Research On Identification Of Structure-Borne Noise Source From High-Speed Railway Bridge Based On Coherence Analysis

In recent years, high-speed railway in China experienced a rapid developing period; however, the accompanied noise pollution problem is paid growing concern at the same time. Due to its low frequency characteristics, the structure-borne noise radiated from bridge has the strong obstacle-crossing ability and is difficult to attenuation. At present, there is no effective measure to control this structure-borne noise. So it is necessary to study the local vibration of bridge and the noise radiation mechanism firstly; and then the main noise source should be identified to provide a theoretical and technical support for the noise reduction of bridge.In this thesis, a kind of noise source identification method based on coherence theory is presented with the in-situ data in a viaduct of Cheng-Guan Railway, noise radiation mechanism of local vibration in the bridge is discussed, and the main noise source are calculated and analyzed in detail. The main contents are as follows:1) The characteristics and applicable scope of commonly used noise source identification method are summarized, and a kind of noise source identification method combining spectral analysis and coherence theory is determined based on the structural characteristics of bridge, the theory about acoustic radiation efficiency of bridge is given;2) The spectral analysis method, the coherence analysis method and partial coherence analysis methods are systematically discussed, the iterative solution of optimal conditional input system and the calculation of the optimal frequency response function are given, then the corresponding Matlab code is programmed and the effectiveness of partial coherence analysis as the noise source identification method is proven by a numerical case;3) The measured data of noise and vibration of cross-section in box girder are analyzed in time domain and frequency domain; the local vibration and the noise radiation mechanism of cross-section in box girder are discussed; the structure-borne noise area and the complex noise area are determined qualitatively; the shortcomings of the current noise evaluation criteria for low-frequency structural noise are given;4) The spectral characteristics and coherence relationship of vibration of the bridge and near-surface noise are analyzed by the combination of spectral analysis and coherence function analysis, and the effects of the vehicle speed, driving track, and the location of cross-section in the box girder on the noise spectrum characteristics and coherent relationship are discussed;5) Through conditional spectrum and partial coherence functions, separation and identification of structure-borne noise sources are analyzed based on the theory of partial coherence, then the impact area of the structure-borne noise can be got the multiple coherence function, finally the independent contribution to environmental noise and its spectral characteristics of structure-borne noise radiated from the various parts of the local vibration will be obtained.Analysis above shows that the coherence theory combined with spectral analysis is an effective method to separate and identify the structure-borne noise and to get their independent contribution and the spectrum features of each noise source, and this study can be guidance for noise reduction measures for bridges.