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A comparative linear and nonlinear dynamic analysis of compliant cylindrical journal bearings
KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Machine Design (Div.).ORCID iD: 0000-0002-7914-1636
KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Machine Design (Div.).
2013 (English)In: Mechanism and machine theory, ISSN 0094-114X, E-ISSN 1873-3999, Vol. 64, 80-92 p.Article in journal (Refereed) Published
Abstract [en]

Dynamic behaviour of compliant cylindrical journal bearings is investigated using linear and nonlinear numerical approaches. Journal motion orbits based on linearized dynamic coefficients are compared to the journal trajectories obtained by the nonlinear transient analysis. Obtained results are presented in terms of orbit amplitude, shape and location. The influence of compliant liner thickness, viscoelastic properties and deformation model is also investigated. A linear model is found to deliver acceptable results at a relatively small shaft unbalance under low to average loads. However, with a journal amplitude motion greater than 37% of the bearing diametral clearance, the linear model should not be used to analyse journal transient motion. Plane strain hypothesis is found to be a proper substitute for a full deformation model when a compliant liner is thinner than 2 mm (for the bearing geometry used in this study). It was also shown that the liner viscoelasticity should be taken into account whenever a compliant liner is relatively thick (in our case, 2 mm). Viscoelasticity of the liner decreases journal amplitude compared to a pure elastic liner.

Place, publisher, year, edition, pages
2013. Vol. 64, 80-92 p.
Keyword [en]
Compliant bearing, Viscoelasticity, Nonlinear analysis
National Category
Mechanical Engineering
Identifiers
URN: urn:nbn:se:kth:diva-91639DOI: 10.1016/j.mechmachtheory.2013.01.008ISI: 000316790800006Scopus ID: 2-s2.0-84874674934OAI: oai:DiVA.org:kth-91639DiVA: diva2:510889
Note

QC 20130506. Updated from submitted to published.

Available from: 2012-03-19 Created: 2012-03-19 Last updated: 2017-12-07Bibliographically approved
In thesis
1. Nonlinear Isoviscous Behaviour of Compliant Journal Bearings
Open this publication in new window or tab >>Nonlinear Isoviscous Behaviour of Compliant Journal Bearings
2012 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

Plans to shut down nuclear power plants in some European countries as well as increased electricity production by wind and solar power will increase the work load on hydroelectric power plants in the future. Also, due to the power grid regulations, hydroelectric power plants undergo more frequent start-ups and shut-downs. During such transient periods, a large amplitude shaft motion can occur, especially in the power plants with vertical shafts. Large shaft motion is not desirable because it can lead to a machine failure. Furthermore, performance limitations of conventional white metal or babbitted bearings call for the development of new bearing designs. An outstanding tribological performance can be achieved by introducing compliant polymer liners. At the same time, bearings with compliant liners may alter rotor-bearing system dynamic behaviour compared to the systems with conventional white metal bearings. The research approach of this thesis is to employ nonlinear analysis to provide further understanding of the compliant bearing dynamic response to synchronous shaft excitation.

Plain cylindrical journal bearings with different compliant liner thicknesses were analysed using a nonlinear approach. The numerical model was verified with an in-house developed code at steady state conditions. Results obtained by the numerical models showed good agreement. After verification of the numerical model for fixed geometry journal bearings, models for tilting pad journal bearings were developed. Results for the tilting pad journal bearing with three pads with line pivot geometry were compared with published data in dynamic conditions. A good agreement was obtained between the two numerical models. The effect of pad pivot geometry on bearing dynamic response was investigated. Vertical and horizontal shaft configurations were compared in terms of the effect of preload factor, pivot offset, tapers and pad inclination angles. Influence of the viscoelastic properties of compliant liners was also studied. All these factors significantly affect bearing dynamic response. It is shown how these factors should be selected to control the journal orbit sizes. It was also shown that the compliant liner provides lower maximum oil film pressure and thicker minimum oil film thickness in the bearing mid-plane in both static and dynamic operating conditions.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2012. 40 p.
Series
TRITA-MMK, ISSN 1400-1179 ; 2012:06
Keyword
Compliant Journal Bearings
National Category
Tribology
Identifiers
urn:nbn:se:kth:diva-91490 (URN)978-91-7501-285-8 (ISBN)
Presentation
2012-03-29, B242, Brinellvägen 85, Stockholm, 10:00 (English)
Opponent
Supervisors
Projects
Swedish Hydropower Centre
Note

