裂纹悬臂梁的扭转弹簧模型及其实验验证

将含裂纹悬臂梁转化为由扭转弹簧联接两段弹性梁构成的连接体,得到理论计算含裂纹梁振动频率的特征方程。确立了求解裂纹梁固有频率的数值计算流程．计算得到了裂纹深度和位置变化时裂纹悬臂梁振动固有频率的变化规律。进行了裂纹悬臂梁的弯曲振动台架实验,验证了本文提出的扭转弹簧模型及固有频率数值计算方法的有效性。     

基于小波有限元法的悬臂梁裂纹识别的试验研究

利用小波有限元法求解了裂纹悬臂梁的前三阶固有频率,并将其拟合成以裂纹位置和深度作为变量的固有频率解曲面;将实测的裂纹梁前三阶固有频率作为裂纹识别反问题的输入,绘制出各阶固有频率等高线,三条等高线的交点预测出裂纹存在的位置和深度。试验结果验证了算法的有效性,这为其实际应用提供了有力的试验依据。     

基于ANSYS的悬臂梁模态分析

用ANSYS软件对悬臂梁进行有限元模态分析,得到悬臂梁的固有频率和振型。求解悬臂梁横振动方程,得到悬臂梁横振动的固有频率及横振动的一般解。利用MATLAB软件画出其振型曲线,与ANSYS分析结果吻合极好,验证了用ANSYS软件进行模态分析的可靠性。     

大型水轮发电机组轴系固有频率现场测试与识别

大型水轮发电机组转轴系统动态固有频率是机组结构优化设计涉及的最重要技术指标之一,现场实测机组轴系固有频率具有十分重要的工程实际意义。本文针对两台200M以上大型机组振动特性现场实测、转轴系统动态固有频率识别,以及尝试采用悬挂重锤(由 150mm×1600mm圆钢制成,重2．2 kN)对运行中的转轴实施冲击激振试验等内容作了全面介绍。     

原子力显微镜(AFM)力传感器及其固有频率的测试

由悬臂梁与探针集成件(Cantilever stylus)组成的力传感器是原子力显微镜的一个关键部件,固有频率(resonant frequency)是悬臂梁与探针集成件的一个重要技术指标,本文介绍了对力传感器的要求、力传感器的设计、检测力传感器的方法,着重介绍了一种采用光学象散原理组成的传感器的固有频率测试系统与方法。     

阀控缸的液压弹簧刚度和固有频率及加速时间

本文从分析液压弹簧刚度入手,讨论了四通阀控液压缸伺服系统的固有频率。为确定系统的加速时间提供了一种方法。通过试验,结论得到了验证。     

旋转柔性悬臂梁的固有频率分析

在精确描述柔性梁非线性变形基础上,利用Lagrange方程推导出考虑动力刚化项的一次近似刚柔耦合动力学方程。忽略柔性梁纵向变形的影响,给出一次近似简化模型,引入无量纲变量,对简化模型作无量纲化处理,首先分析模态截断数对固有频率的影响,其次研究一次近似简化模型和零次近似简化模型的振动特性。研究发现,梁固有频率与模态截断数有关,合理的模态截断数应随无量纲角速度的增大而适当增加;一次近似简化模型的固有频率随无量纲角速度和系统径长比的增大而增大,零次近似简化模型的固有频率随无量纲角速度增大而减小;一次近似简化模型下梁横向弯曲振动不存在物理意义上的共振失稳现象。现有典型文献的相关结论值得商榷。     

弹簧质量系统固有频率忽略自身质量的计算误差

介绍了单自由度弹簧质量系统固有频率的计算方法,并用不同的方法,比较了忽略弹簧质量和考虑弹簧质量对于固有频率计算值的影响.     

