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| 2. |
- Lundberg, Oskar, 1980-
(författare)
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On the influence of surface roughness on rolling contact forces
- 2016
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Road vehicle tyres, railway wheels and ball bearings all generate rolling contact forces which are transferred within a finite area of contact between the rolling element and the substrate. Either it is visible or not for the human eye, a certain degree of roughness is always present on the contacting surfaces and it influences the generation of both vertical and lateral contactforces. The purpose of this investigation is to enhance the understanding and modelling of the influence from small-scale surface roughness on the generation of rolling contact forces. To this end, a computationally efficient method to include roughness-induced contact nonlinearities in the dynamic modelling of rolling contacts is proposed. The method is implemented in a time domain model for vertical wheel–track interaction to model rolling-induced rail vibrations, showing good agreement with measurements. Furthermore, a test rig is developed and used for the investigation of tyre–road rolling contact forces. Detailed studies are performed on the influence of substrate roughness on the resulting contact forces for a tyre tread block which is rolling at different operating conditions. The choice of substrate as well as the rolling velocity and the slip ratio is observed to have significant influence on the resulting friction coefficient. For high slip ratios, stick–slip oscillations appear, exhibiting frequency content which is largely dependent on the choice of substrate. The outcomes of this study can potentially be used to improve future tyre–road contacts with respect to wear, traction and noise generation.
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| 3. |
- Lundberg, Oskar, 1980-, et al.
(författare)
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A compact internal drum test rig for measurements of rolling contact forces between a single treadblock and a substrate
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- A novel test rig design is presented which enables detailed studies of the three force components generated in the impact and release phase of rolling contact between a tyre tread block and a substrate. The design of the compact internal drum test rig provides realistic impact and release angles for the tread block-substrate contact and enables force measurements at high rolling speeds with a high signal-to-noise ratio. Measurements of the rolling contact forces are presented for different values of rolling velocity, static pre-load and acceleration. It is demonstrated that this test rig provides results which contribute to the understanding of tyre--road interaction and can be used as input to modelling-based development of both tyres and roads aiming for improved handling, safety, energy efficiency and comfort.
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| 4. |
- Afzal, Mohammad, 1987-
(författare)
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Numerical modelling and analysis of friction contact for turbine blades
- 2015
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- High cycle fatigue failure of turbine and compressor blades due to resonance in the operating frequency range is one of the main problems in the design of gas turbine engines. To suppress excessive vibrations in the blades and prevent high cycle fatigue, dry friction dampers are used by the engine manufacturers. However, due to the nonlinear nature of friction contact, analysis of such systems becomes complicated.This work focuses on the numerical modelling of friction contact and a 3D friction contact model is developed. To reduce the computation time in the Newton-iteration steps, a method to compute the Jacobian matrix in parallel to the contact forces is proposed. The developed numerical scheme is successfully applied on turbine blades with shroud contact having an arbitrary 3D relative displacement. 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 the cyclic symmetry boundary condition for a periodic structure.The developed 3D coupled numerical contact model is compared with a 3D contact model having uncoupled tangential motion and drawback of the uncoupled contact model is discussed. Furthermore, presence of higher harmonics in the nonlinear contact forces is analyzed and their effect on the excitation of the different harmonic indices (nodal diameters) of the bladed disk are systematically presented. Moreover, due to the quasi-analytical computation of the Jacobian matrix, the developed scheme is proved to be effective in solving the equations of motion and significant reduction in time is achieved without loss of accuracy.
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| 5. |
- 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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| 6. |
- Erenchun, A., et al.
(författare)
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Model of an elevator system to characterize the influence of the isolator on the vibration transmission
- 2020
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Ingår i: Proceedings International Conference on Noise and Vibration Engineering (ISMA2020) / International Conference on Uncertainty in Structural Dynamics (USD). - : KU Leuven. ; , s. 2715-2729
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Konferensbidrag (refereegranskat)abstract
- Vibrations are a common issue in elevator installations, where a drive machine that holds and pulls the cabin and the counterweight composes the electromechanical system. In order to reduce the space needed by the installation, nowadays the drive machine is usually mounted upon a frame that is fixed to the guide rails. Therefore, vibration transmission can occur through the machine to the cabin or even to the building. With the purpose of reducing this vibration transmission, the use of isolators under the machine is a widely employed solution. These isolators are often selected just taking into account the static loads, due to the lack of information about the dynamic behavior of the system. The present research develops a theoretical model of an elevator system to study the influence of the isolators on vibration transmission.
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| 7. |
- Sun, Jia
(författare)
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Rotating Structure Modeling and Damping Measurements
- 2011
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The structural damping is of importance to suppress the vibration amplitude of compressor blades rotating at high angular velocity under a high cycle impact. To avoid the appearance of the high cycle fatigue (HCF), damping materials may be applied to the compressor blades. To quantify the effect while using damping materials, a numerical tool needs to be developed for the damping prediction of a dynamic rotating blade. This thesis is divided into two parts: Paper A develops a dynamic model of a rotating blade and Paper B a damping structure model including measurements.In Paper A, a dynamic rotating blade model is developed by using a plate model at an arbitrary stagger angle. Hamilton’s principle is applied to derive a system of equations of motion and the corresponding boundary conditions. Numerical simulation is implemented to perform eigenfrequency analysis by the Extended Galerkin method. In addition, parametric analysis is performed with respect to rotation speed and stagger angle, respectively. Results show a good agreement with those of the finite element method. Finally, forced response analysis is determined for two cases; a point force and a distribution force, using a proportional damping model.In Paper B, unconstrained and constrained damping techniques are applied to increase the structural damping of the blades, including measurement and modeling results. Two specimens, titanium and stainless steel, are treated by aluminum oxide and epoxy coating material. Measurement results show that both treatments give damping increase, where aluminum oxide is more effective for damping improvement than the corresponding epoxy treatment. The unconstrained damping layer model is used to predict the total material damping of the combined structure as well as the material damping of coating layer. Furthermore, the constrained-layer model is used to optimize the damping configuration. Two compressor blades in titanium and stainless steel are tested in air and vacuum. One reason is being that the radiation loss factor increases the total damping comparing with that under vacuum condition. The calculation of radiation loss factor is performed to match the measurement data. Finally, increased material damping decreases peak stress and therefore increases the life time of the compressor blades.
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| 8. |
- Zea, Elias, 1989-
(författare)
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Sound field separation with microphone arrays
- 2017
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Sound field analysis is a fundamental tool in the design, manufacturing, testing and diagnosis of machines and transportation means, as well as the legislations that regulate noise levels in order to minimize environmental pollution. Customary solutions to the problem of sound field analysis are microphone array technologies such as near-field acoustic holography (NAH) and beamforming. One of the challenges of using these technologies often lies in the difficulty for separating disturbing sounds from the target source, specially when these are correlated. For example, NAH requires that no reflecting surfaces are found in the vicinity of the array, which is in theory only possible in an echo-free chamber. On the other hand, beamforming is most suitably used to separate uncorrelated sound sources, which is not the case of, for instance, the noise generated by the contact between the wheel of a train and a railway track. The present thesis examines the research problems of separating a sound source from its reflections, and separating the rail noise from the total noise radiated by a passing train. The overall goal of the thesis is to push the limits of microphone array technologies in the context of sound field separation, to the end of minimizing the cost and complexity of measurements and analyses. The proposed separation methods are formulated in the wavenumber domain, and the measurements are done with uniform single layer microphone arrays. The problem of separating reflections is addressed in three different papers: (i) compact sources and a parallel reflector, (ii) planar source and a parallel reflector, and (iii) a perpendicular reflector with respect to the microphone array, and the common requirement is the knowledge of the reflector impedance. The problem of separating rail noise is studied in a fourth paper, and the proposed method is formulated such that it does not require prior knowledge of the rail properties. Upon the findings obtained in the papers, a comprehensive description of areas for future work, as well as strategies to approach them, is given at the end of the thesis.
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| 9. |
- Kari, Leif
(författare)
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Dynamic Vibration Absorbers
- 2008. - 1
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Ingår i: Handbook of Noise and Vibration Control. - Hoboken, New Jersey : John Wiley & Sons. - 9780471395997 ; , s. 745-752
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Bokkapitel (refereegranskat)
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| 10. |
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