| 1. |
- Alberdi-Muniain, Ane, et al.
(author)
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Direct energy flow measurement in magneto-sensitive vibration isolator systems
- 2012
-
In: Journal of Sound and Vibration. - : Elsevier. - 0022-460X .- 1095-8568. ; 331:9, s. 1994-2006
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Journal article (peer-reviewed)abstract
- The effectiveness of highly nonlinear, frequency, amplitude and magnetic field dependent magneto-sensitive natural rubber components applied in a vibration isolation system is experimentally investigated by measuring the energy flow into the foundation. The energy flow, including both force and velocity of the foundation, is a suitable measure of the effectiveness of a real vibration isolation system where the foundation is not perfectly rigid. The vibration isolation system in this study consists of a solid aluminium mass supported on four magneto-sensitive rubber components and is excited by an electro-dynamic shaker while applying various excitation signals, amplitudes and positions in the frequency range of 20-200 Hz and using magneto-sensitive components at zero-field and at magnetic saturation. The energy flow through the magneto-sensitive rubber isolators is directly measured by inserting a force transducer below each isolator and an accelerometer on the foundation close to each isolator. This investigation provides novel practical insights into the potential of using magneto-sensitive material isolators in noise and vibration control, including their advantages compared to traditional vibration isolators. Finally, nonlinear features of magneto-sensitive components are experimentally verified.
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| 2. |
- Berggren, Eric, et al.
(author)
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Identification of Substructure Properties of Railway Tracks by Dynamic Stiffness Measurements and Simulations
- 2010
-
In: Journal of Sound and Vibration. - : Elsevier BV. - 0022-460X .- 1095-8568. ; 329:19, s. 3999-4016
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Journal article (peer-reviewed)abstract
- A new vehicle has been developed to measure dynamic vertical track stiffness while in motion. This technique allows the resonance behaviour of the track below 50 Hz to be measured. Soft soils like clay and peat are the main causes of resonance below 20 Hz. By means of simulation studies with the software VibTrain, soft soil resonance behaviour may be characterized using a few key parameters originating from track stiffness measurements, such as the minimum phase delay and corresponding frequency of the receptance transfer function. Statistical models are built to relate these key parameters with substructure properties, such as embankment thickness, shear wave velocity and thickness of the soft soil layer using pattern recognition methods. Two case studies are used to show the methodology, and the results are verified using Ground Penetration Radar (GPR) measurements and borehole investigations. Models are also developed from the statistical relationship between GPR-data and stiffness measurements. It is shown that embankment thickness is the easiest quantity to estimate, but indicative results are also presented for the other quantities (shear wave velocity and thickness of soil layer).
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| 3. |
- Besselink, Bart, et al.
(author)
-
A comparison of model reduction techniques from structural dynamics, numerical mathematics and systems and control
- 2013
-
In: Journal of Sound and Vibration. - : Elsevier BV. - 0022-460X .- 1095-8568. ; 332:19, s. 4403-4422
-
Research review (peer-reviewed)abstract
- In this paper, popular model reduction techniques from the fields of structural dynamics, numerical mathematics and systems and control are reviewed and compared. The motivation for such a comparison stems from the fact that the model reduction techniques in these fields have been developed fairly independently. In addition, the insight obtained by the comparison allows for making a motivated choice for a particular model reduction technique, on the basis of the desired objectives and properties of the model reduction problem. In particular, a detailed review is given on mode displacement techniques, moment matching methods and balanced truncation, whereas important extensions are outlined briefly. In addition, a qualitative comparison of these methods is presented, hereby focusing both on theoretical and computational aspects. Finally, the differences are illustrated on a quantitative level by means of application of the model reduction techniques to a common example.
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| 4. |
- Blom, Peter, et al.
(author)
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A non-linear constitutive audio frequency magneto-sensitive rubber model including amplitude, frequency and magnetic field dependence.
- 2011
-
In: Journal of Sound and Vibration. - : Elsevier. - 0022-460X .- 1095-8568. ; 330:5, s. 947-954
-
Journal article (peer-reviewed)abstract
- 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.
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| 5. |
- Bodén, Hans, et al.
(author)
-
Aeroacoustics research in Europe : The CEAS-ASC report on 2012 highlights
- 2013
-
In: Journal of Sound and Vibration. - : Elsevier BV. - 0022-460X .- 1095-8568. ; 332:25, s. 6617-6636
-
Research review (peer-reviewed)abstract
- The Council of European Aerospace Societies (CEAS) Aeroacoustics Specialists Committee (ASC) supports and promotes the interests of the scientific and industrial aeroacoustics community on an European scale and European aeronautics activities internationally. In this context, "aeroacoustics" encompasses all aerospace acoustics and related areas. Each year the committee highlights some of the research and development projects in Europe. This paper is a report on highlights of aeroacoustics research in Europe in 2012, compiled from information provided to the ASC of the CEAS. During 2012, a number of research programmes involving aeroacoustics were funded by the European Commission. Some of the highlights from these programmes are summarized in this paper, as well as highlights from other programmes funded by national programmes or by industry. Enquiries concerning all contributions should be addressed to the authors who are given at the end of each subsection.
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| 6. |
- Bodén, Hans
(author)
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One-sided multi-port techniques for characterisation of in-duct samples with nonlinear acoustic properties
- 2012
-
In: Journal of Sound and Vibration. - : Elsevier BV. - 0022-460X .- 1095-8568. ; 331:13, s. 3050-3067
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Journal article (peer-reviewed)abstract
- Single sided multi-port system identification techniques, using sinusoidal excitation, for studying nonlinear energy transfer to higher harmonics for samples only accessible from one side such as perforated liners used as wall treatment in aircraft engine ducts are presented. The starting point is the so called polyharmonic distortion theory used for studying microwave systems. Models of different level of complexity are developed and the system identification results are compared. Experimental results, including error analysis, for a perforate sample are presented. The use of these techniques for analysing nonlinear energy transfer to higher harmonics and to improve the understanding of the physical phenomena involved are illustrated.
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| 7. |
- Cameron, Christopher J., et al.
