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  • 1. Andro, B.
    et al.
    Chaigne, S.
    Schmitt, T.
    Shah, Asif L.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Vibration monitoring. KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL.
    Simplified integral energy method: Application to pass by noise2006In: Int. Congr. Sound Vib., ICSV, 2006, p. 2919-2926Conference paper (Refereed)
    Abstract [en]

    The pass-by noise measurements defined in a standard procedure constitute a legal test for every new vehicle. Nowadays, the improvements of the engineering process allow automotive manufacturers to reduce the vehicle development cycles. Consequently, the acoustic optimization of the vehicle applied to reduction of the exterior noise needs to be considered as soon as possible to avoid repeated road tests depending strongly on the environmental conditions. At the early stage of the development process, Renault would like therefore to use an accurate tool which predicts the engine compartment contribution to pass-by noise. This model will give indications to answer technical issues like: The influence of acoustical materials or height of the vehicle on pass-by noise in the high frequency range. In medium and high frequency domains, classical numerical methods such as the Finite Element Method (FEM) or the Boundary Element Method (BEM) are not well suited to predict the engine contribution because of the prohibitive computation time and memory occupation. Some energy methods such as statistical energy Analysis (SEA) will only give global values in each substructure and are not suited to outside airborne noise propagation. In this paper, a simplified integral energy method is developed to predict the noise induced by the engine sources during the pass-by noise test in the medium and high frequency range. We will consider a local energy balance and solve an integral equation to predict the noise emitted by the engine in a short computation time. One of the main contributions of this paper is the calculation of the visibilities between elements to take into account the presence of the engine. Standard pass-by noise measurements done on a test track are compared with those obtained by the simplified energy method.

  • 2.
    Bodén, Hans
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Vibration monitoring.
    Non-linear system identification techniques for determination of the acoustic properties of perforates2015In: 21st AIAA/CEAS Aeroacoustics Conference, American Institute of Aeronautics and Astronautics, 2015Conference paper (Refereed)
    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.

  • 3. Heo, Yong-Ho
    et al.
    Ih, Jeong-Guon
    Bodén, Hans
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Vibration monitoring.
    In-duct identification of a rotating sound source with high spatial resolution2015In: Journal of Sound and Vibration, ISSN 0022-460X, E-ISSN 1095-8568, Vol. 357, p. 51-73Article in journal (Refereed)
    Abstract [en]

    To understand and reduce the flow noise generation from in-duct fluid machines, it is necessary to identify the acoustic source characteristics precisely. In this work, a source identification technique, which can identify the strengths and positions of the major sound radiators in the source plane, is studied for an in-duct rotating source. A linear acoustic theory including the effects of evanescent modes and source rotation is formulated based on the modal summation method, which is the underlying theory for the inverse source reconstruction. A validation experiment is conducted on a duct system excited by a loudspeaker in static and rotating conditions, with two different speeds, in the absence of flow. Due to the source rotation, the measured pressure spectra reveal the Doppler effect, and the amount of frequency shift corresponds to the multiplication of the circumferential mode order and the rotation speed. Amplitudes of participating modes are estimated at the shifted frequencies in the stationary reference frame, and the modal amplitude set including the effect of source rotation is collected to investigate the source behavior in the rotating reference frame. By using the estimated modal amplitudes, the near-field pressure is re-calculated and compared with the measured pressure. The obtained maximum relative error is about -25 and -10 dB for rotation speeds at 300 and 600 rev/mm, respectively. The spatial distribution of acoustic source parameters is restored from the estimated modal amplitude set. The result clearly shows that the position and magnitude of the main sound source can be identified with high spatial resolution in the rotating reference frame.

  • 4.
    Kabral, Raimo
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Du, Lin
    Åbom, Mats
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Vibration monitoring.
    Optimum Sound Attenuation in Flow Ducts Based on the "Exact" Cremer Impedance2016In: Acta Acoustica united with Acustica, ISSN 1610-1928, E-ISSN 1861-9959, Vol. 102, no 5, p. 851-860Article in journal (Refereed)
    Abstract [en]

    The Cremer impedance (Acustica 3, 1953) [1] is the locally reacting boundary condition that maximizes the attenuation of a certain mode in a uniform wave guide taken as the lowest order mode or "plane" wave. This paper presents the analysis of the "exact" Cremer impedance model, i.e., the high frequency asymptotic results proposed by Tester for uniform mean flow (JSV 28(2), 1973) [2] are extended to lower frequencies. It is shown that significantly larger attenuation per unit length can be obtained using the exact instead of the asymptotic solution. However, for sufficiently low frequencies the "exact" Cremer solution and optimum attenuation is requiring a wall impedance with a negative real part, i.e. an active boundary. In addition, the effect of a finite length on the resulting attenuation is studied using a finite element method for solving the convected wave equation. Finally, it is demonstrated how a silencer can be built that realize the optimum Cremer impedance at a given frequency by using a micro-perforated panel and locally reacting cavities. The performance of the optimized silencer is determined experimentally and the results are compared to the prediction of the finite element model.

