| 1. |
- Rämmal, Hans, et al.
(författare)
-
Experimental facility for the complete determination of sound transmission in turbochargers
- 2010
-
Ingår i: SAE Technical Papers. - 400 Commonwealth Drive, Warrendale, PA, United States : SAE International. ; , s. SAE Technical Paper 2010-01-1424-
-
Konferensbidrag (refereegranskat)abstract
- In this paper a unique experimental facility designed for a complete determination of the sound transmission in turbochargers is introduced. The facility can be used to characterize the passive acoustic effect for turbocharger compressors and turbines working in realistic operating conditions by extracting the acoustic two-port data. The acoustic pressure transmission loss results for a passenger car turbocharger compressor and turbine measured in up- and downstream directions regarding the mean flow are presented. The data are obtained for various operating points of the turbocharger and the influence of operating conditions on the sound transmission is discussed.
|
|
| 2. |
- Rämmal, Hans, 1976-
(författare)
-
Methods for Modelling and Characterization of In-Duct Sources
- 2005
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Methods to characterize acoustic sources in flow ducts have been investigated. In the first part of this thesis a measurement procedure to characterize an air terminal device using an acoustic one-port source model based on the two microphone technique has been tested and validated. In order to provide a prediction of flow noise generation at different operating points for the device a scaling law was derived. Successful validation experiments were performed. In the second part a new method based on the multi-load technique was developed and used to characterise the source data of various piston-engines with non-linear behaviour. The source characterisation results were compared to results obtained using the well-known linear two-load technique. It was shown that the new non-linear multi-load technique gave improved results when the source was slightly non-linear. In the third part an improved method to characterize noise sources in high temperature flowducts has been suggested. As a test environment for the standard two microphone technique a helium-air mixture has been used to simulate acoustical conditions similar to hot exhaust gas systems. In order to test the method the passive acoustic properties of automotive diesel engine and an unflanged flow duct termination have been experimentally determined. The experimental results for duct termination have been compared to theoretical predictions. Keywords: Acoustic source, one–port, source model, duct termination, source impedance, reflection coefficient, source strength, IC-engine, flow duct, multi-load method, non-linear
|
|
| 3. |
- Rämmal, Hans, et al.
(författare)
-
Modified multi-load method for non-linear source characterization
- 2004
-
Ingår i: ICSV11-St Petersburg.
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Linear frequency domain prediction codes are used for calculation of low frequency sound transmission in and sound radiation from IC-engine exhaust systems. To calculate insertion loss of mufflers or the level of radiated sound information about the engine as an acoustic source is needed. The source model used in the low frequency plane wave range is the linear time invariant 1-port model. The acoustic source data is usually obtained from experimental tests where multi-load methods and especially the two-load method are most commonly used. The exhaust pulsations of an IC-engine are of high level, which means that the engine is not a perfectly linear and time invariant source. It is therefore of interest to develop source models and experimental techniques that try to take this non-linearity into account. In this paper a modified version of the two-load method to improve the characterization of the non-linear acoustic 1-port sources has been developed and tested. Simulation results from various source configurations of a simplified IC-engine model were used to validate the method. The influence of parameters controlling the linearity of the system was investigated. The time-variance of the source model was varied and the source characterization quality using the two-load method and the modified two-load method was evaluated.
|
|
| 4. |
- Rämmal, Hans, et al.
(författare)
-
Modified multi-load method for nonlinear source characterisation
- 2007
-
Ingår i: Journal of Sound and Vibration. - : Elsevier BV. - 0022-460X .- 1095-8568. ; 299:4-5, s. 1094-1113
-
Tidskriftsartikel (refereegranskat)abstract
- Linear frequency domain prediction codes are useful for calculation of low-frequency sound transmission in duct and pipe systems. To calculate insertion loss of mufflers or the level of radiated sound information about the acoustic source is needed. The source model used in the low-frequency plane wave range is the linear time invariant one-port model. The acoustic source data is usually obtained from experimental tests where multi-load methods and especially the two-load method are most commonly used. The exhaust pulsations of for example an IC-engine are of high level, and the engine is not a perfectly linear and time invariant source. It is therefore of interest to develop source models and experimental techniques that try to take this nonlinearity into account. In this paper a modified version of the two-load method to improve the characterisation of nonlinear acoustic one-port sources has been developed and tested. Simulation results as well as experimental data from various source configurations for a modified compressor and experimental data from 6-cylinder turbocharged truck diesel engine were used to validate the method. The influence of parameters controlling the linearity of the system was investigated. The time-variance of the source model was varied and the accuracy of source characterisation results using the two-load method and the modified two-load method was evaluated.
|
|
| 5. |
- Rämmal, Hans, 1976-
(författare)
-
Studies of flow duct acoustics with applications to turbocharged engines
- 2009
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- A number of experimental and theoretical studies, performed in the field of technical flow duct acoustics are presented in this thesis. The acoustical methods treated are implemented on turbocharged IC-engines and engine gas exchange system components. A new method based on the well-known two-load technique has been developed. The method was applied to characterise the source data of various piston-engines with non-linear behaviour including a 6 cylinder turbo-charged truck diesel engine. The source characterisation results were compared to the results obtained using the linear two-load technique. It was demonstrated that the new non-linear multi-load technique gives improved results when the source is slightly non-linear. The use of active one-port models has been tested to characterize an air terminal device (ATD) as a source of flow generated noise. In order to predict the noise generation at different operating points of the device a scaling law was derived and verified. In the experimentally derived scaling law a flow speed dependence of 3 was found for the narrow band spectra, corresponding to a dipole-like behavior of the source in the plane wave range. The proposed technique was validated successfully and the results indicated a good prediction of in-duct sound generation by the air terminal device. Sound reflection from hot flow duct openings has been investigated experimentally. The reflection coefficient was measured for flow temperatures up to 500 ºC and jet velocities up to 108m/s. The results have been compared with famous Munt’s theory. It was concluded that at low Mach number and Helmholz number cases the results agree well with the Munt’s model. This was the first experimental validation of the theory for hot flow conditions. Experimental procedures to determine the sound transmission through automotive turbo-charger compressors were developed and described in detail. An overview of a unique turbocharger testing facility established at KTH CICERO in Stockholm is given. The facility can be used to measure acoustic two-port data for turbo-compressors. Results from measurements on a passenger car turbo-compressor are presented and the influence of operating conditions on the sound transmission is discussed. Current wave action models developed in CMT for computation of the gas exchange processes in I.C. engines have been implemented to determine the acoustic wave transmission through the turbo- compressor. The models are validated with the experimental data and the results are presented for different operating conditions of a Volvo passenger car turbo-compressor.
|
|
| 6. |
|
|
| 7. |
- Tiikoja, Heiki, et al.