(author)
-
On the balancing of structural and acoustic performance of a sandwich panel based on topology, property, and size optimization
- 2014
-
In: Journal of Sound and Vibration. - : Elsevier BV. - 0022-460X .- 1095-8568. ; 333:13, s. 2677-2698
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Journal article (peer-reviewed)abstract
- Balancing structural and acoustic performance of a multi-layered sandwich panel is a formidable undertaking. Frequently the gains achieved in terms of reduced weight, still meeting the structural design requirements, are lost by the changes necessary to regain acceptable acoustic performance. To alleviate this, a design method for a multifunctional load bearing vehicle body panel is proposed which attempts to achieve a balance between structural and acoustic performance. The approach is based on numerical modelling of the structural and acoustic behaviour in a combined topology, size, and property optimization in order to achieve a three dimensional optimal distribution of structural and acoustic foam materials within the bounding surfaces of a sandwich panel. In particular the effects of the coupling between one of the bounding surface face sheets and acoustic foam are examined for its impact on both the structural and acoustic overall performance of the panel. The results suggest a potential in introducing an air gap between the acoustic foam parts and one of the face sheets, provided that the structural design constraints are met without prejudicing the layout of the different foam types.
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| 8. |
- Cao, Zhigang, 1983, et al.
(author)
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Dynamic response of a poroelastic half-space to accelerating or decelerating trains
- 2013
-
In: Journal of Sound and Vibration. - : Elsevier BV. - 1095-8568 .- 0022-460X. ; 332:11, s. 2777-2794
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Journal article (peer-reviewed)abstract
- The dynamic response of a fully saturated poroelastic half-space due to accelerating or decelerating trains is investigated by a semi-analytical method. The ground is modeled as a saturated poroelastic half-space and Blot's theory is applied to characterize the soil medium, taking the coupling effects between the soil skeleton and the pore fluid into account. A detailed track system is considered incorporating rails, sleepers and embankment, which are modeled as Euler-Bernoulli beams, an anisotropic Kirchhoff plate, and an elastic layer, respectively. The acceleration or deceleration of the train is simulated by properly choosing the time history of the train speed using Fourier transforms combined with Fresnel integrals in the transformed domain. The time domain results are obtained by the fast Fourier transform (FFT). It is found that the deceleration of moving trains can cause a significant increase to the ground vibrations as well as the excess pore water pressure responses at the train speed 200 km/h. Furthermore, the single-phase elastic soil model would underestimate the vertical displacement responses caused by both the accelerating and decelerating trains at the speed 200 km/h.
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| 9. |
- Cao, Zhigang, 1983, et al.
(author)
-
Semi-analytical analysis of the isolation to moving-load induced ground vibrations by trenches on a poroelastic half-space
- 2012
-
In: Journal of Sound and Vibration. - : Elsevier BV. - 1095-8568 .- 0022-460X. ; 331:4, s. 947-961
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Journal article (peer-reviewed)abstract
- A semi-analytical model is proposed to investigate the screening efficiency of trenches to moving-load induced ground vibrations. The ground is modeled as a fully saturated poroelastic half-space governed by Biot's dynamic poroelastic theory. The trenches are obtained by placing three rectangular elastic layers with appropriate width upon the poroelastic half-space. By Helmholtz decomposition, the displacement fields of the elastic layers are decomposed into three scalar potentials. Analytical solutions are obtained based on Fourier transform and Fourier series in the transformed domain. The time-domain results are obtained by the fast Fourier transform (FFT). The different performances of trenches on a saturated poroelastic half-space and a single-phase elastic half-space to the moving load-induced ground vibration are identified. It is found that the discrepancy of the screening efficiencies between the two models becomes significant when the load speed approaches the Rayleigh wave speed of the ground surface. Also, some parametric studies for the screening efficiency of the trench on the poroelastic half-space are presented.
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| 10. |
- Dovstam, Krister, et al.
(author)
-
On linear modeling of interface damping in vibrating structures
- 2012
-
In: Journal of Sound and Vibration. - : Elsevier BV. - 0022-460X .- 1095-8568. ; 331:19, s. 4299-4312
-
Journal article (peer-reviewed)abstract
- Dissipation of mechanical vibration energy at contact interfaces in a structure, commonly referred to as interface damping, is an important source of vibration damping in built-up structures and its modeling is the focus of the present study. The approach taken uses interface forces which are linearly dependent on the relative vibration displacements at the contact interfaces. The main objective is to demonstrate a straightforward technique for simulation of interface damping in built-up structures using FE modeling and simple, distributed, damping forces localized to interfaces where the damping occurs. As an illustration of the resulting damping the dissipated power is used for evaluation purposes. This is calculated from surface integrals over the contact interfaces and allows for explicit assessment of the effect of simulated interface forces for different cases and frequencies. The resulting loss factor at resonance is explicitly evaluated and, using linear simulations, it is demonstrated that high damping levels may arise even though the displacement differences between contacting surfaces at damped interfaces may be very small.
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| 11. |
- Finnveden, Svante
(author)
-
A quantitative criterion validating coupling power proportionality in statistical energy analysis
- 2011
-
In: Journal of Sound and Vibration. - : Elsevier. - 0022-460X .- 1095-8568. ; 330:1, s. 87-109
-
Journal article (peer-reviewed)abstract
- The response of two general spring-coupled elements is investigated to develop a unifying approach to the weak coupling criterion in Statistical Energy Analysis (SEA). First, the coupled deterministic equations of motion are expressed in the bases given by the Uncoupled elements' eigenmodes. Then, an iterative solution is expressed as a succession of exchanges between elements, where uncoupled motion provides the start approximation, converging lithe 'coupling eigenvalue' is less than unity, in which case coupling is said to be weak. This definition is related to whether response is 'local' or 'global', encompassing a number of previously defined coupling strength definitions, applying for deterministically described structures. A stochastic ensemble is defined by that its members are equal to the investigated structure but the elements have random frequencies. It is required that the coupling eigenvalue be less than unity for all members of the ensemble. This requirement generates the title subject of the article: 'the modal interaction strength'. It is similar to the previously defined coupling strength criterion characterising the ensemble average energy flow in uni-dimensional waveguides. Finally, SEA models are formulated in terms of the uncoupled elements' modal data.
