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- Thiery, Florian, et al.
(author)
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Dynamics of a Jeffcott rotor with rigid blades rubbing against an outer ring
- 2012
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In: Chaotic Modeling and Simulation (CMSIM). - 2241-0503. ; , s. 643-650
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Journal article (other academic/artistic)abstract
- The non-linear behaviour of rub-impact systems have been studied recentlyby approximating rotor-stator systems as rubbing cylinders. In reality, therotor shape is more complex, resulting in richer dynamics over smaller parameter ranges. In this paper, a bladed turbine is modelled using a Jeffcott rotor with three rigid beams attached to the mass center. The contact forces are described by a radial restoring force induced by the massless outer ring, and a tangential Coulomb frictional force. The results are presented in bifurcation diagrams and compared with a previous model described by three flexible beams entering in contact with a fixed ring assuming large displacement beam theory. This paper shows that the two models described give similarities in the overall bifurcation diagram, only showing greater differences in localized frequency ranges.
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- Thiery, Florian
(author)
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Evaluation of strong nonlinearities in hydropower systems
- 2014
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Licentiate thesis (other academic/artistic)abstract
- In hydropower systems, it is essential to avoid catastrophic failures that leads to human and economic losses. Unfortunately, the rotor can behave abnormally since several nonlinear effects occur during start-up, shut downs or when running at nominal speed. Weak nonlinear interaction in the tilting pad bearings, electromagnetic interaction between the generator and rotor or fluid-structure interaction in turbines are typical nonlinear effects that appear. Moreover, strong nonlinearities can also occur due to blade contacts and assembly errors. These types of nonlinearities can be strong in case of bad design of the rotor, and it could even lead to catastrophes in the worst case. Due to the complexity of the blade contact nonlinearity, it is first necessary to evaluate the general properties of the system using a simple model such as the Jeffcott rotor. Studies of nonlinearities are performed using common tools such as Poincare sections, bifurcation diagrams, Maximum Lyapunov Exponent, Lyapunov Spectrum and 3-dimensional plots of the Fast Fourier Transform . The results obtained are also compared with an experimental rig to validate the models proposed. The second part of the thesis is dedicated to real hydropower systems with complex geometry. A focus is made on the numerical methods to employ as well as reduction methods to gain computation time. The aim is to verify that the inherent properties of simple bladed are also present in complex systems. Further numerical simulations of the system at nominal speed will be studied as function of unbalance forces and damping properties. In this case, the tools used in simple rotors system can help us evaluate under which conditions a catastrophic failure can be avoided in any hydropower system.
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