(författare)
-
Sound transmission in automotive turbochargers
- 2011
-
Ingår i: SAE technical paper series. - 400 Commonwealth Drive, Warrendale, PA, United States : SAE International. - 0148-7191.
-
Tidskriftsartikel (refereegranskat)abstract
- Turbochargers are common parts of a modern automotive engine. This paper presents an overview of the recent studies performed in the competence center for gas exchange studies at KTH on the sound transmission in turbochargers. The compressor and turbine of the turbochargers are treated as acoustic 2-ports and the scattering matrix for these devices are determined. A unique experimental facility established in the competence center for gas exchange research at KTH has been utilized to study the turbochargers at a variety of operating conditions systematically selected from compressor and turbine charts. A description of the experimental procedures to determine the acoustic 2-port data including techniques implemented to improve the quality of the results is presented. Results from a number of experiments on various modern automotive turbochargers including a unit with variable turbine geometry (VTG) are included. By plotting the up- and downstream transmission loss data against a dimensionless (He-number) frequency scale general characteristics for the sound transmission of turbochargers is found.
|
|
| 8. |
- Tiikoja, Heiki, et al.
(författare)
-
Test-rig for complete acoustic characterization of turbochargers
- 2010
-
Ingår i: 16th AIAA/CEAS Aeroacoustics Conference (31st AIAA Aeroacoustics Conference). - 9781600867446
-
Konferensbidrag (refereegranskat)abstract
- The aim of this paper is to present description of a novel experimental facility designed and set up in KTH Cicero Centre for complete acoustic characterization of turbochargers. The facility is created to determine both the passive (scattering) and active (source) acoustic properties of automotive turbochargers. In this paper the currently most accurate experimental technique to determine the passive acoustic effect of the turbocharger is described. A detailed overview of the test-rig is given together with the mathematical procedures followed to obtain the acoustic 2-port data for turbochargers. The results, including transmission loss and scattering matrix elements, are presented for the compressor and turbine side of a typical automotive turbocharger working in a number of different operating conditions. The influence of the operating conditions on the passive acoustic effect of the device is studied and summarized.
|
|
| 9. |
- Wallin, Hans Petter, et al.
(författare)
-
Sound and vibration
- 2010. - 2., rev. uppl.
-
Bok (övrigt vetenskapligt/konstnärligt)
|
|
| 10. |
- Albertson, F., et al.
(författare)
-
Comparison of different methods to couple nonlinear source descriptions in the time domain to linear system descriptions in the frequency domain - Application to a simple valveless one-cylinder cold engine
- 2006
-
Ingår i: Journal of Sound and Vibration. - : Elsevier BV. - 0022-460X .- 1095-8568. ; 291:05-mar, s. 963-985
-
Tidskriftsartikel (refereegranskat)abstract
- In duct acoustics the fundamental sound generating mechanisms must often be described by nonlinear time domain models. A linear frequency domain model is in many cases sufficient for describing the sound propagation in the connected duct system. This applies both for fluid machines such as IC-engines and compressors and for musical wind instruments. Methods for coupling a nonlinear source description to a linear system description have been proposed by several authors. In this paper some of those methods are compared concerning accuracy, calculation time and the possibility to perform parametric studies. The model problem used is a simple piston-restriction system connected to a linear system with varying complexity. The piston and restriction are considered as the source part and are modelled nonlinearly.
|
|
| 11. |
- Allam, Sabry, et al.
(författare)
-
Development of acoustic models for high frequency resonators for turbocharged IC-engines
- 2012
-
Ingår i: SAE Technical Paper 2012-01-1559, 2012. - 400 Commonwealth Drive, Warrendale, PA, United States : SAE International.
-
Konferensbidrag (refereegranskat)abstract
- Automotive turbo compressors generate high frequency noise in the air intake system. This sound generation is of importance for the perceived sound quality of luxury cars and may need to be controlled by the use of silencers. The silencers usually contain resonators with slits, perforates and cavities. The purpose of the present work is to develop acoustic models for these resonators where relevant effects such as the effect of a realistic mean flow on losses and 3D effects are considered. An experimental campaign has been performed where the two-port matrices and transmission loss of sample resonators have been measured without flow and for two different mean flow speeds. Models for two resonators have been developed using 1D linear acoustic theory and a FEM code (COMSOL Multi-physics). For some resonators a separate linear 1D Matlab code has also been developed. Different models, from the literature, for including the effect of mean flow on the acoustic losses at slits and perforates have been implemented in the codes and compared to the experimental data. Correct modeling of acoustic losses for resonators with complicated geometry is important for the simulation and development of new and improved silencers, and the present work contributes to this understanding. The developed models give acceptable agreement with the measured results even with flow but can be improved for 3D FEM if correct CAD data is available. The 1D linear theory can be used for simple geometries and to get a general overview related to the resonance frequencies and damping level.
|
|
| 12. |
- Allam, Sabry, et al.
(författare)
-
Methods for Accurate Determination of Acoustic Two-Port Data in Flow Ducts
- 2005
-
Ingår i: 12th International Congress on Sound and Vibration 2005. - 9781627481496
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Measurement of plane wave acoustic transmission properties, so called two-port data, of flow duct components is important in many applications. It is an important tool for instance in the development of mufflers for IC-engines. Accurate measurement of the acoustic two port data can be used not only to determine the transmission loss but also to determine physical properties like flow resistivty as well as speed of sound and impedance. Measurement of two-port data is difficult when the flow velocity in the measurement duct is high because of the flow noise contamination of the measured pressure signals. Techniques to improve the acoustic two-port determination have been tested in this paper. A number of possible configurations for connecting loudspeakers to the flow duct have been investigated. It was found that using a perforate pipe section with about 50% porosity between the loudspeaker side branch and the duct gave the best signal-to-noise ratio out of the studied configurations. Different signal processing techniques have been tested for reducing the adverse effects of flow noise at the microphones. The most successful techniques require a reference signal which can be either the electric signal being input to the loudspeakers or one of the microphone signals. As a reference technique stepped sine excitation with cross-spectrum based frequency domain averaging was used. This technique could give good results for most cases. Using a periodic signal (saw-tooth) and synchronised time domain averaging good results could be obtained if a sufficient number of averages was used. At flow velocities higher than M=0.2 about 10000 averages were needed. Random excitation together with cross-spectrum based frequency domain averaging also gave good result if the same number of averages was used. Ordinary frequency domain averaging is not sufficient at high flow velocities. It was also shown that using cross-spectrum based frequency domain averaging an improvement could be obtained if the microphone with the highest signal-to-noise ratio at each frequency was used as the reference microphone rather than a fixed microphone.
|
|
| 13. |
- Allam, Sabry, et al.
