| 1. |
- Thompson, David, et al.
(författare)
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Assessment of measurement-based methods for separating wheel and track contributions to railway rolling noise
- 2018
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Ingår i: Applied Acoustics. - : Elsevier. - 0003-682X .- 1872-910X. ; 140, s. 48-62
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Tidskriftsartikel (refereegranskat)abstract
- The noise produced during a train pass-by originates from several different sources such as propulsion noise, noise from auxiliary equipment, aerodynamic noise and rolling noise. The rolling noise is radiated by the wheels and the track and is excited by the wheel and rail unevenness, usually referred to as roughness. The current TSI Noise certification method, which must be satisfied by all new mainline trains in Europe, relies on the use of a reference track to quantify the noise from new vehicles. The reference track is defined by an upper limit of the rail roughness and a lower limit of the track decay rate (TDR). However, since neither the rail roughness nor the track radiation can be completely neglected, the result cannot be taken as representing only the vehicle noise and the measurement does not allow separate identification of the noise radiated by wheel and track. It is even likely that further reductions in the limit values for new rolling stock cannot be achieved on current tracks. There is therefore a need for a method to separate the noise into these two components reliably and cheaply. The purpose of the current study is to assess existing and new methods for rolling noise separation. Field tests have been carried out under controlled conditions, allowing the different methods to be compared. The TWINS model is used with measured vibration data to give reference estimates of the wheel and track noise components. Six different methods are then considered that can be used to estimate the track component. It is found that most of these methods can obtain the track component of noise with acceptable accuracy. However, apart from the TWINS model, the wheel noise component could only be estimated directly using three methods and un- fortunately these did not give satisfactory results in the current tests.
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| 2. |
- Afzal, Mohammad, et al.
(författare)
-
An analytical calculation of the Jacobian matrix for 3D friction contact model applied to turbine blade shroud contact
- 2016
-
Ingår i: Computers & structures. - : Elsevier. - 0045-7949 .- 1879-2243. ; 177, s. 204-217
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Tidskriftsartikel (refereegranskat)abstract
- An analytical expression is formulated to compute the Jacobian matrix for 3D friction contact modeling that efficiently evaluates the matrix while computing the friction contact forces in the time domain by means of the alternate frequency time domain approach. The developed expression is successfully used for the calculation of the friction damping on a turbine blade with shroud contact interface having an arbitrary 3D relative displacement. The analytical expression drastically reduces the computation time of the Jacobian matrix with respect to the classical finite difference method, with many points at the contact interface. Therefore, it also significantly reduces the overall computation time for the solution of the equations of motion, since the formulation of the Jacobian matrix is the most time consuming step in solving the large set of nonlinear algebraic equations when a finite difference approach is employed. The equations of motion are formulated in the frequency domain using the multiharmonic balance method to accurately capture the nonlinear contact forces and displacements. Moreover, the equations of motion of the full turbine blade model are reduced to a single sector model by exploiting the concept of cyclic symmetry boundary condition for a periodic structure. Implementation of the developed scheme in solving the equations of motion is proved to be effective and significant reduction in time is achieved without loss of accuracy.
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| 3. |
- Afzal, Mohammad, et al.
(författare)
-
Numerical analysis of multiple friction contacts in bladed disks
- 2018
-
Ingår i: International Journal of Mechanical Sciences. - : Elsevier. - 0020-7403 .- 1879-2162. ; 137, s. 224-237
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Tidskriftsartikel (refereegranskat)abstract
- The damping potential of multiple friction contacts in a bladed disk is investigated. Friction contacts at tip shrouds and strip dampers are considered. It is shown that friction damping effectiveness can be potentially increased by using multiple friction contact interfaces. Friction damping depends on many parameters such as rotational speed, engine excitation order and mode family and therefore it is not possible to damp all the critical resonances using a single kind of friction contact interface. For example, a strip damper is more effective for the low nodal diameters, where blade/disk coupling is strong. The equations of motion of the bladed disk with multiple friction contacts are derived in the frequency domain for a cyclic structure with rotating excitations. A highly accurate method is used to generate the frequency response function (FRF) matrix. Furthermore, a finite element contact analysis is performed to compute the normal contact load and the contact area of the shroud interface at operating rotational speed. The multiharmonic balance method is employed in combination with the alternate frequency time domain method to find the steady state periodic solution. A low-pressure turbine bladed disk is considered and the effect of the engine excitation level, strip mass, thickness and the accuracy of FRF matrix on the nonlinear response curve are investigated in detail.
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| 4. |
- Afzal, Mohammad, 1987-
(författare)
-
On efficient and adaptive modelling of friction damping in bladed disks
- 2017
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This work focuses on efficient modelling and adaptive control of friction damping in bladed disks. To efficiently simulate the friction contact, a full-3D time-discrete contact model is reformulated and an analytical expression for the Jacobian matrix is derived that reduces the computation time drastically with respect to the classical finite difference method. The developed numerical solver is applied on bladed disks with shroud contact and the advantage of full-3D contact model compared to a quasi-3D contact model is presented. The developed numerical solver is also applied on bladed disks with strip damper and multiple friction contacts and obtained results are discussed. Furthermore, presence of higher harmonics in the nonlinear contact forces is analyzed and their effect on the excitation of the different nodal diameters of the bladed disk are systematically presented. The main parameters that influence the effectiveness of friction damping in bladed disks are engine excitation order, contact stiffnesses, friction coefficient, relative motion at the friction interface and the normal contact load. Due to variation in these parameters during operation, the obtained friction damping in practice may differ from the optimum value. Therefore, to control the normal load adaptively that will lead to an optimum damping in the system despite these variations, use of magnetostrictive actuator is proposed. The magnetostrictive material that develops an internal strain under the influence of an external magnetic field is employed to increase and decrease the normal contact load. A linearized model of the magnetostrictive actuator is used to characterize the magnetoelastic behavior of the actuator. A nonlinear static contact analysis of the bladed disk reveals that a change of normal load more than 700 N can be achieved using a reasonable size of the actuator. This will give a very good control on friction damping once applied in practice.
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| 5. |
- Amlinger, Hanna, et al.
