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1
Content available Vibration control of rotors mounted in hydrodynamic bearings lubricated with magnetically sensitive oil by changing their load capacity
Zapoměl Jaroslav, Ferfecki Petr
Bulletin of the Polish Academy of Sciences. Technical Sciences
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2021
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Vol. 69, nr 6
art. no. e137988
EN
Rotors of rotating machines are often mounted in hydrodynamic bearings. Loading alternating between the idling and full load magnitudes leads to the rotor journal eccentricity variation in the bearing gap. To avoid taking undesirable operating regimes, its magnitude must be kept in a certain interval. This is offered by the hydrodynamic bearings lubricated with smart oils, the viscosity of which can be changed by the action of a magnetic field. A new design of a hydrodynamic bearing lubricated with magnetically sensitive composite fluid is presented in this paper. Generated in the electric coil, the magnetic flux passes through the bearing housing and the lubricant layer and then returns to the coil core. The action of the magnetic field on the lubricant affects the apparent fluid viscosity and thus the position of the rotor journal in the bearing gap. The developed mathematical model of the bearing is based on applying the Reynolds equation adapted for the case of lubricants exhibiting the yielding shear stress. The results of the performed simulations confirmed that the change of magnetic induction makes it possible to change the bearing load capacity and thus to keep the rotor journal eccentricity in the required range. The extent of control has its limitations. A high increase in the loading capacity can arrive at the rotor forced vibration’s loss of stability and induce large amplitude oscillation.
2
Content available remote Kinematically Excited Vibration of an Asymmetric Rotor/Bearing System With Magnetic Lubricant
Perek A., Kurnik W.
Machine Dynamics Research
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2015
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Vol. 39, No. 4
5-19
EN
The paper is concerned with transverse dynamics of a rigid rotor supported in a semi-active slide bearing lubricated with a magnetic fluid. Attention is focused on modeling and simulation of forced vibrations of an asymmetric rotor supported in a rolling bearing at one end and in a slide bearing, on the other one. The slide bearing is treated as a nonlinear flexible support with visco-elastic properties controlled by an external magnetic field via a ferrofluid used as a bearing lubricant. The considered dynamical system is a discrete model of real rotor of Rotor Kit RK-4 by Bentley Nevada, a laboratory device being used for educational and research purposes. The aim of the study is to find how a magnetically induced modification of the magnetic fluid affects the resonant behavior of the rotor under harmonic kinematic excitation by the rotor housing movement. Computer simulations are used to obtain resonant curves of nonlinear relative rotor/housing vibrations. The effects of magnetically controlled viscosity of the lubricant fluid are presented as changes of shape and maximum values of the resonant curves as well as a shift of the resonance zone in the excitation frequency domain.
3
Content available remote Stability and Resonant Behaviour of a Rotor in Slide Bearings with Bingham Fluid As a Lubricant
Perek A.
Machine Dynamics Research
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2012
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Vol. 36, No. 2
84-94
EN
The paper is concerned with a dynamic analysis of a rigid rotor supported in hydrodynamic bearings with rheological properties of the lubricant controlled by an external magnetic field. A fluid viscosity is an adaptive parameter, which controlled by the applied magnetic field, actively influence the dynamics of the rotor. Such an active lubricant can be identified with a magnetic fluid. Magnetic fluid as a suspension of sufficiently small ferro-particles can be treated as a homogenous substance, and used as a lubricating medium (Berkovsky et al., 1993, Miszczak and Wierzcholski). Due to magnetic interactions, it shows a non-Newtonian behaviour, which, with an appropriate synthesis of liquid, can be described by the Bingham model. In the following two effects of a magnetic fluid as a bearing lubricant are applied - increase of viscosity with the magnetic field and drop with the angular speed of the rotor. Both can be used to modify rotor dynamics to supply faster uplift to contactless rotation and desired resonant properties. Numerical simulations of nonlinear equations of the rotor transverse vibrations excited by unbalance forces show considerable influence of the magnetically controlled viscosity on the magnitude and position of the resonant zone. Magnetic field and shear rate- dependent effective lubricant viscosity influence the critical rotation speed of the rotor.
4
Wyważanie wirnika sztywnego z luzem między łożyskiem i obudową
Zachwieja J.
Modelowanie Inżynierskie
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2010
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T. 9, nr 40
265-272
PL
W pracy przedstawiono wyniki analizy ruchu wirnika w sytuacji, gdy promieniowe ustalenie łożyska w obudowie nie jest prawidłowe. Wyznaczoną doświadczalnie trajektorię przemieszczenia czopa wału filtrowano metodą EMD, natomiast charakter drgań określono przy wykorzystaniu transformacji Hilberta-Huanga. Zbadano również efektywność wyważania wirnika na podstawie zmodyfikowanej metody współczynników wpływu, optymalizującej amplitudy drgań łożysk przy występowaniu anizotropowości zewnętrznej układu.
