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  • 301.
    Blanco, Blas
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Kari, Leif
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Gil-Negrete, Nere
    Alonso, Asier
    Modelling of the track supports with elements over elastic foundation together with dynamic internal degrees of freedom2018Inngår i: Proceedings of ISMA 2018 - International Conference on Noise and Vibration Engineering and USD 2018 - International Conference on Uncertainty in Structural Dynamics2018, Pages 3255-326828th International Conference on Noise and Vibration Engineering, ISMA 2018 and 7th International Conference on Uncertainty in Structural Dynamics, USD 2018; Leuven; Belgium; 17 September 2018 through 19 September 2018 / [ed] W. Desmet, B. Pluymers, D. Moens, W. Rottiers, KU Leuven - Departement Werktuigkunde , 2018, s. 3255-3268Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Formulation of the Timoshenko elements is improved with the use of internal degrees of freedom (iDOF) representing the local displacements, leading to a new finite element approach specially devoted to the numeric analysis of the track dynamics. The dynamic formulation of the local displacement is proved to correct the frequency content of the track model. Regarding time domain studies, this approach avoids the displacement underestimation and shear discontinuity between elements, which are sources of inaccuracies and irregular behaviour.  Those rail sections located above the supports are modelled with Timoshenko element over elastic foundation (TEEF), and the rest with conventional Timoshenko elements (TIM4). By using TEEF prompt disruption of the contact force at support surpassing is avoided, and the frequency response of the track around the `pinned-pinned' frequency is corrected. Moreover the TEEF formulation is extended in order to account for the sleeper pitch rotation, and evaluation of its influence over the track dynamics is performed. 

  • 302.
    Blanco, Blas
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Kari, Leif
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Gil-Negrete, Nere
    Giménez, José Germán
    Alonso, Asier
    Assessment of the influence of railway track periodicity, load speed and support modelling on the rolling noise emissionManuskript (preprint) (Annet vitenskapelig)
    Abstract [en]

    The presented methodology jointly accounts for the railway track periodicity and the moving load nature at noise predictions. This modelling approaches rail and sleepers employing the Timoshenko beam theory, and it is formulated to be directly implemented into noise software based on irregularity strip technique. By means of precalculated time domain responses with an analytical track model, the periodicity and moving track dynamics are addressed. In the same way, the propagative behaviour in moving conditions of waves along the rail is characterised by comparison of the responses at several positions.Regarding track support modelling, the usual point modelling is substituted by a distributed representation in order to explore the advantages of accounting for the support length. A numerical model fulfils this task and avoids boundary effects utilising infinite elements. Distributed modelling achieves a more realistic representation of the track geometry. It prevents exaggeration of the amplitude at the `pinned-pinned' frequencies without resorting to overestimation of the steel loss factors. This improvement is especially useful when overvalued rail damping leads to predicted track decay rate (TDR) higher than the one experimentally measured.Finally, the impact of periodicity, load speed and support modelling are assessed through the sound power level (SWL) results.  The predictions are performed with a software package, CRoNoS (CAF Rolling Noise Software), developed by CAF S.A. Moving conditions has a limited impact on the SWL, while modelling of the foundation as periodic is important at tracks with hard pad types, and distributed support modelling becomes significant when realistic values of the steel loss factor are used.

  • 303.
    Blandineau, Pauline
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Flygdynamik.
    Wake Vortex Encounter Detection and Severity Assessment from Flight Data2012Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
    Abstract [en]

    Hazards associated to Wake Vortex Encounters (WVE) are increasing with the growing traffic and the appearance of super heavy aircrafts such as the A380. The project comes with the need from airports and airlines to clearly analyze the phenomenon by detecting WVE and quantifying their strength from Flight Data Recorder data. A tool is developed with this purpose using Roll Control Ratio as severity metric. Flight data from flight simulator are used for first analyses. The obtained results are encouraging and enable proposed improvements and consideration to further work.

  • 304.
    Blaszykowski, Sylvain
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Fordonsdynamik.
    Design, modeling and implementation of the power train of an electric racing car: Control of a permanent magnet machine and implementation of a torque vectoring process in a FSAE car2013Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
    Abstract [en]

    This work emphasize the design, implementation and optimization of an electric power train for a Formula Student racing car.

    As a first part, theory and control of a PMSM machine, in an automotive context is investigated: a CAN bus communication system has been implemented and a field weakening strategy. Precise modeling of the car has then been performed using CarMaker, developed by IPG and making it possible to perform accurate tests and forecast regarding the performances of the vehicle. This model was then used to develop and test different launch control strategies together with a torque vectoring strategy and study the influence of different parameters on the vehicle performances.

