Frequency Effects in Tilting-Pad Journal Bearing Dynamic Coefficients

Parsell, J. K.; Allaire, Paul E.; Barrett, Lloyd

doi:10.1080/05698198308981496

Cited by 54 publications

(22 citation statements)

References 9 publications

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“…If the influence of limited pivot stiffness is neglected the predicted characteristics of the dynamic coefficients presented in Fig. 6a are similar to the ones presented earlier by Parsell et al [7]. Stiffness coefficients increase while damping decreases for descending frequency ratio.…”

Section: Sensitivity Analysissupporting

confidence: 71%

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A Theoretical Study on Frequency Effects on Tilting-Pad Journal Bearing Dynamic Coefficients

Hagemann

Schwarze

2015

Proceedings of the 9th IFToMM International Conference on Rotor Dynamics

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The quantitative impact of pivot position, pivot support stiffness, and deformation on frequency dependency of a stiffness (K) and damping (C) KC matrix model for tilting-pad journal bearings is investigated. A theoretical model for prediction of frequency influences is introduced neglecting inertia effects. Predictions based on this model are validated with test data taken from literature. The results achieve good agreement with experimental data. A sensitivity analysis is performed providing the following key results: (i) all three investigated parameters possibly exhibit non negligible frequency influences, (ii) significant misinterpretations are possible if single influencing parameters on the operation conditions are disregarded or only roughly estimated, (iii) a frequency independent KCM model is suitable for off-center pivot position and sub-synchronous frequency ratios, (iv) a state-space model separating rotor and pad movement is necessary to model all theoretical possible effects by a linear model with frequency independent coefficients for a certain rotor speed.

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Section: Sensitivity Analysissupporting

confidence: 71%

“…Another alternative to model tilting-pad journal bearings dynamically is a state-space model developed based on a theoretical analysis of the system. One of the first studies using this approach is presented by Parsell et al [7]. State-space models have been extended to include radial pad motion due to limited pad stiffness [8].…”

Section: Introductionmentioning

confidence: 99%

A Theoretical Study on Frequency Effects on Tilting-Pad Journal Bearing Dynamic Coefficients

Hagemann

Schwarze

2015

Proceedings of the 9th IFToMM International Conference on Rotor Dynamics

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“…seen to be unstable. Parsell, et al (9) previously determined that the synchronous reduction technique, which is somewhat simpler, to be adequate for most stability analyses.…”

Section: Flg 7-cascade Dlagram Of Y1 Motion For Bearlng Set 2-load Omentioning

confidence: 98%

“…A set of equations for calculating the effect of frequency ratio o n the reduced dynamic coefficients for tilting-pad bearings was derived (9). T h e authors showed that increasing the preload reduced the effect of frequency ratio o n the reduced coefficients.…”

Section: Introductionmentioning

confidence: 99%

Experiments and Stability Predictions of Two Sets of Tilting Pad Bearings on an Overhung Rotor

Zuck

Flack

Knight

et al. 1988

Tribology Transactions

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Avr overl~~cng rotor was experimentally tested i n two sets of five shoe tilling pail 6enrings. The preload factors of the two sets were 0.1 rriid 0.5, respectively. The rotor had critical speeds at 3 0 0 0 nni16800 I p~n When mounted on the Jirst set of bearings, the rotor re~tu~ineil .stnOleJi)r speeds over I 1 000 rpm. However, when mounted i n the second set i f be(~ring~s the system went unstable due to whip irt 1 0 4 0 0 rpm. A ttieoretical ana1y.si.s was performed on the stability rf the mtor system to determine f the bearings were the cause of ttic wl~ip. Tire nnnlysis indicc~tes thal the system is margznally stable, the bearing design. T h e load carrying capacity is also affected by the design parameters.A typical five shoe tilting pad bearing is shown in Fig. 1. Each pad has a radius of curvature Rp, which is not necessarily equal to the nominal bearing radius Rb. If Rp is larger than Rb, which is usually the case, the bearing is said to be positively preloaded since each pad when centered forms a converging-diverging wedge which generates a hydrodynamic load. T h e preload factor m is defined as: n,id thnt SIIL(LII cro.s.s couplings generuled by the disk-shaft mountings m = 1 -cbl(Ry -R ) rlestnbilized tlie system. Also, pad inertia has little affect on the [I1 stn0ility cf this pnrticular rotor. The system was predicted to be the Another important parameter is the offset factor a which most stable when ~r~ounted on the bearings with a preload of 0.1, is defined as: so tlrc~t the j)redicted trends with varying preload were correct. The prc!dictiol~s c~lso indicnte that subsynchronozlsly reduced bearing a = PIX 121 coiflicicnts ( a s opposed to syncttronously reduced coefficients) sliould be ii.sail i n .stobilily nnelyses.

