Reynolds number and scale effects on aerodynamic properties of streamlined bridge decks

Tingting Ma,Chaotian Feng 한국풍공학회 2022 Wind and Structures, An International Journal (WAS Vol.34 No.4

Section model test, as the most commonly used method to evaluate the aerostatic and aeroelastic performances of long-span bridges, may be carried out under different conditions of incoming wind speed, geometric scale and wind tunnel facilities, which may lead to potential Reynolds number (Re) effect, model scaling effect and wind tunnel scale effect, respectively. The Re effect and scale effect on aerostatic force coefficients and aeroelastic characteristics of streamlined bridge decks were investigated via 1:100 and 1:60 scale section model tests. The influence of auxiliary facilities was further investigated by comparative tests between a bare deck section and the deck section with auxiliary facilities. The force measurement results over a Re region from about 1×105 to 4×105 indicate that the drag coefficients of both deck sections show obvious Re effect, while the pitching moment coefficients have weak Re dependence. The lift coefficients of the smaller scale models have more significant Re effect. Comparative tests of different scale models under the same Re number indicate that the static force coefficients have obvious scale effect, which is even more prominent than the Re effect. Additionally, the scale effect induced by lower model length to wind tunnel height ratio may produce static force coefficients with smaller absolute values, which may be less conservative for structural design. The results with respect to flutter stability indicate that the aerodynamic-dampingrelated flutter derivatives 2 ∗ and 1 ∗ 3 ∗ have opposite scale effect, which makes the overall scale effect on critical flutter wind speed greatly weakened. The most significant scale effect on critical flutter wind speed occurs at +3° wind angle of attack, which makes the smallscale section models give conservative predictions.

A study of the wake effects on the wind characteristics and fatigue loads for the turbines in a wind farm

Kim, Soo-Hyun,Shin, Hyung-Ki,Joo, Young-Chul,Kim, Keon-Hoon Elsevier 2015 RENEWABLE ENERGY Vol.74 No.-

<P><B>Abstract</B></P> <P>With 9 multi-megawatt (MW) wind turbines and a total capacity of 22 MW, Yeongheung Wind Farm is one of the major wind farm projects in Korea. Because there are many wind turbines installed in a small area, the wake effects on the wind turbine power and load need to be investigated carefully.</P> <P>This study analyzes the wind data measured before and after the construction of Yeongheung Wind Farm to examine the wake effect from the wind farm on the mean wind speed, wind shear, and turbulence intensity. Although mean wind speeds were similar in both periods, turbulence intensity and wind shear were significantly increased due to the wake effect by nearby turbines. Power performance and fatigue load analyses of the wind models for each time period were performed using the multi-MW wind turbine model. The wake effect caused the wind speed distribution of Period 2 to be lower than that of Period 1 in the wind speed range of 5–15 m/s, resulting in an about 7% reduction in annual energy production (AEP). Because there was only 0.4% difference in AEP loss between the results obtained using steady and dynamic power curve, we found that the mean wind speed had more influence on AEP than did turbulence intensity. From fatigue analysis, it was determined that the high turbulence intensity and the wind shear gradient in Period 2 caused the high fluctuation of loads, increasing the damage equivalent load (DEL) of Period 2 by 30–50% from Period 1. Although the wind speed distribution of Period 2 was certainly lower than IEC class IIIC, the fatigue loads showed up to 20% higher results for almost all load components. Therefore, we were able to confirm that high turbulence intensity significantly increases the fatigue load.</P> <P><B>Highlights</B></P> <P> <UL> <LI> We analyze wind characteristics changes in a wind farm caused by the wake effect. </LI> <LI> Turbulence intensity and wind shear gradient increase significantly due to wake effect. </LI> <LI> Power performance and fatigue load of typical multi-MW class wind turbine analyzed. </LI> <LI> AEP calculation shows that AEP of Period 2 was much lower than that of Period 1. </LI> <LI> High turbulence intensity due to wake effect significantly increases fatigue load. </LI> </UL> </P>

Wind load effects and equivalent static wind loads of three-tower connected tall buildings based on wind tunnel tests

