Design of noise attenuating devices incorporating elastic porous structures

Aygun, Haydar

Abstract

The deflection of a non-porous (aluminium) plate has been theoretically and numerically studied for clamped and simply supported boundary conditions. Measurements of the deflection of poroelastic plates subject to mechanical vibration have been made and the results compared with predictions based on previously published theory. The agreement between measurements and predictions is fairly good. The radiation impedance matrix has been defined, and computed including direct terms and cross-coupling terms. Three vibroacoustic indicators of porous and non-porous plates have been calculated. To extend previous work, the effects of fluid loading on the vibration of rectangular, clamped, porous, elastic plates and on their radiated sound power are considered. This requires an extra term in the equations of the plate vibration, corresponding to the additional external force acting on the plate. For vibrating rectangular plates, fluid-structure coupling is a very complex phenomenon since the plate modes are coupled by the fluid.
Two contributions have been made to studies of the usefulness of poroelastic plates for noise control in ducts containing mean flow. Measurements of the acoustic insertion loss of poroelastic plates with different perforations, mounted transversely across a flow duct, are presented. The insertion losses of two such poroelastic plates are compared to those of a similar but non-porous plate. It is demonstrated that the insertion losses of the porous and non-porous plates are very similar without mean airflow but slightly different in the presence of air flow. The sound transmission loss of a porous plate mounted in the flow duct and separated from the walls by an air cavity is calculated from sound pressure measurements in flow duct. The results show that introduction of air flow increases the transmission loss and shifts the maximum in the TL to lower frequency. Introducing the air flow in the flow duct has been found to increase the plate deflection.
Finally, a porous plate has been tested in a large impedance tube to investigate the effects of structural vibration and sound radiation from a porous plate on its acoustic surface impedance. The resonant frequencies observed in the surface acoustic impedance are close to those predicted by the theory of the deflection of poroelastic plates which in turn are close to those observed in the measured deflection spectrum.

Citation

Aygun, H. (2006). Design of noise attenuating devices incorporating elastic porous structures. (Thesis). University of Hull. Retrieved from https://hull-repository.worktribe.com/output/4224373

• Thesis Type: Thesis
• Deposit Date: Oct 12, 2022
• Publicly Available Date: Feb 24, 2023
• Keywords: Engineering
• Public URL: https://hull-repository.worktribe.com/output/4224373
• Additional Information: Department of Engineering, The University of Hull
• Award Date: Feb 1, 2006