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  • 51.
    Karlberg, Magnus
    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.
    Rotordynamical modelling of a fibre refiner during production2007In: Journal of Sound and Vibration, ISSN 0022-460X, E-ISSN 1095-8568, Vol. 303, no 3-5, p. 440-454Article in journal (Refereed)
    Abstract [en]

    A key component in panel board production is the fibre refiner, whose task is to break cellulose wood chips into slender fibres. This refining process takes place between a rotor and a stator, where a gap of around 0.5 mm is found. In the development of these refiners predicting the dynamics is important; hence, mathematical models are needed. For refiners and other applications like brakes, turbines, and compressors, the interaction between the rotor and the surrounding medium can in many situations be significant. In addition to external load, this interaction can also change the characteristics of the system, which should be considered in the design process. Today, there exists no validated load model for fibre refiner process. Hence, the aim of this paper is to suggest one.Measured axial force data were divided into a constant part and a superimposed oscillating part with different frequencies. For both parts a linear dependence on the gap between the stator and the rotor was assumed. Finally, a four degrees of freedom (dof) model was used to fit a pressure distribution to the axial force model.This process load model led to stiffness and external loads that can be both time dependant. If the pressure distribution only shows a radial variation along the refining zone, all the external loads except the axial one will vanish. The number of functions describing the stiffness parameters also decrease from eight to four. In one case, four stiffness coefficients vanish, whereas the remaining coefficients become constant. This occurs if the process load does not follow the angular vibrations and there is no gap dependence on the oscillating parts of the process load. Numerical simulations showed that by applying a specific process load model, the vibration orbit changed from the unbalance response by means of shape and vibration origin. The unstable domain was further increased when the process load model was applied.Measurements are necessary to select a realistic process model for a specific application. The derived model can be used in product development to choose suitable system parameters and thus to avoid dynamical problems.

  • 52.
    Karlberg, Magnus
    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.
    Rotordynamical simulations of a fibre refiner during production2011In: Journal of Sound and Vibration, ISSN 0022-460X, E-ISSN 1095-8568, Vol. 330, no 18/19, p. 4460-4473Article in journal (Refereed)
    Abstract [en]

    A key component in panel board production is the refiner, whose task is to break raw cellulose wood chips into slender fibres, done by a relative angular motion between stator and rotor. The main problem in predicting the dynamics of these machines is to model the complicated fibre breaking process, since the refining process leads to a three-phase flow (solid wood, water and steam) between the stator and rotor. By modelling the rotor as a rigid body, the process can only contribute by a resulting force and a resulting moment. Through this approach and axial force measurements, it has been shown that the refining process can be treated as a time dependent stiffness matrix and external load. The objective for this paper is to predict and explain dynamical characteristics of fibre refiners during production in such a way that the results can be used already at early stages of the product development process. Two different pressure distribution cases are studied, i.e. one axisymmetric with only radial variations and one non-axisymmetric. It is found that the axisymmetric case only excited forward modes, while the non-axisymmetric case excited all modes. The time dependent stiffness matrix resulted in unstable domains, but also in stable domains with intermittent high amplitudes.

  • 53.
    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.

  • 54.
    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

  • 55.
    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.

  • 56.
    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)
  • 57.
    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.

  • 58.
    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.

  • 59.
    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.

  • 60.
    Lundström, L.
    et al.
    Division for Electricity and Lightning Research, Uppsala University, Ångström Laboratory.
    Gustavsson, Rolf
    Vattenfall Research & Development.
    Aidanpää, Jan-Olov
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Dahlbäck, N.
    Division for Electricity and Lightning Research, Uppsala University, Ångström Laboratory.
    Leijon, Mats
    Division for Electricity and Lightning Research, Uppsala University, Ångström Laboratory.
    Influence on the stability of generator rotors due to radial and tangential magnetic pull force2007In: IET Electric Power Applications, ISSN 1751-8660, E-ISSN 1751-8679, Vol. 1, no 1, p. 1-8Article in journal (Refereed)
    Abstract [en]

    Forces due to nonuniform airgaps in rotating electrical machines have been a research topic for over 100 years. However, most research in the area of rotating electrical machines has been performed on motors. Large forces in hydropower generators can lead to expensive damage and failures. Therefore, it is of interest to calculate the forces that arise in a large synchronous generator with an eccentric rotor and study the influence these forces have on the stability of the generator rotor. A 74 MVA synchronous hydropower generator was simulated with an eccentric rotor, using a time-stepping finite-element technique. The forces were calculated using Coulomb's virtual-work method and simulations were performed for no-load and load cases. The resulting force was found to be reduced significantly when a damper winding was taken into account. An interesting effect of the rotor damper winding was that it reduced the eccentricity force and introduced a force component perpendicular to the direction of eccentricity. The results from the finite-element simulations were used to determine how the forces affect the stability of the generator rotor. Damped natural eigenfrequencies and damping ratio for load and no-load conditions are presented. When applying the forces computed in the time-dependent model, the damped natural eigenfrequencies were found to increase and the stability of the generator rotor was found to be reduced compared with when the forces were computed in a stationary model.

  • 61.
    Lundström, Niklas
    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 consequences of electromagnetic pull due to deviations in generator shape2007In: Journal of Sound and Vibration, ISSN 0022-460X, E-ISSN 1095-8568, Vol. 301, no 1-2, p. 207-225Article in journal (Refereed)
    Abstract [en]

    Results from earlier measurements on hydropower generators have indicated relatively large eccentricities and shape deviations in the rotor and stator. These non-symmetric geometries produce an attraction force between the rotor and the stator, called unbalanced magnetic pull (UMP). The UMP force can produce large vibrations which can be dangerous to the machine. A mathematical model is developed to describe the shapes of the rotor and stator, and the corresponding UMP is obtained through the law of energy conservation. The target of the paper is to analyse the dynamics of a generator due to shape deviations in the rotor and stator. As rotor-model, a balanced Jeffcott rotor is used. A linearization of the UMP indicates the importance of considering the nonlinear effects. The stability of some attractors are analysed and the generator dynamics are further investigated by simulating the basin of attraction. The magnitudes are approximately obtained when the shape deviations become dangerous for the generator. It is concluded which shape deviations that are more dangerous than others. In hydropower generator maintenance the shapes of the rotor and stator are frequently measured. The results from this paper can be used to evaluate such measurements and estimate the stability and robustness by simulations.

