Rotordynamic and Thermal Analyses of Compliant Flexure Pivot Tilting Pad Gas Bearings PDF Download
Are you looking for read ebook online? Search for your book and save it on your Kindle device, PC, phones or tablets. Download Rotordynamic and Thermal Analyses of Compliant Flexure Pivot Tilting Pad Gas Bearings PDF full book. Access full book title Rotordynamic and Thermal Analyses of Compliant Flexure Pivot Tilting Pad Gas Bearings by Kyu-Ho Sim. Download full books in PDF and EPUB format.
Author: Kyu-Ho Sim
Publisher:
ISBN:
Category :
Languages : en
Pages :
Get Book Here
Book Description
Rotordynamic and thermal analyses of compliant flexure pivot tilting pad gas bearings were performed. First, compliant flexure pivot tilting pad gas bearings with pad radial compliance (CFTPBs) were introduced and designed for high-speed oil-free micro turbomachinery. The pad radial compliance was for accommodation of large rotor growth at high speeds. Parametric studies on pivot offset, preload, and tilting stiffness were performed using non-linear orbit simulations and coast-down simulations for an optimum design. Second, coast-down tests for imbalance response and stability of typical rotor-bearing system with a rigid rotor and two CFTPBs designed from the above design studies were conducted over operating speeds up to 55 krpm. Prediction of synchronous rotordynamic responses was made in terms of critical speed for various imbalance modes by using a rotordynamic analysis software (XLTRC), combined with dynamic force coefficients from the perturbation analysis. For stability analyses, a generalized orbit simulation program was developed considering both the translational and angular rotor motions with two different bearings. Linear stability analyses for the conical vibration mode were also performed by using XLTRC and the perturbation analysis based on the Lund method. Predictions of whirl speed showed good agreement to the tests, but the estimated onset speed of instability appeared lower than the measured instability. Finally, a new thermo-hydrodynamic analysis model of a typical rotor-bearing system with CFTPBs was presented, accompanying linear perturbation analyses to investigate thermal effects on the rotordynamic performance. A numerical procedure was established for solving the generalized Reynolds equation, the 3-D energy equation, and the associated boundary conditions at the pad inlet flow and solid walls (rotor and pad) simultaneously. Parametric studies were conducted on nominal clearance and external load. Nominal clearance showed significant influence on temperature fields, and external load had uneven thermal effects among pads. Case studies with heat flux and temperature boundary conditions on the rotor end surface were performed to simulate various working conditions of the bearing. Large rotor thermal growth due to the high rotor temperature showed noticeable influence on rotordynamic performance by increasing direct stiffness and damping coefficients.
Author: Kyu-Ho Sim
Publisher:
ISBN:
Category :
Languages : en
Pages :
Get Book Here
Book Description
Rotordynamic and thermal analyses of compliant flexure pivot tilting pad gas bearings were performed. First, compliant flexure pivot tilting pad gas bearings with pad radial compliance (CFTPBs) were introduced and designed for high-speed oil-free micro turbomachinery. The pad radial compliance was for accommodation of large rotor growth at high speeds. Parametric studies on pivot offset, preload, and tilting stiffness were performed using non-linear orbit simulations and coast-down simulations for an optimum design. Second, coast-down tests for imbalance response and stability of typical rotor-bearing system with a rigid rotor and two CFTPBs designed from the above design studies were conducted over operating speeds up to 55 krpm. Prediction of synchronous rotordynamic responses was made in terms of critical speed for various imbalance modes by using a rotordynamic analysis software (XLTRC), combined with dynamic force coefficients from the perturbation analysis. For stability analyses, a generalized orbit simulation program was developed considering both the translational and angular rotor motions with two different bearings. Linear stability analyses for the conical vibration mode were also performed by using XLTRC and the perturbation analysis based on the Lund method. Predictions of whirl speed showed good agreement to the tests, but the estimated onset speed of instability appeared lower than the measured instability. Finally, a new thermo-hydrodynamic analysis model of a typical rotor-bearing system with CFTPBs was presented, accompanying linear perturbation analyses to investigate thermal effects on the rotordynamic performance. A numerical procedure was established for solving the generalized Reynolds equation, the 3-D energy equation, and the associated boundary conditions at the pad inlet flow and solid walls (rotor and pad) simultaneously. Parametric studies were conducted on nominal clearance and external load. Nominal clearance showed significant influence on temperature fields, and external load had uneven thermal effects among pads. Case studies with heat flux and temperature boundary conditions on the rotor end surface were performed to simulate various working conditions of the bearing. Large rotor thermal growth due to the high rotor temperature showed noticeable influence on rotordynamic performance by increasing direct stiffness and damping coefficients.
