Influence of Trailing-Edge Wear on the Vibrational Behavior of Wind Turbine Blades

To study the impact of the trailing-edge wear on the vibrational behavior of wind-turbine blades,unworn blades and trailing-edge worn blades have been assessed through relevant modal tests.According to these experiments,the natural frequencies of trailing-edge worn blades-1,-2,and-3 increase the most in the second to fourth order,thefifth order increases in the middle,and thefirst order increases the least.The damping ratio data indi-cate that,in general,thefirstfive-order damping ratios of trailing-edge worn blades-1 and trailing-edge worn blades-2 are reduced,and thefirstfive-order damping ratios of trailing-edge worn blades-3 are slightly improved.The mode shape diagram shows that the trailing-edge worn blades-1 and-2 have a large swing in the tip and the blade,whereas the second-and third-order vibration shapes of the trailing edge-worn blade-3 tend to be improved.Overall,all these results reveal that the blade’s mass and the wear area are the main fac-tors affecting the vibration characteristics of wind turbine blades.

Effects of Finite Aspect Ratio and Noncircular Plasma Flux Surface on Electron Temperature Gradient Driven Modes

A gyrokinetic model with integral eigenmode equations is developed based on the local equilibrium of shaped tokamak plasmas. Effects of main geometric parameters （finite aspect ratio, elongation, triangularity, and Shafranov shift gradient） on the electrostatic electron temper- ature gradient （ETG） driven modes are investigated numerically. It is found that the finite aspect ratio has a general stabilizing effect, while the elongation can be either stabilizing or destabilizing, depending on the poloidal wavelength of the mode and other parameters. It is shown that a low aspect ratio enhances the stabilizing effect of elongation, and weakens its destabilizing effect as well.

锈蚀钢筋混凝土T梁的疲劳性能试验

为探明我国早期建造的公路钢筋混凝土T梁桥纵筋锈蚀后的疲劳性能,加工制作10根实际锈蚀率在4.12%~13.72%之间的钢筋混凝土T梁试件,对其开展疲劳应力比在0.25~0.67范围内的疲劳试验。试验结果表明:轻度锈蚀T梁试件的挠度、弯曲裂缝宽度和材料应变均呈现明显的前期快速发展-中期稳定变化-后期迅速增长的“三阶段发展”特征,疲劳破坏一般以弯曲裂缝超限为标志;中度或重度锈蚀T梁试件承受应力比小于0.30左右的疲劳荷载作用时,前者中期平稳发展阶段基本消失,后者甚至会发生低周疲劳破坏;当应力比不超过0.31时,中度和重度锈蚀试件相比轻度锈蚀试件的疲劳寿命分别减小了约48%和71%;当应力比从0.66减小到0.31时,中度和重度锈蚀试件的疲劳寿命分别减小了约85%和90%。由于中度或重度锈蚀的公路钢筋混凝土T梁的实际疲劳寿命远低于200万次的设计疲劳寿命,故设计和运维中应采取措施减小主筋锈蚀率及疲劳应力幅值。

基于逆全极点滤波器的高频PWM噪声整形方法

高频开关功率放大器具有高功率、低纹波、高响应的优点,是高加速、高精度定位系统的核心部件。为了解决高频PWM中开关频率与占空比分辨率的矛盾,该文分析调制中噪声整形的基本原理,采用误差反馈结构提取PWM量化噪声进行数字整形,阐述噪声整形滤波器设计约束条件。提出通过逆全极点无限脉冲响应(IIR)滤波器获得有限脉冲响应(FIR)噪声整形滤波器的简明设计方法,仿真及实验表明,该文提出的方法可利用低阶FIR整形滤波器获得平坦的通带和高整形衰减。在不足9位的PWM中,4阶的FIR噪声整形滤波器能够恢复调制信号在10 kHz频段内约40 dB的信噪比损失。

Test and numerical investigations on static and dynamic characteristics of extra-wide concrete self-anchored suspension bridge under vehicle loads

