A comprehensive study of modal characteristics of a cylindrical manipulator with both link and joint flexibility

A thorough understanding of modal characteristics of vibrating manipulators is essential for improved dynamic positioning accuracy. Presented in this work is an extensive investigation of a cylindrical manipulator, consisting of a revolute and a prismatic joint. In general, for high-speed, flexible manipulators, modal properties depend mainly upon the following factors: (1) physical dimensions and material properties of components (such as arms and joints), which remain unchanged for a chosen manipulator; (2) a manipulator's position (or orientation) as a result of joint actuations; (3) the rigid-elastic coupling effect; and (4) the centrifugal stiffening effect due to the influence of internal axial force on the lateral stiffness. This work is intended to study the effects of each of the above factors on modal characteristics of the manipulator, and gives insight into the susceptibility of the modal parameters to each factor. In addition, joint flexibility has substantial influence on modal properties of a robotic system, depending on the relative importance of joint torsional stiffness to the stiffness of other members, such as the bending stiffness of arms. In the situation where the manipulator moves at a high speed, both rigid-elastic coupling and centrifugal stiffening effects can become important.     

辊压自动化传输设备桥式起重机吊架力学特性研究

以辊压自动化传输设备集中驱动桥式起重机吊架为研究对象,针对通过传统设计方法设计出的桥式起重机吊架,采用有限单元法对吊架进行强度和刚度考核,并进行模态分析。通过强度和刚度分析发现,通过传统手段设计出的吊架具有较大的安全富裕度,造成一定的资源浪费,可进行优化;通过模态分析可直观地分析吊架的动态特性,发现薄弱环节,有意识地避开吊架的固有频率,以免发生共振。     

Experimental and numerical investigation of modal properties for liquid-containing structures

The dynamic response of liquid-containing structures is governed by their modal properties, which are affected by the mass of liquid and other fluid-structure interaction mechanisms. Therefore, knowledge of the effects of different parameters on modal properties is helpful in conducting a precise dynamic response analysis. In this paper, the effects of liquid on the modal properties of two structures, i.e., a pipe structure and a cylindrical storage tank, are investigated experimentally. The experimental results are then used to construct accurate analytical/numerical models for these structures. The models are capable of regenerating the experimental dynamic characteristics of the structures with an acceptable accuracy, indicating a proper modeling of the effects of liquid and the corresponding interaction mechanisms.     

线性变参数振动系统的全局辨识

制造系统中存在大量振动特性随特定参数变化而变化的线性变参数振动系统。这类线性变参数振动系统的辨识目前主要通过局部辨识方法,为了准确辨识需要在不同调度变量下进行大量实验,往往效率很低。为了准确而高效地辨识线性变参数振动系统,提出一种全局辨识方法。对调度变量连续变化的线性变参数振动系统持续施加激励,将系统的振动微分方程进行时域离散,利用过完备字典函数库对离散模型进行表征,并利用稀疏回归进行求解,即可根据调度变量数据和系统的激励-响应数据一次辨识得到系统模型。以实际机床刀尖结构的模态参数数据,建立线性变参数振动系统代理模型进行验证。在单调度变量和多调度变量案例中,全局辨识得到的模态参数平均误差均在2.7%以下,充分显示了所提出全局辨识方法的有效性,也验证了线性变参数振动系统全局辨识的可行性。     

Effects of Joint Controller on Analytical Modal Analysis of Rotational Flexible Manipulator

Modal analysis is a fundamental and important task for modeling and control of the flexible manipulator. However, almost all of the traditional modal analysis methods view the flexible manipulator as a...     

低温管系中支吊架的设计与应用

管道支吊架在管道系统中经常是不被重视的部分,但实际上其结构及布置的合理性对于管道系统的安全至关重要.论文较全面介绍了低温输送管线系统中支吊架设计应考虑的相关要点,包括支吊架合理布置的重要性、管道支吊架的分类和常见各种结构形式、管道支吊架的材料选择,管道支吊架的选用原则,管道支吊架的布置要点等.由于管道支架的结构和布置必须首先满足管系的推力值,所以根据不同类型的管架着重给出了相关推力及跨距计算方法.     

