| 1. |
- Afzal, Mohammad, 1987-, et al.
(author)
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Adaptive control of normal load at the friction interface of bladed disks using giant magnetostrictive material
- 2020
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In: Journal of Intelligent Materials Systems and Structures. - : SAGE Publications. - 1045-389X .- 1530-8138. ; 31:8, s. 1111-1125
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Journal article (peer-reviewed)abstract
- A novel application of magnetostrictive actuators in underplatform dampers of bladed disks is proposed for adaptive control of the normal load at the friction interface to achieve the desired friction damping in the structure. Friction damping in a bladed disk depends on operating parameters, such as rotational speed, engine excitation order, nodal diameter normal contact load, and contact interface parameters, such as contact stiffness and friction coefficient. The operating parameters have a fixed value, whereas the contact interface parameters vary in an unpredictable way at an operating point. However, the ability to vary some of these parameters such as the normal contact load in a controlled manner is desirable to attain an optimum damping in the bladed disk at different operating conditions. Under the influence of an external magnetic field, magnetostrictive materials develop an internal strain that can be exploited to vary the normal contact load at the friction interface, which makes them a potentially good candidate for this application. A commercially available magnetostrictive alloy, Terfenol-D is considered in this analysis that is capable of providing magnetostrain up to 2 × 10-3 under prestress and a blocked force over 1500 N. A linearized model of the magnetostrictive material, which is accurate enough for a direct current application, is employed to compute the output force of the actuator. A nonlinear finite element contact analysis is performed to compute the normal contact load between the blade platform and the underplatform damper as a result of magnetostrictive actuation. The nonlinear contact analysis is performed for different actuator mounting configurations and the obtained results are discussed. The proposed solution is potentially applicable to adaptively control vibratory stresses in bladed disks and consequently to reduce failure due to high-cycle fatigue. Finally, the practical challenges in employing magnetostrictive actuators in underplatform dampers are discussed.
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| 2. |
- Amiri, A., et al.
(author)
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A replacement model to simulate the nonlinear dynamics of electro-responsive liquid crystal coatings
- 2023
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In: AIP Advances. - : AIP Publishing. - 2158-3226. ; 13:3
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Journal article (peer-reviewed)abstract
- An electric circuit replacement model is proposed to simulate the key nonlinear dynamics of electro-responsive liquid crystal polymer networks (LCNs). LCNs are known for having great potential to be integrated into smart functional surfaces due to their ability to generate various surface patterns. However, due to their complex molecular dynamics, low-order dynamic models that can accurately describe and predict their dynamic behavior are still lacking. In light of this research gap, we develop a lumped-parameter replacement model based on the observed dynamics in the experimental data and the physics of LCN dielectric properties. The unique assembly of lumped parameters in its simplest form describes the transformation of a high-frequency input voltage to a relatively slow increase in the local height of the LCN coating in between the electrodes, serving as an excitation mechanism to induce height change. The nonlinear dynamics of this height increase, as a function of both excitation frequency and voltage, is described by the proposed model. Furthermore, the comparison of the simulation results with the experimental data from LCN shows that key LCN response characteristics are captured well by the model. This model makes it possible to accurately predict and control the response of the electro-responsive LCN surfaces to obtain a predefined desired deformation pattern, which is a vital requirement for integrating them in haptic and smart surface devices.
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| 3. |
- Aulitto, Alessia, et al.
(author)
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Experimental study of a slit in the presence of a bias flow under medium- and high-level acoustic excitations
- 2023
-
In: International Journal of Spray and Combustion Dynamics. - : SAGE Publications. - 1756-8277 .- 1756-8285. ; 15:2, s. 117-126
-
Journal article (peer-reviewed)abstract
- This work presents an experimental investigation of the acoustic properties of a slit in the presence of a bias flow under moderate- and high-acoustic excitations. Impedance tube experiments are discussed for a geometry inspired by deep punching resulting in a cut in the plate. The acoustic transfer impedance of the plate is discussed for several bias flow velocities, acoustic excitation, and different frequencies. In the range considered for this study, a bias flow appears to have two main effects, globally enhancing the sound absorption of the plate and creating a protective layer downstream of the plate due to the interaction between the slits. A maximum of the enhancement factor is found at a specific ratio between the acoustic velocity and the bias flow velocity. Two simple asymptotic behaviors are found, dominated by the flow or by the acoustic excitation, respectively. The behavior of the inertance is complex. Globally the inertance decreases with decreasing flow Strouhal number while its dependency on the amplitude of the acoustic velocity is less obvious.
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| 4. |
- Ganji, Hamed F., et al.
(author)
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A framework for suppression of thermoacousitc instability using the nyquist criterion
- 2023
-
In: Proceedings of the 29th International Congress on Sound and Vibration, ICSV 2023. - : Society of Acoustics.
-
Conference paper (peer-reviewed)abstract
- To simulate complex multiphysics and multiscale phenomena, such as thermoacoustic combustion instabilities, a comprehensive model is often created by combining subsystems. This approach allows the contribution of acoustic terminations to be separated from the acoustic response of the flame, potentially providing a systematic approach to suppressing thermoacoustic instabilities. In this paper, we present a framework for developing terminations and silencers using the Nyquist criterion and winding number. Firstly, we determine the dispersion relation to establish the system's eigen-frequencies. Then, by distinguishing between the Nyquist diagram and the Nyquist criterion and using the argument (arg) of the dispersion relation, we propose two thermoacoustic stability criteria. This approach is similar to the theory used in microwave technology. Using this methodology, we can develop a systematic method for characterizing the quality of specific combustion devices and provide guidelines for designing stable acoustic embeddings in thermoacoustic systems. To validate this approach, we will perform an eigenvalue analysis on a classical duct-flame-duct test case, and the results will demonstrate the effectiveness of this analogy in solving thermoacoustic problems.
