Experimental Analyses of a First Generation Foil Bearing: Startup Torque and Dynamic Coefficients

2011 ◽  
Vol 133 (9) ◽  
Author(s):  
Laurent Rudloff ◽  
Mihai Arghir ◽  
Olivier Bonneau ◽  
Pierre Matta
Keyword(s):  
Dynamic Characteristics ◽  
First Generation ◽  
Static Load ◽  
Excitation Frequency ◽  
Base Plate ◽  
Test Rig ◽  
Dynamic Coefficients ◽  
Foil Bearing ◽  
Lift Off ◽  
Stiffness And Damping

This paper presents the results of the experimental analysis of static and dynamic characteristics of a generation 1 foil bearing of 38.1 mm diameter and L/D=1. The test rig is of floating bearing type, the rigid shaft being mounted on ceramic ball bearings and driven up to 40 krpm. Two different casings are used for startup and for measurement of dynamic coefficients. In its first configuration, the test rig is designed to measure the startup torque. The foil bearing casing is made of two rings separated by a needle bearing to enable an almost torque free rotation between the foil bearing and the static load. The basic results are the startup torque and the lift-off speed. In its second configuration, a different casing is used to measure the impedances of the foil bearing. Misalignment is a problem that is minimized by using three flexible stingers connecting the foil bearing casing to the base plate of the test rig. The test rig enables the application of a static load and of the dynamic excitation on the journal bearing casing and can measure displacements, forces, and accelerations. Working conditions consisted of static loads comprised between 10 N and 50 N and rotation frequencies ranging from 260 Hz to 590 Hz. Excitation frequencies comprised between 100 Hz and 600 Hz are applied by two orthogonally mounted shakers for each working condition. Stiffness and damping coefficients are identified from the complex impedances and enable the calculation of natural frequencies. The experimental results show that the dynamic characteristics of the tested bearing have a weak dependence on the rotation speed but vary with the excitation frequency.

Experimental Analyses of a First Generation Foil Bearing: Start-Up Torque and Dynamic Coefficients

2010 ◽  
Author(s):  
Laurent Rudloff ◽  
Mihai Arghir ◽  
Olivier Bonneau ◽  
Pierre Matta
Keyword(s):  
Dynamic Characteristics ◽  
Static Load ◽  
Excitation Frequency ◽  
Base Plate ◽  
Test Rig ◽  
Dynamic Coefficients ◽  
Foil Bearing ◽  
Start Up ◽  
Lift Off ◽  
Stiffness And Damping

The paper presents the results of the experimental analysis of static and dynamic characteristics of a generation 1 foil bearing of 38.1 mm diameter and L/D = 1. The test rig is of floating bearing type, the rigid shaft being mounted on ceramic ball bearings and driven up to 40 krpm. Two different casings are used for start-up and for measurement of dynamic coefficients. In its first configuration, the test rig is designed to measure the start-up torque. The foil bearing casing is made of two rings separated by a needle bearing for enabling an almost torque free rotation between the foil bearing and the static load. The basic results are the start up torque and the lift off speed. In its second configuration a different casing is used for measuring the impedances of the foil bearing. Misalignment is a problem that is minimized by using three flexible stingers connecting the foil bearing casing to the base plate of the test rig. The test rig enables the application of a static load and of the dynamic excitation on the journal bearing casing, and can measure displacements, forces and accelerations. Working conditions consisted of static loads comprised between 10 N and 50 N and rotation frequencies ranging from 260 Hz to 590 HZ. Excitation frequencies comprised between 100 Hz are 600 Hz are applied by two orthogonally mounted shakers for each working condition. Stiffness and damping coefficients are identified from the complex impedances and enable the calculation of natural frequencies. The experimental results show that the dynamic characteristics of the tested bearing have a weak dependence on the rotation speed but vary with the excitation frequency.

