| 1. |
- Abadikhah, Hossein, 1987, et al.
(författare)
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A hierarchy of dynamic equations for micropolar plates
- 2015
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Ingår i: Journal of Sound and Vibration. - : Elsevier BV. - 1095-8568 .- 0022-460X. ; 357, s. 427-436
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Tidskriftsartikel (refereegranskat)abstract
- This work considers homogeneous isotropic micropolar plates adopting a power series expansion method in the thickness coordinate. Variationally consistent equations of motion and end boundary conditions are derived in a systematic fashion up to arbitrary order for extensional and flexural displacement cases. The plate equations are asymptotically correct to all studied orders. Numerical results are presented for various orders of the present method, other approximate theories as well as the exact three dimensional theory. The results illustrate that the present approach may render benchmark solutions provided higher order truncations are used, and act as engineering plate equations using low order truncation.
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| 2. |
- Abadikhah, Hossein, 1987, et al.
(författare)
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A hierarchy of dynamic equations for solid isotropic micropolar circular cylinders
- 2019
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Ingår i: Journal of Sound and Vibration. - : Elsevier BV. - 1095-8568 .- 0022-460X. ; 440, s. 70-82
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Tidskriftsartikel (refereegranskat)abstract
- This work considers the derivation procedure and evaluation of dynamic equations for isotropic micropolar circular cylinders by adopting a power series expansion method in the radial coordinate. Variationally consistent equations of motion together with pertinent sets of boundary conditions are expressed in a systematic fashion up to arbitrary order. The numerical results cover eigenfrequencies, mode shapes and field distributions over cross sections for axisymmetric and flexural motion adopting different sets of end boundary conditions for equations of different truncation orders of the present method. The results illustrate that the present approach may render benchmark solutions provided that higher order equations are used, and act as accurate approximate engineering solution for lower order equations.
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| 3. |
- Abdeljaber, Osama, et al.
(författare)
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Active vibration control of flexible cantilever plates using piezoelectric materials and artificial neural networks
- 2016
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Ingår i: Journal of Sound and Vibration. - : Elsevier. - 0022-460X .- 1095-8568. ; 363, s. 33-53
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Tidskriftsartikel (refereegranskat)abstract
- The study presented in this paper introduces a new intelligent methodology to mitigate the vibration response of flexible cantilever plates. The use of the piezoelectric sensor/actuator pairs for active control of plates is discussed. An intelligent neural network based controller is designed to control the optimal voltage applied on the piezoelectric patches. The control technique utilizes a neurocontroller along with a Kalman Filter to compute the appropriate actuator command. The neurocontroller is trained based on an algorithm that incorporates a set of emulator neural networks which are also trained to predict the future response of the cantilever plate. Then, the neurocontroller is evaluated by comparing the uncontrolled and controlled responses under several types of dynamic excitations. It is observed that the neurocontroller reduced the vibration response of the flexible cantilever plate significantly; the results demonstrated the success and robustness of the neurocontroller independent of the type and distribution of the excitation force.
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| 4. |
- Abdeljaber, Osama, et al.
(författare)
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Optimization of chiral lattice based metastructures for broadband vibration suppression using genetic algorithms
- 2016
-
Ingår i: Journal of Sound and Vibration. - : Elsevier. - 0022-460X .- 1095-8568. ; 369, s. 50-62
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Tidskriftsartikel (refereegranskat)abstract
- One of the major challenges in civil, mechanical, and aerospace engineering is to develop vibration suppression systems with high efficiency and low cost. Recent studies have shown that high damping performance at broadband frequencies can be achieved by incorporating periodic inserts with tunable dynamic properties as internal resonators in structural systems. Structures featuring these kinds of inserts are referred to as metamaterials inspired structures or metastructures. Chiral lattice inserts exhibit unique characteristics such as frequency bandgaps which can be tuned by varying the parameters that define the lattice topology. Recent analytical and experimental investigations have shown that broadband vibration attenuation can be achieved by including chiral lattices as internal resonators in beam-like structures. However, these studies have suggested that the performance of chiral lattice inserts can be maximized by utilizing an efficient optimization technique to obtain the optimal topology of the inserted lattice. In this study, an automated optimization procedure based on a genetic algorithm is applied to obtain the optimal set of parameters that will result in chiral lattice inserts tuned properly to reduce the global vibration levels of a finite-sized beam. Genetic algorithms are considered in this study due to their capability of dealing with complex and insufficiently understood optimization problems. In the optimization process, the basic parameters that govern the geometry of periodic chiral lattices including the number of circular nodes, the thickness of the ligaments, and the characteristic angle are considered. Additionally, a new set of parameters is introduced to enable the optimization process to explore non-periodic chiral designs. Numerical simulations are carried out to demonstrate the efficiency of the optimization process.
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| 5. |
- Abdeljaber, Osama, et al.
(författare)
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Real-time vibration-based structural damage detection using one-dimensional convolutional neural networks
- 2017
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Ingår i: Journal of Sound and Vibration. - : Elsevier. - 0022-460X .- 1095-8568. ; 388, s. 154-170
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Tidskriftsartikel (refereegranskat)abstract
- Structural health monitoring (SHM) and vibration-based structural damage detection have been a continuous interest for civil, mechanical and aerospace engineers over the decades. Early and meticulous damage detection has always been one of the principal objectives of SHM applications. The performance of a classical damage detection system predominantly depends on the choice of the features and the classifier. While the fixed and hand-crafted features may either be a sub-optimal choice for a particular structure or fail to achieve the same level of performance on another structure, they usually require a large computation power which may hinder their usage for real-time structural damage detection. This paper presents a novel, fast and accurate structural damage detection system using 1D Convolutional Neural Networks (CNNs) that has an inherent adaptive design to fuse both feature extraction and classification blocks into a single and compact learning body. The proposed method performs vibration-based damage detection and localization of the damage in real-time. The advantage of this approach is its ability to extract optimal damage-sensitive features automatically from the raw acceleration signals. Large-scale experiments conducted on a grandstand simulator revealed an outstanding performance and verified the computational efficiency of the proposed real-time damage detection method.
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| 6. |
- Aggestam, Emil, 1992, et al.
(författare)
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Multi-objective optimisation of transition zones between slab track and ballasted track using a genetic algorithm
- 2019
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Ingår i: Journal of Sound and Vibration. - : Elsevier BV. - 1095-8568 .- 0022-460X. ; 446, s. 91-112
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Tidskriftsartikel (refereegranskat)abstract
- The vertical dynamic vehicle–track interaction in a transition between ballasted track and slab track is simulated in the time domain using an extended state-space vector approach. A complex-valued modal superposition technique is applied for the linear, time-invariant and non-periodic finite element model of the railway track. By considering a multi-objective optimisation problem solved by a genetic algorithm, the maximum dynamic loads on the track structure are minimised with respect to the selected design variables. To reduce the risk of long-term degradation of track geometry due to ballast/subgrade settlement, the transition zone is designed to minimise the influence of the track stiffness gradient between the two different track forms. The methodology is demonstrated by minimising the maximum wheel–rail contact force and the maximum pressure between sleeper/panel and foundation, while the selected design variables are distributions of rail pad stiffness and sleeper spacing adjacent to the transition. From the solution of the optimisation problem, non-dominated fronts are obtained illustrating potential for a significant reduction of the dynamic loads. It is shown that the optimised design leads to a more uniform distribution of load on the foundation reducing the risk of differential track settlement. The influences of the length of the transition zone and direction of travel on the maximum dynamic loads are investigated. Prescribed irregularities in longitudinal level may be accounted for but have been neglected in the optimisation as the optimised design would be more influenced by the given irregularity than by the stiffness gradient.
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| 7. |
- Alenius, Emma, et al.
