• Tribology and Lubricants
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• 제24권3호
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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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• 제13권2호
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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.

• 소음진동
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• 제2권3호
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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.

• 대한의용생체공학회:의공학회지
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• 제6권1호
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• pp.13-18
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• 1985

A solution scheme for the squeeze film problem using the Newton-Raphson method with a tangential matrix is presented. The integration of elasticity equation is done with the aid of isoparametric elements and the film thickness under a sinusoidal load is obtained. A new squeeze-suction phenomenon which shoㅁvs the possibility oi maintaining fluid film under cyclic positive load conditions is observed for small load and Period and large compliance parameter cases. Thia could be an interesting result in applications like the viscous hydroplaning and the biological joints.

• Tribology and Lubricants
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• 제14권3호
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• pp.24-31
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• 1998

A new type squeeze film damper is proposed and its dynamic characteristics are investigated experimentally. The new one has a pulsating flow supply system which properly adds high pressure oil to the oil film of the damper so that the rotor vibration can be controlled actively. As the result, the amplitude of the rotor vibration can be reduced considerably. The algorithm which compensates the phase lag of servo valve as well as the high-performance servo valve are required in order that a new type squeeze film damper can be more effective device to attenuate the rotor vibration than typical one.

• 한국안전학회지
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• 제12권1호
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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.

• Tribology and Lubricants
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• 제11권1호
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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.

• 한국정밀공학회지
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• 제9권3호
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• pp.61-66
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• 1992

This paper addresses on the determination of damping coefficients of an infinitely long squeeze film damper operating with an electro-rheological (ER) fluid. The ER fluid behaves as Bingham fluid with an electric field dependent yield shear stress. AS phenomenological model of the fluid is adopted for the relationship between the yield shear and the intensity of the electric field imposed on the fluid domain. The model is then incorporated with the governing equation and associated boundary conditions of the squeeze film damper executing a circula centered orbit for the expression of dimension- less damping coefficients. Numerical simulation is performed to evaluate the performance improvement of the proposed squeeze film damper.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2002년도 추계학술대회논문초록집
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• pp.343.2-343
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• 2002

Squeeze film dampers(SFDs) are designed and analyzed for radial superconducting bearings. The designed SFDs are mounted on the superconductors submerged in liquid nitrogen such that the dampers should supply additional damping to the relatively underdamped superconducting bearing support. Basic theory of SFD with superconducting bearing are introduced. Rotordynamic simulations are provided to support the feasibility of the superconducting magnetic bearings mounted on SFDs for a horizontal flywheel energy storage system.

• Tribology and Lubricants
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• 제15권4호
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• pp.304-313
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• 1999

High-speed rotors set a lot of high vibration and stability problems especially when the speed of rotation is going through the first or the second critical speed. The aim of this paper is to investigate the possibility of an active control of a rigid rotor with squeeze film damper which has a good configuration of easily controlled end seal clearances and/or adjustment of a feed pressure. A theoretical method is presented and some numerical results are compared with test measurements. Both results show that the vibration or bit sizes are decreased when the end seal gap decreases with constant supply pressure, and when the supply oil pressure increases with constant seal gap. The experimental results show also a pleasing similarity on both orbit sizes and their decrement ratio compared with theoretical analysis. The possibility of an active control with the squeeze film damper was verified by adjusting the seal gap and the supply pressure.