The influence of the combi-bearing on the rotordynamics of ahydro power unit

Abstract: The hydro power in Sweden today is facing higher demands on efficiencyand reliability, while at the same time the hydro power stationstoday serve as a "power reserve" and can be forced to several starts& stops each day. This demands a greater knowledge of the rotordynamicalproperties of the hydro power units, with for example higheraccuracy in predicting the eigenfrequencies.When modelling a hydro power unit today, all bearings are usuallymodelled as purely radial which is not entirely true. In this thesis theinfluence of the combi-bearing is studied. The combi-bearing consistsof a radial and an axial part - which, in comparison with the purelyradial model, introduces a bending stiffness. The bending stiffness affectssome of the eigenfrequencies of a hydro power unit and it is concludedthat the frequencies with a corresponding eigenvector with largeangular-amplitudes in the combi-bearing are affected the most.The combi-bearing is then allowed to have a misalignment in thefoundation and the effects of this misalignment are studied. It is shownthat a misalignment will cause a coupling between the vibration-modes,making it possible for a lateral excitation to generate an axial vibrationand vice versa.The thesis consist of an analytical part where a model of the combibearingis achieved and of a numerical part where the results of the mentioned model are studied.