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Evaluation of strong nonlinearities in hydropower systems
Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
2014 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

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.

Place, publisher, year, edition, pages
Luleå tekniska universitet, 2014.
Licentiate thesis / Luleå University of Technology, ISSN 1402-1757
Research subject
Solid Mechanics
URN: urn:nbn:se:ltu:diva-26375Local ID: df6df5f7-a616-4922-8ab8-10f40edc29e5ISBN: 978-91-7439-864-9ISBN: 978-91-7439-865-6 (PDF)OAI: diva2:999537
Godkänd; 2014; 20140211 (flothi); Nedanstående person kommer att hålla licentiatseminarium för avläggande av teknologie licentiatexamen. Namn: Florian Thiery Ämne: Hållfasthetslära/Solid Mechanics Uppsats: Evaluation of Strong Nonlinearities in Hydropower Systems Examinator: Professor Jan-Olov Aidanpää, Institutionen för teknikvetenskap och matematik, Luleå tekniska universitet Diskutant: Professor Ilmar Santos, Technical University of Denmark, Lyngby, Denmark Tid: Torsdag den 20 mars 2014 kl 09.00 Plats: E243, Luleå tekniska universitetAvailable from: 2016-09-30 Created: 2016-09-30Bibliographically approved

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