  • 305.
    Blom, Peter
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Exploring the vibration control potential of magneto-sensitive rubber2005Licentiatavhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    Two new aspects of the dynamic behaviour in the audible frequency range of magneto-sensitive (MS) rubber are highlighted: the existence of an amplitude dependence of the shear modulus—referred to as the Fletcher–Gent effect—for even small displacements, and the appearance of large MS effects. These results have been obtained experimentally and are subsequently used to model two examples of magneto-sensitive rubber isolators to show how by means of MS rubber they can be improved. The first model calculates the transfer stiffness of a torsionally excited isolator and the second one the energy flow into the foundation for a bushing inserted between a vibrating mass and an infinite plate. In both examples notable improvements in isolation can be obtained

  • 306.
    Blom, Peter
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet. KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Magneto-sensitive rubber in the audible frequency range2006Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    The dynamic behaviour in the audible frequency range of magneto-sensitive (MS) rubber is the focus of this thesis consisting of five papers A-E. Paper A presents results drawn from experiments on samples subjected to different constant shear strains over varying frequencies and magnetic fields. Main features observed are the existence of an amplitude dependence of the shear modulus referred to as the Fletcher-Gent effect for even small displacements, and the appearance of large MS effects. These results are subsequently used in Paper B and C to model two magneto-sensitive rubber isolators, serving to demonstrate how, effectively, by means of MS rubber, these can be readily improved. The first model calculates the transfer stiffness of a torsionally excited isolator, and the second one, the energy flow into the foundation for a bushing inserted between a vibrating mass and an infinite plate. In both examples, notable improvements in isolation are obtainable. Paper D presents a non-linear constitutive model of MS rubber in the audible frequency range. Characteristics inherent to magneto-sensitive rubber within this dynamic regime are defined: magnetic sensitivity, amplitude dependence, elasticity and viscoelasticity. A very good agreement with experimental values is obtained. In Paper E, the magneto-sensitive rubber bushing stiffness for varying degrees of magnetization is predicted by incorporating the non-linear magneto-sensitive audio frequency rubber model developed in Paper D, into an effective engineering formula for the torsional stiffness of a rubber bushing. The results predict, and clearly display, the possibility of controlling over a large range through the application of a magnetic field, the magneto-sensitive rubber bushing stiffness.

  • 307.
    Blom, Peter
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Strukturakustik.
    Kari, Leif
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Strukturakustik.
    A non-linear constitutive audio frequency magneto-sensitive rubber model including amplitude, frequency and magnetic field dependence.2011Inngår i: Journal of Sound and Vibration, ISSN 0022-460X, E-ISSN 1095-8568, Vol. 330, nr 5, s. 947-954Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A novel constitutive model of magneto-sensitive rubber in the audible frequency range is presented. Characteristics inherent to magneto-sensitive rubber within this dynamic regime are defined: magnetic sensitivity, amplitude dependence, elasticity and viscoelasticity. Prior to creating the model assumptions based on experimental observations concerning these components are formulated. The first observation is that not only does the rubber display a strong amplitude dependence even for small strains, but also the magnetic sensitivity is strongly amplitude dependent. The second and third are, respectively, that the elastic component is magneto-sensitive, whereas the viscoelastic dependence on magnetic induction appears to be small. Thus, the model is developed from these assumptions and parameters are optimized with respect to experimental values for one case and subsequently validated for others; a very good agreement is obtained.

  • 308.
    Blom, Peter
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Strukturakustik.
    Kari, Leif
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Strukturakustik.
    Amplitude and frequency dependence of magneto-sensitive rubber in a wide frequency range2005Inngår i: Polymer testing, ISSN 0142-9418, E-ISSN 1873-2348, Vol. 24, nr 5, s. 656-662Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Two new aspects of the dynamic behaviour in the audible frequency range of magneto-sensitive (MS) rubber are highlighted: the existence of an amplitude dependence of the shear modulus - referred to as the Fletcher-Gent effect - for even small displacements, and the appearance of large MS effects. In order to illustrate these two features, results are presented of measurements performed in the audible frequency range on two different kinds of rubber: silicone and natural rubber with a respective iron particle volume concentration of 33%. The particles used are of irregular shape and randomly distributed within the rubber. An external magnetic field of 0-0.8 T is applied. Both kinds of rubber are found to be strongly amplitude dependent and, furthermore, displaying large responses to externally applied magnetic fields - a maximum of 115%. Also included are graphs of measurements on silicone and natural rubber devoid of iron particles. Those results support the conclusion that introducing iron particles in the rubber gives rise to a strong, non-negligible, amplitude dependence in the entire frequency range.

