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  • 151.
    Åbom, Mats
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Acoustic multi-ports with application to duct acoustics2010In: 17th International Congress on Sound and Vibration 2010, ICSV 2010: Volume 5, 2010, p. 3930-3942Conference paper (Refereed)
    Abstract [en]

    In this paper the development of multi-port models to describe linear acoustic problems in ducts with flow is presented. From an engineering point of view this field covers many important applications ranging from ventilation ducts in vehicles or buildings to intake/exhaust ducts on ICengines and power plants. Historically the use of multi-port models for ducts started in the 1920's, when the four-pole (2-port) filter models used by electrical engineers were applied to analyse transmission of low frequency 1D (plane) waves with application to automotive mufflers. An important step was then taken in 1971, when Cremer presented the idea that such "black box" models can be applied to describe aerodynamically generated sound in ducts. This implies that any fluid machine or unsteady flow process can be modelled as a "black box", with a "passive part" that describes how incident waves are scattered and an "active part" that describes the sound generation. The active part is normally assumed independent of the acoustic state, which makes the "black box" or acoustic multi-port model consistent with Lighthills acoustic analogy.

  • 152.
    Åbom, Mats
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL.
    Method for reducing noise of a high power combustion engine2003Patent (Other (popular science, discussion, etc.))
  • 153. Åbom, Mats
    New measurement and control approach for refiners and beaters2001Patent (Other (popular science, discussion, etc.))
  • 154. Åbom, Mats
    Sensor arrays in acoustic spectroscopy2001Patent (Other (popular science, discussion, etc.))
  • 155.
    Åbom, Mats
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL.
    Allam, Sabry
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Dissipative silencers based on micro-perforated plates2013In: SAE Technical Papers, 2013, Vol. 6Conference paper (Refereed)
    Abstract [en]

    Micro-perforated plates (MPP:s) can be defined as a perforated plate where the hole impedance is dominated by viscous losses. This will always be true for sufficiently low frequencies or small holes. In addition for a standard MPP the perforation ratio is chosen so that the normalized acoustic resistance is between 1-2, which yields optimum damping for incident plane waves. Historically MPP:s have been used as panel absorbers to reduce reflections in rooms and enclosures. More recently the potential for machinery and vehicle applications has come into focus, e.g., dissipative exhaust silencers. Some advantages offered by a MPP solution, when compared to traditional dissipative silencers, are that it can reduce the weight and the problem with fibre breakout. In this paper the work on cylindrical MPP dissipative silencers at KTH is summarized. One important question being how an optimum damping is achieved, for a certain frequency band and for a given volume (length & area ratio) of the silencer.

  • 156.
    Åbom, Mats
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL.
    Allam, Sabry
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL. Industrial Education College, Cairo, Egypt .
    Boij, Susann
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL.
    Aero-acoustics of flow duct singularities at low mach numbers2006In: Collection of Technical Papers - 12th AIAA/CEAS Aeroacoustics Conference, 2006, p. 3708-3717Conference paper (Refereed)
    Abstract [en]

    This paper describes the application of an acoustic 2-port model to describe flow generated noise in ducts. An experimental procedure that enables determination of both the passive (the scattering matrix) as well as the active (source) 2-port data is described. The method is applied to investigate the aero-acoustics of an orifice plate in a duct. The passive data is compared with a simple quasi-stationary model and the active part is analyzed using a scaling law procedure, based on the assumption of a compact dipole source.

  • 157.
    Åbom, Mats
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering. KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx).
    Kabral, Raimo
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering. KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx).
    Turbocharger noise - Generation and control2014In: SAE technical paper series, ISSN 0148-7191, Vol. 2014Article in journal (Refereed)
    Abstract [en]

    An important part of modern engine design is the concept of downsizing where a key role is carried by the charging devices. These devices are effective aero-acoustic sources forming a coupled acoustic system with the connected flow-channel components. At KTH a unique test facility for determination of the complete acoustic Two-port for turbochargers has been built. Using this facility both the passive (transmission & reflection) as well as the active (sound generation) data for turbochargers can be measured at a given operating point. One important issue which has been studied in detail using this data is the coupling between the aerodynamic and acoustic fields close to "surge". In addition, the control of compressor noise is an increasing concern. For instance heavy duty diesels and light duty engines with screw (roots) compressors can create strong charging harmonics well below 10 kHz. The standard noise control solution for these cases is to build a series of resonators. As an alternative KTH has developed a novel compact and very efficient silencer in the form of an expansion chamber with locally reacting cavities. The cavities consists of a micro-perforated plate in front of a closed air volume. The micro-perforate and volume are then chosen so that the cavity impedance equals the so called Cremer impedance at a target frequency. This ensures a very high damping at one frequency (hundreds of dB/m) and using this concept compact silencers with a damping higher than 30 dB in octave around the target frequency can be designed.

  • 158.
    Åbom, Mats
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Karlsson, Mikael
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Can acoustic multi-port models be used to predict whistling2010In: 16th AIAA/CEAS Aeroacoustics Conference (31st AIAA Aeroacoustics Conference), 2010, p. 2010-4009-Conference paper (Refereed)
    Abstract [en]

    In duct aeroacoustic problems can be described using so called acoustic multi-port models. Such models represent a linear and time-invariant aeroacoustic model, which split the problem in a passive part, a scattering matrix in the frequency domain, describing the reflection and transmission and an active part describing the source strength. In accordance with Lighthill one normally assumes in this kind of model that the source part is uncoupled from the acoustic field. However, this assumption can be relaxed and it is fully possible to assume that the source strength can be affected by incident sound waves via a linear and time-invariant mechanism. The most general frequency domain model for this is a matrix which formally can be added to the scattering matrix describing the passive part. This leads to a model that has the same structure as the traditional multi-port model, but where the scattering matrix also contains information about fluid-acoustic interaction effects which is the origin for creating fluid driven feedback loops or whistles. The implication of these ideas is that multi-port models can be used to analyze amplification of sound and whistling.

  • 159.
    Åbom, Mats
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Karlsson, Mikael
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Kierkegaard, Axel
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    On the use of linear aero-acoustic methods to predict whistling2009In: 16th International Congress on Sound and Vibration 2009, ICSV 2009, 2009, p. 2406-2413Conference paper (Refereed)
    Abstract [en]

    In duct aero-acoustic problems can be described using so called acoustic multi-port models. Such models represent a linear and time-invariant aero-acoustic model, which split the problem in a passive part, a scattering matrix in the frequency domain, describing the reflection and transmission and an active part describing the source strength. In accordance with Lighthill one normally assumes in this type of model that the source part is uncoupled from the acoustic field. However, this assumption can be relaxed and it is fully possible to assume that the source strength can be affected by incident sound waves via a linear and time-invariant mechanism. The most general frequency domain model for this is a matrix which formally can be added to the scattering matrix describing the passive part. This leads to a model that has the same structure as the traditional multi-port model, but where the scattering matrix also contains information about fluid-acoustic interaction effects which is the origin for creating fluid driven feedback loops or whistles.

1234 151 - 159 of 159
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