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.

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

2015 ◽  
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 sub synchronous whirl motions. Mechanically preloading BFBs through shimming is a common, low cost practice that shows improvements in rotordynamic stability. However, there is absence of empirical information related to the force coefficients (structural and rotordynamic) of shimmed BFBs. This paper details a concerted study towards assessing the effect of shimming on a first generation BFB (L=38.1 mm, D =36.5 mm). Three metal shims, 120° 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. Static load tests show that shimming produces nonlinear static load vs. deflection curves leading to a larger structural stiffness 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 sub synchronous whirl motions amplitudes that were conspicuous when operating with the original bearing.

Measurement of Structural Stiffness and Damping Coefficients in a Metal Mesh Foil Bearing

2009 ◽  
Vol 132 (3) ◽  
Author(s):  
Luis San Andrés ◽  
Thomas Abraham Chirathadam ◽  
Tae-Ho Kim
Keyword(s):  
Loss Factor ◽  
Copper Wire ◽  
Mechanical Energy ◽  
Excitation Frequency ◽  
Viscous Damping ◽  
Structural Stiffness ◽  
Metal Mesh ◽  
Equivalent Viscous Damping ◽  
Damping Coefficients ◽  
Stiffness And Damping

Engineered metal mesh foil bearings (MMFBs) are a promising low cost bearing technology for oil-free microturbomachinery. In a MMFB, a ring shaped metal mesh provides a soft elastic support to a smooth arcuate foil wrapped around a rotating shaft. This paper details the construction of a MMFB and the static and dynamic load tests conducted on the bearing for estimation of its structural stiffness and equivalent viscous damping. The 28.00 mm diameter 28.05 mm long bearing, with a metal mesh ring made of 0.3 mm copper wire and compactness of 20%, is installed on a test shaft with a slight preload. Static load versus bearing deflection measurements display a cubic nonlinearity with large hysteresis. The bearing deflection varies linearly during loading, but nonlinearly during the unloading process. An electromagnetic shaker applies on the test bearing loads of controlled amplitude over a frequency range. In the frequency domain, the ratio of applied force to bearing deflection gives the bearing mechanical impedance, whose real part and imaginary part give the structural stiffness and damping coefficients, respectively. As with prior art published in the literature, the bearing stiffness decreases significantly with the amplitude of motion and shows a gradual increasing trend with frequency. The bearing equivalent viscous damping is inversely proportional to the excitation frequency and motion amplitude. Hence, it is best to describe the mechanical energy dissipation characteristics of the MMFB with a structural loss factor (material damping). The experimental results show a loss factor as high as 0.7 though dependent on the amplitude of motion. Empirically based formulas, originally developed for metal mesh rings, predict bearing structural stiffness and damping coefficients that agree well with the experimentally estimated parameters. Note, however, that the metal mesh ring, after continuous operation and various dismantling and re-assembly processes, showed significant creep or sag that resulted in a gradual decrease in its structural force coefficients.

Measurement of Structural Stiffness and Damping Coefficients in a Metal Mesh Foil Bearing

2009 ◽  
Author(s):  
Luis San Andre´s ◽  
Thomas Abraham Chirathadam ◽  
Tae-Ho Kim
Keyword(s):  
Loss Factor ◽  
Copper Wire ◽  
Mechanical Energy ◽  
Excitation Frequency ◽  
Viscous Damping ◽  
Structural Stiffness ◽  
Metal Mesh ◽  
Equivalent Viscous Damping ◽  
Damping Coefficients ◽  
Stiffness And Damping

