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  • 1.
    Cha, Matthew
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Machine Elements.
    Dynamic Performance and Design Aspects of Compliant Fluid Film Bearings2015Doctoral 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.

  • 2.
    Cha, Matthew
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Machine Design (Div.).
    Nonlinear Isoviscous Behaviour of Compliant Journal Bearings2012Licentiate 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.

  • 3.
    Cha, Matthew
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.).
    Glavatskih, Sergei
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.).
    Journal vibration: Influence of compliant bearing design2012In: Proceedings Of The ASME 11th Biennial Conference On Engineering Systems Design And Analysis, Vol 4, 2012, p. 657-664Conference paper (Refereed)
    Abstract [en]

    In this paper, the nonlinear dynamic behaviour of vertical and horizontal rotors in compliant tilting pad journal bearings has been investigated. White metal and compliant bearings with line pivot pads are compared. The dynamic response of four pad bearings with different preload factors is studied. The effect of viscoelasticity is also considered in comparison with purely elastic compliant and white metal liners. The influence of radial clearance and pad offset is analysed. It is shown how pad design parameters such as preload factor, pivot offset, viscoelasticity of the liner, and radial clearance can be selected to control the size of the journal orbit in compliant bearings.

  • 4.
    Cha, Matthew
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Machine Design (Div.). Waukesha Bearings, United Kingdom .
    Glavatskih, Sergei
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Machine Design (Div.). Ghent University, Belgium .
    Misalignment effects in journal bearings with compliant liner tilting padsManuscript (preprint) (Other academic)
  • 5.
    Cha, Matthew
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Machine Design (Div.). Waukesha Bearings, United Kingdom .
    Glavatskih, Sergei
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Machine Design (Div.). Ghent University, Belgium .
    Nonlinear dynamic behaviour of vertical and horizontal rotors in compliant liner tilting pad journal bearings: Some design considerations2015In: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 82, p. 142-152Article in journal (Refereed)
    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.

  • 6.
    Cha, Matthew
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Machine Design (Div.).
    Glavatskih, Sergei
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Machine Design (Div.).
    Nonlinear Dynamic Response of Compliant Journal Bearings2012In: CSNDD 2012 – International Conference on Structural Nonlinear Dynamics and Diagnosis, EDP Sciences, 2012, p. 10005-Conference paper (Refereed)
    Abstract [en]

    This paper investigates the dynamic response of the compliant tilting pad journal bearings subjected to synchronous excitation. Bearing compliance is affected by the properties of pad liner and pad support geometry. Different unbalance eccentricities are considered. It is shown that bearing dynamic response is non-linear. Journal orbit complexity increases with pad compliance though the orbit amplitudes are marginally affected at low loads. At high loads, the journal is forced to operate outside the bearing clearance. The polymer liner reduces the maximum oil film pressure by a factor of 2 when compared to the white metal liner. The nonlinear dynamic response of compliant tilting pad journal bearings is thoroughly discussed.

  • 7.
    Cha, Matthew
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Machine Design (Div.).
    Isaksson, Patrik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics.
    Glavatskih, Sergei
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Machine Design (Div.).
    Influence of pad compliance on nonlinear dynamic characteristics of tilting pad journal bearings2013In: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 57, p. 46-53Article in journal (Refereed)
    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.

  • 8.
    Cha, Matthew
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Machine Design (Div.).
    Kuznetsov, Evgeny
    Glavatskih, Sergei
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Machine Design (Div.).
    A comparative linear and nonlinear dynamic analysis of compliant cylindrical journal bearings2013In: Mechanism and machine theory, ISSN 0094-114X, E-ISSN 1873-3999, Vol. 64, p. 80-92Article in journal (Refereed)
    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.

  • 9.
    Cha, Matthew
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Machine Design (Div.). Waukesha Bearings, United Kingdom .
    Santos, Ilmar
    Technical University of Denmark, Denmark.
    Glavatskih, Sergei
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Machine Design (Div.). Ghent University, Belgium .
    Dynamic characteristics of polymers related to compliant bearing desigManuscript (preprint) (Other academic)
  • 10. Simmons, Gregory F.
    et al.
    Cha, Matthew
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Machine Design (Div.).
    Aidanpaa, Jan-Olov
    Cervantes, Michel J.
    Glavatskih, Sergei
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Machine Design (Div.). Department of Mechanical Construction and Production, Ghent University, Belgium.
    Steady state and dynamic characteristics for guide bearings of a hydro-electric unit2014In: Proceedings of the Institution of mechanical engineers. Part J, journal of engineering tribology, ISSN 1350-6501, E-ISSN 2041-305X, Vol. 228, no 8, p. 836-848Article in journal (Refereed)
    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.

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