(författare)
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Large eddy simulations of acoustic-flow interaction at an orifice plate
- 2015
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Ingår i: Journal of Sound and Vibration. - : Elsevier BV. - 0022-460X .- 1095-8568. ; 345, s. 162-177
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Tidskriftsartikel (refereegranskat)abstract
- The scattering of plane waves by an orifice plate with a strong bias flow, placed in a circular or square duct, is studied through large eddy simulations and dynamic mode decomposition. The acoustic-flow interaction is illustrated, showing that incoming sound waves at a Strouhal number of 0.43 trigger a strong axisymmetric flow structure in the orifice in the square duct, and interact with a self-sustained axisymmetric oscillation in the circular duct orifice. These structures then generate a strong sound, increasing the acoustic energy at the frequency of the incoming wave. The structure triggered in the square duct is weaker than that present in the circular duct, but stronger than structures triggered by waves at other frequencies. Comparing the scattering matrix with measurements, there is a good agreement. However, the results are found to be sensitive to the inflow, where the self-sustained oscillation in the circular duct simulation is an artefact of an axisymmetric, undisturbed inflow. This illustrates a problem with using an undisturbed inflow for studying vortex-sound effects, and can be of interest when considering musical instruments, where the aim is to get maximum amplification of specific tones. Further, it illustrates that at the frequency where an amplification of acoustic energy is found for the orifice plate, the flow has a natural instability, which is suppressed by non-axisymmetry and incoming disturbances.
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| 8. |
- Avci, Onur, et al.
(författare)
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Wireless and real-time structural damage detection : a novel decentralized method for wireless sensor networks
- 2018
-
Ingår i: Journal of Sound and Vibration. - : Elsevier. - 0022-460X .- 1095-8568. ; 424, s. 158-172
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Tidskriftsartikel (refereegranskat)abstract
- Being an alternative to conventional wired sensors, wireless sensor networks (WSNs) are extensively used in Structural Health Monitoring (SHM) applications. Most of the Structural Damage Detection (SDD) approaches available in the SHM literature are centralized as they require transferring data from all sensors within the network to a single processing unit to evaluate the structural condition. These methods are found predominantly feasible for wired SHM systems; however, transmission and synchronization of huge data sets in WSNs has been found to be arduous. As such, the application of centralized methods with WSNs has been a challenge for engineers. In this paper, the authors are presenting a novel application of 1D Convolutional Neural Networks (1D CNNs) on WSNs for SDD purposes. The SDD is successfully performed completely wireless and real-time under ambient conditions. As a result of this, a decentralized damage detection method suitable for wireless SHM systems is proposed. The proposed method is based on 1D CNNs and it involves training an individual 1D CNN for each wireless sensor in the network in a format where each CNN is assigned to process the locally-available data only, eliminating the need for data transmission and synchronization. The proposed damage detection method operates directly on the raw ambient vibration condition signals without any filtering or preprocessing. Moreover, the proposed approach requires minimal computational time and power since 1D CNNs merge both feature extraction and classification tasks into a single learning block. This ability is prevailingly cost-effective and evidently practical in WSNs considering the hardware systems have been occasionally reported to suffer from limited power supply in these networks. To display the capability and verify the success of the proposed method, large-scale experiments conducted on a laboratory structure equipped with a state-of-the-art WSN are reported.
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| 9. |
- Du, Lin, et al.
(författare)
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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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| 10. |
- Gao, K., et al.
(författare)
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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
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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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| 11. |
- Gao, K., et al.
(författare)
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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
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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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| 12. |
- Germonpré, M., et al.
(författare)
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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
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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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| 13. |
- 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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| 14. |
- Hoever, Carsten, 1979, et al.
(författare)
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A model for investigating the influence of road surface texture and tyre tread pattern on rolling resistance
- 2015
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Ingår i: Journal of Sound and Vibration. - : Elsevier BV. - 1095-8568 .- 0022-460X. ; 351, s. 161-176
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Tidskriftsartikel (refereegranskat)abstract
- The reduction of rolling resistance is essential for a more environmentally friendly road transportation sector. Both tyre and road design can be utilised to reduce rolling resistance. In both cases a reliable simulation tool is needed which is able to quantify the influence of design parameters on the rolling resistance of a tyre rolling on a specific road surface. In this work a previously developed tyre/road interaction model is extended to account for different tread patterns and for losses due to small-scale tread deformation. Calculated contact forces and tyre vibrations for tyre/road interaction under steady-state rolling are used to predict rolling losses in the tyre. Rolling resistance is calculated for a series of different tyre/road combinations. Results are compared with rolling resistance measurements. The agreement between simulations and measurements is generally very good. It is found that both the tyre structure and small-scale tread deformations contribute to the rolling losses. The small-scale contribution depends mainly on the road roughness profile. The mean profile depth of the road surface is identified to correlate very well with the rolling resistance. Additional calculations are performed for non-traditional rubberised road surfaces, however, with mixed results. This possibly indicates the existence of additional loss mechanisms for these surfaces.
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| 15. |
- Holmberg, Andreas, et al.
(författare)
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A frequency domain linearized Navier-Stokes method including acoustic damping by eddy viscosity using RANS
- 2015
-
Ingår i: Journal of Sound and Vibration. - : Elsevier BV. - 0022-460X .- 1095-8568. ; 346, s. 229-247
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, a method for including damping of acoustic energy in regions of strong turbulence is derived for a linearized Navier-Stokes method in the frequency domain. The proposed method is validated and analyzed in 2D only, although the formulation is fully presented in 3D. The result is applied in a study of the linear interaction between the acoustic and the hydrodynamic held in a 2D T-junction, subject to grazing flow at Mach 0.1. Part of the acoustic energy at the upstream edge of the junction is shed as harmonically oscillating disturbances, which are conveyed across the shear layer over the junction, where they interact with the acoustic field. As the acoustic waves travel in regions of strong shear, there is a need to include the interaction between the background turbulence and the acoustic field. For this purpose, the oscillation of the background turbulence Reynolds stress, due to the acoustic Field, is modeled using an eddy Newtonian model assumption. The time averaged flow is first solved for using RANS along with a k-epsilon turbulence model. The spatially varying turbulent eddy viscosity is then added to the spatially invariant kinematic viscosity in the acoustic set of equations. The response of the 2D T-junction to an incident acoustic field is analyzed via a plane wave scattering matrix model, and the result is compared to experimental data for a T-junction of rectangular ducts. A strong improvement in the agreement between calculation and experimental data is found when the modification proposed in this paper is implemented. Discrepancies remaining are likely due to inaccuracies in the selected turbulence model, which is known to produce large errors e.g. for flows with significant rotation, which the grazing flow across the T-junction certainly is A natural next step is therefore to test the proposed methodology together with more sophisticated turbulence models.
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| 16. |
- Holmberg, Andreas, 1982-, et al.
(författare)
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Aeroacoustics of rectangular T-junctions subject to combined grazing and bias flows - An experimental investigation
- 2015
-
Ingår i: Journal of Sound and Vibration. - : Elsevier BV. - 0022-460X .- 1095-8568. ; 340, s. 152-166
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Tidskriftsartikel (refereegranskat)abstract
- Scattering matrices are determined experimentally and used to study the low amplitude interaction, between the acoustic and the hydrodynamic fields in a T-junction of rectangular ducts. In particular, combinations of grazing and bias flows are investigated in the study. It is observed that for all flow combinations, waves incident on the junction at the downstream side only are attenuated, while waves incident at the other branches may be amplified or attenuated, depending on the Strouhal number. When bias in flow is introduced to a grazing flow, there is first an increase and then a decrease in both amplification and attenuation, as the bias in-flow Mach number is increased. Comparing with T-junctions of circular ducts, the interaction is stronger for rectangular duct junctions.
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| 17. |
- Kabral, Raimo, et al.
