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  • 1.
    Afzal, Md
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Arteaga, I. Lopez
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Kari, Leif
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    Kharyton, V.
    INVESTIGATION OF DAMPING POTENTIAL OF STRIP DAMPER ON A REAL TURBINE BLADE2016Inngår i: PROCEEDINGS OF THE ASME TURBO EXPO: TURBINE TECHNICAL CONFERENCE AND EXPOSITION, 2016, VOL 7A, AMER SOC MECHANICAL ENGINEERS , 2016Konferansepaper (Fagfellevurdert)
    Abstract [en]

    This paper investigates the damping potential of strip dampers on a real turbine bladed disk. A 3D numerical friction contact model is used to compute the contact forces by means of the Alternate Frequency Time domain method. The Jacobian matrix required during the iterative solution is computed in parallel with the contact forces, by a quasi-analytical method. A finite element model of the strip dampers, that allows for an accurate description of their dynamic properties, is included in the steady-state forced response analysis of the bladed disk. Cyclic symmetry boundary conditions and the multiharmonic balance method are applied in the formulation of the equations of motion in the frequency domain. The nonlinear forced response analysis is performed with two different types of boundary conditions on the strip: (a) free-five and (b) elastic, and their influence is analyzed. The effect of the strip mass, thickness and the excitation levels on the forced response curve is investigated in detail.

  • 2.
    Afzal, Mohammad
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Strukturakustik.
    Numerical modelling and analysis of friction contact for turbine blades2015Licentiatavhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    High cycle fatigue failure of turbine and compressor blades due to resonance in the operating frequency range is one of the main problems in the design of gas turbine engines. To suppress excessive vibrations in the blades and prevent high cycle fatigue, dry friction dampers are used by the engine manufacturers. However, due to the nonlinear nature of friction contact, analysis of such systems becomes complicated.

    This work focuses on the numerical modelling of friction contact and a 3D friction contact model is developed. To reduce the computation time in the Newton-iteration steps, a method to compute the Jacobian matrix in parallel to the contact forces is proposed. The developed numerical scheme is successfully applied on turbine blades with shroud contact having an arbitrary 3D relative displacement. The equations of motion are formulated in the frequency domain using the multiharmonic balance method to accurately capture the nonlinear contact forces and displacements. Moreover, the equations of motion of the full turbine blade model are reduced to a single sector model by exploiting the concept of the cyclic symmetry boundary condition for a periodic structure.

    The developed 3D coupled numerical contact model is compared with a 3D contact model having uncoupled tangential motion and drawback of the uncoupled contact model is discussed. Furthermore, presence of higher harmonics in the nonlinear contact forces is analyzed and their effect on the excitation of the different harmonic indices (nodal diameters) of the bladed disk are systematically presented. Moreover, due to the quasi-analytical computation of the Jacobian matrix, the developed scheme is proved to be effective in solving the equations of motion and significant reduction in time is achieved without loss of accuracy.

     

     

     

  • 3.
    Afzal, Mohammad
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet. KTH.
    On efficient and adaptive modelling of friction damping in bladed disks2017Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    This work focuses on efficient modelling and adaptive control of friction damping in bladed disks. To efficiently simulate the friction contact, a full-3D time-discrete contact model is reformulated and an analytical expression for the Jacobian matrix is derived that reduces the computation time drastically with respect to the classical finite difference method. The developed numerical solver is applied on bladed disks with shroud contact and the advantage of full-3D contact model compared to a quasi-3D contact model is presented. The developed numerical solver is also applied on bladed disks with strip damper and multiple friction contacts and obtained results are discussed. Furthermore, presence of higher harmonics in the nonlinear contact forces is analyzed and their effect on the excitation of the different nodal diameters of the bladed disk are systematically presented. The main parameters that influence the effectiveness of friction damping in bladed disks are engine excitation order,  contact stiffnesses,  friction coefficient, relative motion at the friction interface and the normal contact load. Due to variation in these parameters during operation, the obtained friction damping in practice may differ from the optimum value. Therefore, to control the normal load adaptively that will lead to an optimum damping in the system despite these variations, use of magnetostrictive actuator is proposed. The magnetostrictive material that develops an internal strain under the influence of an external magnetic field is employed to increase and decrease the normal contact load. A linearized model of the magnetostrictive actuator is used to characterize the magnetoelastic behavior of the actuator.  A nonlinear static contact analysis of the bladed disk reveals that a change of normal load more than 700 N can be achieved using a reasonable size of the actuator. This will give a very good control on friction damping once applied in practice.