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“…Including the flexibility THEORETICAL MODEL of the pivot in their models, Springer ( 6 ) , Rouch (7) and Parsell et al (8) investigated theoretically the dynamic p r o p erties of these bearings for predicting rotor instabilities. More information concerning instabilities in tilting-pad journal bearings can be found in recent experimental studies by Flack and Zuck ( 9 ) and Lie et al ( 1 0 ) .…”

Section: Introductionmentioning

confidence: 99%

On the Adjusting of the Dynamic Coefficients of Tilting-Pad Journal Bearings

Santos

1995

Tribology Transactions

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This paper gives a theoretical and experimental contribution to the problem of active modiJication of the dynamic coefficients of tiltingpad journal bearings, aiming to increase the damping and stability of rotating systems. The theoretical studies for the calculation of the bearing coeficients are based on the fluid dynamics, specifically on the Rqrnolds equation, on the dynamics of multibody systems and on Premnted aa a Soclety of Triboiogists and Lubrication Engineers paper at the ASMEISTLE Tribology Conference in Lahaina, Hewaii, ~c t o b e r 16-20, 1994 Flnal manuscript approved August 3, 1994 some concepts of the hydraulics. The experiments are carried out by means of a test rig specially designed for this investigation. The four pads of such a bearing are mounted on fourflexible hydraulic chambers which are connected to a proportional valve. The chamber pressures are changed by means of the proportional valve, resulting in a displacement of the pads and a modification of the bearing gap. By changing the gap, one can adjust the dynamic coeficients of the bearing. With help of an experimental procedure for identihing the bearing coef/icients, theoretical and experimental results are compared and discussed. The advantages and the limitation of such hydrodynamic bearings in their controllable form are eualuated with regard to application on the high-speed machines. di,. hi, = damping and stiffness coefficient of oil film -d . . j;.. 'J' 'I = reduced damping and stiffness coefficients of the bearing h ( x , t ) = gap function kt, = hydrodynamic force on the equilibrium position k~ = membrane stiffness 4 = stiffness of the hydraulic chamber, membrane + oil P I~I P z X * P l y . P z Y = hydraulic pressure in each chamber p(%%t) = hydrodynamic pressure distribution Qxl QY = oil flow, hydraulic control 1 = time '+xL"_'Y = control voltage of the servo valve (% y.2) = coordinate system fixed on the pad z j = { A [ , A q , A t p A~p } T j , = displacement of the j th rotor-pad subsystem -4 = amplitude of the motion of the j th rotor-pad subsystem A = membrane area 6 ( 0 ) . E ( 0 ) = reduced damping and stiffness matrices of a tilting-pad journal bearing FpE = hydrodynamic force acting on the pad in the 5 direction s = { F Z F,q Fe Mpq }Ti, = perturbation force Fi = amplitude of the perturbation force = components of the force F, acting over the rotor in the F, and q directions = amplitude of the forces in the 5 and qdirection acting over the rotor = hydrodynamic momentum acting on the pad = pad radius = complex stiffness matrix of the j th rotor pad subsystem = oil volume in the chamber and pipes = inertial coordinate system = rotor displacement in the coordinate systems (X-Y) or (6-q) = pad angle = compressibility module of the oil = position angle of the j th pad = tilt motion of the j t h pad = oil viscosity = oil density = linear motion of the j th pad in the 5 direction = vibration amplitude of the rotor in the 5 and directions = supply pressure of the hydraulic control system = small translation and rotation of...

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Frequency Effects in Tilting-Pad Journal Bearing Dynamic Coefficients

Cited by 54 publications

References 9 publications

A Theoretical Study on Frequency Effects on Tilting-Pad Journal Bearing Dynamic Coefficients

A Theoretical Study on Frequency Effects on Tilting-Pad Journal Bearing Dynamic Coefficients

Experiments and Stability Predictions of Two Sets of Tilting Pad Bearings on an Overhung Rotor

On the Adjusting of the Dynamic Coefficients of Tilting-Pad Journal Bearings

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