Research
10 . Manipulating acoustic waves radiation direction
Duct liners can be used to generate Acoustic surface waves (ASWs). In this work, it is shown that by changing the liner geometry, it is possible to control acoustic wave radiation direction by manipulating ASWs and the relationship between the radiation direction and the liner parameters. We illustrate the physical mechanism of controlling the radiation direction and its verification using numerical simulations. Using this concept, we can manipulate the ASW radiation direction, which is very important for practical applications of directional acoustic propagation. A lined duct with manipulated radiation is shown on the right.
Related Publications:
- M. Farooqui, Y. Aurégan and V. Pagneux, Manipulating acoustic surface waves radiation direction using Liner surface modes, Metamaterials, Espoo, Finland, 27-31 Aug, 2018.
- M. Farooqui, Y. Aurégan and V. Pagneux, Manipulating acoustic waves radiation direction using Liner surface modes, 2018. (Manuscript under preparation)
9. Self-cloaking inside ducts
An acoustic cloak for back-scattering suppression inside ducts is proposed in the audible range where plane waves are bended around the object using liner surface modes. It is shown that a liner based on array of tubes can possesses no-reflection and wave-front bending properties, which could partially approximate an ideal invisibility cloak with inhomogeneous and anisotropic distribution of material parameters. The cloak is effective in a broadband frequency band, and the cloaking band is a function of the boundary impedance. It is numerically demonstrated that the concealed arbitrary object and the silent zone together can be almost completely shielded to the background medium for broadband frequency range. The extra-ordinary ability of the obstacle to self-cloak itself by virtue of its dimensions is also demonstrated for excessive broadband range. Extreme dispersion effects giving rise to slow sound leads to phase distortion of the wave.
Related Publications:
- M. Farooqui, Y. Aurégan and V. Pagneux, Using liner surface modes in ducts to make obstacles reflectionless, Scientific Reports, volume 9, Article number: 6981 (2019)
- M. Farooqui, Y. Aurégan and V. Pagneux, Guiding acoustic waves over obstacles using linear surface modes, Euro-Noise, Crete, Greece, 27-31 May, 2018
8. Beamed Acoustic Meta-Materials
The attenuation of low-frequency sound is very difficult because the intrinsic dissipation of materials is inherently weak in this regime. Here we present a beam acoustic metamaterial, comprising an elastic cantilevered beam and coupled micro-slits that aims to totally absorb airborne sound at extremely low-frequency with extra-ordinary broadband absorption ranging from 300–2,500 Hz. Our samples can reach quasi perfect absorption at frequencies where the relevant sound wavelength in air is 50 times the cavity thickness. The multiphysical coupling between the beam structure, micro-slit and the cavity helps in achieving a metamaterial that resembles an open cavity at extremely low frequency. In addition, this coupling leads to extraordinary broadband absorption at higher frequencies.
Related Publications:
- Y. Aurégan and M. Farooqui, In-parallel resonators to increase the absorption of subwavelength acoustic absorbers in the mid-frequency range, Scientific Reportsvolume 9, Article number: 11140 (2019)
- M. Farooqui and Y. Aurégan, Compact beam liners for low frequency noise, 24th AIAA/CEAS Conference, Atlanta, United States, 25-29 June 2018.
- M. Farooqui, M.E. D’Elia and Y. Aurégan , Traitement acoustique à base de micro-fentes et de plaques déformables, CFA '18, Le Havre, France, 23-27 Avril, 2018
- M. Farooqui and Y. Aurégan, Beam type metamaterial for low frequency sound attenuation, 2018. (Manuscript under preparation)
7. Mild-slope Equation for Acoustic Waves (Inspired from Water waves)
The problem of low-frequency sound propagation in slowly varying ducts with smoothly varying lining is analysed inspired by water wave propagation on a mild-slope bed. A simple 1D Mild Slope Equation is derived by direct application of the classical Galerkin method. It is shown that mild-slope equation can serve as a good alternative to computationally expensive Helmholtz equations to solve such kind of problem. The results from the mild-slope equation agrees well with FEM based solutions of Helmholtz equation. The water wave propagation (Bottom Picture) is analogous to acoustic wave propagation over an obstacle (Figure (c) on right ).
Related Publications:
- M. Farooqui, Y. Aurégan and V. Pagneux, Acoustic Propagation in lined ducts with varying cross-section using a Mild-Slope approximation , 2018. arXiv:1809.03277
- M. Farooqui, Y. Aurégan and V. Pagneux, One dimensional modelling of self-cloaking inside ducts using liners, Symposium on Acoustic Metamaterials, 7-9 Nov 2018 Xàtiva (Spain).
6. Explicit Eckart wave-numbers (Inspired from Water waves )
For acoustic waves in lined ducts, at given frequencies, the dispersion relation leads to a transcendental equation for the wavenumber that has to be solved by numerical methods. Based on Eckart explicit expression initially derived for water waves, accurate explicit approximations are proposed for the wavenumber of the fundamental mode in lined ducts. While Eckart expression is 5 % accurate, some improved approximations can reach maximum relative error of less than 0.0000002 %. The cases with small dissipation part in the admittance of the liner and/or axisymmetric ducts are also considered.
Related Publication:
5. Patched acoustic Meta-materials
The objective of this study is to develop a physical approach to model and synthesize programmable Bulk Moduli and densities to feasibly control the wave propagation pattern, creating quiet zones in the targeted fluid domain. Traditional passive noise control techniques using Helmholtz resonators have size limitations at low frequency due to the large wavelengths. Promising noise reductions, with flush mounted Aluminum / Steel patches with no such constraints can be obtained building on local resonance phenomenon implemented in acoustic meta-material techniques. We introduced locally resonant Aluminum patches flush mounted to an acoustic duct walls aiming at creating frequency stop bands at the low frequency zone. These patches behave similar to Helmholtz resonators designed for a particular resonance frequency.
Related Publications:
- Farooqui, M. Elnady, T., and Akl, W. ,“Sound attenuation in ducts using locally resonant periodic flush mounted flexible Aluminum patches,” Journal of Acoustical Society of America, 2016.
- Farooqui, M., Elnady, T., and Akl, W. ,“Validation of low frequency noise attenuation using locally resonant patches,” Journal of Acoustical Society of America ,2016
- M. Farooqui, T. Elnady and W. Akl, Low Frequency Noise Attenuation inside Ducts using locally resonant periodic flush mounted Steel Patches, Euro-Noise, Maastricht, Netherlands, 01-03 June, 2015.
- Farooqui M., Akl W. and Elnady T., Sound Attenuation in Ducts using Locally Resonant Periodic Flush Mounted Flexible Silicon Patches, 166th Meeting of Acoustical Society of America, San Francisco, CA, United States, 02-06 December, 2013.
- M. Farooqui, T. Elnady and W. Akl, Sound Attenuation in Ducts using locally resonant periodic flush mounted flexible Silicon Patches, 2nd International Conference on Phononic Crystals/Metamaterials, Phonon Transport and Opto-mechanics, Sharm-el-Sheikh, Egypt, 02-05 June 2013.
4. Modelling and Characterization of Porous acoustic Absorbents (Guest Researcher @ SCANIA CV ,Sweden)
A novel Metallic porous absorbing material was studied in this work which was a part of Secondments at SCANIA AB. This material proved to be a similar or better sound absorber compared to the conventional porous absorbers, but with a robust and less degradable properties. A new way of characterizing the porous absorber from a simple Transmission loss measurement was proposed. This Transmission loss measurement can be used to extract the complex effective sound speed and density, fundamental porous material properties.
Related Publication:
3. Inverse extraction of Grazing flow impedance of perforate and Micro-perforates.
The objective of this work is to measure the performance of perforates which have grazing flow on their both sides. The perforate sample is placed in the middle of two rectangular ducts with solid walls, see picture above. The technique uses the complex acoustic pressure measured at twelve positions at the walls of the two ducts, upstream and downstream of the lined section, and educes the impedance with a mode-matching method. First, the ability of the code to reproduce the pressure field for given impedance is tested. Second, the ability to educe the correct impedance for a given pressure distribution is tested. This configuration represents a four-port. In order to fully characterize this multi-port, four different excitation from the four different inlets/outlets are needed. This work finds application for perforates applied as cooling fan blades or can lead to their usage in guide vanes and several other systems which have grazing flow on both sides.
Related Publications:
- Farooqui, M., Elnady, T., and Abom, M., Impedance of a perforate with grazing flow on both sides, 2016, 22nd AIAA/CEAS Conference, Lyon, France, 30 May-1 June, 2016.
- Farooqui, M., Elnady, T., and Abom, M., Investigation of the impedance of a micro-perforated plate with two-sided grazing flow, 2017, 173rd Meeting of the Acoustical Society of America, Boston, MA, United States, 25-28 June 2017.
2. Slowing sound using Acoustic Meta-Materials (Guest Researcher @ LAUM, France)
Sound absorption by a structure with straight rectangular tubes loaded by periodically distributed resonators. The phenomenon of slow sound propagation associated with its inherent dissipation can be efficiently used to design broad band sound absorbing meta-materials. This work is about a quasi-labyrinthine structure flush mounted to a duct, comprising of coplanar quarter wavelength resonators that aims to slow the speed of sound and act as a prefect attenuator at selective resonance frequencies. Here, a thin subwavelength material is presented that can be flush mounted to a duct and which gives a large wide band attenuation at remarkably low frequencies in air flow channels. To decrease the material thickness, the sound is slowed in the material using folded side branch tubes.
Related Publication:
1. Design of better Helmholtz resonators for noise attenuation in pipelines
This work was a part of M.Sc. thesis based on a collaborative project of Saudi Aramco and Dresser-Rand titled “Noise reduction in Centrifugal compressors”.A thorough design methodology of one and two degrees of freedom Helmholtz resonators leading to optimised transmission loss is described and validated in this paper.
Related Publications:
- Samir Mekid, M Farooqui, “Design of one and two degree of freedom Helmholtz resonators as an add-on solution for noise attenuation in pipelines.” Vol. 40, No. 3, Dec 2012,Journal of Australian Acoustical Society.
- Samir Mekid, M Farooqui, Z Liu, “Geometry Effects on the Noise Reduction of Helmholtz Resonators". Canadian Acoustics, Vol.42, No. 2, May. 2014. ISSN 2291-1391.
- Maaz Farooqui, Samir Mekid, Simulation of noise attenuation using one and two degree of Freedom Helmholtz resonators in pipelines, Proceedings of ASME 11th Biennial Conference on Engineering Systems Design and Analysis, Nantes, France, 2012.
- Maaz Farooqui, Samir Mekid, Atif Aliuddin, Abdul Aziz Al Hamoud, Geometry effects on the Noise reduction of Helmholtz resonators. Proceedings of ASME 11th Biennial Conference on Engineering Systems Design and Analysis, Nantes, France, 2012.
