Reduction of the Dynamic Load Capacity in a Squeeze Film Damper Operating With a Bubbly Lubricant

1999 ◽  
Vol 121 (4) ◽  
pp. 703-709 ◽  
Author(s):  
S. E. Diaz ◽  
L. A. San Andre´s
Keyword(s):  
Volume Fraction ◽  
Load Capacity ◽  
Effective Means ◽  
Theoretical Models ◽  
Operating Conditions ◽  
Qualitative Description ◽  
Squeeze Film ◽  
Damping Force ◽  
Hydrostatic Force ◽  
Discharge Pressure

Squeeze film dampers (SFDs) are effective means to reduce vibrations and to suppress instabilities in rotor-bearing systems. However, at operating conditions while traversing critical speeds with large orbital whirl motions, ingestion and entrapment of air into the thin lands of SFDs generates a bubbly mixture (air in lubricant) that is known to reduce the dynamic film pressures and the overall damping capability. This pervasive phenomenon lacks proper physical understanding and sound analytical modeling. An experimental investigation to quantify the forced performance of a SFD operating with a controlled bubbly mixture is detailed. Tests are conducted in a constrained circular orbit SFD to measure the dynamic squeeze film pressures and journal motion at two whirl frequencies (8.33 and 16.67 Hz) as the air content in the mixture increases from 0 percent to 100 percent. The analysis of period-averaged film pressures reveals a zone of uniform low pressure of magnitude equal to the discharge pressure, independently of the mixture composition. The uniform pressure zone extends as the mixture void fraction increases. Radial and tangential film forces are estimated from the dynamic pressures at two axial locations of measurement. The tangential (damping) force decreases proportionally with the mixture volume fraction, while a radial hydrostatic force remains nearly invariant. The experimental results quantify effects previously known by qualitative description only, thus providing a benchmark towards the development of sound theoretical models.

Reduction of the Dynamic Load Capacity in a Squeeze Film Damper Operating With a Bubbly Lubricant

1998 ◽  
Author(s):  
Sergio E. Diaz ◽  
Luis A. San Andrés
Keyword(s):  
Volume Fraction ◽  
Load Capacity ◽  
Effective Means ◽  
Theoretical Models ◽  
Operating Conditions ◽  
Qualitative Description ◽  
Squeeze Film ◽  
Damping Force ◽  
Hydrostatic Force ◽  
Discharge Pressure

Squeeze film dampers (SFDs) are effective means to reduce vibrations and to suppress instabilities in rotor-bearing systems. However, at operating conditions while traversing critical speeds with large orbital whirl motions, ingestion and entrapment of air into the thin lands of SFDs generates a bubbly mixture (air in lubricant) which is known to reduce the dynamic film pressures and the overall damping capability. This pervasive phenomenon lacks proper physical understanding and sound analytical modeling. An experimental investigation to quantify the forced performance of a SFD operating with a controlled bubbly mixture is detailed. Tests are conducted in a constrained circular orbit SFD to measure the dynamic squeeze film pressures and journal motion at two whirl frequencies (8.33 and 16.67 Hz) as the air content in the mixture increases from 0% to 100%. The analysis of period-averaged film pressures reveals a zone of uniform low pressure of magnitude equal to the discharge pressure, independently of the mixture composition. The uniform pressure zone extends as the mixture void fraction increases. Radial and tangential film forces are estimated from the dynamic pressures at two axial locations of measurement. The tangential (damping) force decreases proportionally with the mixture volume fraction, while a radial hydrostatic force remains nearly invariant. The experimental results quantify effects previously known by qualitative description only, thus providing a benchmark towards the development of sound theoretical models.

