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The influence of the combi-bearing on the rotordynamics of a hydro power unit
2008 (English)Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
Abstract [en]

The hydro power in Sweden today is facing higher demands on efficiency and reliability, while at the same time the hydro power stations today serve as a ”power reserve” and can be forced to several starts & stops each day. This demands a greater knowledge of the rotordynamical properties of the hydro power units, with for example higher accuracy in predicting the eigenfrequencies. When modelling a hydro power unit today, all bearings are usually modelled as purely radial which is not entirely true. In this thesis the influence of the combi-bearing is studied. The combi-bearing consists of a radial and an axial part - which, in comparison with the purely radial model, introduces a bending stiffness. The bending stiffness affects some of the eigenfrequencies of a hydro power unit and it is concluded that the frequencies with a corresponding eigenvector with large angular-amplitudes in the combi-bearing are affected the most. The combi-bearing is then allowed to have a misalignment in the foundation and the effects of this misalignment are studied. It is shown that a misalignment will cause a coupling between the vibration-modes, making it possible for a lateral excitation to generate an axial vibration and vice versa. The thesis consist of an analytical part where a model of the combibearing is achieved and of a numerical part where the results of the mentioned model are studied.

Place, publisher, year, edition, pages
Keyword [en]
Technology, Hydro power unit, Campbell-diagram, Eigenfrequencies, Combi-, bearing, coupled equations, excitation: eigenvector, mode-shapes, FEM, Finite element model, Euler-Bernoulli, Beam, element, Misalignment, axial bearing: stiffness, matrix, gyroscopic effect, rotordynamics
Keyword [sv]
URN: urn:nbn:se:ltu:diva-51306ISRN: LTU-EX--08/195--SELocal ID: 883629bc-e4d9-46a2-b6e5-7865dbcaafaeOAI: diva2:1024667
Subject / course
Student thesis, at least 30 credits
Educational program
Engineering Physics, master's level
Validerat; 20101217 (root)Available from: 2016-10-04 Created: 2016-10-04Bibliographically approved

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