  • 62. Lundström, Niklas
    et al.
    Aidanpää, Jan-Olov
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Dynamics in large generators due to oval rotor and triangular stator shape2011In: Acta Mechanica Sinica, ISSN 0567-7718, E-ISSN 0459-1879, Vol. 27, no 1, p. 18-27Article in journal (Refereed)
    Abstract [en]

    Earlier measurements in large synchronous generators indicate the existence of complex whirling motion, and also deviations of shape in both the rotor and the stator. These non-symmetric geometries produce an attraction force between the rotor and the stator, called unbalanced magnetic pull (UMP). The target of this paper is to analyse responses due to certain deviations of shape in the rotor and the stator. In particular, the perturbation on the rotor is considered to be of oval character, and the perturbations of the stator are considered triangular. By numerical and analytical methods it is concluded for which generator parameters harmful conditions, such as complicated whirling motion and high amplitudes, will occur. During maintenance of hydro power generators the shapes of the rotor and stator are frequently measured. The results from this paper can be used to evaluate such measurements and to explain the existence of complex whirling motion.

  • 63. Lundström, Niklas
    et al.
    Aidanpää, Jan-Olov
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Grafström, Anton
    Department of Forest Resource Management, Swedish University of Agricultural Sciences.
    Small shape deviations causes complex dynamics in large electric generators2014In: European Physical Journal: Applied physics, ISSN 1286-0042, E-ISSN 1286-0050, Vol. 66, no 2, article id 130447Article in journal (Refereed)
    Abstract [en]

    We prove that combinations of small eccentricity, ovality and/or triangularity in the rotor and stator can produce complex whirling motions of an unbalanced rotor in large synchronous generators. It is concluded which structures of shape deviations that are more harmful, in the sense of producing complex whirling motions, than others. For each such structure, we derive simplified equations of motions from which we conclude analytically the relation between shape deviations and mass unbalance that yield non-smooth whirling motions. Finally we discuss validity of our results in the sense of modeling of the unbalanced magnetic pull force

  • 64.
    Lundström, Niklas L. P.
    et al.
    Umeå University, Department of Mathematics and Mathematical Statistics.
    Aidanpää, Jan-Olov
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Whirling frequencies and amplitudes due to deviations of generator shape2008In: International Journal of Non-Linear Mechanics, ISSN 0020-7462, E-ISSN 1878-5638, Vol. 43, no 9, p. 933-940Article in journal (Refereed)
    Abstract [en]

    Earlier measurements in large synchronous generators indicate the existence of backward whirling motion, and also relatively large deviations of shape in both the rotor and the stator. These non-symmetric geometries produce an attraction force between the rotor and the stator, called unbalanced magnetic pull (UMP). The target of this paper is to analyse the whirling frequencies and amplitude of the response for large synchronous generators with a high number of poles, due to deviations of shape in the rotor and stator. A mathematical model is developed to describe the shapes of the rotor and stator, and the corresponding UMP is obtained by using the law of energy conservation. The UMP is analysed due to different deviations of shape. The result gives the average angular frequency and the magnitude of the UMP for certain deviations of shape. From this result, the whirling frequency and the amplitude of the corresponding response can be approximated. Simulations of the response of a Jeffcott rotor model show good agreement with the theoretical results of the UMP for some generator geometries. The conclusion is that different whirling frequencies, both backward and forward whirling, can occur in these machines due to deviations in shape of the generator. Therefore, the shape of the generator can excite resonance vibrations on several other frequencies than the rotation frequency. During maintenance of hydropower generators the shapes of the rotor and stator are frequently measured. The results from this paper can be used to evaluate such measurements and to explain the existence of complicated whirling motion.

  • 65. 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.

  • 66. Luneno, Jean-Claude
    et al.
    Aidanpää, Jan-Olov
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Gustavsson, Rolf
    Vattenfall Research & Development.
    Effects of shaft flexibility and gyroscopic coupling on instability threshold speeds of rotor-bearing systems2010In: 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. 537-543Conference paper (Refereed)
    Abstract [en]

    The driving speeds at which self-excited motions occur in rotor-bearing systems are commonly referred to as "instability threshold". These speeds and the magnitude of rotor (journal) trajectories are two important variables characterising the limits and states of a rotating machinery. The hydrodynamic lubrication in journal-bearing provides damping and reduces friction on rotor systems; therefore the journal amplitude should not exceed the bearing radial clearance. Linear bearing models are not able to accurately predict the journal trajectories for rotor-bearing system operating in conditions where the system does not have period one solutions, or when the journal motion is larger than 20-30% of the bearing radial clearance. Therefore the nonlinear bearing impedance descriptions method was used to model the hydrodynamic reaction forces. Two cases were analysed: 1) a rigid non-symmetric rotor and 2) a flexible non-symmetric rotor. The two models consist of a rotor supported by two identical finite-length hydrodynamic journal bearings of length to diameter ratio L/D=1, with same lubricant properties. The flexible non-symmetric rotor was modelled by the finite element method (FEM). Simulation results show that the instability threshold of the rigid non-symmetric rotor-bearing system (case1) depends on the low stability characteristics of the less loaded bearing. But when the shaft flexibility and the gyroscopic coupling effect are taken into account; the instability threshold increases for the flexible non-symmetric rotor-bearing system (case2). The gyroscopic coupling effect does not only increase the instability threshold, but the journal trajectories magnitude has also significantly increased. This is normally not a preferable condition since high vibrations will induce heat and stress in babbited bearing.

  • 67.
    Luneno, Jean-Claude
    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.
    Gustavsson, Rolf
    Vattenfall Research & Development.
    Experimental verification of a combi-bearing model for vertical rotor systems2013In: Journal of Vibration and Acoustics-Transactions of the ASME, ISSN 1048-9002, E-ISSN 1528-8927, Vol. 135, no 3Article in journal (Refereed)
    Abstract [en]

    Combi-bearing is a combined thrust-journal bearing design used in vertical hydropower rotors. The dynamic characteristics of this component (combi-bearing) were analytically modeled by Luneno et al. (2011, "Model Based Analysis of Coupled Vibrations Due to the Combi-Bearing in Vertical Hydroturbogenerator Rotors," ASME J. Vib. Acoust., 133, p. 061012). This analytic model was inserted into a finite element model of a vertical rotor rig and numerically simulated. In this paper, the simulated vertical rotorbearings system is a small-scale vertical machine constructed to validate the analytically derived combi-bearing model. Good agreement was found between the simulation and experimental results. The simulation and experimental results showed that the journal (radial) bearing's position relative to the contact point between the combi-bearing's collar and the rotor influences the rotor system's fundamental natural frequencies. Therefore, the combi-bearing model needs to be included into rotor dynamic models. Neglecting the effect of this component may cause significant errors in the predicted results. Copyright

  • 68.
    Luneno, Jean-Claude
    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.
    Gustavsson, Rolf
    Vattenfall Research & Development.
    Model based analysis of coupled vibrations due to the combi-bearing in vertical hydroturbogenerator rotors2011In: Journal of Vibration and Acoustics-Transactions of the ASME, ISSN 1048-9002, E-ISSN 1528-8927, Vol. 133, no 6, article id 061012Article in journal (Refereed)
    Abstract [en]