Engineered Metal Mesh Foil Bearings (MMFB) are a promising low cost bearing technology for oil-free microturbomachinery. In a MMFB, a ring shaped metal mesh (MM) provides a soft elastic support to a smooth arcuate foil wrapped around a rotating shaft. The paper details the construction of a MMFB and the static and dynamic load tests conducted on the bearing for estimation of its structural stiffness and equivalent viscous damping. The 28.00 mm diameter, 28.05 mm long bearing, with a metal mesh ring made of 0.3 mm Copper wire and compactness of 20%, is installed on a test shaft with a slight preload. Static load versus bearing deflection measurements display a cubic nonlinearity with large hysteresis. The bearing deflection varies linearly during loading, but nonlinearly during the unloading process. An electromagnetic shaker applies on the test bearing loads of controlled amplitude over a frequency range. In the frequency domain, the ratio of applied force to bearing deflection gives the bearing mechanical impedance, whose real part and imaginary part give the structural stiffness and damping coefficients, respectively. As with prior art published in the literature, the bearing stiffness decreases significantly with the amplitude of motion and shows a gradual increasing trend with frequency. The bearing equivalent viscous damping is inversely proportional to the excitation frequency and motion amplitude. Hence, it is best to describe the mechanical energy dissipation characteristics of the MMFB with a structural loss factor (material damping). The experimental results show a loss factor as high as 0.7 though dependent on the amplitude of motion. Empirically based formulas, originally developed for metal mesh rings, predict bearing structural stiffness and damping coefficients agreeing well with the experimentally estimated parameters. Note, however, that the metal mesh ring, after continuous operation and various dismantling and reassembly processes, showed significant creep or sag that resulted in a gradual decrease of its structural force coefficients.

Metal Mesh Foil Bearing: Effect of Motion Amplitude, Rotor Speed, Static Load, and Excitation Frequency on Force Coefficients

2011 ◽  
Vol 133 (12) ◽  
Author(s):  
Luis San Andrés ◽  
Thomas Abraham Chirathadam
Keyword(s):  
Energy Dissipation ◽  
High Speed ◽  
Mechanical Energy ◽  
Excitation Frequency ◽  
Wire Mesh ◽  
Test Element ◽  
Metal Mesh ◽  
Force Coefficients ◽  
Damping Coefficients ◽  
Mechanical Energy Dissipation

Metal mesh foil bearings (MMFBs), simple to construct and inexpensive, are a promising bearing technology for oil-free microturbomachinery operating at high speed and high temperature. Prior research demonstrated the near friction-free operation of a MMFB operating to 60 krpm and showing substantial mechanical energy dissipation characteristics. This paper details further experimental work and reports MMFB rotordynamic force coefficients. The test rig comprises a turbocharger driven shaft and overhung journal onto which a MMFB is installed. A soft elastic support structure akin to a squirrel cage holds the bearing, aiding to its accurate positioning relative to the journal. Two orthogonally positioned shakers excite the test element via stingers. The test bearing comprises a cartridge holding a Copper wire mesh ring, 2.7 mm thick, and a top arcuate foil. The bearing length and inner diameter are 38 mm and 36.5 mm, respectively. Experiments were conducted with no rotation and with journal spinning at 40–50 krpm, with static loads of 22 N and 36 N acting on the bearing. Dynamic load tests spanning frequencies from 150 to 450 Hz were conducted while keeping the amplitude of bearing displacements at 20 µm, 25 µm, and 30 µm. With no journal spinning, the force coefficients represent the bearing elastic structure alone because the journal and bearing are in contact. The direct stiffnesses gradually increase with frequency while the direct damping coefficients drop quickly at low frequencies (< 200 Hz) and level off above this frequency. The damping combines both viscous and material types from the gas film and mesh structure. Journal rotation induces airborne operation with a hydrodynamic gas film separating the rotor from its bearing. Hence, cross-coupled stiffness coefficients appear although with magnitudes lower than those of the direct stiffnesses. The direct stiffnesses, 0.4 to 0.6 MN/m within 200–400 Hz, are slightly lower in magnitude as those obtained without journal rotation, suggesting the air film stiffness is quite high. Bearing direct stiffnesses are inversely proportional to the bearing motion amplitudes, whereas the direct equivalent viscous damping coefficients do not show any noticeable variation. All measurements evidence a test bearing system with material loss factor (γ) ∼ 1.0, indicating significant mechanical energy dissipation ability.

Metal Mesh Foil Bearing: Effect of Motion Amplitude, Rotor Speed, Static Load, and Excitation Frequency on Force Coefficients

2011 ◽  
Author(s):  
Luis San Andre´s ◽  
Thomas Abraham Chirathadam
Keyword(s):  
Energy Dissipation ◽  
High Speed ◽  
Mechanical Energy ◽  
Excitation Frequency ◽  
Wire Mesh ◽  
Test Element ◽  
Metal Mesh ◽  
Force Coefficients ◽  
Damping Coefficients ◽  
Mechanical Energy Dissipation

