Applied sciences

Bulletin of the Polish Academy of Sciences Technical Sciences

Content

Bulletin of the Polish Academy of Sciences Technical Sciences | 2023 | 71 | 6

Authors and Affiliations

Tomasz Szolc
1
ORCID: ORCID

  1. Institute of Fundamental Technological Research, Polish Academy of Sciences, ul. Pawi´nskiego 5B, 02-106 Warsaw, Poland
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Abstract

Many industrial rotating machines driven by asynchronous motors are often affected by detrimental torsional vibrations. In this paper, a method of attenuation of torsional vibrations in such objects is proposed. Here, an asynchronous motor under proper control can simultaneously operate as a source of drive and actuator. Namely, by means of the proper control of motor operation, it is possible to suppress torsional vibrations in the object under study. Using this approach, both transient and steady-state torsional vibrations of the rotating machine drive system can be effectively attenuated, and its precise operational motions can be assured. The theoretical investigations are conducted by means of a structural mechanical model of the drive system and an advanced circuit model of the asynchronous motor controlled using two methods: the direct torque control – space vector modulation (DTC-SVM) and the rotational velocity-controlled torque (RVCT) based on the momentary rotational velocity of the driven machine working tool. From the obtained results it follows that by means of the RVCT technique steady-state torsional vibrations induced harmonically and transient torsional vibrations excited by switching various types of control on and off can be suppressed as effectively as using the advanced vector method DTC-SVM.
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Authors and Affiliations

Paweł Hańczur
1 2
Tomasz Szolc
1
ORCID: ORCID
Robert Konowrocki
1
ORCID: ORCID

  1. Institute of Fundamental Technological Research of the Polish Academy of Sciences, ul. Pawinskiego 5B, 02-106 Warsaw, Poland
  2. Schneider Electric Polska Sp. z o.o, ul. Konstruktorska 12, 02-673 Warsaw, Poland
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Abstract

A gyroscopic rotor exposed to unbalance and internal damping is controlled with an active piezoelectrical bearing in this paper. The used rotor test-rig is modelled using an FEM approach. The present gyroscopic effects are then used to derive a control strategy which only requires a single piezo actuator, while regular active piezoelectric bearings require two. Using only one actuator generates an excitation which contains an equal amount of forward and backward whirl vibrations. Both parts are differently amplified by the rotor system due to gyroscopic effects, which cause speed-dependent different eigenfrequencies for forward and backward whirl resonances. This facilitates eliminating resonances and stabilize the rotor system with only one actuator but requires two sensors. The control approach is validated with experiments on a rotor test-rig and compared to a control which uses both actuators.
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Authors and Affiliations

Jens Jungblut
1
ORCID: ORCID
Daniel Franz
1
Christian Fischer
1
ORCID: ORCID
Stephan Rinderknecht
1
ORCID: ORCID

  1. Institute for Mechatronic Systems, Technical University Darmstadt, 64287, Germany
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Abstract

A new approach to calculations based on the modal synthesis method is proposed for the evaluation of structural and dry-friction damping effects on self-excited vibrations due to aeroelastic instability in bladed turbine wheels. The method described herein is used to study dry-friction damping of self-excited vibration of an industrial turbine wheel with 66 blades. For evaluating damping effects, the blade couplings are applied to this particular turbine wheel. Therefore, neighbouring blades are interconnected by rigid arms that are fixed on one side to one blade and are in frictional contact on their free side with the other blade. Due to relatively normal motions in contacts, the prescribed contact forces vary over time. The aerodynamic excitation arises from the spatially periodical flow of steam through the stator blade cascade. In this paper, we attempt to model flow-induced instabilities with the Van der Pol model linked to relative motion between neighbouring blades. The proposed modal synthesis method as ROM is a computationally efficient solution allowing substantial parametrization. The effect of the angles of contact surfaces on the wheel dynamics and on the level of the self-excitation suppression will be discussed herein.
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Authors and Affiliations

Luděk Pešek
1
ORCID: ORCID
Pavel Šnábl
1
ORCID: ORCID
Chandra Shekhar Prasad
1

  1. Institute of Thermomechanics of the CAS, v. v. i., Dolejškova 1402/5, 182 00 Praha 8, Czech Republic
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Abstract

