外文翻译--UG模态分析

附 录 A 1. 关于软件接口连接 UG 为三位建模软件，有较为完善的分析功能，在独立建模是可进行质量，面积，体积，强度等多方面计算，可自行编程进行导入式分析。 UG 软件近几年在国内开始运用，仍存在许多不足，在本次毕业设计中所体现的主要问题在于软件的不完全兼容， UG 建模软件与 ANSYS 分析软件存在结构稍复杂模型不可执行布尔操作及分析，主要原因通过解读导入程序得知，在 ANSYS 分析软件中对 UG实体建模程序转换不完全，所导致建模文件丢失性较大。存在软件版本配合问题，同为高版本软件时导入文件出现丢失情况较小。如 UG7.5与 ANSYS12.0之间导入文件时仅丢失少部分文件，同平面建模相对导入性较好。适于结构简单模型进行运用。 2. 模态实验应考虑的问题 实验模态分析就是以控制理论为基础，从所测得的输入、输出信息中去辨识结构的模态参数。近几年来，实验模态技术发展很快，各种测试手段日益更新，模态参数识别软件也层出不穷，这为我们获得结构的较为准确的模态参数带来极大方便。 （ 1）激振方法 激振方法的选择包括两方面内容：采用什么样的激振信号；采用单点激振还是多点激振。问题的中心在于是否能够提供足够的能量，把需要 的频段中的模态全部激发出来。激励信号可采用随机信号、脉冲信号等。随机信号可用白噪声发生器产生，试验中选用了 0-160Hz白噪声信号，其优点是，能量均匀分布在频带上，且在较宽频率范围内对结构进行激励，总的激振力水平，便如平均值、均方值等是可以控制的；其缺点是泄漏误差大。用锤击法提供脉冲信号，该方法的优点是设备简单，不需要精心设计安装激振器的夹具，便于现场测试或在线测试；激振点可以灵活，敲击力方向可以任意；测试精度能满足一定要求，高于随机激励。缺点是激振力频率范围不易控制；仅适合于低频，高频模态不易激出来；由于 振动能量分散，从而信噪比小；锤击有时可能过载，使结构进入非线性范围。固定的激振点是经过多点试敲后选定的。模态分析的频域法有两种：单点激振法和多点激振法。多点激振法需要昂贵的多点激振设备，试验过程复杂，但计算比较简单；单点激振法所需设备简单，试验也较容易，但计算方法要复杂上些。在本次实验中根据现有条件，采用单点激振法。 （ 2）固定方式 在进行部件模态实验分析时，首先要确定被测物体的固定方式。固定方式一般有两种：一种是按照其实际工作状的方式约束，这种固定方式主要是用于较波折部件或在振动台上进行试 验；二是悬吊式。由于本次实验对象是车架，不可能选择实际工作状态方式，故采用橡皮绳悬吊式，使其处于自由状态下进行分析。结构处于自由状态具有最多的自由度，这样得到的模态参数便于与其他部件一起进行整体结构的综合模态分析。具体悬吊方江是：车架左右纵梁前后端各用一根橡皮绳将整个车架吊挂在大型吊架上，即为四点悬吊式。经实测，车架挂上后，系统的固有频率（所谓的 “ 刚体模态频率 ” ）中的最高者为 0.816Hz，小于第一阶弹性模态频率（ FI=20.67Hz）的 1/5，可近似认为被吊的车架处于自由状态，这样可以防止悬挂的刚体模戊与 车架的弹性模态发生耦合。 （ 3）激励方式 采用电磁式激振器，最大激振力为 200N。激振器的推杆顶端连接一个力传感器，力传感器固定在车架后横梁右下部。为了保证测试精度，不能让被测物体有附加约束而产生其它外力，例如，对结构激振时，除了产生垂直振动外，还将产生回转（转角），这时如果因为有激振器连接限制其转动，就会产生附加的弯矩。为了解决这一问题，激振器和被测物体之间的推杆需要有一定的侧向弹性，这样既能保证在激振方向有一定的刚度，不影响激振力的传递，双能减少在侧向对回转的约束。另外，推力杆的自振 频率应远离被测物体的模态频率。在试验中要求顶杆与车架之间不能脱离，顶杆与力传感器间不能有任何松动和间隙。此次试验采用顶杆与力传感器间通过螺纹连接。为防止顶杆与车架脱离，将力传感器固定在一个小底座上，该底座用螺纹与一磁铁相联，同时将磁铁块吸附在车架上。还应注意激振点不应与测试频段内任何一阶振型的节点相重合。因此在进行正式试验以前应先进行预测。 ? （ 4）试验频段的选择 试验频段的选择应考虑到汽车在运行条件下可能的激振频率范围，通常认为，远离振源频带的模态对结构的实际振动影响（贡献量）较小。通俗 的说法就是 “ 低频激励激不出高频模态 ” 。事实上，高频模态贡献的大小，除与激振频率有关外，还与激振力的分布状况有关。此外，如果部件进行综合分析，以求整体结构的模态，为使整体模态具有更高的精确度，部件模态试验的频段也应适当放宽，以求得稍多的模态。总值年模态过少，而各部件之间的连接点较少时，就不便于对整车进行综合分析。 考虑到汽车的运行速度与路面条件以及车架与其他部件进行综合分析的需要，选取 0-120Hz作为其试验频段。 （ 5）测点布置 测点布置原则是：布置在悬架支点，纵、横梁连接点和 刚度变化较显著的点上；尽可能使车架纵梁布点均匀，左右对称布置。这样，既便于今后的模态综合，又不致使识别的模态失真。测点布置、测点数量的选择还应考虑到以下两方面的要求：能够明确显示在试验频段内所有模态的基本特征及互相间的区别；保证所关心的结构点（如与其它结构的连接点），都在所选的测量点之中。为提高信噪比，测点不应选在各阶振型节点附近；在研究的主要部位，测点布置应较为密集。用压电式加速度传感器测量各测点在垂直方向上的振动加速度响应，并将信号记录在磁带机上（锤击法时），或现场采集信号，实时处理得到频响函数，存储于 微机硬盘（白噪声激励时）。 测振时加速度计安装正确与否，对测量结果的正确性有很大的影响。安装方式多种多样，我们根据测试频段及车架的构造，采用永久磁铁吸附法的安装方式以求简便、准确。 （ 6）为提高测试精度应采取的措施 1） 仔细标定系统灵敏度。在机械阻抗测量时，我们校正的不仅是单个传感器的灵敏度，而是力传感器与加速度传感器灵敏度的相对比值。具体方法见参考文献。 2） 冲击力的大小决定于激起各阶模态所需之能量水平，但过大的冲击力会造成局部非线性，所以锤击时要控制冲击力的大小。 同时锤击的动作要迅速，不能抖动，特别要防止试件反弹造成二次冲击。 3)为了减少谱泄漏，在处理时应采用数据窗。对冲击激励函数分析，采用指数衰减数据窗可以减少噪声总电平。 4)为检查模态参数可靠性，可采取互易性来检验，即根据阻抗矩阵的对称性，在 P点激振、 L点测振的响应与 L点激振、 P点测振的响应相同。 5） 进行数据处理时，首先需要确定触发系统。脉冲信号采用信号触发。即当有一脉冲信号过来时，才进行一次触发平均。为减少随机误差，应进行多次平均。 6） 考虑到架结构的阻尼较小，频响函数 的半功率带较窄，故应尽量提高频率分辨率。 7） 传递函数可信性检验。所有时域信号均在微机上显示，正常时才往下进行。每个传递函数都用相干函数检验，相干函数绝大多数都在 0.85以上。 8） 力谱要符合要求，幅值差不大于 3dB。 附 录 B for software interfaces connection UG for three modeling software, there are more complete analysis, in the modeling is available to the area, volume, quality and strength for the various programming for import by itself, but in the analysis. UG software in the past few years at home and begin to use many. at the graduation design by the main problem lies in the software is not entirely compatible, modeling and UG ANSYS analysis software is a model not perform complicated structure and analysis, boolean The main reason by interpreting the importer, the analysis software ANSYS UG entity modeling applications for conversion, not by modeling papers missing. there is sexual older version match, with the high edition software import file a missing information. as a smaller UG7. 