Design and structural performance measurements of a novel multi-cantilever foil bearing

2014 ◽  
Vol 229 (10) ◽  
pp. 1830-1838 ◽  
Author(s):  
Kai Feng ◽  
Xueyuan Zhao ◽  
Zhiyang Guo
Keyword(s):  
Dynamic Characteristics ◽  
Dynamic Load ◽  
Dynamic Stiffness ◽  
Excitation Frequency ◽  
Viscous Damping ◽  
Equivalent Viscous Damping ◽  
Foil Bearing ◽  
Load Tests ◽  
Stiffness And Damping ◽  
Motion Amplitude

With increasing need for high-speed, high-temperature, and oil-free turbomachinery, gas foil bearings (GFBs) have been considered to be the best substitutes for traditional oil-lubricated bearings. A multi-cantilever foil bearing (MCFB), a novel GFB with multi-cantilever foil strips serving as the compliant underlying structure, was designed, fabricated, and tested. A series of static and dynamic load tests were conducted to measure the structural stiffness and equivalent viscous damping of the prototype MCFB. Experiments of static load versus deflection showed that the proposed bearing has a large mechanical energy dissipation capability and a pronounced nonlinear static stiffness that can prevents overly large motion amplitude of journal. Dynamic load tests evaluated the influence of motion amplitude, loading orientation and misalignment on the dynamic stiffness and equivalent viscous damping with respect to excitation frequency. The test results demonstrated that the dynamic stiffness and damping are strongly dependent on the excitation frequency. Three motion amplitudes were applied to the bearing housing to investigate the effects of motion amplitude on the dynamic characteristics. It is noted that the bearing dynamic stiffness and damping decreases with incrementally increasing motion amplitudes. A high level of misalignment can lead to larger static and dynamic bearing stiffness as well as to larger equivalent viscous damping. With dynamic loads applied to two orientations in the bearing midplane separately, the dynamic stiffness increases rapidly and the equivalent viscous damping declines slightly. These results indicate that the loading orientation is a non-negligible factor on the dynamic characteristics of MCFBs.

EXPERIMENTAL INVESTIGATION OF A FOIL BEARING STRUCTURE WITH A POLYMER COATING UNDER DYNAMIC LOADS

Tribologia ◽  
2018 ◽  
Vol 281 (5) ◽  
pp. 5-12 ◽  
Author(s):  
Paweł BAGIŃSKI ◽  
Grzegorz ŻYWICA
Keyword(s):  
Excitation Frequency ◽  
Dynamic Loads ◽  
Test Rig ◽  
Static Tests ◽  
Structural Part ◽  
Foil Bearing ◽  
Wide Range ◽  
Load Tests ◽  
Excitation Force ◽  
Stiffness And Damping

This paper presents the results of research on the structural elements of a prototypical foil bearing in terms of its dynamic loads. In the framework of dynamic tests, several dozens of measurement series were carried out on a test rig specially prepared for this purpose. Dynamic excitations were applied using an electromagnetic exciter that enables changing the amplitude and frequency of the excitation force. Owing to this, it was possible to determine characteristics of the tested system in a wide range of loads and frequencies. A value of 400 Hz was assumed as the upper limit of the excitation frequency. The test rig enabled considering the direction of dynamic loads, which, as it turned out, had a significant impact on the obtained results. The research findings show that both the amplitude and frequency of an excitation force have a major impact on the stiffness and damping of the structural part of the foil bearing. The results of dynamic load tests complement the results of static tests performed earlier.

Structural Stiffness and Damping Coefficients of a Multileaf Foil Bearing With Bump Foils Underneath

2013 ◽  
Vol 136 (4) ◽  
Author(s):  
Ye Tian ◽  
Yanhua Sun ◽  
Lie Yu
Keyword(s):  
Excitation Frequency ◽  
Magnetic Bearing ◽  
Damping Capacity ◽  
Structural Stiffness ◽  
Test Rig ◽  
Domain Identification ◽  
Damping Coefficients ◽  
Foil Bearing ◽  
Applied Forces ◽  
Stiffness And Damping

This paper presents a multileaf foil bearing (MLFB), which consists of four resilient top foils and four stiff bump foils underneath; thus, a high supporting capacity and a high damping capacity can be achieved. A specially designed test rig is used to identify the structural stiffness and damping coefficients of the MLFB. The rotor of the test rig is supported by two journal MLFBs and a thrust active magnetic bearing (AMB) and the static and dynamic loads are applied by two radial AMBs. The tests on MLFBs were conducted under conditions of no shaft rotation at different angular positions and journal displacements with different excitation frequency. A frequency domain identification method is presented to determine the stiffness and damping coefficients. Static measurements show nonlinear deflections with applied forces, which varies with the orientation of the load angular position. The dynamic measurements show that the stiffness and equivalent viscous damping change with the excitation frequency. Furthermore, the stiffness and damping coefficients are related to the operating position where dynamic load tests were conducted. The investigation provides extensive measurements of the static and dynamic characteristics of the MLFB. These results can serve as a benchmark for the calibration of analytical tools under development.

Identification of Dynamic Characteristics of Gas Foil Thrust Bearings Using Base Excitation

2016 ◽  
Author(s):  
Tae Ho Kim ◽  
Moon Sung Park ◽  
Jongsung Lee ◽  
Young Min Kim ◽  
Kyoung-Ku Ha ◽  
...  
Keyword(s):  
Dynamic Characteristics ◽  
Dynamic Load ◽  
Loss Factor ◽  
Load Capacity ◽  
Excitation Frequency ◽  
Vibrational Amplitude ◽  
Test Rig ◽  
Thrust Bearings ◽  
Bearing Plate ◽  
Bearing Stiffness

Gas foil bearings (GFBs) have clear advantages over oil-lubricated and rolling element bearings, by virtue of low power loss, oil-free operation in compact units, and rotordynamic stability at high speeds. However, because of the inherent low gas viscosity, GFBs have lower load capacity than the other bearings. In particular, accurate measurement of load capacity and dynamic characteristics of gas foil thrust bearings (GFTBs) is utmost important to widening their applications to high performance turbomachinery. In this study, a series of excitation tests were performed on a small oil-free turbomachinery with base excitations in the rotor axial direction to measure the dynamic load characteristics of a pair of six-pad, bump-type GFTBs, which support the thrust collar. An electromagnetic shaker provided dynamic sine sweep loads to the test bench (shaking table), which held rigidly the turbomachinery test rig for increasing excitation frequency from 10 Hz to 200 Hz. The magnitude of the shaker dynamic load, represented as an acceleration measured on the test rig, was increased up to 9 G (gravity). An eddy current sensor installed on the test rig housing measured the axial displacement (or vibrational amplitude) of the rotor thrust collar during the excitation tests. The axial acceleration of the rotor relative to the test rig was calculated using the measured displacement. A single degree-of-freedom base excitation model identified the frequency-dependent dynamic load capacity, stiffness, damping, and loss factor of the test GFTB for increasing shaker dynamic loads and increasing bearing clearances. The test results show that, for a constant shaker force and the test GFTB with a clearance of 155 μm, an increasing excitation frequency increases the dynamic load carried by the test GFTB, i.e., bearing reaction force, until a certain value of the frequency where it jumps down suddenly because of the influence from Duffing’s vibrations of the rotor. The bearing stiffness increases and the damping decreases dramatically as the excitation frequency increases. Generally, the bearing loss factor ranges from 0.5 to 1.5 independent of the frequency. As the shaker force increases, the bearing dynamic load, stiffness, damping, and loss factor increase depending on the excitation frequency. Interestingly, the agreements between the measured GFTB dynamic load versus the thrust runner displacement, the measured GFTB static load versus the structural deflection, and the predicted static load versus the thrust runner displacement are remarkable. Further tests with increasing GFTB clearances of 155, 180, 205, and 225 μm revealed that the vibrational amplitude increases and the jump-down frequency decreases with increasing clearances. The bearing load increases, but the bearing stiffness, damping, and loss factor decrease slightly as the clearance increases. The test results after a modification of the GFTB by rotating one side bearing plate by 30° relative to the other side bearing plate revealed insignificant changes in the dynamic characteristics. The present dynamic performance measurements provide a useful database of GFTBs for use in microturbomachinery.

scholarly journals The Effect of the Pivot Stiffness on the Performances of Five-Pad Tilting Pad Bearings

Lubricants ◽  
2019 ◽  
Vol 7 (7) ◽  
pp. 61 ◽  
Author(s):  
Phuoc Vinh Dang ◽  
Steven Chatterton ◽  
Paolo Pennacchi
Keyword(s):  
Excitation Frequency ◽  
Experimental Results ◽  
Dynamic Force ◽  
Dynamic Coefficients ◽  
Pivot Bearing ◽  
Tilting Pad ◽  
In Series ◽  
Stiffness And Damping ◽  
Tilting Pad Journal Bearings

