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CONTENTS
Volume 32, Number 2, February 2021
 

Abstract
The aim of the current study is to compare the performance of large 2 MW and 3 MW wind turbines operating on existing onshore wind farms using Blade Element Momentum (BEM) theory and Angular Momentum (AM) theory and illustrate the performance characteristic curves of the turbines as a function of wind speed (U∞). To achieve this, the measurement data obtained from two different Wind Energy Power Plants (WEPPs) located in the Hatay region of Turkey was used. Two different horizontal-axis wind turbines with capacities of 2 MW and 3 MW were selected for evaluation and comparison. The hub-height wind speed (UD), turbine power output (P), atmospheric air temperature (Tatm) and turbine rotational speed (Ω) data were used in the evaluation of the turbine performance characteristics. Curves of turbine power output (P), axial flow induction factor (α), turbine rotational speed (Ω), turbine power coefficient (CP), blade tip speed ratio (λ), thrust force coefficient (CT) and thrust force (T) as a function of U∞ were obtained for the 2 MW and 3 MW wind turbines and these characteristic curves were compared. Results revealed that, for the same wind speed conditions, the higher-capacity wind turbine (3 MW) was operating at higher turbine power coefficient rates, while rotating at lower rotational speed ratios than the lower-capacity wind turbine (2 MW).

Key Words
wind energy; renewable energy; Horizontal-Axis Wind Turbine (HAWT); wind power curve; Blade Element Momentum (BEM) theory

Address
Mehmet Bilgili:Department of Mechanical Engineering, Faculty of Ceyhan Engineering, Cukurova University, 01950 Adana, Turkey

Firat Ekinci:Department of Energy System Engineering, Faculty of Engineering, Adana Alparslan Turkes Science and Technology University, 01120 Adana, Turkey

Tugce Demirdelen:Department of Electrical and Electronics Engineering, Faculty of Engineering, Adana Alparslan Turkes Science and Technology University, 01120 Adana, Turkey

Abstract
Non-synoptic winds generated by tornadoes, downbursts or gust fronts exhibit significant non-stationarity and can cause significant wind load effect on flexible structures such as long-span bridges. However, conventional assumptions on stationarity used to evaluate the structural wind-induced vibration are inadequate. In this paper, an efficient frequency domain scheme based on fast CQC method, which can predict non-stationary buffeting random responses of long-span bridges, is presented, and then this approach is applied to evaluate the buffeting response of a long-span suspension bridge located in a complex mountainous wind environment as an example. In this study, the data-driven method based on one available measured wind speed sample is firstly presented to establish non-stationary wind models, including time-varying mean wind speed, time-varying intensity envelope function and uniformly modulated fluctuating spectrum. Then, a linear time-variant (LTV) system based on the proposed scheme can be generally applied to calculate the non-stationary buffeting responses. The effectiveness and accuracy of the proposed scheme are verified through Monte Carlo time domain simulation implemented in ANSYS platform. Also, the transient effect nature of the bridge responses is further illustrated by comparison of the non-stationary, quasi-stationary and steady-state cases. Finally, buffeting response analysis with traditional stationary treatment (10 min constant mean plus stationary wind fluctuation) is performed to illustrate the importance of the non-stationary characteristics embedded in original wind speed samples.

Key Words
buffeting response; non-stationary wind; mountainous terrain; suspension bridge; aerodynamic forces; separable wind spectrum

Address
Yanwen Su:China Railway Eryuan Engineering Group Co. Ltd, Chengdu, Sichuan 610031, China

Guoqing Huang:School of Civil Engineering, Chongqing University, Chongqing, 400044, China

Yongping Zeng:China Railway Eryuan Engineering Group Co. Ltd, Chengdu, Sichuan 610031, China

Abstract
This paper describes a wind tunnel test on a 1:25 scale model of TTU building with several adjustable openings in order to comprehensively study the characteristics of fluctuating internal pressures, especially the phenomenon of the increase in fluctuating internal pressures induced by tangential flow over building openings and the mechanism causing that. The effects of several factors, such as wind angle, turbulence intensity, opening location, opening size, opening shape and background porosity on the fluctuating internal pressures at oblique wind angles are also described. It has been found that there is a large increase in the fluctuating internal pressures at certain oblique wind angles (typically around 60° to 80°). These fluctuations are greater than those produced by the flow normal to the opening when the turbulence intensity is low. It is demonstrated that the internal pressure resonances induced by the external pressure fluctuations emanating from flapping shear layers on the sidewall downstream of the windward corner are responsible for the increase in the fluctuating internal pressures. Furthermore, the test results show that apart from the opening shape, all the other factors influence the fluctuating internal pressures and the internal pressure resonances at oblique wind angles to varying degrees.