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| 5. |
- Ganji, Hamed F., et al.
(author)
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Assessment of the acoustic scattering matrix of a heat exchanger using ssCFD-LNSE simulation
- 2022
-
In: Internoise 2022. - : The Institute of Noise Control Engineering of the USA, Inc..
-
Conference paper (peer-reviewed)abstract
- The risk of thermoacoustic instability is present in any combustion appliance. The instability results from a closed loop feedback between unsteady combustion, heat-transfer and acoustic modes of the system. To predict the system acoustics, all constituting elements of the appliance need to be modelled. A heat-exchanger is a element where the gas faces complex fluid dynamics and heat transfer processes. Therefore, modelling of (thermo)-acoustic properties of a heat exchanger is challenging. In this paper, a computational approach is proposed to characterize the acoustic properties of a generic heat exchanger in both laminar and turbulent flow regimes. A hybrid Computational Fluid Dynamics - Computational Aero-Acoustics (CFD-CAA) method is used based on the linearized Navier-Stokes equation, called ssCFD-LNSE. The core idea in this approach is to efficiently model acoustic wave propagation with inclusion of mean flow and temperature fields. ssCFD-LNSE is performed by splitting the quantities of the total field into a mean part (obtained from CFD) and a (acoustic) perturbation part modelled within the LNSE solver. The goal of this research is to assess the two-port acoustic scattering matrix of an array of tubes, as a generic model of a heat-exchanger, with a hot cross flow.
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| 6. |
- Ganji, Hamed F., et al.
(author)
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Characterization and identification of thermoacoustic behavior of flames anchored on burner decks with multiple perforations; Transfer Function (de)composition approach
- 2022
-
In: Internoise 2022 - 51st International Congress and Exposition on Noise Control Engineering. - : The Institute of Noise Control Engineering of the USA, Inc..
-
Conference paper (peer-reviewed)abstract
- The appearance of thermoacoustic instability in combustion systems depends on thermoacoustic property (e.g., Transfer Function (TF)) of used burner/flame. Therefore, an attractive approach to cope with the instability is the purposeful design of the burner thermoacoustics. One of the ideas of how the flame TF can be altered/designed is based on the heuristic idea that the acoustic response of one flame can be counteracted by the appropriately phased response of another flame. For the particular case of premixed, burner deck anchored conical flames, the TF depends on the diameter of perforation. It suggests the concept of combining different size and shape of perforations in one burner deck. In the present work, the acoustic response of sintered ceramic fibre burners with mixed perforation is investigated using the TF (de)composition principle. By this approach, the cumulative flame TF can be represented as a weighted sum of elemental TF's of the groups of flames on the basis of the additive nature of the individual flame heat release rate. The capability of this principle to offer a designing framework for optimization of burner deck patterns aiming desirable acoustic characteristics will be tested by a course of measurements. Possible simplifications and extensions of the TF (de)composition principle will be discussed.
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| 7. |
- Gomez, Erik
(author)
-
Centrifugal pendulum vibration absorbers in heavy-duty truck powertrains : Modelling, simulation and experimental investigations
- 2021
-
Doctoral thesis (other academic/artistic)abstract
- The heavy-duty vehicle industry is facing big challenges to reduce CO2 emissions. Although electrification is on the rise, the combustion engine will used for some time to come. Unfortunately, CO2 reduction methods, such as downspeeding, down-sizing and increased cylinder gas-pressure, result in increased torsional vibrations and noise which must be addressed. Conventional torsional vibration reduction methods alone, such as the clutch-damper, will not suffice. The centrifugal pendulum vibration absorber (CPVA) is a torsional vibration reduction device that has not conventionally been used in heavy-duty vehicles and is herein investigated.This work presents analytical, simulation and experimental investigations of the CPVA. First, a model of a centrifugal pendulum vibration absorber with a general suspension architecture is derived with Kane's method. The model allows for different pendulum paths and relative rotation of the pendulum body with respect to the rotor. A normal-force friction loss of the pendulum is developed together with a measurement method to determine the friction coefficient. The measurement method may also be used to validate the pendulum model parameters without any special test-apparatus other than standard accelerometers and a data acquisition system. The developed CPVA model is then included in a torsional model of the complete powertrain including gas-pressure based excitation from the engine model. The powertrain model is developed to simulate transient and quasi-steady state conditions in the time-domain. Also, a continuous model of the end-stops of the pendulum are implemented which also facilitates the simulation.It is concluded that it is important to include the system dynamics of the powertrain in the final design of the CPVA. Also, by exploiting the frequency veering property of the CPVA, powertrain resonances can be completely eliminated.
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| 8. |
- Gomez, Erik, et al.
(author)
-
Low rotational-speed aspects of centrifugal pendulum vibration absorbers
- 2020
-
In: Proceedings of ISMA 2020 - International Conference on Noise and Vibration Engineering and USD 2020 - International Conference on Uncertainty in Structural Dynamics. - : Katholieke Universiteit Leuven, Dept Werktuigkunde. ; , s. 3053-3063
-
Conference paper (peer-reviewed)abstract
- The performance of the centrifugal pendulum vibration absorber (CPVA) is investigated in the low rotational-speed regime in the context of a heavy-duty combustion engine. With the given dimensions and properties of heavy-vehicle engines, special considerations must be taken into account in the analysis of the CPVAs in the low speed regime. In this study, bifilar-suspended pendula absorbers attached to the engine flywheel, tuned to absorb the main engine firing order, is modeled analytically. Friction damping is included in the pendulum model and the effects of the performance by varying the pendulum path curve is studied in the low rotational-speed regime. The low rotational-speed is due to engine down-speeding, resulting in excessive torsional vibration in the driveline. In order to maintain or improve NVH and fulfill legal requirements, the excess torsional vibration must be addressed to gain the emission benefits of down-speeding. Simulation and analysis of the CPVA behaviour is therefore paramount for heavy-vehicle manufacturers to understand and thus make well balanced decisions to fulfill environmental goals.
