Haÿne Lecocq, Bénédicte (2006) Study of acoustic comportment of cavitary materials. PhD thesis Acoustique, ENSAM 2006ENAM0050.

Full text available as: - Thèse_B_Hayne.pdf ( 7623 Kb )

Licence: Copyright

Abstract

Environmental noise and noise in the interiors, is a major concern. Companies, in sectors as varied as car industry, electric household appliances or aeronautics, focus on reduction of sound level of their products. In order to reduce noise, the use of passive acoustic absorbing materials, like foams, glass wools or rock, may represent a solution. Other materials offer absorbing properties because of their reactivity, for example, materials with resonators cavities. In this category, honeycombs type materials are employed more and more frequently, not only because of their rigidity weight ratio particularly interesting from a mechanical point of view, but also because of their acoustic properties, in particular in the nacelles of the engines of planes. However, physical phenomena intervening in this attenuation are not well known. The control of acoustic behaviour of these materials, starting from their dimensioning, is not completely acquired. Consequently, the research items presented in this thesis are carried out to contribute to the definition of physical phenomena relating to the behaviour of Helmholtz cavities and honeycomb materials when exposed to different physical influences: acoustic wave, acoustic wave associated to an air flow, or, with vibrations. This study, largely guided by experimentation, required the design and the realization of many test benches in order to understand and to measure the various phenomena in order to validate the theories presented. A new approach is proposed for modeling honeycomb materials which takes into account the influence of resonators cavities of the structure by a mechanical analogy. The results of simulation are compared with those of the experimentation. The methodology of the experimental design was used to seek the dimensional ratios of cavities optimizing the global sound attenuation. Finally, an innovative theory is developed on physical phenomena intervening in sound attenuation caused by cavities exposed at the same time to an air flow and an acoustic wave. The experiments permitted to validate the hypothesis that there is a reactive control consisted of self-adaptation of the response of the cavity to external acoustic excitation.

Statistiques de consultation

Repository Staff Only: edit this item