    The studies presented in this paper focus on analyzing how the combined thrust-journal bearing (commonly called combi-bearing) influences the dynamics of hydropower rotors. Thrust bearing is a component used in vertical rotating machinery and shafts designed to transmit thrust. The total axial load is carried by the single thrust bearing. Any design, manufacture, or assembly error in this component (thrust bearing) would certainly influence the functionality of the entire machine. The analyzed combi-bearing is an existing machine component used in the hydropower unit Porjus U9 situated in northern Sweden. This combi-bearing is a fluid-film lubricated tilting-pad thrust and journal bearings combined together. Only linear fluid-film stiffness was taken into account in the model while fluid-film damping and pads inertia effects were not taken into account. The linearized model shows that the combi-bearing couples the rotor's lateral and angular motions. However, if the thrust bearing's pads arrangement is not symmetrical or if all the pads are not angularly equidistant the rotor axial and angular motions are also coupled. This last case of coupling will also occur if the thrust bearing equivalent total stiffness is not evenly distributed over the thrust bearing. A defective pad or unequal hydrodynamic pressure distribution on the pads' surfaces may be the cause. The Porjus U9's simulation results show that the combi-bearing influences the dynamic behavior of the machine. The rotor motions' coupling due to combi-bearing changes the system's natural frequencies and vibration modes.

  • 69. Luneno, Jean-Claude
    et al.
    Aidanpää, Jan-Olov
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Gustavsson, Rolf
    Vattenfall Research & Development.
    Oil induced instability: analytic study and experimental verification on flexible rotor supported by a journal-bearing at one end2010In: Proceedings of the 8th IFToMM International Conference on Rotordynamics: September 12-15, 2010, KIST, Seoul, Korea, 2010Conference paper (Refereed)
    Abstract [en]

    Oil induced instability, is a frequently encountered phenomenon causing system instability for rotors supported by hydrodynamic journal-bearings. In this paper a flexible rotor, simply supported at one end and with oil lubricated journal-bearing at the other, is analytically modelled. The rotor system is modelled in two ways namely as a discrete system by finite element method (FEM) with nonlinear journal-bearing and as a lumped inertia system with linear journal-bearing. The analysed rotor-bearing system is a Bently Nevada Rotor Kit Model RK4 with Oil whirl/whip option. Results obtained from the simulation of the discrete rotor model with a nonlinear journal-bearing indicate at which rotational speed the oil induced instability (oil whirl) will occur. Campbell diagrams are shown for the lumped inertia rotor model with linear journal-bearing and the critical speeds are predicted. From the results the accuracy of the analytical speed-dependent bearing coefficients are evaluated. These coefficients were derived from the nonlinear bearing impedance descriptions by D. Childs. The bearing impedance descriptions method is a method valid for all L/D (length to diameter) ratios, and all journal eccentricities. The simulation time is significantly reduced by using a lumped inertia rotor model with linear journal-bearing. Critical speed obtained from Campbell diagram predicts a threshold speed of instability which is about 0.35% higher than that predicted by the discrete rotor model with a nonlinear journal-bearing. Compared with results collected from experiment, the simulation results predict a threshold speed of instability which is about 5.69% higher (linear analysis), or 5.36% higher (nonlinear analysis).

  • 70.
    Luneno, Jean-Claude
    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.
    Gustavsson, Rolf K.
    Vattenfall Research & Development.
    Misalignment in combi-bearing: A cause of parametric instability in vertical rotor systems2013In: Journal of engineering for gas turbines and power, ISSN 0742-4795, E-ISSN 1528-8919, Vol. 135, no 3Article in journal (Refereed)
    Abstract [en]

    The dynamic characteristics of the combi-bearing (combined thrust-journal bearing) in vertical rotor systems were analytically modeled and experimentally verified in the authors' previous publications. An angular misalignment, which may be caused by a possible manufacturing or assembling error, is introduced in the combi-bearing's rotating collar. A new model of the defective combi-bearing has been derived. The derived model shows that the angular misalignment in the combi-bearing's rotating collar generates an asymmetry in the rotor system at the combi-bearing's location. The rotor system's stiffness in its two translational X and Y directions differ at the combi-bearing's location. Constant parameters and/or coefficients in rotating asymmetric structures appear to change with time when observed in the stationary frame. These time dependent parameters (coefficients) are the source of the so-called parametric instability in rotating systems. If the collar angular misalignment is located in the X-Z plane all rotor motions in this plane at the contact point between the combi-bearing and the rotor will be coupled. A parametric instability is observed within certain ranges of the rotor speed, depending on the magnitude of the angular misalignment

  • 71.
    Mill, O.
    et al.
    Svenska Kraftnät.
    Dahlbäck, N.
    Vattenfall.
    Worman, A
    Kungliga tekniska högskolan, KTH.
    Knutsson, Sven
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering.
    Johansson, F.
    Kungliga tekniska högskolan, KTH.
    Andreasson, Patrik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Yang, J.
    Kungliga tekniska högskolan, KTH.
    Lundin, U.
    UU.
    Aidanpää, Jan-Olov
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Nilsson, H.
    CTH.
    Cervantes, Michel
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Glavatskih, Sergei
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Analysis and development of hydro power research: synthesis within Swedish Hydro Power Centre2010Report (Other academic)
    Abstract [en]

    The market for hydropower re-investments in Sweden is approx 2.5 billion SEK/yr the coming decade. Large investments will also be carried out in Swedish tailing dams. This will result in challenging projects and need of experts. A crucial factor for a successful management of these challenges is the supply of engineers and researchers with hydro power and dam skills and knowledge. Swedish Hydro Power Centre (Svenskt vattenkraftcentrum, SVC) is a competence centre for university education and research environments within hydro power and mining dams. SVC comprises of two knowledge areas: Hydraulic Engineering and Hydro Turbines and Generators, respectively. SVC builds high-quality and long term sustainable knowledge at selected universities...