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| 9. |
- Gomez, Erik, et al.
(author)
-
Normal-force dependant friction in centrifugal pendulum vibration absorbers : Simulation and experimental investigations
- 2021
-
In: Journal of Sound and Vibration. - : Academic Press. - 0022-460X .- 1095-8568. ; 492
-
Journal article (peer-reviewed)abstract
- A model of the normal-force dependant friction loss between the rotor and pendula is developed for bifilar centrifugal pendulum vibration absorbers (CPVAs). The normal-force is dominantly dependant on the rotor rotational velocity but also dependant on the pendulum path. Simulation results of the pendulum with the proposed normal-force friction model agree well with novel experimental results. Order-response simulations of the rotor-CPVA model with the proposed friction model reveal accuracy improvements on the prediction of the rotor oscillation amplitude at different rotational velocities in comparison to existing friction formulations. Derivation of the equations of motion of the rotor-CPVA is performed by Kane's method and solved numerically. The developed experimental setup is used to validate the model parameters such as friction coefficients, path parameters and relative pendulum rotation without necessitating a special test-apparatus other than standard vibration measurement equipment. CPVAs are commonly used to reduce torsional vibration created by reciprocating engines. To reduce emissions, heavy-duty vehicles manufactures are downsizing and downspeeding the combustion engine while maintaining the power output. Unfortunately, this gives rise to increased torsional vibration in the powertrain. The CPVA is a device that can reduce the torsional vibration and thus help fulfill environmental goals.
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| 10. |
- Gomez, Erik R., et al.
(author)
-
Powertrain shuffle-mode resonance suppression by means of flywheel mounted torsichrone centrifugal pendulum vibration absorbers
- 2022
-
In: Journal of Sound and Vibration. - : Elsevier BV. - 0022-460X .- 1095-8568. ; 534
-
Journal article (peer-reviewed)abstract
- A flywheel mounted centrifugal pendulum absorber (CPVA) is designed to completely suppress the low frequency shuffle-mode resonance of a heavy-duty truck powertrain by exploiting the eigenfrequency veering property of the CPVA. The shuffle-mode is excited by the half-order torque of a five-cylinder engine in a downspeeded powertrain during cruising conditions. It is shown that the design of the CPVA may be performed by linear analysis of the CPVA and powertrain system. The linear design is then validated by full nonlinear simulations of the powertrain. A complete suppression of the shuffle-mode resonance is achieved with relatively small total mass of the pendula which makes it highly possible to implement in practice. Downspeeding and downsizing of combustion engines, without sacrificing the power output, are methods to reduce emissions, although, resulting in increased noise and vibration using conventional vibration reduction technology. The CPVA is an order tuned device that can help to reduce the increased vibrations and thus help to reduce the environmental impact of heavy-duty vehicles.
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| 11. |
- Gomez, Erik, et al.
(author)
-
Torsional vibrations in heavy-truck powertrains with flywheel attached centrifugal pendulum vibration absorbers
- 2022
-
In: Mechanism and machine theory. - : Elsevier BV. - 0094-114X .- 1873-3999. ; 167
-
Journal article (peer-reviewed)abstract
- A nonlinear centrifugal pendulum vibration absorber (CPVA) with normal-force dependant friction loss is investigated in a torsional model of a downspeeded powertrain of a heavy-truck. The engine model includes gas-pressure excitation and the existing pendulum model is extended to include a continuous formulation of end-stops at the end of the pendulum-path. Furthermore, the friction loss of the pendulum is experimentally determined. A pendulum-path parameter-study in the complete powertrain model is conducted to consider the effects of the system dynamics on the CPVA. It is shown that the performance of the CPVA is affected by the powertrain system-dynamics and thus important to consider in the design of the CPVA. Downspeeding of the engine by appropriate gearing of the driveline is a measure to decrease the CO2 emissions. However, downspeeding increases the torsional vibration and noise of the powertrain with conventional torsional vibration reduction methods. The CPVA can be used to reduce the torsional vibration and thus facilitate to reach environmental goals.
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| 12. |
- Kojourimanesh, Mohammad, et al.
(author)
-
Evaluation of the thermo-acoustic instability frequency and growth rate via input reflection coefficient measurement for central heating equipment
- 2024
-
In: Combustion and Flame. - : Elsevier BV. - 0010-2180 .- 1556-2921. ; 263
-
Journal article (peer-reviewed)abstract
- Experimental measurement methods and theoretical evaluations based on low-order modeling approaches for both the growth rate and frequency at the onset of thermo-acoustic combustion instability are proposed, and their performance is evaluated. The developed techniques are demonstrated through a systematic measurement of the linear growth rate and frequency of evolving oscillations in the laboratory setup and also applied for the thermo-acoustic qualification of an industrial domestic boiler and a heat cell unit (combination of a burner with a heat-exchanger). Generic measurements have been done for a burner deck with premixed surface-stabilized Bunsen-type flames. The industrial domestic boiler and the heat cell unit are equipped with burners of a similar type but differ by their perforation pattern. They have been tested at different conditions and the experimental and theoretical results are compared. Two modeling strategies are tested: 1- in Laplace domain, with estimating a rational function in the complex domain to fit the measured frequency response, 2- exclusively in frequency domain, without estimating a rational function. Both methods include measurement of the frequency response of two reflection coefficients from i) the upstream part of the system, Rup, and ii) burner with flame completed by the downstream part of the appliance, Rin. Within the first approach, a procedure for an analytic continuation of the measured frequency response to the complex domain is applied and complex eigenfrequencies are calculated by solving the corresponding dispersion equation. An alternative approach was proposed by Kopitz and Polifke and allows estimating both the frequency of oscillation and the growth rate from the analysis of the polar plot of the system's characteristic equation in the frequency domain. The comparison shows that the unstable frequencies can be predicted accurately by both tested modeling strategies. This conclusion holds also for the tested industrial applications. The prediction of the instability growth rates is closer to the measured one when the modeling method in the complex domain is used. However, the frequency domain analysis provides less accurate, but still reasonable estimates of the growth rates and frequencies. Moreover, a good overview of thermo-acoustic performance of each industrial boiler/burner at different conditions is obtained via Rin measurements.
