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  • 1.
    Aidanpää, Jan-Olov
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Analysis of multiple solutions in bifurcation diagrams to avoid unexpected dynamics2009Conference paper (Refereed)
    Abstract [en]

    In mechanical applications it is essential that unexpected dynamics are avoided. The industry wants to build reliable machines that are not sensitive to initial conditions. Therefore, a simple method has been developed to extract all sets of stable bifurcation diagrams. The method gives a designer a good overview of possible dynamics and thereby the possibility to select a safe operating region. The method is described and demonstrated with a rub-impact rotor. The practical usage of this method is to help the designer to determine if parameter ranges exist where coexistent solutions will appear. Thereby one can design the system to work in parameter ranges where only one acceptable solution exists.

  • 2.
    Aidanpää, Jan-Olov
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Dynamics of some vibro-impacting systems with amplitude constraints1995Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    This thesis concerns the dynamics of some vibro-impacting systems with fixed or moving amplitude constraints. It is based on and includes five papers, marked A to E. Simple models of three different vibro-impacting systems with applications in the fields of impact hammers, granular flow and disk brakes in vehicles are analysed. A 2-DOF (two-degree-of-freedom) model of a threshold-limited impact hammer is studied (Paper A). The stability of a class of periodic motions is analysed. For some parameter values these periodic motions are found to be qualitatively similar to the ones observed for a corresponding 1-DOF system. At other parameter combinations, however, new kinds of periodic or chaotic motions can be observed. For low damping, phenomena resembling antiresonance for linear systems can also be observed. Granular shear flows show a transitional behaviour in the rapid flow regime as the shear speed or the concentration of the grains is varied. The motion can, for example, change from smooth and orderly to erratic and turbulent. Some aspects of this transitional behaviour in granular shear flow are studied numerically, analytically and experimentally (Papers B, C and D). Simple vibro-impacting models are suggested to get some analytical insight into the dynamics of shear layers. Results from a 1-DOF model show that for high forcing frequencies, which correspond to high shear speeds, periodic as well as chaotic motions can exist, whereas, for low forcing frequencies the vibrations are completely damped out to a stationary state (Paper B). Stability of this stationary state is studied analytically (Paper C), and experimentally (Paper D), where the motions of granular particles in a transparent shear cell are followed by using video techniques. For low shear speeds a single shear layer adjacent to the bottom boundary of the shear cell is observed. As the shear speed is increased, a transition to a random like state involving many layers is found to occur. In order to understand the phenomenon of squeal in disk brakes, a 3-DOF model is suggested to simulate the dynamics of a brake pad. The region of contact between the brake pad and the disk is described by using a coefficient of friction and distributed stiffness. The brake pad is allowed to have adjustable support locations and possibilities of impacts with its surroundings. The equilibrium state of the pad is determined by using a static analysis. The assumption is that the instability of this stationary state is a possible explanation of squeal, therefore, the stability is analysed in detail. Examples of different kinds of pad motions are presented. A rich variety of motions are found to exist including periodic, seemingly chaotic, stationary behaviour in slip, vibrations with full contact with the disk, stick-slip and impacts.

  • 3.
    Aidanpää, Jan-Olov
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Multiple solutions in a rub-impact Jeffcott rotor2004In: Extended abstracts, proceedings: 10th international symposium on transport phenomena and dynamics of rotating machinery / [ed] Dieter Bohn, Aachen: Inst. of steam and gas turbines, RWTH , 2004Conference paper (Refereed)
  • 4.
    Aidanpää, Jan-Olov
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Multiple solutions in an amplitude limited Jeffcott rotor including rubbing and stick-slip effect2005In: Proceedings ASME 2005 International Design Engineering Technical Conferences & Computers and Information in Engineering Conference: DETC 2005, American Society of Mechanical Engineers , 2005, p. 1091-1096Conference paper (Refereed)
    Abstract [en]

    The non-linear behaviour of rub-impact rotors have been studied in several papers. In such systems rich dynamics have been found together with the coexistence of solutions within some specific parameter ranges. In this paper an attempt is made to find all stable solutions for an amplitude limited Jeffcott rotor including rubbing and stick-slip effect. The recently suggested "multi bifurcation diagram method" is used to find and extract stable sets of bifurcation diagrams. A system is chosen where the linear stationary amplitude only exceeds the clearance in a narrow region near the natural frequency. Therefore large regions in frequency are expected to have only the linear stationary response. The results show that it is only for very low frequencies that one single solution exists. Even though periodic motions are dominant, there exist large ranges in frequency with quasi-periodic or chaotic motions. For the studied cases, three coexisting stable solutions are most common. In one case as many as four stable solutions was found to coexist. For rotors with large clearances (no impacts necessary) it is still possible to find several coexisting motions. For all cases the stick motion is the most severe one with large amplitudes and high backward whirl frequencies. In real situations the consequence of this stick motion is machine failure. These high amplitude motions were found to be stable over large frequency ranges. From the stability analysis it was found that this rolling motion can be avoided by low spin speed, low contact stiffness, low coefficient of friction, small ratio of disc radius/clearance or high damping ratio. In a design situation the parameters are seldom known with high accuracy. Therefore, it is of interest to know all solutions for parameter intervals. The multi-bifurcation diagram can be used in such situations to design a robust machine or at least be prepared for unwanted dynamics.

  • 5.
    Aidanpää, Jan-Olov
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Review of Mechanical Vibrations by S.S. Rao2007In: Proceedings of the Institution of mechanical engineers. Part C, journal of mechanical engineering science, ISSN 0954-4062, E-ISSN 2041-2983, Vol. 221, no 1, p. 135-Article in journal (Other academic)
  • 6.
    Aidanpää, Jan-Olov
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Rotor dynamical analysis of failure due to rotor-stator contact in an overhung rotor2006In: 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 264Conference paper (Refereed)
    Abstract [en]

    Two new 1MW fans in a remote gas cleaning plant have failed within 12 days of operation. Due to high costs a rapid repair and modification was performed without any deeper investigation or measurements. Since the driving frequency was far below the critical speed, a theory was that contact between rotating and stationary part was the reason for failure. In this paper the rotor dynamics is studied by an amplitude limited 4DOF overhung rotor. Simulations indicate that in addition to the ordinary unbalance response there can exist a high amplitude rolling contact mode between the disc and the stationary parts. By analysis of basin of attraction it is concluded that contact is a possible cause for the failure if the damping ratio is low, coefficient of friction is high and the rotor is eccentrically positioned relative to the stator. Measurements on the system are however necessary before a satisfying explanation can be given.