The role of the pivot flexibility in tilting-pad journal bearings (TPJBs) has become essential, particularly for bearings working at high applied load and relatively high rotor speeds. Predictions from a simple bearing model with rigid pivots show incorrect estimation of the dynamic coefficients in comparison with the experimental results. Normally, the more flexible the pad pivot, the lower the dynamic coefficients because the stiffness of the pivot takes in series with the stiffness and damping of the oil film. This paper investigates the influence of pivot stiffness on the dynamic force coefficients of two different five-pad TPJBs as a function of the applied static load and excitation frequency: rocker-backed pivot and spherical pivot bearings. In order to highlight the effect of the pivot stiffness in the spherical pivot bearing, displacement restriction components and elastic copper made shims have been used. Firstly, a thermo-elasto-hydrodynamic model for the static and dynamic characteristics of the two bearings is described. This model takes into account the flexibility of both pad and pivot. The pivot stiffnesses calculated by means of the Hertz theory and those obtained by experiments have been introduced and compared in the model. The clearance profiles of two tested bearing and the shaft center loci obtained by measurement and prediction are also shown. The dynamic coefficients of the two bearings obtained from the numerical simulation were compared with the experimental results. By the analysis it can be concluded that the effect of the pivot flexibility on the clearance profile, the shaft locus and on the dynamic coefficients is very significant. More important, it is important to estimate the pivot stiffness of each single pad using experimental measurements.

Dynamic Characteristics of Spiral-Grooved Opposed-Hemisphere Gas Bearings

2016 ◽  
Vol 139 (3) ◽  
Author(s):  
Guangwei Yang ◽  
Jianjun Du ◽  
Weiping Ge ◽  
Tun Liu ◽  
Xiaowei Yang
Keyword(s):  
Dynamic Characteristics ◽  
Degrees Of Freedom ◽  
Dynamic Stiffness ◽  
Translational Motion ◽  
Coupling Coefficients ◽  
Dynamic Coefficients ◽  
Large Eccentricity ◽  
The Stability ◽  
Stiffness And Damping ◽  
Gas Bearing

The traditional eight-coefficient bearing model only considers the translational motion of the bearings and neglects the tilting motion and coupling effects between them. In this paper, the dynamic characteristics of the spiral-grooved opposed-hemisphere gas bearing considering five degrees-of-freedom are studied, and 50 dynamic coefficients including the translational, tilting, and coupling components are completely calculated. The Reynolds equations and their perturbed equations are solved by the finite element method to obtain the dynamic stiffness and damping coefficients. The effects of the tilting motion on the dynamic coefficients and response are analyzed, respectively. The results show that the coupling coefficients between the translational and tilting motions, which have been neglected in most previous studies, are significant at large eccentricity ratio. But these coupling coefficients have little effect on the dynamic response. On the other hand, the influences of the tilting motion on the synchronous response and natural frequency are remarkable and will decrease the stability of the rotor bearing system.

Structural and Rotordynamic Force Coefficients of a Shimmed Bump Foil Bearing: An Assessment of a Simple Engineering Practice

2015 ◽  
Vol 138 (1) ◽  
Author(s):  
Luis San Andrés ◽  
Joshua Norsworthy
Keyword(s):  
Loss Factor ◽  
High Speed ◽  
Static Load ◽  
Low Cost ◽  
Mechanical Energy ◽  
Excitation Frequency ◽  
Engineering Practice ◽  
Force Coefficients ◽  
Damping Coefficients ◽  
Stiffness And Damping

