Change search
Refine search result
1 - 9 of 9
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Rows per page
  • 5
  • 10
  • 20
  • 50
  • 100
  • 250
Sort
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
Select
The maximal number of hits you can export is 250. When you want to export more records please use the Create feeds function.
  • 1.
    Thiery, Florian
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Evaluation of strong nonlinearities in hydropower systems2014Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    In hydropower systems, it is essential to avoid catastrophic failures that leads to human and economic losses. Unfortunately, the rotor can behave abnormally since several nonlinear effects occur during start-up, shut downs or when running at nominal speed. Weak nonlinear interaction in the tilting pad bearings, electromagnetic interaction between the generator and rotor or fluid-structure interaction in turbines are typical nonlinear effects that appear. Moreover, strong nonlinearities can also occur due to blade contacts and assembly errors. These types of nonlinearities can be strong in case of bad design of the rotor, and it could even lead to catastrophes in the worst case. Due to the complexity of the blade contact nonlinearity, it is first necessary to evaluate the general properties of the system using a simple model such as the Jeffcott rotor. Studies of nonlinearities are performed using common tools such as Poincare sections, bifurcation diagrams, Maximum Lyapunov Exponent, Lyapunov Spectrum and 3-dimensional plots of the Fast Fourier Transform . The results obtained are also compared with an experimental rig to validate the models proposed. The second part of the thesis is dedicated to real hydropower systems with complex geometry. A focus is made on the numerical methods to employ as well as reduction methods to gain computation time. The aim is to verify that the inherent properties of simple bladed are also present in complex systems. Further numerical simulations of the system at nominal speed will be studied as function of unbalance forces and damping properties. In this case, the tools used in simple rotors system can help us evaluate under which conditions a catastrophic failure can be avoided in any hydropower system.

  • 2.
    Thiery, Florian
    Luleå University of Technology, Department of Engineering Sciences and Mathematics.
    Simplified models to evaluate nonlinear dynamics in hydropower rotors2016Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    In hydropower systems, it is essential to avoid catastrophic failures that lead to human and economic losses. Unfortunately, a hydropower rotor can behave abnormally since several nonlinear effects occur during start-up, shut-downs or when running at nominal speed. Weak nonlinear interaction in the bearings, electromagnetic interaction between the generator and rotor or fluid-structure interaction in turbines are typical nonlinear effects that may appear. Moreover, strong nonlinearities can also occur due to blade contacts and assembly errors. These types of nonlinearities can be dangerous in case of bad design of the rotor, and it could even lead to catastrophes in the worst case. In this thesis, simple models are used to describe the different types of nonlinearities, with focus on blade rubbing, bearings and electromagnetic interaction. These interactions are usually investigated on Jeffcott rotors or rigid rotors to reduce the dimension of the design space to a few important parameters only. The dynamics of the system are evaluated by using common tools such as Poincare sections, bifurcation diagrams, Maximum Lyapunov Exponent (MLE), Lyapunov spectrum and waterfall plots of the Fast Fourier Transform (FFT). The numerical results have been compared with experimental results to ensure that these models are satisfying in our range of study. Once these simple models have been verified, they can be used to simulate the full hydropower rotor by including all interaction types. A focus is made on the numerical methods to employ and reduction methods to gain computation time, as well as to know under which circumstances the nonlinear interactions have to be included in comparison with the linear analysis. As a result, this work intends to provide guidelines about the models to use to perform dynamic simulations on fullscale turbines and to know when a linear model can be sufficient to evaluate a machine at design stage or when changing any mechanical component in the hydropower rotor.

  • 3.
    Thiery, Florian
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Aidanpää, Jan-Olov
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Comparison of contact dynamics in bladed Jeffcott rotors2013Conference paper (Other academic)
  • 4.
    Thiery, Florian
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Aidanpää, Jan-Olov
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Dynamics of a Jeffcott rotor with rigid blades rubbing against an outer ring2012In: Chaotic Modeling and Simulation (CMSIM), ISSN 2241-0503, E-ISSN 2241-0503, p. 643-650Article in journal (Other academic)
    Abstract [en]

    The non-linear behaviour of rub-impact systems have been studied recentlyby approximating rotor-stator systems as rubbing cylinders. In reality, therotor shape is more complex, resulting in richer dynamics over smaller parameter ranges. In this paper, a bladed turbine is modelled using a Jeffcott rotor with three rigid beams attached to the mass center. The contact forces are described by a radial restoring force induced by the massless outer ring, and a tangential Coulomb frictional force. The results are presented in bifurcation diagrams and compared with a previous model described by three flexible beams entering in contact with a fixed ring assuming large displacement beam theory. This paper shows that the two models described give similarities in the overall bifurcation diagram, only showing greater differences in localized frequency ranges.