  • 309.
    Blom, Peter
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Strukturakustik.
    Kari, Leif
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Strukturakustik.
    Magneto-sensitive rubber in the audible frequency range2005Inngår i: CONSTITUTIVE MODELS FOR RUBBER IV / [ed] Per-Erik Austrell, Leif Kari, London: Taylor & Francis, 2005Konferansepaper (Fagfellevurdert)
  • 310.
    Blom, Peter
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Strukturakustik.
    Kari, Leif
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Strukturakustik.
    Smart audio frequency energy flow control by magneto-sensitive rubber isolators2008Inngår i: Smart materials and structures (Print), ISSN 0964-1726, E-ISSN 1361-665X, Vol. 17, nr 1Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A magneto-sensitive rubber isolator inserted between a source and an infinite plate is modelled in the audible frequency range, and the energy flow into the plate with the rubber subjected to a magnetic field applied perpendicular to the axial displacement is calculated. Subsequently the result is compared to the corresponding energy flow for zero magnetic induction; upon the application of an external magnetic field the rubber becomes stiffer, thus shifting the internal resonances of the isolator. This is a fast and reversible process enabling adaption of the isolator to rapidly changing audio frequency conditions by simply turning on and off a magnetic field. In the application example considered, the energy flow into the plate at the first internal dynamic peak stiffness frequency is reduced by approximately 7 dB-a large difference in a sound and vibration context-by inducing magnetic saturation of the rubber.

  • 311.
    Blom, Peter
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Strukturakustik.
    Kari, Leif
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Strukturakustik.
    The frequency, amplitude and magnetic field dependent torsional stiffness of a magneto-sensitive rubber bushing2011Inngår i: International Journal of Mechanical Sciences, ISSN 0020-7403, E-ISSN 1879-2162, Vol. 60, nr 1, s. 54-58Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A dynamic torsional stiffness model of a magneto-sensitive circular annular rubber bushing is presented where influences of frequency, amplitude and magnetic field dependence are included. This is achieved by employing a newly developed non-linear magneto-sensitive audio frequency constitutive equation in an engineering formula for the torsional stiffness of a rubber bushing. The engineering stiffness formula predicts the frequency and amplitude dependent stiffness in a simple way, based on geometric dimensions and the shear modulus. The shear modulus is provided by the rubber model. The results from these calculations predict and clearly display the possibility of controlling over a large frequency range, through the application of a magnetic field, the magneto-sensitive rubber bushing stiffness.

  • 312.
    Blomberg, Karl
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Marina system.
    Gross, Jonas
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Marina system.
    Conceptual Study of a USV for theSwedish Navy2014Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
    Abstract [en]

    This thesis is an initial conceptual study of an unmanned surface vehicle (USV) for the

    Swedish Navy. The purpose is to highlight challenges and possibilities connected to

    unmanning a vessel and to suggest one specific concept.

    Generating one concept meant weighing characteristics of different hull types against one

    another to derive a valuable compromise. The generated concept includes a feature of

    longitudinal bulkheads separating an inner, dry volume from outer ballast volumes. The

    latter fill with seawater at low velocities, causing the hull to partly submerge which in turn

    decreases signature and increases ballistic protection within the semi-submerged speed

    range. The!concept!measures 6.2 by 2.3 meters, weigh, approximately 1800 kg and may

    reach a calm water top speed of 44 knots. Investigating needs and potentials of an

    unmanned vessel within the Swedish Navy resulted in a set of requirements, including the

    possibility to arm the USV. This study investigates feasibility of carrying the SAAB Trackfire

    remote weapon platform aboard.

    Development of the initial USV concept was focused on aspects of naval architecture,

    including the making of a!general arrangement, evaluating materials, a structural design,

    stability and power need analysis. Although unmanned vessels are likely to be subject to

    lessened structural safety factors as opposed to manned, scantling determination is based

    on DNV rules for classification of High Speed, Light Craft and Naval Surface Craft.

     

  • 313.
    Boden, Hans
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    IC-Engine Exhaust and Intake System Acoustic Source Characterization2014Inngår i: SAE International Journal of Engines, ISSN 1946-3936, E-ISSN 1946-3944, Vol. 7, nr 3, s. 1579-1584Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    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.

  • 314.
    Bodén, Hans
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    Acoustic characterisation of perforates using non-linear system identification techniques2007Inngår i: 13th AIAA/CEAS Aeroacoustics Conference (28th AIAA Aeroacoustics Conference), American Institute of Aeronautics and Astronautics, 2007Konferansepaper (Fagfellevurdert)
    Abstract [en]

    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.

