멱법칙 기반의 풍하중과 건축구조기준의 고도분포계수(Kzr)를 이용한 풍하중의 비교분석

김예준,조영민 한국전산유체공학회 2023 한국전산유체공학회지 Vol.28 No.3

Wind load is an essential consideration in all building design. It refers to the force of the wind on the building and is a crucial factor in determining the strength and stability of the structure. There are several reasons why it is important to set wind load for calculating building wind. Firstly, wind load is one of the significant loads that a building must withstand. Resistance to wind load is essential to prevent structural damage during high wind events such as storms, hurricanes, and tornadoes. By setting wind load, engineers can determine the wind pressure that the building will experience and design the structure accordingly. Secondly, wind load affects the performance and energy efficiency of the building. The front of the building is typically the primary obstacle to wind load and can have a significant impact on the building's energy consumption. By setting wind load, designers can optimize the building's appearance to minimize energy consumption and improve the building's performance. In this study, we compared and analyzed wind loads calculated using the power law method and the altitude distribution coefficient of wind speed (Kzr) that varies depending on the surface condition. Through this comparison, we were able to analyze the differences in the wake resulting from wind load settings and determine the wind load settings according to the ground environment.

변동풍력의 연직분포를 고려한 건축물의 풍하중 평가

류혜진(Ryu, Hye-Jin),신동현(Shin, Dong-Hyeon),하영철(Ha, Young-Cheol) 대한건축학회 2019 大韓建築學會論文集 : 構造系 Vol.35 No.7

The wind tunnel test makes it possible to predict the wind loads for the wind resistant design. There are many methods to evaluate wind loads from data obtained from the wind tunnel test and these methods have advantages and disadvantages. In this study, two of these methods were analyzed and compared. One is the wind load evaluation method by fluctuating displacement and the other is the wind load evaluation method considering vertical profile of fluctuating wind force. The former method is evaluated as the sum of the mean wind load of the average wind force and the maximum value of the fluctuating wind load. The latter method is evaluated as the sum of the mean wind load and maximum value of the background wind load, and the maximum value of the resonant wind load. Two methods were applied to the wind tunnel test to compare the evaluated wind loads according to the two methods, with a maximum difference of about 1.2 times. The wind load evaluated by the method considering vertical profile of the fluctuating wind force (VPFWF) was larger than the wind load evaluated by the method by fluctuating displacement (FD). Especially, the difference of the wind load according to the two methods is large in the lower part of the building and the wind load is reversed at a specific height of the building. VPFWF of evaluating resonant wind loads and background wind loads separately is more reasonable.

Design Principles for Wind Turbine Earthquake and Wind Load Combinations

Elif Altunsu,Onur Gunes,Ali Sarı 한국강구조학회 2022 International Journal of Steel Structures Vol.22 No.3

With the ongoing changes in the modern world, the usage of renewable energy sources is increasing. The negative impact of fossil fuels on global warming has led to the search for clean energy sources. Wind energy, which is the most widely used of those sources, is discussed in this study. Numerous studies have been undertaken in this regard, but seismic eff ects are only newly being considered. In addition to having strong wind zones, Turkey is located in a geographical position through which active fault lines pass. The presence of high wind zones overlapping with these fault lines necessitates seismic analysis for turbines planned to be built in the country. Analysis of wind and seismic load simulation is diffi cult with traditional structural design programs. In this study, coeffi cients including wind loads are suggested for civil engineers who plan to analyze wind turbines with only seismic eff ects. For this purpose, a horizontal axis steel wind turbine with a 5 MW scale is analyzed in this work considering a series of wind and seismic loads in the area around Gelibolu. These environmental eff ects are evaluated under diff erent operating conditions of the turbine, including normal operation with no earthquake loads, park condition with earthquake loads, idling condition with wind loads, normal operation with earthquake loads, and idling condition with earthquake and wind loads. The full system model of the turbine is developed with the FAST fi nite element program employing a special code for wind turbines developed by the National Renewable Energy Laboratory. As a result of the analysis, it is concluded that seismic loads acting with the wind signifi cantly change the internal forces. Damping eff ects occur when seismic and wind loads act at the same time. For this reason, wind loads need to be reduced by a certain coeffi cient in some cases. Coeffi cients are proposed here for application in initial designs and load combinations for certain wind and earthquake conditions.

