风力机叶片损伤演化模拟

根据风力机叶片的实际铺层和使用状况,以刚度退化模型为基础,发展了一个适合于风力机叶片的损伤演化模型,模型的基本思路是以单层板的刚度退化规律为基础,结合强度退化来预测整个叶片的损伤演化过程。考虑材料的各向异性性质,对叶片材料各组分的性能退化进行了分析,用3个标量来累积不同方向的损伤,给出了损伤累积规律。通过材料试验拟合出了损伤累积公式中的相关系数,最后模拟了某叶片真实疲劳试验过程,并将模拟结果与试验结果进行了比较,证实了模型的可用性。     

恒幅载荷下复合材料剩余刚度退化模型

在分析现有纤维增强复合材料层合板疲劳累积损伤模型的基础上,根据复合材料层合板疲劳损伤演变过程和剩余刚度退化规律,提出一种用于描述恒幅疲劳载荷作用下复合材料层合板刚度退化规律的模型.该模型适用于描述复合材料层合板的三阶段非线性刚度退化轨迹.通过T300/HT3复合材料层合板、玻璃纤维/环氧复合材料层合板以及T300/QY...     

基于Ansys与nCode联合仿真的风力机叶片疲劳分析

为了研究风力机叶片疲劳破坏问题,文章建立了某1.5 MW商用叶片模型,通过Ansys与nCode软件联合仿真,对其进行了疲劳寿命分析。为进一步研究叶片疲劳损伤规律,对叶片在各个疲劳载荷工况下的损伤进行了分析,结果表明:疲劳损伤主要位于叶根前缘和前缘与主梁连接处,并且主要出现在风速较大、发生次数较多、纵向湍流强度较强的工况;叶片总体疲劳寿命约为24.5 a,满足疲劳强度设计要求。     

大型风机叶片疲劳加载模式的能耗分析

设计了两套风机叶片疲劳加载试验方案:液压缸强迫加载模式和偏心质量块共振加载模式,并给出了两种模式下的能量耗散方程。采用多级载荷加载试验获得沿叶片展向的挠度分布情况和加载点刚度值,通过叶片的自由衰减试验获得阻尼比值。最后对aeroblade1.5-40.3风机叶片进行1个振动周期的能耗计算,得出在相同振幅下,共振加载模式的能耗小于强迫加载模式能耗的1/3。研究结果为后续的风机叶片疲劳加载试验打下基础。     

风电叶片疲劳试验载荷确定方法研究

文章以1.0MW风电叶片(DF64A)为例,研究了在单点单轴恒幅值加载方式下,疲劳试验的疲劳载荷计算方法。根据Bladed软件仿真得出的叶片在风场的疲劳载荷谱(Markov矩阵),利用疲劳损伤理论分析方法及有限元软件研究分析了叶片疲劳试验载荷设计点的位置;最终确定了疲劳载荷设计点在单轴疲劳载荷My作用下的疲劳损伤值;并给出了单点恒幅值加载方式下,该位置的静态载荷参数和动态加载载荷。最终确定出试验方案。     

随机载荷下风电叶片复合材料剩余强度概率模型

为对随机载荷作用下风电叶片复合材料(即纤维增强复合材料)的剩余强度进行评估,并考虑载荷的随机性及材料性能的分散性对剩余强度概率分布的影响。首先,根据Miner理论及全概率公式建立随机载荷作用下风电叶片复合材料疲劳寿命的预测模型;然后,基于剩余强度与剩余寿命取决于材料内部同一损伤状态的假设,推导出随机载荷作用下风电叶片复合材料剩余强度的概率模型;最后,通过风电叶片复合材料层合板(由多个单层板粘接在一起组成的整体结构)的静强度实验数据与疲劳寿命实验数据对所建模型的有效性进行验证。结果表明:所建模型能反映风电叶片复合材料剩余强度退化的一般规律,对随机载荷作用下风电叶片复合材料的寿命预测及可靠性评估具有一定指导意义。     

