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  • 1.
    Aidanpää, Jan-Olov
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Gustavsson, Rolf K.
    Vattenfall, VRD.
    Lundström, Niklas L. P.
    Umeå university.
    Karlsson, Martin
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Calleecharan, Yogeshwarsing
    Nässelqvist, Mattias
    Karlberg, Magnus
    Lundin, Urban
    Uppsala University.
    Developments in rotor dynamical modeling of hydropower units2009In: Proceedings of the IUTAM Symposium on Emerging Trends in Rotor Dynamics: held in New Delhi, India, March 23 - March 26, 2009 / [ed] Kshitij Gupta, Dordrecht: Encyclopedia of Global Archaeology/Springer Verlag, 2009Conference paper (Refereed)
  • 2.
    Karlberg, Magnus
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Karlsson, Martin
    Karlsson, Lennart
    Näsström, Mats
    Dynamics of rotor systems with clearance and weak pedestals in full contact2010In: 13th International Symposium on Transport Phenomena and Dynamics of Rotating Machinery 2010 (ISROMAC-13): Honolulu, Hawaii, USA, 4 - 7 April 2010, Red Hook, NY: Curran Associates, Inc., 2010, p. 531-536Conference paper (Refereed)
    Abstract [en]

    Many rotating machineries are supported by bearings with clearance, which are further clamped in, compared to the bearing stiffness, weak pedestals. As have been reported in several studies, it is essential to choose a proper clearance in order to avoid unwanted vibrations. When rotating machineries supported by bearings with clearance are subjected to stationary loads (gravity, magnetic pull etc.), it may not loose contact between the shaft and the bearing (i.e. full contact). However, even in full contact unwanted dynamics can occur which is of interest in this paper. It is found that the clearance give raise to anisotropic pedestal stiffness. It is further shown that some of the resonance frequencies decrease with the clearance.

  • 3. Karlsson, Martin
    Activity: Flow annual meeting 20102010Conference paper (Other (popular science, discussion, etc.))
  • 4. Karlsson, Martin
    Activity: OpenFOAM Workshop2007Conference paper (Other (popular science, discussion, etc.))
  • 5.
    Karlsson, Martin
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Electromechanical interactions in hydropower rotor systmes2010Conference paper (Refereed)
  • 6.
    Karlsson, Martin
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Electro-mechanical modelling and analysis of hydroelectric rotor systems2006Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    Hydroelectric power generation supplies about 20 percent of the world's electricity and is the most important renewable energy converting industry. The installed capacity of Hydro-electrical power generation is approximately 700GW with a production of 2600TWh/year. The technically feasible potential of hydro power is 14000TWh/year. In many countries, the hydroelectric generation where build in the 20th century on a regulated energy market, where the units served base load. Nowadays hydroelectric generation are more and more used to serve intermittent load on a deregulated market. This has lead to a new way to use old constructions, and it becomes interesting to study the characteristics of these machines, used for the demands of the 21th century. The aim of the research project of this thesis is to characterise, model and simulate old in service hydro electrical power generating units, to improve the design to the demands of today. This thesis presents three different models for hydro power rotor systems. The first model is developed to study the fundamental dynamics of the whole rotor system and includes simplified models for the unsymmetrical electro- magnetic field and the fluid interaction in the turbine. The model has been evaluated with on-site measurements. From the first model it has been shown that the fundamental excitation frequencies due to the electro-magnetic field can be described on a simple form. The results from this model also indicate that the fluid dynamical interaction in the turbine has to be model more in detail to determine both amplitudes and frequencies of excitations. The second model is concerning the generator of the rotor system. The model is divided into one electro-magnetic finite element model and one simplified mechanical model. Simulation and analysis are carried out due to the reactive power produced by the generator. It has been shown that the reactive power influence the natural frequencies, steady state response and stability of the rotor system. The third model presented in the thesis is developed for characterisation of hydro power rotor systems by use of the electro-mechanical interaction in the generator. The model consists of a finite element model with rotor dynamical applications. Simulations are carried out for one commercial hydro power unit and the results are compared with measurements. The results indicates that the suggested method excite a few eigenfrequencies. It is concluded that the method needs to be improved in order to separate response due to electro-mechanical and fluid dynamical excitations.

