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  • 1. Luneno, Jean-Claude
    et al.
    Aidanpää, Jan-Olov
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Use of nonlinear journal-bearing impedance descriptions to evaluate linear analysis of the steady-state imbalance response for a rigid symmetric rotor supported by two identical finite-length hydrodynamic journal bearings at high eccentricities2010In: Nonlinear dynamics, ISSN 0924-090X, E-ISSN 1573-269X, Vol. 62, no 1-2, p. 151-165Article in journal (Refereed)
    Abstract [en]

    This paper concerns the investigation of validity limits of linear models in predicting rotor trajectory inside the bearing clearance for a rigid symmetric rotor supported by two identical journal bearings operating at high eccentricities. The inherent nonlinearity of hydrodynamic journal bearings becomes strong for eccentricities grater than 60% of the bearing clearance where most existing linear models are not able to accurately predict the rotor trajectory. The usefulness of nonlinear journal-bearing impedance description method in this investigation is due to the analytical formulations of the linearised bearing coefficients, and the analytical nonlinear bearing models. These analytically derived bearing coefficients do not require any numerical differentiation (or integration) and are therefore more accurate for large eccentricities. The analytically derived nonlinear bearing models markedly decrease the simulation time while valid for all L/D (length to diameter ratios) and all eccentricities. The results contained in this paper show that linear models derived from the nonlinear impedance descriptions of the Moes-cavitated (π-film) finite-length bearing can predict the steady-state imbalance response of a symmetric rigid rotor supported by two identical journal bearings at high eccentricities. This is, however, only the case when operating conditions are below the threshold speed of instability and when the system has period-one solutions. The error will become larger closer to the resonance speed.

  • 2.
    Thiery, Florian
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Aidanpää, Jan-Olov
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Nonlinear vibrations of a misaligned bladed Jeffcott rotor2016In: Nonlinear dynamics, ISSN 0924-090X, E-ISSN 1573-269X, Vol. 86, no 3, p. 1807-1821Article in journal (Refereed)
    Abstract [en]

    This paper describes the numerical and experimental investigation of the nonlinear vibration of a bladed Jeffcott rotor. The nonlinearity in the system is due to discontinuities caused by multiple contacts with an outer ring as well as the nonlinear deformation of the massless blades. Contacts occur since the rotor shaft is initially misaligned by displacing the outer ring in one direction. The aim of the paper is to develop a simple model of bladed rotor and verify whether the global dynamics of the numerical simulations can be observed experimentally. The experimental rig and data acquisition are presented in detail together with the experimental procedures. The results between the numerical simulation and experiments are compared in terms of bifurcation diagrams and waterfall plots. An overall correlation is observed between the numerical and experimental study in the case of stiff blades, with differences mainly in localized frequency ranges due to parameter variation.

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