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| 13. |
- Kojourimanesh, Mohammad, et al.
(author)
-
Intrinsic thermo-acoustic instability criteria based on frequency response of flame transfer function
- 2022
-
In: Internoise 2022. - : The Institute of Noise Control Engineering of the USA, Inc..
-
Conference paper (peer-reviewed)abstract
- A study of Intrinsic Thermo-Acoustic (ITA) instability behavior of flames anchored to a burner deck is performed by introducing a mapping between the Flame Transfer Function, FTF(s), defined in the complex (Laplace) domain and the experimentally measured Flame Frequency Response, FFR(iω). The conventional approach requires a system identification procedure to obtain the FTF(s) from the measured FFR(iω). Next, root-finding techniques are applied to define the complex eigenfrequencies. The common practice is to fit the FTF(s) by a rational function that may lead to artifacts like spurious poles and zeros. The purpose of the present work is to establish instability criteria which are directly applicable in the frequency domain. The particular case is considered where the acoustic boundary conditions at both sides of the flame are anechoic. Therefore, the pure ITA mode is treated. First, the causality of the measured FFR(iω) is checked. Then, the criteria of the ITA mode instability applicable to the FFR(iω) phase and magnitude, are derived. Causality properties are used to find the unstable frequency, growth rate, and even the maximum possible value of the linear growth rate. In addition, a procedure is explained to reconstruct the flame transfer function in the complex plane s from the measured flame frequency response which could be an alternative method to study the FTF behavior in the complex domain instead of its estimation with a rational function.
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| 14. |
- Kojourimanesh, M., et al.
(author)
-
Mobius transformation between reflection coefficients at upstream and downstream sides of flame in thermoacoustics systems
- 2021
-
In: "Advances in Acoustics, Noise and Vibration - 2021" Proceedings of the 27th International Congress on Sound and Vibration, ICSV 2021. - : Silesian University Press.
-
Conference paper (peer-reviewed)abstract
- An alternative approach to assess the conditions for the onset of thermoacoustics combustion instability is proposed. The method is based on the analysis of the relation between the reflection coefficient of combustor upstream section (subsystems) with respect to the burner/flame, Rup, and the input reflection coefficient, Rin, as observed from the inlet of the burner with flame and all downstream subsystems of a combustion appliance. The instability of the combustor can be determined by evaluating the system dispersion relation expressed in the terms of these two reflection coefficients. The properties of the relation between Rin, the reflection coefficient of the burner downstream subsystems, Rdn, and elements of the flame transfer matrix, TM, of the burner are investigated. This relation has the form of the well-known Mobius transformation. Using the well-developed theory of the transformation, we derive the necessary conditions of Rdn to ensure that the magnitude of Rin becomes less than 1 in a frequency range. This condition results in a passive thermoacoustics stability of the system's operation. Furthermore, an optimum value of Rdn is derived which provides a minimum value of Rin at given entries of the burner TM. The practical application of the developed theory provides suitable criteria and guidelines for designing passive acoustic properties at the downstream side of the combustion appliance.
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| 15. |
- Kojourimanesh, Mohammad, et al.
(author)
-
Stability criteria of two-port networks, application to thermo-acoustic systems
- 2022
-
In: INTERNATIONAL JOURNAL OF SPRAY AND COMBUSTION DYNAMICS. - : SAGE Publications. - 1756-8277 .- 1756-8285. ; 14:1-2, s. 82-97
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Journal article (peer-reviewed)abstract
- System theory methods are developed and applied to introduce a new analysis methodology based on the stability criteria of active two-ports, to the problem of thermo-acoustic instability in a combustion appliance. The analogy between thermo-acoustics of combustion and small-signal operation of microwave amplifiers is utilized. Notions of unconditional and conditional stabilities of an (active) two-port, representing a burner with flame, are introduced and analyzed. Unconditional stability of two-port means the absence of autonomous oscillation at any embedding of the given two-port by any passive network at the system's upstream (source) and downstream (load) sides. It has been shown that for velocity-sensitive compact burners in the limit of zero Mach number, the criteria of unconditional stability cannot be fulfilled. The analysis is performed in the spirit of a known criterion in microwave network theory, the so-called Edwards-Sinsky's criterion. Therefore, two methods have been applied to elucidate the necessary and sufficient conditions of a linear active two-port system to be conditionally stable. The first method is a new algebraic technique to prove and derive the conditional and unconditional stability criteria, and the second method is based on certain properties of Mobius (bilinear) transformations for combinations of reflection coefficients and scattering matrix of (active) two-ports. The developed framework allows formulating design requirements for the stabilization of operation of a combustion appliance via purposeful modifications of either the burner properties or/and of its acoustic embeddings. The analytical derivations have been examined in a case study to show the power of the methodology in the thermo-acoustics system application.
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| 16. |
- Kojourimanesh, M., et al.