  • 7.
    Aidanpää, Jan-Olov
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Two vibroimpacting systems with amplitude constraints1992Licentiate thesis, comprehensive summary (Other academic)
  • 8.
    Aidanpää, Jan-Olov
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Gupta, R.B.
    Periodic and chaotic behaviour of a threshold-limited two-degree-of-freedom system1993In: Journal of Sound and Vibration, ISSN 0022-460X, E-ISSN 1095-8568, Vol. 165, no 2, p. 305-327Article in journal (Refereed)
    Abstract [en]

    A two-degree-of-freedom impact oscillator with proportional damping is considered. The maximum displacement of one of the masses is limited to a threshold value by a rigid wall, which gives rise to a non-linearity in the system. Impacts between the mass and the wall are described by a coefficient of restitution. The behaviour of the system is rich and includes features like period doublings, period havings, jumps, chaos, etc. Periodic motions of the system are studied by analytical methods. The influence of system parameters such as damping, coefficient of restitution, distribution of masses and clearance, etc., is studied for some extreme values of these parameters. The stability of a class of periodic motions is investigated. Parameter ranges which result in stable periodic multiple impacts are identified. Application of the results to the design of impact tools is discussed.

  • 9.
    Aidanpää, Jan-Olov
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Gustavsson, Rolf K.
    Vattenfall, VRD.
    Lundström, Niklas L. P.
    Umeå university.
    Karlsson, Martin
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Calleecharan, Yogeshwarsing
    Nässelqvist, Mattias
    Karlberg, Magnus
    Lundin, Urban
    Uppsala University.
    Developments in rotor dynamical modeling of hydropower units2009In: Proceedings of the IUTAM Symposium on Emerging Trends in Rotor Dynamics: held in New Delhi, India, March 23 - March 26, 2009 / [ed] Kshitij Gupta, Dordrecht: Encyclopedia of Global Archaeology/Springer Verlag, 2009Conference paper (Refereed)
  • 10.
    Aidanpää, Jan-Olov
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Lindkvist, Göran
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Dynamics of a rubbing Jeffcott rotor with three blades2011In: Chaos Theory: Modeling, Simulation and Applications: Selected Papers from the 3rd Chaotic Modeling and Simulation International Conference (CHAOS2010) / [ed] Christos H. Skiadas; Ioannis Dimotikalis; Charilaos Skiadas, Singapore: World Scientific Publishing Co Pte Ltd , 2011, Vol. Part II. Invited and Contributed Papers, p. 97-104Conference paper (Refereed)
  • 11.
    Aidanpää, Jan-Olov
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Lundström, Niklas L. P.
    Umeå university.
    Complex dynamic responses due to deviations of generator shape2009In: 10th Conference on Dynamical Systems - Theory and Applications: DSTA-2009, December 7-10, Łódź, Poland, 2009Conference paper (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 and eccentric. It is concluded that harmful conditions can occur due to high amplitudes especially when the whirling of the rotor changes from forward to backward. 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.

  • 12.
    Aidanpää, Jan-Olov
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Shen, Hayley
    Clarkson University, Potsdam, NY.
    Onset of transition for cohesive and viscous granular flows1998In: Journal of engineering mechanics, ISSN 0733-9399, E-ISSN 1943-7889, Vol. 124, no 10, p. 1073-1079Article in journal (Refereed)
    Abstract [en]

    A theory for determining the onset of rapid flow or termination of quasi-static flow in a cohesive granular material mixed in a viscous interstitial fluid is presented. This theory is based on a one-dimensional model introduced in an earlier paper. Linear stability analysis is used to find the combination of material properties and flow rate for which a quasi-static flow becomes unstable, indicating the onset of rapid flow. This theory yields a quantitative criterion to select appropriate constitutive laws for viscous and cohesive granular material. This criterion is a linear approximation of the theoretical result. While it provides the critical condition for quasi-static flow to terminate, it does not give the transitional constitutive law before a rapid flow is fully developed, for which a second power law dependence on the strain rate applies. Nonetheless, the analysis and modeling effort presented in this work are necessary first steps toward a general quantification of how granular materials, with identical physical composition, can behave in drastically different ways.

  • 13.
    Aidanpää, Jan-Olov
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Shen, Hayley H.
    Gupta, Ram B.
    Uppsala universitet.
    Experimental and numerical studies of shear layers in granular shear cell1996In: Journal of engineering mechanics, ISSN 0733-9399, E-ISSN 1943-7889, Vol. 122, no 3, p. 187-196Article in journal (Refereed)
    Abstract [en]

    The stability of a shear layer inside a granular material in a gravity field is studied experimentally and numerically. A shear cell is built of transparent acrylic to visualize the motion of the granular material. This shear cell consists of two concentric cylinders containing layers of uniform spheres in the annular space between the cylinders. The shearing motion of the spheres is produced by rotating the bottom boundary of the cell. Friction of the cylinder walls resists the shear motion, thus creating a single shear layer adjacent to the bottom boundary, while the rest of the layers above move with constant speed as a solid body. As the rotation speed of the bottom boundary increases, two layers adjacent to the bottom boundary begin to shear. This shearing zone quickly thickens and dilates as the rotational speed increases. The transition of this shear motion from a single layer to many layers of shearing is studied by video recording. The initiation of this transition is observed to depend on the material properties and the number of layers overlaying the shear layer. A one-dimensional numerical model is constructed to bring insight into this transitional phenomenon.

  • 14.
    Aidanpää, Jan-Olov
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Shen, Hayley H.
    Department of Civil and Environmental Engineering, Clarkson university.
    Gupta, Ram B.
    Division of Solid Mechanics, School of Engineering, Uppsala University.
    Stability and bifurcations of a stationary state for an impact oscillator1994In: Chaos, ISSN 1054-1500, E-ISSN 1089-7682, Vol. 4, no 4, p. 621-630Article in journal (Refereed)
    Abstract [en]

    The motion of a vibroimpacting one-degree-of-freedom model is analyzed. This model is motivated by the behavior of a shearing granular material, in which a transitional phenomenon is observed as the concentration of the grains decreases. This transition changes the motion of a granular assembly from an orderly shearing between two blocks sandwiching a single layer of grains to a chaotic shear flow of the whole granular mass. The model consists of a mass-spring-dashpot assembly that bounces between two rigid walls. The walls are prescribed to move harmonically in opposite phases. For low wall frequencies or small amplitudes, the motion of the mass is damped out, and it approaches a stationary state with zero velocity and displacement. In this paper, the stability of such a state and the transition into chaos are analyzed. It is shown that the state is always changed into a saddle point after a bifurcation. For some parameter combinations, horseshoe-like structures can be observed in the Poincare sections. Analyzing the stable and unstable manifolds of the saddle point, transversal homoclinic points are found to exist for some of these parameter combinations

  • 15.
    Aidanpää, Jan-Olov
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Shen, H.H.
    Clarkson University, Potsdam, NY.
    Gupta, R.
    Luleå tekniska universitet.
    Babic, M.
    University of Notre Dame, Notre Dame, IN.
    A model for the transitional behavior of simple shear flows of disks1992In: Studies in Applied Mechanics, ISSN 0922-5382, Vol. 31, p. 301-310Article in journal (Refereed)
    Abstract [en]

    A simple one-dimensional model is suggested to simulate some aspects of the dynamics of granular shear flows. The model consists of a viscoelastic packet bouncing between two harmonically oscillating walls. The amplitude and frequency of the wall motion are related to the concentration and shear rate respectively. The dynamics of the system is studied and it is shown that periodic as well as chaotic motions are possible for different parameters and initial conditions. Results are presented in the form of time histories, power spectral densities, phase diagrams, Poincaré maps and bifurcation diagrams. Some of the characteristics present in the two-dimensional granular shear flows are present in this simple model. It is promising that such analysis can provide better understanding of the transitional behavior of the constitutive relation between the rapid shear and the quasi-static flows.

