which is used as an optimizer. A pattern search algorithm was more recently incorporated to enhance the optimization capability, especially the calculation time and consistency of the solutions. The blade optimization is an aspect that is highly dependent on experience and requires significant consideration on rotor control strategies, wind data, and generator type. In this study, the effects of rotor control strategies including fixed speed and fixed pitch, variable speed and fixed pitch, fixed speed and variable pitch, and variable speed and variable pitch algorithms on optimal blade shapes and rotor performance are investigated using optimized blade designs. The effects of environmental wind data and the objective functions used for optimization are also quantitatively evaluated using the HARP_Opt tool. Performance indices such as annual energy production, thrust, torque, and roof-flap moment forces are compared.

Key Words
blade element momentum theory (BEMT); pattern search; blade shape optimal design; parametric study; rotor control strategy; wind data

Address
Jin-Hak Yi and Gil-Lim :Coastal Development and Ocean Energy Research Division, Korea Institute of Ocean Science and Technology, Gyeonggi 426-744, Republic of Korea;
Department of Convergence Study on the Ocean Science and Technology, Ocean Science and Technology
Ye Li:State Key Lab of Ocean Engineering, School of Naval Architecture, Ocean and Civil Engineering, Shanghai
Jiao Tong University, Shanghai 200240, China
School, Korea Maritime and Ocean University, Busan, Republic of Korea


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