Author: Aaron Michael Rimpel
Publisher:
ISBN:
Category :
Languages : en
Pages :
Get Book Here
Book Description
Hydrodynamic flexure pivot tilting pad gas bearings (FPTPGBs) can enable successful operation of oil-free microturbomachinery. This work presents the experimental and analytical study of such bearings with different damper configurations. A test rig was constructed that could safely operate a ~28.6 mm, 0.8 kg rotor beyond 120 krpm. A time domain orbit simulation, which integrates nonlinear equations of motion for the rotor-bearing elements, was implemented as the primary analysis tool to predict rotor-bearing responses to imbalance, the presence and location of critical speeds, etc. Complementary analyses were also performed with a model that uses linear bearing impedance coefficients to predict system natural frequencies. Imbalance response testing verified that the rotor-bearing system behaved linearly in the region above the critical speed, and orbit simulations predicted the response to a calibrated imbalance with notable agreement. Viscoelastic dampers added behind the FPTPGB pads delayed the onset of subsynchronous vibrations (from 43 krpm without damper to above 50 krpm with damper) of the system with bearing clearance increased by shims. Midrange subsynchronous vibrations initiated at ~20 krpm were eventually suppressed by ~25 krpm due to the stabilizing effect of rotor centrifugal growth. The viscoelastic dampers had a negligible effect on suppressing these midrange subsynchronous vibrations in experiments, but this was not demonstrated in simulations, presumably due to much lower stiffness contribution of the damper at lower frequencies. The ideal, perfectly aligned models in the simulations were able to tolerate shims up to only 10% of nominal clearance, but the test rig exhibited surprising stability with shims as much as 200% of nominal clearance; this increase may be caused by imposed eccentricities due to misalignments in the test rig. FPTPGBs supported by compliant bump foils can have the ability to tolerate rotor misalignments and shock loading like foil gas bearings. Simulation studies on imbalance response characteristics for several bearing shell mass and support stiffness configurations present initial design guidelines for the application. Namely, results showed that FPTPGBs favored large bearing shell mass and large support stiffness, while FPTPGBs with radial compliance favored small bearing shell mass with large support stiffness.
Author: Adnan Mahmoud Al-Ghasem
Publisher:
ISBN:
Category :
Languages : en
Pages :
Get Book Here
Book Description
This thesis presents the dynamic and static forced performance of a flexure-pivot tilting-pad bearing load between pad (LBP) configuration for different rotor speeds and bearing unit loadings. The bearing has the following design parameters: 4 pads with pad arc angle 72° and 50% pivot offset, pad axial length 0.0762 m (3 in), pad radial clearance 0.254 mm (0.010 in), bearing radial clearance 0.1905 mm (0.0075 in), preload 0.25 and shaft nominal diameter of 0.11684 m (4.600 in). The dynamic coefficients and the static performance parameters of the FPB have been compared with the theoretical predictions using the isothermal analysis from the rotordynamic software suite XLTRC2-XLTFPBrg. The bearing shows a small attitude angle, about 10°, which indicates small crosscoupling stiffnesses. The pad temperatures increase in the circumferential direction of rotation with speed and load. The pads maximum temperature was measured near the trailing edge. The dependency of the stiffness and damping coefficients on the excitation frequency has been studied. The frequency dependency in the dynamic coefficients was removed by introducing an added mass coefficient to the bearing model. The direct added mass coefficients were around 32 kg. The direct stiffness and damping coefficients increase with load, while increasing and decreasing with rotor speed, respectively. A small whirl frequency ratio (WFR) was found of about 0.15, and it decreases with load and increases with speed. A comparison between the dynamic stiffnesses using a Reynolds equation and the bulk-flow Navier-Stokes models with the experimental dynamic stiffnesses shows that the Reynolds model (even for laminar flows) is not adequate, and that the bulk-flow model should be used for rotordynamic coefficients prediction. The bulk-flow model in general predicts well the static performance parameters and the direct dynamic coefficients, and underpredicts the cross-coupled coefficients (overpredicts the stability).