(författare)
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Investigation of turbocharger compressor surge inception by means of an acoustic two-port model
- 2018
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Ingår i: Journal of Sound and Vibration. - : Academic Press. - 0022-460X .- 1095-8568. ; 412, s. 270-286
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Tidskriftsartikel (refereegranskat)abstract
- The use of centrifugal compressors have increased tremendously in the last decade being implemented in the modern IC engine design as a key component. However, an efficient implementation is restricted by the compression system surge phenomenon. The focus in the investigation of surge inception have mainly been on the aerodynamic field while neglecting the acoustic field. In the present work a new method based on the full acoustic 2-port model is proposed for investigation of centrifugal compressor stall and surge inception. Essentially, the compressor is acoustically decoupled from the compression system, hence enabling the determination of sound generation and the quantification of internal aero-acoustic coupling effects, both independently of the connected pipe system. These frequency dependent quantities are indicating if the compressor is prone to self-sustained oscillations in case of positive feedback when installed in a system. The method is demonstrated on experimentally determined 2-port data of an automotive turbocharger centrifugal compressor under a variety of realistic operating conditions.
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| 18. |
- Kroon, Lars, et al.
(författare)
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Neutral inclusions for diffusive acoustic fields
- 2017
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Ingår i: Journal of Sound and Vibration. - : ACADEMIC PRESS LTD- ELSEVIER SCIENCE LTD. - 0022-460X .- 1095-8568. ; 295, s. 80-89
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Tidskriftsartikel (refereegranskat)abstract
- We predict scattering cancellation in diffusive transport of acoustics waves propagating through multiple scattering media in the stationary limit. This would enable sensing of diffusive sound without disrupting the exterior acoustic field. We present design schemes for making spherical or cylindrical core-shell structures with multiple layers, characterized by homogenous and isotropic diffusion coefficients, neutral to an arbitrary applied multipole field. The double-layered sphere is found to support transparency to two concurrent multipole fields and unique cloaking solutions of arbitrary multipole order. One extra degree of freedom is provided by every layer added to the core-shell structure which may be exploited with our iterative formula for effective diffusivity for cloaking of additional field terms. From this we pass over to the long wavelength limit of ballistic sound and provide formulas for effective mass densities of multi-layered structures in spherical and cylindrical geometries with respect to multipole pressure fields. (C) 2017 Elsevier Ltd. All rights reserved.
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| 19. |
- Kårekull, Oscar, et al.
(författare)
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Revisiting the Nelson-Morfey scaling law for flow noise from duct constrictions
- 2015
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Ingår i: Journal of Sound and Vibration. - : Elsevier BV. - 0022-460X .- 1095-8568. ; 357, s. 233-244
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Tidskriftsartikel (refereegranskat)abstract
- The semi empirical scaling law by Nelson and Morfey [1] predicts the noise generation from constrictions in ducts with low Mach number flows. The results presented here demonstrate that the original model loose accuracy for constrictions of high pressure loss. An extension based on a momentum flux assumption of the dipole forces is suggested and is evaluated against measurement results for orifice geometries of higher pressure loss than earlier evaluated. A prediction model including constrictions at flow duct terminations is also suggested. Improved accuracy for the predictions of the new model are found for orifice geometries of both high and low pressure loss inside and at end of ducts. The extended model is finally evaluated by measurementson a regular ventilation air terminal device.
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| 20. |
- Li, Xin, 1985, et al.
(författare)
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Simulation of vertical dynamic vehicle-track interaction in a railway crossing using Green's functions
- 2017
-
Ingår i: Journal of Sound and Vibration. - : Elsevier BV. - 1095-8568 .- 0022-460X. ; 410, s. 318-329
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Tidskriftsartikel (refereegranskat)abstract
- Vertical dynamic vehicle-track interaction in the through route of a railway crossing is simulated in the time domain based on a Green's function approach for the track in combination with an implementation of Kalker's variational method to solve the non-Hertzian, and potentially multiple, wheel-rail contact. The track is described by a linear, three-dimensional and non-periodic finite element model of a railway turnout accounting for the variations in rail cross-sections and sleeper lengths, and including baseplates and resilient elements. To reduce calculation time due to the complexity of the track model, involving a large number of elements and degrees-of-freedom, a complex-valued modal superposition with a truncated mode set is applied before the impulse response functions are calculated at various positions along the crossing panel. The variation in three-dimensional contact geometry of the crossing and wheel is described by linear surface elements. In each time step of the contact detection algorithm, the lateral position of the wheelset centre is prescribed but the contact positions on wheel and rail are not, allowing for an accurate prediction of the wheel transition between wing rail and crossing rail. The method is demonstrated by calculating the wheel-rail impact load and contact stress distribution for a nominal S1002 wheel profile passing over a nominal crossing geometry. A parameter study is performed to determine the influence of vehicle speed, rail pad stiffness, lateral wheelset position and wheel profile on the impact load generated at the crossing. It is shown that the magnitude of the impact load is more influenced the wheel-rail contact geometry than by the selection of rail pad stiffness.
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| 21. |
- Li, Xin, 1985, et al.
(författare)
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Simulation of wheel–rail impact load and sleeper–ballast contact pressure in railway crossings using a Green's function approach
- 2019
-
Ingår i: Journal of Sound and Vibration. - : Elsevier BV. - 1095-8568 .- 0022-460X. ; 463
-
Tidskriftsartikel (refereegranskat)abstract
- A method for the simulation of dynamic vehicle–track interaction and evaluation of measures to improve the design of railway crossings is presented. To accurately represent the high-frequency dynamics and non-linear contact conditions of the vehicle–track system, the vertical interaction between a wheelset and the crossing is simulated in the time domain using a Green's function approach based on extensive finite element models of track and wheelset in combination with an implementation of Kalker's variational method to solve the non-Hertzian, and potentially multiple, wheel–rail contact. Both wheels of the wheelset in simultaneous contact with the crossing rail and the outer rail are considered. Rigid and flexible wheelset models are compared. The sampled contact geometry of the crossing, including the discrete irregularity between the wing rail and the crossing nose, is used to determine a three-dimensional surface geometry between each pair of adjacent rail cross-sections. A parameter study is performed to investigate the influence of crossing design on the maximum vertical wheel–rail contact force and the contact pressure generated at the sleeper–ballast interface. It is concluded that a design with a combination of increased sleeper width, softer rail pads and implementation of under sleeper pads (USP) will reduce the track stiffness gradients in the crossing panel and mitigate the risk of differential track settlement by lowering the sleeper–ballast contact pressure.
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| 22. |
- Lundberg, Oskar, et al.
(författare)
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A nonlinear state-dependent model for vibrations excited by roughness in rolling contacts
- 2015
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Ingår i: Journal of Sound and Vibration. - : Elsevier BV. - 0022-460X .- 1095-8568. ; 345:9, s. 197-213
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Tidskriftsartikel (refereegranskat)abstract
- A state-dependent method to model contact nonlinearities in rolling contacts is proposed. By pre-calculation of contact stiffness and contact filters as functions of vertical relative displacement, a computationally efficient modelling approach based on a moving point force description is developed. Simulations using the state-dependent model have been analysed by comparison with measurements. Results from the investigated case consisting of a steel ball rolling over a steel beam having two different degrees of roughness - show good agreement between nonlinear simulations and measured beam vibrations. The promising results obtained with the proposed method are potentially applicable to wheel rail interaction and rolling element bearings.
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| 23. |
- Lundberg, Oskar E., et al.