(author)
-
Thermo-acoustic flame instability criteria based on upstream reflection coefficients
- 2021
-
In: Combustion and Flame. - : Elsevier BV. - 0010-2180 .- 1556-2921. ; 225, s. 435-443
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Journal article (peer-reviewed)abstract
- A prospective method to assess thermo-acoustic instabilities based on two reflection coefficients measured from the upstream side of the burner is presented and experimentally validated. In order to compose a model which allows predicting the onset of thermo-acoustic instability of combustion in a practical appliance, one has to characterize the thermo-acoustic properties of the burner including the flame as an acoustically active element and acoustic properties of all other (usually passive) components of the combustion appliance both upstream as well as downstream of the burner. This kind of modeling strategy usually faces serious practical problems related to the need of measurements/modeling at the hot downstream part of the system. In the present work, we propose a measurement and a system modeling approach which relies on two acoustic measurements, namely reflection coefficients, only at the cold (burner upstream) part of the combustion appliance. Both reflection coefficients, termed upstream and input, can be readily measured using standard acoustic techniques. The need to measure the input reflection coefficient of an acoustically active subsystem may impose difficulties related to the acoustic instability of the measurement setup itself. The approach and technical solution to handle this problem via a special modification of the excitation source (loudspeaker box) is proposed. The dispersion relation to search for system eigen frequencies is represented in a form that couples the reflection coefficients of the upstream part of the appliance and input reflection coefficient from the downstream part as observed through the burner with flame. This form of the dispersion relation is commonly used in the theory of radio-frequency circuits and recently introduced for thermo-acoustic problems. The proposed method is applied to burners with premixed burner-stabilized Bunsen-type flames. The observed instability conditions and oscillation frequencies are compared with predictions of the proposed modeling approach and reveal good correspondence.
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| 17. |
- Liu, Xiaowan, et al.
(author)
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Measurements and modelling of dynamic stiffness of a railway vehicle primary suspension element and its use in a structure-borne noise transmission model
- 2021
-
In: Applied Acoustics. - : Elsevier BV. - 0003-682X .- 1872-910X. ; 182
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Journal article (peer-reviewed)abstract
- The noise inside railway vehicles is transmitted by both structure-borne and airborne paths and, although there are many sources, the rolling noise is often the most important. This paper focuses on the structure-borne transmission of rolling noise in a metro vehicle. Measurements are presented first of the vertical and lateral dynamic stiffness of a primary suspension element consisting of conical rubber/metal elements. Results are presented for various constant preloads over the frequency range 60600 Hz. An analytical model of the suspension element is also developed, based on a mass-spring system and including wave motion within the rubber elements. The dynamic stiffness results are used in a finite element model of the running gear, consisting of the bogie frame, wheelsets and suspension elements. The excitation is provided by the combined wheel/rail roughness at the contact point. This model is used to calculate the blocked forces at the connection points between the secondary suspension elements and the car body. The blocked forces are combined with measured vibro-acoustic transfer functions from these mounting points to the vehicle interior to determine the structure-borne noise inside the vehicle. The proposed methodology is validated against measurements during operation in terms of acceleration levels, blocked forces and structure-borne noise levels inside the vehicle, showing reasonably good agreement. Including the dynamic stiffness for the primary suspension leads to improved agreement between 100 and 500 Hz compared with using a constant stiffness.
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| 18. |
- Manzari, Luca, et al.
(author)
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A method for the observation of the anelastic behaviour of anisotropic porous materials using digital image correlation
- 2020
-
In: Journal of Sound and Vibration. - : ACADEMIC PRESS LTD- ELSEVIER SCIENCE LTD. - 0022-460X .- 1095-8568. ; 474
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Journal article (peer-reviewed)abstract
- This paper proposes an experimental method for observing the anelastic anisotropic behaviour of poroelastic media. The setup relies on three-dimensional digital image correlation, enabling the acquisition of full-field displacement data from the visible faces of a vibrating cubic material sample. The latter is placed in a vacuum chamber, loaded with a seismic mass and excited uniaxially. The observability and relevance of the three-dimensional displacement field is assessed by means of a numerical simulation. A homogenised fully anisotropic model is used, implemented using the finite element method. Thus, a set of material properties obtained using single-point data is considered as the reference configuration for the numerical method. Selected experimental and numerical results are presented, highlighting the importance and the advantages that full-field observations yield over single-point measurements.
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| 19. |
- Manzari, Luca
(author)
-
High-speed stereo imaging for the characterization of anisotropic viscoelastic media
- 2020
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Doctoral thesis (other academic/artistic)abstract
- This thesis proposes an experimental method for observing and characterizing the viscoelastic properties of anisotropic media using high-speed white light stereo imaging. The method uses short-time video recordings of a specimen undergoing forced harmonic motion.The three-dimensional displacement field of the specimen is then resolved using digital image correlation.Measuring for a short time has multiple advantages: it minimizes the conditioning of the specimen, and gives meaningful results when true stationary conditions are inaccessible (e.g. because of relaxation processes, or changes in the environmental conditions that cannot be accounted for).Moreover, it enables a reduction of the data storage needs and the computational costs associated with the image acquisition and processing.To overcome the intrinsic limitations of a Fourier-based approach for short time records, an optimization algorithm is used to determine the point-wise amplitude, phase and frequency of the full-field harmonic motion.This approach maximizes signal-to-noise ratio, is suitable for the identification of non-linear behaviors and tolerates data records that are non-uniformly spaced in time (e.g. because of momentary data losses and failure of the image matching algorithms).The measurement accuracy is increased by proposing a method to extract the frame of reference of the specimen on a per-frame bases, and express the measured displacement field therein.A cube of melamine foam and a pantographic sheet have been observed using the proposed method, and the measured data compared with the outcome of linear viscoelastic numerical models.The added information obtained about the melamine is believed to improve the accuracy of the characterization of its viscoelastic behavior, and the observation of the pantographic sheet represents and absolute first in the experimental studies of its dynamics.