  • 7.
    Karlsson, Martin
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Modelling and analysis of multiphysical interactions in hydropower rotor systems2008Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    In this thesis the objective is to develop rotordynamical models of hydropower units, where coupling between mechanical, electromagnetic and fluid dynamical system systems is of certain interest. Both fluid-rotor and electromechanical interactions are known to change the system coefficients of the rotor system, which affects eigenfrequencies, damping, stability and response. In addition, external forces from the magnetic field and the hydraulic system can excite the rotor system. Both system coefficients and external excitations are important considerations during design and operation of a hydropower unit, in order to obtain reliable design and operations. Hydropower rotor systems differ from other rotating systems because they rotate with comparably low rotational speed and the total mass of the rotor system is high. The relative airgap in the generator is small compared to a turbo generator, which results in larger electromagnetic forces. Detailed electromechanical force models of large synchronous generators are a missing part of the scientific literature and there is an industrial need for better models. When including hydraulic forces in a rotordynamical model of a hydropower system, industrial rules of thumb are normally used. Hence, there is a need for better multi-physical models in rotordynamical models of hydropower rotor systems. The electromechanical model of synchronous generators for hydropower has been developed, from only considering radial electromagnetic forces to considering both radial and tangential force. The latter is induced due to a change in the magnetic field when the rotor is in an eccentric position, which induces current in the damper winding of the rotor and changes the magnitude and direction of the electromagnetic force. The current in the damper winding is dependent on whirling, eccentricity and change of eccentricity; hence, the electromagnetic forces are significantly dependent on the motion of the rotor. The electromagnetic forces are implemented as stiffness and damping matrices in the mechanical model, leading to significant changes in the system's eigenfrequency and damping. Computational fluid dynamics (CFD) has been used to analyse fluid forces and moments acting on the turbine runner. Since rotordynamical analysis is normally carried out for a small model during a long simulation time and CFD-models normally has a large degree of freedom, it is of certain interest to develop models that are computationally efficient. The influence of the details on the upstream flow in the inlet boundary conditions have been analysed in order to obtain computationally efficient boundary conditions. It is shown that the obtained forces and moments increase from an insignificant size for a boundary condition with a perfectly distributed inlet flow to a significant size for a boundary condition, based on more information from the upstream domain. CFD has also been used to determine torsional system coefficients, such as added polar inertia and damping, due to the flow through a hydraulic turbine. It is shown that these coefficients have a significant effect and that it decreases the eigenfrequency and increases the damping ratio of the mechanical system. In addition to the numerical work, two different approaches to identify sources of excitations and the system's eigenfrequencies at industrial units have been suggested. The first approach uses a simplified mathematical model for the electromagnetic forces that occur due to shape deviations in the airgap of the generator, together with an assumption of the frequency content of the fluid forces on the turbine runner. The calculated frequency content at the bearings is compared with on-site measurements and an idea of the possible sources of vibrations is given. The other approach uses the changes in electromagnetic forces at a sudden loss of the magnetic field in the generator to excite the system's eigenfrequencies. It is shown that a few of the eigenfrequencies can be identified with this method. However, when the torque of the generator suddenly decreases due to the loss of magnetic field, the control system of the turbine decreases the mass flow through the turbine, leading to more separations of the flow and a broad-banded excitation that perturbs the measurements. The general conclusion of this thesis states the importance of including multi-physical interactions in a rotordynamical model for analysis of design and operation. It is further concluded that the electromagnetic forces of a synchronous generator show similar characteristics to the ones presented for asynchronous generators with both radial and tangential components, and not only a radial force component as earlier research stated. The damper winding for an asynchronous whirling acts as a damper for all the motion simulated in this thesis, since as the whirling deviates from syncronous whirl, the currents in the damper winding will change and induce a force that dampens the motion. The boundary conditions of a CFD- model of a hydraulic turbine have a large effect on the obtained resulting rotordynamical forces and moments. Hence, it is important to consider accurate inlet boundary conditions in a CFD-model for calculation of rotordynamical forces and moments. The added polar inertia and damping due to the flow through the turbine in a torsional dynamic model have a large effect on the system characteristics of the torsional system, which is an important consideration. The suggested methods for on-site measurements are concluded to be useful. However, they require a better modelling of both the electromagnetic forces (especially the model of shape deviations of the generator airgap) and the fluid-rotor interactions (especially at part discharge and transient operation). There are still several topics concerning rotordynamics in hydropower units that are of interest for further research; for example, continuing development of fluid-rotor interactions of hydraulic turbines and electromagnetic forces. Further research regarding accurate modelling of vertical bearings, as well as models for transient analysis of the whole system, are also suggested.