Metal mesh foil bearings (MMFBs), simple to construct and inexpensive, are a promising bearing technology for oil-free microturbomachinery operating at high speed and high temperature. Prior research demonstrated the near friction-free operation of a MMFB operating to 60 krpm and showing substantial mechanical energy dissipation characteristics. This paper details further experimental work and reports MMFB rotordynamic force coefficients. The test rig comprises of a turbocharger driven shaft and overhung journal onto which a MMFB is installed. A soft elastic support structure akin to a squirrel cage holds the bearing, aiding to its accurate positioning relative to the journal. Two orthogonally positioned shakers excite the test element via stingers. The test bearing comprises of a cartridge holding a Copper wire mesh ring, 2.7 mm thick, and a top arcuate foil. The bearing length and inner diameter are 38 mm and 36.5 mm, respectively. Experiments were conducted with no rotation and with journal spinning at 40–50 krpm, with static loads of 22 N and 36 N acting on the bearing. Dynamic load tests spanning frequencies from 150 to 450 Hz were conducted while keeping the amplitude of bearing displacements at 20 μm, 25 μm, and 30 μm. With no journal spinning, the force coefficients represent the bearing elastic structure alone since the journal and bearing are in contact. The direct stiffnesses gradually increase with frequency while the direct damping coefficients drop quickly at low frequencies (< 200 Hz) and level off above this frequency. The damping combines both viscous and material types from the gas film and mesh structure. Journal rotation induces airborne operation with a hydrodynamic gas film separating the rotor from its bearing. Hence, cross-coupled stiffness coefficients appear though with magnitudes lower than those of the direct stiffnesses. The direct stiffnesses, 0.4 to 0.6 MN/m within 200–400 Hz, are slightly lower in magnitude as those obtained without journal rotation suggesting the air film stiffness is quite high. Bearing direct stiffnesses are inversely proportional to the bearing motion amplitudes, whereas the direct equivalent viscous damping coefficients do not show any noticeable variation. All measurements evidence a test bearing system with material loss factor (γ) ∼ 1.0, indicating significant mechanical energy dissipation ability.

THE CALCULATION OF DYNAMIC CHARACTERISTICS OF BEARINGS RADIAL PETAL MICRO-TURBINES DISTRIBUTED POWER SYSTEMS

2021 ◽  
Vol 2 ◽  
pp. 150-158
Author(s):  
A.V. SYTIN ◽  
А.А. KIRICHEK ◽  
О.А. IVANOV ◽  
S.S. VNUYKOV
Keyword(s):  
High Speed ◽  
Excitation Frequency ◽  
Small Towns ◽  
Theory Of Elasticity ◽  
Lubricant Layer ◽  
Mass Model ◽  
Industrial Enterprises ◽  
Damping Coefficients ◽  
Gas Dynamic ◽  
Stiffness And Damping

The paper briefly describes the current state of distributed energy systems, which acts as an advanced supplier of electric and thermal energy to small towns, towns and villages, industrial enterprises, livestock farms, etc. The main working unit of this type of systems are micro turbine installations of low power. For these types of installations, the most critical and critical part is the rotary support unit. The article deals with the issues of modeling dynamic processes in rotor-bearing units in the presence of lobed gas-dynamic bearings with corrugated elements, which are currently promising supports for rotors of high-speed machines. A solution to the complex problem of calculating lobe gas-dynamic bearings based on a joint solution of gas dynamics, thermo physics and the theory of elasticity is presented. On the basis of the dynamics equations, a single-mass model of a rigid symmetric rotor on elastic supports consisting of several elastic-pliable layers: thin-walled lobes and corrugated elements is presented. The determination of the pressure field is based on the solution of the Reynolds equation, generalized to the case of a two-dimensional turbulent flow of a viscous compressible lubricant. Based on the expressions of the theory of elasticity, the problem of calculating the deformations of the lobe and the circular corrugated element of the lobe bearing under the action of gas-dynamic forces in the lubricating layer is considered. By linearization under the assumption of small displacements from the equilibrium position, based on the Taylor series expansion in the vicinity of the stationary position, the dependences of the stiffness and damping coefficients for this type of support are determined. In this case, the stiffness of the system "lubricating gas layer-petal-corrugated element" is represented as the sum of the successively connected: the stiffness of the gas lubricant layer, the stiffness of the elastic petal and the stiffness of the corrugated element. Damping system LGDP is the same way "lubricating air layer – petal – circular corrugated elements", which can be represented as the sum of series-connected dampers: a layer of gas lubrication, damping and damping petal corrugation. The article presents the stiffness and damping coefficients calculated by this method, depending on the ratio of the excitation frequency of the rotor pin to the angular velocity.

