| 51. |
- Bodén, Hans
(författare)
-
One-sided multi-port techniques for characterisation of in-duct samples with nonlinear acoustic properties
- 2012
-
Ingår i: Journal of Sound and Vibration. - : Elsevier BV. - 0022-460X .- 1095-8568. ; 331:13, s. 3050-3067
-
Tidskriftsartikel (refereegranskat)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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| 52. |
- Boij, Susann, et al.
(författare)
-
Scattering and absorption of sound at flow duct expansions
- 2006
-
Ingår i: Journal of Sound and Vibration. - : Elsevier BV. - 0022-460X .- 1095-8568. ; 289:3, s. 577-594
-
Tidskriftsartikel (refereegranskat)abstract
- The scattering of plane acoustic waves at area expansions in flow ducts is analysed using the vortex sheet model where the flow at the expansion is modelled as a jet, with a vortex sheet emanating from the edge. Of particular interest is the influence of the flow field on acoustic scattering and absorption. First, it is demonstrated that the stability properties of the shear layer can be simulated by modifying the edge condition within the vortex sheet model. To this end the accuracy for the region where the shear layer is changing from unstable to stable is improved by introducing a gradually relaxed Kutta edge condition with empirically derived coefficients. For low Strouhal numbers the vortex sheet model applies and for higher Strouhal numbers the two models converge. Second, it is demonstrated that the acoustic transmission through the jet expansion region can be determined by neglecting the scattering there. Incorporating this assumption, the vortex sheet model reproduces well the experimental results on transmission and absorption for an area expansion. This result supports the assumption that the main part of the scattering occurs at the area expansion at least for the low-frequency range. Furthermore, the influence of the flow field is particularly strong for small Strouhal numbers.
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| 53. |
- Bonfiglio, P., et al.
(författare)
-
Aspects of computational vibration transmission for sandwich panels
- 2007
-
Ingår i: Journal of Sound and Vibration. - : Elsevier BV. - 0022-460X .- 1095-8568. ; 303:3-5, s. 780-797
-
Tidskriftsartikel (refereegranskat)abstract
- This paper considers elastic wave propagation and vibration transmission in lightweight composite structures. Specifically a spectral finite element method (SFEM) is developed as an effective numerical tool for the analysis of wave motion in uniform laminated elastic media. In short, SFEM combines a standard finite element method in the direction of layering together with analytical solutions for the remaining direction. This partial discretization leads naturally, via the variational formulation, to dispersion relations for uniform sections of built-up laminates and thus provides valuable information for a wave propagation analysis. Dynamic responses of the vibrating structures are also investigated and numerical simulations compared against a standard finite element method. The predicted transfer accelerances obtained for the steel beam and two sandwich panels are compared with measured data from laboratory experiments.
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| 54. |
- Boström, Anders E, 1951, et al.
(författare)
-
Acoustics of an obstacle inside a reactive silencer
- 1983
-
Ingår i: Journal of Sound and Vibration. - 1095-8568 .- 0022-460X. ; 87, s. 603-619
-
Tidskriftsartikel (refereegranskat)abstract
- The transmission and reflection coefficients of sound in a cylindrical duct containing several discontinuities are investigated. A building-block method, which gives the transmission and reflection coefficients for a complex system from those of the parts, is applied to bifurcations, sudden area changes with or without extended inlets, and spherical obstacles (which may be lossy). In some cases the solution can be interpreted in terns of multiple reflections. When the length between the discontinuities are small it is important to include also non-propagating modes, and this is especially true when the sudden area change is obtained from the area change with extended inlet in the limit of vanishing inlet. For an expansion chamber (a portion of the duct with a larger radius) with or without an obstacle and with or without inlets a number of numerical results with variation in frequency are presented. Numerical results for the various building-block elements of the expansion chamber are also considered.
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| 55. |
- Cameron, Christopher J., et al.
(författare)
-
On the balancing of structural and acoustic performance of a sandwich panel based on topology, property, and size optimization
- 2014
-
Ingår i: Journal of Sound and Vibration. - : Elsevier BV. - 0022-460X .- 1095-8568. ; 333:13, s. 2677-2698
-
Tidskriftsartikel (refereegranskat)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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| 56. |
- Cao, Zhigang, 1983, et al.
