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Nonlinear Isoviscous Behaviour of Compliant Journal Bearings
KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Machine Design (Div.).ORCID iD: 0000-0002-7914-1636
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 [en]
Compliant Journal Bearings
National Category
Tribology
Identifiers
URN: urn:nbn:se:kth:diva-91490ISBN: 978-91-7501-285-8 (print)OAI: oai:DiVA.org:kth-91490DiVA: diva2:510440
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
List of papers
1. A comparative linear and nonlinear dynamic analysis of compliant cylindrical journal bearings
Open this publication in new window or tab >>A comparative linear and nonlinear dynamic analysis of compliant cylindrical journal bearings
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.

Keyword
Compliant bearing, Viscoelasticity, Nonlinear analysis
National Category
Mechanical Engineering
Identifiers
urn:nbn:se:kth:diva-91639 (URN)10.1016/j.mechmachtheory.2013.01.008 (DOI)000316790800006 ()2-s2.0-84874674934 (Scopus ID)
Note

QC 20130506. Updated from submitted to published.

Available from: 2012-03-19 Created: 2012-03-19 Last updated: 2017-12-07Bibliographically approved
2. Influence of pad compliance on nonlinear dynamic characteristics of tilting pad journal bearings
Open this publication in new window or tab >>Influence of pad compliance on nonlinear dynamic characteristics of tilting pad journal bearings
2013 (English)In: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 57, 46-53 p.Article in journal (Refereed) Published
Abstract [en]

The effect of pad compliance on the dynamic response of tilting pad journal bearings is investigated. Pad compliance is varied by changing pivot geometry and Young's modulus of pad backing and pad liner. Two pad support configurations are considered: one that allows only circumferential tilt and another one that allows both circumferential and axial tilts. Journal orbits, oil film pressure and oil film thickness are compared and discussed. It is shown that higher pad backing compliance significantly increases the journal orbit size and results in an increase in oil film pressure while oil film thickness is decreased. With a compliant liner, oil film pressure is decreased while oil film thickness is increased. Tapers at the pad edges are essential to increase the global minimum oil film thickness in compliant liner bearings.

Keyword
Tilting pad journal bearing, Compliance, Line pivot, Ball-socket pivot
National Category
Tribology
Identifiers
urn:nbn:se:kth:diva-107432 (URN)10.1016/j.triboint.2012.07.005 (DOI)000311474800006 ()2-s2.0-84864545767 (Scopus ID)
Note

QC 20130109. Updated from submitted to published.

Available from: 2013-01-09 Created: 2012-12-11 Last updated: 2017-12-07Bibliographically approved
3. Nonlinear dynamic behaviour of vertical and horizontal rotors in compliant liner tilting pad journal bearings: Some design considerations
Open this publication in new window or tab >>Nonlinear dynamic behaviour of vertical and horizontal rotors in compliant liner tilting pad journal bearings: Some design considerations
2015 (English)In: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 82, 142-152 p.Article in journal (Refereed) Published
Abstract [en]

Dynamic behaviour of vertical and horizontal rotors in journal bearings with line pivot pads is investigated. Two bearing designs are compared: one with white metal pads and another with compliant liner pads. The influence of elasticity of the liner on the journal orbits is investigated. Some practical aspects of the compliant liner pad design are discussed. Compliant bearing design parameters such as preload factor, pivot offset, radial clearance, viscoelasticity, and pad inclination to control the size of the journal orbit are considered.

Keyword
Compliant liner, Tilting pad journal bearings, Journal orbit, Bearing design parameters
National Category
Mechanical Engineering
Identifiers
urn:nbn:se:kth:diva-159971 (URN)10.1016/j.triboint.2014.10.011 (DOI)000347753200015 ()2-s2.0-84921461767 (Scopus ID)
Note

Updated from "Manuscript" to "Article". QC 20150306

Available from: 2015-03-06 Created: 2015-02-12 Last updated: 2017-12-04Bibliographically approved

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