Wind field simulation and wind‐induced responses of large wind turbine tower‐blade coupled structure

Herein, by a case study on a 5‐MW wind turbine system developed by Nanjing University of Aeronautics and Astronautics, the wind field simulation and wind‐induced vibration characteristics of wind turbine tower‐blade coupled systems is analyzed. First, the blade‐nacelle‐tower‐basis integrated finite element model with centrifugal forces induced by rotational blades is established. Then, based on a harmony superposition method and the modified blade element‐momentum theory, the fluctuating wind field of tower‐blade coupled systems is simulated, which considers wind shear effect, tower shadow effect, rotational effect, blade‐tower dynamic and model interaction effects. Finally, the wind‐induced dynamic responses and wind vibration coefficients of the wind turbine tower‐blade coupled structure are discussed through the ‘consistent coupled method’ previously proposed by us. The results indicate that the wind‐induced responses of a large wind turbine tower‐blade coupled structure present complicated modal responses and multimode coupling effect. Additionally, the rotational effect would amplify aerodynamic loads on blades with high frequency, wind‐induced dynamic responses and wind vibration coefficients of wind turbine tower. The centrifugal force effect could also amplify natural vibration frequency of the tower‐blade coupled system and reduce the wind‐induced dynamic responses and wind vibration coefficients of wind turbine tower. The research could contribute to wind‐resistant design of structure for a large‐scale wind turbine tower‐blade system. Copyright © 2014 John Wiley & Sons, Ltd.     

2.5MW海上风力发电机钢塔筒地震响应分析

以福建某海滩单机容量为2.5MW海上风力发电机为原型,应用ABAQUS有限元软件分别建立风力发电塔的地基刚接模型和考虑土与结构相互作用的质量-弹簧-阻尼模型.通过给模型施加地震波,对风力发电塔体系进行地震动力作用时程分析.主要研究了土与结构相互作用（Soil-structure interaction,SSI）对风力发电塔体系地震响应的影响.研究表明,SSI效应降低了风力发电塔的地震应力响应,增加了其地震位移响应.     

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.     

Stochastic seismic response analysis of offshore wind turbine including fluid‐structure‐soil interaction

This paper presents the stochastic seismic response analysis of offshore wind turbines subjected to multi‐support seismic excitation by using a three‐dimensional numerical finite element model considering viscous boundaries. The seawater‐offshore wind turbine‐soil interaction system is modelled by the Lagrangian (displacement‐based) fluid and solid‐quadrilateral‐isoparametric finite elements. The random seismic excitation is described by the filtered white noise model and applied to each support point of the three‐dimensional finite element model of the coupled interaction system. The research conducts a parametric study to estimate the effects of variable seawater level, different foundation soil types and support site conditions on the stochastic behaviour of the offshore wind turbine coupled interaction system. The finite element model of coupled interaction system was also analyzed to examine the effect of the surrounding ice sheet on the stochastic response of the coupled system with and without ice sheet. The results obtained for different cases are compared with each other. Copyright © 2010 John Wiley & Sons, Ltd.     

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.     

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.     

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。     

兆瓦级风力发电结构地震作用研究

近年来,国内外的风力发电发展迅速,位于地震高烈度区的风电场越来越多,风电结构的抗震设计日趋重要。然而,目前国内外还没有针对风力发电结构抗震设计的成熟标准。虽然IEC等规范给出了简略的风电结构抗震计算方法,但这些简化对于这种特殊的高耸结构是否准确合理还需要验证。为了论证IEC简化方法、底部剪力法、振型分解反应谱法等国内外的规范方法对风力发电机构地震作用评估的合理性,文中采用这些规范方法对风电结构的地震作用做了分析。选取了一组实际地震波,使它们的反应谱与规范反应谱相接近,用这一组实际地震波的反应谱对风电结构进行振型分解反应谱法计算。计算结果与规范反应谱方法很接近,说明这组地震波能够反映规范反应谱的特性。以这组地震波作为输入,用有限元方法对风电结构进行了地震作用计算。通过对规范方法和有限元方法的结果进行比较,发现规范方法在风电结构的抗震设计中是偏于保守的。     

