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Cost-Effective Design Modification of a Sleeve Bearing with Large Bearing Clearance
Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.ORCID iD: 0009-0000-8078-5036
Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.ORCID iD: 0000-0001-6016-6342
Vattenfall AB Research and Development, 814 26 Älvkarleby, Sweden.ORCID iD: 0000-0003-2812-2985
2024 (English)In: Applied Sciences, E-ISSN 2076-3417, Vol. 14, no 3, article id 1214Article in journal (Refereed) Published
Abstract [en]

In 2015, a 45 MW vertical hydropower machine exhibited excessive vibration after refurbishment. Measurements revealed a substantial bearing clearance at the lower generator guide bearing. Consequently, the bearing was unable to generate sufficient opposing force to drive the rotor toward the bearing center, resulting in more pronounced overall system vibration. Addressing this challenge required a cost-effective and feasible solution for mitigating the vibration problem. To this end, a design modification was implemented wherein the lower generator guide bearing (originally a sleeve bearing) was modified to a four-lobe bearing by offsetting the two halves of the bearing twice in two axes. Numerical simulations and experimentations were conducted, and the dynamics of the machine before and after the design modification were investigated. Both the simulation and experimental results showed that the machine with the four-lobe bearing improved the system stability and reduced the vibration amplitudes. The numerical simulation result demonstrated that, due to the design modification, the first and second critical speeds were effectively eliminated for a speed range of up to three times the nominal speed. Furthermore, for nominal operation with unbalanced magnetic pull, the four-lobe bearing provided a stability advantage in terms of the modal parameters relative to the original sleeve bearing.

Place, publisher, year, edition, pages
MDPI, 2024. Vol. 14, no 3, article id 1214
Keywords [en]
hydropower, four-lobe bearing, sleeve bearing, journal bearing, vertical rotors, rotordynamics, bearing coefficient
National Category
Other Mechanical Engineering Applied Mechanics
Research subject
Machine Design
Identifiers
URN: urn:nbn:se:ltu:diva-105019DOI: 10.3390/app14031214OAI: oai:DiVA.org:ltu-105019DiVA, id: diva2:1849534
Projects
Swedish Hydropower Centre-SVC
Funder
Swedish Energy AgencySwedish National GridEnergy ResearchLuleå University of TechnologyKTH Royal Institute of TechnologyChalmers University of TechnologyUppsala UniversityLund University
Note

Validerad;2024;Nivå 2;2024-04-08 (hanlid);

Full text license: CC BY 4.0

Available from: 2024-04-08 Created: 2024-04-08 Last updated: 2024-04-22Bibliographically approved
In thesis
1. Rotordynamic Modeling and Characterization of Support Elements in Vertical Machines
Open this publication in new window or tab >>Rotordynamic Modeling and Characterization of Support Elements in Vertical Machines
2024 (English)Doctoral thesis, comprehensive summary (Other academic)
Alternative title[sv]
Rotordynamiska Modellering och Karakterisering av Stödelement i Vertikala Maskiner
Abstract [en]

The dynamic properties of rotating machines are highly influenced by supporting elements, such as bearings, seals, damping elements or housings. They play a significant role in regulating the characteristics of the interaction between the rotating and stationary parts of machines. Over the past few years, numerous research studies have been published focusing on the dynamics of such devices across a wide range of applications. The advancement of the research has significantly contributed to enhancing their performance and ensuring the smooth operation of rotating machinery by minimizing excessive vibrations that can lead to catastrophic failure. The research work in this thesis explores the dynamics of supporting elements in vertical rotating machinery, with a particular focus on hydropower applications. In fact, some of the concepts are generic and can be applied to horizontal rotors or any other types of rotating machines. Using numerical simulation and actual measurements, their contribution to the system’s overall performance was investigated. These include the self-induced vibration in vertical application tilting pad journal bearings, and vibration issues observed on a hydropower unit attributed to large bearing clearance. Also, particular attention was given to the influence of the squeeze film damper on the rotor-stator contact dynamics of hydropower units, using tools such as Poincaré maps and bifurcation diagrams.

Moreover, achieving optimal design of such devices requires, among other key aspects, accurate and reliable simulation models to facilitate the prediction and evaluation of their characteristics at any stage in the product development process. In rotordynamic simulations, a common approach for incorporating bearing forces in the system equation is by representing them with stiffness and damping coefficients. For a small vibrational amplitude about a static position, linearized bearing coefficient assumptions can be valid. This is especially applicable for operation under a large radial static load, such as in horizontal rotors, due to the dead weight of the rotor. For vertical rotors, however, the weight of the rotor acts axially, and the radial bearing load is usually low. The bearing coefficients show nonlinearity, making them dependent on the trajectory of the rotor. Therefore, the linear bearing assumption, which is valid for horizontal rotors, does not hold true for vertical rotors. This makes the simulation of a vertical machine more complicated as it typically involves solving the fluid film lubrication model. The classical numerical models can sometimes be computationally demanding and require impractically long computational time. An efficient and fast numerical simulation method which does not significantly affect the accuracy of the result is critical to facilitating the simulation processes effectively. This thesis details the suggested simplifications employed on the bearing models and transformation matrices in the numerical integration procedure. The results from these models were validated using experiments to ensure their reliability.

Place, publisher, year, edition, pages
Luleå: Luleå University of Technology, 2024
Series
Doctoral thesis / Luleå University of Technology 1 jan 1997 → …, ISSN 1402-1544
Keywords
Rotordynamic, Support Element, Bearing, Squeeze Film Damper, Hydropower, Vertical Machine
National Category
Applied Mechanics
Research subject
Machine Design
Identifiers
urn:nbn:se:ltu:diva-105194 (URN)978-91-8048-552-4 (ISBN)978-91-8048-553-1 (ISBN)
Public defence
2024-06-18, B192, Luleå tekniska universitet, Luleå, 09:00 (English)
Opponent
Supervisors
Available from: 2024-04-22 Created: 2024-04-22 Last updated: 2024-05-17Bibliographically approved

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Benti, Gudeta BerhanuAidanpää, Jan-Olov

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