旋转悬臂梁动力学的B样条插值方法

采用B样条插值方法对旋转悬臂梁的动力学特性进行研究。考虑柔性梁的纵向拉伸变形和横向弯曲变形,计入由于横向弯曲变形引起的纵向缩短,即非线性耦合项。利用B样条插值方法对柔性梁的变形场进行离散。采用Lagrange方程建立系统的动力学方程,并编制旋转悬臂梁动力学仿真软件。进行动力学仿真,将B样条插值方法的仿真结果与假设模态法、有限元法进行比较分析,验证了提出的方法的正确性,并表明B样条插值方法作为变形体离散法在柔性多体系统动力学中具有优良性能和应用价值。     

疲劳裂纺对悬臂梁振动特性影响的理论分析

研究了疲劳理解纹对悬臂梁的固有频率及强迫振动响应的影响,使用余弦函数描述疲劳裂纹的开合过程。计算结果表明,疲劳裂不仅使悬臂梁的固有频率下降,而且引起非线性强迫振动响应。     

Sensitivity of fundamental mode shape and static deflection for damage identification in cantilever beams

Fundamental mode shape and static deflection are typical features frequently used for identification of damage in beams. Regarding these features, an interesting question, still pending, is which one is most sensitive for use in damage identification. The present study addresses the key sensitivity of these features for damage identification in cantilever beams, wherein these features are extremely similar in configurations. The intrinsic relation between the fundamental mode shape and static deflection is discussed, and in particular, an explicit generic sensitivity rule describing the sensitivity of these features to damage in cantilever beams is proposed. The efficiency of this rule in identifying damage is investigated using Euler-Bernoulli cantilever beams with a crack. The validity of the approach is supported by three-dimensional elastic finite element simulation, incorporating the potential scatter in actual measurements. The results show that the generic sensitivity rule essentially provides a theoretical basis for optimal use of these features for damage identification in cantilever beams.     

On the natural frequencies of helical compression springs

The linearized disturbance equations governing the resonant frequencies of a helical spring subjected to a static axial compressive load are solved numerically using the transfer matrix method for clamped ends and circular cross-section to produce frequency design charts. The effect of varying the number of turns of the spring is investigated, and in the limit of large numbers of turns, our results validate earlier work on the vibration of helical compression springs in which the helix was modeled as an elastic beam with rigidities corresponding to those of unclosed circular rings.     

A high-resolution and large force-range load cell by means of nonlinear cantilever beams

In the present work, we describe a nonlinear stiffening load cell with high resolution (the ability to detect 1% changes in the force) that can function over a large force range (5 orders of magnitude), and exhibit minimal hysteresis and intrinsic geometric protection from force overload. The stiffening nature of the load cell causes its deflection and strain to be very sensitive to small forces and less sensitive to large forces. High stiffness at high forces prevents the load cell from over-straining. We physically implement the nonlinear springs with cantilever beams that increasingly contact rigid surfaces with carefully chosen curvatures as more force is applied. We analytically describe the performance of the load cell as a function of its geometric and material parameters. We also describe a method for manufacturing the mechanical component of the load cell out of one monolithic part, which decreases hysteresis and assembly costs. We experimentally verify the theory for two load cells with two different sets of parameters.     

Closed-form solutions for crack detection problem of Timoshenko beams with various boundary conditions

An analytical approach for crack identification procedure in uniform beams with an open edge crack, based on bending vibration measurements, is developed in this research. The cracked beam is modeled as two segments connected by a rotational mass-less linear elastic spring with sectional flexibility, and each segment of the continuous beam is assumed to obey Timoshenko beam theory. The method is based on the assumption that the equivalent spring stiffness does not depend on the frequency of vibration, and may be obtained from fracture mechanics. Six various boundary conditions (i.e., simply supported, simple–clamped, clamped–clamped, simple–free shear, clamped–free shear, and cantilever beam) are considered in this research. Considering appropriate compatibility requirements at the cracked section and the corresponding boundary conditions, closed-form expressions for the characteristic equation of each of the six cracked beams are reached. The results provide simple expressions for the characteristic equations, which are functions of circular natural frequencies, crack location, and crack depth. Methods for solving forward solutions (i.e., determination of natural frequencies of beams knowing the crack parameters) are discussed and verified through a large number of finite-element analyses. By knowing the natural frequencies in bending vibrations, it is possible to study the inverse problem in which the crack location and the sectional flexibility may be determined using the characteristic equation. The crack depth is then computed using the relationship between the sectional flexibility and the crack depth. The proposed analytical method is also validated using numerical studies on cracked beam examples with different boundary conditions. There is quite encouraging agreement between the results of the present study and those numerically obtained by the finite-element method.     