  • 16.
    Aidanpää, Jan-Olov
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Shen, H.H.
    Gupta, R.B.
    Babic, M.
    One-dimensional model for the transition from periodic to chaotic motions in granular shear flows1993In: Mechanics of materials (Print), ISSN 0167-6636, E-ISSN 1872-7743, Vol. 16, no 1-2, p. 153-161Article in journal (Refereed)
    Abstract [en]

    A simple one-dimensional mechanical model to simulate some aspects of the dynamics of granular flow is suggested. The model consists of a visco-elastic packet bouncing between two oscillating walls. The motion of the walls is prescribed to be harmonic. The amplitude and frequency of the wall motion are related to the concentration and shear rate, respectively. The dynamics of the system is studied for various parameter combinations and it is shown that periodic as well as chaotic motions are possible for different parameters and initial conditions. Results are presented in the form of time histories, power spectral densities, phase diagrams, Poincare plots and bifurcation diagrams. This simple one-dimensional model presents many features that are analogous to those observed in the two-dimensional simple shear flow of disks.

  • 17. Angantyr, Anders
    et al.
    Aidanpää, Jan-Olov
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    A pareto-based genetic algorithm search approach to handle damped natural frequency constraints in turbo Generator rotor system design2004In: Journal of engineering for gas turbines and power, ISSN 0742-4795, E-ISSN 1528-8919, Vol. 126, no 3, p. 619-625Article in journal (Refereed)
    Abstract [en]

    The detailed design of a turbo generator rotor system is highly constrained by feasible regions for the damped natural frequencies of the system. A major problem for the designer is to find a solution that fulfills the design criterion for the damped natural frequencies. The bearings and some geometrical variables of the rotor are used as the primary design variables in order to achieve a feasible design. This paper presents an alternative approach to search for feasible designs. The design problem is formulated as an optimization problem and a genetic algorithm (GA) is used to search for feasible designs. Then, the problem is extended to include another objective (i.e., multiobjective optimization) to show the potential of using the optimization formulation and a Pareto-based GA in this rotordynamic application. The results show that the presented approach is promising as an engineering design tool

  • 18.
    Angantyr, Anders
    et al.
    ALSTOM Power Sweden AB.
    Aidanpää, Jan-Olov
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Constrained optimization of gas turbine tilting pad bearing designs2006In: Journal of engineering for gas turbines and power, ISSN 0742-4795, E-ISSN 1528-8919, Vol. 128, no 4, p. 873-878Article in journal (Refereed)
    Abstract [en]

    This paper presents the constrained optimization of the tilting pad bearing design on a gas turbine rotor system. A real coded genetic algorithm with a robust constraint handling technique is used as the optimization method. The objective is to develop a formulation of the optimization problem for the late bearing design of a complex rotor-bearing system. Furthermore, the usefulness of the search method is evaluated on a difficult problem. The effects considered are power loss and limiting temperatures in the bearings as well as the dynamics at the system level, i.e., stability and unbalance responses. The design variables are the bearing widths and radial clearances. A nominal design is the basis for comparison of the optimal solution found. An initial numerical experiment shows that finding a solution that fulfills all the constraints for the system design is likely impossible. Still, the optimization shows the possibility of finding a solution resulting in a reduced power loss while not violating any of the constraints more than the nominal design. Furthermore, the result also shows that the used search method and constraint handling technique works on this difficult problem.

  • 19. Angantyr, Anders
    et al.
    Aidanpää, Jan-Olov
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Optimization of a rotor-bearing system with an evolutionary algorithm2004In: 10th International Symposium on Transport Phenomena and Dynamics of Rotating Machinery: ISROMAC-2004 / [ed] Dieter Bohn, Aachen: Inst. of steam and gas turbines, RWTH , 2004Conference paper (Refereed)
  • 20. Angantyr, Anders
    et al.
    Andersson, Johan
    Linköping University.
    Aidanpää, Jan-Olov
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Constrained optimization based on a multiobjective evolutionary algorithm2003In: The 2003 congress on evolutionary computation: CEC 2003, Piscataway, NJ: IEEE Communications Society, 2003, p. 1560-1567Conference paper (Refereed)
    Abstract [en]

    A criticism of Evolutionary Algorithms (EAs) might be the lack of efficient and robust generic might be the lack of officient and robust generic methods to handle constraints. The most widespread approach for constrained search problems is to use penalty methods. EAs have received increased interest during the last decade due to the ease of handling multiple objectives., A constrained Optimization problem or an unconstrained multiobjective problem may in principle be two different ways to pose the same underlying I problem. In this paper an alternative approach for the constrained optimization problem is presented. The method is a variant of a multiobjective real coded Genetic Algorithm (CA) inspired by the penalty approach. It is evaluated on six different constrained single objective problems found in the literature. The results show that the proposed method performs well in terms of efficiency, and that it is rohust for a majority of the test problems.

  • 21.
    Calleecharan, Yogeshwarsing
    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 hydropower generator subjected to unbalanced magnetic pull2011In: Proceedings of the Institution of mechanical engineers. Part C, journal of mechanical engineering science, ISSN 0954-4062, E-ISSN 2041-2983, Vol. 225, no 9, p. 2076-2088Article in journal (Refereed)
    Abstract [en]

    Eccentricity leading to unbalanced magnetic pull (UMP) in electrical machines is a significant concern in industry. The UMP is known to be composed of two components: a radial component and a tangential one. Models that are used in industry tend to include the radial component alone. In this article, a Jeffcott rotor model together with a new UMP model that incorporates both radial and tangential UMP constituents is studied for an industrial hydropower generator. Characterizing the UMP as springs permits the model to inherit UMP stiffness contribution. Interesting dynamics are observed with the new model for a wide range of external forcing frequencies. It is shown firstly that the new UMP model is sensitive to forcing frequency in the rotor movements. Secondly, it is found that this sensitivity to forcing frequency increases with decreasing rotor system stiffness. Moreover, quasi-periodic motion in the rotor displacements is observed and it is noted that the rotor does not need to be forced by frequencies above its critical speed for this less desirable motion to occur. Thus, it becomes interesting to be able to account for the UMP stiffness contribution in order to curb machine malfunction which might result from these UMP forces

  • 22.
    Calleecharan, Yogeshwarsing
    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.
    On the dynamics of an hydropower generator subjected to unbalanced magnetic pull2011Conference paper (Other academic)
    Abstract [en]

