Wind‐induced fatigue of large HAWT coupled tower–blade structures considering aeroelastic and yaw effects

An efficient approach for predicting wind‐induced fatigue in large horizontal axis wind turbine coupled tower–blade structures subject to aeroelastic and yaw effects is presented. First, aerodynamic loads under yaw conditions are simulated based on the harmonic superposition method and modified blade element momentum theory, in which wind shear, tower shadow, tower–blade interactions, aeroelastic, and rotational effects are taken into account. Then, a nonlinear time‐history of wind‐induced responses under simulated aerodynamic loads is obtained. Finally, based on these results, wind‐induced fatigue damage and lifespan are predicted according to linear cumulative damage theory. For completeness, the influences of mean wind speed, aeroelasticity, and yaw angle on horizontal axis wind turbine fatigue life are discussed. The results indicate that the aerodynamic loads and residual fatigue life can be estimated accurately by the proposed model, which can be used to simulate the 3D wind fields of wind turbines under given wind conditions. The wind energy of the wind turbine blade is mainly concentrated at its edge and is weaker at the hub. Estimation of wind turbine fatigue life is therefore suggested to be based on the component with the shortest life, being the blade root. Furthermore, yaw conditions significantly shorten fatigue life and should not be ignored. Fatigue life is also rather sensitive to mean wind speed.     

Mitigation of tower and out-of-plane blade vibrations of offshore monopile wind turbines by using multiple tuned mass dampers

Offshore wind turbines are vulnerable to external vibration sources such as wind and wave excitations due to the increasing size and flexibility. It is necessary to mitigate the excessive vibrations of offshore wind turbines to ensure the safety and serviceability during their operations. Some research works have been carried out to control the excessive vibrations of the tower and the in-plane vibrations of blades. Very limited study focuses on the out-of-plane vibration mitigation of blades. In the present study, a detailed finite element (FE) model of the latest NREL 5MW wind turbine is developed by using the FE code ABAQUS. The tower and blades are explicitly modelled, and the rotating of the blades is considered. Multiple tuned mass dampers (MTMDs) are proposed to be installed in the tower and each blade to simultaneously mitigate the out-of-plane vibrations of the tower and blades when the wind turbine is subjected to the combined wind and wave loadings. The effectiveness and robustness of the proposed method are systematically investigated. Numerical results show that MTMDs can effectively mitigate the out-of-plane vibrations of the tower and blades when the wind turbine is in either the operational or parked condition.     

Wind field simulation of large horizontal‐axis wind turbine system under different operating conditions

This paper proposes a technique of generating turbulent wind velocities on large horizontal‐axis wind turbine systems under different operating conditions. The rotational sampling effect, vertical wind shear and coherence between wind velocities at blades and on the tower were taken into account. Coordinate system of wind time series at certain discrete sampling points on the vertical plane of the wind turbine is generated by the hybrid weighted amplitude wave superposition and proper orthogonal decomposition (POD) methods. The POD eigenmodes on the blades after updating locations were calculated subsequently using B‐spline surface interpolation method, and the rotationally sampled wind velocities are reconstructed by taking advantage of POD method again. Examples are subsequently presented to validate this proposed technique and demonstrate the generation of wind velocities under different operating conditions. The results show that the simulated spectrum of turbulent wind velocities at blades corresponds well to the measured data and that on the tower agrees well with the fixed point Kaimal spectrum. The reasonable sampling points spacing is suggested to be about 10 m for the wind field simulation of wind turbine system. The proposed method is of great advantage in accuracy and efficiency, which is greatly significant for the fine analysis of multi‐megawatt wind turbines. Copyright © 2015 John Wiley & Sons, Ltd.     