向量式有限元膜单元及其在膜结构褶皱分析中的应用

向量式有限元法是一种基于点值描述和向量力学理论的分析方法,可有效模拟结构的空间大位移、大转动行为。推导了三角形膜单元的向量式有限元基本公式,详细阐述了通过逆向运动获得单元节点纯变形位移以及在变形坐标系下求解单元节点内力的方法。在此基础上编制了膜单元的计算程序,并通过算例分析验证了理论推导的正确性及所编制程序的可靠性。进一步将向量式有限元引入膜结构的褶皱分析,采用主应力 主应变准则和修正本构矩阵方法处理膜结构的褶皱问题,对一典型膜结构在面外荷载作用下的力学行为及褶皱发展情况进行跟踪分析,成功捕捉了从褶皱出现、褶皱大范围扩展直至褶皱最终消失的全过程,证明了该方法在膜结构皱褶分析中可有效克服传统有限元方法存在的单元刚度矩阵奇异、迭代不易收敛等问题。     

基于向量式有限元的实体结构非线性行为分析

基于向量式有限元基本理论,推导了四节点四面体实体单元的基本理论计算式,通过参考平面的逆向运动来获得单元节点纯位移,进而通过变形坐标系获得单元节点内力。将双线性弹塑性材料本构模型引入向量式有限元实体单元,以实现考虑塑性硬化效应时实体结构的材料非线性行为分析。针对实体结构的碰撞接触行为,通过实体外表面质点和三角形网格面的单向碰撞检测来处理碰撞检测问题,采用基于中央差分的罚接触力响应方法来处理碰撞响应问题。弹塑性材料和碰撞接触均作为单独的计算分析模块引入向量式有限元实体单元。算例分析表明,所编制的向量式有限元实体单元程序可以有效实现线性和非线性材料情况下实体结构的静动力、大变形、大转动以及碰撞接触行为分析,验证了所提理论计算式和编制程序计算结果的可信度。     

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.     

Numerical Modeling of Dynamic Behavior of Annular Tuned Liquid Dampers for Applications in Wind Towers

Abstract: In this study, the performance of annular liquid tanks as a tuned liquid damper (TLD) in mitigating the vibration of wind turbines was investigated using a numerical model. A proposed hybrid wind tower model composed of a concrete shaft and a steel mast with a height of 150 m was simulated using a single‐degree‐of‐freedom system. The structural domain including the tank wall and a rigid mass was modeled using finite element method, while the fluid domain was simulated by finite volume method using CFX software. A parametric study was carried out to investigate the behavior of annular TLD under harmonic loads for different mass and frequency ratios as well as displacement amplitudes. The damping characteristics of the annular TLD model were derived by comparing the numerical results with an equivalent linear model. In addition, the effectiveness of annular TLD was estimated by comparing the numerically calculated damping ratios with those corresponding to the optimum damping ratio values derived for a particular mass ratio based on the concept of tuned mass damper. It was found that that the annular TLD is effective when the amplitude of excitation is small. Moreover, the response of TLD in terms of nonlinear free surface sloshing and the energy dissipated by the system was discussed. Finally, the effectiveness of annular TLD in reducing the structural response of wind turbine towers under random vibrations was evaluated and discussed.     

Reliability-based design of wind turbine blades

Reliability-based design of wind turbine blades requires identification of the important failure modes/limit states along with stochastic models for the uncertainties and methods for estimating the reliability. In the present paper it is described how reliability-based design can be applied to wind turbine blades.For wind turbine blades, tests with the basic composite materials and a few full-scale blades are normally performed during the design process. By adopting a reliability-based design approach, information from these tests can be taken into account in a rational way during the design process. In the present paper, a probabilistic framework for design of wind turbine blades are presented and it is demonstrated how information from tests can be taken into account using the Maximum-Likelihood method and Bayesian statistics.In a numerical example, the reliability is estimated for a wind turbine blade in both ultimate and fatigue limit states. Information from tests is used to formulate the stochastic models used in the limit state equations. Partial safety factors for use in traditional deterministic design are estimated using the stochastic models.     

