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Environmental protection involves various complexities, like reduction of vibroacoustic pollution generated by motor vehicles. This type of pollution, generated from vehicle operations, presents significant challenges in mitigation efforts. According to this, it results the need to develop a methodology aimed at identifying and analysing the sources of noises and vibrations typical of both normal vehicle functioning and component failures. These sources mainly concentrate within the engine compartment. Thus, the configuration of the sensors to analyze the vehicle noise and vibration behaviour should be adapted to the identified categories of open or closed vibroacoustic volumes. The goal of this study is to demonstrate, by practical experiments, that in case of an open volume, accelerometers should predominate in the sensors array, whereas for a closed vibroacoustic volume, a more balanced distribution with microphones may be appropriate. This classification of vibroacoustic volumes serves as basic criteria for the design of sensors network in vibroacoustic studies of vehicles. [ABSTRACT FROM AUTHOR]

Heating, ventilating and air-conditioning (HVAC) systems represent a major source of inside buildings noise with a negative effect on the acoustical environment. Therefore, it is necessary to add attenuation to the system. This is provided by sound attenuators or silencers manufactured in different geometrical configurations and with various absorptive lining materials. The paper deals with the insertion loss, as a performance criterion for in-duct noise, of some dissipative silencers types. The measured data are compared in order to establish the efficiency of every tested silencer type. Third-octave band analysis of random noise of an air handling unit (AHU) from a HVAC system is realized without and with silencers (ducts fitted). Insertion loss measurements are made in an anechoic room using a test facility that agrees the requirements of ISO 7235:2009. The results highlight the effects of the silencers geometry, pressure-air flow and loading relations upon the sound attenuation level. The silencers selection could be a difficult task for the designers which have to consider all these parameters.

The paper presents a theoretical analysis of a nonlinear system with dry friction and unbalanced rotational mass. The equations of motion are deduced and integrated numerically. Then, the size and orientation of the normal reaction force can be obtained. The model predicts a rotation motion phase followed by an oscillation one. The experimental results obtained using a laboratory set-up are in very good agreement to the predictions of the theoretical model. [ABSTRACT FROM AUTHOR]

Scuffing diagnose of rolling element bearings can be made by the analysis of the bearing friction forces which are the most sensitive indicator of bearing defects. Scuffing limits in angular contact ball bearings are estimated by an original algorithm and computer code. The theoretical model has been sustained by an experimental investigation. Scuffing tests were performed on 7206 angular contact ball bearing included in an original test. In order to evidence the scuffing occurrence, data acquisition board and powerful and flexible software create an efficient virtual instrument. [ABSTRACT FROM AUTHOR]