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| 12. |
- Heo, Yong-Ho, et al.
(author)
-
In-duct identification of fluid-borne source with high spatial resolution
- 2014
-
In: Journal of Sound and Vibration. - : Elsevier BV. - 0022-460X .- 1095-8568. ; 333:23, s. 6074-6089
-
Journal article (peer-reviewed)abstract
- Source identification of acoustic characteristics of in-duct fluid machinery is required for coping with the fluid-borne noise. By knowing the acoustic pressure and particle velocity field at the source plane in detail, the sound generation mechanism of a fluid machine can be understood. The identified spatial distribution of the strength of major radiators would be useful for the low noise design. Conventional methods for measuring the source in a wide duct have not been very helpful in investigating the source properties in detail because their spatial resolution is improper for the design purpose. In this work, an inverse method to estimate the source parameters with a high spatial resolution is studied. The theoretical formulation including the evanescent modes and near-field measurement data is given for a wide duct. After validating the proposed method to a duct excited by an acoustic driver, an experiment on a duct system driven by an air blower is conducted in the presence of flow. A convergence test for the evanescent modes is performed to find the necessary number of modes to regenerate the measured pressure field precisely. By using the converged modal amplitudes, very-close near-field pressure to the source is regenerated and compared with the measured pressure, and the maximum error was -16.3 dB. The source parameters are restored from the converged modal amplitudes. Then, the distribution of source parameters on the driver and the blower is clearly revealed with a high spatial resolution for kR < 1.84 in which range only plane waves can propagate to far field in a duct. Measurement using a flush mounted sensor array is discussed, and the removal of pure radial modes in the modeling is suggested.
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| 13. |
- Holmberg, Andreas, et al.
(author)
-
Accurate experimental two-port analysis of flow generated sound
- 2011
-
In: Journal of Sound and Vibration. - : Elsevier BV. - 0022-460X .- 1095-8568. ; 330:26, s. 6336-6354
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Journal article (other academic/artistic)abstract
- In the study of in-duct aero-acoustic phenomena two-port analysis based upon in-duct measurements has become an important method for the plane wave region. However already at moderate Mach numbers (0.2 - 0.3) the errors in the results can be hard to suppress. Ways of dealing with this includes the use of over-determination methods and methods of obtaining more accurate wave numbers. In this paper different methods for the determination of the source data and the scattering matrix are evaluated. For the source data in the form of a cross spectrum matrix an over-determination method is introduced. In addition, a method of obtaining the mean Mach number from experimentally determined wave numbers is described.In order to evaluate the methods measurements are conducted at a mean Mach number of 0.2 for two test cases – an empty duct and a mixer plate inside the duct. The main improvements in the scattering matrix results are achieved by discarding measurements from an abundant set, based upon the measured coherence between excitation and fluctuating pressures. For the source part, it is shown that the error in the magnitude of the source cross spectrum matrix can be significantly suppressed by having additional (> 2) reference microphones on each side of the two-port.The mean Mach number obtained from an experimentally determined wave number is observed to yield more accurate scattering matrix results in both phase and magnitude, than that based upon flow velocity measurements at one point and an assumed flow profile.
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| 14. |
- Hosseini-Hashemi, Sh., et al.
(author)
-
Accurate free vibration analysis of thick laminated circular plates with attached rigid core
- 2012
-
In: Journal of Sound and Vibration. - : Elsevier BV. - 0022-460X .- 1095-8568. ; 331:25, s. 5581-5596
-
Journal article (peer-reviewed)abstract
- This paper deals with the free vibration behavior of laminated transversely isotropic circular plates with axisymmetric rigid core attached at the center. The governing equations of motion are obtained based on Mindlin's first-order shear deformation plate theory. Two possible categories of vibration modes related to up-down translation of the core and wobbly rotation of the core about a diameter are studied. Accurate natural frequencies hitherto not reported in the literature are presented for a wide range of thickness-to-radius ratio, inner-to-outer radius ratio, mass and moment of inertia ratios of the core and various boundary conditions at the outer edge of the plate. Numerical results are compared with those of a three-dimensional finite element method (3-D FEM) to demonstrate the high accuracy and reliability of the current analysis.
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| 15. |
- Jansson, Ida
(author)
-
On the notion of a rotating fluid force induced by swirling flow
- 2014
-
In: Journal of Sound and Vibration. - : Elsevier BV. - 0022-460X .- 1095-8568. ; 333:25, s. 7076-7083
-
Journal article (peer-reviewed)abstract
- The Bently/Muszynska (B/M) model shows that oil whirl and oil whip are both self-sustained vibrations associated with two unstable modes of a rotor–fluid system. The model includes a rotating fluid damping and inertia force. In certain configurations, the rotating damping force overcomes the frictional internal damping of the rotor and pushes the rotor into a stable limit cycle of circular orbiting. Such a notion of a rotating fluid force is based on bulk-flow models of fluid-filled clearances that could be approximated as narrow since the tangential velocity of the fluid then translates to one angular velocity at a certain radial distance defined by an average radius. This paper scrutinizes the assumption of a rotating fluid inertia force and pinpoints the additional inertial effects of the swirling flow as the gap width increases. These effects are clarified by deriving the equation of motion of a body with a mass subjected to motion-induced fluid forces of a confined swirling flow. We show that the inertial effects of the swirling flow counteract the destabilizing effect of the rotating damping force. However, if the body mass is larger than the displaced fluid mass, instability follows. The frequency of the unstable mode is unchanged by the additional inertial effects and is always equal to the frequency of the damping that induces the instability.
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| 16. |
- Jourdain, Guillaume, 1984, et al.