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| 20. |
- Saxena, V., et al.
(author)
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Designing an acoustic termination with a variable reflection coefficient to investigate the probability of instability of thermo-acoustic systems
- 2021
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In: "Advances in Acoustics, Noise and Vibration - 2021" Proceedings of the 27th International Congress on Sound and Vibration, ICSV 2021. - : Silesian University Press.
-
Conference paper (peer-reviewed)abstract
- This paper presents results of the development of an acoustic device to be utilized as a duct termination with variable reflection coefficient. This study is motivated by the idea to experimentally evaluate the probability of instability of a thermo-acoustic system where combustion acts as an active acoustic element, and this termination acts as a passive acoustic element that can be configured to a desired value of the reflection coefficient at the upstream side of the flame and burner for lab-scaled physical modelling of, for instance, domestic boilers. This termination consists of a cylinder containing a stack of truncated hollow cones with narrow gap in between and a telescopic tube. The gap between the adjacent cones, and sound-absorbing fibrous material (“Acotherm”) placed in the cavity of these cones produce a low reflection coefficient in the frequency range between 40 and 800 Hz. Longitudinal displacement of these cones inside the cylinder generates a reflection coefficient with magnitude ranging from 0.2 to 0.9. The telescopic tube with an adjustable length (between 0.85 - 1.38 m) allows to achieve a wide range of phases of reflection coefficient. The steps taken to optimize the design and performance of this termination in presence of flame are presented here.
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| 21. |
- Saxena, Vertika, et al.
(author)
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Designing variable reflection coefficient for upstream and downstream terminations to study their effect on flame thermoacoustics
- 2022
-
In: INTERNATIONAL JOURNAL OF SPRAY AND COMBUSTION DYNAMICS. - : SAGE Publications. - 1756-8277 .- 1756-8285. ; 14:3-4, s. 251-265
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Journal article (peer-reviewed)abstract
- In this paper, the design, construction and results of experiments performed on a generic combustion system are presented. The setup is supplemented by various weakly frequency-dependent variable reflection coefficient (RC) devices as upstream and downstream acoustic terminations. The main objective of building such terminations is to provide a method to study burner/flame stability when it is placed between various acoustic configurations (RC: 0.1-0.9) and to determine the figure of merit of a burner based on the evaluation of its map of (in-)stability. Furthermore, burner design parameters such as the burner perforation pattern (holes diameter, pitch, perforation area, etc.) which will provide combustion stability for the widest range of burner's acoustic embedding conditions are identified. The experimental setup comprises of an upstream acoustic termination, a telescopic tube with adjustable length is placed after the upstream termination followed by the burner and the quartz tube. On the top of the quartz tube, the replaceable downstream terminations are installed. Nine downstream terminations are constructed by stacking plates of 0.25 mm thickness separated by spacers ranging from 0.1 to 1 mm thickness. Particularly, for the burners tested in this setup, the smallest hole diameter burner (with the largest perforation area) results in the largest stable region on the stability map in the parameter space. An increase in the flow velocity leads to an increase in the frequency of instability and makes a stable system tend to become unstable, while an increase in the equivalence ratio contributes to stabilizing system instability
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| 22. |
- Sjöstrand, Jakob, et al.
(author)
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Effect of normal load evolution on transient torsional vibrations during clutch engagement
- 2020
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In: Proceedings of ISMA 2020 - International Conference on Noise and Vibration Engineering and USD 2020 - International Conference on Uncertainty in Structural Dynamics. - : KU Leuven Department Mechanical Engineering Division. ; , s. 1433-1447
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Conference paper (peer-reviewed)abstract
- Different models of the evolving normal load in the clutch friction interface and their respective influence on friction induced torsional driveline vibrations, during clutch engagement, are examined. This is done in the context of driveline vibrations of heavy duty vehicles with combustion engines. In prior studies of clutch synchronisation a lot of focus has been devoted to the characteristics of the coefficient of friction. A negative gradient of the coefficient of friction, with respect to slipspeed, can lead to driveline instabilities, sometimes referred to as clutch start-up judder. However, the way in which the normal load evolves, and consequently how the friction torque builds up during synchronization, has been given less attention. This study compares the influence of a linear evolution of the normal load to a quadratic evolution. It is shown that the slope of the normal load at the beginning of synchronization is pivotal to the excitation of driveline vibrations, where a decrease of the slope effectively reduces the self-excited vibrations.
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| 23. |
- Sjöstrand, Jakob, 1987-
(author)
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Transient vibrations from dry clutch operation in heavy-duty truck powertrains : Modelling, simulation and validation
- 2021
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Licentiate thesis (other academic/artistic)abstract
- For internal combustion engines used in heavy-duty vehicles, increased engine efficiency and consequently reduced CO2 emissions can be obtained if the engine speed can be kept within an optimal speed range. This requires swift and frequent gear shifts where the dry friction clutch is utilized. Enhanced dry clutch simulation models and a better understanding of the involved phenomena can assist the development towards swifter gear shifts and help reduce CO2 emissions. The work presented in this thesis focuses on the modelling of dry clutch systems for heavy-duty applications and their effect on the torsional response of the driveline during transient events such as clutch engagement and disengagement. During these events it is primarily the first vibration mode of the driveline that is active and consequently it is possible to greatly reduce theof degrees of freedom (DOFs) of the powertrain model and still capture the relevant dynamics of the powertrain. The reduced set of differential equationsdescribe the torsional motion of the powertrain and the equations of motion are solved numerically in the time-domain. From a mathematical point ofview, the equations of motion turn "stiff" when the clutch is locked. This issue is resolved by utilizing numerical solution techniques suitable for stiff differential equations. In the simulations it was observed that no engine torque fluctuations were transferred through the slipping clutch. Consequently the response of the driveline is purely modal during sliding. If the gradient of the coefficient of friction is negative the modal response is possibly unstable with exponentially growing vibration amplitudes as an effect. Moreover, the way in which the clamp load evolves during clutch engagement is found to severely effect the excitation of transient vibrations during clutch synchronization. It can be shown that reducing the gradient of the evolving clamp load at the onset of sliding will reduce the amplitude of the friction induced vibrations. Reducing the torsional vibration amplitudes will help avoid the jerky motion of the vehicle during launch and increase comfort for driver and passengers.