    Eccentricity leading to unbalanced magnetic pull (UMP) in electrical machines is a significant concern in industry. The UMP is known to be composed of two components: A radial component and a tangential one. Models that are used in industry currently tend to include the radial component alone. In this paper, a Jeffcott rotor model together with a new UMP model that incorporates both radial and tangential UMP constituents is studied for an industrial hydropower generator. Characterising the UMP as springs permits the model to inherit UMP stiffness contribution. Interesting dynamics are observed with the new model for a wide range of external forcing frequencies. It is shown firstly that the new UMP model is sensitive to forcing frequency in the rotor movements. Moreover, complex dynamics in the displacements of the rotor are observed for some forcing frequencies and it is noted that the rotor does not need to be forced by frequencies above its critical speed for this less desirable motion to occur. Eigenvalue-based stability analysis is performed and shows that damping of the rotor and of the bearings are important when non-synchronous whirling of the rotor is considered. Accounting for both components of UMP is an important cornerstone in the generation of better rotor design parameters which can help to curb rotor-stator malfunction and can contribute in the design of long lasting rotors to the betterment of hydropower technology.

  • 23.
    Calleecharan, Yogeshwarsing
    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.
    On the dynamics of an hydropower generator subjected to unbalanced magnetic pull2011In: The Institution of Engineering and Technology 8th International Conference on Computation in Electromagnetics: (CEM 2011), Wroclaw, Poland, 11-14 April 2011, 2011, p. 50-51Conference paper (Refereed)
    Abstract [en]

    Eccentricity leading to unbalanced magnetic pull (UMP) in electrical machines is a significant concern in industry. The UMP is known to be composed of two components: A radial component and a tangential one. Models that are used in industry currently tend to include the radial component alone. In this paper, a Jeffcott rotor model together with a new UMP model that incorporates both radial and tangential UMP constituents is studied for an industrial hydropower generator. Characterising the UMP as springs permits the model to inherit UMP stiffness contribution. Interesting dynamics are observed with the new model for a wide range of external forcing frequencies. It is shown firstly that the new UMP model is sensitive to forcing frequency in the rotor movements. Moreover, complex dynamics in the displacements of the rotor are observed for some forcing frequencies and it is noted that the rotor does not need to be forced by frequencies above its critical speed for this less desirable motion to occur. Eigenvalue-based stability analysis is performed and shows that damping of the rotor and of the bearings are important when non-synchronous whirling of the rotor is considered. Accounting for both components of UMP is an important cornerstone in the generation of better rotor design parameters which can help to curb rotor-stator malfunction and can contribute in the design of long lasting rotors to the betterment of hydropower technology.

  • 24.
    Calleecharan, Yogeshwarsing
    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.
    Stability analysis of an hydropower generator subjected to unbalanced magnetic pull2011In: IET Science, Measurement & Technology, ISSN 1751-8822, E-ISSN 1751-8830, Vol. 5, no 6, p. 231-243Article in journal (Refereed)
    Abstract [en]

    Eccentricity leading to unbalanced magnetic pull (UMP) in electrical machines is a significant concern in industry. The UMP is known to be composed of two components: A radial component and a tangential one. Models that are used in industry currently tend to include the radial component alone. In this study, a Jeffcott rotor model together with a new UMP model that incorporates both the radial and tangential UMP constituents is studied for an industrial hydropower generator. Characterising the UMP as springs permits the proposed model to inherit UMP stiffness contribution. It is shown firstly that the new UMP model is sensitive to forcing frequency in the rotor movements and secondly, that this sensitivity to forcing frequency increases with decreasing rotor system stiffness. Moreover, quasi-periodic motion in the rotor displacements is observed for some forcing frequencies and system stiffnesses. Eigenvalue-based stability analysis is performed and shows that damping and stiffness of the rotor and of the bearings are important when non-synchronous whirling of the rotor comes into play. Accounting for both UMP components is an important cornerstone in the generation of better rotor designs which can help to curb rotor-stator malfunction and can contribute in the design of long lasting rotors.

  • 25.
    Calleecharan, Yogeshwarsing
    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, Product and Production Development.
    Brauer, J.P
    No-load electromagnetic simulations of a hydropower generator considering the effect of rotor whirling2015In: Balkan Journal of Electrical and Computer Engineering, ISSN 2147-284X, Vol. 3, no 3, p. 124-134Article in journal (Refereed)
    Abstract [en]

    Electromagnetic (EM) analysis of hydropower generators iscommon practice but there is little emphasis on studying the effect of rotorwhirling in the analysis. This paper explores the effect on electromagneticanalysis as the rotor is allowed to whirl both in forward and inbackward directions under no-load conditions. As a hydropower generatorrotor shaft can experience whirling when under eccentric operation,the objective is to examine how whirling can affect the unbalancedmagnetic pull (UMP), flux densities, damper currents, and ohmic lossesin a synchronous hydropower generator. These results are obtained ina commercial FEM-based EM field modelling software package thatallows various degrees of freedom in motion types and multiple motioncomponents to be set. It is seen that backward whirling tends to inducehigher eddy currents than forward whirling does.

  • 26.
    Calleecharan, Yogeshwarsing
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Jauregui, Ricardo
    DEE Universitat Politècnica de Catalunya , El Grupo de Compatibilidad Electromagnética GCEM, Barcelona.
    Aidanpää, Jan-Olov
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Estimating forces in mixed eccentricities motion for purley dynamic eccentric rotor centre motion in a hydropower generator and their validation against EM simulations2015In: Balkan Journal of Electrical and Computer Engineering, ISSN 2147-284X, Vol. 3, no 2, p. 78-87Article in journal (Refereed)
    Abstract [en]

    Electromagnetic analysis of hydropower generators is commonpractice but there is little emphasis on studying the effect ofrotor whirling in the analysis. This paper demonstrates the use ofthe unbalanced magnetic pull (UMP) curves based on purely dynamiceccentricity motion for a wide range of whirling frequencies in theprediction of the steady state UMP in the case of mixed eccentricitiesmotion. The latter motion type is more realistic in practice. Actualelectromagnetic (EM) simulations are also carried out for these mixedeccentricities motion cases in order to verify the proposed method. Goodagreement between the UMP from the actual EM simulations and theUMP predictions are made when low eccentricities exist. The proposedmethod is thus very useful since firstly, very few EM software packagescan handle mixed eccentricities motion and secondly, since actual EMsimulations of intricate rotor centre motion are time-consuming, theproposed method is a big time saver. A modified feature selective validation(FSV) method, the FSV-UPC, is also applied to assess the similarities andthe differences in the force computations.