不同测试方法下试验模态分析的对比

以实模态分析理论为基础,对钻架模型系统进行典型试验模态分析和基于ODS(Operation Deflection Shapes)测试方法为基础的试验模态分析,分别识别出系统的模态参数,并进行对比分析.     

Modal synthesis of systems with prescribed eigenproperties

Modal synthesis of conservative systems is aimed at determining physically realizable parameters that ensure their required eigenproperties. The agreement is achieved by similarity of the dynamical matrix to its spectral matrix. The linear space of parameters is shown to contain the set of trajectories of virtual sequences of similar matrices. Similarity trajectories are known to give evidence about the evolution of systems, which is controlled by variation of elements of the modal matrix. It is shown that similar matrices may have modal invariants, which provide for optimization of system properties, and in particular, of those which are related to the realization of principal forms of vibrations.     

基于模态理论的白车身静刚度计算方法

以线性系统的模态理论为基础,将简单矩形框架的弹性体模态与静刚度之间的关联性推广到白车身,推导出了具体的数学表达式,再以此为依据,通过有限元分析直接提取各阶弹性体模态参数,从而获取车身静刚度,改变了以往依靠柔度矩阵和大型试验来计算静刚度的方法。研究结果表明,模态理论方法和传统静力学方法所得到的静刚度相差在10%以内,说明白车身的整体静态柔度可以用模态柔度贡献量之和表达,且这种计算方法具有较高精度,能为低阶模态和刚度性能的目标设定提供参考。同时,各阶模态的柔度贡献量的大小可以作为低阶模态识别的重要依据。最后将有限元计算结果与白车身静刚度试验结果作对比,其误差控制在8%以内,其中由模态方法计算的扭转刚度误差低于3%,因此说明此次有限元分析是可靠的。     

A NEW METHOD FOR STRUCTURAL MODEL UPDATING AND JOINT STIFFNESS IDENTIFICATION

A new model updating method is presented here with emphasis on identification of joint stiffnesses. A so-called reduced-order characteristic polynomial (ROCP) is first defined in terms of the measured natural frequency, the partial modal properties predicted from a flawed FEM model and the model parameters to be updated or identified. Based on the premise that each of the measured natural frequencies is a root of the ROCP, a set of non-linear equations becomes immediately available from which the interested model parameters can be determined. The experimental data required are simply the measured natural frequencies, rather than the usually incomplete and less-accurate displacement or FRF data. In addition, there is no modal matching needed here, which can lead to a considerable saving of the resources and efforts spent on measurements and correlation analyses. The proposed technique is verified by using simulation data. The current scheme is easily generalised into an advanced optimisation formulation, which would allow various constraints to be explicitly imposed upon the model parameters and a wide spectrum of algorithms to be directly used for finding a solution.     

页岩气井下开采管路气固耦合振动特性分析

页岩气开采过程中,井下管路内气体与管路的耦合作用,会引起管路振动,这是此类管路振动失效的主要原因。管路振动响应特性与井下管路长度、气体流速及压力等参数有直接关系,因此,研究这些参数的影响对揭示页岩气管路振动规律,提高井下管路安全性及寿命有重要意义。针对页岩气井下管路,在ADINA软件平台中建立有限元分析模型,进行振动模态分析,研究管路长度、气体流速及压力对管路气固耦合振动特性的作用规律。研究结果为页岩气井下管路振动实验研究提供理论指导,同时为气固耦合振动特性研究奠定基础。     

