scholarly journals Effect of Temperature and Electric Field on the Damping and Stiffness Characteristics of ER Fluid Short Squeeze Film Dampers

2013 ◽  
Vol 2013 ◽  
pp. 1-10
Author(s):  
H. P. Jagadish ◽  
L. Ravikumar
Keyword(s):  
Electric Field ◽  
Strain Rate ◽  
Effect Of Temperature ◽  
Squeeze Film ◽  
Shear Strain Rate ◽  
Jet Engine ◽  
Squeeze Film Dampers ◽  
Stiffness And Damping ◽  
Rotor Dynamic ◽  
Er Fluid

Squeeze film dampers are novel rotor dynamic devices used to alleviate small amplitude, large force vibrations and are used in conjunction with antifriction bearings in aircraft jet engine bearings to provide external damping as these possess very little inherent damping. Electrorheological (ER) fluids are controllable fluids in which the rheological properties of the fluid, particularly viscosity, can be controlled in accordance with the requirements of the rotor dynamic system by controlling the intensity of the applied electric field and this property can be utilized in squeeze film dampers, to provide variable stiffness and damping at a particular excitation frequency. The paper investigates the effect of temperature and electric field on the apparent viscosity and dynamic (stiffness and damping characteristics) of ER fluid (suspension of diatomite in transformer oil) using the available literature. These characteristics increase with the field as the viscosity increases with the field. However, these characteristics decrease with increase in temperature and shear strain rate as the viscosity of the fluid decreases with temperature and shear strain rate. The temperature is an important parameter as the aircraft jet engine rotors are located in a zone of high temperature gradients and the damper fluid is susceptible to large variations in temperature.

scholarly journals Internal Damper Characteristics of Rotor System with Submerged ER Fluid Journal Bearing

1997 ◽  
Vol 3 (1) ◽  
pp. 61-71 ◽  
Author(s):  
Siyoul Jang ◽  
John A. Tichy
Keyword(s):  
Shear Stress ◽  
Electric Field ◽  
Shear Strain ◽  
Yield Stress ◽  
Electric Fields ◽  
Journal Bearing ◽  
Shear Strain Rate ◽  
Newtonian Flow ◽  
Damping Coefficients ◽  
Er Fluid

Electro-Rheological (ER) fluid behavior is similar to Bingham fluid’ s. Only when the shear stress magnitude of ER fluid exceeds the yield stress, Newtonian flow results. Continuous shear strain rate equation about shear stress which simulates Bingham-like fluid shows viscosity variations. Shear yield stress is controlled by electric fields. Electric fields in circumferential direction around the journal are also changeable because of gap distance. These values make changes of spring and damping coefficients of journal bearings compared to Newtonian flow case. Implicit viscosity variation effects according to shear strain rates of fluid are included in generalized Reynolds' equation for submerged journal bearing. Fluid film pressure and perturbation pressures are solved using switch function of Elord's algorithm for cavitation boundary condition. Spring and damping coefficients are obtained for several parameters that determine the characteristics of ER fluids under a certain electric field. From these values stability region for simple rotor-bearing system is computed. It is found that there are no big differences in load capacities with the selected electric field parameters at low eccentric region and higher electric field can support more load with stability at low eccentric region.

Squeeze Film Dampers: Amplitude Effects at Low Squeeze Numbers

1975 ◽  
Vol 97 (4) ◽  
pp. 1366-1370 ◽  
Author(s):  
Martin H. Sadd ◽  
A. Kent Stiffler
Keyword(s):  
Reynolds Equation ◽  
Dynamic Performance ◽  
Squeeze Film ◽  
Periodic Disturbance ◽  
Squeeze Film Dampers ◽  
Parallel Surfaces ◽  
Load Characteristics ◽  
Squeeze Number ◽  
Stiffness And Damping ◽  
Film Stiffness

Gaseous squeeze film dampers are analyzed to determine the effect of periodic disturbance amplitude on the dynamic performance. Both circular and rectangular parallel surfaces are investigated. A solution of the nonlinear Reynolds equation is obtained by expanding the pressure in powers of the squeeze number σ, retaining up to and including terms 0(σ2). The time dependent load characteristics are found. The effect of disturbance amplitude on the film stiffness and damping is given.