  • 72.
    Mohammed, Omar D.
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Rantatalo, Matti
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Aidanpää, Jan-Olov
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Dynamic modelling of a one-stage spur gear system and vibration-based tooth crack detection analysis2015In: Mechanical systems and signal processing, ISSN 0888-3270, E-ISSN 1096-1216, Vol. 54, no 1, p. 293-305Article in journal (Refereed)
    Abstract [en]

    For the purpose of simulation and vibration-based condition monitoring of a geared system, it is important to model the system with an appropriate number of degrees of freedom (DOF). In earlier papers several models were suggested and it is therefore of interest to evaluate their limitations. In the present study a 12 DOF gear dynamic model including a gyroscopic effect was developed and the equations of motions were derived. A one-stage reduction gear was modelled using three different dynamic models (with 6, 8 and 8 reduced to 6 DOF), as well as thedeveloped model (with 12 DOF), which is referred as the fourth model in this paper. The time-varying mesh stiffness was calculated, and dynamic simulation was then performed for different crack sizes. Time domain scalar indicators (the RMS, kurtosis and the crest factor) were applied for fault detection analysis. The results of the first model showa clearly visible difference from those of the other studied models, which were made more realistic by including two more DOF to describe the motor and load. Both the symmetric and the asymmetric disc cases were studied using the fourth model. In the case of disc symmetry, the results of the obtained response are close to those obtained from both the second and third models. Furthermore, the second model showed a slight influence from inter-tooth friction, andtherefore the third model is adequate for simulating the pinion’s y-displacement in the case of the symmetric disc. In the case of the asymmetric disc, the results deviate from those obtained in the symmetric case. Therefore, for simulating the pinion’s y-displacement, the fourth model can be considered for more accurate modelling in the case of the asymmetric disc.

  • 73.
    Mohammed, Omar D.
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Rantatalo, Matti
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Aidanpää, Jan-Olov
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Dynamic modelling of gear system with gyroscopic effect and crack detection analysis2015In: Proceedings of the 9th IFToMM International Conference on Rotor Dynamics / [ed] Paolo Pennacchi, Encyclopedia of Global Archaeology/Springer Verlag, 2015, Vol. X, p. 1303-1314Conference paper (Refereed)
    Abstract [en]

    In this paper a 12 DOF gear dynamic model was developed and the equations of motions were derived. A one-stage reduction gear was modelled with gyroscopic effect of the gear disc, and both cases of symmetric and asymmetric disc were studied. Gear mesh stiffness was calculated for different crack sizes, and dynamic response was simulated. Time domain scalar indicators (the RMS, kurtosis and the crest factor) were applied for fault detection analysis. In the case of asymmetric disc the simulation shows results that are different from those obtained in the symmetric case. The coupling terms have an effect on the obtained pinion’s displacement which is studied for fault detection analysis. Therefore, for simulating the pinion’s displacement, this model can be considered for more accurate modelling in case of asymmetric disc.

  • 74.
    Mohammed, Omar D.
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Rantatalo, Matti
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Aidanpää, Jan-Olov
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Improving mesh stiffness calculation of cracked gears for the purpose of vibration-based fault analysis2013In: Engineering Failure Analysis, ISSN 1350-6307, E-ISSN 1873-1961, Vol. 34, p. 235-251Article in journal (Refereed)
    Abstract [en]

    For the purpose of vibration-based condition monitoring and to prevent occurrence of catastrophic gear failures it is important to improve the simulated dynamic response of the studied gear model. The time varying gear mesh stiffness will contribute to the dynamic response of a geared system. Some previously applied methods for stiffness calculation, described in the literature, show good agreement with the results obtained with FEM simulation for smaller crack sizes. However, when larger crack sizes are reached, these methods show an increasing deviation from FEM simulation results. A reduction in the gear mesh stiffness can be considered to assess the status of tooth damage and, therefore, by increasing the accuracy of the calculated mesh stiffness, dynamic simulations of a gear can be improved. In this paper a new method is presented for calculating the gear mesh stiffness for a propagating crack in the tooth root. The influence of gear mesh stiffness on the vibration-based fault detection indicators, the RMS, kurtosis and the crest factor, is investigated. Different crack sizes are examined by using this new method for sizes up to around 50% of the total tooth root thickness. When compared to FEM simulations, the presented method shows more accurate results for calculations of the gear mesh stiffness (for the studied model) than the previously suggested methods.

  • 75.
    Mohammed, Omar D.
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Rantatalo, Matti
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Aidanpää, Jan-Olov
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Kumar, Uday
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Vibration signal analysis for gear fault diagnosis with various crack progression scenarios2013In: Mechanical systems and signal processing, ISSN 0888-3270, E-ISSN 1096-1216, Vol. 41, no 1-2, p. 176-195Article in journal (Refereed)
    Abstract [en]

    There are different analytical scenarios assumed for crack propagation in the gear tooth root. This paper presents an investigation of the performance of statistical fault detection indicators (the RMS and kurtosis) for three different series of crack propagation scenarios, to compare these scenarios from a fault diagnostics point of view. These scenarios imply different forms of cracks with propagation by a certain step of crack depth. The 1st scenario assumes a crack being extended through the whole tooth width with a uniform crack depth distribution, while the 2nd scenario assumes the crack being extended through the whole tooth width with a parabolic crack depth distribution, and finally in the 3rd scenario the crack is assumed to be propagating in both the depth and the length directions simultaneously. The time-varying gear mesh stiffness has been investigated using the program code developed in the present research, and the crack propagation can be modelled with any of the presented crack propagation scenarios. Dynamic simulation has been performed to obtain the residual signals of all the studied cases for each crack propagation scenario. The comparison of the statistical indicators applied to the residual signals shows that in the 1st scenario the faults are most easily detectable, since in this scenario there is a change in the indicators implying a dramatic decrease in the gear mesh stiffness. The fault detection in the 2nd scenario is more difficult, as the crack propagates with no significant reflection on the mesh stiffness loss. The 3rd proposed scenario should receive more attention in research because it could occur in reality in case of non-uniform load distribution. However, with this scenario it is difficult to perform early fault detection, since there is a very slight change in the statistical indicators at the beginning of the crack propagation. After which, these indicators show a significant change when the crack grows deeper which implies a serious crack propagation condition.

  • 76.
    Nässelqvist, Martin
    et al.
    Vattenfall Research & Development.
    Gustavsson, Rolf
    Vattenfall Research & Development.
    Aidanpää, Jan-Olov
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    A methodology for protective vibration monitoring of hydropower units based on the mechanical properties2013In: Journal of Dynamic Systems Measurement, and Control, ISSN 0022-0434, E-ISSN 1528-9028, Vol. 135, no 4Article in journal (Refereed)
    Abstract [en]

