Study On Precision Of Front Signal Of Experimental Modal Analysis And Produce On Virtual Intrusment Of Modal Analysis

With the development of computer technology, vibration measurement and virtual instrument, the experimental modal analysis has become an important engineering application technique since 1960s. So far, the correlative theoretical mode research has been perfected and gradually turned to the engineering application in various industries. The technique has become more and more popular, especially in the fields of mechanism, architecture, aviation, spaceflight, shipping, and automobile and so on. A variety of modal analysis softwares with different functions and levels have emerged inland and overseas. With the advancement of science and technology, the request of the precision of analysis result to the softwares has become higher in many engineering structures. However, due to the introduction of errors in structure itself, transducer, data acquirement, data processing, and parameter identification and so on, the result is usually not that precise. Hence, on the above situations, this dissertation produces a set of virtual instrument for modal analysis, with a deep and thorough research into the precision problem of frequency response function measurement of front signal processing.The dissertation first introduces the correlative research background and study status about experimental modal analysis inland and overseas, together with a systematical depiction of the basic knowledge about this analysis. Started from mechanics mode, the theoretical mode of modal analysis has been drawn, illustrating the principle of experimental modal analysis from both the positive and negative viewpoint. Based on the operation procedure, a complete process of experimental modal analysis is introduced, including the preparation before the experiment (the allocation, debugging and calibration of structure, the allocation of test nodes about impact and response, etc), the construction of geometrical structure mode, the original data acquisition of time field, the frequency response function measurement, the modal parameter identification, the validity of modal mode, the output of result parameter and mode shape and so on.Two means have been applied to the specific research on the precision of frequency response function measurement. The spectrum correction method of frequency extracting is used to first have spectrum correction of the original data of time field so as to improve the precision of spectrum. After the original data of time field of all test nodes and test directions are corrected, they are then used to measure the frequency response functions where the identification of modal parameters are based and a better precision result is received. The other is the method of higher-order spectral analysis, of which the high quality of noise non-sensitivity is used. After the bispectrum of the original data is measured, it is then used to reconstruct the DFT of the original data in the aim of reducing noise. Finally, the frequency response functions are measured, using the DFT data of reconstruction, and modal parameters are identified. The validity of the two methods has been testified respectively by the simulation result and the actual result of a simple supported beam, where a better precision result of modal parameters is gained.The dissertation also gives an emphasis on the programming process on the functional configuration of the QLVMA-2 virtual instrument of modal analysis. Concise and intelligible, and easy and quick to handle, the instrument adopts a graphical operation interface, embodying perfectly the characteristic of a'virtual'apparatus. The whole process of experimental modal analysis can be carried out on the QLVMA-2, including constructing mode of geometrical structure, the data acquisition of nodes on structure, frequency response functions measurement, modal parameter identification, display of result parameters and mode shapes, validity of modal mode, and so on. Based on the introduction, the validity and applicability of the QLVMA-2 virtual instrument of modal analysis is confirmed through a series of structure analysis examples, such as a simple supported beam, an armor plate, an I-Beam, a steel frame, and an autocycle frame. Compared with some distinguished modal analysis softwares inland and overseas and Abaqus which is a software of finite element analysis, the testified results also prove the reliability and accuracy of the QLVMA-2.The dissertation finally closes with a conclusion of the writer's research work and presents an expectation of the following research direction.