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  • 1.
    Backström, Daniel
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Nilsson, Anders
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Flexural vibrations of a three-layer sandwich beam - Using ordinary fourth order beam theory in combination with frequency dependent parameters to predict the flexural dynamics of a sandwich beam2005In: Sandwich Structures7: Advancing with Sandwich Structures and Materials / [ed] Thomsen, OT; Bozhevolnaya, E; Lyckegaard, A, 2005, p. 567-575Conference paper (Refereed)
    Abstract [en]

    The purpose of this work has been to evaluate the possibility of using modified lower order methods - such as the Bernoulli-Euler or Timoshenko beam theories with frequency dependent parameters - to calculate the response of sandwich beams subject to different end conditions. The models have been verified by measurements on a freely suspended asymmetric sandwich beam with aluminium laminates and a plastic foam core, indicating good agreement.

  • 2.
    Backström, Daniel
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL.
    Nilsson, Anders
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL.
    Modelling the flexural vibration of a sandwich beam using modified timoshenko theory2005In: 12th International Congress on Sound and Vibration 2005: ICSV 2005, 2005, p. 4944-4951Conference paper (Refereed)
    Abstract [en]

    The flexural vibration of an asymmetric sandwich beam is modelled using Timoshenko theory with frequency dependent parameters. The advantage of this approach, as compared to using modified Bernoulli-Euler theory, is the independence of the frequency dependent parameters on the boundary conditions of the beam. Using Bernoulli-Euler theory, the apparent bending stiffness would have to depend on the particular end conditions of the beam configuration in order to achieve the best possible accuracy. Using instead Timoshenko theory, with frequency dependent bending stiffness and shear modulus parameters, this problem is avoided. The results are compared to measurements and to the results obtained from a previously derived 6th order sandwich beam theory, which takes into account the effects of pure bending of the entire beam, core shear and its coupling to the bending of the laminates, and rotational inertia. The possibility of implementing the approach in existing Timoshenko beam elements in commercial FEM programs is discussed.

  • 3.
    Backström, Daniel
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL.
    Nilsson, Anders
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL.
    Some properties of the energy flow corresponding to flexural waves in sandwich beam structures2006In: EURONOISE 2006 - The 6th European Conference on Noise Control: Advanced Solutions for Noise Control, 2006, p. 7P-Conference paper (Refereed)
    Abstract [en]

    The energy flow corresponding to the propagation of flexural waves in sandwich beam structures is investigated. A previously derived 6th order theory describing the bending of sandwich beams is utilized and important properties such as group velocity and energy transmission through joints are analyzed and compared to those expected from classical beam theory. The results could be applied in the method of statistical energy analysis (SEA) in order to predict the vibration level of different members of composite structures composing sandwich beam elements.

  • 4.
    Backström, Daniel
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Nilsson, Anders Christian
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Modelling the vibration of sandwich beams using frequency dependent parameters2007In: Journal of Sound and Vibration, ISSN 0022-460X, E-ISSN 1095-8568, Vol. 300, no 3-5, p. 589-611Article in journal (Refereed)
    Abstract [en]

    Various types of sandwich beams with foam or honeycomb cores are currently used in the industry, indicating the need for simple methods describing the dynamics of these complex structures. By implementing frequency-dependent parameters, the vibration of sandwich composite beams can be approximated using simple fourth-order beam theory. A higher-order sandwich beam model is utilized in order to obtain estimates of the frequency-dependent bending stiffness and shear modulus of the equivalent Bernoulli-Euler and Timoshenko models. The resulting predicted eigenfrequencies and transfer accellerance functions are compared to the data obtained from the higher-order model and from measurements.

  • 5. Bonfiglio, P.
    et al.
    Pompoli, F.
    Peplow, Andrew T.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL.
    Nilsson, Anders Christina
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL.
    Spectral element and experimental analysis of lightweight sandwich structures2006In: 13th International Congress on Sound and Vibration 2006, 2006, p. 2240-2247Conference paper (Refereed)
    Abstract [en]

    The dynamic response of the vibrating structures are studied with the standard finite element method against the more computationally efficient spectral finite element method. First a simple beam structure is modelled with the standard method and newly developed spectral elements; which has the advantage that dispersion relations for all beam structures may be developed. Some numerical examples are given to illustrate and validate the developed method and studies of the measured responses of structures that may be used for vehicle panels are compared.