The present work is aimed at studying the mechanic properties of the extra-wide concrete self-anchored suspension bridge under static and dynamic vehicle loads. Based on the field test using 12 heavy trucks and finite element simulations, the static deformations of different components, stress increments and distributions of the girder, as well as the vibration characteristics and damping ratio of the Hunan Road Bridge were analyzed, which is the widest self-anchored suspension bridge in China at present. The dynamic responses were calculated using the Newmark-β integration method assisted by the simulation models of bridge and vehicles, the influences on the dynamic impact coefficient(DIC) brought by the vehicle parameters, girder width, eccentricity travel and deck flatness were also researched. The spatial effect of the girder is obvious due to the extra width, which performs as the stress increments distribute unevenly along the transverse direction, and the girder deflections and stress increments of the upper plate change as a "V" and "M" shape respectively under the symmetrical vehicle loads affected by the shear lag effect, cross slope and local effect of the wheels, the maximum of stress increments are located in the junctions with the inner webs. The obvious girder torsional deformation and the apparent unevenness of the hanger forces between the two cable planes under the eccentric vehicle loads, together with the mode shapes such as the girder transverse bending and torsion which appear relatively earlier, all reflect the weakened torsional rigidity of the extra-wide girder. The transverse displacements of towers are more obvious than the longitudinal ones. As for the influences on the DIC, the static effect of the heavier vehicles plays a major role when pass through with a higher speed and the changes of vehicle suspension stiffness generate greater impacts than the suspension damp. The values of DIC in the vehicle-running side during the eccentric travel, affected by the restricts from the static effects of the eccentric moving trucks, are significantly smaller than the vehicle-free side, the increase in the road roughness is the most sensitive one among the above influential factors. The results could provide references for the design, static and dynamic response analysis of the similar extra-wide suspension bridges.

Dynamic behavior of reinforced concrete frame structure during construction

The effects of concrete's time-variant elastic modulus,casting structural components,assembling temporary shoring framework system,and shock by operating construction equipment on dynamic behavior of the reinforced concrete frame structure during construction were investigated. The dynamic tests of an eight-storey reinforced concrete frame structure during full-scaled stages of the sixth storey construction cycle were carried out by ambient vibration. Natural frequencies,corresponding mode shapes and damping ratio were determined by power spectrum processing the tested signal data in frequency domain. The changes of frequencies,mode shapes and damping ratios at different construction stages were given. The results show that natural frequencies and modal damping ratios reach the maximum at stage of casting fresh concrete,especially for higher modes. Modal damping ratios at each construction stage are less than 5% of those during usage.

Identification of Structural Parameters Based on HHT and NExT

Signal processing approaches are widely used in the field of earthquake engineering,especially in the identification of structural modal parameters.Hilbert-Huang Transformation(HHT)is one new signal processing approach,which can be used to identify the modal frequency,damping ratio,mode shape,even the interlayer stiffness of the shear-type structure,incorporating with Natural Excitation Technique(NExT)method to take information from the response records of the structure.The stiffness of the structure is of great importance to judge the loss of its bearing capacity after earthquake.However,all of modal parameters are required to calculate the stiffness of the structure by use of HHT and NExT,which means that the response records shall contain all of modal information.However,it has been found that the responses of the structure recorded only contain the former order modal information;even it is excited by earthquake.Therefore,it is necessary to found a formula(formulas)to calculate the stiffness only using limited modal parameters.In this paper,the calculation formulas of the interlayer stiffness of shear-type structure are derived by using of the flexibility method,which indicate that all of interlayer stiffnesses could be worked out as long as any one set of modal parameters is obtained.After that,Taking Sheraton-Universal Hotel subjected to North Bridge earthquake in 1994 as an example,HHT and NExT are used to identify its modal parameters,the derived formulas are used to calculate the interlayer stiffnesses,and their applicability and accuracy are verified.

新型十字形负泊松比蜂窝结构的抗冲击性能

负泊松比力学超材料具有高可设计性、轻量化以及抗冲击方面的优势,引起学者们的关注,对内凹六边形结构、手性结构等经典构型进行了广泛研究。提出了一种新型的十字形负泊松比蜂窝结构,基于能量法对该结构泊松比的解析式进行了推导,所得解析解与有限元结果吻合良好,证明了推导方法的有效性;针对不同冲击速度和不同杆长比例系数的十字形蜂窝结构的变形模式、冲击载荷下的名义应力应变曲线以及能量吸收特性进行了研究。结果表明:杆长比例系数越小,泊松比越小;冲击速度和杆长比例系数会影响十字形蜂窝结构的变形模式、冲击载荷下的名义应力应变曲线和平台应力;十字形蜂窝结构的体吸能在中速冲击下会随应变增大出现增长加快现象,而高速冲击下体吸能增长趋势不再随应变增大出现加快但呈现出规律的波浪形增长。