(författare)
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Impact of PWM switching frequency on the radiated acoustic noise from a traction motor
- 2017
-
Ingår i: 2017 20th International Conference on Electrical Machines and Systems, ICEMS 2017. - : Institute of Electrical and Electronics Engineers Inc.. - 9781538632468
-
Konferensbidrag (refereegranskat)abstract
- The radiated acoustic noise from a traction motor at low speeds is dominated by the noise of electromagnetic origin. For a motor operated from pulse width modulated (PWM) converters, the switching frequency of the converter will have a large impact on the noise. The total harmonic distortion of the motor phase currents and thus also the exciting forces, will decrease with increasing switching frequency. Furthermore, changing the switching frequency will shift the frequencies of the exciting forces, hence have an influence on the coincidence with structural resonances of the motor. Tests have been performed on a traction motor and a decrease in sound pressure level with increasing switching frequency has been quantified and analyzed.
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| 6. |
- Amlinger, Hanna, et al.
(författare)
-
Operational deflection shapes of a PWM-fed traction motor
- 2016
-
Ingår i: Conference Proceedings of the Society for Experimental Mechanics Series. - Cham : Springer. - 9783319300832 ; , s. 209-217
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Konferensbidrag (refereegranskat)abstract
- Operational deflection shapes of an asynchronous traction motor for railway applications are investigated. The radiated noise from the tractionmotor on a train is, especially at low speeds, dominated by noise generated by electromagnetic forces. The tested motor is fed by a pulse-width-modulated (PWM) frequency converter for which the voltage is modulated as a series of pulses that are switched with a certain frequency. In this case, PWM force lines can be expected to influence the radiated noise. Therefore, detailed knowledge about the frequencies and deflection shapes of vibrations generated by PWM forces is of great importance for understanding and controlling the radiated noise and its spectral content. Vibration levels are measured on the stator shield and the operational deflection shapes are studied for several PWM switching frequencies and motor speeds. The deflection shapes with the largest vibration levels are determined. These are then compared to the expected excitation resulting from the pure PWM force lines. Changing the switching frequency, will shift the frequencies of the exciting forces. An appropriate selection of the PWM switching frequency is therefore important for the resulting acoustic radiation from the motor.
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| 7. |
- Amlinger, Hanna
(författare)
-
Reduction of Audible Noise of a Traction Motor at PWM Operation
- 2018
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- A dominating source for the radiated acoustic noise from a train at low speeds is the traction motor. This noise originates from electromagnetic forces acting on the structure resulting in vibrations on the surface and thus radiated noise. It is often perceived as annoying due to its tonal nature. To achieve a desirable acoustic behavior, and also to meet legal requirements, it is of great importance to thoroughly understand the generation of noise of electromagnetic origin in the motor and also to be able to control it to a low level.In this work, experimental tests have been performed on a traction motor operated from pulse width modulated (PWM) converter. A PWM converter outputs a quasi-sinusoidal voltage created from switched voltage pulses of different widths. The resulting main vibrations at PWM operation and their causes have been analyzed. It is concluded that an appropriate selection of the PWM switching frequency, that is the rate at which the voltage is switched, is a powerful tool to influence the noise of electromagnetic origin. Changing the switching frequency shifts the frequencies of the exciting electromagnetic forces. Further experimental investigations show that the trend is that the resulting sound power level decreases with increasing switching frequency and eventually the sound power level reaches an almost constant level. The underlying physical phenomena for the reduced sound power level is different for different frequency ranges. It is proposed that the traction motor, similar to a thin walled cylindrical structure, shows a constant vibration over force response above a certain frequency. This is investigated using numerical simulations of simplified models. Above this certain frequency, where the area of high modal density is dominating, the noise reducing effect of further increasing the switching frequency is limited.
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| 8. |
- Botling, Fredrik, et al.
(författare)
-
Combined Experimental and Analytical Vibro-Acoustic Model of an Electrical Motor
- 2016
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- A vibro-acoustic modal model of a traction motor forrailway applications is presented based on an experimentalmodal analysis of the system. Noise requirements forrailway traction motors are getting more and moredemanding as part of the overall levels of new rolling stock.It is therefore of great interest to understand and predict thevibro-acoustic behaviour of electromagnetic noisegenerated by traction motors. The modal parameters arederived from an experimental modal analysis. The primarysource for the radiated sound of the tested traction motor isthe radial deflections of the stator shield. The modalparameters for the radial deflections are implemented in areduced order modal model in a state space format usingMatlab/Simulink. Only the structural modes that have amatch in both the frequency and the spatial domain withthe electromagnetic excitation force will cause animportant vibro-acoustic response. This makes it possibleto create an accurate and efficient reduced order modalmodel with only a fraction of the total number of structuralmodes. The simulation results from the modal model arecompared to measured levels of vibration and acousticmeasurements of the motor.
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| 9. |
- Botling, Fredrik
(författare)
-
Modelling and simulation of electromagnetic audible noise generated by traction motors
- 2016
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- An annoying tonal noise is produced by modern electrical trains duringacceleration and deceleration. This noise is caused by electromagneticforces generating structural vibrations, especially from the traction motors.The electromagnetic noise is dominant at low train speeds and affectsboth the passengers on the train and on platforms, as well as peopleliving near the track. The focus on this issue has increased the last years,both regarding legislation, contractual requirements and also because ofexpectations from citizens and travelers. To be able to design low noiseelectric drive systems, a thorough understanding of the cause and thepossibility to predict the electromagnetic noise is needed. This thesisdescribes the modelling and simulation of an complete multi-physicsreal-time environment for prediction and analysis of the electromagneticnoise. The simulation results are validated against measurements of thestructural vibration and acoustic response of a real traction motor fed bya power converter running in the entire operational range.
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| 10. |
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| 11. |
- Botling, Fredrik, et al.
(författare)
-
Modelling framework for electromagnetic noise generation from traction motors
- 2016
-
Ingår i: Journal of Notes on Numerical Fluid Mechanics and Multidisciplinary Design. - Cham : Springer Nature. - 1612-2909.
-
Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- Electromagnetic noise from traction motors is often the single most dominating noise source from trains at low trainspeeds. This electromagnetic noise is tonal and annoying for both passengers on the train and people near the track andon the platform. A thorough understanding of the cause and the prediction of the electromagnetic noise is needed to beable to design low noise components. This paper describes a real time multi-physics modelling framework forprediction of the audible electromagnetic noise generated by traction motors fed by power converters. The cause of theelectromagnetic noise is influenced by several different domains. To be able to fully simulate the final acoustic sound,all these domains needs to be modelled and simulated together. Simulations of some relevant operational conditionsfor acoustic noise generation has been performed and discussed. Some of these results have been compared to realmeasurements from a converter fed traction motor.
