Design And Development Of Virtual Experiment Modal Analysis Instrument

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 systemoffers 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.