Research On The System Of Experiment Modal Analysis For Mechanical Structure

Experiment modal analysis is the process to establish mathematic model of describing structure's vibration characteristic based on experiment. It provides the key method for the dynamic's characteristic parameters identification. And it plays the important role in structural designing and modifying. While the key step in the experiment modal analysis is modal parameters identification. So, How to improve the accuracy of the results of modal parameters identification in order to provide better serves to the structural designing and modifying is now being researched by many engineers.This paper has done many researches on the basis of the theories of modal analysis. In order to improve the accuracy of estimation results of frequency response function, this paper analyses some factors which can affect the accuracy of the results of modal parameters identification. According to the noise influence of the frequency response function, this paper puts forward an arithmetic for the optimization of frequency response function by using least-square method, and also analyses different parameters identification methods which can also affect the accuracy of the results of modal parameters identification. Based on these, two methods, component analysis method and orthogonal polynomial fitting method, which are widely used, have been done some researches, and arithmetic has been carried out. An experiment had been made to compare the two methods. To obtain the better accuracy of the results of modal parameters identification, this paper also dose some pilot study on modal parameters identification based on HHT and wavelet de-noising. The experiment shows that this method can improve the accuracy better.Based on the research on the basic theories of experimental modal analysis and analyzing the current research on corresponding software both at home and abroad, an experimental modal analysis software system is studied and developed by Visual C++, which is an object oriented programming software. According to the constitution of experimental modal analysis system and its main function, the software system has been divided into four function modules, which are structural building module, data acquisition module, frequency response function's analysis module, and parameters identification module. The software system adopts multi-view idea, which has four views and one module one view. Each view has its own menu and toolbar. Three test methods have been provided in the system, that are single input single output and single input multi-output, and single input single output has two forms, changing excitation point and changing response point. Parameters identification module gives two methods which are component analysis method and orthogonal polynomial fitting method, and it also has interface for any other methods.In order to test the experimental modal analysis system's correctness, a plane's experimental modal analysis has been done by this system and compared the results with the software ME'scopeVES. The compared results show that the system has the same accuracy with the software ME'scopeVES. At the end, an actual measurement of freely supported beam in vibration platform has been done to identify its parameters using this system, and the freely supported beam 's freedom frequencies, damping ratios and vibration mode have been identified.