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Dynamic Performance and Design Aspects of Compliant Fluid Film Bearings

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Dynamic Performance and Design Aspects of Compliant Fluid Film Bearings KTH Industrial Engineering and Management DYNAMIC PERFORMANCE AND DESIGN ASPECTS OF COMPLIANT FLUID FILM BEARINGS Matthew Y.J Cha KTH Royal Institute of Technology School of Industrial Engineering and Management Department of Machine Design Cover figure : Waukesha Bearings Combined Thrust and Journal Bearing Assembly: Solid Polymer Tilting Pad Thrust Bearing with Polymer Lined Tilting Pad Journal Bearing TRITA – MMK 2014:13 ISSN 1400-1179 ISRN/KTH/MMK/R-14/13-SE ISBN 978-91-7595-398-4 Dynamic Performance and Design Aspects of Compliant Fluid Film Bearings Academic thesis, which with the approval of Kungliga Tekniska Högskolan, will be presented for public review in fulfillment of the requirements for a Doctorate of Engineering in Machine Design. Public review: Kungliga Tekniska Högskolan, Gladan, Brinellvägen 83, Stockholm, on April 22, 2015 Printed in Sweden Universitetsservice US-AB PREFACE I am very thankful to Lord Jesus Christ. This work is dedicated for the Glory of God. I give my deepest gratitude to my wife, Woori. She has given me a big support and love. And she waited patiently for me to complete my thesis and taking care of our two lovely children. I would also like to thank my children, Ye-Eun and Ye-Lang for growing up healthy and bringing joy to my family. I want to thank both of my parents and families in Canada for their care, love and support. I would like to thank my supervisor, Professor Sergei Glavatskih for giving me an opportunity to study and research under his guidance. He has brought me into the field of fluid film bearings and there are many things to learn and absorb from his expertise. His valuable discussion, support and help are gratefully acknowledged. Without his supervision and friendship, this work was not possible to accomplish. I would also like to thank Evgeny Kuznetsov for his contribution to Paper A and Patrik Isaksson for his contribution to Paper B. Also I would like to thank Professor Ilmar Santos from Denmark Technical University for the permission to use their test-rig to measure polymer characteristics and his contribution to Paper E. I also would like to thank Gregory Simmons for our thoughtful discussion which lead to Paper F. Also many thanks go to my former colleagues at KTH Royal Institute of Technology for making the research environment enjoyable. Special thanks also go to my new colleagues at Waukesha Bearings UK for their warm welcome when I joined in August 2014. Among many of my new colleagues at Waukesha Bearings, I would like to emphasize big thanks to Tim Renard (Director of Engineering) and Richard Livermore-Hardy (Engineering Manager, UK) for creating a job in the UK office and allowing me to continue my adventure in the field of fluid film bearings. This research is supported by the Swedish Hydropower Centre (SVC). SVC has been established by the Swedish Energy Agency, Elforsk and Svenska Kraftnät in partnership with academic institutions. Matthew Y.J Cha Stockholm April 2015 “Scientists discover the world that exists; Engineers create the world that never was.” Theodore von Karman ABSTRACT 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. ABSTRAKT På grund av statliga regleringar tillsammans med hälso- och säkerhetsskäl, ställs det allt högre krav på att minska farliga och förorenande kemikalier från fossila bränslen. Därför läggs allt större resurser på att använda förnyelsebar energi som vatten, vind och sol för att producera el. Utöver det, finns en ökande efterfrågan från kraftverksindustrin att driva kraftverk under högre belastning samtidigt som effektförlusterna hålls minimala. Dessa krav driver konventionella hydrodynamiska lager till dess mekaniska och termiska gränser. Detta kräver utveckling av nya lagersystemkonstruktioner. Enastående tribologisk prestanda i egenskap av låg uppstartsfriktion, utmärkt motståndskraft mot kemiska angrepp och mot skärning kan uppnås genom att införa ett mjukt polymerfoder. Samtidigt kan hydrodynamiska lager med mjuka foder förändra dynamisk beteende av rotorsystem jämfört med rotorsystem med konventionella vitmetall lager. Forskningsansatsen med denna avhandling är att införa ett mjukt polymerfoder på lagerytan och undersöka effekten av lagerdesignparametrar på dess dynamiska respons vid synkron axelexcitation. Cylindriska radiallager med olika fodertjocklekar analyserades med hjälp av en finita elementmodel (FEM). Den numeriska modellen jämfördes med en egenutvecklad kod baserad på finita differensmetoden (FDM) för ett lager vid stationära förhållanden. Resultat som erhållits genom de numeriska modellerna visade god överensstämmelse. Efter verifiering av den numeriska modellen för cylindriska radiallager med fast geometri togs även modeller för radiallager med självinställande block fram. Dynamisk beteende för lager med tre block jämfördes med publicerade data. God överenstämmelse erhölls mellan de två numeriska modellerna. Effekten av pivotgeometri på dynamisk respons av lager med självinställande block undersöktes. Vertikala och horisontella axelkonfigurationer jämfördes med avseende på effekten av förspänningsfaktor, radiellt spel, pivot offset, och blockets lutningsvinklar. Även inverkan av de elastiska egenskaperna hos polymerfoder studerades. Alla dessa faktorer påverkar betydligt lagrets dynamiska respons. I avhandlingen beskrivs hur dessa faktorer bör väljas för att på bästa sätt styra axelns rörelse i lagret. Effekten av snedställningar hos axeln i radiallager med självinställande block analyserades för last centrerad mellan pivotpunkter samt last centrerad rakt över pivotpunkten. Hänsyn har också tagits fram till termiska effekter. Signifikanta förbättringar i lagerprestanda erhölls med polymerfoder jämfört med vitmetall lager. Vidare har olika polymera material (PTFE, UHMWPE, ren PEEK och PEEK-kompositer) karakteriserats med hjälp av frekvensfunktioner (FRF). Det visades att om exciteringsfrekvensen ökas, minskas den ekvivalenta styvheten något, men för ekvivalent dämpning minskade den exponentiellt om excitationsfrekvensen ökar. Dessutom hade PTFE liknande ekvivalent styvhet jämfört med PEEK. När det gäller ekvivalent dämpning, hade PTFE något högre dämpning jämfört med PEEK eller UHMWPE. Det visades att då exiteringsfrekvensen
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