基于模态应变能的海洋平台损伤定位试验研究

针对海洋平台等大型复杂土木工程结构，研究了基于振动响应测试的结构损伤诊断方法。采用特征系统实现算法，仅利用输出响应进行模态参数识别，基于模态应变能的变化来进行损伤定位。为了验证该方法的有效性，制造了钢质导管架式海洋平台模型，进行了振动台试验。模型预先在某些典型构件处设置了法兰连接件用来模拟损伤，针对斜撑构件测试了多种单损伤和两损伤工况。针对各种损伤工况进行了模态识别和损伤检测，试验结果表明，基于输出响应的模态应变能法进行斜撑损伤定位是可行的。     

机夹式球头铣刀有限元及试验模态分析

针对加工过程中机夹式球头铣刀振动控制和铣削稳定性优化等问题,基于通用有限元软件ABAQUS建立了机夹式球头铣刀的有限元模型,对其模态特性进行有限元分析,给出了前6阶固有频率和振型;同时采用锤击激振法对球头铣刀进行了模态试验,应用模态参数识别的新技术PolyMAX方法对试验结果进行了处理,获得了模态参数识别稳态图,拾取了可能的模态频率,并将所得试验结果与有限元模态分析结果作了比较,计算了仿真值与试验值之间的误差,分析了出现误差的主要原因。研究结果表明,有限元模态分析结果与模态试验结果相吻合,模态频率误差在13%以内,较好地反映了结构的物理特性,同时验证了有限元模型的合理性,分析结果为球头铣刀振动控制和铣削稳定性研究提供了依据。     

基于ANSYS的塔式起重机结构动态分析

利用ANSYS建立某塔式起重机有限元模型,对其进行瞬态动力学分析和模态分析,计算获得在三种典型工况下结构的位移,分析了起升动载系数;并在三种典型工况下受载变形后的振动进行了探讨,计算获得受栽后的结构振动频率,并将受载后的振动频率和振型与塔机自由振动的频率和振型进行了对比分析.     

桁架结构有限元及试验模态分析

在ABAQUS软件中分别用梁单元和壳单元建立了桁架有限元模型,并利用有限元模态分析得到其低阶固有频率和振型。同时采用锤激法对中间节臂架进行了试验模态分析,利用LMS PolyMAX分析方法对试验结果进行了处理,并与有限元模态分析结果比较。结果表明:两种简化模型的有限元模态分析与试验结果相吻合,频率误差均在10%以内,验证了有限元模型的正确性和可靠性,确保了臂架系统有限元分析的准确性。     

挖掘机式冲击器工作装置的谐响应分析

参考30 t级机型建立挖掘机式冲击器两种典型工况姿态的三维模型,将模型导入ANSYS Workbench中建立较高网格精度的有限元模型。对工作装置进行模态分析获得两种工况的频率和振型,然后采用模态叠加法进行谐响应分析获得两种工况工作装置关键部位沿X、Y和Z向的在频域的位移响应曲线。为了解挖掘机式冲击器工作装置关键部位的幅频特性,挖掘机和冲击器的频率匹配提供一定的依据。     

柴油机缸盖结构有限元模态分析和模态测试

利用有限元分析软件ANSYS对造型十分复杂的某发动机缸盖结构建立了有限元模型,而后进行了自由模态分析计算,得到了该缸盖结构的低阶振动模态频率与模态振型.为验证模态分析模型的正确性,对该缸盖结构进行了模态试验测试,用锤击法对缸盖结构进行振动激励,利用测试软件获取缸盖结构的低阶振动模态频率与振型.通过有限元模态分析与模态测试结果的对比,验证了有限元模态分析模型与结果合理性,为该类型发动机缸盖结构设计与优化提供了参考依据.     

测量噪声对海洋平台损伤检测的影响研究

振动信号模态识别是检测海洋平台损伤的有效手段,但在实际检测中存在多种干扰因素,其中测量噪声对损伤检测结果有显著影响。基于此,在局部测量的基础上进行振动试验研究,明确测量噪声、模态参数与海洋平台损伤检测结果的关系。     

某车型引擎盖模态分析及优化

为了使引擎盖的固有频率避开汽车发动机的工作频率,需要对引擎盖的模型进行分析。以某车型的引擎盖作为研究对象,将引擎盖的CAD模型导入Hypermesh软件中,得到该引擎盖的有限元模型,依据模态分析理论进行模态仿真;采用多点激励单点响应的办法,通过力锤敲击法获得引擎盖试验模态。将仿真结果与试验结果进行对比可知,除第一阶固有频率误差稍大外,2-5阶的试验结果与仿真结果保持了很好的一致性;1阶振型为引擎盖的弯曲振动,2-5阶振型为引擎盖的局部振动,前五阶振型的形态基本相同。通过比较试验模态和仿真模态,验证有限元模型的正确性。在匀速工况下,发动机对引擎盖的激振频率为100±1.67 Hz,与引擎盖的第五阶频率比较相近,为了避免共振的发生,需要对引擎盖的模态进行优化,提高整车动态感知水平。     

基于模态相关分析的发动机曲轴箱模型修正

以发动机曲轴箱为例,给出一种复杂结构有限元模型合理性验证的方法。采用锤击法测得曲轴箱的试验模态频率和固有振型,应用Ansys建立有限元模型并进行了计算模态分析,对试验模态和有限元模态进行模态相关分析,检验有限元模型的合理性。修正后的有限元模型,与实验的前5阶频率和振型基本吻合。     

基于FEM的新型运煤敞车的结构模态分析

基于有限元分析方法,对运煤敞车的结构简化、单元选取、边界及约束处理等建模技术进行阐述.应用ANSYS对运煤敞车空车和重车进行计算模态分析.结果表明,该敞车空车和重车模态振型基本相同,但同振型的空车模态频率均比重车高.与试验模态相比,车体刚体振动的模态频率与试验结果误差相对较大,而弹性振动的模态频率较接近,这为车体的轻量化设计提供了合理的设计模型.     

Y-24手持式凿岩机模态分析

凿岩机动态特性对其工作性能有着重要影响。应用DASP测试系统通过实验模态的方法,对Y-24手持式凿岩机进行参数识别,获得其固有频率、阻尼和振型,结果表明凿岩机冲击频率27Hz低于其一阶固有频率37.6Hz,避免共振;隔振材料降低了手柄振动量,减少对人体的危害,这为Y-24手持式凿岩机结构设计提供了依据。     

Measurement and correlation of high frequency behaviors of a very flexible beam undergoing large deformation

A correlation method of high frequency behaviors of a very flexible beam undergoing large displacement is presented. The suggested method based on the experimental modal analysis leads to more accurate correlation results because it directly uses the modal parameters of each mode achieved from experiment. First, the modal testing and the parameter identification method are suggested for flexible multibody dynamics. Due to the flexibility of a very thin beam, traditional testing methods such as impact hammer or contact type accelerometer are not working well. The suggested measurement with high speed camera, even though the test beam is very flexible, is working well. Using measurements with a high speed camera, modal properties until the 5th mode are measured. And After measuring each damping ratio until the 5th mode, a generic damping model is constructed using inverse modal transformation technique. It’s very interesting that the modal transformation technique can be also applied even in the ANCF simulation which uses the global displacement and finite slope as the nodal coordinates. The results of experiment and simulation are compared until the 5th mode frequency, respectively, by using ANCF forced vibration analysis. Through comparison between numerical simulation and experiment, this study showed that the proposed generic damping matrix, modal testing and parameter identification method is very proper in flexible multibody dynamic problems undergoing large deformation.     

Experimental modal test of the spiral bevel gear wheel using the PolyMAX method

To verify the effectiveness and correctness of free modal analysis results from a Spiral bevel gear (SBG) wheel by using Finite element method (FEM), an experimental platform was constructed through the free-hanging support of the SBG wheel. The experiment used the hammer knock percussion for excitation and a three-directional acceleration sensor as signal acquisition equipment and utilized the LMS modal analysis module. The geometric model of the SBG wheel was constructed using an eight-node octagon instead of the SBG wheel outer contour. The experiment then extracted the modal parameters of the wheel using the PolyMAX method and obtained the first- and second-order natural frequencies, damping ratios, and mode shapes of the SBG wheel at 0-7 kHz during the experimental modal test. The results of the experimental test were compared with those of the FEM free modal analysis. The first- and second-order natural frequency error rates by FEM were 0.25 % and 0.45 %, respectively. The experimental modal test result verified the rationality of the model by FEM, thus showing that the result of modal analysis by FEM is reliable and providing a basis for the dynamic characteristic analysis of SBG.     