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| 12. |
- Botling, Fredrik, et al.
(författare)
-
Vibro-acoustic modal model of a traction motor for railway applications
- 2016
-
Ingår i: Conference Proceedings of the Society for Experimental Mechanics Series. - Cham : Springer. - 9783319300832 ; , s. 197-208
-
Konferensbidrag (refereegranskat)abstract
- A vibro-acoustic modal model of a traction motor for railway applications is presented based on an experimental modal analysis of the system. Noise requirements for railway traction motors are getting more and more demanding as part of the overall levels of new rolling stock. It is therefore of great interest to understand and predict the vibro-acoustic behaviour of electromagnetic noise generated by traction motors. The modal parameters are derived from an experimental modal analysis. The primary source for the radiated sound of the tested traction motor is the radial deflections of the stator shield. The modal parameters for the radial deflections are implemented in a reduced order modal model in a state space format using Matlab/Simulink. Only the structural modes that have a match in both the frequency and the spatial domain with the excited electromagnetic force will cause important vibro-acoustic response. This makes it possible to create an accurate and efficient reduced order modal model with only a fraction of the total number of structural modes. The simulation results from the modal model are compared to measurements of operational deflection shapes and acoustic measurements of the motor.
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| 13. |
- Chen, Lin Strobin, et al.
(författare)
-
ACOUSTIC SCATTERING BEHAVIOR OF A 2D FLAME WITH HEAT EXCHANGER IN CROSS-FLOW
- 2016
-
Ingår i: ICSV 2016 - 23rd International Congress on Sound and Vibration. - : International Institute of Acoustics and Vibrations. - 9789609922623
-
Konferensbidrag (refereegranskat)abstract
- In practical heat production systems, premixed flames with cold heat exchanger in cross-flow is a widely used configuration. Self-excited thermoacoustic instabilities often occur in such systems. A practical way to predict the presence of the instabilities is the network model approach. In the present study, the configuration flame - heat exchanger is analyzed numerically. We first analyze the system as a network of segregated elements. Based on the resulting acoustic scattering matrix, the role of the heat exchanger as an amplifier of the flame resonant frequencies will be discussed. Then, results from the 1D network modeling are compared to results of compressible numerical simulations, performed for several distances between flame and heat exchanger. Finally, the limits to the validity of the segregated network model approach are discussed.
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| 14. |
- Gomez, Erik, et al.
(författare)
-
Multiple-order excitation and response of centrifugal pendulum vibration absorbers
- 2018
-
Ingår i: Proceedings of ISMA 2018 - International Conference on Noise and Vibration Engineering and USD 2018 - International Conference on Uncertainty in Structural Dynamics. - : KU Leuven - Departement Werktuigkunde. - 9789073802995 ; , s. 4305-4319
-
Konferensbidrag (refereegranskat)abstract
- The multiple-order response of a rotor equipped with a centrifugal pendulum vibration absorber (CPVA) is investigated in this study. CPVAs have been used in the abatement of torsional vibrations since the 1930s and have been extensively researched but seldom with a focus on the full multiple-harmonic response. Although the firing order in reciprocating engines dominates in amplitude, the higher-order harmonics have impact on driveline-related noise issues. This investigation is conducted in order to understand if an higher-order amplification can stem from the design of the CPVA or if this phenomenon is due an interaction between other powertrain components. Therefore, an isolated rotor-CPVA system is studied. The investigated rotor is subjected to an oscillating torque consisting of single- and multiple-order harmonics. The equations of motion are derived by Kane s method and the multiple-harmonic response of the system is analyzed. The linear steady-state response is compared with numerical time integration of the equations of motion.
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| 15. |
- Hoeijmakers, Maarten, et al.
(författare)
-
Flame dominated thermoacoustic instabilities in a system with high acoustic losses
- 2016
-
Ingår i: Combustion and Flame. - : Elsevier. - 0010-2180 .- 1556-2921. ; 169, s. 209-215
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Tidskriftsartikel (refereegranskat)abstract
- The thermoacoustic stability behaviour of a flame is experimentally investigated in the presence of large acoustic losses. Recently it has become clear that under such conditions an instability can occur due to an intrinsic local feedbackloop at the heat source. The experimental results confirm that despite significant acoustic losses, thermoacoustic instabilities can still be present. These findings imply that the effectiveness of passive thermoacoustic damping devices is limited by the intrinsic stability properties of the flame. (C) 2016 The Combustion Institute. Published by Elsevier Inc. All rights reserved.
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| 16. |
- Hoeijmakers, Maarten, et al.
(författare)
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Flames in context of thermo-acoustic stability bounds
- 2015
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Ingår i: Proceedings of the Combustion Institute. - : Elsevier BV. - 1540-7489. ; 35, s. 1073-1078
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Tidskriftsartikel (refereegranskat)abstract
- Bounds are derived for the acoustic losses such that a thermoacoustic system with a given flame can be guaranteed to be stable. The analysis is based on the flame's acoustic input-to-output properties represented by its scattering matrix. The developed analytical and numerical techniques allow estimating the maximum reflection coefficients (equivalently - acoustic losses) which are sufficient to ensure stable operation of a given burner. It is shown that the calculated numerical upper-bound is less conservative than the analytical one. The frequency dependence of the required acoustic losses provides (i) a thermo-acoustic signature of the flame and (ii) guidelines for the proper design of the up-and downstream acoustics from the flame. The method is illustrated on two burners/flames of premixed multiple Bunsen type. The frequency dependence of the upper bounds allows to identify those frequency ranges where the flame is more likely to cause instability of the complete system.
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| 17. |
- Hosseini, N., et al.