Key Words
fluctuating internal pressure; opening building; wind tunnel test; oblique wind angle; external pressure fluctuations; internal pressure resonance

Address
Sheng Chen:State Key Laboratory of Disaster Reduction in Civil Engineering. Tongji University. Shanghai 200092. China

Peng Huang:State Key Laboratory of Disaster Reduction in Civil Engineering. Tongji University. Shanghai 200092. China

Richard G.J. Flay:Department of Mechanical Engineering. The University of Auckland. Private Bag 92019. Auckland 1142. New Zealand

Abstract
The snow cornice mass on the formation zone had triggered avalanches which led to the loss of human life and property. Snow cornice is formed due to flow separation on the leeward side. Effect of lee slope is more prominent in the formation of snow cornices as compared to the windward slope. The analysis of wind flow pattern has been carried out to evaluate the performance of a jet roof. Computational Fluid Dynamics (CFD) analysis of wind flow over a 2D hill model was carried out using RNG based k-ε turbulence models available in ANSYS Fluent. Effect of varying leeward hill slope (1:2 to 1:6) on flow separation for the given windward slope was observed and a critical slope of 1:4 was found at which the separation zone ceased to exist. The modification of wind flow over a hill due to the installation of jet roof was simulated. It was observed that jet roof had significantly modified the wind flow pattern around hill ridgeline and ultimately snow cornice formation had mitigated. The results of the wind flow pattern were validated with the wind data collected at the experimental site, Banihal Top (Jammu and Kashmir, India). The wind flow simulation over the hill and mitigation of cornice formation by the jet roof has been explained in the present paper.

Key Words
computational fluid dynamics; turbulence; wind; jet roof; separation zone

Address
Ganesh Kumar:Defence Geo-Informatics Research Establishment, Defence Research and Development Organization,Himparisar, Sector-37A, Chandigarh, PIN-160036, India

Ajay Gairola:Civil Engineering Department, Indian Institute of Technology, Roorkee, Uttarakhand, PIN-247667, India

Aditya Vaid:Defence Geo-Informatics Research Establishment, Defence Research and Development Organization,Himparisar, Sector-37A, Chandigarh, PIN-160036, India


Abstract
Wind load acting on a standalone structure is different from that acting on a similar structure which is surrounded by other structures in close proximity. The presence of other structures in the surrounding can change the wind flow regime around the principal structure and thus causing variation in wind loads compared to a standalone case. This variation on wind loads termed as interference effect depends on several factors like terrain category, geometry of the structure, orientation, wind incident angle, interfering distances etc., In the present study, a three building configuration is considered and the mean pressure coefficients on each face of principle building are determined in presence of two interfering buildings. Generally, wind loads on interfering buildings are determined from wind tunnel experiments. Computational fluid dynamic studies are being increasingly used to determine the wind loads recently. Whereas, wind tunnel tests are very expensive, the CFD simulation requires high computational cost and time. In this scenario, Artificial Neural Network (ANN) technique and Support Vector Regression (SVR) can be explored as alternative tools to study wind loads on structures. The present study uses these data-driven approaches to predict mean pressure coefficients on each face of principle building. Three typical arrangements of three building configuration viz. L shape, V shape and mirror of L shape arrangement are considered with varying interfering distances and wind incidence angles. Mean pressure coefficients (Cp mean) are predicted for 45 degrees wind incidence angle through ANN and SVR. Further, the critical faces of principal building, critical interfering distances and building arrangement which are more prone to wind loads are identified through this study. Among three types of building arrangements considered, a maximum of 3.9 times reduction in Cp mean values are noticed under Case B (V shape) building arrangement with 2.5B interfering distance. Effect of interfering distance and building arrangement on suction pressure on building faces has also been studied. Accordingly, Case C (mirror of L shape) building arrangement at a wind angle of 45° shows less suction pressure. Through this study, it was also observed that the increase of interfering distance may increase the suction pressure for all the cases of building configurations considered.

