Estimation of Acoustic Impedance for Surfaces Delimiting the Volume of an Enclosed Space

Piechowicz, Janusz; Czajka, Ireneusz

doi:10.2478/v10168-012-0013-8

Cited by 7 publications

(13 citation statements)

References 3 publications

(4 reference statements)

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“…Piechowicz et. al [10][11][12] have developed a numerical scheme that relies on a boundary element method applied to the Helmholtz-Kirchoff equation to evaluate the acoustic impedance of obstacles and/or boundaries internal to closed domain from pressure information taken at a finite set of interior points. To the author's knowledge no prior work has tackled the evaluation of the broadband acoustic impedance (2) at one or multiple boundaries of a computational domain without the use of regularization techniques or iterative methods.…”

Section: Motivation and Previous Workmentioning

confidence: 99%

“…Upon solving the iHS system (13), the impedance at the m-th IB face associated to the i-th velocity component can be directly evaluated as,…”

Section: Proposed Algebraic Closure Of the Inverse Helmholtz Problemmentioning

confidence: 99%

“…A meshless, direct method to determine unknown boundary conditions to the Helmholtz problem was proposed by Jin & Zheng [10] relying on the method of fundamental solutions and truncated singular value decomposition regularization. Piechowicz et al [11,12,13] have developed a numerical scheme that relies on a boundary element method applied to the Helmholtz-Kirchoff equation to evaluate the acoustic impedance of obstacles and/or boundaries internal to a closed domain from pressure information taken at a finite set of interior points. To the best of authors' knowledge no prior work has tackled the evaluation of the spatial distribution of the broadband acoustic impedance (2) over one or multiple boundaries of a computational domain without the use of regularization or iterative techniques.…”

Section: Introductionmentioning

confidence: 99%

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Surface Impedance Determination via Numerical Resolution of the Inverse Helmholtz Problem

Patel

Gupta

Scalo

2017

23rd AIAA/CEAS Aeroacoustics Conference

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Assigning boundary conditions, such as acoustic impedance, to the frequency domain thermoviscous wave equations (TWE), derived from the linearized Navier-Stokes equations (LNSE) poses a Helmholtz problem, solution to which yields a discrete set of complex eigenfunctions and eigenvalue pairs. The proposed method -the inverse Helmholtz solver (iHS) -reverses such procedure by returning the value of acoustic impedance at one or more unknown impedance boundaries (IBs) of a given domain, via spatial integration of the TWE for a given real-valued frequency with assigned conditions on other boundaries. The iHS procedure is applied to a second-order spatial discretization of the TWEs on an unstructured staggered grid arrangement. Only the momentum equation is extended to the center of each IB face where pressure and velocity components are co-located and treated as unknowns. The iHS is finally closed via assignment of the surface gradient of pressure phase over the IBs, corresponding to assigning the shape of the acoustic waveform at the IB. The iHS procedure can be carried out independently for different frequencies, making it embarrassingly parallel, and able to return the complete broadband complex impedance distribution at the IBs in any desired frequency range to arbitrary numerical precision. The iHS approach is first validated against Rott's theory for viscous rectangular and circular ducts. The impedance of a toy porous cavity with a complex geometry is then reconstructed and validated with companion fully compressible unstructured Navier-Stokes simulations resolving the cavity geometry. Verification against one-dimensional impedance test tube calculations based on time-domain impedance boundary conditions (TDIBC) is also carried out. Finally, results from a preliminary analysis of a thermoacoustically unstable cavity are presented.

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Section: Motivation and Previous Workmentioning

confidence: 99%

“…Upon solving the iHS system (13), the impedance at the m-th IB face associated to the i-th velocity component can be directly evaluated as,…”

Section: Proposed Algebraic Closure Of the Inverse Helmholtz Problemmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Surface Impedance Determination via Numerical Resolution of the Inverse Helmholtz Problem

Patel

Gupta

Scalo

2017

23rd AIAA/CEAS Aeroacoustics Conference

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“…1). The anal- ysis of the registered signals allowed the calculation of the data matrix containing the acoustic pressure amplitudes registered in individual measurement points and the respective phase shift angles between the signal emitted by the source and the signals registered by the microphones, and additionally the velocity amplitudes for the source diaphragm vibration [7]. The measurements have been carried out in an empty room, without windows, 6.67 × 3.9 × 2.85 m 3 in size.…”

Section: Experimental Studiesmentioning

confidence: 99%

Determination of Acoustic Impedance of Walls Based on Acoustic Field Parameter Values Measured in the Room

Piechowicz

Czajka

2013

Acta Phys. Pol. A

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Acoustic eld in enclosed rooms in the low frequency range can be described by the wave model, based on solution of the wave equation. Solution to the wave equation for acoustic eld in the room can be obtained using numerical procedures, e.g. the boundary elements method. Determination of acoustic impedance of the room walls surface material, based on the knowledge of the distribution of acoustic pressure amplitudes in the enclosed space, requires application of the inverse boundary elements method and gathering a proper set of input data. The paper presents the possibilities of analysis of acoustic properties for industrial-type rooms, by using inverse methods in the low frequency range.

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“…However, when examining machinery noise it seems necessary to achieve even better results of analysis. This requires a more precise definition of the sound absorption coefficients because it seems that, depending on the values of these coefficients, the boundary conditions and values of the parameters characterising the acoustic field can be changed (Piechowicz, 2009;Piechowicz, Czajka, 2012). In this paper the issue of which parameters characterizing the sound field are the most sensitive to the changes in the values of the absorption coefficients and how these changes in the values of these coefficients influence the obtained acoustic parameters will be discussed.…”

Section: Introductionmentioning

confidence: 99%

Sensitivity Analysis of Acoustic Field Parameters on a Change of Boundary Conditions in a Room

Suder-Dębska¹,

Czajka²,

Czechowski³

2015

Archives of Acoustics

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The area of environmental protection concern minimises the impact that technical objects have on the environment. Usually the most effective way of protecting the environment is to influence the source of the problem. For this reason studies are conducted to modify the construction of machines, power machines in particular, so as to minimise their impact on the environment.In the case of environmental protection from noise it is most convenient to carry out measurements in an anechoic chamber. Unfortunately, this is possible only in very limited circumstances. In all other cases measurements are performed using an engineering method or the survey method, both of which are described in the standards and by taking into account the so-called environmental corrections. The obtained results are burdened with greater error than those of measurements in an anechoic chamber. Therefore, it would seem advantageous to develop a method of obtaining similar and reliable results as those in an anechoic chamber, but in a reverberant field. The authors decided to use numerical modelling for this purpose.The main objective of this work is a comprehensive analysis of the numerical model of a laboratory designed for acoustic tests of selected power machines. The geometry of a room comprising an area of analysis is easy to design. The main difficulty in modelling the phenomena occurring in the analysed area can be the lack of knowing the boundary conditions. Therefore, the authors made an attempt to analyse the sensitivity of various acoustic parameters in a room in order to change these boundary conditions depending on the sound absorption coefficient.

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Estimation of Acoustic Impedance for Surfaces Delimiting the Volume of an Enclosed Space

Cited by 7 publications

References 3 publications

Surface Impedance Determination via Numerical Resolution of the Inverse Helmholtz Problem

Surface Impedance Determination via Numerical Resolution of the Inverse Helmholtz Problem

Determination of Acoustic Impedance of Walls Based on Acoustic Field Parameter Values Measured in the Room

Sensitivity Analysis of Acoustic Field Parameters on a Change of Boundary Conditions in a Room

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