    It is important to monitor the radial loads in hydropower units in order to protect the machine from harmful radial loads. Existing recommendations in the standards regarding the radial movements of the shaft and bearing housing in hydropower units, ISO-7919-5 (International Organization for Standardization, 2005, "ISO 7919-5: Mechanical Vibration-Evaluation of Machine Vibration by Measurements on Rotating Shafts-Part 5: Machine Sets in Hydraulic Power Generating and Pumping Plants, " Geneva, Switzerland) and ISO-10816-5 (International Organization for Standardization, 2000, "ISO 10816-5: Mechanical Vibration-Evaluation of Machine Vibration by Measurements on Non-Rotating Parts-Part 5: Machine Sets in Hydraulic Power Generating and Pumping Plants, " Geneva, Switzerland), have alarm levels based on statistical data and do not consider the mechanical properties of the machine. The synchronous speed of the unit determines the maximum recommended shaft displacement and housing acceleration, according to these standards. This paper presents a methodology for the alarm and trip levels based on the design criteria of the hydropower unit and the measured radial loads in the machine during operation. When a hydropower unit is designed, one of its design criteria is to withstand certain loads spectra without the occurrence of fatigue in the mechanical components. These calculated limits for fatigue are used to set limits for the maximum radial loads allowed in the machine before it shuts down in order to protect itself from damage due to high radial loads. Radial loads in hydropower units are caused by unbalance, shape deviations, dynamic flow properties in the turbine, etc. Standards exist for balancing and manufacturers (and power plant owners) have recommendations for maximum allowed shape deviations in generators. These standards and recommendations determine which loads, at a maximum, should be allowed before an alarm is sent that the machine needs maintenance. The radial bearing load can be determined using load cells, bearing properties multiplied by shaft displacement, or bearing bracket stiffness multiplied by housing compression or movement. Different load measurement methods should be used depending on the design of the machine and accuracy demands in the load measurement. The methodology presented in the paper is applied to a 40MW hydropower unit; suggestions are presented for the alarm and trip levels for the machine based on the mechanical properties and radial loads

  • 77.
    Nässelqvist, Martin
    et al.
    Vattenfall Research & Development.
    Gustavsson, Rolf
    Vattenfall Research & Development.
    Aidanpää, Jan-Olov
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Design of Test Rig for Rotordynamic Simulations of Vertical Machines2012Conference paper (Refereed)
    Abstract [en]

    Most of the applications for fluid film bearings have horizontally oriented rotors. This has led to commercial software developers using algorithms and calculations for bearing properties based on machines with a horizontally oriented rotor. This means that the shaft has a set operating point in the bearing based on static radial loads caused by the dead weight of the rotor, magnetic pull forces etc. Large hydropower units generally have vertically oriented shafts. In such systems with vertical rotors, there is no predetermined operating point. This paper presents the design of a test rig that was built at Vattenfall R&D during 2010-2011 in order to study and compare dynamic behaviour of vertical and horizontal rotors. The test rig consists of two bearings and a Jeffcott rotor. The bearings are 4-pad tilting-pad bearings and the operating speed of the test rig is from 0 to 3000 rpm. Radial load and shaft displacement are measured at each bearing using strain gauges and inductive displacement sensors. In the test rig presented in this paper, the excitation of shaft motion is self-induced, i.e. the shaft motion is caused by dead weight of the rotor and applied mass unbalance. Initial tests were performed in order to evaluate the test rig and differences in behaviour between bearing properties when the test rig is in vertical and horizontal position. Results from initial tests indicate that the bearing load - shaft eccentricity ratio is independent of the type of eccentricity, static or dynamic. In vertical operation at high dynamic eccentricities the load and eccentricity orbits have rectangular shapes due to the difference in stiffness for load on pads and load between pads. For vertical rotating systems using tilting pad bearings with a low number of pads and operating at high dynamic radial loads, the bearing properties can possibly cause excitation of natural frequencies at n times the nominal speed, where n is the number of pads.

  • 78.
    Nässelqvist, Mattias
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Gustavsson, R.
    Vattenfall Power Consultant AB Mechanical and Process Engineering, Kyrkogatan 4, Gävle.
    Aidanpää, Jan-Olov
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Bearing load measurement in a hydropower unit using strain gauges installed inside pivot pin2012In: Experimental mechanics, ISSN 0014-4851, E-ISSN 1741-2765, Vol. 52, no 4, p. 361-369Article in journal (Refereed)
    Abstract [en]

    To determine a machine's mechanical condition it is of importance to know the radial bearing forces in the machine. Radial forces are caused by magnetic pull forces in the generator, clamped shafts, mass unbalance and flow properties around the turbine. Measuring the shaft displacement in the bearing or the bearing housing acceleration is not sufficient for status determination of a vertical hydropower unit. It is the magnitude and frequencies of the radial forces in combination with structure properties which give information as to whether a measured value is harmful or not. This paper presents an alternative method for measurement of radial bearing load in a hydropower unit. The method presented in this paper is based on strain measurements on pivot pins. The pivot pins are placed behind the bearing pad and the radial loads acting on the pad propagate through the pivot pin. New pivot pins were purchased and equipped with strain gauges. The new pivot pins were calibrated and a transfer function between applied load and measured output voltage was identified for each pivot pin. After calibration the pivot pins were installed in a vertical hydropower unit. Measurements were performed for several different operating modes of the hydropower unit. To verify that the measured load levels were of right order of magnitude, the radial bearing loads were calculated from numerical simulations of bearing properties and shaft eccentricity measurements. The two methods for determining bearing load showed almost the same results. This indicates that either method can be used to determine bearing load

  • 79. Nässelqvist, Mattias
    et al.
    Gustavsson, Rolf
    Vattenfall Research & Development.
    Aidanpää, Jan-Olov
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Case study of resonance phenomena in a vertial hydropower unit2008In: 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]

    In 2005 a vertical 42 MW hydropower unit was upgraded in Sweden. One of the requirements was that the dynamic behaviour of the machine should not be affected. Resonance problems became apparent after the hydropower unit was re-commissioned and, in order to remedy this, new measurements and calculations were undertaken. While measuring, the machine went into resonance twice. During normal operation the shaft displacement showed high amplitudes at a frequency of twice the machine's nominal speed. At resonance the displacement amplitude increased and a dominant frequency occurred at ~2.4x nominal speed. To explain the reason for the resonances, new rotor dynamic calculations were performed using non-isotropic bearing and bracket properties. This model showed good correlation between calculated and measured values for the lowest eigenfrequencies. Probable explanations for the resonance are shape deviation in the generator, misalignment of the shaft and low damping of some critical eigenfrequencies close to twice the nominal speed.

