| 1. |
- Afzal, Mohammad, 1987-, et al.
(författare)
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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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Ingår i: Journal of Intelligent Materials Systems and Structures. - : SAGE Publications. - 1045-389X .- 1530-8138. ; 31:8, s. 1111-1125
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Tidskriftsartikel (refereegranskat)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.
(författare)
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A replacement model to simulate the nonlinear dynamics of electro-responsive liquid crystal coatings
- 2023
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Ingår i: AIP Advances. - : AIP Publishing. - 2158-3226. ; 13:3
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Tidskriftsartikel (refereegranskat)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.
(författare)
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Experimental study of a slit in the presence of a bias flow under medium- and high-level acoustic excitations
- 2023
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Ingår i: International Journal of Spray and Combustion Dynamics. - : SAGE Publications. - 1756-8277 .- 1756-8285. ; 15:2, s. 117-126
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Tidskriftsartikel (refereegranskat)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.
(författare)
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A framework for suppression of thermoacousitc instability using the nyquist criterion
- 2023
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Ingår i: Proceedings of the 29th International Congress on Sound and Vibration, ICSV 2023. - : Society of Acoustics.
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Konferensbidrag (refereegranskat)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.
(författare)
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Assessment of the acoustic scattering matrix of a heat exchanger using ssCFD-LNSE simulation
- 2022
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Ingår i: Internoise 2022. - : The Institute of Noise Control Engineering of the USA, Inc..
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Konferensbidrag (refereegranskat)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.
(författare)
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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
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Ingår i: Internoise 2022 - 51st International Congress and Exposition on Noise Control Engineering. - : The Institute of Noise Control Engineering of the USA, Inc..
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Konferensbidrag (refereegranskat)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
(författare)
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Centrifugal pendulum vibration absorbers in heavy-duty truck powertrains : Modelling, simulation and experimental investigations
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)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.
(författare)
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Low rotational-speed aspects of centrifugal pendulum vibration absorbers
- 2020
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Ingår i: 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
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Konferensbidrag (refereegranskat)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.
(författare)
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Normal-force dependant friction in centrifugal pendulum vibration absorbers : Simulation and experimental investigations
- 2021
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Ingår i: Journal of Sound and Vibration. - : Academic Press. - 0022-460X .- 1095-8568. ; 492
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Tidskriftsartikel (refereegranskat)abstract
- A model of the normal-force dependant friction loss between the rotor and pendula is developed for bifilar centrifugal pendulum vibration absorbers (CPVAs). The normal-force is dominantly dependant on the rotor rotational velocity but also dependant on the pendulum path. Simulation results of the pendulum with the proposed normal-force friction model agree well with novel experimental results. Order-response simulations of the rotor-CPVA model with the proposed friction model reveal accuracy improvements on the prediction of the rotor oscillation amplitude at different rotational velocities in comparison to existing friction formulations. Derivation of the equations of motion of the rotor-CPVA is performed by Kane's method and solved numerically. The developed experimental setup is used to validate the model parameters such as friction coefficients, path parameters and relative pendulum rotation without necessitating a special test-apparatus other than standard vibration measurement equipment. CPVAs are commonly used to reduce torsional vibration created by reciprocating engines. To reduce emissions, heavy-duty vehicles manufactures are downsizing and downspeeding the combustion engine while maintaining the power output. Unfortunately, this gives rise to increased torsional vibration in the powertrain. The CPVA is a device that can reduce the torsional vibration and thus help fulfill environmental goals.
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| 10. |
- Gomez, Erik R., et al.
(författare)
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Powertrain shuffle-mode resonance suppression by means of flywheel mounted torsichrone centrifugal pendulum vibration absorbers
- 2022
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Ingår i: Journal of Sound and Vibration. - : Elsevier BV. - 0022-460X .- 1095-8568. ; 534
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Tidskriftsartikel (refereegranskat)abstract
- A flywheel mounted centrifugal pendulum absorber (CPVA) is designed to completely suppress the low frequency shuffle-mode resonance of a heavy-duty truck powertrain by exploiting the eigenfrequency veering property of the CPVA. The shuffle-mode is excited by the half-order torque of a five-cylinder engine in a downspeeded powertrain during cruising conditions. It is shown that the design of the CPVA may be performed by linear analysis of the CPVA and powertrain system. The linear design is then validated by full nonlinear simulations of the powertrain. A complete suppression of the shuffle-mode resonance is achieved with relatively small total mass of the pendula which makes it highly possible to implement in practice. Downspeeding and downsizing of combustion engines, without sacrificing the power output, are methods to reduce emissions, although, resulting in increased noise and vibration using conventional vibration reduction technology. The CPVA is an order tuned device that can help to reduce the increased vibrations and thus help to reduce the environmental impact of heavy-duty vehicles.
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