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Dynamic Modeling of Hydropower Generators
Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.ORCID iD: 0000-0002-4185-2395
2022 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

Modeling the dynamics of hydropower generators has been the aim pursued by many studies, as providing a reliable model would lead to more cost-effective designs. Hydropower generators comprise many parts, tilting-pad bearings, shaft, rotor rim, and stator among them, that contribute to the system's nonlinearities. In this thesis, the dynamics of hydropower generator is studied first by characterizing tilting-pad bearings. Multiple pad bearings are common in the industry; an eight-pad tilting-pad bearing has been studied on vertical rotors. Previous studies have shown that multiple pad bearings display stiffness and damping coefficients dependent on eccentricity and position. A model for eight-pad tilting pad bearings has been proposed and compared to experiments. The effect of cross-coupled phenomena was also investigated.

On the other hand, the generators are not rigid bodies, and the flexibility of either rotor rim or stator influences the distribution of the magnetic field, thus the force distribution. An uneven force distribution endangers the integrity of the machine. This thesis also proposes a model for a generator with flexible rotor rims and rigid stators using Lagrange equations, considering the centrifugal and Coriolis effects, the electromagnetic interaction between rotor and stator, and static and dynamic eccentricities. This model was tried on a generator prototype, discussing the impact of the connecting plates and the magnetic forces on the natural frequencies and the effect of static eccentricity.

Place, publisher, year, edition, pages
Luleå: Luleå University of Technology, 2022. , p. 119
Series
Licentiate thesis / Luleå University of Technology, ISSN 1402-1757
National Category
Applied Mechanics
Research subject
Machine Design
Identifiers
URN: urn:nbn:se:ltu:diva-88896ISBN: 978-91-8048-016-1 (print)ISBN: 978-91-8048-017-8 (electronic)OAI: oai:DiVA.org:ltu-88896DiVA, id: diva2:1631249
Presentation
2022-03-03, C305, Luleå Tekniska Universitet, Luleå, 09:00 (English)
Opponent
Supervisors
Projects
Swedish Hydropower Centre - SVCAvailable from: 2022-01-24 Created: 2022-01-24 Last updated: 2023-09-05Bibliographically approved
List of papers
1. Rotordynamic Characterization of Tilting-Pad Bearings With Eight Pads in Vertical Rotors 
Open this publication in new window or tab >>Rotordynamic Characterization of Tilting-Pad Bearings With Eight Pads in Vertical Rotors 
2022 (English)In: Journal of energy resources technology, ISSN 0195-0738, E-ISSN 1528-8994, Vol. 144, no 1, article id 010902Article in journal (Refereed) Published
Abstract [en]

It has been documented that stiffness and damping for a four-pad bearing are dependent not only on the magnitude of the load but also on the position of the rotor in the bearing. However, eight-pad bearings are not commonly employed on horizontal turbines, and the presence of several pads in the bearing will decisively affect the dynamics of the system. This paper evaluates the stiffness and damping coefficients of tilting-pad bearings with eight pads and explores the main frequencies acting on the forced response of a vertical rotor. The bearing properties were modeled as a function of eccentricity and position in the stationary coordinate system by Navier–Stokes equations whose results are taken from commercial software. The simulated unbalanced response is compared to experimental results; the changing position of the shaft produces a periodic stiffness and damping, which is dependent on the number of pads. Cross-coupled coefficients influence is discussed, showing that their absence makes an accurate model for the mean values. The results indicate that simulation of vertical rotors with eight-pad bearings can be simplified which allow more effective simulations and dynamic analysis. 

Place, publisher, year, edition, pages
American Society of Mechanical Engineers (ASME), 2022
Keywords
tilting-pad bearing, vertical rotor
National Category
Applied Mechanics
Research subject
Machine Design
Identifiers
urn:nbn:se:ltu:diva-86562 (URN)10.1115/1.4051803 (DOI)000720985000005 ()2-s2.0-85121689564 (Scopus ID)
Funder
Swedish Energy AgencyLuleå University of Technology
Note

Validerad;2022;Nivå 2;2022-01-01 (johcin)

Available from: 2021-08-12 Created: 2021-08-12 Last updated: 2024-04-19Bibliographically approved
2. Dynamic model for hydropower generators with floating rotor rim
Open this publication in new window or tab >>Dynamic model for hydropower generators with floating rotor rim
Show others...
2023 (English)In: Mechanical systems and signal processing, ISSN 0888-3270, E-ISSN 1096-1216, Vol. 183, article id 109645Article in journal (Refereed) Published
Abstract [en]

For rotordynamic analysis of hydropower units, the generator is treated as a rotating rigid body. However, previous studies have confirmed that certain designs of generators are elastic, so the complex geometry of generators cannot be considered rigid. This work produced a model of hydropower generators with floating rotor rims, consisting of a rigid hub and a flexible rotor rim coupled with flexible connections. The model takes into account the influence of centrifugal and Coriolis effects, and the electromagnetic interaction between rotor and stator. The model also reproduces the dynamics of the generator with static and dynamic eccentricities. A generator prototype was employed to test the model, showing its different applications. Once validated by empirical data, this model could be used when designing generators.

Place, publisher, year, edition, pages
Elsevier, 2023
Keywords
Rotordynamics, Magnetic force, Generator model, Hydropower, Dynamic modeling, Curved beam
National Category
Applied Mechanics
Research subject
Machine Design
Identifiers
urn:nbn:se:ltu:diva-88899 (URN)10.1016/j.ymssp.2022.109645 (DOI)000877355300003 ()2-s2.0-85135882306 (Scopus ID)
Projects
Swedish Hydropower Centre - SVC
Funder
Swedish Energy AgencyLuleå University of TechnologyChalmers University of TechnologyUppsala UniversityLund University
Note

Validerad;2022;Nivå 2;2022-08-19 (hanlid);

Funder: Energiforsk, Svenska Kraftnät, KTH Royal Institute of Technology

Available from: 2022-01-24 Created: 2022-01-24 Last updated: 2024-04-19Bibliographically approved

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Rondon, David

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