(författare)
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The influence of surface roughness on the contact stiffness and the contact filter effect in nonlinear wheel-track interaction
- 2016
-
Ingår i: Journal of Sound and Vibration. - : Academic Press. - 0022-460X .- 1095-8568. ; 366, s. 429-446
-
Tidskriftsartikel (refereegranskat)abstract
- A state-dependent contact model including nonlinear contact stiffness and nonlinear contact filtering is used to calculate contact forces and rail vibrations with a time-domain wheel-track interaction model. In the proposed method, the full three-dimensional contact geometry is reduced to a point contact in order to lower the computational cost and to reduce the amount of required input roughness-data. Green's functions including the linear dynamics of the wheel and the track are coupled with a point contact model, leading to a numerically efficient model for the wheel-track interaction. Nonlinear effects due to the shape and roughness of the wheel and the rail surfaces are included in the point contact model by pre-calculation of functions for the contact stiffness and contact filters. Numerical results are compared to field measurements of rail vibrations for passenger trains running at 200 kph on a ballast track. Moreover, the influence of vehicle pre-load and different degrees of roughness excitation on the resulting wheel-track interaction is studied by means of numerical predictions.
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| 24. |
- Negreira, Juan, et al.
(författare)
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Psycho-vibratory evaluation of timber floors - Towards the determination of design indicators of vibration acceptability and vibration annoyance
- 2015
-
Ingår i: Journal of Sound and Vibration. - : Elsevier BV. - 0022-460X .- 1095-8568. ; 340, s. 383-408
-
Tidskriftsartikel (refereegranskat)abstract
- In timber housing constructions, vibrations can be a nuisance for inhabitants. Notably, the vibrational response of wooden floor systems is an issue in need of being dealt with more adequately in the designing of such buildings. Studies addressing human response to vibrations are needed in order to be able to better estimate what level of vibrations in dwellings can be seen as acceptable. In the present study, measurements on five different wooden floors were performed in a laboratory environment at two locations in Sweden (SP in Växjö and LU in Lund). Acceleration measurements were carried out while a person either was walking on a particular floor or was seated in a chair placed there as the test leader was walking on the floor. These participants filled out a questionnaire regarding their perception and experiencing of the vibrations in question. Independently of the subjective tests, several static and dynamic characteristics of the floors were determined through measurements. The ultimate aim was to develop indicators of human response to floor vibrations, specifically those regarding vibration acceptability and vibration annoyance, their being drawn based on relationships between the questionnaire responses obtained and the parameter values determined on the basis of the measurements carried out. To that end, use was made of multilevel regression. Although the sample of floors tested was small, certain clear trends could be noted. The first eigenfrequency (calculated in accordance with Eurocode 5) and Hu and Chui׳s criterion (calculated from measured quantities) proved to be the best indicators of vibration annoyance, and the Maximum Transient Vibration Value (computed on the basis of the accelerations experienced by the test subjects) to be the best indicator of vibration acceptability.
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| 25. |
- Nielsen, Jens, 1963, et al.
(författare)
-
A hybrid model for prediction of ground-borne vibration due to discrete wheel/rail irregularities
- 2015
-
Ingår i: Journal of Sound and Vibration. - : Elsevier BV. - 1095-8568 .- 0022-460X. ; 345, s. 103-120
-
Tidskriftsartikel (refereegranskat)abstract
- A hybrid model for the prediction of ground-borne vibration due to discrete wheel and rail irregularities, such as wheel flats, dipped welds and insulated rail joints, is presented. The hybrid model combines the simulation of vertical wheel-rail contact force in the time domain, accounting for parametric excitation due to sleeper periodicity and impact excitation induced by loss of wheel-rail contact, and calculation of ground-borne vibration in the frequency-wavenumber domain considering a layered soil model. The model is demonstrated by investigating the influence of wheel flat size and vehicle speed on maximum vertical wheel-rail contact force and free field ground vibration. It is shown that magnitudes of impact load and ground vibration are increasing with increasing wheel flat length (and depth), but the influence of vehicle speed is not as evident. Higher vehicle speeds often lead to loss of wheel-rail contact and severe impact loads but the frequency content of such impact loads is shifted to higher frequencies which may be less significant for ground vibration.
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| 26. |
- Nielsen, Jens, 1963, et al.
(författare)
-
Railway track geometry degradation due to differential settlement of ballast/subgrade – Numerical prediction by an iterative procedure
- 2018
-
Ingår i: Journal of Sound and Vibration. - : Elsevier BV. - 1095-8568 .- 0022-460X. ; 412, s. 441-456
-
Tidskriftsartikel (refereegranskat)abstract
- An iterative procedure for numerical prediction of long-term degradation of railway track geometry (longitudinal level) due to accumulated differential settlement of ballast/subgrade is presented. The procedure is based on a time-domain model of dynamic vehicle–track interaction to calculate the contact loads between sleepers and ballast in the short-term, which are then used in an empirical model to determine the settlement of ballast/subgrade below each sleeper in the long-term. The number of load cycles (wheel passages) accounted for in each iteration step is determined by an adaptive step length given by a maximum settlement increment. To reduce the computational effort for the simulations of dynamic vehicle–track interaction, complex-valued modal synthesis with a truncated modal set is applied for the linear subset of the discretely supported track model with non-proportional spatial distribution of viscous damping. Gravity loads and state-dependent vehicle, track and wheel–rail contact conditions are accounted for as external loads on the modal model, including situations involving loss of (and recovered) wheel–rail contact, impact between hanging sleeper and ballast, and/or a prescribed variation of non-linear track support stiffness properties along the track model. The procedure is demonstrated by calculating the degradation of longitudinal level over time as initiated by a prescribed initial local rail irregularity (dipped welded rail joint).
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| 27. |
- Okhovat, Reza, 1984, et al.
(författare)
-
Dynamic equations for an isotropic spherical shell using the power series method and surface differential operators
- 2017
-
Ingår i: Journal of Sound and Vibration. - : Elsevier BV. - 1095-8568 .- 0022-460X. ; 393, s. 415-424
-
Tidskriftsartikel (refereegranskat)abstract
- Dynamic equations for an isotropic spherical shell are derived by using a series expansion technique. The displacement field is split into a scalar (radial) part and a vector (tangential) part. Surface differential operators are introduced to decrease the length of all equations. The starting point is a power series expansion of the displacement components in the thickness coordinate relative to the mid-surface of the shell. By using the expansions of the displacement components, the three-dimensional elastodynamic equations yield a set of recursion relations among the expansion functions that can be Used to eliminate all but the four of lowest order and to express higher order expansion functions in terms of those of lowest orders. Applying the boundary conditions on the surfaces of the spherical shell and eliminating all but the four lowest order expansion functions give the shell equations as a power series in the shell thickness. After lengthy manipulations, the final four shell equations are obtained in a relatively compact form which are given to second order in shell thickness explicitly. The eigenfrequencies are compared to exact three-dimensional theory with excellent agreement and to membrane theory.
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| 28. |
- Ottermo, Fredric, 1975-, et al.
(författare)
-
Location of aerodynamic noise sources from a 200 kW vertical-axis wind turbine
- 2017
-
Ingår i: Journal of Sound and Vibration. - London : Elsevier. - 0022-460X .- 1095-8568. ; 400, s. 154-166
-
Tidskriftsartikel (refereegranskat)abstract
- Noise levels emitted from a 200 kW H-rotor vertical-axis wind turbine have been measured using a microphone array at four different positions, each at a hub-height distance from the tower. The microphone array, comprising 48 microphones in a spiral pattern, allows for directional mapping of the noise sources in the range of 500 Hz to 4 kHz. The produced images indicate that most of the noise is generated in a narrow azimuth-angle range, compatible with the location where increased turbulence is known to be present in the flow, as a result of the previous passage of a blade and its support arms. It is also shown that a semi-empirical model for inflow-turbulence noise seems to produce noise levels of the correct order of magnitude, based on the amount of turbulence that could be expected from power extraction considerations.
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| 29. |
- Papaioannou, Georgios, et al.