(författare)
-
Over-determination in acoustic two-port data measurement
- 2006
-
Ingår i: ICSV13-Vienna. - 9781627481502
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Measurement of plane wave acoustic transmission properties, so called two-port data, of flow duct components is important in many applications. It is an important tool for instance in the development of mufflers for IC-engines. Measurement of two-port data is difficult when the flow velocity in the measurement duct is high because of the flow noise contamination of the measured pressure signals. The plane wave acoustic two-port is a 2x2 matrix containing 4 complex quantities at each frequency. To experimentally determine these unknowns the acoustic state variables on the inlet and outlet side must be measured for two independent test cases. The two independent test cases can be created by: changing the acoustic load on the outlet side leading to the so-called two-load technique or by using one acoustic source on the inlet side and one acoustic source on the outlet side leading to the so-called two-source technique. In the latter case the independent test cases are created by first using the source on the inlet side and then the source on the outlet side. As pointed out by Åbom it is also possible to run both sources simultaneously to create more than two independent test cases. This over-determination could be used to improve the measurement results for instance if the data is contaminated by flow-noise. In this paper over-determination is tested by applying up to 5 different test cases. This procedure has been applied to a single orifice test object.
|
|
| 14. |
|
|
| 15. |
|
|
| 16. |
- Bodén, Hans, 1954-, et al.
(författare)
-
A study of annoyance caused by ground based activities at Bromma airport
- 2010
-
Ingår i: 17th International Congress on Sound and Vibration (ICSV17).
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Bromma airport is located nearby the city centre of Stockholm Sweden. There are a number of residential areas around the airport. The paper reports results from a measurement campaign and a questionnaire survey investigation among the people living in the area Bromma kyrka, located approximately 500 meters from the airport. The objective of the study was to identify the most annoying sound sources related to ground activities at the airport. This means that the noise events caused by starting and landing airplanes were identified using information from the airport, so that they could be separated from the noise caused by ground based activities. The survey showed that the most annoying ground based noise sources within the airport wee, airplane warm ups and airplane taxiing. Starting and landing airplanes were also important source of annoyance. The most important source of noise annoyance from outside the airport boundaries was road traffic. The results from the survey were compared with the measured noise levels giving reasonable correlation between recorded high noise level events and logged annoyance events.
|
|
| 17. |
- Bodén, Hans, et al.
(författare)
-
A study of high level tonal and broadband random excitation for acoustic liners
- 2017
-
Ingår i: 23rd AIAA/CEAS Aeroacoustics Conference, 2017. - Reston, Virginia : American Institute of Aeronautics and Astronautics. - 9781624105043
-
Konferensbidrag (refereegranskat)abstract
- This paper discusses the effect of high level broad band and tonal acoustic excitation on the acoustic properties of perforates. It is based on an experimental study of the nonlinear properties of these types of samples without mean grazing or bias flow. In previous studies multiple tone and high acoustic excitation levels were studied. Both normal incidence impedance tube measurements and liners placed in a grazing incidence configuration were considered. It is known from previous studies that high level acoustic excitation at one frequency will change the acoustic impedance of perforates at other frequencies, thereby changing the boundary condition seen by the acoustic waves. The combination of tones as well as the relative phase between frequency components has also been shown to influence the result. There is usually also a broadband random level excitation in combination with the harmonic tonal excitation. The effect of this combination on the acoustic properties of a perforate has been studied.
|
|
| 18. |
- Bodén, Hans
(författare)
-
Acoustic characterisation of perforates using non-linear system identification techniques
- 2007
-
Ingår i: 13th AIAA/CEAS Aeroacoustics Conference (28th AIAA Aeroacoustics Conference). - : American Institute of Aeronautics and Astronautics. - 9781624100031
-
Konferensbidrag (refereegranskat)abstract
- This paper discusses the use of nonlinear system identification techniques for determination of linear acoustic impedance and non-linear acoustic properties of perforates and other facing sheets used in aircraft engine liners.
|
|
| 19. |
- Bodén, Hans, et al.
(författare)
-
Acoustic Properties of an In-Duct Orifice Subjected to Bias Flow and High Level Acoustic Excitation
- 2012
-
Ingår i: Proceedings of the 10th International conference on Flow-Induced Vibration (& Flow-Induced Noise). - 9780954858346 ; , s. 187-193
-
Konferensbidrag (refereegranskat)abstract
- This paper experimentally investigates the acousticproperties of an orifice with bias flow under medium andhigh sound level excitation. The test included no bias flowand two bias speeds for three different frequencies. Experimentalresults are compared and discussed with theory.It is shown that bias flow makes the acoustic propertiesmuch more complex compared theory and with theno bias flow case, especially when velocity ratio betweenacoustic particle velocity and mean flow velocity is nearunity.
|
|
| 20. |
- Bodén, Hans
(författare)
-
Acoustic properties of perforates under high level multi-tone excitation
- 2013
-
Ingår i: 19th AIAA/CEAS Aeroacoustics Conference. - Reston, Virginia : American Institute of Aeronautics and Astronautics. - 9781624102134
-
Konferensbidrag (refereegranskat)abstract
- This paper discusses the effect of high level multi-tone acoustic excitation on the acoustic properties of perforates. It is based on a large experimental study of the nonlinear properties of these types of samples without mean grazing or bias flow. Compared to previously published results the present investigation concentrates on the effect of multiple harmonics. It is known from previous studies that high level acoustic excitation at one frequency will change the acoustic impedance of perforates at other frequencies, thereby changing the boundary condition seen by the acoustic waves. This effect could be used to change the impedance boundary conditions and for instance increase the absorption. It could obviously also pose a problem for the correct modelling of sound transmission through ducts lined with such impedance surfaces. Experimental results are compared to a quasi-stationary model. The effect of the combination of frequency components and phase in the excitation signal is studied.
|
|
| 21. |
- Boden, Hans, et al.