基于模态参数进行连续梁损伤诊断的数值研究

以一矩形等截面二跨梁有限元模型为研究对象 ,通过数值模拟 ,利用梁损伤前后一阶振型的改变率、前四阶振型曲率的绝对差值以及两个特征参数 ,分别实现了连续梁的损伤诊断。

浮置板轨道的模态分析

为了研究低频振动对地铁线路附近精密仪器的影响，设计一种新型参数的浮置板轨道。应用MIDAS／GTS软件，对浮置板轨道进行三维的模态分析，得到6种不同分析工况下轨道的固有频率、振型和振型参与质量，并进一步研究浮置板轨道的传导比。结果表明：①设计的浮置板轨道基本频率为5．7～8．2Hz，弹簧刚度不变、支承间距增大，或者支承间距不变、减小弹簧刚度，均可以降低浮置板轨道的基本频率；②浮置板轨道的振型以道床板振动为主，同一支承间距下，弹簧刚度不同，浮置板轨道振型相似；同种弹簧刚度下，支承间距不同，振型在低阶部分差别较大，在高阶部分相似；③浮置板轨道的基本频率越低，浮置板轨道的传导比峰值就越小。

应县木塔环境振动试验

对于复杂的塔状古建筑物,建立一个合适的简化的数学模型是不易实现的。与强迫振动试验相比,环境振动试验比较简单、方便,所确定出的小振幅水平下的木塔结构动力特性具有足够的精度。本文首先结合应县木塔结构环境振动测试实例对环境振动测试方法作了简要介绍,并采用随机信号数据频域分析方法对测试数据进行了分析,确定木塔结构的自振频率。同时,依据不同测点在固有频率处响应的比及零迟时互相关函数确定木塔结构的振型。最后,本文依据自功率谱和互功率谱采用半功率点法计算各振型的阻尼比。本文分析结果表明,在两水平方向上木塔的振动特性存在些微差异,第一振型阻尼比较第二振型阻尼比大。

基于附加质量的试验模态振型质量归一化

针对桥梁结构试验模态振型的质量归一化,探讨了基于附加质量的试验模态振型质量归一化法,给出它的4种方法。以通扬运河大桥和张家港河大桥的有限元模型为对象,对4种方法计算质量归一化因子的精度,以及质量块的数量和质量、传感器数量、模态振型误差、质量块质量的误差对精度的影响进行了仿真研究。仿真结果说明了基于附加质量的试验模态振型质量归一化法的可行性和可靠性,在实际工程应用中可实现桥梁各阶试验模态振型较高精度的质量归一化。

改进的特征值灵敏度在结构损伤识别中的应用

传统的特征值灵敏度分析中忽略了振型变化的影响,导致特征值灵敏度难以准确地识别出结构损伤。为提高特征值灵敏度的准确性,利用未损伤结构的振型线性表示损伤情况下结构振型的变化,进而改进了特征值灵敏度的理论分析方法。在不同的损伤工况下,计算数值模型改进前后的特征值灵敏度,验证表明改进后的特征值灵敏度具有更高的精度。以孔洞直径和位置均未知的实际结构为研究对象,利用改进后灵敏度方法准确识别了结构损伤的位置和程度,与结构的孔洞直径和位置实测值相吻合,表明了改进后灵敏度方法具有准确实用性,从而弥补了传统特征值灵敏度法在结构损伤识别中的缺陷。

基于环境振动测试的高层钢筋混凝土结构模态参数识别

根据高层钢筋混凝土结构环境振动测试数据，采用随机信号的频域分析方法，确定了高层结构的自振频率；基于不同测点在固有频率处的响应比及零迟时互相关函数确定了结构的振型；运用自功率谱和互功率谱，采用半功率点法计算了各阶振型的阻尼比。结果表明，环境振动测试能够较好地识别高层结构的1—3阶振型。对实测自振周期与《建筑结构荷载规范》的公式和数值模拟结果进行比较，发现：结构的层数小于20层时，实测值与《规范》规定的值最接近；结构超过20层时，实测值小于《规范》规定的值和数值模拟的结果。

北京国贸三期工程高含钢率型钢混凝土异型柱试验研究

以北京国贸三期实际工程为背景,对其核心筒中型钢混凝土异型组合柱进行试验研究。这种柱含钢率高,型钢造型复杂,是一种新型构件。通过对这类构件的轴压、压弯和剪切试验,全面研究构件相应的破坏特征、承载力、滞回性能和延性,并对比研究型钢分散配置后不同连接方式以及不同轴压比的影响。研究表明,这类构件性能良好,且连接板的设置与轴压比大小对性能有直接影响,设计时应予以充分的考虑。通过试验研究提出高含钢率型钢混凝土柱抗剪及压弯承载力计算方法,其计算结果与试验结果符合较好。

