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Dynamic Performance and Design Aspects of Compliant Fluid Film Bearings
KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Machine Elements.ORCID iD: 0000-0002-7914-1636
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 [en]
Compliant bearing, dynamic performance, design aspects
National Category
Tribology
Research subject
Machine Design
Identifiers
URN: urn:nbn:se:kth:diva-163560ISBN: 978-91-7595-398-4 (print)OAI: oai:DiVA.org:kth-163560DiVA: diva2:801113
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
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
4. Misalignment effects in journal bearings with compliant liner tilting pads
Open this publication in new window or tab >>Misalignment effects in journal bearings with compliant liner tilting pads
(English)Manuscript (preprint) (Other academic)
National Category
Mechanical Engineering
Identifiers
urn:nbn:se:kth:diva-163577 (URN)
Note

QS 2015

Available from: 2015-04-09 Created: 2015-04-09 Last updated: 2015-04-09Bibliographically approved
5. Dynamic characteristics of polymers related to compliant bearing desig
Open this publication in new window or tab >>Dynamic characteristics of polymers related to compliant bearing desig
(English)Manuscript (preprint) (Other academic)
National Category
Mechanical Engineering
Identifiers
urn:nbn:se:kth:diva-163578 (URN)
Note

QS 2015

Available from: 2015-04-09 Created: 2015-04-09 Last updated: 2015-04-09Bibliographically approved
6. Steady state and dynamic characteristics for guide bearings of a hydro-electric unit
Open this publication in new window or tab >>Steady state and dynamic characteristics for guide bearings of a hydro-electric unit
Show others...
2014 (English)In: Proceedings of the Institution of mechanical engineers. Part J, journal of engineering tribology, ISSN 1350-6501, E-ISSN 2041-305X, Vol. 228, no 8, 836-848 p.Article in journal (Refereed) Published
Abstract [en]

Experiments are conducted using a 10-MW Kaplan hydropower machine which is outfitted with an extensive array of sensors to determine oil film thickness, pad load and oil temperature in all three guide bearings as well as motion of the shaft in relation to both the bearing housings and the concrete foundation. Test results for all journal bearings are compared to a commercial rotor dynamics model and results for the central journal bearing are compared to a multi-physics model to provide insight into the machine's steady state and dynamic characteristics and their variations during normal operation.

Keyword
Tilting pad, hydropower, journal bearing
National Category
Mechanical Engineering
Identifiers
urn:nbn:se:kth:diva-150531 (URN)10.1177/1350650114533101 (DOI)000340210500002 ()2-s2.0-84904610818 (Scopus ID)
Note

QC 20140912

Available from: 2014-09-12 Created: 2014-09-05 Last updated: 2017-12-05Bibliographically approved

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