(författare)
-
An approach for minimizing the number of objective functions in the optimization of vehicle suspension systems
- 2018
-
Ingår i: Journal of Sound and Vibration. - : Academic Press. - 0022-460X .- 1095-8568. ; 435, s. 149-169
-
Tidskriftsartikel (refereegranskat)abstract
- In recent studies, the suspension parameters of a vehicle model are estimated using multi-objective optimization procedures with genetic algorithms in order to overcome the well known conflict of ride comfort and road holding. However, the researchers sometimes end up using more than one objective function representing the same requirement, growing the dimension of the optimization problem. Thus, the optimization procedure becomes very quickly ineffective and the merits of the GAs are put aside because of the increased computational time of the simulations. This work focuses on indicating that the inconsiderate selection of objective functions noticed in the literature, in order to obtain the optimum solution of a suspension design, doesn’t lead to extra quality in the solution. In this direction, six objective functions widely used in the literature depicting the ride comfort and the road holding, were selected. In our experiments, various SOO approaches (Part A) and two MOO approaches (Part B and C) were selected, where Part B is proposing a novel way of handling the optimization objectives. All the MOO approaches presented combine GAs for obtaining the Pareto set and a sorting algorithm for pointing out their optimum solution among the Pareto alternatives. The optimum solutions of the two approaches are presented and compared in terms of convergence and computational time, concluding to the fact that the economy in the objective functions could provide not only a better solution but also could save significant computational time.
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| 30. |
- Peerlings, Luck, 1988-, et al.
(författare)
-
Experimental investigation of the aero-acoustic interaction at an area-expansion
- 2019
-
Ingår i: Journal of Sound and Vibration. - : Academic Press. - 0022-460X .- 1095-8568. ; 457, s. 197-211
-
Tidskriftsartikel (refereegranskat)abstract
- Experimental results on the aero-acoustic interaction at an area expansion are scarce. In this study, new experimental data is acquired of the aero-acoustic interaction at an area expansion and compared with recent modeling efforts. The aero-acoustic interaction at an area expansion with expansion ratio eta = 0.309 is investigated by measuring the scattering matrix for plane waves at 5 different flow speeds in the incompressible regime. The experimental results are complimented with a comprehensive uncertainty analysis to determine the precision of the data. The scattering coefficients together with derived quantities such as absorption coefficients and dimensionless end corrections are compared against recent analytical results. It is shown that there is consistent deviation between the models and measurement results for certain scattering coefficients. The measured end correction on Strouhal number close to the critical Strouhal number shows a relatively abrupt change. This in comparison with the models, where the change is predicted to be more gradual. Similar observations are made for the absorption coefficient for waves incident upstream of the area expansion, although a qualitative comparison is difficult to make in this case because of the strong influence of the flow downstream of the area-expansion on the results.
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| 31. |
- Pignier, Nicolas, 1988-, et al.
(författare)
-
Identifying equivalent sound sources from aeroacoustic simulations using a numerical phased array
- 2017
-
Ingår i: Journal of Sound and Vibration. - : Elsevier. - 0022-460X .- 1095-8568. ; 394C, s. 203-219
-
Tidskriftsartikel (refereegranskat)abstract
- An application of phased array methods to numerical data is presented, aimed at identifying equivalent flow sound sources from aeroacoustic simulations. Based on phased array data extracted from compressible flow simulations, sound source strengths are computed on a set of points in the source region using phased array techniques assuming monopole propagation. Two phased array techniques are used to compute the source strengths: an approach using a Moore-Penrose pseudo-inverse and a beamforming approach using dual linear programming (dual-LP) deconvolution. The first approach gives a model of correlated sources for the acoustic field generated from the flow expressed in a matrix of cross- and auto-power spectral values, whereas the second approach results in a model of uncorrelated sources expressed in a vector of auto-power spectral values. The accuracy of the equivalent source model is estimated by computing the acoustic spectrum at a far-field observer. The approach is tested first on an analytical case with known point sources. It is then applied to the example of the flow around a submerged air inlet. The far-field spectra obtained from the source models for two different flow conditions are in good agreement with the spectra obtained with a Ffowcs Williams-Hawkings integral, showing the accuracy of the source model from the observer's standpoint. Various configurations for the phased array and for the sources are used. The dual-LP beamforming approach shows better robustness to changes in the number of probes and sources than the pseudo-inverse approach. The good results obtained with this simulation case demonstrate the potential of the phased array approach as a modelling tool for aeroacoustic simulations.
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| 32. |
- Rehbinder, Göran
(författare)
-
Motion of a torsion pendulum immersed in a linear viscous liquid. Influence of wave phenomena
- 2015
-
Ingår i: Journal of Sound and Vibration. - : Elsevier. - 0022-460X .- 1095-8568. ; 361, s. 272-289
-
Tidskriftsartikel (refereegranskat)abstract
- A cylindrical pendulum, which is suspended by an elastic rod or wire and immersed in a viscid liquid in a cylindrical container, can undergo rotating oscillations. The propagation velocity of vorticity perturbations in the gap between the cylinder and the container is assumed to be finite. This means that the acceleration of the liquid is characterized by not only the viscosity but also by a relaxation time constant. The propagation velocity of elastic torsional waves in the rod is assumed to be finite. The equations that describe the motion of such a complicated compound system are linear and have been solved in closed form. The solution shows that there is a considerable deviation between the exact solution and the simple quasi-steady solution. The most remarkable conclusion is that the classical quasi-steady solution for very weak damping is incompatible with the general solution. Propagation of elastic waves in the suspension rod and propagation of vorticity waves in the liquid have a great influence on the rotational motion of the pendulum. The purpose of this study is to formulate the criteria that make the classical quasi-steady analysis valid. The derived solution permits also measurement of viscosity and a conceivable relaxation coefficient of the liquid as well.
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| 33. |
- Sack, Stefan, 1989-, et al.
(författare)
-
Investigation of orifice aeroacoustics by means of multi-port methods
- 2017
-
Ingår i: Journal of Sound and Vibration. - : Academic Press. - 0022-460X .- 1095-8568. ; 407, s. 32-45
-
Tidskriftsartikel (refereegranskat)abstract
- Comprehensive methods to cascade active multi-ports, e.g., for acoustic network prediction, have until now only been available for plane waves. This paper presents procedures to combine multi-ports with an arbitrary number of considered duct modes. A multi-port method is used to extract complex mode amplitudes from experimental data of single and tandem in-duct orifice plates for Helmholtz numbers up to around 4 and, hence, beyond the cut-on of several higher order modes. The theory of connecting single multi-ports to linear cascades is derived for the passive properties (the scattering of the system) and the active properties (the source cross-spectrum matrix of the system). One scope of this paper is to investigate the influence of the hydrodynamic near field on the accuracy of both the passive and the active predictions in multi-port cascades. The scattering and the source cross-spectrum matrix of tandem orifice configurations is measured for three cases, namely, with a distance between the plates of 10 duct diameter, for which the downstream orifice is outside the jet of the upstream orifice, 4 duct diameter, and 2 duct diameter (both inside the jet). The results are compared with predictions from single orifice measurements. It is shown that the scattering is only sensitive to disturbed inflow in certain frequency ranges where coupling between the flow and sound field exists, whereas the source cross-spectrum matrix is very sensitive to disturbed inflow for all frequencies. An important part of the analysis is based on an eigenvalue analysis of the scattering matrix and the source cross-spectrum matrix to evaluate the potential of sound amplification and dominant source mechanisms.
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| 34. |
- Sack, Stefan, et al.