风力发电塔系统TMD控制振动台试验研究

通过不同桨叶转速、不同地震动输入下的风力发电塔系统在TMD控制下的振动台对比试验,研究TMD对风力发电塔系统的控制效果及其影响因素;在试验的基础上,利用ANSYS软件对风力发电塔系统建模,对其在有无TMD控制下的地震反应进行有限元模拟,并与试验结果进行比较,得到与振动台试验相一致的结论。     

Comparison of wind‐induced dynamic property of super‐large cooling tower considering different four‐tower interferences

Dynamic amplification effects caused by tower‐group interference is the most critical causes of wind‐induced destructions of super‐large cooling tower (SLCT), and four‐tower combinations are the most common tower‐group combining form. However, the dynamic amplification effects of SLCT of different four‐tower arrangements have not been studied systematically so far. The highest (220 m) SLCT in the world was taken as the target to conduct SLCT wind pressure measurement under 320 wind tunnel test conditions. Firstly, the stability performance under the design wind loads was analyzed. Then, the dynamic time‐history analysis was carried out, and the distribution characteristics of peak factors and values of extreme response were discussed. Furthermore, with a new concept parameter “tower‐group wind vibration coefficient” for the wind‐resistance design of SLCT, the distribution laws of two‐dimensional (2D), one‐dimensional (1D), and global tower‐group wind vibration coefficient were revealed under different four‐tower interferences. On these bases, we recommend the design parameters for wind‐resistance study of SLCT and the priority of four‐tower combination forms. The study showed that the dynamic effects of SLCT under different four‐tower arrangements were significantly different from each other and the tower‐group wind vibration coefficients proposed in this paper can reflect the interference effects of tower‐group more efficient than traditional design method. The results may become a useful database for the wind‐resistance design of SLCT and provide clues for the optimization of four‐tower arrangements in power plants.     

Improving the wind‐induced human comfort of the Beijing Olympic Tower by a double‐stage pendulum tuned mass damper

With five sub towers and a maximum height of 246.8 m, the Beijing Olympic Tower (BOT) is a landmark of Beijing. The complex structural properties and slenderness of the BOT render it prone to wind loading. As far as the wind‐induced performance of this structure is concerned, this paper thus aims at a tuned mass damper‐based mitigation system for controlling the wind‐induced acceleration response of the BOT. To this end, the three‐dimensional wind loading of various wind directions are simulated based on the fluctuating wind force obtained by the wind tunnel test, by which the wind‐induced vibration is evaluated in the time domain by using the finite element model. A double‐stage pendulum tuned mass damper (DPTMD), which is capable of controlling the long period dynamic response and requires only a limited space of installation, is optimally designed at the upper part of the tower. Finally, the wind‐induced response of the structure with and without DPTMD is compared with respect to various wind directions and in both the time and frequency domains. The comparative results show that the wind‐induced accelerations atop the tower with the wind directions of 45, 135, 225, and 315° are larger than those with the other directions. The DPTMD significantly reduces the wind‐induced response by the maximum acceleration reduction ratio of 30.05%. Moreover, it is revealed that the control effect varies noticeably for the five sub towers, depending on the connection rigidity between Tower1 and each sub tower.     

Application of vector form intrinsic finite element on integrated simulation of wind turbine

Large wind turbine system is a periodic time‐varying system with many rigid‐flexible coupling bodies. It is difficult to deal with the singular stiffness matrix produced by the rotation of blades via the traditional finite element method. However, the vector form intrinsic finite element (VFIFE) method can effectively solve the geometric deformation of elastic continuum, the nonlinear or discrete constitutive model, the coupling motion continuum, and rigid body. In this study, a solver program of space beam element is developed by VFIFE method, and three typical examples are chosen to verify its accuracy. And then the integrated simulation of wind turbine system is established, and its dynamic response is analyzed. The natural frequencies of the turbine system, which are obtained by modal parameter identification, can agree well with the results obtained by traditional finite element method. The weighted amplitude wave superposition method and the proper orthogonal decomposition method as well as B‐spline surface interpolation are employed to obtain the wind time series of wind turbine under the normal operation condition. The wind‐induced dynamic response of wind turbine system is calculated by VFIFE method. The numerical results can reflect the periodic influence of gravity on the internal forces of blades and the interaction between blades and the tower.     

