The requirements for a special approach for the quality assessment of small high-speed centrifugal fans are outlined and a new parameter designating the noise levels from the product in comprehensive form will be discussed and described as a criterion for such quality assessment.By applying techniques of signal processing and condition monitoring, the sources of the vibration and noise in different sections of the product can be identified, then the noise from each source from different components can be determined. Using this criterion, more aspects of the quality of the products can be assessed and suggestions to improve the quality of the products can be made. Finally, the assessment of a number ofvacuum cleaner motor/fan units available in the commercial market will be presented and compared with conventional specifications. It will be shown that the new parameter provides a more useful indication of appliance quality.
In noise and vibration control, damping treatment and isolation of structures are often applied to dissipate the energy of flexural vibrations and to reduce the transmission of energy to the surroundings. However, these treatments must be carefully designed because the present requirements of the size, power and noise levels resulting from commercial competition are very restrictive and usually there is little space to put additional material. In this paper, the statistical energy analysis (SEA) method has been used to optimize such treatment. The power balance equations have been established for a motor-fan-casing unit, and the design and possible modifications have been analysed with an SEA model. The energy transmission paths within the structure have been clearly identified and the test results confirmed the accuracy of this model. The optimum has been determined and lower noise levels have been verified by tests. A significant reduction in noise level has been achieved and the example has shown that an SEA model is very useful for analysing structures with regard to noise and vibration levels.
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