(författare)
-
Numerical eduction of active multi-port data for in-duct obstructions
- 2017
-
Ingår i: Journal of Sound and Vibration. - : Academic Press. - 0022-460X .- 1095-8568. ; 411, s. 328-345
-
Tidskriftsartikel (refereegranskat)abstract
- A numerical method for aeroacoustic source characterization of in-duct components at frequencies beyond the cut-on frequencies of several acoustic modes is presented. Assuming linearity and time invariance, any ducted component can be fully characterized using a network (multi-port) model including source strength and scattering. A two-step multi-source approach is applied to numerical data in order to educe the multi-port characteristics. First, a scale resolving compressible flow simulation, here the Improved Delayed Detached Eddy Simulation (IDDES), is run to compute the channel flow that also contains the acoustic sources. Second, a linear acoustic computation, here the Linearized Navier Stokes Equations (LNSE), around a mean flow is solved for different acoustic loads to determine the component's scattering. The work uncovers the high potential of two-step numerical multi-port eduction methods. Particularly, it is shown that the acoustic source power spectra can be accurately extracted from IDDES data and the total acoustic power prediction is very good. Furthermore, a good result in the scattering data obtained from a second computationally inexpensive LNSE computation is achieved. The approach is interesting when describing mid-size duct systems, for example ventilation systems in aircraft and buildings, with a moderate number of higher order modes propagating in the considered frequency range. Therefore, the increasing availability of compressible flow data opens a wide field of applications.
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| 35. |
- Staaf, Henrik, 1976, et al.
(författare)
-
Achieving increased bandwidth for 4 degree of freedom self-tuning energy harvester
- 2018
-
Ingår i: Journal of Sound and Vibration. - : Elsevier BV. - 1095-8568 .- 0022-460X. ; 420, s. 165-173
-
Tidskriftsartikel (refereegranskat)abstract
- The frequency response of a self-tuning energy harvester composed of two piezoelectric cantilevers connected by a middle beam with a sliding mass is investigated. Measurements show that incorporation of a free-sliding mass increases the bandwidth. Using an analytical model, the system is explained through close investigation of the resonance modes. Resonance mode behavior further suggests that, by breaking the symmetry of the system, even broader bandwidths are achievable.
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| 36. |
- Sundström, Elias, et al.
(författare)
-
Acoustic signature of flow instabilities in radial compressors
- 2018
-
Ingår i: Journal of Sound and Vibration. - : Elsevier. - 0022-460X .- 1095-8568. ; 434, s. 221-236
-
Tidskriftsartikel (refereegranskat)abstract
- Rotating stall and surge are flow instabilities contributing to the acoustic noise generated in centrifugal compressors at low mass flow rates. Their acoustic generation mechanisms are exposed employing compressible Large Eddy Simulations (LES). The LES data are used for calculating the dominant acoustic sources emerging at low mass flow rates. They give the inhomogeneous character of the Ffowcs Williams and Hawkings (FW-H) wave equation. The blade loading term associated with the unsteady pressure loads developed on solid surfaces (dipole in character) is found to be the major contributor to the aerodynamically generated noise at low mass flow rates. The acoustic source due to the velocity variations and compressibility effects (quadrupole in character) as well as the acoustic source caused by the displacement of the fluid due to the accelerations of the solid surfaces (monopole in character) were found to be not as dominant. We show that the acoustic source associated with surge is generated by the pressure oscillation, which is governed by the tip leakage flow. The vortical structures of rotating stall are interacting with the impeller. These manipulate the flow incidence angles and cause thereby unsteady blade loading towards the discharge. A low-pressure sink between 4 and 6 o'clock causes a halving of the perturbation frequencies at low mass flow rates operating conditions. From two point space-time cross correlation analysis based on circumferential velocity in the diffuser it was found that the rotating stall cell propagation speed increases locally in the low pressure zone under the volute tongue. It was also found that rotating stall can coexist with surge operating condition, but the feature is then seen to operate over a broader frequency interval.
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| 37. |
- Surendran, Aswathy, et al.
(författare)
-
Aeroacoustic response of an array of tubes with and without bias-flow
- 2018
-
Ingår i: Journal of Sound and Vibration. - : Academic Press. - 0022-460X .- 1095-8568. ; 434, s. 1-16
-
Tidskriftsartikel (refereegranskat)abstract
- Heat exchangers, consisting of tube arrays in a cross-flow are a vital component of power generation systems. They are of interest from an acoustic point of view, because they can reflect, transmit and absorb an incident sound wave; in other words, they have the potential to act as a sound absorber and even as a passive control device to prevent a thermoacoustic instability in the power generation system. This paper presents a fundamental study of the aeroacoustic response of a tube array with and without bias-flow (also called cross-flow). The study has a theoretical and experimental side. On the theoretical side, a new model, based on the assumption of quasi-steady flow, was developed to predict the acoustic reflection and transmission coefficient of a tube array with bias-flow. Also, the model by Huang and Heckl (Huang and Heckl, 1993, Acustica 78, 191-200) for the case without bias-flow was evaluated. On the experimental side, flow-duct experiments using a multi-microphone technique were performed to validate the predictions from both models. The agreement was found to be very good for low frequencies. The measurements revealed the limit of validity of the quasi-steady model in terms of the Strouhal number. Although this limit is quite low, our quasi-steady model can serve as a valuable tool for designers of heat exchangers.
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| 38. |
- Temiz, Muttalip Askin, et al.
(författare)
-
Non-linear acoustic transfer impedance of micro-perforated plates with circular orifices
- 2016
-
Ingår i: Journal of Sound and Vibration. - : Academic Press. - 0022-460X .- 1095-8568. ; 366, s. 418-428
-
Tidskriftsartikel (refereegranskat)abstract
- A practical description of the transitional behavior of micro -perforated plates (MPPs) is provided between the linear and strongly non-linear regimes. Micro -perforated plates are efficient sound absorbers whose application areas vary from room acoustics to duct acoustics. Although there are accurate models for the linear and strongly non-linear acoustic behavior of MPPs, the transition from one to another has not been a focus of interest so far. A series of measurements are performed with MPP samples for various excitation amplitudes. The deviation from the linear impedance is found to be a function of excitation amplitude and oscillating viscous boundary layer thickness, expressed in terms of the Strouhal number and the Shear number. Typical for MPPs is a Shear number of order unity, implying that the viscous boundary layer thickness is in the order of the perforation radius. Using the measurement data, expressions are proposed for calculating the non-linear acoustic resistance and reactance for circular perforations with sharp square edges. Some additional data is provided for the higher Shear number range. The behavior at low amplitudes for high Shear numbers deviates strongly from the typical MPP behavior. This is due to local vortex shedding at the sharp edges of the perforation.
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| 39. |
- Torstensson, Peter, 1981-, et al.
(författare)
-
Wheel–rail impact loads and noise generated at railway crossings : Influence of vehicle speed and crossing dip angle
- 2019
-
Ingår i: Journal of Sound and Vibration. - : Academic Press. - 0022-460X .- 1095-8568. ; 456, s. 119-136
-
Tidskriftsartikel (refereegranskat)abstract
- Wheel–rail impact loads and noise at railway crossings are calculated by applying a hybrid prediction model. It combines the simulation of non-linear vertical dynamic vehicle‒track interaction in the time domain and the prediction of sound pressure level using a linear frequency-domain model. The two models are coupled based on the concept of an equivalent roughness spectrum. The time-domain model uses moving Green's functions for the linear vehicle and track models, accounting for wheel structural flexibility and a discretely supported rail with spatially-varying beam properties, and a non-Hertzian wheel–rail contact model. Three-dimensional surface geometry of the wheel and crossing is accounted for in the solution of the wheel–rail contact. The hybrid model is compared against field measurements and is demonstrated by investigating the influence of vehicle speed and crossing geometry on the radiated impact noise. Based on simulation results, it is concluded that the impact loads and noise can be mitigated by reducing the effective dip angle at the crossing, which is determined by the vertical trajectory of the wheel when making the transition between wing rail and crossing nose.
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| 40. |
- Wang, Bochao, et al.