(author)
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Application of dynamic mode decomposition to acoustic-modes identification and damping in a 3-dimensional chamber with baffled injectors
- 2013
-
In: Journal of Sound and Vibration. - : Elsevier BV. - 1095-8568 .- 0022-460X. ; 332:18, s. 4308-4323
-
Journal article (peer-reviewed)abstract
- The dynamic mode decomposition (DMD) is applied to a 3-dimensional chamber in order to identify acoustic resonant modes and quantify their damping. The DMD is one of post-processing methods, which can be applicable with acoustic field information in a full or a partial domain from numerical and experimental data. For application of the DMD method, the 3-dimensional chamber with baffled injectors is selected, in which gaps in baffled injectors enhanced acoustic damping and it has been shown that there exists an optimum gap for maximum damping in the previous works. Damping coefficients are evaluated in order to investigate whether the DMD method is able to predict the influence of gaps in baffled injectors on the damping of the first tangential (1T) mode or not. In addition to the IT mode, the first longitudinal (1L) mode, the 1T1L mode, and higher modes are extracted and damping coefficients for them are estimated using the DMD method on 2-dimensional planes and they reveal that the baffle gap affects significantly only specific modes and show a good agreement with the damping factors from the previous work in predicting the optimum gap for maximum acoustic damping.
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| 17. |
- Karlberg, Magnus, et al.
(author)
-
Rotordynamical simulations of a fibre refiner during production
- 2011
-
In: Journal of Sound and Vibration. - : Elsevier BV. - 0022-460X .- 1095-8568. ; 330:18/19, s. 4460-4473
-
Journal article (peer-reviewed)abstract
- A key component in panel board production is the refiner, whose task is to break raw cellulose wood chips into slender fibres, done by a relative angular motion between stator and rotor. The main problem in predicting the dynamics of these machines is to model the complicated fibre breaking process, since the refining process leads to a three-phase flow (solid wood, water and steam) between the stator and rotor. By modelling the rotor as a rigid body, the process can only contribute by a resulting force and a resulting moment. Through this approach and axial force measurements, it has been shown that the refining process can be treated as a time dependent stiffness matrix and external load. The objective for this paper is to predict and explain dynamical characteristics of fibre refiners during production in such a way that the results can be used already at early stages of the product development process. Two different pressure distribution cases are studied, i.e. one axisymmetric with only radial variations and one non-axisymmetric. It is found that the axisymmetric case only excited forward modes, while the non-axisymmetric case excited all modes. The time dependent stiffness matrix resulted in unstable domains, but also in stable domains with intermittent high amplitudes.
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| 18. |
- Karlsson, Mikael, et al.
(author)
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Aeroacoustics of T-junctions : An experimental investigation
- 2010
-
In: Journal of Sound and Vibration. - : Elsevier BV. - 0022-460X .- 1095-8568. ; 329:10, s. 1793-1808
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Journal article (peer-reviewed)abstract
- An experimental method for determining the aeroacoustic properties of side branch orifices allowing for any combination of grazing and bias flow is presented. The geometry studied, a T-junction, is treated as an active acoustic three-port. The passive properties, describing the reflection and transmission of an incident acoustic wave, are described by a system matrix while the active properties are described by a source vector. Expressions for the acoustic impedance under various mean flow and acoustic incidence configurations are developed. In addition, methods for identifying regions where the system can generate sound, by studying only the passive properties, are discussed. A self-sustained oscillation is triggered at one of the identified regions by coupling a resonant system to the three-port.
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| 19. |
- Karlsson, Mikael, et al.
(author)
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Quasisteady model of the acoustic scattering of a T- Junction
- 2011
-
In: Journal of Sound and Vibration. - : Elsevier BV. - 0022-460X .- 1095-8568. ; 330:21, s. 5131-5137
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Journal article (peer-reviewed)abstract
- T-junctions are common elements in flow duct networks. It is shown that for low Strouhal numbers, based on the duct diameter, their acoustic scattering properties can be described using an incompressible quasi-steady model. Models are derived for systems subjected to combinations of grazing and bias mean flow, and are shown to work in both the limiting cases that is, grazing or bias flow alone as well as for the joining or dividing flow configurations. The upper Strouhal number for which the quasi-steady models are applicable is limited by flow-acoustic interaction effects, which differ significantly between the different flow configurations. Generally the models are applicable up to Strouhal numbers of approximately 0.1-0.2, which is comparable with previous published models for other configurations such as bends and orifices. This range is sufficient to make the model useful in many important engineering applications.
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| 20. |
- Kierkegaard, Axel, et al.
(author)
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Simulations of the scattering of sound waves at a sudden area expansion
- 2012
-
In: Journal of Sound and Vibration. - : Elsevier. - 0022-460X .- 1095-8568. ; 331:5, s. 1068-1083
-
Journal article (peer-reviewed)abstract
- The scattering of acoustic plane waves at a sudden area expansion in a flow duct is simulated using the linearized Navier-Stokes equations. The aim is to validate the numerical methodology for the flow duct area expansion, and to investigate the influence of the downstream mean flow on the acoustic scattering properties. A comparison of results from numerical simulations, analytical theory and experiments is presented. It is shown that the results for the acoustic scattering obtained by the different methods gives excellent agreement. For the end correction, the numerical approach is found superior to the analytical model at frequencies where coupling of acoustic and hydrodynamic waves is significant. A study with two additional flow profiles, representing a non-expanding jet with infinitely thin shear layer, and an immediate expansion, shows that a realistic jet is needed to accurately capture the acoustic-hydrodynamic interaction. A study with several different artificial jet expansions concluded that the acoustic scattering is not significantly dependent on the mean flow profile below the area expansion. The constructed flow profiles give reasonable results although the reflection and transmission coefficients are underestimated, and this deviation seems to be rather independent of frequency for the parameter regime studied. The prediction of the end correction for the constructed mean flow profiles deviates significantly from that for the realistic profile in a Strouhal number regime representing strong coupling between acousticand hydrodynamic waves. It is concluded that the constructed flow profiles lack the ability to predict the loss of energy to hydrodynamic waves, and that this effect increases with increasing Mach number.
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| 21. |
- Kierkegaard, Axel, et al.
(author)
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Simulations of whistling and the whistling potentiality of an in-duct orifice with linear aeroacoustics
- 2012
-
In: Journal of Sound and Vibration. - : Elsevier. - 0022-460X .- 1095-8568. ; 331:5, s. 1084-1096
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Journal article (peer-reviewed)abstract
- This paper demonstrates a linear aeroacoustic simulation methodology to predict the whistling of an orifice plate in a flow duct. The methodology is based on a linearized Navier-Stokes solver in the frequency domain with the mean flow field taken from a Reynolds-Averaged Navier-Stokes (RANS) solution. The whistling potentiality is investigated via an acoustic energy balance for the in-duct element and good agreement with experimental data is shown. A Nyquist stability criterion based on the simulation data was applied to predict whistling of the orifice when placed in a finite sized duct and experiments were carried out to validate the predictions. The results indicate that although whistling is a non-linear phenomena caused by an acoustic-flow instability feed-back loop, the linearized Navier-Stokes equations can be used to predict both whistling potentiality and a duct system’s ability to whistle or not.
