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Technical Paper

Reducing Sound Radiation of an Automated Transmission by Means of Viscoelastic Multilayer Damping

2010-10-17
2010-36-0512
Brazilian automotive industry has reached a high level of competition and production, and in this scenario noise radiation is a very important factor in which quality, cost and comfort have to meet consumers' impressions of a vehicle. Engineers face today difficult challenges when it comes to improvement of noise emissions: solutions should be fast, cheap and effective. This work presents a recent study to reduce shell noise radiation from an automated transmission mechanism using two solutions of structural damping: modification in the material of the noise source and attenuation of shell movement by using surface patches of viscoelastic sandwich. Although traditionally applied to whole radiating surfaces, the second solution demonstrates that portions of the material applied in proper selected locations are very effective for reduction of shell noise, therefore enabling the usage of smaller sizes of viscoelastic material instead of complete coverings.
Technical Paper

Particle Velocity Measurements as a Breakthrough for Determining Acoustic Absorption Coefficient in Brazilian Trucks

2010-10-17
2010-36-0511
Methods for determining the acoustic absorption coefficient of materials are broadly known in NVH engineering and traditionally rely on measurements performed in specimens carefully prepared such as those used in the Kundt's tube. It is understood that the acoustic behavior of a material slice in a well-controlled test bench provides very different circumstances from those found when the material is used in its application location (in situ condition) mostly because of the structural interactions and the boundary conditions involved. Many questions arise when the goal is to understand which absorbing material will be more effective and, moreover, if its cost is worth enough to solve particular noise issues. To answer those questions, acoustic impedance determination using direct particle velocity measurements were used in this work, in which several absorbing coatings used in specific regions of Brazilian truck cabins were mapped and compared.
Technical Paper

Using Acoustic Particle Velocity Sensors for End of Line Control

2009-05-19
2009-01-2155
Acoustic particle velocity sensors can be an alternative sensor category for end of line testing next to microphones, accelerometers or scanning laser vibrometers. As any other category of transducers, particle velocity sensors have their specific features. The acoustic particle velocity field is far less susceptible to background noise than the sound pressure field, allowing acoustic testing to be carried out in a manufacturing environment with significant background noise levels [2]. Close to a vibrating surface, acoustic particle velocity is a good estimate of the normal structural velocity, allowing non contact vibration measurements [4]. The results of some case studies will be summarized.
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