  • 315.
    Bodén, Hans
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Acoustic properties of perforates under high level multi-tone excitation2013Inngår i: 19th AIAA/CEAS Aeroacoustics Conference, American Institute of Aeronautics and Astronautics, 2013Konferansepaper (Fagfellevurdert)
    Abstract [en]

    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.

  • 316.
    Bodén, Hans
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet. KTH, Skolan för industriell teknik och management (ITM), Centra, Competence Center for Gas Exchange (CCGEx).
    APPLICATION OF NONLINEAR SYSTEM IDENTIFICATION TECHNIQUES FOR DETERMINATION OF ACOUSTIC PROPERTIES OF IN-DUCT COMPONENTS2015Inngår i: PROCEEDINGS OF THE 22ND INTERNATIONAL CONGRESS ON SOUND AND VIBRATION: MAJOR CHALLENGES IN ACOUSTICS, NOISE AND VIBRATION RESEARCH, 2015 / [ed] Crocker, MJ Pawelczyk, M Pedrielli, F Carletti, E Luzzi, S, INT INST ACOUSTICS & VIBRATION , 2015Konferansepaper (Fagfellevurdert)
    Abstract [en]

    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.

  • 317.
    Bodén, Hans
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Strömningsakustik.
    Experimental investigation of harmonic interaction effects for perforates2005Inngår i: Collection of Technical Papers: 11th AIAA/CEAS Aeroacoustics Conference, Monterey, CA, 2005, Vol. 2, s. 1236-1242Konferansepaper (Fagfellevurdert)
    Abstract [en]

    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.

  • 318.
    Bodén, Hans
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Strukturakustik.
    Experimental source characterization techniques for studying the acoustic properties of perforates under high level acoustic excitation2011Inngår i: Journal of the Acoustical Society of America, ISSN 0001-4966, E-ISSN 1520-8524, Vol. 130, nr 5, s. 2639-2647Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    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.

  • 319.
    Bodén, Hans
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Strömningsakustik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    In-duct source characterization for multiple sources2009Inngår i: 16th International Congress on Sound and Vibration 2009, ICSV 2009, 2009, s. 2664-2671Konferansepaper (Fagfellevurdert)
    Abstract [en]

    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.

  • 320.
    Bodén, Hans
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Strömningsakustik.
    International Journal of Aeroacoustics, volume 6, number 12007Collection/Antologi (Fagfellevurdert)
    Abstract [en]

    In November 2005 a Workshop with the title ”Active Control of Aircaft Noise – Concept to Reality” was organised by CEAS-ASC (Council of European Aeronautical Societies – Aeroacoustics Specialist Committee). The Workshop was held at KTH (the Royal Institute of Technology) in Stockholm, Sweden and was chaired by Hans Bodén from KTH and Urban Enborg from A2 Acoustics. This was the ninth in a series of annual Workshops organised by CEAS-ASC. It was co-sponsored by_the American Insitute of Aeronautics and Astronautics (AIAA), CARAN SAAB Engineering, SAAB, Airbus, KTH and the EU through the X2-Noise Thematic Network.

                A total of 20 papers were presented during the two day event divided into four sessions: interior noise, airframe noise flow control, jet noise and fan noise.

                The aim of the Workshop was to summarise the state of the art and to indentyfy breakthroughs needed in order to apply active control in reducing aircraft noise. The technique is most mature in control of interior noise where there are 850 systems flying in regional turnoprop aircraft , business turboprop and some jet aircraft and military aircraft. There has been a lot of work on active control of fan noise both on active liners and using flow control to reduce fan tone noise and active control of buzz saw noise. Also for airframe noise there have been studies e.g., on applying active flow control to highlift devices. Closed-loop flow control has been used in control of cavity tones. Studies have also been made of the use of flow injection for reduction of jet noise. Another technique tested for jet noise reduction is deployable chevrons.

    The present issue contains five of the twenty papers presented at he Workshop. The selection is slanted towards active control of fan noise with two papers on the interesting subject of buzz saw noise reduction, one paper on control of fan tone noise using flow induction and one paper on hybrid passive/active treatment for inlet nacelles. In addition, there is one paper on optimisation of interior noise control.

  • 321.
    Bodén, Hans
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Multi-port techniques for acoustic characterisation of non-linear in-duct discontinuities2009Inngår i: 15th AIAA/CEAS Aeroacoustics Conference (30th AIAA Aeroacoustics Conference), 2009Konferansepaper (Fagfellevurdert)
    Abstract [en]

    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.