风力发电结构动力反应的一体化有限元模型分析

本文通过对风力发电结构系统地震作用下的动力反应的大量研究,提出了一种可用于分析风力发电结构的"桨叶—塔体—基础"一体化有限元模型,并结合土-结构相互作用的分析形成了另一种对比模型。利用上述分析模型对风力发电结构分别进行动力荷载作用下的模态分析和动力时程分析。结果表明,地震作用下考虑土-结构相互作用对风力发电结构动力响应的影响不容忽视,并且可为工程设计提供参考。     

海上风机的分部与整体结构设计现状

海上风机结构是一个相对复杂的结构系统,其动力响应受到多种环境因素影响,且多种荷载之间的相互作用是一种非线性行为。此外,风力机不同组成部分之间都有其独特特性,结构间的耦合作用决定着风机在非平稳环境力作用下的整体动力反应。分别综述了风机叶片的转动与弹性变形的耦合、塔架与叶片的耦合、塔架的优化设计、基础的模型以及结构随参数变化敏感性分析。最后对未来有待于进一步研究的问题进行介绍。     

基于流–固耦合的近海风电基础地震反应分析

结合近海风电单桩及四桩基础支撑体系工程实际场地资料,采用有限元数值分析方法,考虑水–土–结构动力相互作用,即考虑流–固耦合效应、饱和土的多孔介质渗流属性及桩–土接触相互作用,分析结构体系动力特性及地震反应。分析单桩有水与无水及四桩有水与无水4种工况支撑体系的自振特性和单桩有水与无水2种工况支撑体系的地震反应。结果表明:水层对结构低阶频率影响不大,对高阶频率降低幅度较大;水层对体系的水平位移、竖向沉降、峰值加速度及有效应力均有不同程度地削减;地震作用下土体的超静孔隙水压力呈现波动特性;结构的位移及应力响应均能满足规范要求。证明考虑多介质耦合的动力有限元分析方法是解决复杂海上风电基础地震响应的有效方法。     

大跨越输电塔线体系动力特性及风振响应

以正在建设中的世界第一高 3 46 5m的输电塔———江阴大跨越为工程背景 ,建立了考虑输电线、绝缘子和塔架耦合的两塔三段线分析模型 ,用非线性有限元分析方法对大跨越塔线体系进行了风振响应分析 ,并进行了气动弹性模型风洞试验。通过理论计算和试验研究 ,指出输电线对塔架的自振频率影响较小 ,而结构体系风振响应分析则应考虑塔线耦合影响 ,提出的分析方法和得到的结论可供实际工程抗风设计参考     

An experimental and numerical approach to investigate the dynamic response of a four‐flue chimney of a thermo‐electrical plant

This paper describes an experimental procedure and a numerical model for the study of the dynamic behaviour of a chimney of a thermo‐electrical plant. The experimental part is based on the measurement of the structure's dynamic response by means of several accelerometers. Different signals from forced time‐periodic excitations, spanning a range of frequencies, have been collected and compared with those from a finite elements model. In particular, the first four modal shapes and their frequencies are computed. Following this validation, the finite element model has also been applied to investigate the response of the chimney subjected to a generic wind periodic excitation (vortex shedding). The numerical results show good agreement with the experimentally collected data. Copyright © 2003 John Wiley & Sons, Ltd.     

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。     

列车振动下隧道与土体响应的双尺度耦合模拟

 对于土体离散–连续耦合问题,给出通过强化边界耦合力在离散和连续模型中的相容性,将提取边界耦合节点力转化为寻优问题的新方法,并用Lagrange乘子法求解。将此方法嵌入离散–连续双尺度耦合动力模型,模拟列车振动下隧道与土体的动力响应。用相互作用的离散颗粒模拟隧道附近土体,远离隧道的土体用连续模型模拟,编写结构的动力有限元程序嵌入离散元软件中来模拟隧道。通过离散元软件PFC2D和有限差分软件FLAC2D的交互运算实现耦合过程。在耦合边界通过交换速度和力保证耦合模型的连续性,通过自振柱模拟使离散区域土体的宏观性质与连续土体模型一致。通过比较耦合方法与只用连续模型模拟得到的结果,说明提出方法的有效性。双尺度耦合模型可以有效描述动力响应中隧道附近土体的细观特性,并极大降低离散元的模拟规模,减少模拟时间,适用于振动在半无限体中传播时重点考察区域土体的细观分析。