Dynamic Characterization of a Novel Externally Pressurized Compliantly Damped Gas-Lubricated Bearing With Hermetically Sealed Squeeze Film Damper Modules

2018 ◽  
Vol 141 (2) ◽  
Author(s):  
Adolfo Delgado ◽  
Bugra Ertas
Keyword(s):  
Degrees Of Freedom ◽  
Load Capacity ◽  
Operating Conditions ◽  
Experimental Results ◽  
Squeeze Film ◽  
Metal Mesh ◽  
Squeeze Film Damper ◽  
Drive Trains ◽  
Bearing Loads

Ever-increasing demand for cleaner energy is driving the need for higher power density turbomachinery while reducing cost and simplifying design. Gas-lubricated bearings are representing one of the enabling technologies that can help maximize these benefits and have been successfully implemented into turbomachinery applications with rotors weights in the order few kg's. However, load capacity and damping limitations of existing gas bearing technologies prevent the development of larger size oil-free drive trains in the MW power output range. Compliantly damped hybrid gas bearings (CHGBs) were introduced as an alternative design to overcome these limitations by providing external pressurization to discrete tilting pads while retaining flexibility in the bearing support to help tolerate misalignment and rotor-pad geometry changes. Additionally, the CHGB concept addresses damping entitlement through the application of bearing support dampers such as metal mesh. An alternative CHGB design, featuring a novel hermetically seal squeeze film damper (HSFD) in the bearing support, was introduced as alternative approach to metal mesh dampers (MMDs) to further improve bearing damping. This paper details the rotordynamic characterization of a CHGB with modular HSFD for various operating conditions. Direct and cross-coupled stiffness and damping coefficients are presented for different rotor speeds up to 12,500 rpm, frequencies of excitation between 20 and 200 Hz, bearing loads between 200 and 400 lbf, and external hydrostatic pressures reaching 180 psi. Direct comparisons to experimental results for a CHGB using MMD show 3× increase in direct damping levels when using HSFD in the compliant bearing support. In addition to the experimental results, an analytical model is presented based on the implementation of the isothermal compressible Reynolds equation coupled to a flexible support possessing a pad with three degrees-of-freedom. The numerical results capture the direct stiffness and frequency dependency but underpredict the absolute values for both cases when compared to experimental data.

Dynamic Characterization of a Novel Externally Pressurized Compliantly Damped Gas-Lubricated Bearing With Hermetically Sealed Squeeze Film Damper Modules

2018 ◽  
Author(s):  
Adolfo Delgado ◽  
Bugra Ertas
Keyword(s):  
Degrees Of Freedom ◽  
Load Capacity ◽  
Operating Conditions ◽  
Experimental Results ◽  
Squeeze Film ◽  
Metal Mesh ◽  
Squeeze Film Damper ◽  
Drive Trains ◽  
Bearing Loads

Ever-increasing demand for cleaner energy is driving the need for higher power density turbomachinery while reducing cost and simplifying design. Gas lubricated bearings, representing one of the enabling technologies that can help maximize these benefits and have been successfully implemented into turbomachinery applications with rotors weights in the order few kg’s. However, load capacity and damping limitations of existing gas bearing technologies prevents the development of larger size oil-free drive trains in the MW power output range. Compliantly damped hybrid gas bearings (CHGB) were introduced as an alternative design to overcome these limitations by providing external pressurization to discrete tilting pads while retaining flexibility in the bearing support to help tolerate misalignment and rotor-pad geometry changes. Additionally, the CHGB concept addresses damping entitlement through the application of bearing support dampers such a metal mesh. An alternative CHGB design, featuring a novel hermetically seal squeeze film damper (HSFD) in the bearing support, was introduced as alternative approach to metal mesh dampers (MMD) to further improve bearing damping. This paper details the rotordynamic characterization of a CHGB with modular HSFD for various operating conditions. Direct and cross-coupled stiffness and damping coefficients are presented for different rotor speeds up to 12,500 rpm, frequencies of excitation between 20–200 Hz, bearing loads between 200–400 1bf, and external hydrostatic pressures reaching 180psi. Direct comparisons to experimental results for a CHGB using (MMD) shows 3X increase in direct damping levels when using HSFD in the compliant bearing support. In addition to the experimental results, an analytical model is presented based on the implementation of the isothermal compressible Reynolds equation coupled to a flexible support possessing a pad with 3 degrees of freedom. The numerical results capture the direct stiffness and frequency dependency but underpredict the absolute values for both case when compared to experimental data.