  • 322.
    Bodén, Hans
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet. KTH, Skolan för industriell teknik och management (ITM), Centra, Competence Center for Gas Exchange (CCGEx).
    Nonlinear source characterisation techniques for IC-engines2012Inngår i: 19th International Congress on Sound and Vibration 2012, ICSV 2012, 2012, s. 2442-2449Konferansepaper (Fagfellevurdert)
    Abstract [en]

    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.

  • 323.
    Bodén, Hans
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Vibrationsövervakning.
    Non-linear system identification techniques for determination of the acoustic properties of perforates2015Inngår i: 21st AIAA/CEAS Aeroacoustics Conference, American Institute of Aeronautics and Astronautics, 2015Konferansepaper (Fagfellevurdert)
    Abstract [en]

    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.

  • 324.
    Bodén, Hans
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Strömningsakustik.
    On impedance measurements for samples with non-linear acoustic properties2008Inngår i: 14th AIAA/CEAS Aeroacoustics Conference (29th AIAA Aeroacoustics Conference), Vancouver, BC, 2008Konferansepaper (Fagfellevurdert)
    Abstract [en]

    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.

  • 325.
    Bodén, Hans
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Strömningsakustik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    One-sided multi-port techniques for characterisation of in-duct samples with nonlinear acoustic properties2012Inngår i: Journal of Sound and Vibration, ISSN 0022-460X, E-ISSN 1095-8568, Vol. 331, nr 13, s. 3050-3067Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    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.

  • 326.
    Bodén, Hans
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Polyharmonic distortion modelling applied to acoustic characterisation of peforates2011Inngår i: 17th AIAA/CEAS Aeroacoustics Conference 2011 (32nd AIAA Aeroacoustics Conference), 2011Konferansepaper (Fagfellevurdert)
    Abstract [en]

    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. © 2011 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.

  • 327.
    Bodén, Hans
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Recent Advances In  IC-engine acoustic source Characterisation2007Inngår i: 14th International Congress on Sound and Vibration (ICSV14), 2007Konferansepaper (Annet vitenskapelig)
    Abstract [en]

    This paper summarizes work performed at KTH over the years on source characterization for IC-engine exhaust and intake systems. An overview is made of recent advances in experimental and simulation methods for determination of acoustic source data. These include a source model which can consider weakly non-linear sources and application of 1-D CFD codes for extracting source data. Examples are presented for both exhaust and intake systems and for different types of engines. The results show that reasonably accurate results can be obtained using 1-D CFD codes to extract acoustic source data and that the newly developed non-linear multi-load technique has got advantages over the traditional two-load technique for determining source data from experiments.

  • 328.
    Bodén, Hans
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Strömningsakustik.
    Single tone excitation techniques for determination of non-linear acoustic properties of perforates2010Inngår i: Proceedings of the International Conference on Noise and Vibration Engineering, ISMA 2010, 2010, s. 597-609Konferansepaper (Fagfellevurdert)
    Abstract [en]

    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 such as perforates or other material used as top sheets in aircraft engine liners and automotive mufflers. New single sided and 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.

  • 329.
    Bodén, Hans
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Strömningsakustik.
    Study of nonlinear energy transfer for perforated wall treatment using acoustic source characterisation techniques2011Inngår i: 18th International Conference on Sound and Vibration (ICSV18), 2011Konferansepaper (Annet vitenskapelig)
    Abstract [en]

    This paper discusses experimental techniques for obtaining the acoustic properties of in-duct samples with non-linear acoustic characteristics such as perforates used in aircraft engine liners and automotive mufflers. The methods developed are intended 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. Nonlinear energy transfer results in sound generation at higher harmonics at the sample (perforate) surface. The idea here is that these sources can be characterised using linear one-port techniques which are traditionally used for obtaining source data for in-duct sources such as fans or IC-engines. The results of the experimental tests show that these new techniques can give results which are useful for understanding non-linear energy transfer to higher harmonics.

  • 330.
    Bodén, Hans
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    The effect of high level multi-tone excitation on the acoustic properties of perforates and liner samples2012Inngår i: 18th AIAA/CEAS Aeroacoustics Conf. (33rd AIAA Aeroacoustics Conf.), American Institute of Aeronautics and Astronautics, 2012Konferansepaper (Fagfellevurdert)
    Abstract [en]

    This paper discusses the effect of high level multi-tone acoustic excitation on the acoustic properties of perforates and liner samples. It is based on a large experimental study of the nonlinear properties of these types of samples without mean grazing or bias flow. 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. First a quasi-stationary model for the acoustic properties of the perforate is discussed and the results are compared to experimental data. The effect of the combination of frequency components in the excitation signal is studied to find out if it matters if we are using tones which are harmonically related or not. The effect the phase of the frequency components is studied using both the model and experimental data. It is also discussed if a parameter controlling the impedance can be found for an arbitrary combination of tones with different frequencies.