  • 4.
    Afzal, Mohammad
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Strukturakustik. kth.
    Lopez Arteaga, Ines
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Strukturakustik. Eindhoven University of Technology, the Netherlands.
    Kari, Leif
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Strukturakustik.
    A formulation of the Jacobian matrixfor 3D numerical friction contact model applied to turbine blade shroud contactInngår i: Journal of Sound and Vibration, ISSN 0022-460X, E-ISSN 1095-8568Artikkel i tidsskrift (Annet vitenskapelig)
    Abstract [en]

    An analytical expression is formulated to compute the Jacobian matrix for 3D friction contact modelling that eciently evaluates the matrix while computing the friction contact forces in the time domain by means of the alternate frequency time domain approach. The developed expression is successfully used for thecalculation of the friction damping on a turbine blade with shroud contact interface having an arbitrary 3Drelative displacement. The analytical expression drastically reduces the computation time of the Jacobian matrix with respect to the classical finite dierence method, with many points at the contact interface. Therefore,it also significantly reduces the overall computation time for the solution of the equations of motion,since the formulation of the Jacobian matrix is the most time consuming step in solving the large set of nonlinear algebraic equations when a finite dierence approach is employed. The equations of motion are formulated in the frequency domain using the multiharmonic balance method to accurately capture the nonlinear contact forces and displacements. Moreover, the equations of motion of the full turbine blade model are reduced to a single sector model by exploiting the concept of cyclic symmetry boundary condition for aperiodic structure. Implementation of the developed scheme in solving the equations of motion is proved to be effective and significant reduction in time is achieved without loss of accuracy.

  • 5.
    Afzal, Mohammad
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    Lopez Arteaga, Ines
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    Kari, Leif
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    An analytical calculation of the Jacobian matrix for 3D friction contact model applied to turbine blade shroud contact2016Inngår i: Computers & structures, ISSN 0045-7949, E-ISSN 1879-2243, Vol. 177, s. 204-217Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    An analytical expression is formulated to compute the Jacobian matrix for 3D friction contact modeling that efficiently evaluates the matrix while computing the friction contact forces in the time domain by means of the alternate frequency time domain approach. The developed expression is successfully used for the calculation of the friction damping on a turbine blade with shroud contact interface having an arbitrary 3D relative displacement. The analytical expression drastically reduces the computation time of the Jacobian matrix with respect to the classical finite difference method, with many points at the contact interface. Therefore, it also significantly reduces the overall computation time for the solution of the equations of motion, since the formulation of the Jacobian matrix is the most time consuming step in solving the large set of nonlinear algebraic equations when a finite difference approach is employed. The equations of motion are formulated in the frequency domain using the multiharmonic balance method to accurately capture the nonlinear contact forces and displacements. Moreover, the equations of motion of the full turbine blade model are reduced to a single sector model by exploiting the concept of cyclic symmetry boundary condition for a periodic structure. Implementation of the developed scheme in solving the equations of motion is proved to be effective and significant reduction in time is achieved without loss of accuracy.

  • 6.
    Afzal, Mohammad
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    Lopez-Arteaga, Ines
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    Kari, Leif
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    Adaptive control of normal load at the friction interface of bladed disks using giant magnetostrictive materialInngår i: Journal of Vibration and Control, ISSN 1077-5463, E-ISSN 1741-2986Artikkel i tidsskrift (Annet vitenskapelig)
    Abstract [en]

    A novel application of magnetostrictive actuators in underplatform dampers of bladed disks is proposed for adaptive control of the normal load at the friction interface in order to achieve the desired friction damping in the structure. Friction damping in a bladed disk depends on many parameters such as rotational speed, engine excitation order, nodal diameter, contact stiffness, friction coefficient and normal contact load. However, all these parameters have a fixed value at an operating point. On the other hand, the ability to vary some of these parameters such as the normal contact load is desirable in order to obtain an optimum damping in the bladed disk at different operating conditions. Under the influence of an external magnetic field, magnetostrictive materials develop an internal strain that can be exploited to vary the normal contact load at the friction interface, which makes them a potentially good candidate for this application. A commercially available magnetostrictive alloy, Terfenol-D is considered in this analysis that is capable of providing magnetostrain up to 0.002 under prestress and a blocked force over 1500 N. A linearized model of the magnetostrictive material, which is accurate enough for a DC application, is employed to compute the output displacement and the blocked force of the actuator. A nonlinear finite element contact analysis is performed to compute the normal contact load between the blade platform and the underplatform damper as a result of magnetostrictive actuation. The contact analysis is performed for different mounting configurations of the actuator and the obtained results are discussed. The proposed solution is potentially applicable to adaptively control vibratory stresses in bladed disks and consequently to reduce failure due to high-cycle fatigue. Finally, the practical challenges in employing magnetostrictive actuators in underplatform dampers are discussed.