  • 6. Facian, Amparo
    et al.
    Nilsson, Anders
    KTH, Superseded Departments, Vehicle Engineering.
    Feng, Leping
    KTH, Superseded Departments, Vehicle Engineering.
    Nilsson, Eva
    KTH, Superseded Departments, Vehicle Engineering.
    Propagation of structure-borne sound in silencers used in power plants2004In: The 11th International Congress on Sound and Vibration, 2004, p. 1069-1076Conference paper (Refereed)
  • 7.
    Fernàndez, ÈT. I.
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Nilsson, Anders
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL.
    Tyre air cavity influence on tyre-road noise2005Conference paper (Refereed)
    Abstract [en]

    Road traffic noise is nowadays a major environmental pollutant. In the near future traffic noise will increase even further, especially due to the expected increase of heavy traffic. Noise radiated from tyres of the vehicles is a dominating source. The acoustic field inside the tyre has previously been modelled. The first acoustic mode for a standard stationary passenger car tyre is at 225 Hz. The tyre becomes stiffer at these tyre air cavity resonances and radiates comparatively high tonal noise to the exterior at this frequency range. In order to reduce this tonal noise at low frequencies a set of new modified wheels are developed implementing some sound absorbing material inside the tyre. Preliminary sound intensity measurements have been carried out on a static tyre. The influence of the tyre air cavity resonances on the radiated noise is reduced adding sound absorbing material inside the tyre.

  • 8.
    Liu, Bilong
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Feng, Leping
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Nilsson, Anders
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Influence of baffle size and curvature on sound radiated by vibrating panels2004In: Eleventh International Congress on Sound and Vibration, 2004Conference paper (Other academic)
  • 9.
    Liu, Bilong
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL.
    Feng, Leping
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL.
    Nilsson, Anders
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL.
    Influence of overpressure on sound transmission through curved panels2007In: Journal of Sound and Vibration, ISSN 0022-460X, E-ISSN 1095-8568, Journal of sound and vibration, Vol. 302, no 4-5, p. 760-776Article in journal (Refereed)
    Abstract [en]

    A great deal of recent research related to the aeronautic industry has been devoted to the theoretical study of sound transmission through fuselage structures. However, the literature records few test data with reference to the influence of overpressure on sound transmission. In this article, the airborne sound transmission through curved panels under the condition of overpressure at the concave side has been investigated experimentally and it is shown that experimental results agree well with a theoretical prediction due to an infinite cylindrical shell model at relatively high frequencies. Discrepancies, which occur at lower frequencies, can be explained, inter alia, by the influence of the finite size and attached stiffeners of the panel.At frequencies higher than the corresponding ring frequency for the curved panel, both experimental and theoretical predictions reveal that the overpressure at the concave side tends to reduce the sound transmission loss at the rate of about 0.5dB/10000Pa. While at lower frequencies, say well below the ring frequency, the overpressure may increase or reduce sound transmission loss of a finite panel depending on the shift of resonant frequencies resulting from the overpressure.

  • 10.
    Liu, Bilong
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Structural and vibroacoustics.
    Feng, Leping
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Structural and vibroacoustics.
    Nilsson, Anders
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Structural and vibroacoustics.
    Influence of pressurization on sound insulation of curved airplane panels2005In: 12th International Congress on Sound and Vibration 2005: ICSV 2005, 2005, p. 4843-4850Conference paper (Refereed)
    Abstract [en]

    he purpose of this paper is to investigate the pressurization effects on sound transmission through airplane panels. The airborne sound transmission through airplane panels under the condition of overpressure at one side has been investigated by measurement. The test results agree well with the theoretic prediction of infinite cylindrical shell model at high frequencies, but have considerable discrepancies at low frequencies, which, however, are ready to be explained by the influence of finiteness and stiffeners of the panel. When the frequency is higher than the ring frequency of curved panel, both test and theoretic prediction reveal that the overpressure under laboratory conditions tends to reduce the sound transmission loss at the rate of about 0.5dB/10000 Pa. while at low frequencies, say below around the ring frequency, the overpressure may increase the sound transmission loss of ring-stiffened panel, the reason of this behavior is resulted from the shift of the resonant frequencies led by the increased in-plane tension.

  • 11.
    Liu, Bilong
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL.
    Feng, Leping
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Structural and vibroacoustics.
    Nilsson, Anders
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL.
    Sound transmission through curved aircraft panels with stringers and ring frames attachments2007In: Journal of Sound and Vibration, ISSN 0022-460X, E-ISSN 1095-8568, Journal of sound and vibration, Vol. 300, no 3-5, p. 949-973Article in journal (Refereed)
    Abstract [en]

    A numerical approach based on a receptance method has been developed to evaluate the airborne sound insulation of aircraft panels with stringer and ring frame attachments. Theoretical predictions have been compared with laboratory measurements conducted on both model structures and aircraft panels. Certain parameters were varied in this study to gauge stiffener effects on sound transmission through the panel. For large curved aircraft panels studied here, it was found that the ring frames have little influence on sound transmission loss in the frequency range of interest. However, the stringers may have considerable influence on the sound transmission loss. The stringer improves the sound transmission loss for a curved panel in the vicinity of the ring frequency, but may result in a potential deterioration above this frequency. In addition it was found that the sound transmission loss for the composite skin attached with composite stringers was lower than that of the metallic panel attached with metallic stringers. The results suggest that acoustical optimization design for the stringers is necessary to achieve improved airborne sound insulation for aircraft panels

  • 12.
    Nilsson, Anders
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL.
    Response of hull plates due to turbulent boundary layers2005In: International Congress on Noise Control Engineering 2005: INTERNOISE 2005, 2005, p. 3844-3853Conference paper (Refereed)
    Abstract [en]

    A model has been developed for the prediction of velocity levels of ships hull plates which are excited by turbulent boundary layers. The model is based on the theory developed by Corcos. It is found that the velocity of the hull plates strongly depends on the speed of the ship. The acoustic power induced in the hull can be reduced if the thickness of the hull plates is increased. Other parameters like frame distance and height of hull plate are of secondary importance. The effect of turbulent boundary layer excitation is most efficiently reduced by changing the hull shape or by changing the transmission path from the hull plates to the accommodation decks.

  • 13.
    Nilsson, Anders
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL.
    Birgersson, Fredrik
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL.
    Response of hull plates due to turbulent boundary layers2007In: 14th International Congress on Sound and Vibration 2007, ICSV 2007, 2007, p. 2154-2161Conference paper (Refereed)
    Abstract [en]

    A model has been developed for the prediction of velocity levels of ships hull plates which are excited by turbulent boundary layers. The model is based on the theory developed by Corcos. It is found that the velocity of the hull plates strongly depends on the speed of the ship. The acoustic power induced in the hull can be reduced if the thickness of the hull plates is increased. Other parameters like frame distance and height of hull plate are of secondary importance. The effect of turbulent boundary layer excitation is most efficiently reduced by changing the hull shape or by changing the transmission path from the hull plates to the accommodation decks.

  • 14.
    Nilsson, Anders Christian
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL.
    Backström, Daniel
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL.
    Liu, B.
    Some sea parameters for sandwich, composite structures2010In: 17th International Congress on Sound and Vibration 2010, ICSV 2010: Volume 1, 2010, p. 133-140Conference paper (Refereed)
    Abstract [en]

    Some basic parameters used in a traditional SEA calculation are coupling loss factors, modal densities, mobility and energy flow. For calculating the coupling loss factor the group velocity as well as the transmission coefficient for the energy flow from one structure to another must be known. These parameters are derived and discussed for some simple sandwich structures and are compared to the corresponding parameters for homogeneous structure.