  • 331.
    Bodén, Hans
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg. KTH, Skolan för industriell teknik och management (ITM), Centra, Competence Center for Gas Exchange (CCGEx).
    The effect of speed variation on in-duct source data determination2014Inngår i: 21st International Congress on Sound and Vibration 2014, ICSV 2014, 2014, s. 2395-2401Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Experimental acoustic source characterization is used for IC-engines and fluid machines connected to duct or pipe systems. Information about the engine as an acoustic source is needed to calculate insertion loss of mufflers or the level of radiated sound. The source model used in the low frequency plane wave range is often the linear time invariant 1 -port model. The acoustic source data is obtained from experimental tests or from 1 -D CFD codes describing the engine gas exchange process. Multi-load methods and especially the two-load method are most commonly used to extract the source data. The IC-engine is a high level acoustic source and in most cases not completely linear. The real part of the measured source impedance sometimes has negative values which is un-physical. This effect has been attributed to non-linearity and source time variation. Another possible explanation could be speed variation giving measurement errors especially for higher harmonics. In the present paper this effect is studied by re-visiting source data experiments for IC-engine exhausts and comparing the outcome of different methods for extracting the amplitude and phase of the pressure in terms of frequency components or engine orders.

  • 332.
    Bodén, Hans
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Strömningsakustik.
    Two-Port Techniques For Characterisation Of Non-Linear In-Duct Sources2008Inngår i: 15th International Congress on Sound and Vibration (ICSV15), 2008Konferansepaper (Annet vitenskapelig)
    Abstract [en]

    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. Non-linear wave propagation and wave steepening are not taken into account. The paper starts with a review of previous impedance tube measurements made for determining the acoustic impedance of non-linear samples. The effect of using different types of excitation and non-linear harmonic interaction mechanisms are discussed. Experiments were previously made using both pure tone and random excitation and the relevant parameters controlling the non-linearity were discussed. A study of harmonic interaction effects using two-tone excitations was made and later extended to multi-tone excitation for different types of perforates. In the linear case the impedance is independent of the sound field but when the sound pressure level is high the perforate impedance will be dependent on the acoustic particle velocity in the holes. For pure tone excitation it is usually assumed that the impedance will be controlled by the acoustic particle velocity at that frequency, even though the non-linearity will in fact cause energy to be transferred to other frequencies. If the acoustic excitation is random or periodic with multiple harmonics the impedance at a certain frequency may depend on the particle velocity at other frequencies. The results show that the total rms-value of the particle velocity in the holes seems to be the relevant parameter controlling the non-linearity. A study was previously made of using non-linear system identification techniques for this purpose. Multi-port techniques using sinusoidal excitation for better characterization of samples with non-linear properties are developed in the present paper. These new techniques take the non-linear energy transfer into account. 

  • 333.
    Bodén, Hans
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Two-sided multi-port techniques for characterisation of in-duct samples with non-linear acoustic properties2013Inngår i: Acta Acoustica united with Acustica, ISSN 1610-1928, E-ISSN 1861-9959, Vol. 99, nr 3, s. 359-378Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    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 experimental tests show that these new techniques can give results which are useful for understanding non-linear energy transfer to higher harmonics.

  • 334.
    Bodén, Hans
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Strömningsakustik.
    Allam, Sabry
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Holmberg, Andreas
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Åbom, Mats
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Strömningsakustik.
    Experimental Techniques for Aeroacoustics in Low Mach Number Confined Flows: Keynote Paper2011Inngår i: Proceedings of the International Conference on Mechanical Engineering 2011(ICME2011) 18-20 December 2011, Dhaka, Bangladesh, ICME , 2011Konferansepaper (Annet vitenskapelig)
    Abstract [en]

    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.

  • 335.
    Bodén, Hans
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Strömningsakustik.
    Aslan, Johan
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Yousif, Michel
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    A study of annoyance caused by ground based activities at Bromma airport2010Inngår i: 17th International Congress on Sound and Vibration (ICSV17), 2010Konferansepaper (Annet vitenskapelig)
    Abstract [en]

    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.