High speed rotors supported on bump-type foil bearings (BFBs) often suffer from large subsynchronous whirl motions. Mechanically preloading BFBs through shimming is a common, low cost practice that shows improvements in rotordynamic stability. However, there is an absence of empirical information related to the force coefficients (structural and rotordynamic) of shimmed BFBs. This paper details a concerted study toward assessing the effect of shimming on a first generation BFB (L = 38.1 mm and D = 36.5 mm). Three metal shims, 120 deg apart, are glued to the inner surface of the bearing cartridge and facing the underside of the bump foil strip. The shim sets are of identical thickness, either 30 μm or 50 μm. In static load tests, a bearing with shims shows a (nonlinear) structural stiffness larger than for the bearing without shims. Torque measurements during shaft acceleration also demonstrate a shimmed BFB has a larger friction coefficient. For a static load of 14.3 kPa, dynamic loads with a frequency sweep from 250 Hz to 450 Hz are exerted on the BFB, without and with shims, to estimate its rotordynamic force coefficients while operating at ∼50 krpm (833 Hz). Similar measurements are conducted without shaft rotation. Results are presented for the original BFB (without shims) and the two shimmed BFB configurations. The direct stiffnesses of the BFB, shimmed or not, increase with excitation frequency, thus evidencing a mild hardening effect. The BFB stiffness and damping coefficients decrease slightly for operation with rotor speed as opposed to the coefficients when the shaft is stationary. For frequencies above 300 Hz, the direct damping coefficients of the BFB with 50 μm thick shims are ∼30% larger than the coefficients of the original bearing. The bearing structural loss factor, a measure of its ability to dissipate mechanical energy, is derived from the direct stiffness and damping coefficients. The BFB with 50 μm thick shims has a 25% larger loss factor—average from test data collected at 300 Hz to 400 Hz—than the original BFB. Further measurements of rotor motions while the shaft accelerates to ∼50 krpm demonstrate the shimmed BFB (thickest shim set) effectively removes subsynchronous whirl motions amplitudes that were conspicuous when operating with the original bearing.

Experimental Analysis of the Dynamic Characteristics of a Foil Thrust Bearing

2014 ◽  
Author(s):  
Franck Balducchi ◽  
Mihai Arghir ◽  
Romain Gauthier
Keyword(s):  
Dynamic Characteristics ◽  
Experimental Analysis ◽  
Dynamic Models ◽  
Thrust Bearing ◽  
Dynamic Stiffness ◽  
Excitation Frequency ◽  
Test Rig ◽  
Equivalent Damping ◽  
Start Up ◽  
Foil Thrust Bearing

The paper deals with the experimental analysis of the dynamic characteristics of a foil thrust bearing (FTB) designed following the specifications given by NASA in 2009. The start-up characteristics of the same foil bearing were investigated in a recently published paper. The test rig used for start-up measurements was adapted for dynamic measurements. The paper presents the test rig in detail as well as its identified dynamic models. Measurements of the dynamic characteristics of the bump foil structure were performed for static loads comprised between 30 N and 150 N while measurements for the FTB were performed at 35 krpm for 30 N, 60 N and 90 N. Excitation frequencies were comprised between 150 Hz and 750 Hz. Results showed that the dynamic stiffness of the FTB increase with excitation frequency while the equivalent damping decreases. Both stiffness and damping increase with the static load but are smaller at 35 krpm compared to 0 rpm.

Experimental Study on the Dynamic Characteristics of Hydro-Magneto-Electric-Regenerative Shock Absorber

2016 ◽  
Vol 836 ◽  
pp. 9-13
Author(s):  
Harus Laksana Guntur ◽  
Wiwiek Hendrowati
Keyword(s):  
Experimental Study ◽  
Dynamic Characteristics ◽  
Hydraulic System ◽  
Shock Absorber ◽  
Excitation Frequency ◽  
Vehicle Suspension ◽  
Test Rig ◽  
Electric Generator ◽  
Car Suspension ◽  
Regenerative Shock Absorber

Regenerative shock absorber is designed to convert the vibration energy losses from the vehicle suspension into electricity. This paper presents an experimental study on the dynamic characteristics of hydro-magneto-electric-regenerative shock absorber (HMERSA). Study was carried out by developing a prototype of HMERSA and testing its dynamic characteristics. The results were analyzed and discussed. Prototype of the HMERSA consists of hydraulic system and electric generator. The HMERSA was tested using a quarter car suspension test rig with input displacement in various frequency (1.3Hz, 1.5Hz, 1.7Hz) and for HMERSA’s various oil viscousity (ISO VG 10, 32, 46). Sprung mass acceleration and the generated electric power representing the dynamic characteristics of HMERSA were measured. Maximum power 2.5 watt and root mean square acceleration 0.172 m/s2 gained for HMERSA with oil viscousity ISO VG 10 at all excitation frequency.

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