The combination of a continuously modeled rotor supported by two worn nonlinear finite fluid film... more The combination of a continuously modeled rotor supported by two worn nonlinear finite fluid film bearings is the main objective of this work. The rotor was modeled using the Rayleigh equation of motion, and the bearing forces are computed by solving the Reynolds equation using the finite difference method. Additionally the internal damping effect of the rotor is incorporated into the current approach and the wear is introduced using the well known Dufrane wear model. In current work the system appears strongly nonlinear due to both the fluid film forces and the presence of wear. Time histories for system start up and steady state operations under external excitation are analyzed simultaneously in time and frequency domain in order to invest the properties that the wear introduces in the system behavior. Specific components are judged very sensitive to wear development and are used in order to identify the wear extension through the bearing surface.
The hysteretic damping is a measure of the dissipating energy during a period of vibration of the... more The hysteretic damping is a measure of the dissipating energy during a period of vibration of the structure and it is a function of the induced stress particularly at the resonance. The crack presence in a structure introduces a local flexibility modelled by a compliance matrix with dimension depending on the degrees of freedom considered. Here the crack is considered to remain open avoiding thus the nonlinearity due to the closing crack. As a stress function the hysteretic damping is initially arbitrarily selected, then the stress of the structure is calculated and the damping is determined. If the damping is different from the initially selected, the procedure is repeated until selected and calculated hysteretic dampings agree. Experimentally in this work the hysteretic damping is measured using the logarithmic decrement or the half bandwidth methods for the intact and the cracked structure. It has been observed that the presence of a crack in a structure increases substantially t...
ABSTRACT The quality of surface of a journal bearing system affects significantly its performance... more ABSTRACT The quality of surface of a journal bearing system affects significantly its performance and its dynamic characteristics. Manufacturing errors can lead to a series of defects in the surface of the bearing, such as out-of-roundness, misalignment and others. Out-ofroundness can be caused by spindle error motion. Since the prediction of the actual characteristics of a journal bearing should include possible manufacturing errors, modeling a journal bearing with such kinds of surface irregularities could provide with a measure of tolerance towards those defects. In this work the model of a bearing is studied with the ANSYS Multiphysics physical simulation software. The surface of the bearing is formed as a sum of sinusoidal waves with different amplitude and wavelength in order to study the relationship between the out-of-roundness defect and the journal bearing operating properties. The lubricant flow is simulated using the Navier-Stokes equations, giving the opportunity to investigate the effect of the surface irregularities on the lubricant flow characteristics. The wavelength and the amplitude of the roundness error will be related directly with the attitude locus which means influence on the journal bearing equilibrium position. Also roundness will be examined against the friction coefficient of the bearing as well as the load capacity of the bearing. The effect on pressure build up, stiffness and damping coefficients are also examined.
The combination of a continuously modeled rotor supported by two worn nonlinear finite fluid film... more The combination of a continuously modeled rotor supported by two worn nonlinear finite fluid film bearings is the main objective of this work. The rotor was modeled using the Rayleigh equation of motion, and the bearing forces are computed by solving the Reynolds equation using the finite difference method. Additionally the internal damping effect of the rotor is incorporated into the current approach and the wear is introduced using the well known Dufrane wear model. In current work the system appears strongly nonlinear due to both the fluid film forces and the presence of wear. Time histories for system start up and steady state operations under external excitation are analyzed simultaneously in time and frequency domain in order to invest the properties that the wear introduces in the system behavior. Specific components are judged very sensitive to wear development and are used in order to identify the wear extension through the bearing surface.
The hysteretic damping is a measure of the dissipating energy during a period of vibration of the... more The hysteretic damping is a measure of the dissipating energy during a period of vibration of the structure and it is a function of the induced stress particularly at the resonance. The crack presence in a structure introduces a local flexibility modelled by a compliance matrix with dimension depending on the degrees of freedom considered. Here the crack is considered to remain open avoiding thus the nonlinearity due to the closing crack. As a stress function the hysteretic damping is initially arbitrarily selected, then the stress of the structure is calculated and the damping is determined. If the damping is different from the initially selected, the procedure is repeated until selected and calculated hysteretic dampings agree. Experimentally in this work the hysteretic damping is measured using the logarithmic decrement or the half bandwidth methods for the intact and the cracked structure. It has been observed that the presence of a crack in a structure increases substantially t...
ABSTRACT The quality of surface of a journal bearing system affects significantly its performance... more ABSTRACT The quality of surface of a journal bearing system affects significantly its performance and its dynamic characteristics. Manufacturing errors can lead to a series of defects in the surface of the bearing, such as out-of-roundness, misalignment and others. Out-ofroundness can be caused by spindle error motion. Since the prediction of the actual characteristics of a journal bearing should include possible manufacturing errors, modeling a journal bearing with such kinds of surface irregularities could provide with a measure of tolerance towards those defects. In this work the model of a bearing is studied with the ANSYS Multiphysics physical simulation software. The surface of the bearing is formed as a sum of sinusoidal waves with different amplitude and wavelength in order to study the relationship between the out-of-roundness defect and the journal bearing operating properties. The lubricant flow is simulated using the Navier-Stokes equations, giving the opportunity to investigate the effect of the surface irregularities on the lubricant flow characteristics. The wavelength and the amplitude of the roundness error will be related directly with the attitude locus which means influence on the journal bearing equilibrium position. Also roundness will be examined against the friction coefficient of the bearing as well as the load capacity of the bearing. The effect on pressure build up, stiffness and damping coefficients are also examined.
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