  • 336.
    Bodén, Hans
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    Cordioli, J. A.
    Spillere, A. M.
    Effect of flow direction on acoustic liner impedance measurement results2016Inngår i: ICSV 2016 - 23rd International Congress on Sound and Vibration: From Ancient to Modern Acoustics, 2016Konferansepaper (Fagfellevurdert)
    Abstract [en]

    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.

  • 337.
    Bodén, Hans
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    Cordioli, J. A.
    Spillere, A. M. N.
    Serrano, P. G.
    Comparison of the effect of flow direction on liner impedance using different measurement methods2017Inngår i: 23rd AIAA/CEAS Aeroacoustics Conference, 2017, American Institute of Aeronautics and Astronautics, 2017Konferansepaper (Fagfellevurdert)
    Abstract [en]

    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.

  • 338.
    Bodén, Hans
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Efraimsson, Gunilla
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Aeroacoustics research in Europe: The CEAS-ASC report on 2012 highlights2013Inngår i: Journal of Sound and Vibration, ISSN 0022-460X, E-ISSN 1095-8568, Vol. 332, nr 25, s. 6617-6636Artikkel, forskningsoversikt (Fagfellevurdert)
    Abstract [en]

    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.

  • 339.
    Bodén, Hans
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Strömningsakustik.
    Eslami, Armin
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Determination of non-linear acoustic properties of perforates using single tone excitation2010Inngår i: 17th International Congress on Sound and Vibration (ICSV17), 2010Konferansepaper (Annet vitenskapelig)
    Abstract [en]

    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.

  • 340.
    Bodén, Hans
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    Fritzell, Julius
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    A study of high level tonal and broadband random excitation for acoustic liners2017Inngår i: 23rd AIAA/CEAS Aeroacoustics Conference, 2017, American Institute of Aeronautics and Astronautics, 2017Konferansepaper (Fagfellevurdert)
    Abstract [en]

    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.

  • 341.
    Bodén, Hans
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Strömningsakustik.
    Guo, Ying
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    Tözün, Hüseyin Bora
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    Experimental investigation of nonlinear acoustic properties for perforates2006Inngår i: Collection of Technical Papers: 12th AIAA/CEAS Aeroacoustics Conference, Cambridge, MA, 2006, Vol. 1, s. 67-74Konferansepaper (Fagfellevurdert)
    Abstract [en]

    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.

  • 342.
    Bodén, Hans
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    Guo, Ying
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    Tözün, Hüseyin Bora
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    Investigation of Nonlinear Acoustic properties for Perforates2006Inngår i: ICSV13-Vienna / [ed] J. Eberhardsteiner, H.A. Mang, H. Waubke, 2006Konferansepaper (Annet vitenskapelig)
    Abstract [en]

    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 has been made of harmonic interaction effects by using multiple pure tone excitation and random noise excitation.

  • 343.
    Bodén, Hans
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    Khodashenas, Niloofar Sayyad
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    Boij, Susann
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    Experimental study of nonlinear acoustic properties of perforates using band-limited random excitation information2018Inngår i: 25th International Congress on Sound and Vibration 2018, ICSV 2018: Hiroshima Calling, International Institute of Acoustics and Vibration, IIAV , 2018, Vol. 3, s. 1818-1825Konferansepaper (Fagfellevurdert)
    Abstract [en]

    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.

  • 344.
    Bodén, Hans
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Strömningsakustik.
    Torregrosa, A.
    Ollivier, F.
    Peat, K.
    Fairbrother, R.
    Henriksson, B.
    Recouvreur, P.
    Poullard, O.
    Glav, Ragnar
    Scania AB, Sweden.
    Lavrentjev, J.
    Noise from turbo-charged diesel engine exhaust systems2005Inngår i: 12th International Congress on Sound and Vibration 2005: ICSV 2005, 2005, s. 2231-2238Konferansepaper (Fagfellevurdert)
    Abstract [en]

    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.

  • 345.
    Bodén, Hans
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    Zhou, L.
    Cordioli, J. A.
    Medeiros, A. A.
    Spillere, A. M. N.
    On the effect of flow direction on impedance eduction results2016Inngår i: 22nd AIAA/CEAS Aeroacoustics Conference, 2016, 2016Konferansepaper (Fagfellevurdert)
    Abstract [en]

    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. © 2016, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.

  • 346.
    Bodén, Hans
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Zhou, Lin
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet. KTH, Skolan för industriell teknik och management (ITM), Centra, Competence Center for Gas Exchange (CCGEx).
    Acoustic Properties of an In-Duct Orifice Subjected to Bias Flow and High Level Acoustic Excitation2012Inngår i: Proceedings of the 10th International conference on Flow-Induced Vibration (& Flow-Induced Noise): FIV2012, Dublin, Ireland, 3-6 July 2012 FLOW-INDUCED VIBRATION, 2012, s. 187-193Konferansepaper (Fagfellevurdert)
    Abstract [en]

    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.