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| 22. |
- Knutsson, Magnus, et al.
(author)
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The effect of turbulence damping on acoustic wave propagation in tubes
- 2010
-
In: Journal of Sound and Vibration. - : Elsevier BV. - 0022-460X .- 1095-8568. ; 329:22, s. 4719-4739
-
Journal article (peer-reviewed)abstract
- The attenuation of sound due to the interaction between a low Mach number turbulent boundary layer and acoustic waves can be significant at low frequencies or in narrow tubes. In a recent publication by the present authors the acoustics of charge air coolers for passenger cars has been identified as an interesting application where turbulence attenuation can be of importance. Favourable low-frequency damping has been observed that could be used for control of the in-duct sound that is created by the engine gas exchange process. Analytical frequency-dependent models for the eddy viscosity that controls the momentum and thermal boundary layers are available but are restricted to thin acoustic boundary layers. For cases with cross-sections of a few millimetres a model based on thin acoustic boundary layers will not be applicable in the frequency range of interest. In the present paper a frequency-dependent axis-symmetric numerical model for interaction between turbulence and acoustic waves is proposed. A finite element scheme is used to formulate the time harmonic linearized convective equations for conservation of mass, momentum and energy into one coupled system of equations. The turbulence is introduced with a linear model for the eddy viscosity that is added to the shear viscosity. The proposed model is validated by comparison with experimental data from the literature.
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| 23. |
- Kropp, Wolfgang, 1959, et al.
(author)
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On the sound radiation of a rolling tyre
- 2012
-
In: Journal of Sound and Vibration. - : Elsevier BV. - 1095-8568 .- 0022-460X. ; 331:8, s. 1789-1805
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Journal article (peer-reviewed)abstract
- The sound radiation from rolling tyres is still not very well understood. Although details such as horn effect or directivity during rolling have been investigated, it is not clear which vibrational modes of the tyre structure are responsible for the radiated sound power. In this work an advanced tyre model based on Wave Guide Finite Elements is used in connection with a contact model validated in previous work. With these tools the tyre vibrations during rolling on an ISO surface are simulated. Starting from the calculated contact forces in time the amplitudes of the modes excited during rolling are determined as function of frequency. A boundary element model also validated in previous work is applied to predict the sound pressure level on a reference surface around a tyre placed on rigid ground as function of the modal composition of the tyre vibrations. Taking into account different modes when calculating the vibrational field as input into the boundary element calculations, it is possible to identify individual modes or groups of modes of special relevance for the radiated sound power. The results show that mainly low-order modes with relative low amplitudes but high radiation efficiency in the frequency range around 1 kHz are responsible for the radiated sound power at these frequencies, while those modes which are most strongly excited in that frequency range during rolling are irrelevant for the radiated sound power. This fact is very essential when focusing on the design of quieter tyres.
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| 24. |
- Lind-Nordgren, Eleonora, et al.
(author)
-
Optimising open porous foam for acoustical and vibrational performance
- 2010
-
In: Journal of Sound and Vibration. - : Elsevier BV. - 0022-460X .- 1095-8568. ; 329:7, s. 753-767
-
Journal article (peer-reviewed)abstract
- A computational method for designing optimal arrangements of multilayer noise and vibration treatments in general and porous open cell foam in particular is discussed. The method uses finite element solutions to Biot's equations for poroelastic materials and provides data to evaluate cost functions and gradients. The porous material is parameterised using scaling laws linking the microscopic properties to the classical parameters, i.e. averaged elasticity, flow resistivity and characteristic viscous and thermal lengths. The cost function is either in terms of weight or in terms of the pressure response in a finite cavity, complemented with constraints on the other. However, care must be taken when choosing the cost function, as this will greatly affect the outcome of the optimisation. Observations made during the optimisation process indicate a limited number of minima within the parameter range of interest as well as beneficial continuity around these minima, thus enabling a meaningful optimisation. The results suggest that if alterations of the microscopic properties of the foam are made, the foam may be adapted to specific environmental conditions and thereby achieve improved acoustic behaviour as well as reduced weight.
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| 25. |
- Liu, B., et al.
(author)
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Predicted and measured plate velocities induced by turbulent boundary layers
- 2012
-
In: Journal of Sound and Vibration. - : Elsevier BV. - 0022-460X .- 1095-8568. ; 331:24, s. 5309-5325
-
Journal article (peer-reviewed)abstract
- A method for the prediction of velocity levels of a fuselage plate excited by turbulent boundary layers is described. The aim is to identify a method for the prediction of the relative changes of the velocity levels caused by variations of plate geometry and flight conditions. The Corcos, Efimtsov and Chase models are used to characterize the dynamic surface pressure cross-spectra. Predicted results using these models are compared with the result of in-flight measurements of plate velocities. It is found that the Corcos model gives the best agreement with the measured results for three different flight conditions. The Efimtsov extension and Chase models tend to underestimate the plate response in the lower frequency range. It is evident that the velocity level of the plate elements of the fuselage very much depends on the speed of the aircraft. An increase of the speed of the aircraft by 10% is likely to increase the plate velocity level by 3 dB and a reduction of the speed by 10% would give a reduction of 3 dB.
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| 26. |
- Magnevall, Martin, et al.