  • 80. Nässelqvist, Mattias
    et al.
    Gustavsson, Rolf
    Aidanpää, Jan-Olov
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Resonance problems in vertical hydropower unit after turbine upgrade2008In: Hydro technology and the evironment for the new century: 24th IAHR Symposium on Hydraulic Machinery and Systems, October 27 - 31, 2008, Foz do Iguassu, Brazil, Foz do Iguassu, 2008Conference paper (Refereed)
    Abstract [en]

    In 2005 a vertical 42 MW hydropower unit was upgraded in Sweden. The upgrade included the fitting of a new turbine guide bearing, a modified runner, a modified turbine regulator and a new brushless exciter. One of the requirements was that the dynamic behaviour of the machine should not be affected. In spite of the requirements, resonance problems became apparent after the hydropower unit was re-commissioned. Measurements from the re-ommissioning showed poor alignment of the shaft system and shape deviations in the generator. The exchange of the turbine guide bearing from a sleeve bearing to a block bearing also caused changes in the machines dynamic behaviour. Measurements on the unit were conducted at normal operation and resonance. These show that at normal operation, the machine has dominant frequencies at the nominal speed and at twice the nominal speed. When the machine goes into resonance, the dominant frequencies increase to approx. 2.4 times the nominal speed.The machine will undergo a major overhaul in ten years. The objective is to find a solution of the resonance problem that is both inexpensive and possible to implement. The conclusion was drawn that the low damped eigenmode at 2.4 times the nominal speed had been excited and caused the machine to go into resonance. The unit's dynamic sensitivity to different bearing settings was investigated numerically and with tests on site, i.e. bearing clearances were varied. The calculated result was verified against measured resonance frequencies. Agreement between the estimated and measured result was good. Other possible measures to rectify the resonance problems were also analyzed numerically. The effect of making the surrounding structures more rigid, the installation of additional guide bearings, making the shaft system more rigid, etc. were examined. A temporary solution, used for the last six months, is to operate the machine with larger bearing clearances on all bearings. Increased bearing clearance of the turbine guide bearing cause increased damping of the natural frequency at 2.4 times the nominal speed. No problems related to resonance have occurred at the hydropower unit during the last six months.

  • 81.
    Nässelqvist, Mattias
    et al.
    Hydro Power, ÅF, 80320 Gävle.
    Gustavsson, Rolf K.
    Vattenfall Research & Development.
    Aidanpää, Jan-Olov
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Experimental and numerical simulation of unbalance response in vertical test rig with tilting-pad bearings2014In: International Journal of Rotating Machinery, ISSN 1023-621X, E-ISSN 1542-3034, Vol. 2014, article id 309767Article in journal (Refereed)
    Abstract [en]

    In vertically oriented machines with journal bearing, there are no predefined static radial loads, such as dead weight for horizontal rotor. Most of the commercial software is designed to calculate rotordynamic and bearing properties based on machines with a horizontally oriented rotor; that is, the bearing properties are calculated at a static eccentricity. For tilting-pad bearings, there are no existing analytical expressions for bearing parameters and the bearing parameters are dependent on eccentricity and load angle. The objective of this paper is to present a simplified method to perform numerical simulations on vertical rotors including bearing parameters. Instead of recalculating the bearing parameters in each time step polynomials are used to represent the bearing parameters for present eccentricities and load angles. Numerical results are compared with results from tests performed in a test rig. The test rig consists of two guide bearings and a midspan rotor. The guide bearings are 4-pad tilting-pad bearings. Shaft displacement and strains in the bearing bracket are measured to determine the test rig's properties. The comparison between measurements and simulated results shows small deviations in absolute displacement and load levels, which can be expected due to difficulties in calculating exact bearing parameters.

  • 82.
    Rantatalo, Matti
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Aidanpää, Jan-Olov
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Göransson, Bo
    SKF Nova, Göteborg.
    Norman, Peter
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Milling machine spindle analysis using FEM and non-contact spindle excitation and response measurement2007In: International journal of machine tools & manufacture, ISSN 0890-6955, E-ISSN 1879-2170, Vol. 47, no 7-8, p. 1034-1045Article in journal (Refereed)
    Abstract [en]

    In this paper a method for analysing lateral vibrations in a milling machine spindle is presented including finite element modelling (FEM), magnetic excitation and inductive displacement measurements of the spindle response. The measurements can be conducted repeatedly without compromising safety procedures regarding human interaction with rotating high speed spindles. The measurements were analysed and compared with the FEM simulations which incorporated a spindle speed sensitive bearing stiffness, a separate mass and stiffness radius and a stiffness radius sensitive shear deformation factor. The effect of the gyroscopic moment and the speed dependent bearing stiffness on the system dynamics were studied for different spindle speeds. Simulated mode shapes were experimentally verified by a scanning laser Doppler Vibrometer (LDV). With increased spindle speed, a substantial change of the eigenfrequencies of the bearing related eigenmodes was detected both in the simulations and in the measurements. The centrifugal force that acted on the bearing balls resulted in a softening of the bearing stiffness. This softening was shown to be more influential on the system dynamics than the gyroscopic moment of the rotor. The study performed indicates that predictions of high speed milling stability based on 0 rpm tap-test can be inadequate.

  • 83.
    Sandberg, Marcus
    et al.
    Luleå University of Technology, Department of Business Administration, Technology and Social Sciences, Innovation and Design.
    Kokkolaras, Michael
    Aidanpää, Jan-Olov
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Isaksson, Ola
    Larsson, Tobias
    A master-model approach to whole jet engine analysis and design optimization2009In: WCSMO-8: 8th World Congress on Structural and Multidisciplinary Optimization, 2009Conference paper (Refereed)
  • 84.
    Sandberg, Marcus
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Industrilized and sustainable construction.
    Kokkolaras, Michael
    Larsson, Tobias
    Aidanpää, Jan-Olov
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Oldenburg, Mats
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Boart, Patrik
    Volvo Aero Corporation, Sverige.
    Projekt: Strukturell konceptuell konstruktion och analys av helajetmotorer - en METodik för OPtimering, Integration och Automatisering (METOPIA)2009Other (Other (popular science, discussion, etc.))
    Abstract [sv]

    Detta projekt är en fortsättning på förstudieprojektet NFFP4202 - Helmotormodell för systemanalys av mekaniska egenskaper där en plattform, samt en pilot som demonstrerade plattformens förmåga i ett industriellt sammanhang, utvecklades. Detta projekt fokuserar på vidareutveckling av den framtagna plattformen med optimeringsteknologi och simuleringsdriven produktutvecklingsmetodik för att via produktdefinitionen (jetmotorkomponenterna) balansera flera olika funktionsbehov (t ex strukturdynamiska, aerodynamiska, termodynamiska) och skapa möjligheter till effektivare analyser av helmotorkoncept. Resultatet är en metodik innefattande systemangreppssätt, modelluppbyggnad, modellarkitektur samt analys, som tillämpas på ett realistiskt scenario genom en pilot.