  • 27.
    Calleecharan, Yogeshwarsing
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Jauregui, Ricardo
    DEE Universitat Politècnica de Catalunya , El Grupo de Compatibilidad Electromagnética GCEM, Barcelona.
    Aidanpää, Jan-Olov
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Towards a general method for estimating the unbalanced magnetic pull in mixed eccentricities motion including sufficiently large eccentricities in a hydropower generator and their validation against EM simulations2013In: European Physical Journal: Applied physics, ISSN 1286-0042, E-ISSN 1286-0050, Vol. 63, no 2Article in journal (Refereed)
    Abstract [en]

    Electromagnetic (EM) analysis of hydropower generators is common practice but rotor whirling is little studied. This paper suggests a novel semi-analytical method for estimating the steady state unbalanced magnetic pull (UMP) when the rotor centre is undergoing mixed eccentricities motion. The ability to estimate the UMP for mixed eccentricities motion in finite element method (FEM)-based modelling software packages is rare. The proposed methodology in its formulation takes advantage of the fact that a purely dynamic eccentricity motion including non-synchronous whirling and a purely static eccentricity motion can be more amenable to implement in existing FEM-based EM modelling software products for UMP estimation. After these initial separate UMP results are obtained, the proposed method can be applied for virtually any mixed eccentricities motion cases up to sufficiently large eccentricities for quick analysis instead of running the mixed eccentricities simulations directly in a FEM-based software package. Good agreement between the UMP from the actual EM mixed eccentricities motion simulations in a commercial FEM-based software package and the UMP estimations by the novel method is made for a wide range of eccentricities that may commonly occur in practice. A modified feature selective validation (FSV) method, the FSV-UPC, is applied to assess the similarities and the differences in the UMP computations

  • 28.
    Cervantes, Michel
    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, Mechanics of Solid Materials.
    Glavatskih, Sergei
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Karlsson, Thommy
    Interdisciplinary research in full-scale hydropower machines at Porjus, Jokkmokk, Sweden2005In: International Water Power and Dam Construction, ISSN 0306-400X, E-ISSN 1538-6414, Vol. 57, no 12, p. 40-44Article in journal (Other academic)
  • 29.
    Cervantes, Michel
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Aidanpää, Jan-Olov
    Glavatskikh, Sergei
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Karlsson, Thommy
    Group dynamics [hydro power equipment]2005In: International Water Power and Dam Construction, ISSN 0306-400X, E-ISSN 1538-6414, Vol. 57, no 12, p. 40-45Article in journal (Other academic)
    Abstract [en]

    An interdisciplinary research group was created at the Lulea University of Technology in Sweden to help develop world leading competencies and knowledge for cutting-edge technologies in hydro power generation. Based on the studies of this Swedish research group, this paper provides a description of the power system from a dynamic point of view to obtain an overall picture, and is completed with a detailed description of the bearings and turbines. The state-of-the-art in each field is presented, together with suggestions for further development

  • 30.
    Cervantes, Michel
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Jansson, Ida
    Jourak, Amir
    Glavatskih, Sergei
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Aidanpää, Jan-Olov
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Porjus U9A full-scale hydropower research facility2008In: 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]

    Hydropower still faces complex scientific and technical challenges in order to secure the availability and reliability of the power plants despite more than a century of development. The main challenge is due to new market constrains such as electrical market deregulation and introduction of renewable sources of energy. The major problem is related to the dynamic of the rotor involving several fields: hydraulics, power engineering and mechanics. On the other side, the large and growing hydropower world market represents an opportunity for technically advanced companies offering better efficiency. The difficulty to scale rigorously any technical advance makes full-scale experiment a necessity. World unique facilities are available at Porjus, Sweden, for this purpose. The Porjus Hydropower Centre is composed of a Francis (U8) and a Kaplan (U9) turbine of 10 MW, each exclusively dedicated to education, research and development. In order to further investigate specific issues related to availability and reliability, a project was initiated in 2006. The main objective is to make U9 a full-scale hydropower laboratory able firstly to furnish the necessary data for the development of rotor-dynamic models but also turbines and bearings. To this purposes more than 200 sensors have been installed to measure displacements, forces, pressure, film thickness, strains... The work presents an overview of the newly upgrade facility as well as some of the problems faced during the instrumentation of the machine.

  • 31. Cupillard, Samuel
    et al.
    Aidanpää, Jan-Olov
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Influence of the thrust bearing on the natural frequencies of a72-MW hydropower rotor2016In: IAHR symposium on Hydraulic Machinery and Systems, 2016, article id 236Conference paper (Refereed)
    Abstract [en]

    The thrust bearing is an essential element of a hydropower machine. Not only does itcarry the total axial load but it also introduces stiffness and damping properties in the system.The focus of this study is on the influence of the thrust bearing on the lateral vibrations of theshaft of a 72-MW propeller turbine. The thrust bearing has a non-conventional design with alarge radius and two rows of thrust pads. A numerical model is developed to estimate naturalfrequencies. Numerical results are analyzed and related to experimental measurements of arunaway test.The results show the need to include the thrust bearing in the model. In fact, the vibrationmodes are substantially increased towards higher frequencies with the added properties fromthe thrust bearing. The second mode of vibration has been identified in the experimentalmeasurements. Its frequency and mode shape compare well with numerical results.

  • 32.
    Cupillard, Samuel
    et al.
    Hydro-Québec Research Institute, Varennes, Québec, Canada.
    Aidanpää, Jan-Olov
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Influence of the thrust bearing on the natural frequencies of a72-MW hydropower rotor2016In: IOP Conference Series: Earth and Environment, ISSN 1755-1307, E-ISSN 1755-1315, Vol. 49, no 8, article id 082024Article in journal (Refereed)
    Abstract [en]

    The thrust bearing is an essential element of a hydropower machine. Not only does it carry the total axial load but it also introduces stiffness and damping properties in the system. The focus of this study is on the influence of the thrust bearing on the lateral vibrations of the shaft of a 72-MW propeller turbine. The thrust bearing has a non-conventional design with a large radius and two rows of thrust pads. A numerical model is developed to estimate natural frequencies. Numerical results are analyzed and related to experimental measurements of a runaway test. The results show the need to include the thrust bearing in the model. In fact, the vibration modes are substantially increased towards higher frequencies with the added properties from the thrust bearing. The second mode of vibration has been identified in the experimental measurements. Its frequency and mode shape compare well with numerical results.

  • 33.
    Gantasala, Sudhakar
    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.
    A Preliminary Experiment to Excite and Identify Modal Frequencies of a Rotor in the Rotating Frame of Reference2019In: Proceedings of the 10th International Conference on Rotor Dynamics – IFToMM / [ed] Katia Lucchesi Cavalca, Hans Ingo Weber, Cham: Springer, 2019, p. 265-277Conference paper (Refereed)
    Abstract [en]

    The current work uses two types of excitation on a rotating shaft to identify its modal frequencies. The first one is a non-contact excitation where an oscillating magnet is placed near the shaft, eddy currents generated by the oscillating magnetic field excites vibrations in the shaft. In the second type of excitation, a miniature electrodynamical exciter powered by a decoder amplifier board is placed on the shaft to excite vibrations with predefined frequencies in a signal (mp3 format) stored on the USB flash drive connected to the board. The shaft is rotated at different speeds and vibration accelerations are measured using a small data logger placed on the shaft while excited using these two excitation systems. These two types of asynchronous excitation on the shaft excites both forward and backward whirl vibration modes of the rotor system. The modal frequencies are identified at the peak amplitudes in the waterfall plots of the measured vibration accelerations to a chirp excitation of the shaft. A Campbell diagram is plotted with the identified modal frequencies of the shaft in the rotating frame of reference.

