Reduction of sound transmission into a circular cylindrical shell using distributed vibration absorbers and Helmholtz resonators

Abstract

A modal expansion method is used to model a cylindrical enclosure excited by an external plane wave. A set of distributed vibration absorbers ͑DVAs͒ and Helmholtz resonators ͑HRs͒ are applied to the structure to control the interior acoustic levels. Using an impedance matching method, the structure, the acoustic cavity, and the noise reduction devices are fully coupled to yield an analytical formulation of the structural kinetic energy and acoustic potential energy of a treated cylindrical cavity. Lightweight DVAs and small HRs tuned to the natural frequencies of the targeted structural and acoustic modes, respectively, result in significant acoustic and structural attenuation when the devices are optimally damped. Simulations show that significant interior noise reduction can only be achieved by adding damping to both structural and acoustic modes, which are resonant in the frequency bandwidth of interest. In order to be independent of the azimuth angle of the excitation and to avoid unwanted modal interactions, the devices are distributed evenly around the cylinder in rings. This treatment can only achieve good performance if the structure and the acoustic cavity are lightly damped.

Vibro-acoustic noise control treatments for payload bays of launch vehicles: Discrete to fuzzy solutions

“…The work presented here follows similar methods presented in Estéve [30], however, the use of the extensive computing resources enabled the optimisation of a greater number of absorbers and larger computational problems than analysed by Estéve.…”

“…Genetic algorithms (GAs) have been used for many acoustic and vibration optimisation problems such as finding optimal locations for actuators to reduce radiated noise or transmitted vibration [24][25][26][27][28][29][30], and optimisation of structures to reduce the transmission of vibration [31][32][33][34]. A GA is a numerical optimisation method based on the principles of natural selection and genetics.…”

Noise control in enclosures: Modeling and experiments with T-shaped acoustic resonators

“…A 5.9 and 7.4 dB reduction in SPL around frequencies 145 and 228 Hz is predicted, respectively. Notice that the total volume occupied by all six resonators is 0.0022 m 3 , which is only 0.3% of the enclosure volume 0.833 m 3 . Therefore the effect of the physical presence of the resonators inside the enclosure is negligible.…”

“…Recently, a vibroacoustic coupling model was presented by Estève and Johnson to control noise transmitted into a composite cylinder using distributed vibration absorbers and Helmholtz resonators. 2,3 Noise control using long cylindrical tube-shaped resonators for fairing noise control has also been investigated. 4,5 Despite all the effort, the design of acoustic resonators is still limited by a number of factors.…”

“…When properly designed, a passive method using an acoustic resonator can effectively absorb acoustic energy from a targeted acoustic mode. [1][2][3][4][5][6][7][8][9] Ideally, it is desirable to integrate resonators into the host structure to save space, particularly for small enclosures. However, it is difficult to meet this requirement with a classical Helmholtz resonator because of its bulbous profile.…”