Sensitivity analysis of crack detection in beams by wavelet technique

This paper examines the sensitivity of wavelet technique in the detection of cracks in beam structures. Specifically, the effects of different crack characteristics, boundary conditions, and wavelet functions employed are investigated. Crack characteristics studied include the length, orientation and width of slit. The two different boundary conditions considered are simply supported and fixed end support, and the two types of wavelets compared in this study are the Haar and Gabor wavelets. The results show that the wavelet transform is a useful tool in detection of cracks in beam structures. The dimension of the crack projected along the longitudinal direction can be deduced from the analysis. The method is sensitive to the curvature of the deflection profile and is a function of the support condition. For detection of discrete cracks, Haar wavelets exhibit superior performance.     

轴结构件的裂纹参数识别

在带有裂纹的轴结构件中 ,当裂纹较小时轴的裂纹参数与其固有频率的变化率相关联。为此计算轴结构件固有频率的变化率去识别裂纹位置和深度 ,从而为轴结构件的改进设计及带裂纹的轴结构件剩余寿命的估算提供理论依据     

Vibration of two cantilever beams clamped at one end and connected by a rigid body at the other

This study presents the pure bending and coupled bending-torsional vibration characteristics of a beam structure which consists of two cantilever beams and a rigid body at their free ends. This structure is available in many mechanical structures such as robots, space constructions, and optical pickup actuators in optical disc drives (ODDs). In order to depict the vibration of the beam structure originating from the deflection and torsion of two beams, the motion equations and continuity conditions are analytically induced by using energy conservation. In the process that the free vibration problem is solved, two independent characteristic equations are obtained. The former is an equation for the pure bending vibration of two beams, and the latter is for their coupled bending-torsional vibration. It is proved that these characteristic equations are exact by comparing natural frequencies obtained from FEM. As natural frequencies are described in many dimensional variations, the relation between vibration characteristics and the dimensions of the given system is also investigated. Finally, resonant frequencies from test results are presented to confirm the validation of this study for a new type optical pickup actuator. This paper was recommended for publication in revised form by Associate Editor Eung-Soo Shin Kyung Taek Lee received a Ph.D. degree in Mechanical Engineering from Yonsei University, Seoul, Korea in 2003. He joined LG Electronics, Seoul, Korea, in 1989, where he has worked on precise mechanical structures and microactuating systems for optical information storage devices, as a Research Engineer. His current interests include microactuators for position control, haptic elements for mobile devices, and etc.     

基于CAE的YD-2型液压捣固机弹性结构的自振频率的研究

以YD-2型液压捣固机为模型.对其在作业中出现的有害振动形态,采用UG中的Nastran模块对整机结构进行分析,得到其自振频率.再和实验结果进行对比,排除了自振频率和其额定工作频率发生共振的情况.传统的结构自振频率的都是通过整机试验来得到,而利用CAE软件进行分析得到结论不但方便而且可以进行参数化设置、优化设计同步进行.软件计算结果验证了实验结果,对改进捣固振动性能提出了意见.针对试验结果和软件计算结果的差异进行讨论,模型的简化是主要原因.     

基于遗传算法的平板裂纹识别

裂纹的识别是故障诊断领域研究的一个热点问题.基于构件的固有频率变化,从反问题的角度出发,把裂纹的识别问题转化为一个优化问题,将裂纹的相对位置及深度参数转化为二进制编码,提出基于遗传算法的平板构件裂纹的识别方法.为了减少遗传算法的计算量,对遗传算法作了一定的改进.计算结果表明算法计算精度高,计算量小,可广泛的应用于拉深件裂纹识别及结构损伤检测等场合.