(författare)
-
Dynamic response of a poroelastic half-space to accelerating or decelerating trains
- 2013
-
Ingår i: Journal of Sound and Vibration. - : Elsevier BV. - 1095-8568 .- 0022-460X. ; 332:11, s. 2777-2794
-
Tidskriftsartikel (refereegranskat)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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| 57. |
- Cao, Zhigang, 1983, et al.
(författare)
-
Semi-analytical analysis of the isolation to moving-load induced ground vibrations by trenches on a poroelastic half-space
- 2012
-
Ingår i: Journal of Sound and Vibration. - : Elsevier BV. - 1095-8568 .- 0022-460X. ; 331:4, s. 947-961
-
Tidskriftsartikel (refereegranskat)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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| 58. |
- Ceci, Alessandro, et al.
(författare)
-
Computational analysis of the indirect combustion noise generation mechanism in a nozzle guided vane in transonic operating conditions
- 2021
-
Ingår i: Journal of Sound and Vibration. - : Elsevier. - 0022-460X .- 1095-8568. ; 496
-
Tidskriftsartikel (refereegranskat)abstract
- The combustion noise in modern engines is mainly originating from two types of mechanisms. First, chemical reactions in the combustion chamber leads to an unsteady heat release which is responsible of the direct combustion noise. Second, hot and cold blobs of air coming from the combustion chamber are advected and accelerated through turbine stages, giving rise to entropy noise (or indirect combustion noise). In the present work, numerical characterization of indirect combustion noise of a Nozzle Guide Vane passage was assessed using three-dimensional Large Eddy Simulations. The present work offers an overview to the analytical, computational and experimental studies of the topic. Numerical simulations are conducted to reproduce the effects of incoming planar entropy waves from the combustion chamber and to characterize the generated acoustic power. The dynamic features of the flow are addressed by the means of frequency domain and modal analyses techniques such as Fourier Decomposition and Proper Orthogonal Decomposition. Finally, the predicted entropy noise from numerical calculations is compared with the analytical results of an actuator disk model for a stator stage. The present paper proves that the generated indirect combustion noise can be significant for transonic operating conditions. The blade acoustic response is characterized by the excitation of a latent dynamics at the forcing frequency of the planar entropy waves, and it increases as the amplitude of the incoming disturbances increases.
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| 59. |
- Colmenares, Daniel, et al.
(författare)
-
Closed-form solution for mode superposition analysis of continuous beams on flexible supports under moving harmonic loads
- 2022
-
Ingår i: Journal of Sound and Vibration. - : Elsevier BV. - 0022-460X .- 1095-8568. ; 520, s. 116587-
-
Tidskriftsartikel (refereegranskat)abstract
- In this paper, a closed-form solution of the moving harmonic load problem for continuous Euler- Bernoulli beam systems is presented. The generality of the boundary conditions is taken into account by solving the characteristic equation of the system, obtaining its natural frequencies and mode shapes. The undetermined coefficient method is applied to solve the governing differential equation of motion, determining the base functions of the solution space of the problem. For vertical vibrations, three numerical examples of footbridges are presented. The main contribution of this paper is to provide the closed-form solution of the moving harmonic load problem applied to continuous footbridges including the phase angle in the load definition. In this way, it is possible to find the solution in the time domain of the harmonic component of any load spectra.
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| 60. |
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| 61. |
- Dovstam, Krister, et al.
(författare)
-
On linear modeling of interface damping in vibrating structures
- 2012
-
Ingår i: Journal of Sound and Vibration. - : Elsevier BV. - 0022-460X .- 1095-8568. ; 331:19, s. 4299-4312
-
Tidskriftsartikel (refereegranskat)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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| 62. |
- Du, Lin, et al.