Eccentric Operation and Blade-Loss Simulation of a Rigid Rotor Supported by an Improved Squeeze Film Damper

1995 ◽  
Vol 117 (3) ◽  
pp. 490-497 ◽  
Author(s):  
J. Y. Zhao ◽  
E. J. Hahn
Keyword(s):  
Outer Ring ◽  
Squeeze Film ◽  
Rigid Rotor ◽  
Cavitation Model ◽  
Squeeze Film Damper ◽  
Constant Stiffness ◽  
Flexible Support ◽  
Squeeze Film Dampers ◽  
Stiffness And Damping ◽  
Blade Loss

This paper outlines an improved squeeze film damper which reduces significantly the dependence of the stiffness of conventional squeeze film dampers on the vibration amplitudes. This improved damper consists of a conventional squeeze film damper with a flexibility supported outer ring. This secondary flexible support is considered to be massless, and to have a constant stiffness and damping. Assuming the short bearing approximation and the ‘π’ film cavitation model, the performances of this damper in preventing bistable operation and sub-synchronous and nonsynchronous motions are theoretically demonstrated for a rigid rotor supported on a squeeze film damper. Blade-loss simulations are carried out numerically.

scholarly journals Kaybob Revisited: What We Have Learned about Compressor Stability from Self-Excited Whirling

2016 ◽  
Vol 2016 ◽  
pp. 1-17
Author(s):  
Edgar J. Gunter ◽  
Brian K. Weaver
Keyword(s):  
High Pressure ◽  
Squeeze Film ◽  
Rotor Vibration ◽  
Analysis Tools ◽  
Squeeze Film Dampers ◽  
History Of ◽  
Bearing Stiffness ◽  
Stiffness And Damping ◽  
Design Factors

The Kaybob compressor failure of 1971 was an excellent historic example of rotordynamic instability and the design factors that affect this phenomenon. In the case of Kaybob, the use of poorly designed bearings produced unstable whirling in both the low and high pressure compressors. This required over five months of vibration troubleshooting and redesign along with over 100 million modern U.S. dollars in total costs and lost revenue. In this paper, the history of the Kaybob compressor failure is discussed in detail including a discussion of the ineffective bearing designs that were considered. Modern bearing and rotordynamic analysis tools are then employed to study both designs that were considered along with new designs for the bearings that could have ultimately restored stability to the machine. These designs include four-pad, load-between-pad bearings and squeeze film dampers with a central groove. Simple relationships based on the physics of the system are also used to show how the bearings could be tuned to produce optimum bearing stiffness and damping of the rotor vibration, producing insights which can inform the designers as they perform more comprehensive analyses of these systems.

Design Equations for Wire Mesh Bearing Dampers in Turbomachinery

2005 ◽  
Author(s):  
Vivek V. Choudhry ◽  
John M. Vance
Keyword(s):  
Turbine Rotor ◽  
Wire Mesh ◽  
Squeeze Film ◽  
Operational Parameters ◽  
Temperature Changes ◽  
Turbine Oil ◽  
Power Turbine ◽  
Squeeze Film Dampers ◽  
Stiffness And Damping ◽  
Asme Paper

In a previous ASME paper the second author reported experiments on wire mesh bearing dampers (WMD) incorporated in a power turbine rotor-bearing system in order to enable a direct comparison between WMD and squeeze film dampers (SFD). The results showed that both WMD and SFD perform equally well for reducing the rotordynamic amplitudes of vibration. Moreover the WMD were found to have significant advantages over SFD. The damping provided by the wire mesh is independent of temperature changes and presence of turbine oil. Experiments by another investigator showed that WMD are capable of sustaining more than twice the unbalance as compared to SFD, which promises possible application to withstand blade loss loads. This paper presents empirically developed non-dimensional design equations for WMD, capable of predicting stiffness and damping for a wire mesh ‘donut’ subject to changes in various design, installation, and operational parameters.

Optimized Short Bearing Theory for Squeeze Film Dampers

2009 ◽  
Author(s):  
Stephen L. Edney
Keyword(s):  
Closed Form ◽  
Correction Factor ◽  
Closed Form Solution ◽  
Squeeze Film ◽  
Radial Clearance ◽  
Positive Pressure ◽  
Damping Coefficients ◽  
Lubrication Equation ◽  
Squeeze Film Dampers ◽  
Stiffness And Damping

