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研究水平轴风力机叶片的经典颤振稳定性特性。在导出质量刚度均匀分布的旋转挥舞/摆振/扭转叶片的耦合振动偏微分方程组基础上,引入扩展的Theodorsen模型描述非定常气动力的作用。联合采用Galerkin法、特征值法和时间域积分法对所建立的叶片气弹模型进行求解。通过数值分析获得叶片的挥舞弯曲模态、摆振弯曲模态和扭转模态的根轨迹曲线,分析了叶片面内刚度、扭转刚度和预锥角对叶片气弹稳定性的影响。特征值法稳定性的计算结果的精确度和可靠性通过分析模态展开式中模态截断个数N对颤振边界收敛性的影响,得到验证。稳定性分析的时间域数值积分结果的一致性进一步说明特征值法稳定性计算结果正确性。 相似文献
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作为叶片失效的重要原因,颤振一直是风电领域研究重点。以抑制叶片工作过程中的颤振为目的,建立分析模型时应充分考虑实际风速分布特别是风切变和塔影效应对叶片振动的影响,并在离散化后求取平均输入风速。针对小型风力机叶片气动弹性稳定性问题进行综合分析,根据实体结构建立叶片气弹模型,考虑非线性气动力作用时叶片大攻角、大风速工况下产生的高频、高幅失速颤振,模拟典型截面仿真振动位移。通过模型预测控制的滚动优化和误差矫正控制叶片挥舞、摆振两个运动方向的振动频率和幅值,结果表明振动形式实现控制后可在短时间内达到稳定且静差可接受。 相似文献
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将风力机叶片简化为薄壁复合材料封闭截面弯扭耦合变形梁,基于Hamilton原理并结合变分渐进法(VAM),建立风力机叶片的气动弹性力学模型。结构模型包括材料各向异性,截面翘曲,离心载荷,科里奥利加速度,以及预锥角和预扭转角的影响。气动载荷采用叶素动量理论和准定常气动力理论进行描述。将位移按广义坐标进行模态展开,采用Galerkin法导出系统的质量、刚度和阻尼矩阵,采用特征值技术进行叶片颤振性能的数值求解。针对周向反对称刚度配置(CAS)叶片进行数值近似计算,揭示了入流比、预扭转角和纤维铺层角等参数对风力机叶片颤振性能的影响。 相似文献
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颤振是风力机叶片超大化发展必须解决的首要难题,气弹模型测振风洞试验是其最有效的预测方法之一,但传统方法无法精确解决模型相似比和测量精度的难题。本文提出一种基于主梁刚度等效原则的超长柔性叶片气动/刚度映射一体化三维完全气弹模型设计方法,采用高速摄像技术和高频六分量天平进行全风向角同步测振和测力风洞试验;系统研究了 NREL?15 MW 超长柔性叶片的非线性动态响应频谱特性,对比分析了基于叶尖位移与叶根反力的风力机叶片颤振性能和临界失稳状态,发现了采用叶根反力来预测颤振性能的可行性,提出了超长柔性叶片颤振失稳预测的叶根反力法。研究表明:本文提出的气弹模型设计和实验方法能精确有效地模拟风力机叶片动力性能与颤振行为,试验发现超长柔性叶片在桨距角为 93°~96°和 284°~287°区间内发生颤振,颤振区间内颤振临界风速随桨距角的增大呈现先减小后增大的趋势,在桨距角为 94°时达到最小,其风洞临界风速为 5.4 m/s;叶根反力与叶尖位移存在一致发散性和强相关性,提出的叶根反力颤振指标 δ≥2% 时,风力机叶片进入颤振临界状态。 相似文献
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为解决弯扭耦合复合材料薄壁叶片的发散不稳定问题,阐述了风力机叶片准稳态响应及基于回路传输恢复的LQG(LQG with Loop Transfer Recovery,LLTR)理论控制过程。叶片结构模型是基于周向反对称刚度铺层的复合材料薄壁单闭室翼型;翼型的中线轨迹是S809Ⅱ翼型型线。从直升机叶片的失速气动力模型中提取了一种准稳态气动力模型,经过修正后适合于风力机叶片经典颤振和失速颤振临界状态的研究。分别详细研究了基于输入端回路传输恢复及输出端回路传输恢复两种情况下的LLTR控制,并通过弯扭时域响应和控制器响应的数字仿真比较以及奇异值伯德图曲线对比,论证了LLTR控制算法的稳定性及在颤振抑制方面的优越性。控制算法的实时效应也通过半实物仿真实验平台得到了检验。 相似文献
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采用壁板颤振分析的有限元方法,从壁板的正则化弯曲刚度、屈曲临界温升、颤振临界速压和极限环颤振幅值等参数的角度,分析了不同铺层方向和不同铺层顺序对层合复合材料壁板的颤振特性的影响,并给出了几种常见铺层方式层合复合材料壁板的颤振特性。结果表明,在设计复合材料壁板的铺层方向和铺层顺序时,一般可以通过壁板正则化弯曲刚度的大小来对颤振速压进行比较。但是在某些特殊的铺层情况下,随着温度升高,发生频率重合型颤振的耦合模态会发生演变,这时正则化弯曲刚度较大的壁板也有可能在较低的速压下发生颤振。 相似文献
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A method is proposed for estimating the parameters of a mixture of exponential and Weibull distributions for which the accuracy of preliminary estimates obtained by graphical analysis is refined in accordance with the criterion of maximum likelihood. The efficiency of the proposed method is supported by the results of statistical modeling. 相似文献
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Liebert A Wabnitz H Grosenick D Möller M Macdonald R Rinneberg H 《Applied optics》2003,42(28):5785-5792
A novel method for the determination of the optical properties of tissue from time-domain measurements is presented. The data analysis is based on the evaluation of the first moment and the second centralized moment, i.e., the mean time of flight and the variance of the measured distribution of times of flight (DTOF) of photons injected by short (picosecond) laser pulses. Analytical expressions are derived for calculation of absorption and of reduced scattering coefficients from these moments by application of diffusion theory for infinite and semi-infinite homogeneous media. The proposed method was tested on experimental data obtained with phantoms, and results for absorption and reduced scattering coefficients obtained by the proposed method are compared with those obtained by fitting of the same data with analytical solutions of the diffusion equation. Furthermore, the accuracy of the moment analysis was investigated for a range of integration limits of the DTOF. The moment analysis may serve as a comparatively fast method for evaluating optical properties with sufficient accuracy and can be used, e.g., for on-line monitoring of optical properties of biological tissue. 相似文献