(author)
-
Nonlinear structural identification by the "Reverse Path" spectral method
- 2012
-
In: Journal of Sound and Vibration. - : Elsevier BV. - 0022-460X .- 1095-8568. ; 131:4, s. 938-946
-
Journal article (peer-reviewed)abstract
- When dealing with nonlinear dynamical systems, it is important to have efficient, accurate and reliable tools for estimating both the linear and nonlinear system parameters from measured data. An approach for nonlinear system identification widely studied in recent years is "Reverse Path". This method is based on broad-band excitation and treats the nonlinear terms as feedback forces acting on an underlying linear system. Parameter estimation is performed in the frequency domain using conventional multiple-input-multiple-output or multiple-input-single-output techniques. This paper presents a generalized approach to apply the method of "Reverse Path" on continuous mechanical systems with multiple nonlinearities. The method requires few spectral calculations and is therefore suitable for use in iterative processes to locate and estimate structural nonlinearities. The proposed method is demonstrated in both simulations and experiments on continuous nonlinear mechanical structures. The results show that the method is effective on both simulated as well as experimental data.
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| 27. |
- Mauritsson, Karl, 1980, et al.
(author)
-
Dynamic equations for a fully anisotropic elastic plate
- 2011
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In: Journal of Sound and Vibration. - : Elsevier BV. - 1095-8568 .- 0022-460X. ; 330:11, s. 2640-2654
-
Journal article (peer-reviewed)abstract
- A hierarchy of dynamic plate equations is derived for a fully anisotropic elastic plate. Using power series expansions in the thickness coordinate for the displacement components, recursion relations are obtained among the expansion functions. Adopting these in the boundary conditions on the plate surfaces and along the edges, a set of dynamic equations with pertinent edge boundary conditions are derived on implicit form. These can be truncated to any order and are believed to be asymptotically correct. For the special case of an orthotropic plate, explicit plate equations are presented and compared analytically and numerically to other approximate theories given in the literature. These results show that the present theory capture the plate behavior accurately concerning dispersion curves, eigenfrequencies as well as stress and displacement distributions.
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| 28. |
- Pieringer, Astrid, 1979
(author)
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A numerical investigation of curve squeal in the case of constant wheel/rail friction
- 2014
-
In: Journal of Sound and Vibration. - : Elsevier BV. - 1095-8568 .- 0022-460X. ; 333:18, s. 4295-4313
-
Journal article (peer-reviewed)abstract
- Curve squeal is commonly attributed to self-excited vibrations of the railway wheel, which arise due to a large lateral creepage of the wheel tyre on the top of the rail during curving. The phenomenon involves stick/slip oscillations in the wheel/rail contact and is therefore strongly dependent on the prevailing friction conditions. The mechanism causing the instability is, however, still a subject of controversial discussion. Most authors introduce the negative slope of the friction characteristic as a source of the instability, while others have found that squeal can also occur in the case of constant friction due to the coupling between normal and tangential dynamics. As a contribution to this discussion, a detailed model for high-frequency wheel/rail interaction during curving is presented in this paper and evaluated in the case of constant friction. The interaction model is formulated in the time domain and includes the coupling between normal and tangential directions. Track and wheel are described as linear systems using pre-calculated impulse response functions that are derived from detailed finite element models. The nonlinear, non-steady state contact model is based on an influence function method for the elastic half-space. Real measured wheel and rail profiles are used. Numerical results from the interaction model confirm that stick/slip oscillations occur also in the case of constant friction. The choice of the lateral creepage, the value of the friction coefficient and the lateral contact position on the wheel tread are seen to have a strong influence on the occurrence and amplitude of the stick/slip oscillations. The results from the interaction model are in good qualitative agreement with previously published findings on curve squeal.
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| 29. |
- Sabiniarz, Patrik, 1979, et al.
(author)
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A waveguide finite element aided analysis of the wave field on a stationary tyre, not in contact with the ground
- 2010
-
In: Journal of Sound and Vibration. - : Elsevier BV. - 1095-8568 .- 0022-460X. ; 329:15, s. 3041-3064
-
Journal article (peer-reviewed)abstract
- Although tyre/road noise has been a research subject for more than three decades, there is still no consensus in the literature as to which waves on a tyre are mainly responsible for the radiation of sound during rolling. Even the free vibrational behaviour of a stationary (non-rotating) tyre, not in contact with the ground, is still not well understood in the mid- and high-frequency ranges. Thus, gaining an improved understanding of this behaviour is a natural first step towards illuminating the question of which waves on a rolling tyre contribute to sound radiation. This is the topic of the present paper, in which a model based on the waveguide finite element method (WFEM) is used to study free wave propagation, on a stationary tyre, in the range 0-1500 Hz. In the low-frequency region (0-300 Hz), wave propagation is found to be rather straightforward, with two main wave-types present. Both have cross-section modes involving a nearly rigid motion of the belt. For higher frequencies (300-1500 Hz) the behaviour is more complex, including phenomena such as 'curve veering' and waves for which the phase speed and group speed have opposite signs. Wave-types identified in this region include (i) waves involving mainly sidewall deformation, (ii) belt bending waves, (iii) a wave with significant extensional deformation of the central belt region and (iv) a wave with a 'breathing' cross-section mode. The phase speed corresponding to found waves is computed and their radiation efficiency is discussed, assuming free-field conditions. In a future publication, the tyre model will be used in conjunction with a contact model and a radiation model to investigate the contribution of these waves to radiated sound during rolling. (C) 2010 Elsevier Ltd. All rights reserved.
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| 30. |
- Sun, Jia, et al.
(author)
-
A dynamic rotating blade model at an arbitrary stagger angle based on classical plate theory and the Hamilton's principle
- 2013
-
In: Journal of Sound and Vibration. - : Elsevier BV. - 0022-460X .- 1095-8568. ; 332:5, s. 1355-1371
-
Journal article (peer-reviewed)abstract
- A dynamic model based on classical plate theory is presented to investigate the vibration behavior of a rotating blade at an arbitrary stagger angle and rotation speed. The Hamilton's principle is applied to derive the equations of motion, which are discretised by a novel implementation of the fast and efficient collocation method for rotating structures and by the traditional Extended Galerkin method. The results obtained with these methods are compared and validated with results found in the literature and from commercial finite element software. The proposed collocation method leads to a significantly lower computation time than the Extended Galerkin method for the same accuracy. The results show a good agreement with those of the finite element method. Finally, the forced response analysis is determined for two cases; a point force and a distribution force, using a proportional damping model.
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| 31. |
- Sun, Jia, 1981-, et al.