Thrust force and base bending moment acting on a horizontal axis wind turbine with a high tip speed ratio at high yaw angles

Danijel Bosnar,Hrvoje Kozmar,Stanislav Pospíšil,Michael Macháček 한국풍공학회 2021 Wind and Structures, An International Journal (WAS Vol.32 No.5

Onshore wind turbines may experience substantially different wind loads depending on their working conditions, i.e. rotation velocity of rotor blades, incoming freestream wind velocity, pitch angle of rotor blades, and yaw angle of the wind-turbine tower. In the present study, aerodynamic loads acting on a horizontal axis wind turbine were accordingly quantified for the high tip speed ratio (TSR) at high yaw angles because these conditions have previously not been adequately addressed. This was analyzed experimentally on a small-scale wind-turbine model in a boundary layer wind tunnel. The wind-tunnel simulation of the neutrally stratified atmospheric boundary layer (ABL) developing above a flat terrain was generated using the Counihan approach. The ABL was simulated to achieve the conditions of a wind-turbine model operating in similar inflow conditions to those of a prototype wind turbine situated in the lower atmosphere, which is another important aspect of the present work. The ABL and wind-turbine simulation length scale factors were the same (S=300) in order to satisfy the Jensen similarity criterion. Aerodynamic loads experienced by the wind-turbine model subjected to the ABL simulation were studied based on the high frequency force balance (HFFB) measurements. Emphasis was put on the thrust force and the bending moment because these two load components have previously proven to be dominant compared to other load components. The results indicate several important findings. The loads were substantially higher for TSR=10 compared to TSR=5.6. In these conditions, a considerable load reduction was achieved by pitching the rotor blades. For the blade pitch angle at 90o, the loads were ten times lower than the loads of the rotating wind-turbine model. For the blade pitch angle at 12o, the loads were at 50% of the rotating wind-turbine model. The loads were reduced by up to 40% through the yawing of the wind-turbine model, which was observed both for the rotating and the parked wind-turbine model.

대기경계층 공탄성 실험에서 역추정된 동적 풍방향 하중 특성

황재승 대한건축학회지회연합회 2018 대한건축학회연합논문집 Vol.20 No.1

The dynamic along-wind response based on spectral modal analysis has been adopted as a wind load standard in many countries over the world due to the advantage of evaluating the dynamic response by the simple theoretical formula since it has been established in the 1960s. In theoretical evaluation process, the modal wind load spectrum was derived from the spectral density of longitudinal velocity fluctuation, and the spectral modal analysis is performed for the wind-resistant performance. Since the modal wind load spectrum is derived by simplifying wind characteristics such as drag coefficient, turbulence intensity, co-coherence, etc. to facilitate the theoretical development, it is necessary to examine the validity of the simplification. In this study, the aero-elastic model test was performed in the atmospheric boundary layer wind tunnel, and the modal response was separated from the acceleration responses measured from the model test by applying the state space mode decomposition technique. And then modal load was estimated in order to compare with the theoretical modal wind load. Especially, the characteristics of aerodynamic admittance used for the conversion from spectral density of wind velocity to modal wind load spectrum are mainly analyzed and compared with theoretical aerodynamic admittance. From the results, it is shown that the spectrum of estimated dynamic wind load is slightly different with the theoretical wind load spectrum according to the top wind velocity, but the overall spectral characteristics is similar in the frequency signature. Applying the process in this study to the measured response of a structure under natural wind, it can be used for estimating the wind load in the natural environment condition and establishing a wind load model based on in-situ data. 스펙트럼 모드해석에 기반한 풍방향 동적해석법은 1960년대에 정립된 이후, 이론적인 식에 의해서 응답을 평가할 수 있는 장점 때문에 세계 많은 나라에서 풍하중 기준으로 사용되고 있다. 이론식은 변동풍속 스펙트럼으로부터 모달풍하중 스펙트럼을 유도하고 스펙트럼해석에 의한 변동응답을 이용하여 구조물의 내풍성능을 평가할 수 있었다. 모달 풍하중 스펙트럼은 이론적 전개를 용이하게 하기 위하여 풍력계수, 난류강도, 코-코히어런스 등과 같은 바람의 성상을 단순화하여 유도된 것으로 그에 대한 타당성을 검토할 필요가 있다. 본 연구에서는 대기 경계층 풍동에서 공탄성 실험을 수행하고 하중 추정법을 이용하여 풍방향 동적하중을 구하였으며, 이를 이론적인 모달 풍하중 스펙트럼과 비교하였다. 공탄성 실험으로부터 계측된 가속도 응답에 상태공간 모드분해법을 적용하여 모달응답을 구하고 그로부터 풍방향 모달하중을 역추정하고 이론적 모달풍하중과 비교하여 그 특성을 분석하였다. 특히 풍속스펙트럼으로부터 모달 풍하중스펙트럼으로의 변환과정에서 요구되는 공력어드미턴스의 특성을 이론적 어드미턴스와 비교분석하였다. 분석결과 추정된 풍방향 동적하중 스펙트럼은 최상층 풍속에 따라 이론적 풍하중 스펙트럼의 크기가 다소 다르게 반영되어 나타났으나 진동수 특성은 매우 유사한 것을 확인할 수 있었다. 본 연구기법과 과정을 자연풍을 받는 구조물의 실계측 응답에 적용하면 자연환경상태의 풍하중을 분석하고 그에 기반하여 풍하중 모델을 정립하는데 활용 가능할 것으로 사료된다.