Author:
Publisher:
ISBN:
Category :
Languages : en
Pages : 180
Get Book Here
Book Description
Author: Farid Al-Bender
Publisher: John Wiley & Sons
ISBN: 1118926560
Category : Technology & Engineering
Languages : en
Pages : 592
Get Book Here
Book Description
Comprehensive treatise on gas bearing theory, design and application This book treats the fundamental aspects of gas bearings of different configurations (thrust, radial, circular, conical) and operating principles (externally pressurized, self-acting, hybrid, squeeze), guiding the reader throughout the design process from theoretical modelling, design parameters, numerical formulation, through experimental characterisation and practical design and fabrication. The book devotes a substantial part to the dynamic stability issues (pneumatic hammering, sub-synchronous whirling, active dynamic compensation and control), treating them comprehensively from theoretical and experimental points of view. Key features: Systematic and thorough treatment of the topic. Summarizes relevant previous knowledge with extensive references. Includes numerical modelling and solutions useful for practical application. Thorough treatment of the gas-film dynamics problem including active control. Discusses high-speed bearings and applications. Air Bearings: Theory, Design and Applications is a useful reference for academics, researchers, instructors, and design engineers. The contents will help readers to formulate a gas-bearing problem correctly, set up the basic equations, solve them establishing the static and dynamic characteristics, utilise these to examine the scope of the design space of a given problem, and evaluate practical issues, be they in design, construction or testing.
Author: Zolton N. Nemeth
Publisher:
ISBN:
Category : Bearings (Machinery)
Languages : en
Pages : 36
Get Book Here
Book Description
Author: Zolton N. Nemeth
Publisher:
ISBN:
Category : Bearings (Machinery)
Languages : en
Pages : 52
Get Book Here
Book Description
Author: Jeffrey Scott Agnew
Publisher:
ISBN:
Category :
Languages : en
Pages :
Get Book Here
Book Description
Tests are performed on a flexure-pivot-pad tilting-pad bearing with a series integral squeeze film damper in load-between-pads configuration, with both active and locked damper. The damper effects are negated when locked, resulting in a flexure-pivot-pad bearing only. Experimental tests provide static performance data and dynamic stiffnesses from which rotordynamic coefficients are extracted. The following two excitation schemes are implemented: (1) multi-frequency, single direction excitation and (2) single-frequency, rotating load excitation (or "circular excitation"). The XLTRC2 Rotordynamics Software Suite© provides stiffness and damping coefficient, eccentricity, and power loss predictions for the locked damper bearing. Test conditions include the rotor-speed range of 4000-12000 rpm and the unit-load range of 0-862 kPa (0-125 psi). Dynamic tests utilizing the multi-frequency excitation for the locked and active damper bearing configurations both show that the real portion of the dynamic stiffness is well modeled by a quadratic curve fit, and the imaginary portion representing the damping is a linear function of excitation frequency. This means that frequency independent coefficients can be obtained when an added mass term is included. While stiffness coefficients are lower for the active damper bearing, damping coefficients remain almost constant between the locked and active damper configurations. A simulation shows that, although the damping coefficients do not change significantly, the reduced stiffness provided by the damper results in greater effective damping. Static performance tests for the locked and active damper bearing indicate low cross-coupling, as shown by the eccentricity and low attitude angle measurements. Pad metal temperature measurements show a smaller temperature differential along the pad arcs for the active damper bearing, than observed for the locked damper case. Frictional power loss is estimated based on lubricant temperature rise and does not differ significantly for the two bearing configurations.
Author: Edgar J. Gunter
Publisher:
ISBN:
Category : Gas-lubricated journal bearings
Languages : en
Pages : 236
Get Book Here
Book Description
Author: Mechanical Technology Incorporated
Publisher:
ISBN:
Category : Gas-lubricated bearings
Languages : en
Pages : 180
Get Book Here
Book Description