基于遗传算法的海洋平台损伤诊断

海洋平台结构在环境因素下可能出现局部破损,提出一种快速诊断结构损伤的损伤探测方法,而遗传算法因其方法简单及较强的鲁棒性成为近年来发展较快的一种全局优化方法。以海洋平台实测的固有频率和振型为诊断依据,将海洋结构的损伤诊断归结为优化问题,采用遗传算法进行优化搜索。考虑到平台结构刚度的方向性,针对测量噪声和海洋平台模态的特点,提出了一种修正的目标函数作为遗传算法进行损伤诊断的适应度函数。数值模拟和物理模型试验结果表明,该方法能够准确地诊断出导管架海洋平台结构的损伤,改进了进化搜索的鲁棒性,提高了海洋平台结构损伤诊断的可靠性。     

叶片振动响应的长度分形故障特征提取与诊断

为有效地从风力发电机组的振动响应中获得反映叶片响应的动态特征,将其作为叶片运行状态分析的特征量,依此达到对风力机叶片故障的检测与诊断识别.应用有限元分析方法,建立了300 W风力发电机组的动力学模型,通过计算与试验模态分析,分别获得整机组的固有频率和振型,并比较验证了试验模型的合理性.用锤击法测得叶片正常状态和偏心故障下的振动加速度响应信号,应用非线性动力系统的长度分形维数理论,计算其长度分形维数,并将其作为叶片偏心故障诊断识别的特征量.研究结果表明,该方法能有效识别风力机叶片正常状态和偏心故障状态,及其偏心位置和偏心量大小.     

基于模态分析的某型飞机液压管路故障诊断

 针对某型飞机液压管路吸油模块与扩口式直角接头连接处螺纹损坏，接头脱出，导致液压系统漏油的故障，建立了管道有限元动力学模型，进行了管道模态仿真分析。发现故障管道出现了导致管道故障的危险模态，该阶模态频率范围正好在发动机的工作转速范围内，在发动机振动频率的激励下，激发该阶模态振动，引起管道共振，产生很大的作用力，导致连接螺纹损坏和接头脱出，从而形成故障。基于模态分析方法，对该管道进行了改进，有效地避免了该阶模态的出现。实际的飞机管路系统的改进效果表明了分析方法的正确性。     

采用PATRAN/NASTRAN的滚刀主轴频率响应分析

采用有限元分析方法,运用PATRAN/NASTRAN软件,对零传动滚齿机YK3610的滚刀主轴进行模态分析,获得固有频率和振型。在此基础上分析滚刀主轴切削点在工作频率附近及其共振区的频率响应;研究滚刀主轴系统部分节点在其共振区的频率响应。分析结果表明:在工作频率内,主轴切削点的径向响应位移都比较小,能满足设计需求;滚刀主轴低阶固有频率均高于其工作频率,不会发生共振现象;通过在共振区的位移频响分析,发现主轴系统在共振的时候,主轴的后端振动幅值最大,是最危险点,由此提出几点提高主轴系统动静态特性的措施。     

桥梁结构损伤的振动模态检测

首先介绍了桥梁结构损伤检测的振动模态方法的原理及其４ 个要素。总结了用模态参数（固有频率、阻尼比及位移振型）进行损伤检测评估的困难,进而阐述应变模态测量的原理及其用于桥梁结构损伤检测时,相对于位移模态的优势。由于应变模态方法应用于实桥检测受到传统应变测量手段的制约,本文最后提出了一种通过相邻点振动位移的测量,推估桥梁在动载作用下的应力状态,进行实桥损伤检测的途径,并推荐一种新型低频高灵敏度传感器作为位移测量用传感器。     

Vibration modeling and modification of cutting platform in a harvest combine by means of operational modal analysis (OMA)

Vibration in combine cutting platform causes increase in grain loss, reduction of vehicle lifetime and driver’s comfort, and also affects the machine working precision. In order to determine vibration behavior of a mechanical structure, the model which relates acting forces on the structure with the resulting responses of it plays a significant role. For a great deal of mechanical structures, only response data are measurable while the actual loading conditions are unknown. Therefore, the system identification process will need to build on the output-only data. The use of such processes allows the identification of modal models of structures which are excited by unknown ambient vibration. In this contribution, controlled vibration experiments were conducted on cutting platform of a combine in order to recognize and reduce its vibration problem. A finite element model is constructed representing the vibration behavior of the cutting platform. Also, the frequency domain decomposition (FDD) technique is used to estimate the modal parameters of vibrating structures in operational conditions. Then, the finite element model is successfully updated by comparing the estimated results of the operational modal analysis. It is found that there is a resonance condition around 50 Hz. Then, the mass change strategy is used to estimate the scaling-factor and frequency response function (FRF) matrix. Finally, the resonance condition and subsequently vibration of cutting platform is reduced by the structural modification technique. As a result of this modification, natural frequency of fifth mode shape (50 Hz) of the combine cutting platform is shifted to 48 Hz.