某超高压管接头结构参数对接触密封性能的影响分析

超高压液压管接头的研制开发已成为液压系统超高压化进程中亟需解决的问题。介绍了一种新型超高压管接头结构形式,在此基础上利用ANSYS建立了管接头组件的有限元模型,研究了70 MPa 工作压力下,结构参数如锥面角、球头半径、外倾角对管接头接触密封性能的影响。研究结果表明:锥面角对密封区域的接触点中心位置、接触带宽影响较大,球头半径主要影响密封区域的接触带宽度,而外倾角对密封区域的接触应力影响较大。研究结果对于管接头的结构尺度优化具有指导意义,同时为超高压管接头组件的研发提供了技术支撑。     

IDENTIFICATION OF TIME-VARYING MODAL PARAMETERS USING LINEAR TIME-FREQUENCY REPRESENTATION

A new method of parameter identification based on linear time-frequency representation andHilbert transform is proposed to identify modal parameters of linear time-varying systems frommeasured vibration responses. Using Gabor expansion and synthesis theory measured responses arerepresented in the time-frequency domain and modal components are reconstructed by time-frequencyfiltering. The Hilbert transform is applied to obtain time histories of the amplitude and phase angle ofeach modal component, from which time-varying frequencies and damping ratios are identified. The     

基于ANSYS的管子车床主轴动力学分析

借助有限元分析软件ANSYS,对一种具有径向进给功能的管子车床主轴系统进行三维建模,然后选择六面体单元Solid95进行网格划分和模态求解,计算出主轴系统的前五阶固有频率及其振型,验证了主轴系统的固有频率远高于发生共振的临界频率。通过加减谐载荷,在模态分析的基础上进行谐响应分析,计算出主轴系统在激振力作用下的响应位移与响应应力,得到系统的动力响应与系统振动频率的曲线,即幅频曲线,验证了该主轴结构能经受住不同频率的各种正弦载荷。经过以上动态特性的研究,获得了机床主轴组件的动态参数,为机床主轴组件设计和结构改进提供了重要依据。     

EFFECTS OF TESTING,ANALYSIS, DAMAGE,AND ENVIRONMENT ON MODAL PARAMETERS

Experimental and analytical modal analysis techniques have been widely used in civil engineering for a number of years, mostly in seismic applications. Since the beginning of this decade, these techniques have received considerable attention in non-seismic applications such as structural damage detection, analytical model calibration and remote-monitoring systems. In these applications, most studies have concentrated on correlating modal parameters to changes in structural condition. However, for reliable performance of modal techniques in field situations, it is essential to understand and establish the variability of modal parameters due to test procedures and in-service environments of structures. New York has been researching this subject extensively for the past few years, and has tested several structures including (1) a 1/6-scale model highway bridge, (2) an abandoned fracture-critical highway bridge and (3) an in-service highway bridge. Both the abandoned highway bridge and model bridge were tested under intact and simulated-damage conditions. This paper briefly describes these studies. Results indicate that modal frequencies in conjunction with mode shapes may be used to identify the existence of bridge damage or deterioration of interest, but it is difficult to isolate damage locations using these modal parameters. Operating conditions affect the modal properties and are critical in establishing a baseline for structural monitoring.     

The free vibration analysis and optimal design of an adhesively bonded functionally graded single lap joint

In this study, three-dimensional free vibration and stress analyses of an adhesively bonded functionally graded single lap joint were carried. The effects of the adhesive material properties, such as modulus of elasticity, Poisson's ratio and density were found to be negligible on the first ten natural frequencies and mode shapes of the adhesive joint. Both the finite element method and the back-propagation artificial neural network (ANN) method were used to investigate the effects of the geometrical parameters, such as overlap length, plate thickness and adhesive thickness; and the material composition variation through the plate thickness on the natural frequencies, mode shapes and modal strain energy of the adhesive joint. The suitable ANN models were trained successfully using a series of free vibration and stress analyses for various random geometrical parameters and compositional gradient exponents. The ANN models showed that the support length, the plate thickness and the compositional gradient exponent played important role on the natural frequencies, mode shapes and modal strain energies of the adhesive joint whereas the adhesive thickness had a minor effect. In addition, the optimal joint dimensions and compositional gradient exponent were determined using genetic algorithm and ANN models so that the maximum natural frequency and the minimum modal strain energy conditions are satisfied for each natural frequency of the adhesively bonded functionally graded single lap joint.     