Shitang Ke,Hao Wang,Yaojun Ge 국제구조공학회 2016 Structural Engineering and Mechanics, An Int'l Jou Vol.58 No.6

Due to the significant aerodynamic interference from sub-towers and surrounding tall buildings, the wind loads and dynamic responses on main tower of three-tower connected tall building typically change especially compared with those on the isolated single tall building. This paper addresses the wind load effects and equivalent static wind loads (ESWLs) of three-tower connected tall building based on measured synchronous surface pressures in a wind tunnel. The variations of the global shape coefficients and extremum wind loads of main tower structure with or without interference effect under different wind directions are studied, pointing out the deficiency of the traditional wind loads based on the load codes for the three-tower connected tall building. The ESWLs calculation method based on elastic restoring forces is proposed, which completely contains the quasi-static item, inertia item and the coupled effect between them. Then the wind-induced displacement and acceleration responses for main tower of three-tower connected tall building in the horizontal and torsional directions are investigated, subsequently the structural basal and floor ESWLs under different return periods, wind directions and damping ratios are studied. Finally, the action mechanism of interference effect on structural wind effects is investigated. Main conclusions can provide a sientific basis for the wind-resistant design of such three-tower connected tall building.

Wind load and wind-induced effect of the large wind turbine tower-blade system considering blade yaw and interference

S.T. Ke,X.H. Wang,Y.J. Ge 한국풍공학회 2019 Wind and Structures, An International Journal (WAS Vol.28 No.2

The yaw and interference effects of blades affect aerodynamic performance of large wind turbine system significantly, thus influencing wind-induced response and stability performance of the tower-blade system. In this study, the 5MW wind turbine which was developed by Nanjing University of Aeronautics and Astronautics (NUAA) was chosen as the research object. Large eddy simulation on flow field and aerodynamics of its wind turbine system with different yaw angles (0°, 5°, 10°,20°, 30° and 45°) under the most unfavorable blade position was carried out. Results were compared with codes and measurement results at home and abroad, which verified validity of large eddy simulation. On this basis, effects of yaw angle on average wind pressure, fluctuating wind pressure, lift coefficient, resistance coefficient, streaming and wake characteristics on different interference zone of tower of wind turbine were analyzed. Next, the blade-cabin-tower-foundation integrated coupling model of the large wind turbine was constructed based on finite element method. Dynamic characteristics, wind-induced response and stability performance of the wind turbine structural system under different yaw angle were analyzed systematically. Research results demonstrate that with the increase of yaw angle, the maximum negative pressure and extreme negative pressure of the significant interference zone of the tower present a V-shaped variation trend, whereas the layer resistance coefficient increases gradually. By contrast, the maximum negative pressure, extreme negative pressure and layer resistance coefficient of the non-interference zone remain basically same. Effects of streaming and wake weaken gradually. When the yaw angle increases to 45°, aerodynamic force of the tower is close with that when there’s no blade yaw and interference. As the height of significant interference zone increases, layer resistance coefficient decreases firstly and then increases under different yaw angles. Maximum means and mean square error (MSE) of radial displacement under different yaw angles all occur at circumferential 0° and 180° of the tower. The maximum bending moment at tower bottom is at circumferential 20°. When the yaw angle is 0°, the maximum downwind displacement responses of different blades are higher than 2.7 m. With the increase of yaw angle, MSEs of radial displacement at tower top, downwind displacement of blades, internal force at blade roots all decrease gradually, while the critical wind speed decreases firstly and then increases and finally decreases. The comprehensive analysis shows that the worst aerodynamic performance and wind-induced response of the wind turbine system are achieved when the yaw angle is 0°, whereas the worst stability performance and ultimate bearing capacity are achieved when the yaw angle is 45°.

풍하중 효과를 고려한 해상풍력 지지구조물의 유효응력기반 지진해석

김소연,김동현 한국풍력에너지학회 2018 풍력에너지저널 Vol.9 No.1

In this study, seismic analysis of a 3 MW offshore wind turbine support structure was performed by considering the effective stress effect of ground soil and wind load. The pore water pressure was distributed to consider the effective stress effect. A simple formula by Byrne (1991) was used to estimate some parameters and applied to the Finn model. In this paper, seismic analysis based on the total stress and effective stress of the ground was performed, and the responses of offshore wind turbine support structures were compared. In addition, the effect of wind and earthquake load on the ground was also confirmed. As a result of the analysis, the relative displacement is larger in the effective stress analysis, and the displacement difference is larger when the wind load and seismic load are considered simultaneously. It was shown from the results that the effective stress of ground soil should be considered to obtain more reliable responses for offshore wind turbine support structures.