(author)
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General shell model for a rotating pretwisted blade
- 2013
-
In: Journal of Sound and Vibration. - : Elsevier. - 0022-460X .- 1095-8568. ; 332:22, s. 5804-5820
-
Journal article (peer-reviewed)abstract
- A novel dynamic model for a pretwisted rotating compressor blade mounted atan arbitrary stagger angle using general shell theory and including the rotationalvelocity is developed to study the eigenfrequencies and damping properties of thepretwisted rotating blade. The strain-displacement relation and constitutive modelbased on the general (thick) shell theory are applied to bring out the strain energyof the rotating blade. Using the Hamilton’s principle, the variational form of thetotal energy is derived in order to obtain the corresponding weak form for thenumerical simulation. The model is validated by comparing to literature resultsand Ansys results, showing good agreement. Parametric analyses are carried outto study the influence of the rotation velocity, the stagger angle and the radius ofthe disk on the eigenfrequencies of the pretwisted blade. Proportional dampingis included into the proposed model to investigate the influence of rotational velocityon the damping characteristics of the pretwisted rotating blade system. It isshown that, due to inertial and Coriolis eects, damping decreases as the rotation velocity increases for the lower part of the velocity range considered and eitherdecreases or increases depending on the mode order for higher velocities. Furthermore,frequency loci veering as a result of the rotation velocity is observed.The proposed model is an ecient and accurate tool for predicting the dynamicbehavior of compressor blades of arbitrary thickness, stagger angle and pretwist,potentially during the early designing stage of turbomachinery.
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| 32. |
- Svensson, Jonas, 1982, et al.
(author)
-
On the design of structural junctions for the purpose of hybrid passive-active vibration control
- 2010
-
In: Journal of Sound and Vibration. - : Elsevier BV. - 1095-8568 .- 0022-460X. ; 329:9, s. 1274-1288
-
Journal article (peer-reviewed)abstract
- A theoretical investigation of wave scattering and the active modification of wave scattering at structural junctions is presented. A resonant and a non-resonant Euler–Bernoulli beam are coupled, and an external force is introduced at the junction. The external force is intended for feedforward control in order to manipulate the scattering properties at the junction. The purpose of the investigated control law is to make the junction non-reflective in the case of an incident bending wave. The control effort and the resulting power flow are investigated for different properties of the beams. By introducing damping in the resonant beam all incidence wave power is absorbed either passively, in the resonant beam, or actively, by the force. The results form the basis for a discussion of the possible benefits of using such a configuration for hybrid passive–active vibration control. The results show that for certain ratios of bending stiffness and mass the presented hybrid passive–active solution may offer advantages compared to purely passive or purely active solutions.
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| 33. |
- Tiikoja, Heiki, et al.
(author)
-
Experimental investigations of sound reflection from hot and subsonic flow duct termination
- 2014
-
In: Journal of Sound and Vibration. - : Elsevier BV. - 0022-460X .- 1095-8568. ; 333:3, s. 788-800
-
Journal article (peer-reviewed)abstract
- The knowledge of the reflection properties of open end jet ducts is important for different applications, where the flow and high temperature conditions are involved and add complexity to the problem. In this paper, the magnitude of the reflection coefficients together with the respective end-corrections is experimentally determined for hot flow duct openings. A Mach number range up to 0.3 for cold jets and up to 0.12 for a jet temperature of 200 degrees C is treated. The experimental results are compared with the numerical model proposed by Munt (Acoustic transmission properties of a jet duct with subsonic jet flow: 1. The cold jet reflection coefficient, Journal of Sound and Vibration 142 (1990) 413-436) and a good correlation in plane-wave region is demonstrated. To reduce experimental uncertainty, the sound reflection properties at the duct opening are obtained by using an overdetermined two-microphone technique with the implementation of a three pressure transducer array. By introducing a modified multistep version of the stepped sine excitation, the accuracy of data acquisition process is improved without compromising the measurement time.
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| 34. |
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| 35. |
- Torstensson, Peter T, 1981, et al.
(author)
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Dynamic train-track interaction at high vehicle speeds-Modelling of wheelset dynamics and wheel rotation
- 2011
-
In: Journal of Sound and Vibration. - : Elsevier BV. - 1095-8568 .- 0022-460X. ; 330:22, s. 5309-5321
-
Journal article (peer-reviewed)abstract
- Vertical dynamic train-track interaction at high vehicle speeds is investigated in a frequency range from about 20 Hz to 2.5 kHz. The inertial effects due to wheel rotation are accounted for in the vehicle model by implementing a structural dynamics model of a rotating wheelset. Calculated wheel-rail contact forces using the flexible, rotating wheelset model are compared with contact forces based on rigid, non-rotating models. For a validation of the train-track interaction model, calculated contact forces are compared with contact forces measured using an instrumented wheelset. When the system is excited at a frequency where two different wheelset mode shapes, due to the wheel rotation, have coinciding resonance frequencies, significant differences are found in the contact forces calculated with the rotating and non-rotating wheelset models. Further, the use of a flexible, rotating wheelset model is recommended for load cases leading to large magnitude contact force components in the high-frequency range (above 1.5 kHz). In particular, the influence of the radial wheel eigenmodes with two or three nodal diameters is significant. (C) 2011 Elsevier Ltd. All rights reserved.
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| 36. |
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| 37. |
- Van der Kelen, Christophe, 1986-, et al.
(author)
-
On the influence of frequency-dependent elastic properties in vibro-acoustic modelling of porous materials under structural excitation
- 2014
-
In: Journal of Sound and Vibration. - : Elsevier. - 0022-460X .- 1095-8568. ; 333:24, s. 6560-6571
-
Journal article (peer-reviewed)abstract
- The aspects related to the frequency dependence of the elastic properties of porous materials have been largely neglected in the past for several reasons. For acoustic excitation of porous materials, the material behaviour can be quite well represented by models where the properties of the solid frame have little influence. Only recently has the importance of the dynamic moduli of the frame come into focus. This is related to a growing interest in the material behaviour due to structural excitation. Two aspects stand out in connection with the elastic-dynamic behaviour. The first is related to methods for the characterisation of the dynamic moduli of porous materials. The second is a perceived lack of numerical methods able to model the complex material behaviour under structural excitation, in particular at higher frequencies. In the current paper, experimental data from a panel under structural excitation, coated with a porous material, is used in correlation with numerical predictions, involving a frequency-dependent material model for the stiffness properties of the porous material. The results suggest that the frequency dependence is of importance for a correct prediction of the response of trim installations. The change in material behaviour due to the frequency-dependent properties is illustrated in terms of the propagation of the slow wave and the shear wave in the porous material.