(författare)
-
Sound amplification at a rectangular T-junction with merging mean flows
- 2016
-
Ingår i: Journal of Sound and Vibration. - : Academic Press. - 0022-460X .- 1095-8568. ; 367, s. 69-83
-
Tidskriftsartikel (refereegranskat)abstract
- This paper reports a numerical study on the aeroacoustic response of a rectangular T-junction with merging mean flows. The primary motivation of the work is to explain the high sound amplification, recently seen experimentally, when introducing a small merging bias flow. The acoustic results are found solving the compressible Linearized Navier-Stokes Equations (LNSEs) in the frequency domain, where the base flow is first obtained using RANS with a k-epsilon turbulence model. The model predicts the measured scattering data well, including the amplitude and Strouhal number for the peak amplification, if the effect of eddy viscosity damping is included. It is found that the base flow changes significantly with the presence of a small bias flow. Compared to pure grazing flow a strong unstable shear layer is created in the downstream main duct starting from the T-junction trailing edge. This means that the main region of vortex-sound interaction is moved away from the junction to a downstream region much larger than the junction width. To analyze the sound amplification in this region Howe's energy corollary and the growth of acoustic density are used.
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| 63. |
- Enelund, Mikael, 1965, et al.
(författare)
-
Modelling of constrained thin rubber layer with emphasis on damping
- 2007
-
Ingår i: Journal of Sound and Vibration. - : Elsevier BV. - 1095-8568 .- 0022-460X. ; 300:3-5, s. 662-675
-
Tidskriftsartikel (refereegranskat)abstract
- An interface finite element for the rubber layer in a steel-rubber-steel sandwich plate is developed. The novel element is based on a series expansion of the displacement field in the thickness direction. This technique makes it possible to achieve a high resolution of the displacement field in the thickness direction without adding more degrees-of-freedom in this direction. A fractional order viscoelastic model is used to describe the constitutive behavior of rubber. In particular, we consider a "Nitrile" type rubber and fit the model parameters to experiments. The purpose and the predictive capability of the interface element are investigated by calculating the harmonic response of sandwich plates. The results are then compared with measured responses as well as with responses obtained by a commercial general purpose finite element code and an analytical solution for a sandwich beam equation. Finally, we conclude that the interface element is accurate and efficient in the modelling of constrained rubber layers. © 2006 Elsevier Ltd. All rights reserved.
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| 64. |
- Fabre, François, et al.
(författare)
-
Sound Radiation from Railway Wheels including Ground Reflections: A half-space formulation for the Fourier Boundary Element Method
- 2021
-
Ingår i: Journal of Sound and Vibration. - : Elsevier BV. - 1095-8568 .- 0022-460X. ; 493
-
Tidskriftsartikel (refereegranskat)abstract
- Current models for the acoustic radiation from railway wheels assume free field radiation. However, slab tracks are increasingly used for new railway lines. The acoustically hard surface of those tracks makes a re-evaluation of the free field assumption relevant, as such a surface can affect the radiation efficiency of an acoustic radiator. The wheel as the acoustic radiator is most conveniently described in a cylindrical coordinate system, thus making use of its axisymmetry. While this is a viable solution for the structural vibrations, for instance by using the curved Waveguide Finite Element formulation, the axisymmetry breaks when including a reflective plane in the calculation of the acoustic radiation. A convenient method to include an infinitely large, reflective plane is by using half-space Green’s functions in combination with the Boundary Element method. This method can be formulated in cylindrical coordinates using the Fourier series BEM (FBEM). However, the FBEM has not yet been combined with half-space Green’s functions. This paper provides a half-space formulation for the FBEM, which enables e.g. the evaluation of sound radiation of railway wheels over reflective surfaces. Finally, it is shown that the assumption of free field radiation for railway wheels is valid, as there is no major contribution of the reflective plane to the radiation efficiency of the wheel. The developed method is validated against laboratory measurements as well as analytical models.
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| 65. |
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| 66. |
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| 67. |
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| 68. |
- Finnveden, Svante
(författare)
-
A quantitative criterion validating coupling power proportionality in statistical energy analysis
- 2011
-
Ingår i: Journal of Sound and Vibration. - : Elsevier. - 0022-460X .- 1095-8568. ; 330:1, s. 87-109
-
Tidskriftsartikel (refereegranskat)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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| 69. |
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| 70. |
|
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| 71. |
- Finnveden, Svante, et al.