(författare)
-
Aeroacoustic research in Europe : the CEAS-ASC report on 1999 highlights
- 2000
-
Ingår i: Journal of Sound and Vibration. - : Elsevier BV. - 0022-460X .- 1095-8568. ; 237:3, s. 477-482
-
Tidskriftsartikel (refereegranskat)abstract
- This paper is a report on the highlights of aeroacoustics research and development in Europe in 1999, compiled from the information provided to the Aeroacoustics Specialists Committee (ASC) of the Confederation of European Aerospace Societies (CEAS). CEAS presently comprises the national Aerospace Societies of France (AAAF), Germany (DGLR), Italy (AIDAA), The Netherlands (NVvL), Spain (AIAE), Sweden (FTEF), Switzerland (SVFW) and the United Kingdom (RaeS).
|
|
| 22. |
- Bodén, Hans, et al.
(författare)
-
Aeroacoustics research in Europe : The CEAS-ASC report on 2012 highlights
- 2013
-
Ingår i: Journal of Sound and Vibration. - : Elsevier BV. - 0022-460X .- 1095-8568. ; 332:25, s. 6617-6636
-
Forskningsöversikt (refereegranskat)abstract
- The Council of European Aerospace Societies (CEAS) Aeroacoustics Specialists Committee (ASC) supports and promotes the interests of the scientific and industrial aeroacoustics community on an European scale and European aeronautics activities internationally. In this context, "aeroacoustics" encompasses all aerospace acoustics and related areas. Each year the committee highlights some of the research and development projects in Europe. This paper is a report on highlights of aeroacoustics research in Europe in 2012, compiled from information provided to the ASC of the CEAS. During 2012, a number of research programmes involving aeroacoustics were funded by the European Commission. Some of the highlights from these programmes are summarized in this paper, as well as highlights from other programmes funded by national programmes or by industry. Enquiries concerning all contributions should be addressed to the authors who are given at the end of each subsection.
|
|
| 23. |
- Bodén, Hans, et al.
(författare)
-
An experimental study of the effect of flow and high level acoustic excitation on the acoustic properties of perforates and orifices
- 2013
-
Ingår i: 20th International Congress on Sound and Vibration 2013, ICSV 2013. - : International Institute of Acoustics and Vibrations. ; , s. 2545-2552
-
Konferensbidrag (refereegranskat)abstract
- Perforates are for instance used in mufflers for automotive applications and in acoustic liners for aircraft engines. In these applications they are often exposed to high level acoustic excitation in combination with grazing or bias flow. The paper is based on an experimental study of the nonlinear properties of these types of samples without mean grazing or bias flow as well as on a study of an orifice with bias flow under medium and high sound level excitation. The effect of grazing flow is discussed based on data from the literature. It is known from previous studies that high level acoustic excitation at one frequency will change the acoustic impedance of perforates at other frequencies, thereby changing the boundary condition seen by the acoustic waves. This effect could be used to change the impedance boundary conditions and for instance increase the absorption. It could obviously also pose a problem for the correct modeling of sound transmission through ducts lined with such impedance surfaces. Experimental results are compared to a quasi-stationary model. The effect of the combination of frequency components and phase in the excitation signal is studied. The bias flow tests included different flow speeds for different frequencies. The level of acoustic excitation is varied from much smaller to larger than the mean flow velocity. It is shown that bias flow makes the acoustic properties more complex compared to the no bias flow case, especially when the velocity ratio between acoustic particle velocity and mean flow velocity is near unity.
|
|
| 24. |
- Bodén, Hans, 1954-, et al.
(författare)
-
An investigation of perforate reactance under high level and grazing flow excitation
- 2023
-
Ingår i: Proceedings of the 29th International Congress on Sound and Vibration, ICSV 2023. - : Society of Acoustics.
-
Konferensbidrag (refereegranskat)abstract
- Perforates are frequently used as part of sound reducing treatment in for instance aircraft engine and IC engine applications. In these applications they are exposed to fluid flow and high-level acoustic excitation, and this influences the acoustic properties of the perforate, as is well known from many published papers. The acoustic properties are usually described using a transfer impedance. In a previous part of this study the effect on the real part (resistance) of the transfer impedance was studied using both a conventional impedance tube (two-port) setup and an innovative three-port setup. The three-port configuration made it possible to study both the effect of grazing flow and high-level excitation effects separately as well as jointly. The present paper is a follow-up study where the imaginary part (reactance) of the transfer impedance is the focus. Comparisons are made with results from previously published papers and empirical models.
|
|
| 25. |
- Bodén, Hans, 1954-
(författare)
-
APPLICATION OF LINEAR ACOUSTIC SOURCE DATA MEASUREMENT TECHNIQUES FOR TRUCK DIESEL ENGINES
- 2004
-
Ingår i: ICSV12-St Petersburg.
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- IC-engines are known from previous studies to be non-linear sources of exhaust system noise. Never the less linear frequency domain prediction codes are used for calculation of low frequency sound transmission in and sound radiation from IC-engine exhaust systems. To calculate insertion loss of mufflers or the level of radiated sound information about the engine as an acoustic source is needed. The source model used in the low frequency plane wave range is the linear time invariant 1-port model. The acoustic source data is usually obtained from experimental tests where multi-load methods and especially the two-load method are most commonly used. In this paper results from experiments on truck Diesel engines are presented. A number of different techniques for extracting source data are tested and the linearity and time invariance is investigated. The results show that a linear time-invariant model can provide good results.
|
|
| 26. |
- Bodén, Hans, 1954-
(författare)
-
APPLICATION OF NONLINEAR SYSTEM IDENTIFICATION TECHNIQUES FOR DETERMINATION OF ACOUSTIC PROPERTIES OF IN-DUCT COMPONENTS
- 2015
-
Ingår i: PROCEEDINGS OF THE 22ND INTERNATIONAL CONGRESS ON SOUND AND VIBRATION. - : INT INST ACOUSTICS & VIBRATION.