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>

Y자형 건축물의 풍하중 증감계수의 제안

신동현,류혜진,이규익,하영철 한국풍공학회 2023 한국풍공학회지 Vol.27 No.3

KDS 41 12 00의 풍하중 관련 식은 정형적인 건축물에 대한 수많은 연구를 통해 만든 경험식이다. 따라서 비정형 건축물에 대하여 KDS 41 12 00에 따라 풍하중을 산출하면 건축물의 형상이 반영되지 않아 실제 풍하중과 상이할 수 있다. 이에 Y자형 건축물에 대하여 풍동실험에 따른 풍하중과 KDS 41 12 00에 따른 풍하중을 산출하고 비교하고자 하였다. 이를 위해 풍력실험을 수행하였고 최종적으로 두 가지 방법에 따른 풍하중의 비율을 산출하고 이를 풍하중 증감계수로 도출하고자 하였다. 본 연구에서 제시하는 풍하중 증감계수를 KDS 41 12 00에 따라 풍하중 산출 과정에 적용한다면 보다 합리적으로 Y자형 건축물에 대한 풍하중을 산출할 수 있을 것으로 사료된다. The equations related wind load in KDS 41 10 15 are the empirical formula developed through numerous studies on regular buildings. Therefore, when wind load is calculated according to KDS 41 12 00 for an irregular shaped building, the shape of the building is not reflected and it may differ from the actual wind load. Accordingly, the wind load according to the wind tunnel test and the wind load according to KDS 41 12 00 were calculated and compared for the Y-shaped building. To this end, a high frequency force balance was conducted, and finally, the ratio of wind loads according to the two methods was calculated and the increasing and decreasing coefficients for wind load were derived. If the increasing and decreasing coefficients for wind load presented in this study are applied to the wind load calculation process in accordance with KDS 41 12 00, it is considered that the wind load for Y-shaped buildings can be calculated more reasonably.

대스팬 지붕구조물의 등가정적 풍하중 산정에 관한 연구

이명호,김지영,김대영,김상대 한국공간구조학회 2006 한국공간구조학회지 Vol.6 No.1

Gust Factor법은 구조물의 등가정적 풍하중을 평가하는 일반적인 방법으로 구조물의 최대 응답시의 풍하중의 분포가 평균풍하중의 분포와 동일한 형상을 가진다는 가정하에 적용한다. 그러나 대스팬 구조물의 경우 평균 풍하중의 형상과 변동 풍하중의 형상이 다를 수 있어 1차모드뿐 아니라 고차모드의 영향을 고려하여 구조물의 풍응답과 풍하중을 산정하여야 한다. 본 논문에서는 등가정적 풍하중을 산정하기 위하여 현재 사용되고 있는 Gust Factor 법 (GF법), Load-response-correlation법 (LRC법)에 대해 고찰하고, Advanced Conditional Sampling 법 (ACS법)을 제안하였다. ACS법은 최대하중효과를 나타내는 순간에 선택된 풍압분포와 구조물의 동적거동에 의해 발생한 관성력을 합성하여 등가정적풍하중을 산정하는 방법이다. 최대하중 효과는 풍동실험에서 얻어진 풍압데이터를 이용하여 시간이력해석으로 평가한다. 제안된 ACS법과 기존의 GF법 및 LRC법을 지붕 구조물에 적용하여 등가정적 풍하중을 산출하고 이를 상호 비교 분석함으로써 ACS법의 유효성을 검증하고자 한다. The GF(Gust Factor) method is usually used as a method to evaluate equivalent static wind loads for general structures. The GF method is performed on the assumption that the shape of the equivalent static wind load profile is typically similar to that of mean wind loads. The shape of fluctuating wind loads could be quite different with that of the mean wind loads in case of large-span structures. So, the effect of higher modes as well as first mode must be considered to evaluate the wind loads. In this study, the ACS (Advanced Conditional Sampling) method is suggested to evaluate of equivalent static wind loads after investigating about GF and LRC method. The An method ran derive effective static wind loads by combining wind pressures and inertia forces of a structure chosen at a maximum load effect. The maximum load effect is assessed with the time history analysis using pressure data measured in wind tunnel tests. Equivalent static wind loads evaluated using ACS, GF, and LRC methods are compared to verify the effectiveness of ACS method.