(författare)
-
A velocity method for estimating dynamic strain and stress in pipes
- 2000
-
Ingår i: Journal of Sound and Vibration. - : Elsevier BV. - 0022-460X .- 1095-8568. ; 229:1, s. 147-182
-
Tidskriftsartikel (refereegranskat)abstract
- A velocity method for estimating dynamic strain and stress in pipe structures is investigated. With this method, predicted or measured spatial average vibration velocity and theoretically derived strain factors are used to estimate maximum strain at the ends of pipes. Theoretical investigation shows that the strain at a point is limited by an expression proportional to the square root of the strain energy density, which in turn is related to its cross-sectional average. For a reverberant field or for an infinite pipe, the average strain energy density is proportional to the mean square velocity. Upon this basis, the non-dimensional strain factor is defined as the maximum strain times the ratio of the sound velocity to the spatial root mean square vibration velocity. Measurements are made confirming that this is a descriptive non-dimensional number. Using a spectral finite element method, numerical experiments are made varying the pipe parameters and considering all 16 homogeneous boundary conditions. While indicating possible limitations of the method when equipment is mounted on pipes, the experiments verify the theoretical results. The velocity method may become useful in engineering practice for assessments of fatigue life.
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| 72. |
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| 73. |
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| 74. |
- Finnveden, Svante, 1957-
(författare)
-
Evaluation of modal density and group velocity by a finite element method
- 2004
-
Ingår i: Journal of Sound and Vibration. - : Elsevier BV. - 0022-460X .- 1095-8568. ; 273:02-jan, s. 51-75
-
Tidskriftsartikel (refereegranskat)abstract
- A finite element method (FEM), the waveguide-FEM, is used to calculate wave propagation characteristics for built-up thin-walled structures. Such characteristics are determined from a dispersion relation in the form of an eigenvalue problem established from the FE formulation. In particular, vital characteristics such as the modal density, the group velocity and the waveform are evaluated. A description of the evaluation of a dispersion relation for a channel beam, from data given by the FE formulation, is presented. Subsequently, the method for determining the modal density and group velocity from FE input data is shown in detail for the beam structure. To show the versatility of the method a second example considers a statistical energy analysis (SEA), made to establish the degree to which vibrations in a wind tunnel are transmitted to a thin-walled plate mounted into its wall. The critical input datum to the SEA model is the wind tunnel's modal density, which is calculated by the method presented.
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| 75. |
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| 76. |
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| 77. |
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| 78. |
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| 79. |
- Finnveden, Svante, et al.
(författare)
-
Waveguide finite elements for curved structures
- 2008
-
Ingår i: Journal of Sound and Vibration. - : Elsevier. - 0022-460X .- 1095-8568. ; 312:4-5, s. 644-671
-
Tidskriftsartikel (refereegranskat)abstract
- A waveguide finite element formulation for the analysis of curved structures is introduced. The formulation is valid for structures that along one axis have constant properties. It is based on a modified Hamilton's principle valid for general linear viscoelastic motion, which is derived here. Using this principle, material properties such as losses may be distributed in the system and may vary with frequency. Element formulations for isoparametric solid elements and deep shell elements are presented for curved waveguides as well as for straight waveguides. In earlier works, the curved elements have successfully been used to model a passenger car tyre. Here a simple validation example and convergence study is presented, which considers a finite length circular cylinder and all four elements presented are used, in turn, to model this structure. Calculated results compare favourably to those in the literature.
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| 80. |
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| 81. |
- Fraggstedt, Martin, et al.
(författare)
-
Power dissipation in car tyres
- 2008
-
Ingår i: Journal of Sound and Vibration. - 0022-460X .- 1095-8568.
-
Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)
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| 82. |
- Gao, K., et al.