锥筒形风机塔架的风致响应分析

用有限元软件Abaqus对近海2.5MW的锥筒形风机塔架结构进行模态分析。通过质量-弹簧-阻尼单元模拟风机塔架的基础,提取它的前八阶模态进行分析。比较塔架固有频率和叶片的旋转频率,发现二者不会发生共振。在模态分析的基础上对风机结构整体进行风致响应分析,验证结构体系的安全性。通过对风机塔架进行风致动力响应分析,为结构的振动特性诊断和预报以及结构动力特性的优化设计提供依据。     

考虑桨叶旋转效应的海上风力发电高塔系统随机风振响应与动力可靠度分析

研究了考虑桨叶旋转效应的海上风力发电高塔系统随机动力响应与风振可靠度分析.在风场模拟中,桨叶风荷载需要考虑旋转效应的影响.因此,对塔体风荷载,直接采用基于物理机制的随机Fourier谱,而对桨叶风荷载,则采用考虑桨叶旋转机制的随机Fourier谱概念.在此基础上,结合概率密度演化理论,对海上风力发电高塔系统进行了随机动力响应分析以及基于塔顶位移响应的风振动力可靠度分析.结果表明,上述方法能够有效地进行此类结构的随机动力响应及可靠度分析.     

中空夹层钢管混凝土风力机塔架风振性能研究

传统风力发电机组塔架大多为锥形单管钢薄壁细长结构,此类结构在叶片转动及风荷载作用下易发生大的变形和振动。为克服传统风电塔自身发展的局限性并发挥中空夹层钢管混凝土(CFDST)结构优良的力学性能,基于某锥形钢塔筒,通过承载力等效提出CFDST塔筒结构形式,利用ABAQUS软件建立其风振性能有限元模型,对比了两种塔筒的振动模态。从时域和频域对二者在不同荷载工况下的动力响应特征进行对比分析,并对塔筒与叶片是否共振及瞬态冲击荷载下的振动进行了研究。结果表明:CFDST塔筒在保证原有钢塔筒抗弯承载力和刚度的同时,底部截面尺寸减小了25.6%,且不会与叶轮转动产生的谐波激励发生共振; 阻尼对风机塔筒位移、速度、加速度及应力响应幅值影响显著; 与钢塔筒相比,CFDST塔筒在正常运行荷载工况下峰值位移、加速度幅值和最大等效应力分别降低21.1%、30.2%和41.6%,而在暴风荷载工况下,分别减小14.4%、32.2%和36.3%; 研究成果可为相关塔筒的设计优化提供参考。     

Wind‐induced internal pressure effect within a novel super‐large cylindrical–conical steel cooling tower

A cylindrical–conical steel cooling tower (SCT) is a new type of very large thin‐walled, flexible structure. This study focused on the wind loads on the internal and outer surfaces of this structure and its wind‐induced responses. First, using the computational fluid dynamics method, the numerical wind tunnel was conducted to simulate a 189‐m‐high cylindrical–conical SCT, Asia's highest cooling tower that is still under construction. This numerical method was validated by comparing the wind pressures across typical cross sections of the tower model's cylindrical and conical segments with known standard curves. Based on this, the features of the airflow around the typical cross sections and its wake were extracted, and the distribution of mean wind loads along the internal and outer surfaces of the cylindrical and conical sections was obtained. Then functions for estimating the internal and outer surfaces shape factors of the cylindrical and conical segments were obtained by fitting to the simulated data. Furthermore, finite element method was used to analyze the static wind‐induced response of the cylindrical–conical SCT under internal pressure, external pressure, or both internal and external pressure. The effect patterns of internal pressures on the wind‐induced responses of the main tube, stiffening trusses, and auxiliary trusses of the tower were derived from the analysis results. Main findings of the research can provide a reference for design of very large cylindrical–conical SCTs for wind resistance in the future.     

Three‐dimensional coupled wind‐induced vibration calculation method for super high‐rise buildings based on high‐frequency force balance technology

High‐frequency force balance test is a major technical means to evaluate the wind effect of super high‐rise buildings. Most super high‐rise buildings have the characteristic that the first two‐order modal frequencies are close, and thus, considerable modal coupling effects (MCEs) may occur under wind load. For a balance model system (BMS), MCEs increase the difficulty of correcting aerodynamic distortion signals. For the wind‐induced vibration analysis of a structural system (PSS), the calculation results of the wind‐induced response and the equivalent static wind load (ESWL) may be significantly affected without considering MCE. Based on the above‐mentioned signal distortion of BMS and the modal coupling problem of PSS, this study proposes a wind‐induced vibration calculation method for the two coupled systems (BMS and PSS). The method uses the second‐order blind identification technique based on complex modal theory and the Bayesian spectral density method considering full aerodynamic characteristics to achieve effective correction of the distortion signal in BMS. In addition, it deduces the calculation method of the wind‐induced response and ESWL considering the three‐dimensional coupled vibration of a super high‐rise building. The wind effect calculation results of a 528‐m super high‐rise building confirm the necessity and effectiveness of the proposed method.     