Dynamic analysis of wind-vehicle-bridge system considering additional moments of non-uniform winds by wind shielding effect of multi-limb tower

Xu Han,Huoyue Xiang,Xuli Chen,Yong-Le Li 한국풍공학회 2023 Wind and Structures, An International Journal (WAS Vol.36 No.1

To evaluate the wind shielding effect of bridge towers with multiple limbs on high-speed trains, a wind tunnel test was conducted to investigate the aerodynamic characteristics of vehicles traversing multi-limb towers, which represented a combination of the steady aerodynamic coefficient of the vehicle-bridge system and wind environment around the tower. Subsequently, the analysis model of wind-vehicle-bridge (WVB) system considering the additional moments caused by lift and drag forces under nonuniform wind was proposed, and the reliability and accuracy of the proposed model of WVB system were verified using another model. Finally, the factors influencing the wind shielding effect of multi-limb towers were analyzed. The results indicate that the wind speed distributions along the span exhibit two sudden changes, and the wind speed generally decreases with increasing wind direction angle. The pitching and yawing accelerations of vehicles under nonuniform wind loads significantly increase due to the additional pitching and yawing moments. The sudden change values of the lateral and yawing accelerations caused by the wind shielding effect of multi-limb tower are 0.43 m/s2 and 0.11 rad/s2 within 0.4 s, respectively. The results indicate that the wind shielding effect of a multi-limb tower is the controlling factor in WVB systems.

Study on Simulation Analysis of Reduce Speed Effect for Wind Nets in Front of Crop

( Cheng-chang Lien ),( Zhu-yun Yeh ),( Wei-ling Sun ),( Jeng-liang Lin ) 한국농업기계학회 2018 한국농업기계학회 학술발표논문집 Vol.23 No.1

Due to frequent strong winds from its geographical location in Taiwan, which caused serious damage to vegetables and fruit trees, leading to a large loss of agricultural production. Wind nets can be used to reduce the wind speed in front of fruits and vegetables in order to reduce the impact of wind speed. The purpose of this study is to use Computational Fluid Dynamics(CFD), CFD simulation Software was used to simulate wind tunnel experiments with wind nets before fruits and vegetables to understand the wind tunnel with different ventilation rates under certain wind speed 40 m/s, to simulate the change of wind speed and the distribution of flow field behind the wind nets, Analyze and analyze the change of wind field and the effect of reducing the wind. The size of the wind net was 12m^*6m. According to the CFD simulation results, when the strong wind blows through the wind nets, a negative pressure zone will be generated at a horizontal distance of 0h to 10h in the windshield leeway, and the height of the negative pressure zone will gradually decrease as the horizontal distance increases. The height of the negative pressure zone also decreases with the increase of the ventilation rate of the windbreak. In addition, the analysis results show that the ventilation rate of 40% of the windbreak, the negative pressure vortex gradually disappear, and have the best effect of reducing the wind.

A numerical study on the dispersion of the Yangtze River water in the Yellow and East China Seas

Park, Tea-Wook,Oh, Im-Sang The Korean Society of Oceanography 2004 Journal of the Korean Society of Oceanography Vol.39 No.2