scholarly journals Imbalance Response and Damping Force Coefficients of a Rotor Supported on End Sealed Integral Squeeze Film Dampers

1999 ◽  
Author(s):  
Oscar C. De Santiago ◽  
Luis A. San Andrés
Keyword(s):  
High Performance ◽  
Effective Means ◽  
Squeeze Film ◽  
Damping Force ◽  
Damping Coefficients ◽  
Squeeze Film Dampers ◽  
Flow Through ◽  
Structural Isolation ◽  
The Impact ◽  
Severe Penalty

To this date, squeeze film dampers (SFDs) are effective means to reduce vibrations and provide structural isolation in high performance aeroengine systems. Integral squeeze film dampers (ISFDs) offer distinct advantages such as reduced overall weight, accuracy of positioning, and a split segment construction allowing easier assembly, inspection and retrofit. An experimental study is conducted to evaluate the effectiveness of integral dampers in attenuating the imbalance response of a massive test rotor. Damping coefficients for end sealed dampers are identified from the peak rotor responses due to imbalances while passing through the fundamental critical speeds. Impact response measurements at null rotor speed are also conducted to identify system damping coefficients for increasing values of the lubricant temperature. The impact tests and imbalance response measurements demonstrate that end gap seals increase effectively the ISFD viscous damping coefficients and without a severe penalty in the flow through the dampers. The experiments further demonstrate that the amplitudes of rotor synchronous response are proportional to the imbalance displacements without subsynchronous frequencies or (nonlinear) jump responses.

Analysis and Design of Segmented Dampers for Rotor Dynamic Control

1982 ◽  
Vol 104 (1) ◽  
pp. 84-90 ◽  
Author(s):  
D. L. Taylor ◽  
V. S. Fehr
Keyword(s):  
Pressure Distribution ◽  
Dynamic Control ◽  
Design Procedure ◽  
Operating Conditions ◽  
Squeeze Film ◽  
Fluid Viscosity ◽  
Damping Force ◽  
Analysis And Design ◽  
Wide Range ◽  
Parameter Values

Dampers have become of increasing importance in the control of shaft vibration of rotating equipment which must operate through one or more critical speeds. This paper presents the analytical results for the study of a new class of damper, the segmented film damper. A series of isolated segments of fluid are used rather than a continuous film as in the traditional squeeze film damper. This configuration provides energy dissipation through fluid viscosity within the film segments and through oriface flow in the supply and exit ports for each segment. The pressure distribution within an individual segment is developed on the basis of Reynolds equation with appropriate boundary conditions. The effects of various parameters are discussed in terms of this pressure distribution. The geometric effects of multiple segments are derived for both input, how shaft motion excites each segment, and output, how the segments’ pressure distributions combine to provide a net force. The damping force is shown to be linear for a wide range of operating conditions, speed and unbalance, and thus validly expressed in terms of a damping coefficient. Additionally, this class of damper is shown to have no radial stiffness. The limitations and implications for the designer are discussed in detail. A structured design procedure is given for the selection of parameter values, and a design example with numerical values is included.

Effects of Gas Entrainment on Squeeze Film Damper Performance

1987 ◽  
Vol 109 (1) ◽  
pp. 149-154 ◽  
Author(s):  
N. S. Feng ◽  
E. J. Hahn
Keyword(s):  
Load Capacity ◽  
Liquid Mixtures ◽  
Operating Conditions ◽  
Squeeze Film ◽  
Dissolved Gas ◽  
Film Model ◽  
Gas Entrainment ◽  
Squeeze Film Dampers ◽  
Parameter Values ◽  
Theoretical Analyses