(författare)
-
A homogenization approach for characterization of the fluid-solid coupling parameters in Biot's equations for acoustic poroelastic materials
- 2015
-
Ingår i: Journal of Sound and Vibration. - : Elsevier. - 0022-460X .- 1095-8568. ; 351, s. 251-267
-
Tidskriftsartikel (refereegranskat)abstract
- In this paper, a homogenization method is proposed to obtain the parameters of Biot's poroelastic theory from a multiscale perspective. It is assumed that the behavior of a macroscopic material point can be captured through the response of a microscopic Representative Volume Element (RVE) consisting of both a solid skeleton and a gaseous fluid. The macroscopic governing equations are assumed to be Biot's poroelastic equations and the RVE is governed by the conservation of linear momentum and the adopted linear constitutive laws under the isothermal condition. With boundary conditions relying on the macroscopic solid displacement and fluid pressure, the homogenized solid stress and fluid displacement are obtained based on energy consistency. This homogenization framework offers an approach to obtain Biot's parameters directly through the response of the RVE in the regime of Darcy's flow where the pressure gradient is dominating. A numerical experiment is performed in the form of a sound absorption test on a porous material with an idealized partially open microstructure that is described by Biot's equations where the parameters are obtained through the proposed homogenization approach. The result is evaluated by comparison with Direct Numerical Simulations (DNS), showing a superior performance of this approach compared to an alternative semiphenomenological model for estimating Biot's parameters of the studied porous material.
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| 83. |
- Gao, K., et al.
(författare)
-
Computational homogenization of sound propagation in a deformable porous material including microscopic viscous-thermal effects
- 2016
-
Ingår i: Journal of Sound and Vibration. - : Academic Press. - 0022-460X .- 1095-8568. ; 365, s. 119-133
-
Tidskriftsartikel (refereegranskat)abstract
- Porous materials like acoustic foams can be used for acoustic shielding, which is important for high-tech systems and human comfort. In this paper, a homogenization model is proposed to investigate the relation between the microstructure and the resulting macroscopic acoustic properties. The macroscopic absorption ability is due to the microscopic viscous-thermal coupling between an elastic solid skeleton and a gaseous fluid in the associated Representative Volume Element (RVE). The macro-to-micro relation is realized through the boundary conditions of the microscopic RVE, which relies on the macroscopic solid deformation and fluid pressure gradient. By assuming that the variation of the macroscopic energy per unit volume equals the volume average of the variation of the microscopic energy, the macroscopic solid stress and fluid displacement can be calculated from the corresponding microscopic quantities. Making additional assumptions on this approach, Biot's poroelastic theory is recovered. A case study is performed through the simulations of sound absorption in three porous materials, one made from aluminum and two from different polyurethane foams. For simplicity, an idealized partially open cubic microstructure is adopted. The homogenization results are evaluated by comparison with Direct Numerical Simulations (DNS), revealing an adequate performance of the approach for the studied porous material. By comparing the results of different solid materials, it is found that the solid stiffness has a limited effect when resonance does not occur. Nevertheless, due to the absence of the microscopic fluctuation, Biot's model with the parameters obtained from the homogenization approach predicts a higher resonance frequency than the DNS, whereas a full homogenization modification improves the prediction.
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| 84. |
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| 85. |
- Gebretsadik, Elias Kassa, 1975-, et al.
(författare)
-
Dynamic train-turnout interaction in an extended frequency range using a detailed model of track dynamics
- 2009
-
Ingår i: Journal of Sound and Vibration. - : Elsevier BV. - 0022-460X .- 1095-8568. ; 320:4-5, s. 893-914
-
Tidskriftsartikel (refereegranskat)abstract
- A time domain solution method for general three-dimensional dynamic interaction of train and turnout (switch and crossing) that accounts for excitation in an extended frequency range (up to several hundred Hz) is proposed. Based on a finite element (FE) model of a standard turnout design, a complex-valued modal superposition of track dynamics is applied using the first 500 eigenmodes of the turnout model. The three-dimensional model includes the distribution of structural flexibility along the turnout, such as bending and torsion of rails and sleepers, and the variations in rail cross-section and sleeper length. Convergence of simulation results is studied while using an increasing number of eigenmodes. It is shown that modes with eigenfrequencies up to at least 200 Hz have a significant influence on the magnitudes of the wheel-rail contact forces. Results from using a simplified track model with a commercial computer program for low-frequency vehicle dynamics are compared with the results from using the detailed FE model in conjunction with the proposed method.