QC 20120319

Available from: 2012-03-19 Created: 2012-03-16 Last updated: 2015-04-09Bibliographically approved
2. Dynamic Performance and Design Aspects of Compliant Fluid Film Bearings
Open this publication in new window or tab >>Dynamic Performance and Design Aspects of Compliant Fluid Film Bearings
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Due to government regulations together with health and safety reasons, there are increasing demands on reducing hazardous polluting chemicals from fossil fuel power plants. Therefore, more efforts are imposed on using renewable resources such as water, wind, solar and tide to produce clean/green electricity. On top of that, there is another increasing demand from Original Equipment Manufacturers (OEMs) to operate power plants with higher load while keep the power loss to the minimum. These requirements drive conventional fluid film bearings to its mechanical and temperature limits. This calls for the development of new bearing system designs. An outstanding tribological performance such as low start-up and break-away friction, excellent resistance to chemical attack and anti-seizure properties, can be achieved by introducing compliant polymer liners. At the same time, bearings with compliant liners may alter rotor-bearing system dynamic behaviour compared to the systems with conventional white metal bearings. The research approach of this thesis is to implement compliant liner on bearing surface, impose synchronous shaft excitation and investigate the effect of bearing design parameters on bearing dynamic response.

Plain cylindrical journal bearings with different compliant liner thicknesses were analysed using a FEM approach. The numerical model was compared with an in-house developed code based on the finite difference method (FDM) for a bearing operated at steady state conditions. Results obtained by the numerical models showed good agreement. After verification of the numerical model for fixed geometry journal bearings, models for tilting pad journal bearings were developed. Dynamic behaviour of the tilting pad journal bearing with three pads with line pivot geometry was compared with published data. A good agreement was obtained between the two numerical models. The effect of pad pivot geometry on bearing dynamic response was investigated. Vertical and horizontal shaft configurations were compared in terms of the effect of preload factor, radial clearance, pivot offset, and pad inclination angles. Influence of the elastic properties of compliant liners was also studied. All these factors significantly affect bearing dynamic response. It is shown how these factors should be selected to control the journal orbit sizes. Misalignments in compliant tilting pad journal bearings were analysed for load between pivots and load on pivots with consideration of thermal effects. Significant improvements in bearing performance were obtained with compliant bearings compared to white metal bearings. Furthermore, different polymer materials (PTFE, UHMWPE, pure PEEK and PEEK composite) were characterized using Frequency Response Function (FRF). It was shown that as the excitation frequency increased the equivalent stiffness was more or less constant while equivalent damping decreased exponentially. PTFE had similar equivalent stiffness compared to PEEK. As for equivalent damping, PTFE had slightly higher damping compared to PEEK or UHMWPE. Oil film thickness, oil film temperature and loads on tilting pad journal bearing were measured on 10 MW Kaplan hydroelectric power machine. Test results were compared to FEM model. It was shown that stiffness of the supporting structure may be more important to machine performance than the stiffness of the bearing alone.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2015. 56 p.
Series
TRITA-MMK, ISSN 1400-1179 ; 2014:13
Keyword
Compliant bearing, dynamic performance, design aspects
National Category
Tribology
Research subject
Machine Design
Identifiers
urn:nbn:se:kth:diva-163560 (URN)978-91-7595-398-4 (ISBN)
Public defence
2015-04-22, Sal Gladan, Brinellvagen 83, KTH, Stockholm, 13:00 (English)
Opponent
Supervisors
Projects
Swedish Hydropower Centre
Funder
Swedish Energy Agency
Note

QC 20150409

Available from: 2015-04-09 Created: 2015-04-08 Last updated: 2015-04-09Bibliographically approved

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