-
Konferensbidrag (refereegranskat)abstract
- This paper discusses the use of nonlinear system identification techniques for determination of linear and non-linear acoustic properties of in-duct components. Examples include perforates, orifices and acoustic liners. These types of components can for instance be found in aircraft engines, IC-engine exhaust and intake systems and ventilation ducts. Multiple input single output nonlinear system identification techniques are revisited and applied to the problem of nonlinear acoustic characterization of these components. Bi-linear signal analysis techniques are also discussed as well as empirical mode decomposition and Hilbert transform techniques applicable for non-stationary and nonlinear problems. Methods for studying nonlinear harmonic interaction effects, for perforates, using single tone excitation has been studied in previous work by the author. These techniques typically require measurements with a number of different acoustic loads. It would be more attractive to directly be able to extract the nonlinear acoustic properties from a more limited set of experiments using either random or periodic excitation. The idea of treating a nonlinear path as a separate non-linear input after which system identification is performed as for a linear two input one output system are revisited here in an attempt to analyze why unsatisfactory results were obtained in a previous study.
|
|
| 27. |
- Bodén, Hans, et al.
(författare)
-
Comparison of the effect of flow direction on liner impedance using different measurement methods
- 2017
-
Ingår i: 23rd AIAA/CEAS Aeroacoustics Conference, 2017. - Reston, Virginia : American Institute of Aeronautics and Astronautics. - 9781624105043
-
Konferensbidrag (refereegranskat)abstract
- There is an ongoing scientific discussion about the effect of flow on experimental techniques for determination of acoustic liner impedance. This paper contributes to this continuing effort to gain confidence in results obtained under different acoustical and flow excitation configurations. A majority of the test rigs for determination of liner impedance including the effect of mean flow use plane wave excitation on the upstream side of the liner, but some studies have compared the results for downstream acoustic excitation. Especially for the so-called inverse impedance eduction techniques, it has been reported that different flow directions compared to the acoustic excitation can provide different educed impedances. It is still an open question if this results are due to the application of the Ingard-Myers boundary condition, to other errors or flaws in the measurements or a characteristic of the liner itself. This paper revisit some previous published results and compares the result obtained by means of inverse impedance eduction techniques, which in general adopt the Ingard-Myers boundary condition, and in-situ impedance measurements, which do not require the definition of a boundary condition. It is seen that discrepancies between downstream and upstream measurement can be observed in both approaches, and a discussion on such behavior is presented.
|
|
| 28. |
- Bodén, Hans, 1954-
(författare)
-
Determination of flow resistance from acoustic in-duct measurements
- 2004
-
Ingår i: Collection of Technical Papers - 10th AIAA/CEAS Aeroacoustics Conference<em></em>. - : American Institute of Aeronautics and Astronautics. - 1563477130 ; , s. 494-504
-
Konferensbidrag (refereegranskat)abstract
- This paper discusses the use of acoustic measurement techniques for determination of non-linearity and flow resistance of perforates and other facing sheets used in aircraft engine liners. Impedance measurements with pure tone excitation and random noise excitation are discussed as well as a non-linear system identification technique.
|
|
| 29. |
- Bodén, Hans, 1954-, et al.
(författare)
-
Determination of non-linear acoustic properties of perforates using single tone excitation
- 2010
-
Ingår i: 17th International Congress on Sound and Vibration (ICSV17).
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- This paper discusses experimental techniques for obtaining the acoustic properties of in-duct samples with non-linear acoustic characteristics. The methods developed are intended for studies of non-linear energy transfer to higher harmonics for samples accessible from both side such as perforates or other material used as top sheets in aircraft engine liners and automotive mufflers. New double sided multi-port techniques, using sinusoidal excitation, for characterisation of samples with non-linear properties are developed and experimentally tested. The results of the preliminary experimental tests show that these new techniques can give results which are useful for understanding non-linear energy transfer to higher harmonics.
|
|
| 30. |
- Bodén, Hans
(författare)
-
Determination of the acoustic properties of liners under high level multi-tone excitation
- 2016
-
Ingår i: 22nd AIAA/CEAS Aeroacoustics Conference, 2016. - Reston, Virginia : American Institute of Aeronautics and Astronautics. - 9781624103865
-
Konferensbidrag (refereegranskat)abstract
- This paper discusses the effect of high level multi-tone acoustic excitation on the acoustic properties of acoustic liners and perforates. It is based on an experimental study of the nonlinear properties of these types of samples without mean grazing or bias flow. Compared to previous studies results from normal incidence impedance tube measurements are compared to liners placed in a grazing incidence configuration. It is known from previous studies that high level acoustic excitation at one frequency will change the acoustic impedance of perforates at other frequencies, thereby changing the boundary condition seen by the acoustic waves. This effect could be used to change the impedance boundary conditions and for instance increase the absorption. It could also pose a problem for the correct modelling of sound transmission through ducts lined with such impedance surfaces. The effect of the combination of frequency components is also studied.
|
|
| 31. |
- Bodén, Hans, et al.
(författare)
-
Effect of flow direction on acoustic liner impedance measurement results
- 2016
-
Ingår i: ICSV 2016 - 23rd International Congress on Sound and Vibration. - 9789609922623
-
Konferensbidrag (refereegranskat)abstract
- The last twenty years have seen a large development in inverse techniques for the determination of liner impedance under grazing flow conditions, so called impedance eduction techniques. This paper contributes to a continuing effort to gain confidence in results obtained under different acoustical excitation configurations. Many test rigs for determination of liner impedance including the effect of mean flow use plane wave excitation on the upstream side of the liner. Some studies has compared the result for downstream acoustic excitation and found that different acoustic impedances are obtained in the two cases. It is still an open question if this result is due to the application of the Ingard-Myers boundary condition or to other errors or flaws in the measurements. This paper collects data available in the literature to see if the trend of obtaining different results for upstream and downstream excitation is persistent.
|
|
| 32. |
- Bodén, Hans, 1954-
(författare)
-
Experimental investigation of harmonic interaction effects for perforates
- 2005
-
Ingår i: Collection of Technical Papers. - Monterey, CA. - 1563477300 ; , s. 1236-1242
-
Konferensbidrag (refereegranskat)abstract
- This paper presents the results of a small experimental study of acoustic non-linear harmonic interaction effects for perforates. Impedance measurements using multiple pure tone excitation has been used. The results are potentially of interest for perforates and other facing sheets used in aircraft engine liners as well as perforate pipes used in automotive mufflers. Copyright © 2005 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.
|
|
| 33. |
- Bodén, Hans, 1954-, et al.