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| 86. |
- Germonpré, M., et al.
(författare)
-
Contributions of longitudinal track unevenness and track stiffness variation to railway induced vibration
- 2018
-
Ingår i: Journal of Sound and Vibration. - : Elsevier BV. - 1095-8568 .- 0022-460X. ; 437, s. 292-307
-
Tidskriftsartikel (refereegranskat)abstract
- Dynamic train-track interaction originates from excitation mechanisms such as longitudinal track unevenness, parametric excitation due to track stiffness variation and impact excitation due to wheel flats, wheel out-of-roundness and rail joints. Track stiffness variation can be regarded as longitudinal track unevenness in loaded condition, but for the mitigation of track geometry degradation it is important to distinguish between track unevenness in unloaded condition and track stiffness variation. This paper studies how longitudinal track unevenness and track stiffness variation contribute to railway induced vibration. A case study is performed for a railway line in Furet, Sweden. Based on measured track unevenness and stiffness data from the IMV 100 track recording car, the train-track interaction forces and free field vibrations are computed for each of these two excitation mechanisms separately, as well as for a combination of both. The computed free field vibrations are in good agreement with measured vibrations at the same site. The contribution of the track stiffness variation to the interaction forces and free field vibrations is much lower than the contribution of the longitudinal track unevenness. Track stiffness variation can also be modeled as equivalent track unevenness, leading to results slightly different from those obtained when track unevenness and track stiffness variation are modeled separately, and a poorer agreement with the measured vibrations.
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| 87. |
- Gil-Negrete, N., et al.
(författare)
-
A simplified methodology to predict the dynamic stiffness of carbon-black filled rubber isolators using a finite element code
- 2006
-
Ingår i: Journal of Sound and Vibration. - : Elsevier BV. - 0022-460X .- 1095-8568. ; 296:05-apr, s. 757-776
-
Tidskriftsartikel (refereegranskat)abstract
- A new and different approach to the inclusion of the amplitude-dependent effect, known as the Fletcher-Gent effect or Payne effect, in a linear viscoelastic rubber material model is presented to predict the dynamic stiffness of filled rubber isolators using a finite element (FE) code. The technique is based on providing a linear viscoelastic model with the adequate material data set, once the dynamic strain amplitude, to which the rubber mount is subjected, is estimated. A generalized Zener model is adopted to describe the frequency-dependent behaviour of the material through the use of hereditary integrals. The dynamic strain amplitude dependence is not modelled through any friction model or plasticity theory, as usually is in literature. It is introduced by considering the frequency-dependent properties of the compound at an adequate strain value, which enforces the estimation of an equivalent strain value. As a first approximation, a quasi-static value is used as the reference value at which material properties should be provided to the linear viscoelastic model. The technique works directly in frequency domain, the dynamic stiffness of the bushing being directly obtained. The methodology is applied to evaluate the dynamic stiffness of a real bushing in working conditions with very satisfactory results. Despite the assumptions made, especially regarding the estimation of the equivalent strain amplitude value, errors of the predictions fall within the limits usually accepted by rubber manufacturers.
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| 88. |
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| 89. |
- Glav, Ragnar, 1960-, et al.
(författare)
-
Study of a folded resonator including the effects of higher order modes
- 2004
-
Ingår i: Journal of Sound and Vibration. - : Elsevier. - 0022-460X .- 1095-8568. ; 273:4-5, s. 777-792
-
Tidskriftsartikel (refereegranskat)abstract
- This paper presents a derivation of the 2-port matrix for a folded quarter-wave side-branch resonator including higher order modes but neglecting flow interaction effects. The model is restricted to coaxial geometries and two-folds. The derivation is based on the mode matching technique and is verified by measurements done on prototypes. A notable result from these experiments is the effects of a slit-like leakage close to a rigid wall. A parametrical study finally investigates the influence of various lengths and area ratios of the resonator resulting in a set of design rules.
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| 90. |
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| 91. |
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| 92. |
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| 93. |
- Gomez, Erik, et al.
