| 1. |
- Afzal, Mohammad, 1987-, et al.
(författare)
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A formulation of the Jacobian matrixfor 3D numerical friction contact model applied to turbine blade shroud contact
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Ingår i: Journal of Sound and Vibration. - 0022-460X .- 1095-8568.
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- An analytical expression is formulated to compute the Jacobian matrix for 3D friction contact modelling that eciently 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 thecalculation of the friction damping on a turbine blade with shroud contact interface having an arbitrary 3Drelative displacement. The analytical expression drastically reduces the computation time of the Jacobian matrix with respect to the classical finite dierence 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 dierence 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 aperiodic 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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| 2. |
- 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
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Ingår i: Journal of Vibration and Control. - 1077-5463 .- 1741-2986.
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)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 in order to achieve the desired friction damping in the structure. Friction damping in a bladed disk depends on many parameters such as rotational speed, engine excitation order, nodal diameter, contact stiffness, friction coefficient and normal contact load. However, all these parameters have a fixed value at an operating point. On the other hand, the ability to vary some of these parameters such as the normal contact load is desirable in order to obtain 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 0.002 under prestress and a blocked force over 1500 N. A linearized model of the magnetostrictive material, which is accurate enough for a DC application, is employed to compute the output displacement and the blocked 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 contact analysis is performed for different mounting configurations of the actuator 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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| 3. |
- Afzal, Mohammad, 1987-, et al.
(författare)
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Numerical analysis of multiple friction contacts in bladed disks
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Ingår i: International Journal of Mechanical Sciences. - 0020-7403 .- 1879-2162.
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- The damping potential of multiple friction contacts in a bladed disk, tip shroud and strip damper is investigated, showing 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 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 and 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 approximate 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)
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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
(författare)
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Reduction of Audible Noise of a Traction Motor at PWM Operation
- 2018
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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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| 6. |
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| 7. |
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| 8. |
- Botling, Fredrik, et al.
(författare)
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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)
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Modelling and simulation of electromagnetic audible noise generated by traction motors
- 2016
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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. |
- Botling, Fredrik, et al.
(författare)
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Modelling framework for electromagnetic noise generation from traction motors
- 2016
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Ingår i: Journal of Notes on Numerical Fluid Mechanics and Multidisciplinary Design. - Cham : Springer Nature. - 1612-2909.
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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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