(författare)
-
Experimental investigation of nonlinear acoustic properties for perforates
- 2006
-
Ingår i: Collection of Technical Papers. - Cambridge, MA. - 1563478099 - 9781563478093 ; , s. 67-74
-
Konferensbidrag (refereegranskat)abstract
- This paper presents the results of a study of non-linear acoustic properties of perforates and micro-perforates. The results are potentially of interest for perforates and other facing sheets used in aircraft engine liners as well as perforate pipes used in automotive mufflers. In the linear limit the perforate acoustic impedance is independent of the sound field but when the sound pressure level is high it will be dependent on the acoustic particle velocity in the holes. For pure tone excitation the impedance will be controlled by the acoustic particle velocity at that frequency. If the acoustic excitation is random or periodic with multiple harmonics the impedance at a certain frequency will depend on the particle velocity at other frequencies. In this paper a study lias been made of harmonic interaction effects by using multiple pure tone excitation and random noise excitation.
|
|
| 34. |
- Bodén, Hans
(författare)
-
Experimental source characterization techniques for studying the acoustic properties of perforates under high level acoustic excitation
- 2011
-
Ingår i: Journal of the Acoustical Society of America. - : Acoustical Society of America (ASA). - 0001-4966 .- 1520-8524. ; 130:5, s. 2639-2647
-
Tidskriftsartikel (refereegranskat)abstract
- This paper discusses experimental techniques for obtaining the acoustic properties of in-duct samples with non-linear acoustic characteristic. The methods developed are intended both for studies of non-linear energy transfer to higher harmonics for samples only accessible from one side such as wall treatment in aircraft engine ducts or automotive exhaust systems and for samples accessible from both sides such as perforates or other top sheets. When harmonic sound waves are incident on the sample nonlinear energy transfer results in sound generation at higher harmonics at the sample (perforate) surface. The idea is that these sources can be characterized using linear system identification techniques similar to one-port or two-port techniques which are traditionally used for obtaining source data for in-duct sources such as IC-engines or fans. The starting point will be so called polyharmonic distortion modeling which is used for characterization of nonlinear properties of microwave systems. It will be shown how acoustic source data models can be expressed using this theory. Source models of different complexity are developed and experimentally tested. The results of the experimental tests show that these techniques can give results which are useful for understanding non-linear energy transfer to higher harmonics.
|
|
| 35. |
- Bodén, Hans, 1954-, et al.
(författare)
-
Experimental study of nonlinear acoustic properties of perforates using band-limited random excitation information
- 2018
-
Ingår i: 25th International Congress on Sound and Vibration 2018, ICSV 2018. - : International Institute of Acoustics and Vibration, IIAV. - 9781510868458 ; , s. 1818-1825
-
Konferensbidrag (refereegranskat)abstract
- Perforates are used for noise control in automotive mufflers and aircraft engine liners as well as for other vehicles and machines. Their acoustic properties and noise reduction are known to depend on the mean flow field and other parameters such as temperature and acoustic excitation level. It is therefore of interest to understand how the properties of perforates varies with the level of acoustic excitation. This paper gives an overview of high level nonlinear effects on the acoustic properties of perforates. It includes semi-empirical models as well as experimental studies. Methods for studying nonlinear effects and harmonic interaction effects, for perforates, using single tone excitation and Poly-harmonic distortion models or nonlinear scattering matrices are discussed. These techniques typically require measurements with a number of different acoustic loads. It would be more attractive to directly be able to extract the nonlinear acoustic properties from a more limited set of experiments using either random or periodic excitation. Multi input - single output techniques for nonlinear system identification using broadband random excitation has been tried with limited success. One reason is the mixing of the sound pressure signal incident from the acoustic source with the sound pressure transferred to higher frequencies by nonlinear effects at the perforate sample. The present paper includes an attempt to combine band-limited broadband excitation with Poly-harmonic distortion models or nonlinear scattering matrices describing the nonlinear transfer of energy to higher frequencies.
|
|
| 36. |
- Bodén, Hans, 1954-, et al.
(författare)
-
Experimental Techniques for Aeroacoustics in Low Mach Number Confined Flows : Keynote Paper
- 2011
-
Ingår i: Proceedings of the International Conference on Mechanical Engineering 2011(ICME2011) 18-20 December 2011, Dhaka, Bangladesh. - : ICME.
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Measurement of plane wave acoustic transmission properties, so called two-port data, of flow duct components is important in many applications such as in the development of mufflers for IC-engines. Measurement of two-port data is difficult when the flow velocity in the measurement duct is high because of the flow noise contamination of the measured pressure signals. The wall mounted pressure transducers normally used will pick up unwanted flow noise mainly in the form of turbulent pressure fluctuations. The problem is then obtaining a signal-to- noise ratio high enough for quality measurements. Techniques to improve acoustic two-port determination have been developed in this paper, including test rig design, signal processing techniques and over-determination.
|
|
| 37. |
- Boden, Hans
(författare)
-
IC-Engine Exhaust and Intake System Acoustic Source Characterization
- 2014
-
Ingår i: SAE International Journal of Engines. - : SAE International. - 1946-3936 .- 1946-3944. ; 7:3, s. 1579-1584
-
Tidskriftsartikel (refereegranskat)abstract
- The paper gives an overview of techniques used for characterization of IC-engines as acoustic sources of exhaust and intake system noise. Some recent advances regarding nonlinear source models are introduced and discussed. To calculate insertion loss of mufflers or the level of radiated sound information about the engine as an acoustic source is needed. The source model used in the low frequency plane wave range is often the linear time invariant one-port model. The acoustic source data is obtained from experimental tests or from 1-D CFD codes describing the engine gas exchange process. The IC-engine is a high level acoustic source and in most cases not completely linear. It is therefore of interest to have models taking weak non-linearity into account while still maintaining a simple method for interfacing the source model with a linear frequency domain model for the attached exhaust or intake system. The use of source characterization in acoustic design of mufflers is also briefly discussed.
|
|
| 38. |
- Bodén, Hans, 1954-, et al.