Wind loads and load-effects of large scale wind turbine tower with different halt positions of blade

Ke, Shitang,Yu, Wei,Wang, Tongguang,Zhao, Lin,Ge, Yaojun Techno-Press 2016 Wind and Structures, An International Journal (WAS Vol.23 No.6

In order to investigate the influence of different blade positions on aerodynamic load and wind loads and load-effects of large scale wind turbine tower under the halt state, we take a certain 3 MW large scale horizontal axis three-blade wind turbine as the example for analysis. First of all, numerical simulation was conducted for wind turbine flow field and aerodynamic characteristics under different halt states (8 calculating conditions in total) based on LES (large eddy simulation) method. The influence of different halt states on the average and fluctuating wind pressure coefficients of turbine tower surface, total lift force and resistance coefficient, circular flow and wake flow characteristics was compared and analysed. Then on this basis, the time-domain analysis of wind loads and load-effects was performed for the wind turbine tower structure under different halt states by making use of the finite element method. The main conclusions of this paper are as follows: The halt positions of wind blade could have a big impact on tower circular flow and aerodynamic distribution, in which Condition 5 is the most unfavourable while Condition 1 is the most beneficial condition. The wind loads and load-effects of disturbed region of tower is obviously affected by different halt positions of wind blades, especially the large fluctuating displacement mean square deviation at both windward and leeward sides, among which the maximum response occurs in $350^{\circ}$ to the tower top under Condition 8; the maximum bending moment of tower bottom occurs in $330^{\circ}$ under Condition 2. The extreme displacement of blade top all exceeds 2.5 m under Condition 5, and the maximum value of windward displacement response for the tip of Blade 3 under Condition 8 could reach 3.35 m. All these results indicate that the influence of halt positions of different blades should be taken into consideration carefully when making wind-resistance design for large scale wind turbine tower.

Wind loads and load-effects of large scale wind turbine tower with different halt positions of blade

Shitang Ke,Wei Yu,Tongguang Wang,Lin Zhao,Yaojun Ge 한국풍공학회 2016 Wind and Structures, An International Journal (WAS Vol.23 No.6

In order to investigate the influence of different blade positions on aerodynamic load and wind loads and load-effects of large scale wind turbine tower under the halt state, we take a certain 3 MW large scale horizontal axis three-blade wind turbine as the example for analysis. First of all, numerical simulation was conducted for wind turbine flow field and aerodynamic characteristics under different halt states (8 calculating conditions in total) based on LES (large eddy simulation) method. The influence of different halt states on the average and fluctuating wind pressure coefficients of turbine tower surface, total lift force and resistance coefficient, circular flow and wake flow characteristics was compared and analysed. Then on this basis, the time-domain analysis of wind loads and load-effects was performed for the wind turbine tower structure under different halt states by making use of the finite element method. The main conclusions of this paper are as follows: The halt positions of wind blade could have a big impact on tower circular flow and aerodynamic distribution, in which Condition 5 is the most unfavourable while Condition 1 is the most beneficial condition. The wind loads and load-effects of disturbed region of tower is obviously affected by different halt positions of wind blades, especially the large fluctuating displacement mean square deviation at both windward and leeward sides, among which the maximum response occurs in 350 to the tower top under Condition 8; the maximum bending moment of tower bottom occurs in 330 under Condition 2. The extreme displacement of blade top all exceeds 2.5 m under Condition 5, and the maximum value of windward displacement response for the tip of Blade 3 under Condition 8 could reach 3.35 m. All these results indicate that the influence of halt positions of different blades should be taken into consideration carefully when making wind-resistance design for large scale wind turbine tower.