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Rotordynamic and thermal analyses of compliant flexure pivot tilting pad gas bearingsSim, Kyu-Ho 15 May 2009 (has links)
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.
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Rotordynamic and thermal analyses of compliant flexure pivot tilting pad gas bearingsSim, Kyu-Ho 15 May 2009 (has links)
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.
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Fuel economy modeling of light-duty and heavy-duty vehicles, and coastdown studyAtes, Murat 03 September 2009 (has links)
Development of a fuel economy model for light-duty and heavy-duty vehicles is
part of the Texas Department of Transportation’s “Estimating Texas Motor Vehicle
Operating Costs” project. A literature review for models that could be used to predict the
fuel economy of light-duty and heavy-duty vehicles resulted in selection of coastdown
coefficients to simulate the combined effects of aerodynamic drag and tire rolling
resistance.
For light-duty vehicles, advantage can be taken of the modeling data provided by
the United States Environmental Protection Agency (EPA) for adjusting chassis
dynamometers to allow accurate determination of emissions and fuel economy so that
compliance with emissions standards and Corporate Average Fuel Economy (CAFE)
regulations can be assessed. Initially, EPA provided vehicle-specific data that were
relevant to a physics-based model of the forces at the tire-road interface. Due to some
limitations of these model parameters, EPA now provides three vehicle-specific
coefficients obtained from vehicle coastdown data. These coefficients can be related
back to the original physics-based model of the forces at the tire-road interface, but not in
a manner that allows the original modeling parameters to be extracted from the
coastdown coefficients. Nevertheless, as long as the operation of a light-duty vehicle
does not involve extreme acceleration or deceleration transients, the coefficients available
from the EPA can be used to accurately predict fuel economy.
Manufacturers of heavy-duty vehicles are not required to meet any sort of CAFE
standards, and the engines used in heavy-duty vehicles, rather than the vehicles
themselves, are tested (using an engine dynamometer) to determine compliance with
emissions standards. Therefore, EPA provides no data that could be useful for predicting
the fuel economy of heavy-duty vehicles. Therefore, it is necessary to perform heavyduty
coastdown tests in order to predict fuel economy, and use these tests to develop
vehicle-specific coefficients for the force at the tire-road interface. Given these
coefficients, the fuel economy of a heavy-duty vehicle can be calculated for any driving
schedule. The heavy-duty vehicle model developed for this project is limited to pre-2007
calendar year heavy-duty vehicles due to the adverse effects of emissions components
that were necessary to comply with emissions standards that went into effect January
2007. / text
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