老挝东泰钾盐矿床地球化学及其沉积后变化初步研究

呵叻高原是世界上最大的钾盐沉积矿床分布区之一,研究区位于呵叻高原北部的沙空那空盆地东部边缘,钻探资料揭示该地区钾盐资源相当可观。该含盐建造包含上、中、下3个盐段,每个盐段都由一套蒸发岩-碎屑沉积旋回组成,钾盐层主要赋存于下盐段上部。剖面和地层学分析表明,研究区盐构造类型为低结构低成熟度的盐背斜构造,盐体几何形态为一低结构低成熟度的盐背斜,盐背斜轴部矿层厚度较两翼矿层厚得多。岩盐中微量元素Br、K含量及Br×1000/Cl系数的变化指示成盐卤水经过了阶段性的浓缩和淡化过程,并且成盐作用越来越弱。ZK04孔较低的Br含量〔w(Br)=18×10-6〕表明下膏盐层在成盐过程中受到了非海相流体的影响。中膏盐层基底石盐中高K低Br特征表明,下膏盐层残余高浓度卤水影响了其成盐过程,并且该基底石盐很可能又经历了溶解和重结晶过程。

基于除霜的相变蓄热器对空气源热泵性能的影响

针对空气源热泵蓄能除霜系统,提出了串联供热、非连通供热和连通供热3种供热模式,并实验研究了3种供热模式下相变蓄热器对空气源热泵性能的影响.分析实验数据发现非连通供热模式和串联供热模式相比系统主要参数(压缩机吸排气温度和压力)除排气温度升高5℃,其他基本无变化.连通供热模式的吸排气温度和串联供热模式相比分别升高了15℃和30℃,排气压力降低了0.2 MPa.3种供热模式中串联供热模式的性能系数(EER)最高,连通供热模式和非连通供热模式性能系数因参与运行的制冷剂减少而有所降低,连通供热模式的系统性能系数具有较大的提高潜力.

规则型隔震桥梁结构的简化分析方法

由于桥墩的质量与上部结构的质量相比通常是比较小的 ,各桥墩高度和截面大致相同的连续桥梁可以简化为单自由度体系进行抗震设计。当在桥面大梁与桥墩之间设置隔震橡胶支座时 ,上述规则型桥梁可以看作串连型双自由度体系。文中根据桥墩的水平刚度远大于橡胶支座的水平刚度和上部结构的质量甚大于桥墩的特点推导了此双自由度体系的自振特性 (包括自振周期、振型、地震作用的振型参与系数和振型阻尼比 )的简化计算公式。这些公式可以方便地应用于隔震桥梁的抗震设计。此外 ,文中还分析了这些简化公式的计算精度与双自由度体系质量比和刚度比的关系。精度分析和数字实例的计算结果表明 。

焊接节点表面裂纹复合型应力强度因子的数值计算研究

以十字形焊接节点为研究对象,比较ABAQUS、FRANC3D和规范公式计算表面裂纹应力强度因子的结果,验证FRANC3D计算应力强度因子的正确性和高效性。为从数值理论上研究复杂应力场下焊接节点表面裂纹复合型应力强度因子的影响因素,基于FRANC3D建立不同裂纹形状比和焊缝倾斜角度的计算模型。结果表明:随着焊缝倾斜角度的增大,Ⅰ型和Ⅲ型应力强度因子减小,Ⅱ型应力强度因子增大;当焊缝倾斜角度为0°和15°时,裂纹表面点和最深点同时可以忽略Ⅱ型和Ⅲ型应力强度因子的影响;应考虑Ⅱ型和Ⅲ型应力强度因子绝对值对疲劳裂纹扩展的影响。

柱壳结构体系的损伤诊断

由于对柱壳结构的损伤部位和程度进行诊断是确保柱壳结构安全可靠的重要保证,采用振动理论对柱壳结构体系进行损伤分析,利用同阶特征对比值变化量和应变模态差作为损伤诊断因子。数值模拟计算结果表明,这两个变量作为损伤诊断因子,能够凸现柱壳结构的损伤部位及损伤程度大小;运用这两个变量诊断非贯穿性小损伤,能够很好地显现损伤部位和损伤程度;计算结果也表明,柱壳结构对损伤部位较为敏感,腰部损伤比顶部损伤对柱壳结构的影响大。