A three-dimensional numerical model using POM (the Princeton Ocean Model) is established in order to understand the dispersion processes of the Yangtze River water in the Yellow and East China Seas. The circulation experiments for the seas are conducted first, and then on the bases of the results the dispersion experiments for the river water are executed. For the experiments, we focus on the tide effects and wind effects on the processes. Four cases of systematic experiments are conducted. They comprise the followings: a reference case with no tide and no wind, of tide only, of wind only, and of both tide and wind. Throughout this study, monthly mean values are used for the Kuroshio Current input in the southern boundary of the model domain, for the transport through the Korea Strait, for the river discharge, for the sea surface wind, and for the heat exchange rate across the air-sea interface. From the experiments, we obtained the following results. The circulation of the seas in winter is dependent on the very strong monsoon wind as several previous studies reported. The wintertime dispersion of the Yangtze River water follows the circulation pattern flowing southward along the east coast of China due to the strong monsoon wind. Some observed salinity distributions support these calculation results. In summertime, generally, low-salinity water from the river tends to spread southward and eastward as a result of energetic vertical mixing processes due to the strong tidal current, and to spread more eastward due to the southerly wind. The tide effect for the circulation and dispersion of the river water near the river mouth is a dominant factor, but the southerly wind is still also a considerable factor. Due to both effects, two major flow directions appear near the river mouth. One of them is a northern branch flow in the northeast area of the river mouth moving eastward mainly due to the weakened southerly wind. The other is a southern branch flow directed toward the southeastern area off the river mouth mostly caused by tide and wind effects. In this case, however, the tide effect is more dominant than the wind effect. The distribution of the low salinity water follows the circulation pattern fairly well.

Variability of measured modal frequencies of a cable-stayed bridge under different wind conditions

Ni, Y.Q.,Ko, J.M.,Hua, X.G.,Zhou, H.F. Techno-Press 2007 Smart Structures and Systems, An International Jou Vol.3 No.3

A good understanding of normal modal variability of civil structures due to varying environmental conditions such as temperature and wind is important for reliable performance of vibration-based damage detection methods. This paper addresses the quantification of wind-induced modal variability of a cable-stayed bridge making use of one-year monitoring data. In order to discriminate the wind-induced modal variability from the temperature-induced modal variability, the one-year monitoring data are divided into two sets: the first set includes the data obtained under weak wind conditions (hourly-average wind speed less than 2 m/s) during all four seasons, and the second set includes the data obtained under both weak and strong (typhoon) wind conditions during the summer only. The measured modal frequencies and temperatures of the bridge obtained from the first set of data are used to formulate temperature-frequency correlation models by means of artificial neural network technique. Before the second set of data is utilized to quantify the wind-induced modal variability, the effect of temperature on the measured modal frequencies is first eliminated by normalizing these modal frequencies to a reference temperature with the use of the temperature-frequency correlation models. Then the wind-induced modal variability is quantitatively evaluated by correlating the normalized modal frequencies for each mode with the wind speed measurement data. It is revealed that in contrast to the dependence of modal frequencies on temperature, there is no explicit correlation between the modal frequencies and wind intensity. For most of the measured modes, the modal frequencies exhibit a slightly increasing trend with the increase of wind speed in statistical sense. The relative variation of the modal frequencies arising from wind effect (with the maximum hourly-average wind speed up to 17.6 m/s) is estimated to range from 1.61% to 7.87% for the measured 8 modes of the bridge, being notably less than the modal variability caused by temperature effect.

국내 풍력단지 증가에 따른 평활효과(Smoothing Effect) 정량화

김한성(Hansung Kim),최재원(Jaewon Choi),최동구(Dong Gu Choi) 한국신재생에너지학회 2018 신재생에너지 Vol.14 No.1

The number of wind farms in Korea is expected to increase due to the pressure of the post-2020 climate targets. However, this may result in some difficulties for the operation and expansion planning of our power system, due to the characteristics of wind energy, such as its intermittency and non-dispatchability. Generally, a decrease in these characteristics is called the ‘smoothing effect’. In this study, the smoothing effect is defined as a decrease in the variability of the power output. it is well known that the variability of the power output from wind farms is reduced when more wind farms are integrated into the system. A quantitative analysis of the smoothing effect is necessary to predict the variability of wind energy and this can help the power system to be operated or planned more efficiently. In this study, the methodologies of previous studies were applied to 6 wind farms in Korea. As a result, it was found that the smoothing effect in spring and winter was more effective than that in summer and fall and increased with increasing distance between the wind farms. The expected variability obtained from the equation estimated using the quantitative analysis of the smoothing effect was analogous to the variability of the aggregate power output from the entire wind farms in the power system.