It is well established that classical short bearing theory can be applied to assess squeeze film dampers whirling in circular centered orbits. This theory yields accurate values for the stiffness and damping coefficients for designs with small length-to-diameter (L/D) ratios (typically less than 0.5) whirling at amplitudes of less than half the damper radial clearance. For L/D ratio designs above 0.5 and/or whirling amplitudes approaching the damper radial clearance, the short bearing theory increasingly overestimates the stiffness and damping coefficients that stretch its applicability for some designs. There are two limitations with the classical theory that compromise the solution at high L/D ratios and large whirling amplitudes. The first is that as the L/D ratio increases, the unrestricted end flow assumption that forms the basis of the short bearing theory introduces increasingly larger errors. The second is that as the whirling amplitude approaches the damper radial clearance, the stiffness and damping coefficients approach infinity much more rapidly than those from a full solution of the governing lubrication equation. The ideal method for determining more exact values is to numerically solve the full lubrication equation, although not everyone has access to such a code. An alternative approach is to use the expressions presented in this paper that are derived from an optimized solution of the short bearing theory that appreciably reduces the errors introduced at high L/D ratios and whirling amplitudes approaching the damper radial clearance. The optimized solution yields a simple closed form correction factor based on Galerkin’s method that minimizes these errors over the positive pressure region of the oil film. This analytic correction factor increases the accuracy of the short bearing theory for all whirling amplitudes and extends the applicability of the closed form solution to larger L/D ratio damper designs. The simple closed form expressions presented herein apply to a damper whirling in a circular centered orbit for both a partial pi-film cavitated model and a full-film uncaviated model. Examples are given that demonstrate the optimized solution yields stiffness and damping values that are significantly closer to the numerical solution for L/D ratio designs up to 1.0 and/or whirling amplitudes approaching the damper radial clearance.

scholarly journals An Improved Squeeze Film Damper for Rotor Vibration Control: Theoretical Results

1994 ◽  
Author(s):  
J. Y. Zhao ◽  
I. W. Linnett ◽  
E. J. Hahn
Keyword(s):  
Operating Conditions ◽  
Outer Ring ◽  
Squeeze Film ◽  
Squeeze Film Damper ◽  
Constant Stiffness ◽  
Wide Range ◽  
Squeeze Film Dampers ◽  
Secondary Support ◽  
Stiffness And Damping ◽  
Theoretical Results

This paper proposes an improved squeeze film damper which will prevent the bistable operation associated with conventional squeeze film dampers at large unbalances and/or at small bearing parameters. It consists of a conventional squeeze film damper with a flexibly supported outer ring. This secondary flexible support is considered to be massless, and to have a constant stiffness and damping. The effectiveness of this damper in preventing bistable operation is investigated over a wide range of operating conditions for a rigid rotor supported on a centrally preloaded squeeze film damper. It is shown that depending on relevant parameters such as the stiffness ratio between the secondary support and the retaining spring, the damping coefficient of the support, and the mass ratio between the damper outer ring and the rotor, this proposed damper is very effective in preventing bistable operation even for high unbalance conditions.

Pressurized Oil Squeeze Film Dampers

1980 ◽  
Vol 102 (1) ◽  
pp. 41-47 ◽  
Author(s):  
A. Kent Stiffler
Keyword(s):  
Design Methodology ◽  
Squeeze Film ◽  
Rigid Rotor ◽  
Squeeze Film Damper ◽  
Supply Pressure ◽  
Squeeze Film Dampers ◽  
Stiffness And Damping ◽  
Film Stiffness

A pressurized oil squeeze film damper supporting a rigid rotor mounted in antifriction bearings is investigated. Orifice and inherent feed inlets are examined, and it is shown that the clearance determines the inlet resistance for a groove or slot. The film stiffness and damping forces are determined as a function of the restrictor coefficient, rotor unbalance speed and the supply pressure using the short bearing approximation. These forces are related to the system transmissibility. A design methodology for low transmissibilities is presented.

Directionally Controllable Squeeze Film Damper Using Electro-Rheological Fluid

2001 ◽  
Vol 124 (1) ◽  
pp. 105-109 ◽  
Author(s):  
Young Kong Ahn ◽  
Bo-Suk Yang ◽  
Shin Morishita
Keyword(s):  
Electric Field ◽  
Yield Stress ◽  
Apparent Viscosity ◽  
Rotor System ◽  
Squeeze Film ◽  
Flexible Rotor ◽  
Squeeze Film Damper ◽  
Er Fluid

Electro-Rheological (ER) fluid is a class of functional fluid whose yield stress can be changed by an electric field applied to the fluid, which is observed as a variation of apparent viscosity. This functional fluid is applied to a controllable squeeze film damper (SFD) for stabilizing a flexible rotor system. In applying ER fluid to a conventional passive SFD, a pair of rings in the damper can be used as electrodes. When the electrodes are divided into a horizontal pair and a vertical one, the SFD can provide external damping 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.

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