  • 34.
    Gantasala, Sudhakar
    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.
    A Preliminary Experiment to Excite and Identify Modal Frequencies of a Rotor in the Rotating Frame of Reference2019In: Proceedings of the 10th International Conference on Rotor Dynamics – IFToMM / [ed] Cavalca, Katia Lucchesi and Weber, Hans Ingo, Springer Publishing Company, 2019, p. 265-277Chapter in book (Refereed)
    Abstract [en]

    The current work uses two types of excitation on a rotating shaft to identify its modal frequencies. The first one is a non-contact excitation where an oscillating magnet is placed near the shaft, eddy currents generated by the oscillating magnetic field excites vibrations in the shaft. In the second type of excitation, a miniature electrodynamical exciter powered by a decoder amplifier board is placed on the shaft to excite vibrations with predefined frequencies in a signal (mp3 format) stored on the USB flash drive connected to the board. The shaft is rotated at different speeds and vibration accelerations are measured using a small data logger placed on the shaft while excited using these two excitation systems. These two types of asynchronous excitation on the shaft excites both forward and backward whirl vibration modes of the rotor system. The modal frequencies are identified at the peak amplitudes in the waterfall plots of the measured vibration accelerations to a chirp excitation of the shaft. A Campbell diagram is plotted with the identified modal frequencies of the shaft in the rotating frame of reference.

  • 35.
    Gantasala, Sudhakar
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Luneno, Jean-Claude
    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.
    Identification of ice mass accumulated on wind turbine blades using its natural frequencies2018In: Wind Engineering: The International Journal of Wind Power, ISSN 0309-524X, E-ISSN 2048-402X, Vol. 42, no 1, p. 66-84Article in journal (Refereed)
    Abstract [en]

    This work demonstrates a technique to identify information about the ice mass accumulation on wind turbine blades using its natural frequencies, and these frequencies reduce differently depending on the spatial distribution of ice mass along the blade length. An explicit relation to the natural frequencies of a 1-kW wind turbine blade is defined in terms of the location and quantity of ice mass using experimental modal analyses. An artificial neural network model is trained with a data set (natural frequencies and ice masses) generated using that explicit relation. After training, this artificial neural network model is given an input of natural frequencies of the iced blade (identified from experimental modal analysis) corresponding to 18 test cases, and it identified ice masses’ location and quantity with a weighted average percentage error value of 17.53%. The proposed technique is also demonstrated on the NREL 5-MW wind turbine blade data.

  • 36.
    Gantasala, Sudhakar
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Luneno, Jean-Claude
    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 Icing on the Modal Behavior of Wind Turbine Blades2016In: Energies, ISSN 1996-1073, E-ISSN 1996-1073, Vol. 9, no 11, article id 862Article in journal (Refereed)
    Abstract [en]

    Wind turbines installed in cold climate sites accumulate ice on their structures. Icing of the rotor blades reduces turbine power output and increases loads, vibrations, noise, and safety risks due to the potential ice throw. Ice accumulation increases the mass distribution of the blade, while changes in the aerofoil shapes affect its aerodynamic behavior. Thus, the structural and aerodynamic changes due to icing affect the modal behavior of wind turbine blades. In this study, aeroelastic equations of the wind turbine blade vibrations are derived to analyze modal behavior of the Tjaereborg 2 MW wind turbine blade with ice. Structural vibrations of the blade are coupled with a Beddoes-Leishman unsteady attached flow aerodynamics model and the resulting aeroelastic equations are analyzed using the finite element method (FEM). A linearly increasing ice mass distribution is considered from the blade root to half-length and thereafter constant ice mass distribution to the blade tip, as defined by Germanischer Lloyd (GL) for the certification of wind turbines. Both structural and aerodynamic properties of the iced blades are evaluated and used to determine their influence on aeroelastic natural frequencies and damping factors. Blade natural frequencies reduce with ice mass and the amount of reduction in frequencies depends on how the ice mass is distributed along the blade length; but the reduction in damping factors depends on the ice shape. The variations in the natural frequencies of the iced blades with wind velocities are negligible; however, the damping factors change with wind velocity and become negative at some wind velocities. This study shows that the aerodynamic changes in the iced blade can cause violent vibrations within the operating wind velocity range of this turbine.

  • 37.
    Gantasala, Sudhakar
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Luneno, Jean-Claude
    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.
    Investigating How an Artificial Neural Network Model Can Be Used to Detect Added Mass on a Non-Rotating Beam Using Its Natural Frequencies: A Possible Application for Wind Turbine Blade Ice Detection2017In: Energies, ISSN 1996-1073, E-ISSN 1996-1073, Vol. 10, no 2, article id 184Article in journal (Refereed)
    Abstract [en]

    Structures vibrate with their natural frequencies when disturbed from their equilibrium position. These frequencies reduce when an additional mass accumulates on their structures, like ice accumulation on wind turbines installed in cold climate sites. The added mass has two features: the location and quantity of mass. Natural frequencies of the structure reduce differently depending on these two features of the added mass. In this work, a technique based on an artificial neural network (ANN) model is proposed to identify added mass by training the neural network with a dataset of natural frequencies of the structure calculated using different quantities of the added mass at different locations on the structure. The proposed method is demonstrated on a non-rotating beam model fixed at one end. The length of the beam is divided into three zones in which different added masses are considered, and its natural frequencies are calculated using a finite element model of the beam. ANN is trained with this dataset of natural frequencies of the beam as an input and corresponding added masses used in the calculations as an output. ANN approximates the non-linear relationship between these inputs and outputs. An experimental setup of the cantilever beam is fabricated, and experimental modal analysis is carried out considering a few added masses on the beam. The frequencies estimated in the experiments are given as an input to the trained ANN model, and the identified masses are compared against the actual masses used in the experiments. These masses are identified with an error that varies with the location and the quantity of added mass. The reason for these errors can be attributed to the unaccounted stiffness variation in the beam model due to the added mass while generating the dataset for training the neural network. Therefore, the added masses are roughly estimated. At the end of the paper, an application of the current technique for detecting ice mass on a wind turbine blade is studied. A neural network model is designed and trained with a dataset of natural frequencies calculated using the finite element model of the blade considering different ice masses. The trained network model is tested to identify ice masses in four test cases that considers random mass distributions along the blade. The neural network model is able to roughly estimate ice masses, and the error reduces with increasing ice mass on the blade.