(författare)
-
Evaluating thermoacoustic properties of heating appliances considering the burner and heat exchanger as acoustically active elements
- 2018
-
Ingår i: Combustion and Flame. - : Elsevier. - 0010-2180 .- 1556-2921. ; 191, s. 486-495
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Tidskriftsartikel (refereegranskat)abstract
- Heat exchangers are an essential constituent part of many combustion systems. The thermoacoustic instability in such systems is a common problem and it has been studied extensively. However, the heat exchanger has not gained much attention in the field of combustion thermoacoustics, leading to a lack of knowledge about the thermoacoustic interactions between the burner and the heat exchanger. In this paper, a modeling approach is introduced to study these interactions in an academic representation of a heating appliance, comprised of a perforated slit burner and a tube heat exchanger. Both elements are considered thermally and acoustically active. A CFD model is used in a two-dimensional domain to simulate the response of the system to small amplitude broadband velocity perturbations. The thermochemical and acoustic coupling between the burner and the heat exchanger is investigated and a method is introduced to decouple their effects and study them separately. The extents to which this method is valid are addressed by varying the distance between the elements. Results show that as long as the flames do not impinge on the heat exchanger surface, a linear network modeling approach can be applied to construct the acoustic response of the composed configuration from the responses of its constituting elements. This approach requires registering the average velocity on a properly chosen intermediate plane between the burner and heat exchanger. Choosing this plane may be to some point difficult, i.e. when the burner and heat exchanger are close and cannot be considered independent. Moreover, when flame impingement occurs, the interactions between the flame and heat exchanger affect their individual thermoacoustic behaviors and the burner plus heat exchanger assembly needs to be considered as one coupled acoustic element. Particularly, flame impingement changes the phase of the heat absorption response of the heat exchanger and it may significantly alter the acoustic properties of the coupled assembly. The physics lying behind the effects of such interactions on the thermoacoustics of the system is discussed. The obtained results signify that a correct stability prediction of an appliance with burner and heat exchangers requires considering active thermoacoustic behavior of both elements as well as their interactions.
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| 18. |
- Hosseini, N., et al.
(författare)
-
Intrinsic thermoacoustic modes and their interplay with acoustic modes in a Rijke burner
- 2018
-
Ingår i: International Journal of Spray and Combustion Dynamics. - : Sage Publications. - 1756-8277 .- 1756-8285. ; 10:4, s. 315-325
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Tidskriftsartikel (refereegranskat)abstract
- The interplays between acoustic and intrinsic modes in a model of a Rijke burner are revealed and their influence on the prediction of thermoacoustic instabilities is demonstrated. To this end, the system is examined for a range of time delays, temperature ratios and reflection coefficients as adjustable parameters. A linear acoustic network model is used and all modes with frequency below the cut-on frequency for non-planar acoustic waves are considered. The results show that when reflection coefficients are reduced, the presence of a pure ITA mode limits the reduction in the growth rate that usually results from a reduction of the reflection coefficients. In certain conditions, the growth rates can even increase by decreasing reflections. As the time delay of the flame and thus the ITA frequency decreases, the acoustic modes couple to and subsequently decouple from the pure ITA modes. These effects cause the maximum growth rate to alternate between the modes. This investigation draws a broad picture of acoustic and intrinsic modes, which is crucial to accurate prediction and interpretation of thermoacoustic instabilities.
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| 19. |
- Hosseini, N., et al.
(författare)
-
Transfer function calculations of segregated elements in a simplified slit burner with heat exchanger
- 2015
-
Ingår i: 22nd International Congress on Sound and Vibration, ICSV 2015. - : International Institute of Acoustics and Vibrations. - 9788888942483
-
Konferensbidrag (refereegranskat)abstract
- A simplified burner-heat exchanger system is numerically modelled in order to investigate the effects of different elements on the response of the whole system to velocity excitation. We model the system in a 2D CFD code, considering a linear array of multiple Bunsen-type flames with heat exchanger tubes downstream the flames. Thermoacoustic instability is one of the main issues in lean premixed combustion systems, especially domestic boilers. In compact condensing boilers the close distance between the burner surface and the heat exchanger has increased the importance of studying the interactions between the flames and the heat exchanger. The elements corresponding to the heat balance in the system are the flame as heat source and burner deck and heat exchanger as heat sinks. We use both transfer function and transfer matrix approaches to identify the response of these elements to a step function excitation of velocity at the inlet of the domain. Steady-state simulations show that the contribution of the burner deck to the heat balance of the whole system is negligible, leaving the flame and heat exchanger as main contributors to the response of the system. We separately investigate the behavior of these two elements by modeling cases with flame only and heat exchanger only. Then we calculate the behavior of the combined system and compare it to the results of modeling a case with flame and heat exchanger together. These results show that, assuming linear behavior of the elements, it is possible to predict the system behavior via its constructing elements. Further investigations of the effects of other parameters and the limits, within which the assumptions are valid, are currently in progress.
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| 20. |
- Lopez Arteaga, Ines
(författare)
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Rolling noise in road and rail transportation systems
- 2019
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Ingår i: INTER-NOISE 2019 MADRID - 48th International Congress and Exhibition on Noise Control Engineering. - : SOCIEDAD ESPANOLA DE ACUSTICA - Spanish Acoustical Society, SEA. - 9788487985317
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Konferensbidrag (refereegranskat)abstract
- Long term exposure to ground transportation (road and rail traffic) noise is, after air pollution, the main environment-related health stressor in densely populated areas and compromises the quality of life and, indirectly, the life expectations of millions of people. The main source of ground transportation noise at speeds up to 130 km/h in road traffic and up to 300 km/h in rail traffic is rolling noise; noise generated due to the interaction between tyre and road (respectively wheel and rail). Although at first sight noise generation in these two transportation systems might seem unrelated, exploring the common aspects provides valuable insight in current practices for the modeling, prediction and abatement of rolling noise. In this paper the sound and vibration generation mechanisms due to tyre/road and wheel/rail interaction are discussed, focusing on the similarities and differences between the sound and vibration generation mechanisms in these two systems. This perspective is further extended to the discussion of modelling strategies and source characterization methods, with a particular emphasis on the influence of surface roughness on contact force generation. Finally, rolling noise source separation methods are touched upon, since they are a necesary tool to assess the impact of noise and vibration mitigation measures in both road and rail traffic systems.
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| 21. |
- Lopez Arteaga, Ines
(författare)
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Vibro-acoustic sources in ground transportation
- 2017
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Ingår i: Proceedings of ACOUSTICS 2017 Perth. - : Australian Acoustical Society. - 9780909882075
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Konferensbidrag (refereegranskat)abstract
- Long term exposure to ground transportation (road and rail traffic) noise is, after air pollution, the main environmentrelated health stressor in densely populated areas and compromises the quality of life and, indirectly, the life expectations of millions of people. At speeds up to 130 km/h in road traffic and up to 300 km/h in rail traffic the main source of noise is the tyre/road (respectively wheel/rail) interaction. In this paper the sound and vibration generation mechanisms due to tyre/road and wheel/rail interaction are discussed, focusing on the similarities and differences between the sound and vibration generation mechanisms in these two systems. This perspective is further extended to the discussion of contact force modelling and characterization methods in both road and rail traffic systems.