  • 347.
    Bodén, Hans
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Zhou, Lin
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet. KTH, Skolan för industriell teknik och management (ITM), Centra, Competence Center for Gas Exchange (CCGEx).
    An experimental study of the effect of flow and high level acoustic excitation on the acoustic properties of perforates and orifices2013Inngår i: 20th International Congress on Sound and Vibration 2013, ICSV 2013: Volume 3, 2013, International Institute of Acoustics and Vibrations , 2013, s. 2545-2552Konferansepaper (Fagfellevurdert)
    Abstract [en]

    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.

  • 348.
    Bodén, Hans
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    Zhou, Lin
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    Cordioli, J. A.
    Medeiros, A. A.
    Spillere, A. M. N.
    On the effect of flow direction on impedance eduction results2016Inngår i: 22nd AIAA/CEAS Aeroacoustics Conference, 2016, American Institute of Aeronautics and Astronautics Inc, AIAA , 2016Konferansepaper (Fagfellevurdert)
    Abstract [en]

    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.

  • 349. Boelens, O. J.
    et al.
    Badcock, K. J.
    Görtz, Stefan
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Morton, S.
    Fritz, W.
    Karman, S. L., Jr.
    Michal, T.
    Lamar, J. E.
    F-16XL Geometry and Computational Grids Used in Cranked-Arrow Wing Aerodynamics Project International2009Inngår i: Journal of Aircraft, ISSN 0021-8669, E-ISSN 1533-3868, Vol. 46, nr 2, s. 369-376Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The objective of the Cranked-Arrow Wing Aerodynamics Project International was to allow a comprehensive validation of computational fluid dynamics methods against the Cranked-Arrow Wing Aerodynamics Project flight database. A major part of this work involved the generation of high-quality computational grids. Before the grid generation, an airtight geometry of the F-16XL, aircraft was generated by a cooperation of the Cranked-Arrow Wing Aerodynamics Project International partners. Based on this geometry description, both structured and unstructured grids have been generated. The baseline structured (multiblock) grid (and a family of derived grids) has been generated by the National Aerospace Laboratory. Although the algorithms used by the National Aerospace Laboratory had become available just before the Cranked-Arrow Wing Aerodynamics Project International and thus only a limited experience with their application to such a complex configuration had been gained, a grid of good quality was generated well within four weeks. This time compared favorably with that required to produce the unstructured grids in the Cranked-Arrow Wing Aerodynamics Project International. The baseline all-tetrahedral and hybrid unstructured grids have been generated at NASA Langley Research Center and the U.S. Air Force Academy, respectively. To provide more geometrical resolution, trimmed unstructured grids have been generated at the European Aeronautic Defence and Space Company's Military Air Systems, University of Tennessee at Chattanooga SimCenter, Boeing Phantom Works, Royal Institute of Technology, and the Swedish Defence Research Agency. All grids generated within the framework of the Cranked-Arrow Wing Aerodynamics Project International will be discussed in the paper. Both results obtained on the structured grids and the unstructured grids showed a significant improvement in agreement with flight-test data in comparison with those obtained on the structured multiblock grid used during the Cranked-Arrow Wing Aerodynamics Project.

  • 350. Boelens, O. J.
    et al.
    Görtz, Stefan
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Morton, S.
    Fritz, W.
    Lamar, J. E.
    Description of the F-16XL geometry and computational grids used in CAWAPI2007Inngår i: Collection of Technical Papers - 45th AIAA Aerospace Sciences Meeting, 2007, s. 5866-5878Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The objective of the Cranked-Arrow Wing Aerodynamics Project International (CAWAPI) was to allow a comprehensive validation of Computational Fluid Dynamics methods against the CAWAP flight database. A major part of this work involved the generation of high-quality computational grids. Prior to the grid generation an IGES file containing the air tight geometry of the F-16XL aircraft was generated by a cooperation of some of the CAWAPI partners. Based on this geometry description both structured and unstructured grids have been generated. The baseline structured (multi-block) grid (and a family of derived grids) has been generated by the National Aerospace Laboratory NLR. The baseline all-tetrahedral and hybrid unstructured grids were generated at NASA Langley Research Center and the U.S. Air Force Academy, respectively. To provide more geometrical resolution, additional unstructured grids were generated at EADS-MAS, the UTSimCenter, and Boeing Phantom Works. All the grids generated within the framework of CAWAPI will be discussed.

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