Identification of Rotordynamic Force Coefficients of a Metal Mesh Foil Bearing Using Impact Load Excitations

2010 ◽  
Author(s):  
Luis San Andre´s ◽  
Thomas Abraham Chirathadam
Keyword(s):  
High Speed ◽  
Impact Load ◽  
Mechanical Energy ◽  
Excitation Frequency ◽  
Forced Response ◽  
Dynamic Force ◽  
Rotating Shaft ◽  
Metal Mesh ◽  
Force Coefficients ◽  
Shaft Rotation

Metal mesh foil bearings (MMFB) are an inexpensive compliant gas bearing type that aims to enable high speed, high temperature operation of small turbomachinery. A MMFB with an inner diameter of 28.00 mm and length of 28.05 mm is constructed with low cost and common materials. The bearing incorporates a copper mesh ring, 20% in compactness and offering large material damping, beneath a 0.127mm thick preformed top foil. Prior experimentation (published papers) provide the bearing structure force coefficients and the break away torque for bearing lift off. Presently, the MMFB replaces a compressor in a small turbocharger driven test rig. Impact load tests aid to identify the direct and cross-coupled rotor dynamic force coefficients of the floating MMFB while operating at a speed of 50 krpm. Tests conducted with and without shaft rotation show the MMFB direct stiffness is less than its structural (static) stiffness, ∼25% lower at an excitation frequency of 200 Hz. The thin air film acting in series with the metal mesh support, and separating the rotating shaft and the bearing inner surface while airborne, reduces the bearing stiffness. The equivalent viscous damping is nearly identical with and without shaft rotation. The identified loss factor, best representing the hysteretic type damping from the metal mesh, is high at ∼0.50 in the frequency range 0–200 Hz. This magnitude reveals large mechanical energy dissipation ability from the MMFB. The measurements also show appreciable cross directional motions from the unidirectional impact loads, thus generating appreciable cross coupled force coefficients. Rotor speed coast down measurements reveal pronounced subsynchronous whirl motion amplitudes locked at distinct frequencies. The MMFB stiffness hardening nonlinearity produces the rich frequency forced response. The synchronous as well as subsynchronous motions peak while the shaft traverses its critical speeds. The measurements establish reliable operation of the test MMFB while airborne.

Performance Characteristics of Metal Mesh Foil Bearings: Predictions vs. Measurements

2013 ◽  
Author(s):  
Luis San Andrés ◽  
Thomas Abraham Chirathadam
Keyword(s):  
Low Cost ◽  
Excitation Frequency ◽  
Element Model ◽  
Rotating Machinery ◽  
Performance Characteristics ◽  
Dynamic Force ◽  
Metal Mesh ◽  
Force Coefficients ◽  
Foil Bearings ◽  
Damping Coefficients

Proven low-cost gas bearing technologies are sought to enable more compact rotating machinery products with extended maintenance intervals. The paper presents an analysis for predicting the static and dynamic forced performance characteristics of metal mesh foil bearings (MMFBs) which comprise of a top foil supported on a layer of metal mesh of certain compactness. The analysis couples a finite element model of the top foil and underspring support with the gas film Reynolds equation. Comparison of predictions against laboratory measurements with two bearings aims to validate the analysis. The predicted drag friction factor in one bearing (L = D = 28.00 mm) during full film operation is just f ∼ 0.03 at ∼ 50 krpm, agreeing well with measurements at increasing applied loads. The predictions further elucidate the effect of the applied load and rotor speed on the bearing minimum film thickness, journal eccentricity and attitude angle. For a second bearing (L = 38.0 mm, D = 36.5 mm), predicted bearing force coefficients show magnitudes comparable with the measurements, with less than 20% difference, in the 250–350 Hz excitation frequency range. While the predicted direct stiffness coefficients are rather constant, the experimental force coefficients increase with frequency (max. 400 Hz), due mainly to the increasing amplitudes of dynamic force applied to excite the bearing with a set amplitude of motion. The analysis under predicts the direct damping coefficients at high frequencies (>300 Hz). The cross-coupled stiffness and damping coefficients are typically lower (< 40%) than the direct ones. The bearings operated stable at all speeds without any sub synchronous whirl. The reasonable agreement of the predictions with the available test data promote the better design and further development of MMFB supported rotating machinery.