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| 22. |
- Lundberg, Oskar, 1980-, et al.
(författare)
-
A compact internal drum test rig for measurements of rolling contact forces between a single tread block and a substrate
- 2017
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Ingår i: Measurement. - : Elsevier. - 0263-2241 .- 1873-412X. ; 103, s. 370-378
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Tidskriftsartikel (refereegranskat)abstract
- A novel test rig design is presented which enables detailed studies of the three force components generated in the impact and release phase of rolling contact between a tyre tread block and a substrate. The design of the compact internal drum test rig provides realistic impact and release angles for the tread block-substrate contact and enables force measurements at high rolling speeds with a high signal-to-noise ratio. Measurements of the rolling contact forces are presented for different values of rolling velocity, static pre-load and acceleration. It is demonstrated that this test rig provides results which contribute to the understanding of tyre road interaction and can be used as input to modelling-based development of both tyres and roads aiming for improved handling, safety, energy efficiency and comfort.
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| 23. |
- 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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| 24. |
- Lundberg, Oskar E., et al.
(författare)
-
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
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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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| 25. |
- Lundberg, Oskar, et al.
(författare)
-
Experimental study of the rolling contact forces between a tyre tread-block and a road
- 2016
-
Ingår i: Proceedings of the INTER-NOISE 2016 - 45th International Congress and Exposition on Noise Control Engineering. - : German Acoustical Society (DEGA). ; , s. 2179-2184
-
Konferensbidrag (refereegranskat)abstract
- For a rolling tyre, forces arise within the tyre-road contact patch, leading to the excitation of tyre vibrations and in turn to noise radiation. This is the main cause of highway noise and consequently much effort has been made to understand and model the tyre vibrational character as well as the sound radiation. However, when it comes to the generation of contact forces in the tyre-road interface, there is still a demand for future research. Specifically, the understanding and modelling of the influence from tangential force excitation on the resulting tyre-road noise is a complicated topic which involves many parameters such as tread rubber characteristics, road surface character, rolling velocity, rolling resistance and normal load. In this paper, an experimental study of the tangential friction contact forces which arise for a single truck tyre tread block in rolling contact with a road surface is presented. Both the dynamic tangential dynamic stiffness as well as the sliding frictional behavior of the same tread block is experimentally investigated. Moreover, an example measurement with the novel compact internal drum (CID) test rig is presented. The test rig can be used to study the influence on the resulting contact forces from parameters such as rolling velocity, road surface topography and normal load.
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| 26. |
- Lundberg, Oskar, 1980-
(författare)
-
On the influence of surface roughness on rolling contact forces
- 2016
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Road vehicle tyres, railway wheels and ball bearings all generate rolling contact forces which are transferred within a finite area of contact between the rolling element and the substrate. Either it is visible or not for the human eye, a certain degree of roughness is always present on the contacting surfaces and it influences the generation of both vertical and lateral contactforces. The purpose of this investigation is to enhance the understanding and modelling of the influence from small-scale surface roughness on the generation of rolling contact forces. To this end, a computationally efficient method to include roughness-induced contact nonlinearities in the dynamic modelling of rolling contacts is proposed. The method is implemented in a time domain model for vertical wheel–track interaction to model rolling-induced rail vibrations, showing good agreement with measurements. Furthermore, a test rig is developed and used for the investigation of tyre–road rolling contact forces. Detailed studies are performed on the influence of substrate roughness on the resulting contact forces for a tyre tread block which is rolling at different operating conditions. The choice of substrate as well as the rolling velocity and the slip ratio is observed to have significant influence on the resulting friction coefficient. For high slip ratios, stick–slip oscillations appear, exhibiting frequency content which is largely dependent on the choice of substrate. The outcomes of this study can potentially be used to improve future tyre–road contacts with respect to wear, traction and noise generation.
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| 27. |
- Manzari, Luca, et al.
(författare)
-
A fully automated high-speed optical rig for in vacuo, full field, non-contact vibration measurements for viscoelastic, anisotropic materials
- 2018
-
Ingår i: Proceedings of NOVEM 2018 Noise and vibration emerging methods. ; , s. 91-102
-
Konferensbidrag (refereegranskat)abstract
- In this paper, a setup for measuring the three-dimensional displacement field of a test object un-dergoing controlled dynamic excitation in a vacuum chamber is presented. The setup has beendesigned with porous materials in mind, yet is suitable for the measurement of anisotropic vis-coelastic solids in general. To achieve non-contact data acquisition, a stereo high-speed camerasystem measures the displacement of the foundation and of the test object. A laser Doppler vi-brometer is used before the actual measurement to choose an excitation level that maximizes thesignal-to-noise ratio while allowing to ensure that the test object is fully relaxed and stable at thebeginning of every measurement. The setup, comprising both commercial and in-house hardwareand software solutions, addresses the challenges of measuring in vacuum with non-contact tech-niques. All these aspects are discussed in the current paper, and preliminary results are presented.The ultimate objective is to estimate the dynamic properties of a material using inverse methodsand the data obtained.
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| 28. |
- Manzari, Luca, et al.
(författare)
-
Experimental-numerical methods for inverse characterization of the anisotropic-anelastic properties of porous materials, based on dynamic Digital Image Correlation
- 2018
-
Ingår i: Proceedings of ISMA 2018 - International Conference on Noise and Vibration Engineering and USD 2018 - International Conference on Uncertainty in Structural Dynamics. - 9789073802995 ; , s. 687-695
-
Konferensbidrag (refereegranskat)abstract
- One of the major challenges in accurately modeling poroelastic materials is the choice of the parametersrequired for their modeling, immediately followed by the practical difficulty in obtaining them. The direc-tional dependencies of the physical properties further complicate the task of designing experimental setupscapable of providing the macroscopic properties. In the work presented here, the focus has been set on theacquisition of high quality displacement data by means of two high-speed cameras and 3D Digital ImageCorrelation. The obtained displacement field, is fed into a general inverse formulation which is guided by anoptimization tool that minimizes the difference between the predicted and the measured data. As a minimumis found, the corresponding parameters are interpreted as material properties for a certain physical model.The solutions for each iteration are calculated with numerical prediction tools, in the cases discussed herethe finite element method, where it must be ascertained that the numerical errors are kept to a minimal level
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| 29. |
- Manzari, Luca, et al.