  • 7.
    Afzal, Mohammad
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    Lopez-Arteaga, Ines
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet. Eindhoven University of Technology.
    Kari, Leif
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    Numerical analysis of multiple friction contacts in bladed disksInngår i: International Journal of Mechanical Sciences, ISSN 0020-7403, E-ISSN 1879-2162Artikkel i tidsskrift (Annet vitenskapelig)
    Abstract [en]

    The damping potential of multiple friction contacts in a bladed disk, tip shroud and strip damper is investigated, showing that friction damping effectiveness can be potentially increased by using multiple friction contact interfaces. Friction damping depends on many parameters such as rotational speed, engine excitation order and mode family and therefore it is not possible to damp all the critical resonances using a single friction contact interface. For example, a strip damper is more effective for the low nodal diameters, where blade/disk coupling is strong. The equations of motion of the bladed disk with multiple friction contacts are derived in the frequency domain for a cyclic structure with rotating excitations and a highly accurate method is used to generate the frequency response function (FRF) matrix. Furthermore, a finite element contact analysis is performed to compute the normal contact load and the contact area of the shroud interface at operating rotational speed. The multiharmonic balance method is employed in combination with the alternate frequency time domain method to find the approximate steady state periodic solution. A low-pressure turbine bladed disk is considered and the effect of the engine excitation level, strip mass, thickness and the accuracy of FRF matrix on the nonlinear response curve are investigated in detail.

  • 8.
    Afzal, Muhammad
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Strukturakustik.
    Raza, R.
    Du, S.
    Lima, R.B.d
    Zhu, Bin
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Strukturakustik. Hubei Univ, Fac Phys & Elect Technol, Hubei Collaborat Innovat Ctr Adv Organ Chem Mat, Wuhan 430062, Peoples R China.
    Synthesis of Ba0.3Ca0.7Co0.8Fe0.2O3-δ composite material as novel catalytic cathode for ceria-carbonate electrolyte fuel cells2015Inngår i: Electrochimica Acta, ISSN 0013-4686, E-ISSN 1873-3859, Vol. 178, s. 385-391Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This work reports a new composite BaxCa1-xCoyFe1-yO3-delta (BCCF) cathode material for advanced and low temperature solid oxide fuel cells (SOFCs). The BCCF-based composite material was synthesized by sol gel method and investigated as a catalytic cathode for low temperature (LT) SOFCs. XRD analysis of the as-prepared material revealed the dominating BCCF perovskite structure as the main phase accompanied with cobalt and calcium oxides as the secondary phases resulting into an overall composite structure. Structure and morphology of the sample was observed by Field Emission Scanning Electron Microscope (FE-SEM). In particular, the Ba0.3Ca0.7Co0.8Fe0.2O3-delta (BCCF37) showed a maximum conductivity of 143 S cm(-1) in air at 550 degrees C measured by DC 4 probe method. The BCCF at the optimized composition exhibited much higher electrical conductivities than the commercial Ba0.5Sr0.5Co0.8Fe0.2O3-delta (BSCF) perovskite cathode material. A maximum power density of 325 mW cm(-2) at 550 degrees C is achieved for the ceria-carbonate electrolyte fuel cell with BCCF37 as the cathode material.

  • 9. Zhu, B.
    et al.
    Fan, L.
    Deng, H.
    He, Y.
    Afzal, M.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Dong, W.
    Yaqub, A.
    Janjua, N. K.
    Erratum: Corrigendum to “LiNiFe-based layered structure oxide and composite for advanced single layer fuel cells” (J. Power Sources (2016) 316 (37–43))2016Inngår i: Journal of Power Sources, ISSN 0378-7753, E-ISSN 1873-2755, Vol. 324Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The authors regret that the name of author Yunjuan He was misspelled as ‘Yunjune He’ in the original article. The authors would like to apologise for any inconvenience caused.

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