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An approximate analytical expression is derived for the velocity of the front of the wave of change of boiling modes on a
rod and on a plate. The impact of the Thomson effect and of the heater orientation in the gravity field is included. Adequate
agreement is demonstrated between the derived relations and experimental data. 相似文献
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Conventional methods for summation of direct measurement errors are considered. Conditions under which these methods provide consistent results are stated. It is proposed to utilize for characteristic of the total error, its interval estimator or the half-sum of the value obtained by adding up its arithmetic and geometric random errors.Translated from Izmeritel'naya Tekhnika, No. 4, pp. 10–12, April, 1995. 相似文献
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由于空压机进气侧轴承箱蜗壳温度探头密封效果不好,使空压机及其后续管道受到油污染。后将温度探头的O形圈密封改为骨架油封,杜绝了轴承箱漏油问题。文章简介空压机的结构和技术参数,详细介绍了骨架油封的制作和优点。 相似文献
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M. M. Gadenin 《Inorganic Materials》2013,49(15):1352-1356
It is shown that conditions of attainment of marginal states in the material of structural components are formulated on the basis of analysis of force and deformation criteria of formation and development of destruction. The parameters of these criteria are data on types of structural materials, standard and special characteristics of their mechanical properties, structural forms of considered elements of the equipment, and their operating stress loading. In this case, the construction of a system of state equations for describing interrelation of current damage, external actions, and responses to them is based on the concept of calculating variations in properties of materials at all stages of the design life cycle. 相似文献
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V. T. Kornienko 《Strength of Materials》1991,23(7):760-765
The article suggests a method of evaluating the microstructural inhomogeneity of deformation of metals by modeling. The method includes the measurement of deformations of metal according to meshes of a dividing grid with small base and the calculation of the distribution parameters of microdeformations in model representation. It is shown that the modeling method makes it possible objectively to evaluate the microinhomogeneity of deformation of metals independently of the chosen mesh size of the dividing grid. New structural characteristics are introduced: the base and wave of variation expressing the degree of crumbling or amalgamation of metal grains by inhomogeneity of deformation.Translated from Problemy Prochnosti, No. 7, pp. 40–44, July, 1991. 相似文献
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水三相点是开尔文热力学温度的唯一基准点,也是ITS-90国际温标重要的定义固定点。因此,水三相点不确定度分析对整个温标的建立、温度量值传递起着至关重要的作用。近3年来,中国计量科学研究院研制出一系列高质量的水三相点容器,加强了水三相点的研究,为不确定度的分析提供了更为可靠的实验依据。同时,不确定度的分析也是客观评价新研制容器性能的一个重要指标。因此,根据实验结果对新研制容器所复现的水三相点进行了不确定度评定。评定结果表明,其扩展不确定度为0.16mK(k=2.69,P=0.99)。 相似文献