(författare)
-
Toward fully anisotropic viscoelastic material models using an automated high-speed optical rig
- 2018
-
Ingår i: 13TH INTERNATIONAL CONFERENCE ON VIBRATION MEASUREMENTS BY LASER AND NONCONTACT TECHNIQUES, 2018. - : IOP PUBLISHING LTD.
-
Konferensbidrag (refereegranskat)abstract
- This paper describes some of the algorithms that are employed in the post-processing of the data obtained from an automated high-speed optical rig. The setup, entirely designed by some of the authors, is used for measuring the full field displacement in time of anisotropic viscoelastic solids undergoing controlled dynamic excitation. The setup main goal is to provide complex transfer functions relating the three-dimensional sinusoidal displacement on the surface of the sample to the sinusoidal motion of the foundation, suitable for the inverse estimation of the dynamic properties of the material under analysis. The complete automation of the measurement process aims at maximizing repeatability and signal-to-noise ratio. In particular, a stereo high-speed camera system is responsible for the actual measurement, while a laser Doppler vibrometer is used for a preliminary autoranging procedure and for data validation. The camera system does not directly output the high-quality data that is needed for a successful, physically meaningful inverse estimation. Hence, here the algorithms described in this paper come into play. Since digital image correlation (DIC) may fail in some frames or in some regions of the pictures, a mask is applied and calculated for every measurement run to preserve information only where the success rate of the DIC algorithm is higher than a specified threshold. The sample is mounted on a foundation whose sides are flat: random sample consensus (RANSAC) and principal component analysis (PCA) are used to respectively eliminate outliers and find the best fitting plane to the foundation side - the measured displacement field can then be expressed in a local coordinate system, truly relative to the foundation. The transfer functions are now obtained in two steps: first an optimizer is used to fit a cosine to all the measured displacement time-series, then the complex amplitudes representing the motion of the sample faces are divided by the average of the complex amplitudes representing the motion of the foundation.
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| 30. |
- Temiz, Muttalip Askin, et al.
(författare)
-
Modelling vibro-acoustic coupling in flexible micro-perforated plates by a patch-impedance approach
- 2017
-
Ingår i: Applied Acoustics. - : ELSEVIER SCI LTD. - 0003-682X .- 1872-910X. ; 125, s. 80-90
-
Tidskriftsartikel (refereegranskat)abstract
- This study proposes a Finite Element (FE)-based efficient numerical model of the vibro-acoustic coupling in flexible micro-perforated plates (f-MPPs) where each perforation is described as an imposed impedance boundary condition (uniform impedance patch) on the plate. This approach opens the possibility of predicting the influence of perforation distribution on the acoustic performance of f:MPP. Micro perforated plates have been a topic of interest as a promising sound absorber in a wide range of applications, from room acoustics to combustion systems. One great advantage of these plates is that it gives the designer the freedom of choice on material in production. Depending on the material and the dimensions, the acoustical modes of the medium can couple with the structural modes of the plate. This coupling changes the number of absorption peaks, frequency and amplitude of the Helmholtz resonance of the system, therefore the coupling becomes an extra parameter in the design process. Current analytical models superpose the mechanical impedance of the plate with the acoustic impedance of the perforations to compute this coupling. This approach works fairly well for plates with uniform perforation distribution. This study proposes a numerical method which assumes perforations as discrete impedance patches on the flexible plate so that they can be considered separately. The method couples the solution of the Helmholtz equation in air with shell plate theory to model the vibro-acoustic effects and the impedance patches are represented as imposed transfer impedance boundary conditions. The assessment of the method is performed in terms of comparing the calculated absorption coefficient values from the simulations of several test cases, fundamental theories and measurement results from the literature. The simulation results agree both with these theoretical limits and measurement results. The use of the method is illustrated by considering an example of the influence of modification of the spatial distribution of perforations on the sound absorption of a membrane.
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| 31. |
- 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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| 32. |
- Temiz, M. A., et al.
(författare)
-
Numerical estimation of the absorption coefficient of flexible micro-perforated plates in an impedance tube
- 2016
-
Ingår i: ICSV 2016 - 23rd International Congress on Sound and Vibration. - : International Institute of Acoustics and Vibrations. - 9789609922623
-
Konferensbidrag (refereegranskat)abstract
- In this study, we numerically model a vibro-acoustic system consisting of a flexible micro-perforated plate (f-MPP) and an acoustic medium. Combined with a back-cavity, micro-perforated plates are considered as a promising noise control technology due to their tunable, wide-band sound absorption characteristics and robust performance. An MPP consists of a plate with uniformly distributed perforations whose diameters are in the order of a millimeter. These perforations are small enough to dissipate the acoustic perturbations due to the viscous effects caused by the presence of the Stokes layers. When the plate is rigid, the sound dissipation mechanism for a specific frequency bandwidth is determined by the perforation diameter, plate thickness, plate porosity and the back cavity depth. Yet, when the plate is flexible, additional absorption peaks, which cannot be determined by the parameters mentioned before, are observed in the measurements. This phenomenon is due to the vibro-acoustic coupling of the flexible plate and the acoustic medium. To model the vibro-acoustic system numerically, we couple two 3D cylindrical acoustic mediums, i.e. incident and back cavity regions, with a flexible plate consisting of shell elements. The perforations are separately located on the plate as independent transfer admittance elements with impedance values obtained from existing models. The system is disturbed with a plane wave excitation and the assessment of the model is done by comparing the calculated absorption coefficient with the experimental results from the literature. In the future, we plan to investigate the effect of perforation positions with the help of the model built in this study.
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| 33. |
- Temiz, Muttalip Askin, et al.
