• 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.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.

• 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.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2003.05a
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• pp.514-519
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• 2003

The aircraft engine is usually supported by rolling element bearings and has a small damping rate, which is vol y sensitive to external force. The high-performance requirement of the rotors leads to complex assembly designs and are more flexible. Squeeze film dampers (SFDs) are introduced to provide damping while crossing the critical speeds and stability to the rotor s :stem. Hence, the focus of the present investigation is on the decision of an optimal size of the flexible rotor system supported by the squeeze film dampers to minimize the maximum transmitted load and unbalance response over a range operating speeds. The enhanced genetic algorithm (EGA), which was developed by authors, is used in the optimization process. This algorithm is based on the synthesis of a modified genetic algorithm and simplex method. The results show significant benefits in using EGA when compared with nonlinear programming (NLP).

• Journal of KSNVE
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• v.11 no.2
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• pp.301-306
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• 2001

Electro-Rheological (ER) fluid is applied to a controllable squeeze film damper (SFD) for stabilizing a flexibly supported rotor system. ER fluid is a class of functional fluid whose yield stress varies according to the applied electric field strength, which is observed as viscosity variation of the fluid. In applying ER fluid to a SFD, a pair of rings of the damper can be used as electrodes. When the electrodes are divided into a horizontal pair and a vertical one, the SFD can produce damping force in each direction independently. A prototype of the directionally controllable SFD was constructed and its performance was experimentally and numerically investigated in the present work.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2005.11a
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• pp.702-707
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• 2005

The equations of motion of the structure, which is a small scale cantilever beam considering electrostatic force, squeeze film damping and van der Waals force are obtained employing Galerkin's method based on Euler beam theory. The influence of each force is investigated fur changing the size of a small scale cantilever beam which assumed uniform shape. Also the forces which are affected by the required size of a small scale cantilever beam for manufacturing are forecasted.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.39 no.1
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• pp.97-107
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• 2015

An analytical model was developed to estimate the viscous and squeeze-film damping ratios of heat exchanger tubes subjected to a two-phase cross-flow. Damping information is required to analyze the flow-induced vibration problem for heat exchange tubes. In heat exchange tubes, the most important energy dissipation mechanisms are related to the dynamic interaction between structures such as the tube and support and the liquid. The present model was formulated considering the added mass coefficient, based on an approximate model by Sim (1997). An approximate analytical method was developed to estimate the hydrodynamic forces acting on an oscillating inner cylinder with a concentric annulus. The forces, including the damping force, were calculated using two models developed for relatively high and low oscillatory Reynolds numbers, respectively. The equivalent diameters for the tube bundles and tube support, and the penetration depth, are important parameters to calculate the viscous damping force acting on tube bundles and the squeeze-film damping forces on the tube support, respectively. To calculate the void fraction of a two-phase flow, a homogeneous model was used. To verify the present model, the analytical results were compared to the results given by existing theories. It was found that the present model was applicable to estimate the viscous damping ratio and squeeze-film damping ratio.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.21 no.6
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• pp.553-561
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• 2011

A theoretical approach is carried out to predict the quality factors of flexible modes of a microcantilever on a squeeze-film. The frequency response function of an inertially-excited microcantilever beam is derived using an Euler-Bernoulli beam theory. The external force due to squeeze-film phenomenon is developed from the Reynolds equation. Slip boundary conditions are employed at the interfaces between the fluid and the structure to consider the gas rarefaction effect, and pressure boundary condition at both ends of fluid analysis region is enhanced to increase the exactness of predicted quality factors. To the end, an approximate equation is derived for the first bending mode of the microcantilever. Using the approximate equation, the quality factors of the second and third bending modes are calculated and compared with experimental results of previously reported work. The comparison shows the feasibility of the current approach.

• Journal of the Microelectronics and Packaging Society
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• v.7 no.1
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• pp.29-34
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• 2000

In this paper, the damping characteristics for electrostatically driven micro mirror which have deep grooves on their driving electrodes were investigated. A coupled simulation of gas flow and structural displacement of the micro mirror using the Finite-Element-Method is applied to this. The damping farce is caused by squeeze action of the gas film between a moving mirror plate and the electrodes. The grooves decrease the damping force and enable the moving plate to be driven at high speed and low driving voltage.

• Tribology and Lubricants
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• v.16 no.3
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• pp.157-165
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• 2000

A discharge free Electro-Rheological Squeeze Film Damper (ER-SFD) with predetermined-clearances at leakage ends can inherently eliminate electric discharge problems while still supplying stable leakage control. Test results show that the damping force of the slotted-ring ER-SFD is mainly affected by electric voltage, oil supply pressure, position of the damper and ratio of effective surface area of slotted-rings. As the supply voltage is larger, the amplitudes of both slotted ER-SFD and rotor are decreased at first and second critical speeds. The influence of the oil supply pressure and the effective surface area ratio was shown mainly near the first critical speed. The effective surface area ratio of slotted-rings influences the reduction of flexible rotor vibration. As a result, experimental results confirm that the slotted-ring ER-SFD satisfactorily controls the flexible rotor vibration, while eliminates the inherent electric discharge problems in conventional ER-SFDs.