  • 38.
    Gantasala, Sudhakar
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Luneno, Jean-Claude
    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.
    Cervantes, Michel
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Aeroelastic simulations of wind turbine using 13 DOF rigid beam model2016Conference paper (Refereed)
    Abstract [en]

    The vibration behavior of wind turbine substructures is mainly dominated by their first few vibration modes because wind turbines operate at low rotational speeds. In this study, 13 degrees of freedom (DOF) model of a wind turbine is derived considering fundamental vibration modes of the tower and blades which are modelled as rigid beams with torsional springs attached at their root. Linear equations of motion (EOM) governing the structural behavior of wind turbines are derived by assuming small amplitude vibrations. This model is used to study the coupling between the structural and aerodynamic behavior of NREL 5 MWmodel wind turbine. Aeroelastic natural frequencies of the current model are compared with the results obtained from the finite element model of this wind turbine. Quasi-steady aerodynamic loads are calculated considering wind velocity changes due to height and tower shadow effects. In this study, vibration responses are simulated at various wind velocities. The derived 13 DOF simplified model of the wind turbine enables to simulate the influence ofchange in parameters and operating conditions on vibration behavior with less computational effort. Besides that, the results of the simplified models can be interpreted with much ease.

  • 39.
    Gantasala, Sudhakar
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Tabatabaei, Narges
    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.
    Aidanpää, Jan-Olov
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Numerical investigation on the aeroelastic behavior of a wind turbinewith iced blades2018In: Cold Regions Science and Technology, ISSN 0165-232X, E-ISSN 1872-7441Article in journal (Refereed)
  • 40. Gustavsson, Rolf
    et al.
    Aidanpää, Jan-Olov
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    The influence of magnetic pull on the stability of generator rotors2004In: Extended abstracts, proceedings: 10th international symposium on transport phenomena and dynamics of rotating machinery / [ed] Dieter Bohn, Aachen: Inst. of steam and gas turbines, RWTH , 2004Conference paper (Refereed)
  • 41.
    Gustavsson, Rolf K.
    et al.
    Vattenfall Research & Development.
    Aidanpää, Jan-Olov
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Evaluation of impact dynamics and contact forces in a hydropower rotor due to variations in damping and lateral fluid forces2009In: International Journal of Mechanical Sciences, ISSN 0020-7403, E-ISSN 1879-2162, Vol. 51, no 9-10, p. 653-661Article in journal (Refereed)
    Abstract [en]

    Damages due to contact between the runner and the discharge ring have been observed in several hydroelectric power units. The damage can cause high repair costs of the runner and the discharge ring as well as considerable production losses.In this paper a rotor model of a 45 MW hydropower unit is used for the analysis of the rotor dynamical phenomena occurring due to contact between the runner and the discharge ring for different grade of lateral force on the turbine and bearing damping. The rotor model consists of a generator rotor and a turbine, which is connected to an elastic shaft supported by three isotropic bearings. The discrete representation of rotor model consist of 32 degrees of freedom, to increase the speed of the analysis the size of the model has been reduced with the IRS method to a system with 8 degrees of freedom.Results are presented in bifurcation diagrams, maximum contact force, Poincaré map and phase portrait. Simulations indicate that the contact forces between the turbine and the discharge ring are large, with considerable risks for serious damage as a consequence. The analysis shows that the risk for contact and damage are large for relatively small lateral turbine loads when the gap between the turbine and discharge ring is small and the contact stiffness is high.

  • 42.
    Gustavsson, Rolf K.
    et al.
    Vattenfall Research & Development.
    Aidanpää, Jan-Olov
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    The influence of nonlinear magnetic pull on hydropower generator rotors2006In: Journal of Sound and Vibration, ISSN 0022-460X, E-ISSN 1095-8568, Vol. 297, no 3-5, p. 551-562Article in journal (Refereed)
    Abstract [en]

    In large electrical machines the electromagnetic forces can in some situations have a strong influence on the rotor dynamics. One such case is when the rotor is eccentrically displaced in the generator bore. A strong unbalanced magnetic pull will then appear in the direction of the smallest air-gap. In this paper, the influence of nonlinear magnetic pull is studied for a hydropower generator where the generator spider hub does not coincide with the centre of the generator rim. The generator model consists of a four-degree-of-freedom rigid body, which is connected to an elastic shaft supported by isotropic bearings. The influence of magnetic pull is calculated for the case when the generator spider hub deviates from the centre of the generator rim. A nonlinear model of the magnetic pull is introduced to the model by radial forces and transverse moments. In the numerical analysis input parameters typical for a 70 MW hydropower generator are used. Results are presented in stability and response diagrams. The results show that this type of rotor configuration can in some cases become unstable. Therefore, it is important to consider the distance between the centreline of generator spider hub and the centreline of generator rim

  • 43. Gustavsson, Rolf
    et al.
    Lundström, Mattias
    Vattenfall Research & Development.
    Aidanpää, Jan-Olov
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Determination of journal bearing stiffness and damping at hydropower generators using strain gauges2005In: Proceedings of the ASME Power Conference, 2005, American Society of Mechanical Engineers , 2005, p. 933-940Conference paper (Refereed)
    Abstract [en]

    In hydropower generators, the measurement of bearing load, vibration and shaft displacement are wildly used methods for indication of maintenance demand and troubleshooting. When measurement of bearing load and shaft displacement is performed the collected data make it possible to determine the bearing properties, such as stiffness and damping. In this paper a method to determine the bearing stiffness and damping properties for generator journal bearing in hydropower units is presented. The majority of hydropower generators are, however, not equipped with facilities for measurements of bearing loads. To provide the bearings with load sensors it is necessary to reconstruct the bearings, which is associated with heavy expenditures. In this paper an alternative method to obtain the bearing load is utilize, in which strain gauges installed on the generator bearing brackets is used. The collected data in the experiment were obtained from measurements on a 238 MW hydropower generator connected to a Francis type runner. The bracket that holds the generator bearing consists of 18 spokes and each of these spokes has been provided with strain gauges for load measurements. The displacement of the shaft has been measured relative to the generator-bearing casing. The generator-bearing model has been described as a system with two degrees of freedom containing both bearing stiffness and damping matrix as well as displacement and displacement velocity vector. When the calculation of the bearing properties are based on measured data, the irregularity in the calculated stiffness and damping has to be eliminated. To eliminate the unrealistic values of the calculated damping and stiffness, the samples that cause high condition numbers of the displacement - velocity matrix are neglected. The results of the calculation of bearing stiffness and damping are presented in polar plots. This method determines the bearing properties for the generator bearing in a certain point, the point where the generator shaft has its stationary position. The stationary position for the generator shaft depends on the static magnetic pull force acting on the generator rotor and the influence from the turbine. The influence on the bearing characteristics of non-stationary loads as acting on the bearing can be investigated. The non-stationary loads can for instance be rotor unbalance force, influence of thermal expansion and dynamical magnetic pull force. It is thereby possible to evaluate different loads effect on the generator bearing and in which way the bearing properties are affected. Copyright