(författare)
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Normal-force dependant friction in centrifugal pendulum vibration absorbers : Simulation and experimental investigations
- 2021
-
Ingår i: Journal of Sound and Vibration. - : Academic Press. - 0022-460X .- 1095-8568. ; 492
-
Tidskriftsartikel (refereegranskat)abstract
- A model of the normal-force dependant friction loss between the rotor and pendula is developed for bifilar centrifugal pendulum vibration absorbers (CPVAs). The normal-force is dominantly dependant on the rotor rotational velocity but also dependant on the pendulum path. Simulation results of the pendulum with the proposed normal-force friction model agree well with novel experimental results. Order-response simulations of the rotor-CPVA model with the proposed friction model reveal accuracy improvements on the prediction of the rotor oscillation amplitude at different rotational velocities in comparison to existing friction formulations. Derivation of the equations of motion of the rotor-CPVA is performed by Kane's method and solved numerically. The developed experimental setup is used to validate the model parameters such as friction coefficients, path parameters and relative pendulum rotation without necessitating a special test-apparatus other than standard vibration measurement equipment. CPVAs are commonly used to reduce torsional vibration created by reciprocating engines. To reduce emissions, heavy-duty vehicles manufactures are downsizing and downspeeding the combustion engine while maintaining the power output. Unfortunately, this gives rise to increased torsional vibration in the powertrain. The CPVA is a device that can reduce the torsional vibration and thus help fulfill environmental goals.
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| 94. |
- Gomez, Erik R., et al.
(författare)
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Powertrain shuffle-mode resonance suppression by means of flywheel mounted torsichrone centrifugal pendulum vibration absorbers
- 2022
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Ingår i: Journal of Sound and Vibration. - : Elsevier BV. - 0022-460X .- 1095-8568. ; 534
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Tidskriftsartikel (refereegranskat)abstract
- A flywheel mounted centrifugal pendulum absorber (CPVA) is designed to completely suppress the low frequency shuffle-mode resonance of a heavy-duty truck powertrain by exploiting the eigenfrequency veering property of the CPVA. The shuffle-mode is excited by the half-order torque of a five-cylinder engine in a downspeeded powertrain during cruising conditions. It is shown that the design of the CPVA may be performed by linear analysis of the CPVA and powertrain system. The linear design is then validated by full nonlinear simulations of the powertrain. A complete suppression of the shuffle-mode resonance is achieved with relatively small total mass of the pendula which makes it highly possible to implement in practice. Downspeeding and downsizing of combustion engines, without sacrificing the power output, are methods to reduce emissions, although, resulting in increased noise and vibration using conventional vibration reduction technology. The CPVA is an order tuned device that can help to reduce the increased vibrations and thus help to reduce the environmental impact of heavy-duty vehicles.
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| 95. |
- Gustavsson, Rolf K., et al.
(författare)
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The influence of nonlinear magnetic pull on hydropower generator rotors
- 2006
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Ingår i: Journal of Sound and Vibration. - : Elsevier BV. - 0022-460X .- 1095-8568. ; 297:3-5, s. 551-562
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Tidskriftsartikel (refereegranskat)abstract
- In large electrical machines the electromagnetic forces can in some situations have a strong influence on the rotor dynamics. One such case is when the rotor is eccentrically displaced in the generator bore. A strong unbalanced magnetic pull will then appear in the direction of the smallest air-gap. In this paper, the influence of nonlinear magnetic pull is studied for a hydropower generator where the generator spider hub does not coincide with the centre of the generator rim. The generator model consists of a four-degree-of-freedom rigid body, which is connected to an elastic shaft supported by isotropic bearings. The influence of magnetic pull is calculated for the case when the generator spider hub deviates from the centre of the generator rim. A nonlinear model of the magnetic pull is introduced to the model by radial forces and transverse moments. In the numerical analysis input parameters typical for a 70 MW hydropower generator are used. Results are presented in stability and response diagrams. The results show that this type of rotor configuration can in some cases become unstable. Therefore, it is important to consider the distance between the centreline of generator spider hub and the centreline of generator rim.
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| 96. |
- Göransson, Peter, et al.
