| Operating modal analysis is a new technology of modal analysis. The operating modal parameters obtained only by responses of operating machinery or ambient excitation accord with the real operating situations and the boundary conditions, and illustrate the real dynamic behavior of the operating machine. This paper simulates the water supply system of high building with an experimental model of piping system, studies the theory and methods of identification of operating modal parameter with the periodic excitation.Firstly, the vibration and noise signals of the water supply piping system in the operating state are detected and analyzed, and the frequency spectnims of the signals are got, wich provides the theoretic base to operating modal analysis only using the response datas. Based on the experimental modal analysis and finite element analysis, the modal paramenters, such as the modal frequencies and mode shapes, of the pipeline system are obtained experimentally and numerically, which can be regarded as the reference of operating modal analysis.This paper presents the theory and method of operating modal analysis, introduces the difference between operating shape and modal shape, deduces the ODS FRF measurement of operating modal analysis, and draws the conclusion: if the excitation force spectrum can be assumed to be relatively flat over in the frequency range of the modes of interest, men ODS FRFs can be curve fitted to obtain the operating modal parameters.Based on the operating modal analysis of the experimental model of piping system, the frequency domain ODS and the operating modal parameters are obtained. And to satisfy with the condition of white noise excitation, the responses are preprocessed with the technology of band stop filter. The operating modal parameters are obtained and shapes are got by curve fitting the ODS FRFs generated. Compared with the results of experimental mode, it proves that the theory and methods of operating modal analysis are practicable.
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