EN
The occurrence of the clearance between the outer bearing ring and casing is usually the result of progressing wear and tear of components or improper assembling that takes place very often at industrial conditions. The work presents the results of the rotor motion analysis when radial setting of the bearing in the casing is improper. The shaft journal displacement trajectory determined experimentally was filtered by the EMD method (empirical mode decomposition), whereas the vibration nature was determined using the Hilbert-Hunag's transformation. The rotor balancing efficiency was examined also based on the modified impact factor method, optimising the amplitudes of bearing vibrations at the presence of external system anisotropy.
5
Nekotorye voprosy dinamiki rotorov v gidrodinamiceskih podsipnikah
Podolskii M.
Zeszyty Naukowe Politechniki Świętokrzyskiej. Nauki Techniczne
|
2008
|
Z. 10, Vol. 1
173-179
EN
Various ways of solving problems of oil film hydrodynamics with local inertia forces are investigated. Compact formulae for hydrodynamical reaction are received. On the base of these formulae several problems concerning synchronous precession and rotor stability are considered.
6
Content available remote Auto-Balancing of Rotors with a Rigid Bearing
Sperling L., Ryzhik B., Duckstein H., Grobel K. H.
Machine Dynamics Problems
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2004
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Vol. 28, No. 2
45-64
EN
The paper presents a study of automatic balancing of rotors with a fixed point, for example rotors with a rigid bearing. In such rotor systems permitting only tilting oscillations, similarly to the case of the Laval rotor, the full compensation of unbalance is possible by balancing in only one plane. We consider a rotor equipped with an auto-balancing device consisting of a circular track with two moving balls. The investigations include derivation and analysis of existence and stability conditions for synchronous motions, an analysis of non-synchronous biharmonic motions near the critical speed, and a discussion on the influence of the gyroscopic terms, particularly a new type of Sommerfeld effect. The results are confirmed and complemented by computer simulations.
7
Content available remote Aktywne tłumienie drgań rezonansowych sztywnego wirnika podpartego w łożyskach o zarysach niekołowych w przypadku wymuszenia kinematycznego
Starczewski Z.
Zeszyty Naukowe Politechniki Rzeszowskiej. Mechanika
|
2002
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z. 60 [197]
555-560
EN
In the paper the possibility of damping of resonant vibration of a rigid rotor supported on pericycloidal journal bearings with the multiplication factor Kn=3 (three-lobe bearings) is discussed. The effect of application of 2 and 3 pairs of magnetic actuators on limitting resonance amplitudes is examined. As the excitation motion of the fundament (kinematic excitation) is assumed. Exemplary diagrams showing resonant displacements of the rotor and concluding remarks are included in the paper.
8
Content available remote Damping of resonant vibration of a rigid rotor supported on journal bearings with electrofluid
Starczewski Z
Mechanics and Mechanical Engineering
|
2001
|
Vol. 5, nr 2
121-126
EN
The paper is concerned with the problem of damping of resonant vibration in a rigid rotor system supported on journal bearings. The equations of motion of a such system are derived. Kinematic excitation is under investigation. Appropriate diagrams of amplitude and frequency in dependence of the system parameters as well as results and concluding remarks has been included.
9
Content available remote Two-Plane Automatic Balancing
Sperling L., Ryzhik B., Duckstein H.
Machine Dynamics Problems
|
2001
|
Vol. 25, No. 3/4
139-152
EN
A theory of two-plane automatic balancing of rigid rotors is presented. For a rotor with two pairs of compensation balls or rollers the stability of compensation phasing is analysed by employing the method of direct separation of motion. The results are confirmed by computer simulation based on the complete equations of motion linearised in the vibrational co-ordinates.
10
Content available remote Wpływ wzajemnego położenia panewek łożysk o zarysach niekołowych na zmianę progu samowzbudzenia wirnika
Starczewski Z.
Vibrations in Physical Systems
|
2000
|
Vol. 19
258--259
11
Content available remote Aktywne tłumienie drgań sztywnego wirnika łożyskowanego ślizgowo w przypadku wymuszenia kinematycznego
Starczewski Z.
Zeszyty Naukowe Politechniki Rzeszowskiej. Mechanika
|
1999
|
z. 52 [174]
221-226
EN
In the paper possibility of active stabilization of a rigid rotor supported on journal-bearings is presented. Electromagnetic actuators are applied in the method. The system is subjected to kinematic excitation and analysed with respect to different voltages, bearing gaps, rotor masses, and excitation frequencies. Appropriate resonant diagrams are presented.
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