  • 15. Piana, E. A.
    et al.
    Nilsson, Anders Christian
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL.
    Prediction of the sound transmission loss of sandwich structures based on a simple test procedure2010In: 17th International Congress on Sound and Vibration 2010, ICSV 2010, 2010, p. 109-116Conference paper (Refereed)
    Abstract [en]

    Sandwich and honeycomb materials are increasingly used by the vehicle and building industries. Consequently, the prediction of the acoustic properties and in particular the sound transmission loss of sandwich structures is of importance. The dynamic and acoustic properties of a composite sandwich beam or plate depend on the geometry of the structure as well as on the material properties of core and laminates. The method of bonding laminates to core can also influence the dynamic properties of sandwich constructions. For example a bonding substance can increase the spacing between the laminates. In general, the construction of a sandwich plate is often symmetric with respect to the centerline. The thickness of the lightweight core is typically of the order 5 to 75 mm whereas the thickness of the laminates could vary between 0.5 and 8 mm. The E-modulus for a laminate is typically high and much higher than the corresponding modulus for the core. Some of the basic parameters of a sandwich structure can be determined by means of some simple tests on a beam element of the structure. For the test the beam is suspended by strings to simulate free-free boundary conditions. By exciting the beam by an impedance hammer the first ten or more natural frequencies of the beam can be determined. Based on these measurements of natural frequencies and the weight and dimensions of the beam, the static bending stiffness, shear modulus of the core and bending stiffness of the laminates are determined. The data is used to calculate the sound transmission loss of a plate structure being constructed in the same way as the beam. The model can also be used for parameter studies of the influence on the sound transmission loss due to changes of dimensions of laminates, core etc.

  • 16. Smeds, K.
    et al.
    Wolters, F.
    Nilsson, Anders Christian
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL. Widex A/S ORCA Europe, Stockholm, Sweden .
    Båsjö, S.
    Hertzman, S.
    Leijon, Arne
    KTH, School of Electrical Engineering (EES), Communication Theory.
    Objective measures to quantify the perceptual effects of noise reduction in hearing aids2011In: Proceedings of the AES International Conference, 2011, p. 101-108Conference paper (Refereed)
    Abstract [en]

    Twenty listeners with hearing impairment evaluated three noise-reduction algorithms using paired comparisons of speech clarity, noise loudness, and preference. The subjective test produces results in terms of physical signal-to-noise ratios that correspond to equal subjective performance with and without the noise-reduction algorithms. This facilitates a direct test of how well a number of objective performance measures correspond with the subjective test results.

  • 17. Van Der Wal, H. M. M.
    et al.
    Nilsson, Anders Christian
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Sound-transmission measurements on composite and metal fuselage panels for different boundary conditions2005In: Collect. Techn. Pap. Aeroacoustics Conf., 2005, p. 2876-2885Conference paper (Refereed)
    Abstract [en]

    In the framework of the EU-project FACE, sound transmission measurements have been performed by NLR and KTH on a curved and stiffened composite fuselage panel and an aluminium panel with the same structure. Both panels consist of a part with axial stiffeners and a part, suitable for mounting windows, without these stiffeners. The main goals of the measurements are to provide experimental data for validation of numerical models, and experimental determination of the effect of a.o. panel material on the sound transmission. At NLR the panels have been suspended on springs, implementing well defined (free-free) boundary conditions, suppressing flanking noise adequately by a special designed panel support structure. At KTH, the panels have been clamped. In spite of the different boundary conditions, the TL data measured by KTH and NLR TL data show a good agreement for 200 Hz and higher frequencies. Due to the curvature and stiffening, the transmission loss of the panels is much lower than the mass law prediction. For frequencies above about 600 Hz, the transmission loss of the composite panel is significantly lower than that of the metal panel, despite its 6% larger mass. For the frequency band of 250 - 2000 Hz, the transmission loss of the window area of the composite panel is much (up to 5 dB) larger than for the stringer area. It seems that the stringers of the composite panel have some bad influence on the sound transmission loss and should be further investigated.

1 - 17 of 17
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