  • 8.
    Karlsson, Martin
    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, Mechanics of Solid Materials.
    Characteristics of a hydro power rotor system due to a sudden loss of magnetic field2006In: Proceedings - 7th International Conference on Rotor Dynamics: September 25 - 28, 2006, Vienna, Austria / [ed] H. Springer; H. Ecker, Vienna: Institute of Mechanics and Mechatronics, Vienna University of Technology , 2006, article id 88Conference paper (Refereed)
    Abstract [en]

    This paper addresses dynamics of the rotor, which is vertically secured in one immovable hinge and one elastic support. There were received and analyzed equations of dynamics for description of disk-shaped and cylindrical rotor with dynamic unbalance. From the overall system of equations, there was received a system of equations for description of dynamics of the rotor under the impact of only static unbalance or only moment unbalance. There were considered cases of stable rotation of the rotor. There were obtained and analyzed dependencies for definition of all forces and moments, which impact the rotor. There were defined conditions at which stability of the rotor's rotation is secured. Studies encompass basic operational modes of the rotor's rotation. Dynamics of the rotor is described by elementary algebraic equations.

  • 9.
    Karlsson, Martin
    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, Mechanics of Solid Materials.
    Dynamic behaviour in a hydro power rotor system due to the influence of generator shape and fluid dynamics2005In: Proceedings of the ASME Power Conference, American Society of Mechanical Engineers , 2005, Vol. PART B, p. 905-913Conference paper (Refereed)
    Abstract [en]

    Hydro power rotors are subjected to fluid and electromagnetic forces. In this paper measurements and simulations are shown for a hydro power rotor system. The simulation includes the influence of fluid forces in the turbine as well as the electro magnetic pull in the generator. The mechanical rotor system is modelled with the generator and the turbine treated as two rigid bodies, connected to an elastic shaft supported by three bearings. The fluid model in the turbine is based on results from the scientific literature. A model is suggested for the electro magnetic pull due to eccentricity and the shape of the stator core and the rotor rim. Results from the simulation are compared and analyzed with frequency spectrum from vibrations measurements. One can conclude that the unbalance together with geometric properties of the turbine and generator, are possible sources of the most dominant frequency peaks in the measurements

  • 10.
    Karlsson, Martin
    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, Mechanics of Solid Materials.
    Perers, Richard
    Uppsala University.
    Leijon, Mats
    Uppsala University.
    Rotor dynamic analysis of an eccentric hydropower generator with damper winding for reactive load2007In: Journal of applied mechanics, ISSN 0021-8936, E-ISSN 1528-9036, Vol. 74, no 6, p. 1178-1186Article in journal (Refereed)
    Abstract [en]