(författare)
-
Impedance measurements for 3-d printed liners
- 2019
-
Ingår i: 25th AIAA/CEAS Aeroacoustics Conference, 2019. - Reston, Virginia : [publishername] American Institute of Aeronautics and Astronautics Inc, AIAA. - 9781624105883
-
Konferensbidrag (refereegranskat)abstract
- The last twenty years have seen a great development in inverse techniques for the determination of liner impedance under grazing flow conditions, so called impedance eduction techniques. This paper contributes to a continuing effort to gain confidence in the results obtained, specifically in the dependence of the results on fabrication, data acquisition and analysis. It is part of the IFAR Acoustic Liner Challenge were data from multiple test rigs with similar liner configurations fabricated using 3D printing are gathered and compared. Experimental results are reported for two liner configurations obtained in KTH’s advanced impedance eduction flow rig.
|
|
| 39. |
- Bodén, Hans, 1954-
(författare)
-
In-duct source characterization for multiple sources
- 2009
-
Ingår i: 16th International Congress on Sound and Vibration 2009, ICSV 2009. - 9781615677368 ; , s. 2664-2671
-
Konferensbidrag (refereegranskat)abstract
- This paper discusses experimental techniques for detecting if there are multiple sources in a duct and obtaining the acoustic characteristics of these sources. Experimental techniques for in-duct source characterization under plane wave conditions in ducts, when we know the location of the source, are well established. In some cases there can however be sources at both ends of a duct. The paper starts with discussing the possibility to, by using a number of flush mounted microphones in the duct, detect sources located on both sides of the test section and to extract the acoustic source characteristics of the sources. First the sound field in a duct with sources at both ends is discussed and described. The theory for experimental determination of source data is then described. A discussion of the consequences of source correlation is included. The methods are first tested using loudspeakers in a duct.
|
|
| 40. |
- Boden, Hans, et al.
(författare)
-
Linearity tests for in-duct acoustic one-port sources
- 2000
-
Ingår i: Journal of Sound and Vibration. - : Elsevier BV. - 0022-460X .- 1095-8568. ; 237:1, s. 45-65
-
Tidskriftsartikel (refereegranskat)abstract
- Acoustic one-port source data are commonly used to predict the plane wave sound generation in duct and pipe systems connected to fluid machines. The source data are usually determined experimentally, which assumes that linear time-invariant system theory can be used. Since some machines such as IC-engines and compressors generate very high sound levels in the connecting ducts or pipes it is of interest to investigate whether the assumption of linearity is justified. Linearity tests for linear system identification when both input and output signals can be measured are common in the literature. In the case when only the output signal can be measured linearity tests are not so readily found. This paper presents two different linearity coefficients for determining whether an acoustic one-port source under test is linear. Their sensitivity to random noise and their ability to detect non-linearities are investigated by simulations and measurements on several types of machines.
|
|
| 41. |
- Bodén, Hans, 1954-
(författare)
-
Modelling of nonlinear acoustic harmonic interaction effects for perforates
- 2019
-
Ingår i: Proceedings of the 26th International Congress on Sound and Vibration, ICSV 2019. - : Canadian Acoustical Association.
-
Konferensbidrag (refereegranskat)abstract
- The effect of high level multi-tone acoustic excitation on the acoustic properties of acoustic liners and perforates has been discussed in a number of papers. It has mainly been based on experimental studies of the nonlinear properties of these types of samples without mean grazing or bias flow. Comparisons to a simulation model has also been made in some previous papers. In the present paper a model for the harmonic interaction caused by high level excitation will be tested. The idea is to use the so called nonlinear scattering matrix model combined with a semi-empirical model. Results are compared to experimental results for an orifice plate and perforate sample. The research questions of interest are: Can the model previously used to study nonlinear effects at the tonal excitation frequency also be used to describe harmonic interaction effects? That is if we excite the system at a certain frequency can the model describe how much sound that is generated (transferred) at higher harmonics. As part of that investigation nonlinear scattering matrix models will be used both to evaluate simulated and experimental data. This comparison is used to draw conclusions on if the nonlinear scattering matrix model gives physically meaningful results. There are a number of simplifying assumptions made in order to reach the model used so using the simulated results can be a way to investigate under which conditions they are valid.
|
|
| 42. |
- Bodén, Hans, 1954-
(författare)
-
Multi-port techniques for acoustic characterisation of non-linear in-duct discontinuities
- 2009
-
Ingår i: 15th AIAA/CEAS Aeroacoustics Conference (30th AIAA Aeroacoustics Conference). - 9781563479748
-
Konferensbidrag (refereegranskat)abstract
- This paper discusses techniques for obtaining the acoustic properties of in-duct samples with non-linear acoustic characteristics such as perforates and other facing sheets used in aircraft engine liners and automotive mufflers. It is assumed that the non-linearity occurs locally at constrictions or sharp corners. Multi-port techniques using sinusoidal excitation for better characterization of samples with non-linear properties are developed and experimentally tested. These new techniques take non-linear energy transfer between sound field harmonics into account.
|
|
| 43. |
- Bodén, Hans, et al.
(författare)
-
Noise from turbo-charged diesel engine exhaust systems
- 2005
-
Ingår i: 12th International Congress on Sound and Vibration 2005. - 9781627481496 ; , s. 2231-2238
-
Konferensbidrag (refereegranskat)abstract
- This paper summarises the main results of an EU-funded research project, ARTEMIS (G3RD-CT-2001-00511), on noise from turbo-charged Diesel engine exhaust systems. The project started in September 2001 and ended in August 2004 and was co-ordinated by KTH. The project had 10 partners from 6 different European countries, 5 universities and 5 companies including some major truck and car manufacturers. The main objective was to develop new and improved computational tools for predicting noise from exhaust systems. New models for describing the engine as an acoustic source were developed and experimentally tested. They include a linear time-varying source model and a non-linear frequency domain model. Linear time-invariant source data was also determined both from experiments and using 1-D gas-exchange simulations. New and improved models were developed for the turbo-group including non-linear time domain models and a linear time-varying model. New models were developed and experimentally tested for sound transmission through the Diesel particulate filter included in modern Diesel engine after-treatment devices. Improved models were developed for describing perforate mufflers with high mean flow velocities. Improved experimental techniques for determination of transmission properties of duct system components were developed. Models were developed and coded for sound reflection and radiation from tailpipe openings. Full experimental validation of the Munt theory for radiation from open pipes with flow was produced. In conclusion it can be said that the project was successful and gave many useful results.
|
|
| 44. |
- Bodén, Hans
(författare)
-
Non-linear system identification techniques for determination of the acoustic properties of perforates
- 2015
-
Ingår i: 21st AIAA/CEAS Aeroacoustics Conference. - Reston, Virginia : American Institute of Aeronautics and Astronautics.