兆瓦级风力发电机塔架的模态分析

通过对内蒙古武川地区水平轴风力机塔架的两种工况进行现场测试,用DASP系统进一步分析,得出塔架的加速度谱及特征频率;利用ANSYS有限元软件完成塔架的建模和模态分析,考虑了塔顶上方机舱总质量的影响。计算结果与实测结果为避免塔架发生共振和进一步研究风力机塔架的动力反应提供了依据,其中模态数据对风电塔架设计和结构振动控制有一定的参考价值。     

Identification of damping ratio and its influences on wind‐ and earthquake‐induced effects for large cooling towers

Standard 5% damping ratio for high‐rise concrete structures is generally used for dynamic analysis under the action of wind and earthquakes in the existing cooling tower regulations and researches. But considering the unique configuration and material attributes of large cooling towers, the actual damping ratio must be far smaller than the recommended. However, only a few field measurements of damping ratio for large cooling towers have been conducted; neither are there thorough investigation into the qualitative and quantification of wind and seismic effects under different damping ratio. To fill this gap, field measurements of a large cooling tower standing 179 m in northwestern China was performed and acceleration vibration signals at representative positions of the tower under ambient excitation were obtained. The vibration signals were preprocessed combining random decrement technique and natural excitation technique. Three pattern recognition methods (auto‐regressive and moving mean model, Ibrahim time domain, and spare time domain (STD)) were applied to analyze the frequencies, damping ratios, and modes of vibration for the first 10 order modes. Following the line of thought of modal combination, the equivalent synthetic damping ratio was derived. Under 5 damping ratios (0.5%, 1%, 2%, 3%, and 5%), a comparative analysis on the dynamic responses of the cooling tower to wind and single seismic loading by using full transient method was performed. On this basis, the patterns of influence of damping ratio on wind‐induced vibration, wind vibration coefficient, and time history and extrema of seismic responses were extracted. Finally, different combinations of dead weight, wind, temperature in winter, sunshine duration, and seismic intensity and those of accidental seismic effects (8 working conditions) were considered, using equivalent synthetic damping ratio and standard damping ratio. Thus, the most unfavorable working conditions were identified under actual and standard damping ratios for the large cooling tower. Our research findings provide reference for determining the value of damping ratio in large cooling towers and deepening the understanding on the influence mechanism of damping ratio.     

Effects of tuned mass damper on correlation of wind‐induced responses and combination coefficients of equivalent static wind loads of high‐rise buildings

Tuned mass dampers (TMDs) are employed to control the wind‐induced responses of tall buildings. In the meantime, TMD may have an impact on the correlation of wind‐induced responses and combination coefficients of equivalent static wind loads (ESWLs). First, the mass matrix and stiffness matrix were extracted in this paper in accordance with the structural analysis model of two high‐rise buildings, and on that basis, the wind‐induced vibration responses analysis model with and without TMD was established. Second, the synchronous multipoint wind tunnel test to measure the pressure was performed for two high‐rise buildings, and the time history of wind‐induced vibration responses with and without TMD was studied. Finally, the impact of TMD on the correlation of wind‐induced responses and combination coefficients of ESWLs was discussed. The results of two examples suggest that after the installation of TMD, the increase of ρ_xy was 2.1% to 35.0% and ρ_yz was 2.8% to 45.6% at all wind directions for Building 1, and the increase of ρ_xy was 3.9% to 17.1% and ρ_yz was 6.8% to 38.3% for Building 2. The combination coefficients of ESWLs of two buildings were 3% to 6% larger than that of the original structure. The conclusion of this paper can be referenced by the wind resistant design of high‐rise buildings with TMD.     