Identification of Rotordynamic Force Coefficients of a Metal Mesh Foil Bearing Using Impact Load Excitations

2011 ◽  
Vol 133 (11) ◽  
Author(s):  
Luis San Andrés ◽  
Thomas Abraham Chirathadam
Keyword(s):  
High Speed ◽  
Impact Load ◽  
Mechanical Energy ◽  
Excitation Frequency ◽  
Forced Response ◽  
Dynamic Force ◽  
Rotating Shaft ◽  
Metal Mesh ◽  
Force Coefficients ◽  
Shaft Rotation

Metal mesh foil bearings (MMFBs) are inexpensive compliant gas bearing type that aim to enable high speed, high temperature operation of small turbomachinery. A MMFB with an inner diameter of 28.00 mm and length of 28.05 mm is constructed with low cost and common materials. The bearing incorporates a copper mesh ring, 20% in compactness, and offering large material damping beneath a 0.127 mm thick preformed top foil. Prior experimentations (published papers) provide the bearing structure force coefficients and the break away torque for bearing lift off. Presently, the MMFB replaces a compressor in a small turbocharger driven test rig. Impact load tests aid to identify the direct and cross-coupled rotor dynamic force coefficients of the floating MMFB while operating at a speed of 50 krpm. Tests conducted with and without shaft rotation show the MMFB direct stiffness is less than its structural (static) stiffness, ∼25% lower at an excitation frequency of 200 Hz. The thin air film acting in series with the metal mesh support and separating the rotating shaft and the bearing inner surface while airborne reduces the bearing stiffness. The equivalent viscous damping is nearly identical with and without shaft rotation. The identified loss factor, best representing the hysteretic type damping from the metal mesh, is high at ∼0.50 in the frequency range 0–200 Hz. This magnitude reveals large mechanical energy dissipation ability from the MMFB. The measurements also show appreciable cross directional motions from the unidirectional impact loads, thus generating appreciable cross-coupled force coefficients. Rotor speed coast down measurements reveal pronounced subsynchronous whirl motion amplitudes locked at distinct frequencies. The MMFB stiffness hardening nonlinearity produces the rich frequency forced response. The synchronous as well as subsynchronous motions peak while the shaft traverses its critical speeds. The measurements establish reliable operation of the test MMFB while airborne.

Identification of Structural Stiffness and Energy Dissipation Parameters in a Second Generation Foil Bearing: Effect of Shaft Temperature

2010 ◽  
Vol 133 (3) ◽  
Author(s):  
Luis San Andrés ◽  
Keun Ryu ◽  
Tae Ho Kim
Keyword(s):  
Energy Dissipation ◽  
Dynamic Load ◽  
Loss Factor ◽  
Static Load ◽  
Mechanical Energy ◽  
Excitation Frequency ◽  
Structural Stiffness ◽  
Foil Bearings ◽  
Foil Bearing ◽  
Mechanical Energy Dissipation

Established high temperature operation of gas foil bearings (GFB) is of great interest for gas turbine applications. The effects of (high) shaft temperature on the structural stiffness and mechanical energy dissipation parameters of a foil bearing (FB) must be assessed experimentally. Presently, a hollow shaft warmed by an electric heater holds a floating second generation FB that is loaded dynamically by an electromagnetic shaker. In tests with the shaft temperature up to 184°C, the measurements of dynamic load and ensuing FB deflection render the bearing structural parameters, stiffness and damping, as a function of excitation frequency and amplitude of motion. The identified FB stiffness and viscous damping coefficients increase with shaft temperature due to an increase in the FB assembly interference or preload. The bearing material structural loss factor best representing mechanical energy dissipation decreases slightly with shaft temperature while increasing with excitation frequency. Separate static load measurements on the bearing also make evident the preload of the test bearing-shaft system at room temperature. The loss factor obtained from the area inside the hysteresis loop of the static load versus the deflection curve agrees remarkably with the loss factor obtained from the dynamic load measurements. The static procedure offers substantial savings in cost and time to determine the energy dissipation characteristics of foil bearings. Post-test inspection of the FB reveals sustained wear at the locations, where the bumps contact the top foil and the bearing sleeve inner surface, thus, evidences the bearing energy dissipation by dry friction.

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