Squeeze film dampers are frequently used for stabilization and/or vibration control of rotating machinery. Theoretical analyses to date generally assume an incompressible lubricant. In practice, however, depending on the capacity of the lubricant reservoir, the lubricant at damper inlet contains varying amounts of dissolved gas, which come out of solution to form a “spongy” gas-liquid mixture during damper operation. This paper examines theoretically and experimentally the effects such entrained gases have on damper performance, particularly on damper load capacity and the likelihood of multistable operation. It is shown that under certain operating conditions, a significant delay in the onset of bistable operation is predicted, depending on the fluid film model employed. Preliminary tests indicate that at low bearing parameter values (B ≐ 0.02), the homogeneous compressible film model using the Hayward rather than the Isbin viscosity relationship for gas-liquid mixtures provides the best prediction of damper performance. Of the incompressible film models, the zero pressure truncation predictions are generally quite satisfactory and superior to the commonly used π-film predictions.

The analysis on the influence of mixed sliding-rolling motion mode to precision degradation of ball screw

2021 ◽  
pp. 095440622098201
Author(s):  
Qiang Cheng ◽  
Baobao Qi ◽  
Hongyan Chu ◽  
Ziling Zhang ◽  
Zhifeng Liu ◽  
...  
Keyword(s):  
Structural Parameters ◽  
Experimental Tests ◽  
Theoretical Models ◽  
Operating Conditions ◽  
Ball Screw ◽  
Rolling Motion ◽  
Degradation Model ◽  
Sliding Motion ◽  
Factors Analysis ◽  
Motion Mode

The combination of sliding/rolling motion can influence the degree of precision degradation of ball screw. Precision degradation modeling and factors analysis can reveal the evolution law of ball screw precision. This paper presents a precision degradation model for factors analysis influencing precision due to mixed sliding-rolling motion. The precision loss model was verified through the comparison of theoretical models and experimental tests. The precision degradation due to rolling motion between the ball and raceway accounted for 29.09% of the screw precision loss due to sliding motion. Additionally, the total precision degradation due to rolling motion accounted for 21.03% of the total sliding precision loss of the screw and nut, and 17.38% of the overall ball screw precision loss under mixed sliding-rolling motion. In addition, the effects of operating conditions and structural parameters on precision loss were analyzed. The sensitivity coefficients of factors influencing were used to quantitatively describe impact degree on precision degradation.

Coupled effects of surface interaction and damping on electromechanical stability of functionally graded nanotubes reinforced torsional micromirror actuator

2021 ◽  
pp. 030932472110368
Author(s):  
Weidong Yang ◽  
Menglong Liu ◽  
Linwei Ying ◽  
Xi Wang
Keyword(s):  
Casimir Force ◽  
Volume Fraction ◽  
Nonlocal Parameter ◽  
Saddle Points ◽  
Functionally Graded ◽  
Heteroclinic Orbits ◽  
Phase Portraits ◽  
Squeeze Film ◽  
Squeeze Film Damping ◽  
Tilting Angle

This paper demonstrated the coupled surface effects of thermal Casimir force and squeeze film damping (SFD) on size-dependent electromechanical stability and bifurcation of torsion micromirror actuator. The governing equations of micromirror system are derived, and the pull-in voltage and critical tilting angle are obtained. Also, the twisting deformation of torsion nanobeam can be tuned by functionally graded carbon nanotubes reinforced composites (FG-CNTRC). A finite element analysis (FEA) model is established on the COMSOL Multiphysics platform, and the simulation of the effect of thermal Casimir force on pull-in instability is utilized to verify the present analytical model. The results indicate that the numerical results well agree with the theoretical results in this work and experimental data in the literature. Further, the influences of volume fraction and geometrical distribution of CNTs, thermal Casimir force, nonlocal parameter, and squeeze film damping on electrically actuated instability and free-standing behavior are detailedly discussed. Besides, the evolution of equilibrium states of micromirror system is investigated, and bifurcation diagrams and phase portraits including the periodic, homoclinic, and heteroclinic orbits are described as well. The results demonstrated that the amplitude of the tilting angle for FGX-CNTRC type micromirror attenuates slower than for FGO-CNTRC type, and the increment of CNTs volume ratio slows down the attenuation due to the stiffening effect. When considering squeeze film damping, the stable center point evolves into one focus point with homoclinic orbits, and the dynamic system maintains two unstable saddle points with the heteroclinic orbits due to the effect of thermal Casimir force.