In this study, a multi-pad bump-type foil thrust bearing with a taper-land height profile is investigated. A detailed thermo-elastohydrodynamic (TEHD) finite element (FE) model is used comprising all bearing pads instead of only a single pad. Although the single-pad reduction approach is commonly applied, it can not accurately account for the different temperatures, loads, and power losses for individual pads in the case of misalignment. The model accounts for the deformations of the foils on each pad via a Reissner-Mindlin-type shell model. Deformations of the rotor are calculated via the Navier-Lamé equations with thermoelastic stresses and centrifugal effects. The temperature of the top foil and the rotor are calculated with the use of heat diffusion equations. The temperature of each lubricating air film is obtained through a 3D energy equation. Film pressures are calculated with the 2D compressible Reynolds equation. Moreover, the surrounding of the bearing and runner disk is part of the thermodynamic model. Results indicate that the thermal bending of the runner disk as well as top foil sagging are key factors in performance reduction. Due to the bump-type understructure, the top foil sagging effect is observed in simulation results. The study at hand showcases the influence of misalignment between the rotor and the bearing on the bearing performance.
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Authors and Affiliations

Markus Eickhoff
1
ORCID: ORCID
Johannis Triebwasser
1
Bernhard Schweizer
1

  1. Institute of Applied Dynamics, Technical University of Darmstadt, Germany
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Abstract

In modern turbomachinery, the performance and reliability is often limited by shaft vibrations induced by fluid film forces and moments of (i) plain or (ii) profiled annular seals. Therefore, these narrow annuli are mainly responsible for the overall system behaviour, i.e. safe operation and maintenance intervals. However, many studies focus only on the characteristics from the forces due to the translational motion, although the influence of the rotordynamic tilt and moment coefficients is well known. Therefore, these additional coefficients are much less researched. Especially, for profiled seals, the availability of reliable experimental data for validation purpose is rare. To overcome this fact, a test rig is operated at the Chair of Fluid Systems at the Technische Universität Darmstadt. The generic experiments presented here investigate the force and moment characteristic of plain, symmetrically profiled and non-symmetrically profiled annular seals within the relevant parameter range for turbulent flows in pumps. The investigations focus on the influence of the annulus length as well as the pressure difference across the annulus.
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Authors and Affiliations

Maximilian M. G. Kuhr
1
ORCID: ORCID
Peter F. Pelz
ORCID: ORCID

  1. Chair of Fluid Systems, Technische Universität Darmstadt, Otto-Berndt-Straße 2, 64287 Darmstadt, Germany
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Abstract

The presented work focuses on the experimental investigation of a vibroacoustic metamaterial integrated into a spinning circular saw blade. Vibroacoustic metamaterials are a novel technology for broadband vibration reduction. Built from an array of local resonators, a broadband vibration reduction characteristic in the frequency domain (a so-called stop band) can be achieved. A design of a vibroacoustic metamaterial suitable for integration into a circular saw blade is developed and a numerical stop band prediction is performed. The resonators of the vibroacoustic metamaterial are integrated into the saw blade with a water jet cutting machine to create slots, forming flaps that are free to oscillate. The structural dynamic behavior of the saw blade with integrated vibroacoustic metamaterial is experimentally investigated on a rotor dynamic test bench and compared to that of a standard saw blade. The saw blades are excited by an automatic impulse hammer and the resulting out-of-plane vibrations are measured with a laser vibrometer at two different radii. Measurements are conducted at different rotational speeds up to 1800 rpm. Up to rotational speeds of 1000 rpm a stop band characteristic in the frequency range of 1900–2500 Hz is observed.
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Authors and Affiliations

Sebastian Rieß
1
ORCID: ORCID
William Kaal
1
ORCID: ORCID
Sven Herold
1
ORCID: ORCID

  1. Fraunhofer Institute for Structural Durability and System Reliability LBF, 64298, Darmstadt, Germany
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Abstract

A common problem in transient rotordynamic simulations is the numerical effort necessary for the computation of hydrodynamic bearing forces. Due to the nonlinear interaction between the rotordynamic and hydrodynamic systems, an adequate prediction of shaft oscillations requires a solution of the Reynolds equation at every time step. Since closed-form analytical solutions are only known for highly simplified models, numerical methods or look-up table techniques are usually employed. Numerical solutions provide excellent accuracy and allow a consideration of various physical influences that may affect the pressure generation in the bearing (e.g., cavitation or shaft tilting), but they are computationally expensive. Look-up tables are less universal because the interpolation effort and the database size increase significantly with every considered physical effect that introduces additional independent variables. In recent studies, the Reynolds equation was solved semianalytically by means of the scaled boundary finite element method (SBFEM). Compared to the finite element method (FEM), this solution is relatively fast if a small discretization error is desired or if the slenderness ratio of the bearing is large. The accuracy and efficiency of this approach, which have already been investigated for single calls of the Reynolds equation, are now examined in the context of rotordynamic simulations. For comparison of the simulation results and the computational effort, two numerical reference solutions based on the FEM and the finite volume method (FVM) are also analyzed.
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Authors and Affiliations

Simon Pfeil
1
ORCID: