摘要
虚拟仪器技术作为虚拟现实技术的分支，是近年发展起来的一个研究热点。它凭借计算机平台的存储、处理、分析能力，结合计算机软件灵活、适应性强，修改、升级容易等优点，给传统的仪器测控带来巨大冲击。虚拟仪器技术受国家的高度重视，国家自然科学基金连续给予大强度资助，虚拟式试验模态分析仪器系统是自然科学基金资助项目“集成测试机械式虚拟式动态测试仪系统的研究（No.59875090）”及自然科学基金重点项目“面向机械测试的控件化虚拟仪器系统的研究（No.50135050）”的一个组成部分。
本文在总结了国内外试验模态分析涉及的理论、软件等已有成果，分析了现有试验模态分析软件一些不足的基础上，根据虚拟仪器的思想，提出了一种面向图元对象的三维实体结构输入输出方法，建立了基于OpenGL图形工业标准的实体输入输出模型，实现了以结点、梁图元、三角形图元、四边形图元等为基础的三维图形的输入、编辑与动态输出等。在此基础上，完成了试验模态分析的结构输入、数据采集、频谱分析、参数识别、振型输出等功能，开发了面向中小型结构，易于使用的虚拟式试验模态分析仪。
虚拟式试验模态分析仪主要由以下四个子系统组成：
（１） 模型结构输入子系统
（２） 数据采集与处理子系统
（３） 数据分析与模态参数识别子系统
（４） 模态振型输出子系统
仪器在整合四个子系统的基础上，保留了它们的相对独立性。输入输出涉及的图形操作、文件结构等方面与有限元软件保持了高度一致，保证了同有限元结构文件的兼容性；数据采集模块与分析模块不仅可以协同工作，也可以独立进行的数据采集、在线和离线的数据分析与参数识别等。仪器为对中小型结构的试验模态分析提供了单模态参数识别与多模态参数识别等多种参数拟合方法，并预留了增加新的拟合分析算法的接口。
在仪器验证中，首先选择了一悬臂梁进行测试，并将测试结果与其理论解进行了比较，结果表明仪器能较好识别梁的固有频率，求得其模态振型，达到了预期目的；其次对一摩托车架进行了试验模态分析，试验表明仪器能较好地分析出
车架的多阶模态，并显示出其模态振型。总之，虚拟式试验模态分析仪能方便地对中小型结构进行测试，具有性能好、精度高、易升级等优点。
本文着重于虚拟仪器思想在试验模态分析中的应用，为试验模态分析的虚拟仪器化提供了一个可以借鉴的思路，并给出了具体实践。论文在最后还指出了仪器有待完善的问题。
As an embranchment of virtual technologies, virtual instrument technology is becoming a hot issue in recent years. It resorts to the advantages of computer such as saving, processing, analyzing and computer software such as easy upgrading, easy modifying, high flexibility etc, which impacts on traditional measure and control instruments. Our country pay great attention to virtual instrument technology, and National Natural Science Foundation of China (NSFC) has also given strong sustentations to the aspects. Experiment modal analysis (EMA) plays an increasing important role in vibration test, structure designing, mechanical false diagnosis and so on. Virtual EMA instrument is a sub-project of 2 projects supported by NSFC, which includes 'research of integrated test, mechanic and virtual dynamic test instrument system (No. 59875090)' and 'research of mechanic test control oriented virtual instrument system (No. 50135050)'.
This article studies the relevant theories and knowledge of EMA and computer software, points out some deficiencies of present modal analysis technologies in our country, puts forward a method of objected-oriented 3D structure input and output, establishes a 3D input and output model based on OpenGL industrial standard, and realizes the 3D graphic input, edit and dynamic output, which are based on node cell, beam cell, triangle cell and quadrangle cell etc. On this base, the functions such as structure input, data collection, spectrum analysis, parameter identification and vibration shapes output are completed. All the functions are integrated together and a kind of virtual EMA instrument is developed according to the idea of virtual instrument.
Virtual EMA instrument is mainly composed of four sub-systems as follows:
(1) Structure model input sub-system
(2) Data collection and process sub-system
(3) Data analysis and modal parameter identification sub-system
(4) Modal vibration shape output sub-system
The instrument integrates the four sub-systems and remains the relevant independence of each. The input and output sub-systems keep consistency well with FEM software in the aspects of graphic operations and file structures, which insures the compatibility of the EMA system with FEM software. The data collection and analysis sub-systems can not only work together, but also run in independence. The system
offers different methods of parameter identifications for structures test including simple mode and multiple modes, and retains the interface of adding new smooth algorithms.
In order to test the instrument, a standard cantilevered beam is selected. And the results of test are compared with the theoretical ones, which show that the instrument can identify modes of the beam well. The second test aims to a motor frame, we can conclude from the experiment that the instrument can analyze multiple modes of complex structure and display its modal vibration shapes. In short, it can conveniently make a testing and has the advantages of high performance, high precision, low cost and easy upgrade etc.
The article mainly emphasizes on the application of virtual instrument idea in EMA software development. A practical method in the aspect is provided and a kind of virtual EMA instrument is given as an instance. At the end of the article, the problems, which need to be improved in the instrument, are discussed.
引文
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