(författare)
-
A nonlinear constitutive model by spring, fractional derivative and modified bounding surface model to represent the amplitude, frequency and the magnetic dependency for Magneto-sensitive rubber
- 2019
-
Ingår i: Journal of Sound and Vibration. - : Academic Press. - 0022-460X .- 1095-8568. ; 438, s. 344-352
-
Tidskriftsartikel (refereegranskat)abstract
- Magneto-sensitive (MS) rubber is a kind of smart material mainly consisting of magnetizable particles and rubber. Inspired by experimental observation that the shear modulus for MS rubber is strongly dependent on amplitude, frequency and magnetic field; while the impact for the magnetic field and strain to the loss factor is relatively small, a new nonlinear constitutive model for MS rubber is presented. It consists of a fractional viscoelastic model, an elastic model and a bounding surface model with parameters sensitive to the magnetic field. To our knowledge, it is the first time that the bounding surface model is incorporated with the magnetic sensitivity and used to predict the mechanical properties for MS rubber. After comparison with the measurement results, it is found that the shear modulus and the loss factor derived from the simulation fit well with the experimental data. This new constitutive model with only eight parameters can be utilized to describe the amplitude, frequency and the magnetic field dependence for MS rubber. It provides a possible new way to understand the mechanical behavior for MS rubber. More importantly, the constitutive model with an accurate prediction property for the dynamic performance of MS rubber is of interest for MS rubber applications in noise and vibration reduction area.
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| 41. |
- Wei, X. F., et al.
(författare)
-
Mitigation of under-expanded supersonic jet noise through stepped nozzles
- 2019
-
Ingår i: Journal of Sound and Vibration. - : Academic Press. - 0022-460X .- 1095-8568. ; 459
-
Tidskriftsartikel (refereegranskat)abstract
- An experimental investigation into noise reduction of supersonic jets through nozzle trailing-edge modifications was conducted, whereby far-field acoustic measurements were captured for two different stepped nozzles under two distinct under-expanded conditions. When compared to a baseline nozzle, results show that stepped nozzles lead to significant noise reductions at certain polar and azimuthal angles. In particular, a maximum noise reduction of 6 dB is observed for the longest stepped nozzle at a nozzle-pressure-ratio of 4 and 0 degrees azimuthal angle. Spectral analysis shows that the noise reduction is mainly due to reduction in broadband shock associated noise and elimination of jet screech phenomenon. Abrupt changes in nozzle lip lengths of the stepped nozzles appear to disrupt acoustic feedback loop, thus resulting in screech cessation. Qualitative schlieren imaging and quantitative schlieren measurements were subsequently performed to correlate the shock structures and density gradient fields with the resulting noise components. Unlike those produced by the baseline nozzle, shock structures generated by the stepped nozzles are highly irregular and the jet plumes undergo discernible deflections. Lastly, the reduction in broadband shock associated noise is related to the lower shock strengths, as demonstrated by the density gradient profiles.
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| 42. |
- Weng, Chenyang, et al.
(författare)
-
On the calculation of the complex wavenumber of plane waves in rigid-walled low-Mach-number turbulent pipe flows
- 2015
-
Ingår i: Journal of Sound and Vibration. - : Elsevier BV. - 0022-460X .- 1095-8568. ; 354, s. 132-153
-
Tidskriftsartikel (refereegranskat)abstract
- A numerical method for calculating the wavenumbers of axisymmetric plane waves in rigid walled low-Mach-number turbulent flows is proposed, which is based on solving the linearized Navier-Stokes equations with an eddy viscosity model. In addition, theoretical models for the wavenurnbers are reviewed, and the main effects (the viscothermal effects, the mean flow convection and refraction effects, the turbulent absorption, and the moderate compressibility effects) which may influence the sound propagation are discussed. Compared to the theoretical models, the proposed numerical method has the advantage of potentially including more effects in the computed wavenurnbers.The numerical results of the vvavenumbers are compared with the reviewed theoretical models, as well as experimental data from the literature. It shows that the proposed numerical method can give satisfactory prediction of both the real part (phase shift) and the imaginary part (attenuation) of the measured wavenumbers, especially when the refraction effects or the turbulent absorption effects become important.
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| 43. |
- Winroth, Julia, 1981, et al.
(författare)
-
Contact stiffness considerations when simulating tyre/road noise
- 2017
-
Ingår i: Journal of Sound and Vibration. - : Elsevier BV. - 1095-8568 .- 0022-460X. ; 409, s. 274-286
-
Tidskriftsartikel (refereegranskat)abstract
- Tyre/road simulation tools that can capture tyre vibrations, rolling resistance and noise generation are useful for understanding the complex processes that are involved and thereby promoting further development and optimisation. The most detailed tyre/road contact models use a spatial discretisation of the contact and assume an interfacial stiffness to account for the small-scale roughness within the elements. This interfacial stiffness has been found to have a significant impact on the simulated noise emissions but no thorough investigations of this sensitivity have been conducted. Three mechanisms are thought to be involved: The horn effect, the modal composition of the vibrational field of the tyre and the contact forces exciting the tyre vibrations. This study used a numerical tyre/road noise simulation tool based on physical relations to investigate these aspects. The model includes a detailed time-domain contact model with linear or non-linear contact springs that accounts for the effect of local tread deformation on smaller length scales. Results confirm that an increase in contact spring stiffness causes a significant increase of the simulated tyre/road noise. This is primarily caused by a corresponding increase in the contact forces, resulting in larger vibrational amplitudes. The horn effect and the modal composition are relatively unaffected and have minor effects on the radiated noise. A more detailed non-linear contact spring formulation with lower stiffness at small indentations results in a reduced high-frequency content in the contact forces and the simulated noise.
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| 44. |
- Yanaz Çınar, Ö., et al.
(författare)
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Sudden area expansion in ducts with flow – A comparison between cylindrical and rectangular modelling
- 2017
-
Ingår i: Journal of Sound and Vibration. - : Academic Press. - 0022-460X .- 1095-8568. ; 396, s. 307-324
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Tidskriftsartikel (refereegranskat)abstract
- The acoustic properties of an area expansion are analyzed for frequencies where flow acoustic interaction may have a significant influence due to flow separation and vortex shedding. It is investigated why this interaction, which is seen in experimental data on a cylindrical duct as a resonance at a particular Strouhal number of order one, is present in rectangular but not in cylindrical modelling that would be expected to be more realistic; both models consider a plug flow. An analytic method that is suitable for identifying possible reasons for the discrepancies between the two geometries is used. The previously published rectangular model is generalized to the cylindrical case and both models are used to simulate results for all elements in the plane wave scattering matrix and for all parameters for which experimental results are available. The comparison between the two models and between models and measured data is thus not restricted to the flow acoustic induced resonance. The results show that the two geometries in general perform equally when compared with the experimental results, but that the rectangular modelling indeed performs better for some cases. This occurs around a critical Strouhal number, and for higher Mach number. Using the analytic form of the solution, it is shown that the observed discrepancy is related to interaction between the damped hydrodynamic mode and a downstream propagating higher order acoustic mode. Such interaction is not present in the corresponding quiescent duct, and is related to the presence of the shear layer. The analysis shows that the structure of the higher order acoustic modes is different for the cylindrical and rectangular case, respectively, causing the difference in resonant behaviour.
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| 45. |
- Yuan, Z. H., et al.
(författare)
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Benchmark solution for vibrations from a moving point source in a tunnel embedded in a half-space
- 2017
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Ingår i: Journal of Sound and Vibration. - : Elsevier BV. - 1095-8568 .- 0022-460X. ; 387, s. 177-193
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Tidskriftsartikel (refereegranskat)abstract
- A closed-form semi-analytical solution for the vibrations due to a moving point load in a tunnel embedded in a half-space is given in this paper. The tunnel is modelled as an elastic hollow cylinder and the ground surrounding the tunnel as a linear viscoelastic material. The total wave field in the half-space with a cylindrical hole is represented by outgoing cylindrical waves and down-going plane waves. To apply the boundary conditions on the ground surface and at the tunnel-soil interface, the transformation properties between the plane and cylindrical wave functions are employed. The proposed solution can predict the ground vibration from an underground railway tunnel of circular cross-section with a reasonable computational effort and can serve as a benchmark solution for other computational methods. Numerical results for the ground vibrations on the free surface due to a moving constant load and a moving harmonic load applied at the tunnel invert are presented for different load velocities and excitation frequencies. It is found that Rayleigh waves play an important role in the ground vibrations from a shallow tunnel. (C) 2016 Elsevier Ltd. All rights reserved.