    Asymmetry in the magnetic circuit, around the air gap circumference, in a hydroelectric generator will give rise to a unbalanced magnetic pull. In this paper, a hydropower rotor system is modeled and the influence of electro-mechanical forces due to overexcitation is analyzed. The active power has been kept constant and the rotor excitation has been changed in order to vary the output of reactive power. The electromagnetic field is solved with the finite element method. Two electromagnetic models are compared: one with and one without damper winding. The mechanical model of the generator consists of a four degrees of freedom rigid disk connected to an elastic shaft supported by two bearings with linear properties. It has been found that the unbalanced magnetic pull slightly increases for reactive loads resulting in a decrease of natural frequencies and an increase of unbalance response. When the damper winding is included, the magnetic pull will decrease compared to the model without damper winding, and the pull force has two components: one radial and one tangential. The tangential component can influence the stability of the mechanical system for a range of design parameters.

  • 11.
    Karlsson, Martin
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Lundin, Urban
    Uppsala University.
    Aidanpää, Jan-Olov
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Rotordynamical analysis of a fourteen pole synchronous generator due to whirling dependent electromagnetical forces2010Conference paper (Refereed)
  • 12.
    Karlsson, Martin
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Myllerup, Claus
    Lloyd's Register ODS.
    Chan, Dennis
    Lloyd's Register ODS.
    Electromechanical interactions of a variable speed drive driven compressor train2010Conference paper (Refereed)
  • 13.
    Karlsson, Martin
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Nilsson, Håkan
    Chalmers University of Technology.
    Numerical calculations of rotordynamical coefficients and forces on a hydropower turbine runner using Open-FOAM2007Conference paper (Refereed)
  • 14.
    Karlsson, Martin
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Nilsson, Håkan
    Chalmers University of Technology.
    Strömningsexciterade svängningar i vattenkraftturbiner: hur ska strömningen genom en turbin modelleras i en rotordynamisk modell?2007In: Svenska Mekanikdagar 2007: program och abstracts / [ed] Niklas Davidsson; Elianne Wassvik, Luleå: Luleå tekniska universitet, 2007, p. 57-Conference paper (Other academic)
  • 15.
    Karlsson, Martin
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Nilsson, Håkan
    Chalmers University of Technology, Department of Applied Mechanics.
    Aidanpää, Jan-Olov
    Influence of inlet boundary conditions in the prediction of rotor dynamic forces and moments for a hydraulic turbine using CFD2008In: ISROMAC-12: the Twelfth International Symposium on Transport Phenomena and Dynamics of Rotating Machinery ; Honolulu, Hawaii, February 17 - 22, 2008, Pacific Center of Thermal-Fluids Engineering, Honolulu, 2008Conference paper (Refereed)
    Abstract [en]

    The rotordynamic behavior of a hydraulic turbine is influenced by fluid-rotor interactions at the turbine runner. In this paper computational fluid dynamics (CFD) is used to numerically predict the rotordynamical excitation forces due to the flow through a hydraulic turbine runner. The simulations are carried out for three different boundary conditions. One axi-symmetric inlet boundary condition, and two axi-periodic boundary conditions. The two latter are obtained from separate simulations of wicket gate and spiral casing flow. It is found that the inlet boundary condition significantly affects the rotordynamical forces and moments.

  • 16.
    Karlsson, Martin
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Nilsson, Håkan
    Chalmers University of Technology.
    Aidanpää, Jan-Olov
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Numerical estimation of torsional dynamic coefficients of a hydraulic turbine2009In: International Journal of Rotating Machinery, ISSN 1023-621X, E-ISSN 1542-3034Article in journal (Refereed)
    Abstract [en]

    The rotordynamic behavior of a hydraulic turbine is influenced by fluid-rotor interactions at the turbine runner. In this paper computational fluid dynamics (CFDs) are used to numerically predict the torsional dynamic coefficients due to added polar inertia, damping, and stiffness of a Kaplan turbine runner. The simulations are carried out for three operating conditions, one at about 35% load, one at about 60% load (near best efficiency), and one at about 70% load. The runner rotational speed is perturbed with a sinusoidal function with different frequencies in order to estimate the coefficients of added polar inertia and damping. It is shown that the added coefficients are dependent of the load and the oscillation frequency of the runner. This affect the system's eigenfrequencies and damping. The eigenfrequency is reduced with up to 65% compared to the eigenfrequency of the mechanical system without the fluid interaction. The contribution to the damping ratio varies between 30-80% depending on the load. Hence, it is important to consider these added coefficients while carrying out dynamic analysis of the mechanical system.

