Study On Structural Modeling Of Experimental Modal Analysis And Development On Virtual Intrusment Of Modal Analysis

The experimental modal analysis, which is based on the experimental data of input (excitation) and output (response) signals gained by the measurement system of modal experiment, through dynamic signal analysis and modal parameters identification, is to determine some dynamic characteristic parameters of mechanical structure, such as natural frequency, damping ratio, and modal vibration shape, etc. It is widely used in the fields of dynamic response prediction, structure dynamic modification, finite element model updating, dynamic analysis and design, vibration trouble-shooting, default diagnosis, and structural health monitoring, etc. It is an important and necessary method used in the manufactures'design, finalization, application and maintenance of aviation, aerospace, automobile, shipping, bridge, architecture, and mechanical equipments. The Virtual instrument is a special kind of instrument formed by the programs operating on the computer. By means of basic principles of digital signal analysis and computer programming, virtual instrument can realize the functions of the common measuring instruments can. Based on modal analysis technology and virtual instrument, and the application of object-oriented programming(OOP), the software development tool of Visual C++, and the design idea of modularization, a virtual instrument for modal analysis with the given type name of QLVC-MA2 is completely developed in this dissertation.In the dissertation, some relevant technologies to the researching subject, such as modal analysis technology, vibration testing technology and vitual instument are first introduced. Then the theoretical foundation of experimental modal analysis is elaborated. According to the process of experimental modal analysis, the calculation and estimation of frequency response function and the identification of modal parameters are elicited by the concept introduction and formula derivation of modal parameters in multi-degree-of-freedom system. In the section of the identification of modal parameters, some basic definitions, summery of methods, the identification method of orthogonal polynomial and the standardization of modal parameters recognition are mainly introduced.The software developing and hardware platform establishing of QLVC-MA2 virtual modal analysis system are finished in the research of the dissertation, and the QLVC-MA2 virtual modal analysis instrument is also developed by the combination of software and hardware.The object-oriented programming(OOP), software developing platform of Visual C++, software interface of OpenGL graphic processing, and programming idea of modularization are applied in the software system, with its four function modules which are: structure model input, data acquisition, data analysis (modal parameters recognition) and modal parameters output. The research of dissertation also includes structural modeling referring to modules of structure model input and modal parameters output. According to the principles of geometry modeling and solid molding techniques, the structural modeling is established by the aspects of structure and function. In the structure aspect, An improved point-line-plain model is applied, which is based on graphic unit object and sub-structure model. While in the function aspect, the software system can realize the following functions: graph drawing, graph editing, graph display, graph input, animation show and file processing.The establishment of hardware platform is based on the intergration of instruments. On the basis of this, the virtual modal analysis testing system is built by choosing appropriate experiment devices, such as impact force hammer, accelerometer, vibration exciter, etc. The modal analysis is experimented on the structures of simple supported beam, steel frame and autocycle frame.Finally, a conclusion of the research work is made, and the further research direction is also forecast in the dissertation.