• Tribology and Lubricants
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• v.24 no.3
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• pp.147-153
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• 2008

The effect of oil supply pressure on the performance of vapor cavitated short squeeze film dampers is examined. Vapor cavitation is characterized by film rupture occurring as a result of evaporating oils. The pressure of vapor cavity in the film is almost zero in absolute pressure and nearly constant. Pan's model about the shape of vapor cavity is utilized for studying the effect of vapor cavitation on the damping capability of a short squeeze film damper. As the level of oil supply pressure is increasing, vapor cavitation is suppressed so that the direct damping coefficient increases and the cross coupled damping coefficient decreases. Futhermore, the analysis of the unbalance responses of a rigid rotor supported on cavitated squeeze film dampers shows that a significant reduction in rotor amplitude and force transmissibility is possible by controlling the oil supply pressure into short squeeze film dampers.

• Tribology and Lubricants
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• v.13 no.2
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• pp.60-67
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• 1997

ER(electro-rheological) fluids, which are represented as Bingham fluids, have large and reversible changes in yield shear stresses by application of an electric field. In this paper, ER fluids are employed in a short squeeze film damper. The modified Reynolds equation for an ER short squeeze film damper is theoretically solved to get the approximate solutions of pressure profiles and damping coefficients. The theoretical approximate solutions are compared with numerical ones and both results are coincided very well. Both the direct and cross coupled damping coefficients substantially increase with increasing the yield shear stress of ER fluids. Furthermore, the synchronous response analysis of a rigid rotor supported on ER short squeeze film dampers is performed to show the improved damping capability of an ER short squeeze film damper.

• Journal of KSNVE
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• v.2 no.3
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• pp.213-222
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• 1992

The effect of cavitation on the synchronous steady state response of a single rotor supported on cavitated squeeze film dampers executing a circular orbit is investigated theoretically. The Swift-Stieber boundary conditions and a long bearing approximation are utillized to evaluate the direct and the cross coupled damping coefficients of a cavitated squeeze film damper. For typical design parameters, frequency response curves are presented here to exhibit the effect of cavitation on the imbalance response and transmissibilities for both a flexible rotor and a rigid rotor. Investigations show that cavitation occured in a squeeze film damper produces bistable jump phenomena and deteriorates the performance of a squeeze film damper. This arises from that the large cavity causes substantial increment of the cross coupled damping which has radial stiffening effect. Furthermore, the large cavity causes the decrement of the direct damping which has pure damping effect. It is also observed that in the absence of cavitation, both rotor excursion amplitude and imbalance transmissibilities are very well damped.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2011.06a
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• pp.623-624
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• 2011

• Transactions of the Korean Society of Mechanical Engineers
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• v.12 no.5
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• pp.1003-1015
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• 1988

Damping information is required to analyse heat exchangers for flow-induced vibration. The most important energy dissipation mechanisms in heat exchanger tubes are related to the dynamic interaction between tube and support. In liquids, squeeze-film damping is dominat. Simple experiments were carried out of a two-span tube with one intermediate support to investigate the effects of tube-support parameters, such as: tube-support thickness, diametral clearance, tube eccentricity, tube span length, location of tube-support, and nature of dynamic interaction between tube and tube-support. The results show that squeeze-film damping is much larger for lateral-type motion than for rocking-type motion at the support. Eccentricity was found to be very important. Diametral clearance, support thickness and frequency are also very relevant. The effects of these parameters on squeeze-film damping are formulated and proposed in a semi-empirical expression.

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.49 no.1
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• pp.64-69
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• 2000

This paper investigates the equeeze film damping of a perforated planar micromechanical structure that oscillates in the normal direction to the substrate. Special focus has been places on the effect of holes and edges of the perforated planar microstructures on the squeeze film damping of oscillatory motions. Theoretical models and test structures of the squeeze film damping have been developed for the transversely oscillating perforated plates. A set of nine different test structures, having three different sized with three different numbers of perforations, has been fabricated and tested. The experimental Q-factors, measured from the fabricated test structures, are compared with the theoretical values, estimated from finite element analysis. It is found that the finite element analysis overestimates the Q-factors up to 150% of the experimental values. Major discrepancy comes from the inaccuracy of the zero pressure condition, placed by the finite element analysis along the perforated edges.

• Tribology and Lubricants
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• v.11 no.1
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• pp.5-11
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• 1995

This paper addresses the lubrication analysis of a short squeeze film damper operating with electro-rheological (ER) fluids which have large and reversible changes in yield shear stresses with respect to an applied electric field. The ER fluids are assumed to be modeled as Bingham fluids. The governing lubrication equation for the ER short squeeze film damper is developed on the basis of a Bingham fluid model, and the equation is subsequently solved in order to investigate the effects of the ER fluids on the damping capability of the damper. It is shown that a substantial increase in damping (both direct and cross coupled) is accomplished by increasing the yield shear stress of the ER fluids. This significant improvement of the damping capability suggests that the ER short squeeze film damper could be very effective for reducing the vibration and controlling the critical speeds of a rotor system.

• Tribology and Lubricants
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• v.16 no.2
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• pp.75-83
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• 2000

The present paper proposes a new type of an electro-rheological squeeze film damper (ER SFD) of which the damping capacity can be controlled by the application of electric field. The new ER .SFD- is sealed with slotted rings having electrodes at the inside of the constant gap. The ER SFD can provent the problem of electric short which might be occurred in a previous ER SFD. Reynolds lubrication equation for a Newtonian fluid and the end leakage equation for ER fluids are numerically solved to get the pressure distributions and the damping coefficients of the ER SFD. The results show that the damping coefficients greatly increase with increasing the yield shear stress of ER fluid. In addition, the unbalance response analysis of a flexible rotor supported on the new ER SFD implies that the rotor system can be operated with the minimum of rotor amplitude and force transmissibility by controlling the yield shear stress of ER fluids properly.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2002.05a
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• pp.67-70
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• 2002

This paper presents the property of the Squeeze Film Damper (SFD) using Magneto-Rheological fluid (MR fluid). The damping property of a SFD for a flexible rotor system varied according to vibration mode. MR fluid is known as a functional fluid with controllable apparent viscosity of the fluid by applied magnetic field strength. When the MR fluid is applied in the SFD, the SFD using MR fluid can effectively reduce vibrations of the flexible rotor in a wide range of rotating speed by control of the applied magnetic field strength. To investigate in detail the SFD using MR fluid, the SFD to support one mass was constructed and its performance was experimentally investigated in the present study. The damping property of the SFD using MR fluid has viscous damping by Newtonian fluid, but not Coulomb friction by Bingham fluid. Therefore, The system damped by the SFD can be considered as a linear system.

• Journal of the Korean Society of Safety
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• v.12 no.1
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• pp.9-18
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• 1997

This paper is a study on the dynamic characteristics of truncated cone type squeeze film damper(SFD) bearing and rotor system. This model can alter the radial oil film gap which Is Important to the performance of rotor-bearing system and manufactured easily to change the shape concept of traditional circular type SFD bearing. In theoretical analysis, the oil film pressure distribution, the oil film force, the film damping coefficient and the eccentricity ratio, etc. were induced with regard to the film inertia effect. The film damping coefficients and optimum design parameters are calculated. When unbalance parameter U is greater than 0.2, the nonlinear vibration such as "Jump" phenomena appears in the vicinity of rotor critical speed. At this time, the increases of bearing parameter U, journal distance S, Reynolds number Re can control this unstable vibration. The experimental results show that SFD hearing and rotor system which are designed according to the design parameters in the stable region are operated stably in rotational speed 9,600rpm without nonsynchronous behavior.