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| 38. |
- Winroth, Julia, 1981, et al.
(author)
-
Importance of tread inertia and damping on the tyre/road contact stiffness
- 2014
-
In: Journal of Sound and Vibration. - : Elsevier BV. - 1095-8568 .- 0022-460X. ; 333:21, s. 5378-5385
-
Journal article (peer-reviewed)abstract
- Predicting tyre/road interaction processes like roughness excitation, stick-slip, stick-snap, wear and traction requires detailed information about the road surface, the tyre dynamics and the local deformation of the tread at the interface. Aspects of inertia and damping when the tread is locally deformed are often neglected in many existing tyre/road interaction models. The objective of this paper is to study how the dynamic features of the tread affect contact forces and contact stiffness during local deformation. This is done by simulating the detailed contact between an elastic layer and a rough road surface using a previously developed numerical time domain contact model. Road roughness on length scales smaller than the discretisation scale is included by the addition of nonlinear contact springs between each pair of contact elements. The dynamic case, with an elastic layer impulse response extending in time, is compared with the case where the corresponding quasi-static response is used. Results highlight the difficulty of estimating a constant contact stiffness as it increases during the indentation process between the elastic layer and the rough road surface. The stiffness-indentation relation additionally depends on how rapidly the contact develops; a faster process gives a stiffer contact. Material properties like loss factor and density also alter the contact development. This work implies that dynamic properties of the local tread deformation may be of importance when simulating contact details during normal tyre/road interaction conditions. There are however indications that the significant effect of damping could approximately be included as an increased stiffness in a quasi-static tread model.
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| 39. |
- Xin, Tao, et al.
(author)
-
Reducing slab track vibration into bridge using elastic materials in high speed railway
- 2011
-
In: Journal of Sound and Vibration. - : Elsevier BV. - 0022-460X .- 1095-8568. ; 330:10, s. 2237-2248
-
Journal article (peer-reviewed)abstract
- In this paper, the problem of vibration transmission from slab track structures into bridge is studied by theoretical analysis. A vehicle–track–bridge coupling system dynamics model is established based on a multibody dynamics theory and a finite element method. The system model consists of vehicle model, track–bridge model and wheel/rail interaction model. The vehicle model is established based on the multibody dynamics theory, and the tack–bridge model is established by the finite element method. The vehicle model and track–bridge model are coupled through wheel/rail interaction model, and the track irregularities are included. The system dynamic responses are calculated, and the effectiveness of elastic materials in vibration reducing is discussed. The results demonstrate that elastic materials like slab mat layer inserted between slab track and bridge can reduce vibration transmitted from track into the bridge. Some suggestions for the design and application of slab mat are provided in the end of the paper.
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| 40. |
- Zhang, Xuetao, 1955
(author)
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The directivity of railway noise at different speeds
- 2010
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In: Journal of Sound and Vibration. - 1095-8568 .- 0022-460X. ; 329:25, s. 5273-5288
-
Journal article (peer-reviewed)abstract
- For a sound source, directivity is an important parameter to specify. This parameter also reflects the physical feature of the sound generation mechanism. In this article, studies on the directivity of railway noise, by measurement and by theoretical investigation, are discussed extensively and systematically. The two most important noise types, i.e. rolling noise and aerodynamic noise, are focused on. A model of perpendicular dipole pair is proposed to interpret the measurement specified directivity characters of wheel/rail radiation. This model naturally explains why a vibrating railway wheel does not present dipole directivity character and why rail radiation is of different vertical and horizontal directivity characters. Moreover pantograph noise is also found to be of perpendicular dipole components. As for aerodynamic noise around bogies, scattering of the air flow is proposed to be the mechanism of the noise generation; this understanding leads to a different directivity description for the noise component. Directivities of other important noise types are discussed as well; their directivities become understood, although lacking of relevant directivity data. In summary, this study provides applicable directivity functions together with a survey of the directivities of all important railway noise types and components. Hopefully this work will be useful, for railway noise engineering also contribute to understand better railway noise.
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| 41. |
- Östberg, Martin, et al.
(author)
-
Transverse, tilting and cross-coupling stiffness of cylindrical rubber isolators in the audible frequency range-The wave-guide solution
- 2011
-
In: Journal of Sound and Vibration. - : Elsevier. - 0022-460X .- 1095-8568. ; 330:13, s. 3222-3244
-
Journal article (peer-reviewed)abstract
- Audio-frequency wave-guide models for antisymmetric dynamic stiffness of arbitrary long elastomer cylinders are presented. The locally non-mixed boundary conditions at the lateral and radial surfaces are simultaneously satisfied by using the modes corresponding to the dispersion relation for axial waves in cylinders satisfying the stress free boundary conditions at the curved radial boundaries, while the displacement conditions on the flat cylinder ends are satisfied by mode matching. The elastomer is modelled as nearly incompressible with deviatoric visco-elasticity based on a fractional derivative, standard linear solid embodying a Mittag-Leffler relaxation kernel, the main advantage being the minimum parameter number required to successfully model the material properties over a broad frequency band. The stiffness is found to depend strongly on frequency: displaying resonances and anti-resonances. The method is compared with and verified against finite element models. In addition, comparison to thin beam theories, i.e. Euler and Timoschenko theory and a simple shear model, is presented, illustrating the limitations of these models.
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| 42. |
- Brandt, Anders, et al.
(author)
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Sampling and Time-Domain Analysis
- 2010
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In: Sound and Vibration. - : ACOUSTICAL PUBL INC. - 0022-460X. ; 44:5, s. 13-17:May, s. 13-17
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Journal article (peer-reviewed)abstract
- Most noise and vibration measurement and analysis systems are able to record time history signals for subsequent processing. This article deals with some important aspects of recording and processing these data streams in order to maintain analysis integrity.
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