  • 85.
    Sandberg, Marcus
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Industrilized and sustainable construction.
    Kokkolaras, Michael
    Larsson, Tobias
    Lindgren, Lars-Erik
    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, Product and Production Development.
    Oldenburg, Mats
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Projekt: NFFP4 - Helmotormodellering2009Other (Other (popular science, discussion, etc.))
    Abstract [sv]

    Nationella Flygtekniska Forskningsprogrammet NFFP Projekt: V4202 Helmotormodellering

  • 86.
    Sandberg, Marcus
    et al.
    Luleå University of Technology, Department of Business Administration, Technology and Social Sciences, Innovation and Design.
    Kokkolaras, Michael
    Luleå University of Technology, Department of Business Administration, Technology and Social Sciences, Innovation and Design.
    Tyapin, Ilya
    Luleå University of Technology, Department of Business Administration, Technology and Social Sciences, Innovation and Design.
    Isaksson, Ola
    Luleå University of Technology, Department of Business Administration, Technology and Social Sciences, Innovation and Design.
    Aidanpää, Jan-Olov
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Larsson, Tobias
    A knowledge-based master-model approach with application to rotating machinery design2011In: Concurrent Engineering - Research and Applications, ISSN 1063-293X, E-ISSN 1531-2003, Vol. 19, no 4, p. 295-305Article in journal (Refereed)
    Abstract [en]

    Novel rotating machinery design concepts and architectures are being explored to reduce mass, energy consumption, manufacturing costs, and environmental impact while increasing performance. As component manufacturers supply parts to original equipment manufacturers, it is desirable to design the components using a systems approach so that they are optimized for system-level performance. To accomplish that, suppliers must be able to model and predict the behavior of the whole machinery. Traditional computer-aided design/computer-aided engineering master-modeling approaches enable manual changes to be propagated to linked models. Novel knowledge-based master-modeling approaches enable automated coordination of multidisciplinary analyses. In this article, we present a specific implementation of such a knowledge-based master-modeling approach that facilitates multidisciplinary design optimization of rotating machinery. The master-model (MM) approach promotes the existence of a single governing version of the product definition as well as operating scenarios. Rules, scripts, and macros link the MM to domain-specific models. A simple yet illustrative industry application is presented, where rotor-dynamics and displacement analyses are performed to evaluate relocation alternatives for the rear bearing position of a rotating machinery under a ‘fan-blade-off’ load case.

  • 87. Simmons, Gregory F
    et al.
    Aidanpää, Jan-Olov
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Cervantes, Michel
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Glavatskih, Sergei
    Operational transients in the guide bearings of a 10 MW Kaplan turbine2013In: International journal on hydropower and dams, ISSN 1352-2523, Vol. 20, no 5, p. 94-100Article in journal (Refereed)
    Abstract [en]

    Experiments are conducted using a 10 MW Kaplan hydropower machine with a PowerFormerT M generator, the Porjus U9 research machine. This machine is outfitted with an extensive array of sensors to determine oil film thickness, pad tilting, pad load and oil temperature in all three guide bearings as well as motion of the shaft in relation to both the bearing housings and the concrete foundation. Test results for all three guide bearings are examined during both steady state and transient operation.

  • 88. Simmons, Gregory F
    et al.
    Cha, Matthew
    Machine Design, KTH Royal Institute of Technology, SE-10044 Stockholm, Sweden.
    Aidanpää, Jan-Olov
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Cervantes, Michel
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Glavatskih, Sergei
    Steady state and dynamic characteristics for guide bearings of a hydro-electric unit2014In: Proceedings of the Institution of mechanical engineers. Part J, journal of engineering tribology, ISSN 1350-6501, E-ISSN 2041-305X, Vol. 228, no 8, p. 836-848Article in journal (Refereed)
    Abstract [en]

    Experiments are conducted using a 10-MW Kaplan hydropower machine which is outfitted with an extensive array of sensors to determine oil film thickness, pad load and oil temperature in all three guide bearings as well as motion of the shaft in relation to both the bearing housings and the concrete foundation. Test results for all journal bearings are compared to a commercial rotor dynamics model and results for the central journal bearing are compared to a multi-physics model to provide insight into the machine's steady state and dynamic characteristics and their variations during normal operation.

  • 89.
    Soltani Dehkharqani, Arash
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Aidanpää, Jan-Olov
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Engström, Fredrik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Cervantes, Michel
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    A Review of Available Methods for the Assessment of Fluid Added Mass, Damping, and Stiffness With an Emphasis on Hydraulic Turbines2018In: Applied Mechanics Review, ISSN 0003-6900, E-ISSN 1088-8535, Vol. 70, no 5, article id 050801Article in journal (Refereed)
    Abstract [en]

    Fluid added mass, damping, and stiffness are highly relevant parameters to consider when evaluating the dynamic response of a submerged structure in a fluid. The prediction of these parameters for hydraulic turbines has been approached relatively recently. Complex fluid-structure analyses including three-dimensional flow and the need for experiments during operation are the main challenges for the numerical and experimental approaches, respectively. The main objective of this review is to address the impact of different parameters, for example, flow velocity, cavitation, nearby solid structure, and rotational speed on the fluid added mass and damping of Kaplan/Propeller and Francis turbine runners. The fluid added stiffness is also discussed in the last section of the paper. Although studies related to hydraulic turbines are the main objective of this paper, the literature on hydrofoils is also taken into consideration to provide valuable information on topics such as individual runner blades. In this literature survey, the analytical, numerical, and experimental approaches used to determine fluid added parameters are discussed, and the pros and the cons of each method are addressed.

  • 90.
    Soltani Dehkharqani, Arash
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Aidanpää, Jan-Olov
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Engström, Fredrik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Cervantes, Michel
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Fluid added polar inertia and damping for the torsional vibration of a Kaplan turbine model runner considering multiple perturbations2019In: IOP Conference Series: Earth and Environmental Science, Institute of Physics (IOP), 2019, Vol. 240, article id 062007Conference paper (Refereed)
    Abstract [en]

    A water turbine runner is exposed to several perturbation sources with differentfrequencies, phases, and amplitudes both at the design and off-design operations. Rotor-statorinteraction, cavitation, rotating vortex rope, and blade trailing edge vortices are examples of suchperturbations which can disturb the runner. The rotor dynamic coefficients require beingdetermined to perform a reliable dynamic analysis. Fluid added inertia, damping, and stiffnesshave previously been investigated for individual perturbation frequencies for the torsionalvibration of a Kaplan turbine model runner. However, a number of perturbation sources mostlytake place simultaneously and alter the dynamics of the runner. Soltani et al. [1] have evaluatedthe torsional added parameters for a Kaplan turbine runner using numerical simulationsconsidering single perturbation frequency. In the present work, the fluid added parameters areassessed in the presence of multiple perturbation sources. A similar methodology is used. Asingle-degree-of-freedom (SDOF) model for the dynamic model and unsteady ReynoldsaveragedNavier–Stokes approach for the flow simulations are assumed. Perturbations withdifferent frequencies are applied to the rotational speed of the runner to determine the fluid addedparameters for the torsional vibration. A number of previously investigated frequencies arechosen and their combinations are investigated. In addition, two different phase shifts areconsidered between the applied perturbations to study the effect of phase. Two more test caseswith higher perturbation amplitude are also conducted to investigate its influence on the fluidadded inertia and damping. The results are compared with the previous study and the interactionof multiple perturbations on the added parameters is investigated.