风力发电机组的有限元分析及动力特性研究

风力发电近年发展迅猛,中国是世界第一风能大国,安装有大量风力发电机组.风力发电机组受到风荷载和地震等动力作用,通常采用有限元方法建立风力发电机组的动力学模型.由于叶片参数不易获得,有限元建模可将叶轮和机舱质量集中在塔架顶部(模型1),或采用等截面均质梁模拟叶片(模型2).本文基于某65kW风力发电机组试验数据,分析了两种模型动力特性的差异.结果表明:模型1的1、2阶塔架频率与试验数据误差在10%以内,模型2可进一步减小误差.但叶片刚度对风力发电机组频率影响较大,如果叶片刚度选择不当,会造成较大误差.模型1和模型2的1阶塔架模态几乎相同,但2阶模态存在一定差异.     

Theoretical study and experimental verification of vibration control of offshore wind turbines by a ball vibration absorber

In this paper, a ball vibration absorber (BVA) is introduced for vibration control of offshore wind turbines. The dynamic responses of offshore wind turbines equipped with a BVA are presented. Both theoretical and experimental investigations are carried out. An analytical model for the wind turbine tower system with installed BVA is developed based on Lagrange's equation. The BVA-structure integrated equations are derived and solved in both time domain and frequency domain. A series of shaking table tests on a 1/13-scale wind turbine model with and without a BVA were carried out to evaluate the effects of BVA on the vibration mitigation of the wind turbine tower system under earthquakes and equivalent wind-wave loads. Numerical simulations of the system are performed and compared with the experimental results. Good agreement between the numerical and experimental results is observed. The results indicate that BVA could effectively improve the performance of the offshore wind turbine.     

160‐m‐Fachwerkturm für eine Windenergieanlage – Die höchste Windenergieanlage der Welt

160 m self‐supporting lattice tower for a Wind Energy Conversion System. The highest wind energy system in the world. The highest wind energy conversion system of the world have been erected in Laasow near (by) Cottbus. The height of the tower is 160 m, and the height of the whole system up to the tips of the rotor blades is 205 m. The self‐supporting lattice tower from SeeBa supports a turbine EL2500 produced by Fuhrländer. The estimated output of about 7 million kWh corresponds to the consumption of about 1800 4‐person households. The advanced height of the structure represents a major challenge to static and design engineers, to suppliers and to the erection staff. This paper will give a short summary of the requirements concerning the static analysis for this tower. The differences between the present lattice tower and the normally used tubular steel towers will also be pointed out.     

Motion analysis of a floating offshore wind turbine considering rotor-rotation

Development of offshore wind energy is desired as a countermeasure against global warming. This article presents motion analysis of a floating offshore wind turbine during the rotor-rotation under wind loads. A 2 MW downwind turbine is mounted on a floating foundation of the spar-type. The wind loads acting on the rotor blades are calculated using the blade element momentum theory. The multibody dynamics system theory is employed to consider the effect of the rotor-rotation. As a result, the motion of yaw, sway and roll are generated due to the effect of the gyro-moment for the rotor-rotation.     

基于风洞试验的苏通大跨越输电塔风振系数研究

苏通大跨越输电塔的结构形式有别于普通的钢结构杆塔,其塔身下部结构采用钢管混凝土、上部结构采用钢管,质量突变大,主要受风荷载控制,并且塔高超出GB 50009—2012《建筑结构荷载规范》的梯度风高度限制。为此,采用气动弹性模型和刚性模型的边界层风洞试验确定苏通大跨越输电塔的风致响应和气动力,基于试验数据计算不同风向角下的惯性力风振系数、位移风振系数和有效荷载风振系数,并进行对比。并通过有限元分析梯度风高度对惯性力风振系数的影响,同时将有限元分析得到的风振系数分布和加权值与DL/T 5154的风振系数规定作比较。结果表明：上述3种风振系数分布规律并不相同,由其分别确定的等效位移接近于试验值;考虑梯度风高度后,风振系数变小,分布形状影响小;苏通大跨越输电塔的惯性力风振系数加权值小于1.6,且风振系数由下到上不是单调增大。