5 and ANSYS12.0 between the import file was missing document, with a plane model in the import of the better. for simple model be applied. Modal test should consider Experimental modal analysis is to control theory, from the measured input and output information to identify structural modal parameters. In recent years, experimental modal technology has developed rapidly, growing a variety of test methods updated modal parameter identification software is also another, which as we get more accurate structure of the modal parameters of a great convenience. excitation method Exciting choice of methods, including two aspects: what kind of excitation signal； excitation using a single point or multi point excitation. Question is whether the center can provide enough energy, the band needed to stimulate all the modes. Excitation signal can be random signals, pulse signals. Random white noise generator signal is available, test the selected 0-160Hz white noise signal, its advantage is that energy is uniformly distributed in the band, and a wide frequency range of the structure of incentives, the total level of the exciting force, just like a mean, mean square values, etc. can be controlled； its major drawback is that leakage error. Provide pulses with the hammer method, this method has the advantage of simple equipment, do not install the exciter fixture designed for easy field testing or online testing； excitation point can be flexible, percussion force direction can be arbitrary； test accuracy can meet certain requirements, higher than the random excitation. The disadvantage is difficult to control the frequency range of exciting force； only suitable for low frequency, high-frequency modes is not easy to shock them； vibrational energy spread due to noise ratio is small； hammer can sometimes overload the structure into the nonlinear range. The excitation point is fixed multi-point try after the selected after the knock. Modal analysis of frequency-domain method in two ways: single-point excitation method and multi-point excitation method. Multi-point excitation method requires expensive multi-point excitation equipment, the testing process complex, but the calculation is relatively simple； single-point excitation method required simple equipment, the test is relatively easy, but on a more complicated calculation. In this experiment, under the existing conditions, using single-point excitation method. Fixation During the experimental modal analysis of components, the first object to be measured to determine a fixed way. Fixed the way to have two: one is shaped in accordance with the actual work the way constraints, this fixation is mainly used for more twists and turns parts or the vibration table and tested； second is suspended. As the object of this experiment is the frame, means the state can not choose the actual work, so use rubber rope suspended, it is in a free state for analysis. Structure in a free state with the largest degree of freedom, so easy to obtain the modal parameters together with other parts of the overall structure of a comprehensive modal analysis. Jiang is the specific suspension side: left and right frame rails front and back of the rubber with a hanging rope to the frame in a large hanger, that is, four suspended. After measurement, the frame mount, the systems natural frequency (the so-called rigid body mode frequency) in the highest of 0.816Hz, less than the first order elastic modal frequency (FI = 20.67Hz), 1 / 5 , can be approximated that the frame was hanging in a free state, which would prevent suspension rigid with the frame of the elastic modulus E mode coupling occurs. Incentives Using electromagnetic shaker, maximum exciting force of 200N. Exciter putting the top connected to a force sensor, force sensors fixed on the bottom right of the frame after the beams. In order to ensure test accuracy, so that the measured object can not have additional constraints arising from other external forces, for example, excitation of the structure, in addition to generate vertical vibration, it will also produce rotation (angle), then if the connection limit because of the exciter its rotation, will produce additional moments. To solve this problem, between the exciter and the measured object putter need to have some lateral flexibility, so that can