海上风电结构横风向气动力阻尼特性研究

基于横风向气动力阻尼理论计算模型,以NREL-5 MW海上风电机组为例,对其运行过程中横风向气动力阻尼进行计算,并采用FAST软件对计算结果进行验证。之后,研究转速、叶片桨距角和运行方式对横风向气动力阻尼的影响。研究结果表明：NREL-5 MW海上风电机组结构运行状态下的横风向气动力阻尼在0%~0.8%范围内变化,其随风电机组运行转速及叶片桨距角的增大而增大;此外,海上风电机组不同运行方式对其横风向气动力阻尼也会产生较大影响。     

遗留桩坑对临近复合筒型基础倾斜率的影响

针对某海上风电项目,基于ABAQUS三维数值软件定量分析桩坑与复合筒型基础的距离、桩坑尺寸及深度等参数变化对复合筒型基础结构泥面倾斜率的影响,引入可反映桩坑充盈固结程度的系数γ与切线斜率K。结果表明：随着桩坑尺寸增加,复合筒型基础泥面倾斜率呈非线性增长,且均向桩坑所在方向倾斜;桩坑深度大于复合筒型基础入土深度时,基础倾斜率增长较快;研究表明筒型基础泥面倾斜率对大深度、近距离桩坑内部土体强度尤为敏感,拟通过该文研究为复合筒型基础风电机组安装船舶选型及布置提供理论依据。     

考虑风速风向联合概率分布的风电塔筒结构风致疲劳寿命评估

针对风向对风力机塔筒疲劳产生影响的问题,基于实测数据对考虑风速风向联合概率分布的风电塔筒结构的风致疲劳寿命展开研究。首先结合甘肃安西地区37 a的实测风速风向数据,给出风速风向联合概率分布。然后利用主S-N曲线法分别对不同风向和不同风速下风力机塔架结构法兰及门洞区域的响应规律进行分析。最后考虑风速风向联合概率分布,对风电塔筒结构风致疲劳寿命展开研究。结果表明：门洞朝向与风轮朝向的夹角变化和风速的改变均对风电塔筒的风致疲劳寿命有一定影响,其中门洞朝向与风轮朝向夹角为225°时疲劳寿命最长,风速为10~14 m/s时疲劳寿命变化幅度最大;考虑风速风向联合概率分布能更准确地计算风力机结构的风致疲劳寿命,且以此为依据对门洞朝向进行调整可延长其疲劳寿命,因此建议对风电塔架进行设计时,应考虑风电场所在地区的风速风向联合概率分布。     

海上风电单柱复合筒型基础沉放过程分析

单柱复合筒型基础是中国国内自主研发的新型海上风电基础结构型式，以海上风电单柱复合筒型基础为研究对象，通过现场原型试验的方法，对首批海上风电单柱复合筒型基础的沉放过程进行分析，并提供现场施工监测数据。研究结果表明：单柱复合筒型基础可实现吸力安装下沉，且在调平上具有极强的可控性，可为筒型基础今后的施工及沉放研究提供重要的参考数据。     

船舶撞击下海上风电复合筒基础裂纹扩展研究

为研究海上风电复合筒基础遭遇船舶撞击下的开裂情况,采用ABAQUS软件,运用扩展有限元方法(XFEM)模拟分析5000 t船舶以不同速度撞击复合筒基础过渡段时结构混凝土裂纹扩展变化状态。结果表明:5000 t船舶以2 m/s的速度撞击时,该实验复合筒基础结构安全;碰撞持续的时间和最大接触力随速度的增大而增加;该方法可较为准确地预测基础过渡段在冲击荷载下的裂纹扩展情况,可为海上风力发电机组基础结构设计提供参考依据。     

筒间距对四筒导管架基础在砂土中承载特性的影响

导管架吸力筒基础是近年来兴起的一种新型的海上风电基础,目前对其承载特性的研究相对较少。针对四筒导管架海上风力机基础,通过建立不同筒间距的四筒导管架基础有限元模型,研究了筒间距对导管架基础在砂土中极限承载力的影响。研究发现：导管架基础的竖向承载力受筒间距变化的影响不大,而极限水平、抗弯以及抗扭承载力随筒间距的增大而呈现明显的增加趋势。     

海上风电复合筒型基础结构浮运分析

通过使用MOSES软件建立海上风电复合筒型基础结构气浮拖航模型,对气浮结构进行浮态、初稳性高度、频域和时域分析,其模拟分析与理论计算结果吻合,可靠性较高。同时,采用施工现场的拖航条件,通过时域分析能得到复合筒型基础结构拖航时的拖缆力、结构内舱气压和海上风机复合筒型基础结构各向加速度时程变化曲线,结果表明复合筒型基础具有稳定的自浮拖航浮运特性。     