限功率控制下风电机组叶片疲劳损伤研究

基于叶素-动量理论计算风电机组叶片气动载荷,建立其疲劳载荷模型;将叶片简化为悬臂梁,采用雨流计数法、Goodman经验公式和Miner线性累计损伤理论计算风力机叶片疲劳损伤和等效疲劳载荷;根据2种限功率控制策略计算不同限功率水平和湍流强度下风力机叶片单位时间的疲劳损伤量,分析限功率运行工况对叶片疲劳损伤的影响。结果表明,新型限功率控制策略可减少变桨系统的动作频率和动作幅度,但其稳定运行状态对叶片的疲劳损伤量大于传统限功率控制策略。最后通过三维函数拟合得到疲劳损伤函数,可应用于限功率条件下风电场优化调度。     

基于动力学的风力机齿轮传动系统可靠性研究

为正确评估齿轮传动系统齿面接触疲劳寿命,以2 MW风力发电机齿轮传动系统为研究对象,引入风场风速变化规律并选用weibull分布建立随机风速模型。考虑外部风载以及由齿轮、轴承刚度等引起的内部载荷激励,建立行星齿轮传动系统平移-扭转动力学模型,求得传动系统各齿轮副动态啮合力并计算相应的应力历程。针对齿轮传动强度及受载随机性的特点,以轮齿的强度退化表征疲劳效应,基于非线性疲劳损伤累积理论建立剩余强度模型,在传统应力-强度干涉理论的基础上,得到随机风载作用下齿轮传动系统动态可靠度功能函数,通过摄动法对零部件的动态可靠度变化曲线进行描述。结果表明：在强度退化和随机载荷联合作用下,风力机系统各齿轮疲劳可靠度随服役时间出现逐渐下降的趋势,且服役前期可靠度下降趋势较快,中后期下降趋势逐渐减缓,强度退化形式及载荷大小影响着可靠度的变化趋势。该模型反映了齿轮传动系统可靠度随服役时间的变化规律,为产品的可靠性设计及疲劳寿命预测提供了参考。     

RESEARCH ON ANALYSIS APPROACH OF STRENGTH AND FATIGUE LIFE OF HORIZONTAL AXIS WIND TURBINE HUB

针对水平轴风力机轮毂复杂的几何外形、载荷与边界条件,研究其强度和疲劳寿命数值分析方法.应用结构分析软件ANSYS并结合疲劳分析软件FE-safe对风力机轮毂进行强度和多轴疲劳寿命分析.研究了风力机轮毂结构强度数值分析中的一些关键技术问题,如网格划分、载荷施加、边界约束条件的处理及分析技巧等;利用叶片根部极限载荷对轮毂进行强度校核,得出轮毂极限载荷下的应力分布.基于风力机叶片根部随机载荷谱和线性累积损伤方法,研究了轮毂多轴疲劳特性及疲劳寿命分析方法;研究了轮毂材料的S-N曲线定义和各工况下随机载荷谱的分析处理方法.算例表明:本文的工作为水平轴风力机轮毂强度、刚度及多轴疲劳寿命分析等提供了实用的分析方法.     

风力机传动链齿轮齿根疲劳裂纹扩展剩余寿命评估

在叶轮气动载荷模型、柔性传动链模型和齿根弯曲应力模型的基础上,建立了随机风速下风力机传动链齿轮齿根疲劳裂纹扩展剩余寿命计算模型,对不同风速下的齿根弯曲应力进行了计算,分析了随机载荷下裂纹的扩展速率.对1.5 MW风力机太阳轮齿根疲劳裂纹的扩展进行了分析.结果表明:风力机齿轮齿根疲劳裂纹扩展寿命主要受风载荷影响,且紧急制动等冲击对裂纹扩展后期的影响不可忽视.     