Improved infrared temperature mapping of elastohydrodynamic contacts

2009 ◽  
Vol 223 (8) ◽  
pp. 1165-1177 ◽  
Author(s):  
T Reddyhoff ◽  
H A Spikes ◽  
A V Olver
Keyword(s):  
Effective Means ◽  
Field Measurements ◽  
Operating Conditions ◽  
Mapping Technique ◽  
Shear Stresses ◽  
Measured Temperature ◽  
Ir Camera ◽  
Full Field ◽  
Group I ◽  
Increased Sensitivity

An effective means of studying lubricant rheology within elastohydrodynamic contacts is by detailed mapping of the temperature of the fluid and the bounding surfaces within the lubricated contact area. In the current work, the experimental approach initially developed by Sanborn and Winer and then by Spikes et al., has been advanced to include a high specification infrared (IR) camera and microscope. Besides the instantaneous capture of full field measurements, this has the advantage of increased sensitivity and higher spatial resolution than previous systems used. The increased sensitivity enables a much larger range of testable operating conditions: namely lower loads, speeds, and reduced sliding. In addition, the range of test lubricants can be extended beyond high shearing traction fluids. These new possibilities have been used to investigate and compare the rheological properties of a range of lubricants: namely a group I and group II mineral oil, a polyalphaolephin (group IV), the traction fluid Santotrac 50, and 5P4E, a five-ring polyphenyl-ether. As expected, contact temperatures increased with lubricant refinement, for the mineral base oils tested. Using moving heat source theory, the measured temperature distributions were converted into maps showing rate of heat input into each surface, from which shear stresses were calculated. The technique could therefore be validated by integrating these shear stress maps, and comparing them with traction values obtained by direct measurement. Generally there was good agreement between the two approaches, with the only significant differences occurring for 5P4E, where the traction that was deduced from the temperature over-predicted the traction by roughly 15 per cent. Of the lubricants tested, Santotrac 50 showed the highest average traction over the contact; however, 5P4E showed the highest maximum traction. This observation is only possible using the IR mapping technique, and is obscured when measuring the traction directly. Both techniques showed the effect of shear heating causing a reduction in traction.

Modeling and Experimental Validation of the Effective Bulk Modulus of a Mixture of Hydraulic Oil and Air

2014 ◽  
Vol 136 (5) ◽  
Author(s):  
Hossein Gholizadeh ◽  
Doug Bitner ◽  
Richard Burton ◽  
Greg Schoenau
Keyword(s):  
Experimental Data ◽  
Bulk Modulus ◽  
Theoretical Models ◽  
Operating Conditions ◽  
Air Bubbles ◽  
Pressure Sensitivity ◽  
Hydraulic Oil ◽  
Effective Bulk Modulus ◽  
Experimental Apparatus ◽  
Major Factors

It is well known that the presence of entrained air bubbles in hydraulic oil can significantly reduce the effective bulk modulus of hydraulic oil. The effective bulk modulus of a mixture of oil and air as pressure changes is considerably different than when the oil and air are not mixed. Theoretical models have been proposed in the literature to simulate the pressure sensitivity of the effective bulk modulus of this mixture. However, limited amounts of experimental data are available to prove the validity of the models under various operating conditions. The major factors that affect pressure sensitivity of the effective bulk modulus of the mixture are the amount of air bubbles, their size and the distribution, and rate of compression of the mixture. An experimental apparatus was designed to investigate the effect of these variables on the effective bulk modulus of the mixture. The experimental results were compared with existing theoretical models, and it was found that the theoretical models only matched the experimental data under specific conditions. The purpose of this paper is to specify the conditions in which the current theoretical models can be used to represent the real behavior of the pressure sensitivity of the effective bulk modulus of the mixture. Additionally, a new theoretical model is proposed for situations where the current models fail to truly represent the experimental data.

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