guarantee a certain direction in the excitation of stiffness does not affect the transmission of the exciting force, can reduce the double In the lateral constraints on the rotation. In addition, the thrust rod natural frequency away from the modal frequency of the measured object. Required in the test between the ejector and the frame can not be separated from the mandrel and the force between the sensor does not have any loose and gaps. The test used by the ejector and the threaded connection between the force sensor. To prevent the mandrel and the frame out, the force sensor fixed on a small base, the base with a thread associated with a magnet while the magnet adsorption on the frame. Excitation point should also note that the band should not be testing any vibration mode of the nodes coincide. Therefore, during the trial to be preceded by the official forecast. ? the choice of test frequency Test frequency selection should take into account vehicle operating conditions possible in the excitation frequency range, generally considered, away from the local oscillator frequency of modal vibration of the structure of the actual impact (contribution amount) is small. Popular saying that no high-frequency low-frequency laser excitation modes. In fact, the size of the contribution of high-frequency modes, in addition with the excitation frequency, but also with the distribution of the exciting force. In addition, if parts of a comprehensive analysis, the overall structure of the mode in order for the overall mode has a higher accuracy, the test frequency modal components should also be relaxed, in order to achieve slightly more modal. Modal value was too small, and the connection point between the various components when there are fewer, not to facilitate a comprehensive analysis of the vehicle. Taking into account the cars speed and road conditions, and other parts of the frame with a comprehensive analysis of needs, select 0-120Hz band as its pilot. measuring points Measuring points principle is: arranged in the suspension pivot, vertical, beam stiffness of the connection point and the more significant point； distribution frame rails as far as possible uniform, symmetrical layout. In this way, both for the future of the modal synthesis, modal identification without causing distortion. Measuring points, measuring points of the selection should also take into account the following two requirements: the ability to clearly show the band in the test mode all the basic characteristics and differences between each other； to ensure the structural point of interest (such as with the other structures connection point), are among the selected measurement points. To improve the signal to noise ratio, the measuring point should be selected in the vicinity of the first vibration mode node； the main part in the study, measuring points should be more intensive. Piezoelectric acceleration sensor with the measuring points in the vertical vibration acceleration response, and the signal recorded on the tape drive (when the hammer method), or on-site signal acquisition, real-time processing to get frequency response function, stored on computer hard disk (white noise excitation). Vibration when the accelerometer is installed correctly or not, the accuracy of the measurement results have great impact. Install a variety of ways, we test the frequency and the frame according to the structure, the use of permanent magnets in order to assay the installation simple and accurate. To improve test accuracy measures to be taken 1) careful calibration of the system sensitivity. In the mechanical impedance measurements, we corrected the sensitivity of the sensor is not only the individual, but force sensor and acceleration sensor relative sensitivity ratio. Specific methods see reference. 2) The impact depends on the size of the order provoked modal energy level required, but the impact is too large will result in local non-linear, so when the hammer impact force to control the siz