  • 17.
    Karlsson, Martin
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Perers, Richard
    Uppsala University.
    Gustavsson, Rolf
    Aidanpää, Jan-Olov
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Karlsson, Thommy
    Leijon, Mats
    Uppsala University.
    Rotor dynamical analysis of a hydroelectric generator for active power2006In: Proceedings: International Symposium on Water Resources and Renewable Energy Development in Asia : Asia 2006, Bangkok, Thailand, November 30 - December 1, 2006, Singapore: Aqua-Media International , 2006Conference paper (Other academic)
    Abstract [en]

    Asymmetry of the magnetic field in a synchronous generator will induce a magnetic unbalance pull. In this paper, a hydropower rotor system is modelled and the influence of electro-mechanical forces due to different amounts of real power is analysed. The electromagnetic field is solved with the finite element method and coupled with mechanical system as a magnetic stiffness. The mechanical model of the generator consists of a four degree of freedom rigid disc connected to an elastic shaft supported by two bearings with linear properties. It has been found that the unbalance magnetic pull increases for a lover amount of real power leading to a decrease of natural frequencies and an increase of unbalance response. Since many hydropower units are used for both part and full load it becomes important to model the electro-mechanical interaction when developing new generators, in order to improve the mechanical design.

  • 18.
    Karlsson, Martin
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Samuelsson, Henrik
    Lloyd's Register ODS.
    Karlberg, Magnus
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Co-variance driven stochastic subspace identification approach for rotordynamics2010In: 13th International Symposium on Transport Phenomena and Dynamics of Rotating Machinery 2010 (ISROMAC-13), 2010Conference paper (Refereed)
  • 19.
    Karlsson, Martin
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Samuelsson, Henrik
    Lloyd's Register ODS.
    Karlberg, Magnus
    Using operational modal analysis to determine rotordynamic modes2010In: 13th International Symposium on Transport Phenomena and Dynamics of Rotating Machinery 2010 (ISROMAC-13): Honolulu, Hawaii, USA, 4 - 7 April 2010, Red Hook, NY: Curran Associates, Inc., 2010, p. 527-530Conference paper (Refereed)
    Abstract [en]

    Operational Modal Analysis (OMA) has lately been a more and more common tool in structural dynamics. The benefits compared to Experimental Modal Analysis (EMA) are that one does not need any artificial excitation and that the structure does not have to be at rest, which is a requirement of EMA. So far, OMA has won terrain for modal analysis of large structures such as buildings and bridges, and for vehicles such as helicopters and ships. For rotating equipment, OMA has not yet been widely used or evaluated. Rotordynamic modes depend on the operating condition of the rotating equipment (e.g. speed). Hence the fundamental requirement of EMA that the testing object should be at rest is not fulfilled. Mapping of critical speeds during start-up and coursing down gives some important operating information, but it will not give all modal information needed to validate a theoretical model or to verify the requirements of damping. The aim of this paper is to evaluate OMA for rotordynamical modal analysis. A numerical model of rotor is used as test object. The response is analyzed with various SSI methods. The results are presented in a Campbell diagram, showing the frequency dependent rotor modes as well as the structural modes. Values for the damping are presented in a root locus plot. These results agree well when comparing the results with a direct naturalvalue solver for the numerical model. It is concluded that OMA can be applied to rotordynamical applications. However, identifying corresponding modes at different speeds can be difficult at field measurements; hence the authors suggest further research and development of Operational Modal Analysis in this specific area.

1 - 19 of 19
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