海上风电全钢质筒型基础波浪疲劳分析与优化

疲劳是控制海上风电基础结构安全的主要因素之一，针对海上风电全钢质新型筒型基础结构疲劳问题展开研究，基于随机波浪理论与频谱分析方法，阐述了长期海况分布下结构交变应力服从Rayleigh分布的疲劳损伤累积计算方法；借助全钢质海上风电筒型基础基于前述理论开展了疲劳损伤与寿命计算，获得筒型基础主要的疲劳破坏点集中在斜撑与圆柱体连接的位置，并基于此进行了结构局部优化，结果对比表明关键部位的几何优化可极大降低应力集中程度，减小疲劳累积损伤，同时也验证了疲劳计算结果对热点应力水平具有高敏感性。     

四筒型基础气浮过程自振特性及运动响应研究

针对多筒型基础气浮过程中的动力及运动响应问题,设计了筒间距为2.5倍筒直径的四筒型基础,通过比尺为1∶25的物理模型试验并结合数值模拟的方法,对结构在静水中的自振特性和规则波下运动响应的变化规律进行研究。研究结果表明：建立的数值分析模型能够较好地预测结构静水中自振特性以及波浪中运动响应的变化趋势;随着吃水的增加,该四筒型基础的有阻尼摇荡自振周期呈增大的趋势,而附加质量系数和阻尼比呈下降的趋势,结构摇荡运动的附加质量系数取值在1.4～1.7之间变化;吃水的增加能够改善结构的摇荡运动性能,但是增大了结构的垂荡响应以及接近纵摇角最大幅值的周期范围;水越浅,摇荡运动越大。     

变风向通风对池火火焰长度的影响

通过改变风速以及纵向风与燃料表面之间的风向角,研究了风速和风向变化对池火火焰长度的影响.研究结果表明,随着风速的增加,酒精池火和正庚烷池火表现出迥然不同的特征.在本研究工况条件下,酒精池火的火焰长度随着风速的增大先增长,而后逐步缩短;正庚烷池火的火焰长度随着风速的增大首先增长,而当风速增大到一定值后,其火焰长度保持相对稳定.实验发现,酒精池火和正庚烷池火的火焰长度均随着风向角的增大而减小,相同面积的燃料盘,其火焰长度与燃料盘顺风面边长成正比,与背风面等无关.     

The dynamics of an offshore wind turbine in parked conditions: a comparison between simulations and measurements

Offshore wind turbines are complex structures, and their dynamics can vary significantly because of changes in operating conditions, e.g., rotor‐speed, pitch angle or changes in the ambient conditions, e.g., wind speed, wave height or wave period. Especially in parked conditions, with reduced aerodynamic damping forces, the response due to wave actions with wave frequencies close to the first structural resonance frequencies can be high. Therefore, this paper will present numerical simulations using the HAWC2 code to study an offshore wind turbine in parked conditions. The model has been created according to best practice and current standards based on the design of an existing Vestas V90 offshore wind turbine on a monopile foundation in the Belgian North Sea. The damping value of the model's first fore‐aft mode has been tuned on the basis of measurements obtained from a long‐term ambient monitoring campaign on the same wind turbine. Using the updated model of the offshore wind turbine, the paper will present some of the effects of the different design parameters and the different ambient conditions on the dynamics of an offshore wind turbine. The results from the simulations will be compared with the processed data obtained from the real measurements. The accuracy of the model will be discussed in terms of resonance frequencies, mode shapes, damping value and acceleration levels, and the limitations of the simulations in modeling of an offshore wind turbine will be addressed. Copyright © 2014 John Wiley & Sons, Ltd.     

A study of modal damping for offshore wind turbines considering soil properties and foundation types

The modal damping ratio for each mode is crucial to characterize the dynamic behavior of offshore wind turbines and widely used by simulation software in wind turbine engineering, such as Bladed and FAST. In this study, modal damping ratios of offshore wind turbines are systematically studied for different soil properties and foundation types. Firstly, the modal damping ratios and modal frequencies for the first and second modes of a gravity foundation–supported offshore wind turbine are studied. An offshore wind turbine supported by a monopile foundation is then investigated to clarify the characteristics of modal damping ratios and modal frequencies for the monopile foundation. The soil parameters are identified by means of genetic algorithm (GA). Predicted modal damping ratios and modal frequencies as well as modal shapes show good agreement with the field measurements for both foundations. Finally, a sensitivity analysis study is carried out to investigate the effects of soil properties and foundation types on modal damping ratios. For the gravity foundation–supported offshore wind turbine, soil properties affect the modal damping ratio of the second mode largely, but affect that of the first mode little, while for the monopile‐supported offshore wind turbine, soil properties affect the modal damping ratios of the first and second modes significantly. Predicted natural periods and modal damping ratios of the first mode for both foundations by a pair of simple models agree well with those by numerical models.     