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| 24. |
- Tateo, F., et al.
(author)
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Design and experimental validation of a plate with internally resonating lattices for low-frequency vibro-acoustic control
- 2020
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In: Euronoise 2015. - : DC/ConfOrg. ; , s. 995-1000
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Conference paper (peer-reviewed)abstract
- A flexible plate and an internal resonating lattice are combined in an assembly which is characterized by high damping performance and tuned vibration attenuation at low frequencies. The resonating lattice consists of an elastomeric frame equipped with a metallic inclusion which is designed to resonate at selected frequencies. The system achieves high damping performance by combining the frequency-selective properties of internally resonating structures, with the energy dissipation characteristics of their constituent material. Furthermore, tuning and modifying the layout of the resonant lattice allows for tailoring of the resonating properties so that vibration attenuation is obtained over desired frequency ranges. Experimental results show the performances of the resonant assembly and suggest its potential application in vibrations and noise reduction.
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| 25. |
- Wang, Bochao
(author)
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Constitutive models of magneto-sensitive rubber under a continuum mechanics basis and the application in vibration isolation
- 2020
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Doctoral thesis (other academic/artistic)abstract
- Due to its durability, stretchability, relatively low stiffness and high damping, rubber is widely used in engineering anti-vibration fields. However, a major deficiency is that once installed, the mechanical properties of traditional rubber-based devices are fixed where its adaptability to various loading conditions is poor. An alternative to traditional rubber materials is magneto-sensitive (MS) rubber. The main componentsof MS rubber are a rubber matrix and ferromagnetic particles. Under a magnetic field, the modulus of MS rubber can be altered rapidly and reversibly. Therefore, compared with conventional rubber-based devices, the stiffness of MS rubber-based devices can be adapted to various loading conditions and an enhanced vibration reduction effect can be achieved. Measurement results revealed that the mechanical behavior of MS rubber is not simple. To be specific, the dynamic modulus of MS rubber has a magnetic, frequency,amplitude and temperature dependency. In order to promote the applications of MS rubber in the anti-vibration area, models to depict the above properties are needed. The main goal of this thesis is to model the magnetic, frequency, amplitude and temperature dependence of MS rubber under a continuum mechanics basis. The research results regarding the constitutive modeling consist of three papers (Paper A, C and D). The simulation results show a good agreement with the measurement data, which proves the accuracy and feasibility of the developed model. In addition to the constitutive models of MS rubber, an investigation of MS rubber application in the vibration isolation system under harmonic and random loading cases is numerically conducted (Paper B). In order to achieve an enhanced vibration isolation effect, two control algorithms corresponding to the harmonic and random loading are developed. Numerical results verify that the vibration isolation effect ofMS rubber vibration isolator is better than the traditional rubber-based isolator. In this thesis, the model developed for MS rubber deepens the understanding of how magnetic, frequency, amplitude and temperature affect the mechanical performance of MS rubber. Moreover, the research of MS rubber application in vibration isolators and the corresponding control strategies are helpful for the design of MS rubber-based anti-vibration devices.
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| 26. |
- Wildemans, Roeland, et al.
(author)
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Nonlinear dynamics of pure intrinsic thermo-acoustic modes
- 2023
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In: Combustion and Flame. - : Elsevier BV. - 0010-2180 .- 1556-2921. ; 251, s. 112703-
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Journal article (peer-reviewed)abstract
- In this paper the nonlinear dynamics of the pure Intrinsic Thermo-Acoustic (ITA) modes are experimentally investigated for burner stabilized premixed flames by decoupling them from the acoustic modes. Thereto, a setup is used with up- and downstream mufflers that provide close to anechoic boundary conditions. This enables the investigation of the self-excited oscillations of the flame, without the influences of acoustic reflections. An experimental bifurcation analysis is conducted to systematically investigate the different asym ptotic oscillatory states and their transitions. By increasing the upstream velocity, the flame looses stability through a supercritical Hopf bifurcation and reveals limit cycles with a single dominant frequency. For increasing upstream velocity, a low frequent mode appears, resulting in quasi-periodic oscillations. This regime is characterized by a beating phenomenon with simultaneous amplitude and frequency modulations. When the upstream velocity is even further increased, a period doubling bifurcation is observed. To our best knowledge, the experimental investigation of the nonlinear dynamical behavior of pure ITA modes and, in particular, the low frequency oscillation, has not been reported before, and it provides valuable insights towards developing accurate time-domain models of the nonlinear acoustic behavior of premixed flames. Finally, a phenomenological model of two coupled oscillators is introduced that is able to qualitatively reproduce all observed nonlinear oscillations of the flames.
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| 27. |
- Wildemans, Roeland, et al.