Key Words
mean pressure coefficient; Artificial Neural Network (ANN); three building configuration

Address
Shruti Konka:Department of Civil Engineering, BITS Pilani, Hyderabad Campus, Telangana, 500078, India

Shanbhag Rahul Govindray:Department of Mechanical Engineering, BITS Pilani, Hyderabad Campus, Telangana,500078, India

Sabareesh Geetha Rajasekharan:Department of Mechanical Engineering, BITS Pilani, Hyderabad Campus, Telangana,500078, India

Paturu Neelakanteswara Rao:Department of Civil Engineering, BITS Pilani, Hyderabad Campus, Telangana, 500078, India

Abstract
The 246.8-m-tall Beijing Olympic Tower (BOT) is a new landmark in Beijing City, China. Its unique architectural style with five sub-towers and a large tower crown gives rise to complex dynamic characteristics. Thus, it is wind-sensitive, and a double-stage pendulum tuned mass damper (DPTMD) has been installed for vibration mitigation. In this study, a finite-element analysis of the wind-induced responses of the tower based on full-scale measurement results was performed. First, the structure of the BOT and the full-scale measurement are introduced. According to the measured dynamic characteristics of the BOT, such as the natural frequencies, modal shapes, and damping ratios, an accurate finite-element model (FEM) was established and updated. On the basis of wind measurements, as well as wind-tunnel test results, the wind load on the model was calculated. Then, the wind-induced responses of the BOT with the DPTMD were obtained and compared with the measured responses to assess the numerical wind-induced response analysis method. Finally, the wind-induced serviceability of the BOT was evaluated according to the field measurement results for the wind-induced response and was found to be satisfactory for human comfort.

Key Words
high-rise building; multi-tower building; full-scale measurement; structural dynamic property; wind-induced responses; tuned mass damper

Address
Xin Chen:Jiangsu Province Key Laboratory of Structure Engineering, Suzhou University of Science and Technology,1701 Binhe Road, Suzhou, P.R. China

Zhiqiang Zhang:School of Civil Engineering, Southeast University, 2 Sipailou, Nanjing, P.R. China

Abstract
In this study, the artificial neural network (ANN) method was used for estimating the monthly mean wind speed of Sivas, in the central part of Turkey. Eighteen years of wind speed data obtained from nine measurement stations during the period of 2000-2017 at 10 m height was used for ANN analysis. It was found that mean absolute percentage error (MAPE) ranged from 3.928 to 6.662, mean bias error (MBE) ranged from -0.089 to -0.003, while root mean square error (RMSE) ranged from 0.050 to 0.157 and R2 ranged from 0.86 to 0.966. ANN models provide a good approximation of the wind speed for all measurement stations, however, a tendency to underestimate is also obvious.

Key Words
artificial neural network; wind energy; wind speed; Sivas province

Address
Cahit Gurlek:Department of Mechanical Engineering, Sivas Cumhuriyet University, Sivas 58140, Turkey

Mustafa Sahin:Turkish Railway Machines Industry Inc., Sivas 58030, Turkey

Serkan Akkoyun:Department of Physics, Sivas Cumhuriyet University, Sivas 58140, Turkey

Abstract
This study investigates the effects of blade configuration and solidity of Darrieus wind turbine on the starting torque characteristics. Generally, the configuration of Darrieus wind turbine is divided into Troposkien, parabola, Catenary, Sandia, modified-parabola and straight types. A numerical analysis has been carried out using Multiple Stream Tube (MST) method to investigate the effect of blade configuration and solidity of Darrieus wind turbine on the starting torque under the initial low range of rotational speed. The simulation results show that the starting torque of Darrieus wind turbine varies considerably depending on the blade configuration. The initial starting torque was larger with Troposkien, Parabola, Catenary, and Sandia configurations than with modified parabola or straight types. The increase in solidity with increasing number of blades raised the starting torque and improved the dynamic stability during the initial operational speed of Darrieus wind turbine. Additionally, these torque results represent basic data for fluid-structure interaction (FSI) simulation of the steady-dynamic operation of the turbine.

Key Words
starting torque characteristics; blade configuration; solidity; Darrieus wind turbine; multiple stream tube (MST) method

Address
Sung-Cheoul Roh:Department of Environmental Engineering, Yonsei University, 1 Yonseidae-gil, Wonju 26493, Republic of Korea

Seung-Hee Kang:Department of Aerospace Engineering, Jeonbuk National University, 567, Baekje-daero, Deokjin-gu, Jeonju54896, Republic of Korea


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