| 2. |
- Temiz, M. A., et al.
(författare)
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Acoustic end correction in micro-perforated plates - Revisited
- 2014
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Ingår i: 21st International Congress on Sound and Vibration 2014, ICSV 2014. - 9781634392389 ; , s. 1203-1209
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Konferensbidrag (refereegranskat)abstract
- Micro-Perforated plates (MPP) are plates with a porosity of the order of 1% in which the perforation diameter is optimized for absorption of incident acoustic waves. The concept has been introduced by Maa[1], who proposed an analytical model based on the solution for the oscillating viscous flow in a long capillary tube. The finite length of the geometry is taken into account by reactive and resistive end-corrections of Ingard[2]. In order to match experimental data, the single sided resistive end correction of Ingard has been multiplied by a factor a. This factor varies in the literature in the range 2 ≤ α ≤ 4. Bolton and Kim[3] propose the use of CFD to determine these end-corrections. Using a similar approach, our present work proposes an alternative result to their work. We use a linear numerical model based on incompressible Navier-Stokes equations in 2D-axisymmetric coordinates, which is solved in the Fourier domain, rather than the time domain simulation as proposed by Bolton and Kim. Working in the Fourier domain with linearized equations ensures the numerical efficiency and absence of non-linear effects. We furthermore use an alternative procedure to determine the inertial part of the transfer impedance leading to a difference of the order of 10% with the results of Bolton and Kim. Moreover, our results show that resistive and reactive end corrections are mainly a function of the Shear number Sh. The porosity a and plate thickness to perforation diameter ratio t∗ seems to be less important.
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| 3. |
- Temiz, M. A., et al.
(författare)
-
Numerical estimation of the absorption coefficient of flexible micro-perforated plates in an impedance tube
- 2016
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Ingår i: ICSV 2016 - 23rd International Congress on Sound and Vibration. - : International Institute of Acoustics and Vibrations. - 9789609922623
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Konferensbidrag (refereegranskat)abstract
- In this study, we numerically model a vibro-acoustic system consisting of a flexible micro-perforated plate (f-MPP) and an acoustic medium. Combined with a back-cavity, micro-perforated plates are considered as a promising noise control technology due to their tunable, wide-band sound absorption characteristics and robust performance. An MPP consists of a plate with uniformly distributed perforations whose diameters are in the order of a millimeter. These perforations are small enough to dissipate the acoustic perturbations due to the viscous effects caused by the presence of the Stokes layers. When the plate is rigid, the sound dissipation mechanism for a specific frequency bandwidth is determined by the perforation diameter, plate thickness, plate porosity and the back cavity depth. Yet, when the plate is flexible, additional absorption peaks, which cannot be determined by the parameters mentioned before, are observed in the measurements. This phenomenon is due to the vibro-acoustic coupling of the flexible plate and the acoustic medium. To model the vibro-acoustic system numerically, we couple two 3D cylindrical acoustic mediums, i.e. incident and back cavity regions, with a flexible plate consisting of shell elements. The perforations are separately located on the plate as independent transfer admittance elements with impedance values obtained from existing models. The system is disturbed with a plane wave excitation and the assessment of the model is done by comparing the calculated absorption coefficient with the experimental results from the literature. In the future, we plan to investigate the effect of perforation positions with the help of the model built in this study.
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