局部冲刷对复合筒基风电结构体系动力响应影响

建立风力机塔筒-复合筒型基础-冲刷地基的耦合动力分析模型,通过实测数据验证数值模型的准确性.基于已完成的复合筒基地基冲刷试验,在耦合动力模型中实现冲刷地基模型的准确建立,考虑局部冲刷后应力历史对剩余土体参数的影响,分析风力机结构体系的动力响应特征,将计算结果与不考虑冲刷影响的计算结果进行对比.结果表明:地基的冲刷使得风...     

Identification of support structure damping of a full scale offshore wind turbine in normal operation

The support structure damping of a 3.6 MW pitch controlled variable speed offshore wind turbine on a monopile foundation is estimated both in standstill conditions and in normal operation. The net substructure damping is identified from the parameters of an exponential curve fitted to the relative maxima of an impulse response caused by a boat impact. The result is used in the verification of the non aerodynamic damping in normal operation for low wind speeds. The auto-correlation function technique for damping estimation of a structure under ambient excitation was validated against the identified damping from the decaying time series. The Enhanced Frequency Domain Decomposition (EFDD) method was applied to the wind turbine response under ambient excitation, for estimation of the damping in normal operation. The aero-servo-hydro-elastic tool HAWC2 is validated with offshore foundation load measurements. The model was tuned to the damping values obtained from the boat impact to match the measured loads. Wind turbulence intensity and wave characteristics used in the simulations are based on site measurements. A flexible soil model is included in the analysis. The importance of the correctly simulated damping in the model is stressed for accurate load prediction. Differences in the identified damping between the model and the wind turbine are detailed and explained. Discrepancies between simulated and measured loads are discussed.     

不同边界条件下吸力筒导管架式海上风电振动特性分析

  目的  吸力筒导管架是一种具备许多优点的新型海上风电基础,其振动特性与传统基础有着明显的不同。正确处理无限域地基的边界条件对准确分析振动问题至关重要,故对不同边界条件下吸力筒导管架式海上风电的振动特性进行分析。  方法  以某吸力筒导管架式海上风电为分析对象,在ANSYS APDL中建立结构与土体耦合的全三维有限元模型,研究边界条件对自振频率的影响并对相关参数进行敏感性分析。  结果  不同边界条件对整机固有频率影响较大,改变边界条件对结构轴向刚度和扭转刚度的影响大于对弯曲刚度的影响,整机固有频率随着粘弹性边界弹簧刚度、土体弹性模量和筒土摩擦系数的增大而增大。  结论  分析了影响整机固有频率计算精度的相关因素,可为工程计算提供参考。     

Cyclic behavior of unit bucket for tripod foundation system supporting offshore wind turbine via model tests

Offshore wind energy has been growing up as a promising renewable energy source. Recently, tripod suction bucket foundation is rapidly expanding as a foundation system supporting the offshore wind turbine. In offshore environment, wind turbine foundation structures should be designed considering cyclic loading which can lead to permanent deformation of structure, tilting problem, and overall degradation of soil stiffness. However, it is technically difficult to predict the cyclic behavior of the tripod accurately because the cyclic behaviors of the tripod bucket can be inferred from vertical pullout and compression behaviors of each single bucket elements. In this paper, a series of model tests was performed by applying cyclic vertical compression and extension loadings to a single bucket element that is one element of the tripod foundation. Loading directions, level, and rate were controlled for investigating of cyclic behavior of tripod foundation. On the basis of testing results, the permanent deformation and cyclic stiffness response of tripod suction caisson were discussed. Based on the test results, it was confirmed that the cyclic behavior of the single bucket is affected by the load level and rate. In addition, the behavior showed quite different trends with the loading directions: compression, pullout, and two‐way.     

Estimation of turbulence intensity using rotor effective wind speed in Lillgrund and Horns Rev-I offshore wind farms

Turbulence characteristics of the wind farm inflow have a significant impact on the energy production and the lifetime of a wind farm. The common approach is to use the meteorological mast measurements to estimate the turbulence intensity (TI) but they are not always available and the turbulence varies over the extent of the wind farm. This paper describes a method to estimate the TI at individual turbine locations by using the rotor effective wind speed calculated via high frequency turbine data.The method is applied to Lillgrund and Horns Rev-I offshore wind farms and the results are compared with TI derived from the meteorological mast, nacelle mounted anemometer on the turbines and estimation based on the standard deviation of power. The results show that the proposed TI estimation method is in the best agreement with the meteorological mast. Therefore, the rotor effective wind speed is shown to be applicable for the TI assessment in real-time wind farm calculations under different operational conditions. Furthermore, the TI in the wake is seen to follow the same trend with the estimated wake deficit which enables to quantify the turbulence in terms of the wake loss locally inside the wind farm.