  • 5.
    Rumpler, Romain
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL. Creo Dynamics AB, Sweden.
    Göransson, Peter
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Vibration monitoring.
    A fast frequency sweep approach with a priori choice of padé approximants and control of their interval of convergence2015In: COUPLED PROBLEMS 2015: Proceedings of the 6th International Conference on Coupled Problems in Science and Engineering, CIMNE , 2015, p. 881-892Conference paper (Refereed)
    Abstract [en]

    In this work, a solution strategy based on the use of Padé approximants is investigated for efficient solution of parametric finite element problems such as, for example, frequency sweep analyses. An improvement to the Padé-based expansion of the solution vector components is proposed, suggesting the advantageous a priori estimate of the poles of the solution. This allows for the intervals of approximation to be chosen a priori in connection with the Padé approximants to be used. The choice of these approximants is supported by the Montessus de Ballore theorem, proving the convergence of a series of approximants with fixed denominator degrees. An acoustic case study is presented in order to illustrate the potential of the approach proposed by the authors.

  • 6.
    Rynell, Anders
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering. KTH, School of Engineering Sciences (SCI), Centres, VinnExcellence Center for ECO2 Vehicle design. Scania, Sweden.
    Efraimsson, Gunilla
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering. KTH, School of Engineering Sciences (SCI), Centres, VinnExcellence Center for ECO2 Vehicle design.
    Chevalier, M.
    Scania AB, Sweden.
    Åbom, Mats
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Vibration monitoring.
    Acoustic characteristics of a heavy duty vehicle cooling module2016In: Applied Acoustics, ISSN 0003-682X, E-ISSN 1872-910X, Vol. 111, p. 67-76Article in journal (Refereed)
    Abstract [en]

    Studies dedicated to the determination of acoustic characteristics of an automotive cooling package are presented. A shrouded subsonic axial fan is mounted in a wall separating an anechoic- and a reverberation room. This enables a unique separation of the up- and downstream sound fields. Microphone measurements were acquired of the radiated sound as a function of rotational speed, fan type and components included in the cooling module. The aim of the present work is to investigate the effect of a closely mounted radiator upstream of the impeller on the SPL spectral distribution. Upon examination of the SPL spectral shape, features linked specifically to the source and system are revealed. The properties of a reverberant sound field combined with the method of spectral decomposition permit an estimation of the source spectral distribution and the acoustic transfer response, respectively. Additionally, purely intrinsic acoustic properties of the radiator are scrutinized by standardized ISO methods. A new methodology comprising a dipole sound source is adopted to circumvent limitation of transmission loss measurement in the low frequency range. The sound attenuation caused by the radiator alone was found to be negligible.

  • 7.
    Song, Yubao
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Vibration monitoring. National University of Defense Technology, China.
    Feng, Leping
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Vibration monitoring.
    Wen, J.
    Yu, D.
    Wen, X.
    Reduction of the sound transmission of a periodic sandwich plate using the stop band concept2015In: Composite structures, ISSN 0263-8223, E-ISSN 1879-1085, Vol. 128, p. 428-436Article in journal (Refereed)
    Abstract [en]

    The sound transmission of a sandwich plate and its reduction using the stop band concept are investigated in this paper. A periodic sandwich plate consisting of a host plate and the attached structures is designed. The dispersion relation and the stop band of the periodic sandwich plate are studied first. The sound transmission of the periodic and bare sandwich plates is analysed and compared. The reduction from the stop band design (i.e., periodically adding stepped resonators) on the sound transmission of the sandwich plates is studied. The reasons for this reduction are analysed. In addition, the properties of the sandwich plate with different boundary conditions are also briefly studied. The numerical results indicate that the sound transmission is significantly reduced over the stop band of the periodic sandwich plate. The improvement can also exist in the frequency range outside the stop band.

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