(författare)
-
The influence of edge geometry on end-correction coefficients in micro perforated plates
- 2015
-
Ingår i: Journal of the Acoustical Society of America. - : American Institute of Physics (AIP). - 0001-4966 .- 1520-8524. ; 138:6, s. 3668-3677
-
Tidskriftsartikel (refereegranskat)abstract
- Global expressions are proposed for end-correction coefficients in micro perforated plates (MPPs) using non-dimensional parameters. MPPs are sound absorbers with small perforation diameters such that the Stokes boundary layers fill up almost the entire perforation. Sound absorption does not only occur within the perforation, but also takes place just outside of it. The latter contribution plus the outside inertia effect on the transfer impedance of the MPP are referred to as end-corrections. In order to determine them, an analytical solution employing the very thin Stokes layer assumption has been derived. However, this assumption requires empirical coefficients in the end-corrections for accurate results. To explore the effects of various parameters a numerical model is used. This model is verified with open-end reflection coefficient measurements. The most prominent result from this study is that compared to plate thickness, the ratio of perforation diameter to Stokes layer thickness (Shear number) and edge geometry affect the end-correction coefficients more significantly. The effect of plate thickness can be neglected for practical purposes, therefore, expressions for the end-corrections in terms of Shear number and edge geometry are provided. The relative error of these expressions is <3% compared to the numerical results.
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| 34. |
- Zea, Elias, 1989-, et al.
(författare)
-
Experimental Assessment of a Single-layer Near-field Acoustic Holography Method in an Enclosed Space
- 2015
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Planar near-field acoustic holography (PNAH) is preferably performed in anechoic spaces, since the wave-field extrapolation only holds for outgoing waves, which makes the study of certain vibro- acoustic sources a troublesome pursuit. To overcome this limitation, a number of imaging alternatives have been investigated in recent years with the use of double-layer pressure (or particle velocity) measurements, as well as of single-layer pressure and velocity measurements. Unlike these methods, our approach is to use single-layer pressure measurements and extend the PNAH method such that it is valid in the presence of a parallel reflector. In this paper we address the experimental validation of the extended PNAH formulation by means of reconstructing the pressure radiated by an omnidirectional source and exploring a few excitation frequencies. The reconstruction performance is investigated via both the free-field and the extended PNAH techniques.
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| 35. |
- Zea, Elias, 1989-, et al.
(författare)
-
Identification of rail contribution to pass-by noise by a modified wave signature extraction (WSE) method
- 2018
-
Ingår i: INTER-NOISE and NOISE-CON Congress and Conference Proceedings. - : Institute of Noise Control Engineering. ; , s. 617-625
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The present paper explores a modified version the wave signature extraction (WSE) method [1], whose aim is to separate the rail contribution to the pass-by noise of railway vehicles. The method requires a line microphone array parallel to the rail, and two accelerometers on the rail in the ver- tical and lateral direction. The motivation for this work is the need to separate the rail contribution to the pass-by noise of railway vehicles. The WSE method [1] is based on the wavenumber domain filtering of pass-by data measured with a microphone array located in the near-field of the rail. The filter design does not require a priori information of the structural properties of the rail, since the required information is obtained from array pressure data and rail vibration data before and after the train passes in front of the array. The filter is such that it extracts the dispersion plot branches of the first family of horizontal and vertical bending waves (moving band-pass filter). Although the comparison with TWINS simulation data provides very promising results, there are discrepancies at the higher frequencies, possibly due to the onset of new bending wave families. Therefore in the present paper we propose a modified filtering procedure, where a bank of band-pass and low-pass filters are used instead, and the results are compared to the original WSE implementation and the TWINS simulation data. We show that the results in the higher frequency range are improved with respect to the original WSE implementation.
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| 36. |
- Zea, Elias, 1989-, et al.
(författare)
-
On modified wavenumber filters for rail contribution estimations
- 2018
-
Ingår i: Journal of the Acoustical Society of America. - : Acoustical Society of America (ASA). - 0001-4966 .- 1520-8524. ; 144, s. EL286-EL289
-
Tidskriftsartikel (refereegranskat)abstract
- This brief communication exposes an overview of various wavenumber filters to separate the rail contribution to pass-by noise via the wave signature extraction method [Zea, Manzari, Squicciarini, Feng, Thompson, and Lopez Arteaga, J. Sound Vib. 409, 24–42 (2017)]. It has been found that the originally proposed filters underesti- mate the rail noise at frequencies above 1.6 kHz due to the presence of higher-order wave families that is unaccounted for. The goal of this let- ter is thus to propose and examine different filter functions that can cap- ture such waves, and to assess whether the rail contribution estimations can be improved.
|
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| 37. |
- Zea, Elias, 1989-, et al.
(författare)
-
Separation of track contribution to pass-by noise by near-field array techniques
- 2016
-
Ingår i: Proceedings of the 22nd International Congress on Acoustics.
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- A technique to separate the track noise contribution is proposed based on identifying and extracting the track signature from the pass-by noise information measured with a microphone array relatively close to the track. Separation of the contributions of the vehicle and the track in the pass-by noise spectra is a challenging task, which is currently addressed by a combination of direct and indirect measurements and model predictions. Due to the uncertainties in the separation of the track contribution, whether a vehicle will comply with regulations during certification tests is still very much track dependent. Therefore, accurate means to identify the track contribution to the pass-by noise are needed. In this paper we propose to make use of the fact that in a wide frequency range the track is a distributed source that radiates plane waves at a given angle with respect to the track. By measuring the sound field close to the track with a microphone array, the wavenumber spectrum of the radiated sound can be determined. For the track contribution this wavenumber spectrum is tonal and therefore sparse. We make use of this property to design filters that extract the track contribution to the total pass-by noise. This is illustrated with simulations and experiments.
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| 38. |
- Zea, Elias, 1989-, et al.
(författare)
-
Simplified wave signature extraction method for rail contribution estimations
- 2018
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The present paper investigates a modified implementation of the wave signature extraction (WSE) method [1], whose aim is to separate the rail contribution to the pass-by noise of railway vehicles. The method requires a line microphone array parallel to the rail, and two accelerometers on the rail in the vertical and lateral direction. The motivation for this work is the need to separate the rail contribution to the pass-by noise of railway vehicles. The WSE method [1] is based on the wavenumber domain filtering of pass-by data measured with a microphone array located in the near-field of the rail. The filter design does not require a priori information of the structural properties of the rail, since the required information is obtained from array pressure data and rail vibration data before and after the train passes in front of the array. The filter is such that it extracts the dispersion plot branches of the first family of horizontal and vertical bending waves (moving band-pass filter). Although the comparison with TWINS simulation data provides very promising results, there are discrepancies at the higher frequencies, possibly due to the onset of new bending wave families. Therefore in the present paper we assess the performance of a simplified WSE method, where a moving low-pass filter is used instead, and the results are compared to the original WSE implementation and the TWINS simulation data. We show that the results in the higher frequency range are improved with respect to the original WSE implementation.[1] Zea et al. Journal of Sound and Vibration 409, pp. 24–42, 2017
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| 39. |
- Zea, Elias, 1989-, et al.