(författare)
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Measurement and inverse estimation of 3D anisotropic flow resistivity for porous materials
- 2009
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Ingår i: Journal of Sound and Vibration. - : Elsevier BV. - 0022-460X .- 1095-8568. ; 327:3-5, s. 354-367
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents a new methodology for estimating the anisotropic flow resistivity for porous materials. From pressure measurements on a cubic or parallelepiped sample of a porous material, the flow resistivities are determined using inverse estimation. The core of the estimation is a series of 3D solutions to Darcy's law, where the flow resistivity tensor is varied until the sum of the quadratic errors between measured and computed pressures is minimised. The overall approach and experimental set-up used, enabling efficient measurements of high quality, are described in some detail together with the main steps of the measurement and estimation procedures. Results from a fibrous glass wool and a polyurethane foam are discussed and compared to standard measurement data.
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| 97. |
- Hagberg, Mats, 1951, et al.
(författare)
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The association between whole body vibration exposure and musculoskeletal disorders in the Swedish work force is confounded by lifting and posture
- 2006
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Ingår i: Journal of Sound and Vibration. - : Elsevier BV. - 0022-460X .- 1095-8568. ; 298, s. 492-498
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Tidskriftsartikel (refereegranskat)abstract
- This was a cross-sectional study based on material representing the Swedish work-force from a survey conducted in 1999, 2001 and 2003 by Statistics Sweden. Exposure to whole body vibration (WBV) was prevalent among agricultural, forestry, fishery workers and among plant and machinery operators based on a sample of 40,000 employed persons. Approximately 70% responders, that are 9798 persons answered both the interview and the questionnaire for the analysis of exposure-response. Exposure to WBV at least half the working time was associated with prevalence ratios above two for musculoskeletal symptoms in the low back, neck, shoulder/arm and hand among workers. When the exposure factors lifting and frequent bending were added to a multivariate analysis, surprisingly the magnitude of association was low between low back symptoms and WBV exposure. Interestingly, the relation between WBV exposure and symptoms in the neck, shoulder/arm and hand had the same or higher magnitude of association even when the possible confounders were in the model. For the neck, low back and shoulder/arm there was a visible increase in prevalence ratio (as high as 5 times) when combined exposures of WBV, lifting, frequent bending, twisted posture and noise were included in the analysis. © 2006 Elsevier Ltd. All rights reserved.
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| 98. |
- Heo, Yong-Ho, et al.
(författare)
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In-duct identification of a rotating sound source with high spatial resolution
- 2015
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Ingår i: Journal of Sound and Vibration. - : Elsevier BV. - 0022-460X .- 1095-8568. ; 357, s. 51-73
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 99. |
- Heo, Yong-Ho, et al.
(författare)
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In-duct identification of fluid-borne source with high spatial resolution
- 2014
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Ingår i: Journal of Sound and Vibration. - : Elsevier BV. - 0022-460X .- 1095-8568. ; 333:23, s. 6074-6089
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Tidskriftsartikel (refereegranskat)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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| 100. |
- Hillström, L., et al.
(författare)
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Identification of complex modulus from measured strains on an axially impacted bar using least squares
- 2000
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Ingår i: Journal of Sound and Vibration. - : Elsevier BV. - 0022-460X .- 1095-8568. ; 230:3, s. 689-707
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Tidskriftsartikel (refereegranskat)abstract
- The complex modulus of a material with linearly viscoelastic behaviour is identified on the basis of strains which are known, from measurements and sometimes from a free end boundary condition, at three or more sections of an axially impacted bar specimen. The aim is to improve existing identification methods based on known strains at three uniformly distributed sections by increasing the number of sections considered and by distributing them non-uniformly. The increased number of sections results in an overdetermined system of equations from which an approximate solution for the complex modulus is determined using the method of least squares. Through the non-uniform distribution of sections, critical conditions with accompanying large errors at certain frequencies are largely eliminated. Experimental tests were carried out at room temperature with two materials, viz., polypropylene and polymethyl methacrylate, five strain gauge configurations and two kinds of impact excitation. Substantial improvement in the quality of the results for complex modulus was obtained.
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