A methodology for predicting impact-induced acoustic noise in machine systems

A methodology for predicting noise and vibration of machines and their support structures is presented. Included is a heuristic energy-based criterion to assess the importance of dynamic coupling between a mechanism and its support structure based on a simplified analysis of a mechanism operating on a rigid base, which neglects the coupling. Also included is an analysis method that considers the coupling and to be used when the criterion reveals important coupling. The methodology is implemented using highly idealized closed form and more elaborate numerical descriptions and is checked against vibration and sound measurements of a plate subjected to periodic impacts by balls and a beam that rattles within a clearance bearing. The energy-based criterion is found to indicate situations in which mechanism-support coupling affects noise radiation. In some cases the coupling is observed to significantly affect vibration and noise radiation of the support structure, while having a relatively minor effect on mechanism response. Both the simple closed form and numerical descriptions are found to predict noise trends due to variations in machine speed and bearing clearance, and the numerical descriptions more accurately predict overall and band levels of noise radiation.