(författare)
-
Single-layer array method to reconstruct extended sound sources facing a parallel reflector
- 2017
-
Ingår i: Journal of the Acoustical Society of America. - : Acoustical Society of America (ASA). - 0001-4966 .- 1520-8524. ; 141:5, s. 3984-3984
-
Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- The accuracy of sound field reconstruction methods with single-layer microphone arrays is subject to the room or enclosure in which the measurements take place. Thus, the authors recently introduced a single-layer method that can be employed to reconstruct compact sources in the presence of a reflecting surface that is parallel to the array. Now the authors propose a method conceived for extended planar sources such as baffled plates facing a parallel reflector. The method is based on a wavenumber-domain function describing the propagation paths between the source, the reflector and the array. The free-space sound field radiated by the source is then recovered by means of a regularized inversion of the propagation function. Numerical simulations are performed in order to assess the method's performance and potential for source reconstructions. The results are promising and point towards future experimental validation.
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| 40. |
- Zea, Elias, 1989-
(författare)
-
Single layer near-field acoustic imaging in space-invariant reflective environments
- 2015
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The visualization of optical fields, or widely known as photography, is a common practice that can also be applied to acoustic fields. No less than three decades of research in acoustic imaging demonstrate its potential and relevance in plenty applications such as sound source identification and localization, as well as characterization of noise generation mechanisms. In particular, the resolution of the acoustic images can be greatly enhanced by means of measuring the sound in the acoustic near-field. Nevertheless, it is often the case that the field is disturbed by the measurement environment, in the form of noise and reflections, and the source must then be transported to a much quieter place, for instance, an echo-free chamber. Current state-of-the-art methods tackle the aforesaid complications, at the cost, however, of measuring two images instead of one: resulting in twice as many measurement sensors. The contribution of this thesis is the introduction of a novel technique that only requires a single image to be captured, and is specially tailored for acoustic imaging in space-invariant reflective environments, that is, in the presence of reflecting surfaces that are parallel to the measurements.
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| 41. |
- Zea, Elias, 1989-, et al.
(författare)
-
Single layer planar near-field acoustic holography for compact sources and a parallel reflector
- 2016
-
Ingår i: Journal of Sound and Vibration. - : Elsevier. - 0022-460X .- 1095-8568. ; 380, s. 129-145
-
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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| 42. |
- Zea, Elias, 1989-, et al.
(författare)
-
Sound field separation for planar sources facing a parallel reflector
- 2019
-
Ingår i: Applied Acoustics. - : Elsevier BV. - 0003-682X .- 1872-910X. ; 149C, s. 181-191
-
Tidskriftsartikel (refereegranskat)abstract
- We consider the problem of separating and reconstructing the sound field radiated by a planar source, e.g. a vibrating plate, that faces a parallel reflector. For this purpose we propose a Fourier-based technique to process near-field microphone array measurements that are performed on a single plane between the plate and the reflector. A closed-form expression is derived in the wavenumber domain to recover the free-space sound field radiated by the plate. The fundamental assumption is that the plate scatters sound in a locally-reacting fashion. Overall, provided the admittances of the plate and the reflecting surface are known, the results demonstrate that it is possible to recover the free-field sound radiated by the plate with a reasonable accuracy.
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| 43. |
- Zea, Elias, 1989-
(författare)
-
Sound field separation with microphone arrays
- 2017
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Sound field analysis is a fundamental tool in the design, manufacturing, testing and diagnosis of machines and transportation means, as well as the legislations that regulate noise levels in order to minimize environmental pollution. Customary solutions to the problem of sound field analysis are microphone array technologies such as near-field acoustic holography (NAH) and beamforming. One of the challenges of using these technologies often lies in the difficulty for separating disturbing sounds from the target source, specially when these are correlated. For example, NAH requires that no reflecting surfaces are found in the vicinity of the array, which is in theory only possible in an echo-free chamber. On the other hand, beamforming is most suitably used to separate uncorrelated sound sources, which is not the case of, for instance, the noise generated by the contact between the wheel of a train and a railway track. The present thesis examines the research problems of separating a sound source from its reflections, and separating the rail noise from the total noise radiated by a passing train. The overall goal of the thesis is to push the limits of microphone array technologies in the context of sound field separation, to the end of minimizing the cost and complexity of measurements and analyses. The proposed separation methods are formulated in the wavenumber domain, and the measurements are done with uniform single layer microphone arrays. The problem of separating reflections is addressed in three different papers: (i) compact sources and a parallel reflector, (ii) planar source and a parallel reflector, and (iii) a perpendicular reflector with respect to the microphone array, and the common requirement is the knowledge of the reflector impedance. The problem of separating rail noise is studied in a fourth paper, and the proposed method is formulated such that it does not require prior knowledge of the rail properties. Upon the findings obtained in the papers, a comprehensive description of areas for future work, as well as strategies to approach them, is given at the end of the thesis.
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| 44. |
- Zea, Elias, 1989-, et al.
(författare)
-
Wavenumber-domain separation of rail contribution to pass-by noise
- 2017
-
Ingår i: Journal of Sound and Vibration. - : Elsevier. - 0022-460X .- 1095-8568. ; 409, s. 24-42
-
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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| 45. |
- Zhou, H., et al.
(författare)
-
Broadband planar nearfield acoustic holography based on one-third-octave band analysis
- 2016
-
Ingår i: Applied Acoustics. - : Elsevier. - 0003-682X .- 1872-910X. ; 109, s. 18-26
-
Tidskriftsartikel (refereegranskat)abstract
- Planar nearfield acoustic holography (PNAH) is usually based on narrow-band, single frequency analysis, which is time consuming when the source behavior over a broad frequency range is of interest, as is the case with many industrial sources. In this paper a method, broadband planar nearfield acoustic holography based on one-third-octave band analysis (BPNAH), is described. Data relating to the complex band pressure on the hologram is obtained by combining the root-mean-square pressure corresponding to a one-third-octave band with the phase of the pressure corresponding to a single frequency line. Numerical simulations and measurements show that the BPNAH method allows a significant reduction in processing time, while keeping a similar accuracy to the conventional reconstruction, which is based on the summation of frequency by frequency in the corresponding band. As a simple, time-saving and robust technique, the BPNAH method is particularly well adapted to industrial studies.
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