(author)
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Parameter estimation of two coupled oscillator model for pure intrinsic thermo-acoustic instability
- 2023
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In: Nonlinear dynamics. - : Springer Nature. - 0924-090X .- 1573-269X. ; 111:14, s. 12835-12853
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Journal article (peer-reviewed)abstract
- A nonlinear phenomenological model of two coupled oscillators is proposed, which is able to describe the rich nonlinear behaviour stemming from an unstable pure intrinsic thermo-acoustic (ITA) mode of a simple combustion system. In an experimental bifurcation analysis of a pure ITA mode, it was observed that for increasing mean upstream velocity the flames loose stability through a supercritical Hopf bifurcation and subsequently exhibit limit cycle, quasi-periodic and period-2 limit cycle oscillations. The quasi-periodic oscillations were characterised by low frequent amplitude and frequency modulation. It is shown that a phenomenological model consisting of two coupled oscillators is able to reproduce qualitatively all the different experimentally observed regimes. This model consists of a nonlinear Van der Pol oscillator and a linear damped oscillator, which are nonlinearly coupled to each other. Furthermore, a parameter estimation of the model parameters is conducted, which reveals a good quantitative match between the model response and the experimental data. Hence, the presented phenomenological dynamical model accurately describes the nonlinear self-excited acoustic behaviour of premixed flames and provides a promising model structure for nonlinear time-domain flame models.
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| 28. |
- Wildemans, Roeland, et al.
(author)
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Parameter identification of two coupled oscillator model for pure intrinsic thermoacoustic instability
- 2022
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In: Internoise 2022. - : The Institute of Noise Control Engineering of the USA, Inc..
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Conference paper (peer-reviewed)abstract
- In this paper, a nonlinear phenomenological model of two coupled oscillators is presented, which is able to describe the rich nonlinear behaviour stemming from an unstable pure Intrinsic Thermo-Acoustic (ITA) mode of a simple combustion system. In a bifurcation analysis of a pure ITA mode, it was observed that for increasing mean upstream velocity the flames loose stability through a supercritical Hopf bifurcation and subsequently exhibit limit cycle, quasi-periodic and period-2 limit cycle oscillations. The quasi-periodic oscillations were characterized by low frequent amplitude and frequency modulation. It is shown that a phenomenological model consisting of two coupled oscillators is able to reproduce qualitatively all the different experimentally observed regimes. This model consists of a nonlinear Van der Pol oscillator and a linear mass-spring-damper oscillator, which are nonlinearly coupled to each other. Furthermore, a parameter identification of the model parameters is executed, which shows a good quantitative match between the model and the experimental data. Hence, the presented phenomenological dynamical model accurately describes the nonlinear self-excited acoustic behaviour of premixed flames.
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| 29. |
- Xie, G., et al.
(author)
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Virtual Test Method of Structure-Borne Sound for a Metro Bogie
- 2021
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In: Notes on Numerical Fluid Mechanics and Multidisciplinary Design. - Cham : Springer Science and Business Media Deutschland GmbH. ; , s. 186-193
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Conference paper (peer-reviewed)abstract
- This paper presents a virtual test method for structure-borne noise generated from railway running gear. This method combines a number of existing tools to form a system approach. The wheelset and bogie frame are modelled using FEM software Nastran to include details of their construction. The primary springs are simplified to standard CBUSH elements in Nastran with point and transfer stiffness modelled by frequency-dependent complex stiffness, which are tuned against measurements. The wheel-rail contact forces due to roughness excitation are obtained by the wheel-rail interaction tool TWINS. The vibration of the full running gear is simulated in Nastran by applying the wheel-rail contact forces. The forces transmitted to the vehicle body through traction bars and dampers are calculated for predicting structure-borne noise.
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| 30. |
- Zea, Elias, 1989-, et al.
(author)
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Separation of rail and wheel contributions to pass-by noise with sparse regularization methods
- 2020
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In: Journal of Sound and Vibration. - : Academic Press. - 0022-460X .- 1095-8568. ; 487
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Journal article (peer-reviewed)abstract
- This paper proposes a method for separating rail and wheel noise contributions via sparse regularization of microphone array data. The underlying idea is to promote sparse solutions, which jointly approximate the two noise contributions with few non-zero coefficients. The main hypothesis is that the acoustic field radiated by the rail is sparse in a dictionary of plane waves, that the acoustic field radiated by the wheels is sparse in a dictionary of moving sources, and that both acoustic fields are dense in the opposite dictionaries. How well this happens is studied with the coherence between the plane waves and the moving sources. The strength of the proposed approach is that it does not require static tests prior to the pass-by. The separation is performed in three main steps, executed in the time-frequency domain. First, the rail contribution is separated from the total pass-by noise using matching pursuit optimization, promoting solutions with a limited number of plane waves per frequency. Second, the residual between the total pass-by noise and the estimated rail noise is calculated. And third, the wheel contribution is separated from the residual via ℓ1-norm minimization, promoting solutions that are row-sparse at all frequencies. The separation performance is investigated with synthetic data, and validated with experimental data against reference predictions with the TWINS software, for pass-by noise measurements of trains running at 40, 80 and 160 km/h.
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| 31. |
- Zea, Elias, 1989-, et al.
(author)
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Sparsity-driven separation of railway rolling noise with a microphone array
- 2020
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Conference paper (other academic/artistic)abstract
- In this paper we propose the use of sparse reconstruction methods to characterize the pass-by noise of rail-bound transportation vehicles. European trains are homologated with the TSI-NOISE legislation, which specifies the quantification of the vehicle noise alone; that is, irrespective of the track on which the vehicle is running. However, some tracks contribute significantly to the pass-by noise in mid-frequencies, leading to geographically dependent noise emissions of the same vehicle. To remove this dependency from the homologation, the track and vehicle contributions must be separated. This paper proposes the use of sparse reconstruction methods to distinguish between vehicle and rail noise. The approach is based on measurements with a microphone array near the track, and the use of dictionaries of plane waves and moving equivalent sources, to model the track and the vehicle contributions respectively. It is shown that the separated spectra agree well with the reference results predicted with the TWINS software.
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