基于KBE的管道支吊架设计系统

管道支吊架设计工作中，设计人员要经常查阅专业资料对其进行变参数、变结构设计。为解决这个问题，将参数化技术和知识工程结合在一起，开发了基于KBE的管道支吊架智能设计系统Hanger Wizard。该系统利用知识熔接技术、数据库技术、UDF（USer Defined Feature）技术和知识向导界面设计技术，实现了管道支吊架的快速变形设计和支吊架参数与管道参数同步更新。     

Multipixel system for gigahertz frequency-domain optical imaging of finger joints

Frequency-domain optical imaging systems have shown great promise for characterizing blood oxygenation, hemodynamics, and other physiological parameters in human and animal tissues. However, most of the frequency domain systems presented so far operate with source modulation frequencies below 150 MHz. At these low frequencies, their ability to provide accurate data for small tissue geometries such as encountered in imaging of finger joints or rodents is limited. Here, we present a new system that can provide data up to 1 GHz using an intensity modulated charged coupled device camera. After data processing, the images show the two-dimensional distribution of amplitude and phase of the light modulation on the finger surface. The system performance was investigated and test measurements on optical tissue phantoms were taken to investigate whether higher frequencies yield better signal-to-noise ratios (SNRs). It could be shown that local changes in optical tissue properties, as they appear in the initial stages of rheumatoid arthritis in a finger joint, are detectable by simple image evaluation, with the range of modulation frequency around 500 MHz proving to yield the highest SNR.     

Environmental effects on the identified natural frequencies of the Dowling Hall Footbridge

Continuous monitoring of structural vibrations is becoming increasingly common as sensors and data acquisition systems become more affordable, and as system and damage identification methods develop. In vibration-based structural health monitoring, the dynamic modal parameters of a structure are usually used as damage-sensitive features. The modal parameters are often sensitive to changing environmental conditions such as temperature, humidity, or excitation amplitude. Environmental conditions can have as large an effect on the modal parameters as significant structural damage, so these effects should be accounted for before applying damage identification methods. This paper presents results from a continuous monitoring system installed on the Dowling Hall Footbridge on the campus of Tufts University. Significant variability in the identified natural frequencies is observed; these changes in natural frequency are strongly correlated with temperature. Several nonlinear models are proposed to represent the relationship between the identified natural frequencies and measured temperatures. The final model is then validated using independent sets of measured data. Finally, confidence intervals are estimated for the identified natural frequencies as a function of temperature. The ratio of observed outliers to the expected rate of outliers based on the confidence level can be used as a damage detection index.     

用凝聚技术综合时序分析法和有限元法识别机床的结构参数

机床接触面刚度和阻尼的确定是对机床进行动态分析和优化设计的关键问题之一。本文提出了一种识别机床接触刚度和阻尼的新方法,它利用一种新的凝聚技术把时序分析法和有限元法结合起来,从而只要利用一、二个不完全的振型就可以识别机床接触面的结构参数。这方法由两大部分组成。首先利用时序分析法从实验数据序列建立随机的自回滑动平均向量（ARMAV）模型并进而确定机床的模态参数。然后把机床结构有限元模型在某一复频下进行精确凝聚。并根据从时序分析法和凝聚后的有限元模型得出的模态参数必须相等的条件,就可以识别未知的机床结构参数。利用计算机仿真技术对新提出的方法进行了验证,证明它具有很高的识别精度。最后进行了立柱模型实验,对立柱底部的接触刚度和阻尼成功地进行了识别。