  • 44.
    Jansson, Ida
    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.
    Aidanpää, Jan-Olov
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    A monitoring system to estimate the pressure field of a Kaplan runner blade prototype2008In: 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]

    The technical development of hydraulic machinery has gone towards lighter components and higher power concentration levels. A deregulation of the power market world-wide means that the machines experience more transient loads and are sometimes operated at off-design points. Those facts demand a more precise dynamic analysis at the design level of hydraulic machinery than what was formerly customary. Mechanical engineering needs enhanced tools for this purpose. Prediction models need to be validated against experimental data. There are limited possibilities to perform experimental investigations of hydropower prototypes. Fundamental in an experimental dynamic analysis is to determine the forces acting on the machine. This paper is concerned with a monitoring system to estimate the angular resolved pressure field on the suction- and pressure side of a prototype Kaplan runner blade. By measuring the pressure at different positions on the runner blade, we have a tool to determine the hydraulic load acting on the runner. This is part of an experimental dynamic analysis of the behavior of 10 MW prototype of a low-head Kaplan prototype lodged in an old machine hall inaugurated 1914 situated above the polar circle in Porjus, Sweden.

  • 45.
    Jansson, Ida
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Åkerstedt, Hans O.
    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, Mechanics of Solid Materials.
    Lundström, T. Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    The effect of inertia and angular momentum of a fluid annulus on lateral transversal rotor vibrations2012In: Journal of Fluids and Structures, ISSN 0889-9746, E-ISSN 1095-8622, Vol. 28, p. 328-342Article in journal (Refereed)
    Abstract [en]

    An extensive amount of work exists on experimental and theoretical analysis of unsteady flow phenomena in hydraulic turbines. Still, resonance phenomena and self-excited vibrations of the rotor of hydropower machines are not considered as a major problem during normal operation conditions. Nevertheless, in development and research it is not sufficient to rely on earlier experience. An accurate predictive rotor model is crucial in risk assessment of rotor vibrations of hydraulic generator units. This paper discusses the effects of inertia and the rotational energy of the fluid in the turbine on lateral transversal shaft vibrations of hydraulic generator units. There is a lack of agreement among engineers upon how fluid inertia of the turbine should be included in rotor models. The rotational energy of the fluid has a potential risk of feeding self-excited vibrations. A fluid-rotor model is presented that captures the effect of inertia and angular momentum of a fluid annulus on vibrations of an inner rigid cylinder. The purpose of the model is to gain physical understanding of the phenomena at work and it is not applicable to specific turbines. The linearized equation of motion of the cylinder surrounded by a fluid annulus is solved for by one single complex equation. The constrained cylinder has two degrees of freedom in the plane perpendicular to its axis. By the assumption of irrotational cyclic flow, the fluid motion is described by a complex potential function. The motion of the cylinder is described by three parameters. Two surfaces are defined that splits the parameter space into regions with different qualitative behaviour. One surface defines the limit of stability whereas the other defines a limit when the eigenvalues have opposite signs or are both positive. The response to an external periodic rotating force is visualized by the magnitude of the inverse of the complex dynamic stiffness.

  • 46.
    Jansson, Ida
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Åkerstedt, Hans O.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Lundström, Staffan
    Aidanpää, Jan-Olov
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Fluidinducerade reaktionskrafter för vertikalaxlade vattenkraftturbiner och dess betydelse för axelns laterala egensvängningar2009In: Svenska mekanikdagarna: Södertälje 2009, Stockholm: Svenska nationalkommittén för mekanik , 2009, p. 97-Conference paper (Other academic)
  • 47.
    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.
    Evaluation of rotordynamical concepts subjected to rotating unbalance and impulse2002In: Proceedings of the Sixth International Conference on Rotor Dynamics, IFT o MM: Sydney, Australia, September 30 to October 4, 2002 / [ed] Eric Hahn, Sydney: UNSW Printing Services, , 2002, p. 752-758Conference paper (Refereed)
  • 48.
    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.
    Investigation of an unbalanced rotor system with bearing clearance and stabilising rods2004In: Chaos, Solitons & Fractals, ISSN 0960-0779, E-ISSN 1873-2887, Vol. 20, no 2, p. 363-374Article in journal (Refereed)
    Abstract [en]

    The nonlinear vibrations of a rotor system with bearing clearance and stabilising rods are considered. In this paper the main objective is to evaluate effects of applying stabilising rods and from a dynamical point of view find preferable parameter ranges. A piecewise linear two degrees-of-freedom model is proposed. The system is studied and evaluated by analysis of steady state, bifurcation diagrams, Lyapunov exponents and contact force. It is shown how transition lines (which separate different categories of motion), periodicity and sensitivity to small perturbation are affected by the parameters defining the stability rods. By applying specific stabilising rods the periodicity is changed for some parameter ranges, unstable areas are reduced, the total maximum normal contact force is increased while the dynamical part is mainly reduced. The analytical expressions for the transition limits can be used as a design tool to choose suitable parameters. It is concluded that the stability rods should be applied vertically and that high preloading and stiffness prevents the system from impact motion. The stabilising rods are effective tools to avoid nonlinear behaviors but it is necessary to carefully analyse the specific application

  • 49.
    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.
    Nonlinear dynamics due to loss of contact in preloaded spherical roller thrust bearings2004In: Extended Abstracts + Proceedings (CD-ROM) of the 10th International Symposium on Transport Phenomena and Dynamics of Rotating Machinery - ISROMAC-10: Honolulu, Hawaii, USA March 07-11, 2004 / [ed] Dieter Bohn, Aachen: Inst. of steam and gas turbines, RWTH , 2004Conference paper (Refereed)
    Abstract [en]

    Extended Abstracts + Proceedings (CD-ROM) of the 10th International Symposium on Transport Phenomena and Dynamics of Rotating Machinery - ISROMAC-10 (Honolulu, Hawaii, USA March 07-11, 2004)

  • 50.
    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.
    Numerical investigation of an unbalanced rotor system with bearing clearance2003In: Chaos, Solitons & Fractals, ISSN 0960-0779, E-ISSN 1873-2887, Vol. 18, no 4, p. 653-664Article in journal (Refereed)
    Abstract [en]

    The nonlinear vibrations of a rotor system with bearing clearance are considered. The model consists of an unbalanced shaft with two d.o.f connected to a nonrotating massless housing by linear springs and dashpots. The clearance occurs when the housing (modelled as a ring) has a radius less than the stator. The behaviour of this system has been investigated with the use of time histories, Poincare maps, bifurcation diagrams, Lyapunov exponents, phase portraits, cell mapping and design space. Numerical simulations have achieved these results. The main objective was to find possible causes of failure in machines containing this type of clearance. The existence of subharmonic, quasi-periodic or even possible chaotic motion has been found. It is shown that these motions may give raise to bouncing modes, which results in high bearing forces and hence can be a possible cause of failure

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