Influence of a wind turbine service life on the mechanical properties of the material and the blade

This paper presents results out of investigations of the DEBRA‐25 wind turbine blades. Almost unique in the history of modern wind energy, these blades were in operation for 18 years next to a weather station and were investigated afterward. Therefore, the loads experienced in the operational life could be post‐processed accurately with the measured data of the weather station and the turbine. The blades are made of materials that are similar with today's wind turbines. Furthermore, intensive laboratory tests and free field tests have been carried out, and all load assumptions and data and results are still available today. The results include experimental investigations on the moisture content of the load‐carrying material, static and fatigue behavior of the material, the relaxation of the coupling joints, the natural frequencies of the blade and a full scale static blade test. It is shown that the structural performance of the DEBRA‐25 service blades is comparable with modern wind turbine blades. Although some damage was found by visual inspection, the service blade of the DEBRA‐25 showed excellent mechanical behavior in the full scale blade test. Only small changes of the edgewise eigenfrequencies were detected. The pre‐tensioning forces of the IKEA bolts, where the two blade parts are connected, were measured and were still adequate. Copyright © 2012 John Wiley & Sons, Ltd.     

Representation of wind turbine blade responses in power production load cases by linear mode shapes

The wind turbine industry is designing large MW size turbines with very long blades, which exhibit large deflections during their operational life. These large deflections decrease the accuracy of linear models such as linear finite element and modal‐based models, in which the structure is represented by linear mode shapes. The aim of this study is to investigate the competence of the mode shapes to represent the large blade responses in normal operation load cases. For this purpose, blade deflections are projected onto the linear modal space, swept by mode shape vectors. The projection shows the contribution of each mode and the projection error. The blade deflections are calculated by a nonlinear aero‐servo‐elastic solver for power production fatigue load cases with normal turbulence. The mode shapes are calculated at the steady‐state deflected blade position computed at different wind speeds. Three reference turbine blades are used in the study to evaluate the effects of various blade design parameters such as length, stiffness, mass, and prebend. The results show that although the linear mode shapes can represent the flapwise and edgewise deflections accurately, axial and torsional deflections cannot be captured with good accuracy. The geometric nonlinear effects are more apparent in the latter directions. The results indicate that the blade deflections occur beyond the linear assumptions.     

Load analysis of hydraulic‐pneumatic flywheel configurations integrated in a wind turbine rotor

In this paper, the impact on the mechanical loads of a wind turbine due to a previously proposed hydraulic‐pneumatic flywheel system is analysed. Load simulations are performed for the National Renewable Energy Laboratory (NREL) 5‐MW wind turbine using fatigue, aerodynamics, structures, and turbulence (FAST). It is discussed why FAST is applied although it cannot simulate variable rotor inertia. Several flywheel configurations, which increase the rotor inertia of the 5‐MW wind turbine by 15%, are implemented in the 61.5‐m rotor blade. Load simulations are performed twice for each configuration: Firstly, the flywheel system is discharged, and secondly, the flywheel is charged. The change in ultimate and fatigue loads on the tower, the low speed shaft, and the rotor blades is juxtaposed for all flywheel configurations. As the blades are mainly affected by the flywheel system, the increase in ultimate and fatigue loads of the blade is evaluated. Simulation results show that the initial design of the flywheel system causes the lowest impact on the mechanical loads of the rotor blades although this configuration is the heaviest.     