-
Konferensbidrag (refereegranskat)abstract
- This paper discusses the use of nonlinear system identification techniques for determination of linear acoustic impedance and non-linear acoustic properties of perforates and other facing sheets used in aircraft engine liners. Multiple input single output nonlinear system identification techniques are revisited and applied to the problem of nonlinear acoustic characterisation of perforates. Bi-linear signal analysis techniques are also tested as well as Hilbert transform techniques applicable for non-stationary and nonlinear problems. It is shown that random excitation nonlinear system identification techniques have the potential of identifying and characterising non-linear acoustic properties of these types of samples.
|
|
| 45. |
- Bodén, Hans
(författare)
-
Nonlinear source characterisation techniques for IC-engines
- 2012
-
Ingår i: 19th International Congress on Sound and Vibration 2012, ICSV 2012. - 9781622764655 ; , s. 2442-2449
-
Konferensbidrag (refereegranskat)abstract
- A source characterization model for IC-engines, which can take weakly nonlinear source properties into account, is developed in the paper. It is based on so called polyharmonic distortion modeling, used for nonlinear characterization of microwave systems. Comparisons are made with the results from linear source models and another previously published weakly nonlinear source model. The results show that the new nonlinear impedance matrix model gives improvements in the prediction of sound pressure levels in the exhaust system.
|
|
| 46. |
- Bodén, Hans, 1954-, et al.
(författare)
-
On extraction of IC-engine linear acoustic source data from non-linear simulations
- 2004
-
Ingår i: ICSV12-St Petersburg.
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Linear frequency domain prediction codes are used for calculation of low frequency sound transmission in and sound radiation from IC-engine exhaust systems. To calculate insertion loss of mufflers or the level of radiated sound information about the engine as an acoustic source is needed. The source model used in the low frequency plane wave range is the linear time invariant 1-port model. The acoustic source data is usually obtained from experimental tests where multi-load methods and especially the two-load method are most commonly used. These tests are time consuming and expensive. It would therefore be of interest to extract the acoustic source data from existing 1-D CFD codes describing the engine gas exchange process. In this paper a comparison is made between results obtained applying the two-load technique to measurements on a truck Diesel engine and to 1-D CFD simulations of the same engine. The results show that it is possible to obtain reasonably accurate source data estimates from the simulations.
|
|
| 47. |
- Bodén, Hans, 1954-
(författare)
-
On impedance measurements for samples with non-linear acoustic properties
- 2008
-
Ingår i: 14th AIAA/CEAS Aeroacoustics Conference (29th AIAA Aeroacoustics Conference). - Vancouver, BC. - 9781563479397
-
Konferensbidrag (refereegranskat)abstract
- This paper discusses techniques for obtaining the acoustic properties of in-duct samples with non-linear acoustic characteristics such as perforates and other facing sheets used in aircraft engine liners and automotive mufflers. It is assumed that the non-linearity occurs locally at constrictions or sharp corners. The paper starts with a short review of previous impedance tube measurements made for determining the acoustic impedance of non-linear samples. Multi-port techniques using sinusoidal excitation for better characterization of samples with non-linear properties are developed and experimentally tested.
|
|
| 48. |
- Bodén, Hans, 1954-, et al.
(författare)
-
On the effect of flow direction on impedance eduction results
- 2016
-
Ingår i: 22nd AIAA/CEAS Aeroacoustics Conference, 2016. - Reston, Virginia : American Institute of Aeronautics and Astronautics (AIAA).
-
Konferensbidrag (refereegranskat)abstract
- The last twenty years have seen a large development in inverse techniques for the determination of liner impedance under grazing flow conditions, so called impedance eduction techniques. This paper contributes to a continuing e ort to gain confidence in results obtained under different acoustical excitation configurations. Many test rigs use plane wave excitation on the upstream side of the liner for determination of liner impedance including the effect of mean flow. Some studies have compared the result for downstream acoustic excitation and found that different acoustic impedances are obtained in the two cases. It is still an open question if this result is due to the application of the Ingard-Myers boundary condition or to other errors or flaws in the measurements. This paper collects data available in the literature as well as some new data to see if the trend of obtaining di erent results for upstream and downstream excitation is persistent. The Ingard-Myers boundary condition and alternative formulations published in the literature are discussed.
|
|
| 49. |
- Bodén, Hans
(författare)
-
One-sided multi-port techniques for characterisation of in-duct samples with nonlinear acoustic properties
- 2012
-
Ingår i: Journal of Sound and Vibration. - : Elsevier BV. - 0022-460X .- 1095-8568. ; 331:13, s. 3050-3067
-
Tidskriftsartikel (refereegranskat)abstract
- Single sided multi-port system identification techniques, using sinusoidal excitation, for studying nonlinear energy transfer to higher harmonics for samples only accessible from one side such as perforated liners used as wall treatment in aircraft engine ducts are presented. The starting point is the so called polyharmonic distortion theory used for studying microwave systems. Models of different level of complexity are developed and the system identification results are compared. Experimental results, including error analysis, for a perforate sample are presented. The use of these techniques for analysing nonlinear energy transfer to higher harmonics and to improve the understanding of the physical phenomena involved are illustrated.
|
|
| 50. |
- Bodén, Hans
(författare)
-
Polyharmonic distortion modelling applied to acoustic characterisation of peforates
- 2011
-
Ingår i: 17th AIAA/CEAS Aeroacoustics Conference 2011 (32nd AIAA Aeroacoustics Conference). - Reston, Virigina : American Institute of Aeronautics and Astronautics.
-
Konferensbidrag (refereegranskat)abstract
- This paper discusses the possibility to apply polyharmonic distortion modelling, used for nonlinear characterisation of microwave systems, to acoustic characterisation of samples with non-linear properties such as perforates and other facing sheets used in aircraft engine liners and automotive mufflers. In some previous papers multi-port techniques using sinusoidal excitation for characterization of samples with non-linear properties were developed and experimentally tested. These techniques aimed at taking non-linear energy transfer between sound field harmonics into account. Essentially linear system identification theory was however used assuming that superposition applies and that the functions studied are analytical. Polyharmonic distortion modelling does not assume that the function relating waves incident and reflected or transmitted is analytic nor does it assume application of normal superposition. This technique is tested on experimental data obtained from measurements on a perforate mounted in a duct. The similarity to the previously developed nonlinear scattering matrix techniques is demonstrated. It is shown how the results obtained can be used to analyse nonlinear energy transfer to higher harmonics.
|
|