  • 5.
    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.
    Influence of the blades configuration on the dynamics of a 3-bladed Jeffcott rotor2015In: Proceedings of the 9th IFToMM International Conference on Rotor Dynamics / [ed] Paolo Pennacchi, Encyclopedia of Global Archaeology/Springer Verlag, 2015, Vol. II, p. 79-87Conference paper (Refereed)
    Abstract [en]

    The nonlinear behaviour of blade rubbing has usually been investigated using complex modelling for the contact description. However, a simplified model of a 3-bladed Jeffcott rotor with nonlinear beam deformation contacting a fixed ring due to initial misalignment was used to unveil the global dynamic behaviour of the system. Chaotic regions were found at integer fraction of the natural frequency divided by the number of blades. Similarities in the global behaviour have also been observed for a model with rigid blades contacting a flexible casing. Even though the periodic and chaotic properties were observable experimentally, some difference occurred in localized frequency range due to material loss at the blade tip at higher speed. It is also difficult to accurately set all the blades with the exact same slight contact in experimental test rigs. As a result, the global properties of the rotor are also evaluated with two blades of the same length and the third one shorter. The extreme case where one or two blades are out is also investigated. The results are explored in terms of phase plots, Poincaré sections and bifurcation diagrams as function of the rotating speed. It can be seen that the inherent properties can be modified depending on the blades configuration and unbalance forces.

  • 6.
    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.

  • 7.
    Thiery, Florian
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Gantasala, Sudhakar
    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.
    Numerical evaluation of multilobe bearings using the Spectral Method2017In: Advances in Mechanical Engineering, ISSN 1687-8132, E-ISSN 1687-8140, Vol. 9, no 7Article in journal (Refereed)
    Abstract [en]

    Hydropower rotors and pumps have the specificity to be oriented vertically, meaning that the bearing forces have to be evaluated at each time-step depending on the position of the rotor for dynamical analyses. If the bearing forces cannot be evaluated analytically, a suitable numerical method should be used to calculate the pressure distribution over the bearing domain. This process can be computationally expensive as it should be performed for each discrete time-step. As a result, a comparison between the spectral method, the finite difference method, and the finite element method is performed to investigate which method is more adapted to dynamical analysis of the bearing. It is observed that the spectral method has the advantage of having a reasonable simulation time for any eccentricity magnitude with a moderate number of interpolation points. However, this method should be restricted to simple bearing models such as plain bearings or multilobe bearings due to the advantage of finding a global numerical solution directly on the entire bearing/pad domain

  • 8.
    Thiery, Florian
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Gustavsson, Rolf K.
    Vattenfall Research & Development.
    Aidanpää, Jan-Olov
    Luleå University of Technology, Department of Engineering Sciences and Mathematics.
    Dynamics of a misaligned Kaplan turbine with blade-to-stator contacts2015In: International Journal of Mechanical Sciences, ISSN 0020-7403, E-ISSN 1879-2162, Vol. 99, p. 251-261Article in journal (Refereed)
    Abstract [en]

    Rotor-to-stator contacts can occur in hydropower systems due to mechanical and electrical misalignment as well as high unbalance forces. It can result in high impact forces and damages in case of malfunction of the machine. As a result, a real hydropower rotor is studied to evaluate the different types of dynamic motion due to multiple impacts when it is initially misaligned. In this paper, the simplicity of its blade rubbing modelling allows us to evaluate in a fast and efficient way the dynamics of this system as a function of several design parameters. It is observed that the global dynamics of the system are similar to simple bladed Jeffcott rotors when scaled with the number of blades. Since the rotor runs at its operating point, the contact forces are also evaluated at nominal speed. A parametric study - as a function of contact stiffness and damping - is performed and results are given in terms of Poincaré sections, bifurcation diagrams and maximum displacements at steady state. These simulations are used to determine if the system is safe to operate. It can be used to design hydropower rotors by choosing the operating speed in a suitable range, or to analyse if the machine can be stopped before a catastrophe occurs

  • 9.
    Thiery, Florian
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Gustavsson, Rolf K.
    Vattenfall Research & Development.
    Aidanpää, Jan-Olov
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Evaluation of Campbell diagrams for vertical hydropower machines supported by Tilting Pad Journal Bearings2016Conference paper (Refereed)
    Abstract [en]

    In vertically oriented machines with tilting-pad journal bearings, there is no static load that allow tocalculate the bearing properties around a determined static position. As a result, most of simulationsare performed by solving Reynolds equation at each time-step which can result in long computationaltime. To avoid this concern, a simplified model is used that takes in account the variation of unbalanceload depending on the pad configuration. This nonlinear model is used to simulate the dynamics ofa hydropower turbine and compared with the Campbell diagram calculations used from hydropowerindustry standards. A comparison between the linear and nonlinear model is performed to evaluate howaccurate the linear model is and until which limits it can be relevant. In case of qualitative discrepancies inthe results in terms of natural frequencies and damping ratios, an improvement of the Campbell diagramcalculation is proposed to obtain a more accurate linear model.

1 - 9 of 9
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf