Development of Technique for Identification of Excitation Sources Using Vibration Intensity Method

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In determining the effective ways for machine noise control, it is important to clarify the noise sources and their contributions. In a machine structure, the vibration energy exerted on the excitation point is transmitted through beams and/or plates, causes vibration and is radiated as noise from its surface. The noise sources don't always coincide with the excitation points in a structure. Therefore, the identification of excitation sources and vibration energy transmission paths can give a decisive information on the noise and vibration control measures. The vibration intensity (VI) techniques is thought to be useful for this purpose. VI is obtained as vibration power per unit width in a given direction. There are some difficulities in applying this intensity method to diagnostics for practical mechanical structures. The calculation of third-order derivatives from a set of vibration data measured at different points may cause error. Furthermore, transient features of vibration energy flow, which are generally observed in most practical structures, are lost due to the time-averaging process. The objective of this research is to develop a simplified measurement technique applicable to the VI measurement in practical mechanical structures. In the present research, the envelope technique with three-channel VI pick-up was employed to the data processing to analyze transient characteristics of vibration energy flow. Application limits of the present method near boundaries and on curved plates were clarified by experiments and by FEM simulation. Attempts were made to measure the vibration intensity on the practical mechanical structures within the application limits. Time-dependent multipath-transmissions of vibration energy were visualized successfully. It was shown that the application of the present technique can be informative in the diagnostics and control of noise and vibration in practical mechanical structures.