  • 91.
    Soltani Dehkharqani, Arash
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Cervantes, Michel
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics. Waterpower Laboratory, Department of Energy and Process Engineering, Norwegian University of Science and Technology (NTNU), Trondheim.
    Aidanpää, Jan-Olov
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Numerical analysis of fluid-added parameters for the torsional vibration of a Kaplan turbine model runner2017In: Advances in Mechanical Engineering, ISSN 1687-8132, E-ISSN 1687-8140, Vol. 9, no 10, article id 1687814017732893Article in journal (Refereed)
    Abstract [en]

    The impact of fluid on the runner of a hydraulic turbine is a recurrent problem. Fully coupled fluid-structure simulations are extremely time consuming. Thus, an alternative method is required to estimate this interaction to perform a reliable rotor dynamic analysis. In this paper, numerical estimations of the added inertia, damping and stiffness for a Kaplan turbine model runner are presented using transient-flow simulations. A single-degree-of-freedom model was assumed for the fluid-runner interaction, and the parameters were estimated by applying a harmonic disturbance to the angular velocity of the runner. The results demonstrate that the added inertia and damping are important, whereas the stiffness is negligible. The dimensionless added polar inertia is 23-27% of the reference value (ρR5). Damping significantly contributes to the moment at low excitation frequencies, whereas the inertia becomes dominant at higher frequencies.

  • 92.
    Synnegård, Erik
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Gustavsson, Rolf
    Vattenfall Research & Development.
    Aidanpää, Jan-Olov
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Forced Response of a Vertical Rotor with Tilting Pad Bearings2016Conference paper (Refereed)
    Abstract [en]

    This paper evaluates how tilting pad bearings can aect the forced response of a vertical rotor. Thestiness and damping for a tilting pad bearing is dependent on the position in the bearing (load on pador load between pad) and the magnitude of the load. In a vertical machine the position of the shaft inthe bearing will change for each time-step and produce a periodic stiness and damping. This periodicstiness has shown to produce higher frequency components depending on the number of pads. For thefour pad bearing considered in this paper these frequency components are 3 and 5 in the stationarycoordinate system. The aim of this study is to evaluate if the periodic coecients in the bearing couldexcite the system and cause resonance problems. It is found that for high loads the system can be exciteddue to the bearing dynamics at =!n = 0:33 and =!n = 0:2. However at low loads this eect isnegligible.

  • 93.
    Synnegård, Erik
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Gustavsson, Rolf K.
    Vattenfall Research & Development , Vattenfall Power Consultant AB Mechanical and Process Engineering, Kyrkogatan 4, Gävle.
    Aidanpää, Jan-Olov
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Influence of cross-coupling stiffness in tilting pad journal bearings for vertical machines2016In: International Journal of Mechanical Sciences, ISSN 0020-7403, E-ISSN 1879-2162, Vol. 111-112, p. 43-54Article in journal (Refereed)
    Abstract [en]

    This paper evaluates how cross-coupling coefficients affects the dynamics of a vertical rotor with tilting pad journal bearings. For vertical machines, the bearing properties are dependent on the bearing load and direction. As a result, it generally requires that bearing properties are calculated at each time step using the governing fluid dynamic equations. This method gives a good representation of the bearing but computational time increases and can cause stability problems. In this study the bearing properties are instead modelled as a function of eccentricity and its direction. Hence, the bearing properties can be evaluated at each time step without solving Navier-Stokes or Reynold's equation. The main advantage of using this method is to decrease the computational time. The cross-coupling stiffness and damping coefficients are usually neglected since they are small compared to the radial stiffness and damping coefficients. In this paper, the simulated unbalanced response is compared to experimental results and it is seen that the cross-coupling stiffness for vertical machines can influence the dynamics. It is shown that the cross-coupling can be of the same order of magnitude as the radial stiffness component depending on the shaft angular position in the bearing. Including cross-coupling increases higher frequency components and the experiments show similar behaviour. Hence the cross-coupling stiffness and damping coefficients should be included when simulating vertical machines subjected to high loads or when the detailed dynamical behaviour is important to investigate.

  • 94.
    Synnegård, Erik
    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.
    Modeling of visco-elastic supports for hydropower applications2015In: Proceedings of the 9th IFToMM International Conference on Rotor Dynamics / [ed] Paolo Pennacchi, Encyclopedia of Global Archaeology/Springer Verlag, 2015, Vol. XVIII, p. 2189-2197Conference paper (Refereed)
    Abstract [en]

    This paper presents a numerical model of how a visco-elastic support affects the dynamical response of a 42 MW Kaplan turbine that is experiencing resonance problems. The supports are placed between the bearing bracket and the supporting concrete structure. Since the supports are nonlinear, the nodal displacements are solved using a Runge-Kutta time integration method where the visco-elastic supports are implemented as a nonlinear force. To reduce calculation time the number of degrees of freedom of the rotor model is reduced using the Improved Reduction System. Excitation of the system is implemented as a stationary force in the runner with varying frequency. The resulting nodal displacement from the transient simulation is then compared to the system simulated without the supports to show how the machine dynamics are affected. The simulations show that the visco-elastic supports efficiently reduces the displacements in the lower vibration modes. The reduced vibration levels should decrease the probability of resonance problems occurring when running at operating speed.

  • 95.
    Tabatabaei, Narges
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Cervantes, Michel
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Trivedi, Chirag
    Norwegian University of Science and Technology.
    Aidanpää, Jan-Olov
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Numerical Study of Aerodynamic Characteristics of a Symmetric NACA Section with Simulated Ice Shapes2016In: Journal of Physics, Conference Series, ISSN 1742-6588, E-ISSN 1742-6596, Vol. 753 A, article id 022055Article in journal (Refereed)
    Abstract [en]

    To develop a numerical model of icing on wind turbine blades, a CFD simulation was conducted to investigate the effect of critical ice accretions on the aerodynamic characteristics of a 0.610 m chord NACA 0011 airfoil section. Aerodynamic performance coefficients and pressure profile were calculated and compared with the available measurements for a chord Reynolds number of 1.83x106. Ice shapes were simulated with flat plates (spoiler-ice) extending along the span of the wing. Lift, drag, and pressure coefficients were calculated in zero angle of attack through the steady state and transient simulations. Different approaches of numerical studies have been applied to investigate the icing conditions on the blades. The simulated separated flow over the sharp spoilers is challenging and can be seen as a worst test case for validation. It allows determining a reliable strategy to simulate real ice shapes [1] for which the detailed validation cannot easily be provided.

  • 96.
    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)
  • 97.
    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.

  • 98.
    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.

  • 99.
    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.

  • 100.
    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

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