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| 46. |
- Yuan, Z. H., et al.
(författare)
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The influence of pore-fluid in the soil on ground vibrations from a tunnel embedded in a layered half-space
- 2018
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Ingår i: Journal of Sound and Vibration. - : Elsevier BV. - 1095-8568 .- 0022-460X. ; 419, s. 227-248
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Tidskriftsartikel (refereegranskat)abstract
- A computationally efficient semi-analytical solution for ground-borne vibrations from underground railways is proposed and used to investigate the influence of hydraulic boundary conditions at the scattering surfaces and the moving ground water table on ground vibrations. The arrangement of a dry soil layer with varying thickness resting on a saturated poroelastic half-space, which includes a circular tunnel subject to a harmonic load at the tunnel invert, creates the scenario of a moving water table for research purposes in this paper. The tunnel is modelled as a hollow cylinder, which is made of viscoelastic material and buried in the half-space below the ground water table. The wave field in the dry soil layer consists of up-going and down-going waves while the wave field in the tunnel wall consists of outgoing and regular cylindrical waves. The complete solution for the saturated half-space with a cylindrical hole is composed of down-going plane waves and outgoing cylindrical waves. By adopting traction-free boundary conditions on the ground surface and continuity conditions at the interfaces of the two soil layers and of the tunnel and the surrounding soil, a set of algebraic equations can be obtained and solved in the transformed domain. Numerical results show that the moving ground water table can cause an uncertainty of up to 20 dB for surface vibrations.
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| 47. |
- Zea, Elias, 1989-
(författare)
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Compressed sensing of impulse responses in rooms of unknown properties and contents
- 2019
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Ingår i: Journal of Sound and Vibration. - : Academic Press. - 0022-460X .- 1095-8568. ; 459
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Tidskriftsartikel (refereegranskat)abstract
- This paper introduces a method to recover unmeasured room impulse responses (RIRs) in acoustical spaces with unknown properties and contents, by means of a compressed sensing methodology. Methods published in the existing literature have been validated in empty, convex rooms; a limited subset of the many, diverse acoustical spaces one can encounter. It results a challenge to represent such diverse wave phenomena with a sparse set of plane waves or equivalent sources, given the coupling between the sparsity of such representations and hypotheses regarding the properties of the acoustical space and its contents, far-field measurement distances, and other parameters. In contrast to this philosophy, the method introduced in this paper exploits the sparsity inherent to the mathematical structure of the wavefronts present in the RIRs, which without further hypotheses carry themselves all the information about the wave propagation in the room. In essence, the measured RIRs are instead represented with a sparse set of curved elementary functions of various sizes, propagation directions and times of arrival, which are linked with the various shapes and locations of the unknown scatterers and boundaries in the room. The main contribution of this work is thus to enable the measurement of RIRs in more complex acoustical spaces, while keeping the number of microphones to a minimum with the use of compressed sensing. The method is formulated as a sparse optimization problem, and the solution is obtained with an iterative thresholding algorithm whose threshold value is determined from the measurements. An analysis of sensing coherence is included, and the performance of the method is experimentally evaluated with 1D microphone array measurements in two lecture rooms and one meet-ing room. For the sake of comparison, the RIRs are also linearly interpolated using a low-pass filter in the wavenumber-frequency domain. The experimental results demonstrate that the proposed method is superior than linear interpolation in all the cases investigated, motivating further development of the method to higher spatial dimensions. In terms of accuracy, the proposed method attains recovery errors in the same order of magnitude as those attained by methods in the literature, yet here the acoustical spaces have arbitrary contents and exhibit more complex geometries and boundary conditions.
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| 48. |
- Zea, Elias, 1989-, et al.
(författare)
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Single layer planar near-field acoustic holography for compact sources and a parallel reflector
- 2016
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Ingår i: Journal of Sound and Vibration. - : Elsevier. - 0022-460X .- 1095-8568. ; 380, s. 129-145
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Tidskriftsartikel (refereegranskat)abstract
- We consider the problem of planar near-field acoustic holography (PNAH) and introduce a new reconstruction method that can be used to process single layer pressure measurements performed in the presence of a reflective surface that is parallel to the measurement plane. The method is specially tailored for compact sources, or for problems in which the scattered field due to the source can be neglected. The approach consists in formulating a seismic model (WRW model) in wavenumber–space and employ it for sound source reconstructions. The proposed method is validated with numerical and experimental data, and, although the most accurate results are obtained when an estimate of the surface impedance is known beforehand, we show that it can substantially improve the reconstruction performance with respect to that of free-field PNAH.
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| 49. |
- Zea, Elias, 1989-, et al.
(författare)
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Wavenumber-domain separation of rail contribution to pass-by noise
- 2017
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Ingår i: Journal of Sound and Vibration. - : Elsevier. - 0022-460X .- 1095-8568. ; 409, s. 24-42
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Tidskriftsartikel (refereegranskat)abstract
- In order to counteract the problem of railway noise and its environmental impact, passing trains in Europe must be tested in accordance to a noise legislation that demands the quantification of the noise generated by the vehicle alone. However, for frequencies between about 500 Hz and 1600 Hz, it has been found that a significant part of the measured noise is generated by the rail, which behaves like a distributed source and radiates plane waves as a result of the contact with the train's wheels. Thus the need arises for separating the rail contribution to the pass-by noise in that particular frequency range. To this end, the present paper introduces a wavenumber–domain filtering technique, referred to as wave signature extraction, which requires a line microphone array parallel to the rail, and two accelerometers on the rail in the vertical and lateral direction. The novel contributions of this research are: (i) the introduction and application of wavenumber (or plane–wave) filters to pass-by data measured with a microphone array located in the near-field of the rail, and (ii) the design of such filters without prior information of the structural properties of the rail. The latter is achieved by recording the array pressure, as well as the rail vibrations with the accelerometers, before and after the train pass-by. The performance of the proposed method is investigated with a set of pass-by measurements performed in Germany. The results seem to be promising when compared to reference data from TWINS, and the largest discrepancies occur above 1600 Hz and are attributed to plane waves radiated by the rail that so far have not been accounted for in the design of the filters.
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| 50. |
- Zenzerovic, Ivan, 1988, et al.
(författare)
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An engineering time-domain model for curve squeal: Tangential point-contact model and Green's functions approach
- 2016
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Ingår i: Journal of Sound and Vibration. - : Elsevier BV. - 1095-8568 .- 0022-460X. ; 376, s. 149-165
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Tidskriftsartikel (refereegranskat)abstract
- Curve squeal is a strong tonal sound that may arise when a railway vehicle negotiates a tight curve. In contrast to frequency-domain models, time-domain models are able to capture the nonlinear and transient nature of curve squeal. However, these models are computationally expensive due to requirements for fine spatial and time discretization. In this paper, a computationally efficient engineering model for curve squeal in the time domain is proposed. It is based on a steady-state point-contact model for the tangential wheel/rail contact and a Green's functions approach for wheel and rail dynamics. The squeal model also includes a simple model of sound radiation from the railway wheel from the literature. A validation of the tangential point-contact model against Kalker's transient variational contact model reveals that the point-contact model performs well within the squeal model up to at least 5 kHz. The proposed squeal model is applied to investigate the influence of lateral creepage, friction and wheel/rail contact position on squeal occurrence and amplitude. The study indicates a significant influence of the wheel/rail contact position on squeal frequencies and amplitudes. Friction and lateral creepage show an influence on squeal occurrence and amplitudes, but this is only secondary to the influence of the contact position.
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