Load alleviation of wind turbines by yaw misalignment

Vertical wind shear is one of the dominating causes of load variations on the blades of a horizontal axis wind turbine. To alleviate the varying loads, wind turbine control systems have been augmented with sensors and actuators for individual pitch control. However, the loads caused by a vertical wind shear can also be affected through yaw misalignment. Recent studies of yaw control have been focused on improving the yaw alignment to increase the power capture at below rated wind speeds. In this study, the potential of alleviating blade load variations induced by the wind shear through yaw misalignment is assessed. The study is performed through simulations of a reference turbine. The study shows that optimal yaw misalignment angles for minimizing the blade load variations can be identified for both deterministic and turbulent inflows. It is shown that the optimal yaw misalignment angles can be applied without power loss for wind speeds above rated wind speed. In deterministic inflow, it is shown that the range of the steady‐state blade load variations can be reduced by up to 70%. For turbulent inflows, it is shown that the potential blade fatigue load reductions depend on the turbulence level. In inflows with high levels of turbulence, the observed blade fatigue load reductions are small, whereas the blade fatigue loads are reduced by 20% at low turbulence levels. For both deterministic and turbulent inflows, it is seen that the blade load reductions are penalized by increased load variations on the non‐rotating turbine parts. Copyright © 2013 John Wiley & Sons, Ltd.     

Dynamic analysis tool development for swept wind turbine blades

Because of their aeroelastic behavior, swept wind turbine blades offer the potential to increase energy capture and lower fatigue loads. This article describes work to develop a dynamic analysis code for swept wind turbine blades. This work was an outgrowth of a U.S. Department of Energy contract on swept blades, where the authors used the Adams? dynamic software (MSC Software Corporation, Santa Ana, CA, USA). The new code is based on the National Renewable Energy Laboratory's FAST code and allows for lower cost analysis and faster computation times for swept blades. The additions to the FAST code include the geometry and mode shapes required for the bending and twisting motion of the swept blade. In addition, a finite element program to determine mode shapes for the swept blade was developed. Comparisons of results obtained with the new code and analytical solutions for a curved cantilever beam show good agreement in local torsional deflections. Comparisons with field data obtained for a 750 kW wind turbine with swept blades were complicated by uncertainties in the test wind speed and turbine controller settings.Copyright © 2012 John Wiley & Sons, Ltd.     

Model of wind shear conditional on turbulence and its impact on wind turbine loads

We analyse high‐frequency wind velocity measurements from two test stations over a period of several years and at heights ranging from 60 to 200 m, with the objective to validate wind shear predictions as used in load simulations for wind turbine design. A validated wind shear model is thereby proposed for flat terrain and that can significantly decrease the uncertainty associated with fatigue load predictions for wind turbines with large rotors. An essential contribution is the conditioning of wind shear on the 90% quantile of wind turbulence, such that the appropriate magnitude of the design fatigue load is achieved. The proposed wind shear model based on the wind measurements is thereby probabilistic in definition, with shear jointly distributed with wind turbulence. A simplified model for the wind shear exponent is further derived from the full stochastic model. The fatigue loads over different turbine components are evaluated under the full wind measurements, using the developed wind shear model and with standard wind conditions prescribed in the IEC 61400‐1 ed. 3. The results display the effect of the Wöhler exponent and reveal that under moderate turbulence, the effect of wind shear is most pronounced on the blade flap loads. It is further shown that under moderate wind turbulence, the wind shear exponents may be over‐specified in the design standards, and a reduction of wind shear exponent based on the present measurements can contribute to reduced fatigue damage equivalent loads on turbine blades. Although the influence of wind shear on extreme loads was found to be negligible, the IEC 61400‐1 wind shear definition was found to result in non‐conservative estimates of the 50 year extreme blade deflection toward the tower, especially under extreme turbulence conditions. Copyright © 2014 John Wiley & Sons, Ltd.     

风力机叶片动力特性实验台设计

设计开发了一种风力机叶片动力学特性实验台,可以进行风力机叶片的静载荷实验、模态测试、叶片损伤测试、模拟桨叶结冰附着物载荷实验、桨叶疲劳载荷实验以及破坏性实验等。介绍了实验台的设备组成、结构特点以及该实验台的主要功能,在实验台上进行了风力机叶片的静态载荷实验和模态测试,得出了实验用风力机叶片的六阶模态参数,利用MAC、MOV两种模态判定准则对试验结果进行了验证。