Abstract
Unstable lateral vibrations caused by hydrodynamic journal bearings, seals or other fluid-mechanical interactions, are the most common types of rotordynamic instabilities in high-speed turbomachinery. Mechanically, high-speed turbomachines are often modeled as rotorbearing systems. The rotor can usually be assumed as a linear system consisting of shaft and disk elements, whereas the bearings and seals are sources of fluid forces which are highly nonlinear in nature. When large vibration amplitudes occur, e.g. due to unbalance, the linearized coefficient approach may not be accurate enough and the concept of quasi-linear bearing dynamic coefficients is introduced. Studies of the stability of typical rotor-bearing systems are carried out by means of linear, quasi-linear (method of averaging), and nonlinear (direct numerical integration) methods. Results obtained from these methods are compared. The most important finding of this study is that the stability threshold can be favorably or adversely affected by nonlinearity due to unbalance, depending mainly on the shaft flexibility and the type of instability. In the case of bearing induced instability, the addition of unbalance tends to improve the stability of the system. However, for very flexible rotors supported on tilting-pad journal bearings and subjected to aerodynamic cross-coupling, increasing the unbalance lowers the instability threshold.
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Citation Formats
Hung, Chan Siu.
Nonlinear analysis of rotordynamic instabilities in high-speed turbomachinery.
Norway: N. p.,
1992.
Web.
Hung, Chan Siu.
Nonlinear analysis of rotordynamic instabilities in high-speed turbomachinery.
Norway.
Hung, Chan Siu.
1992.
"Nonlinear analysis of rotordynamic instabilities in high-speed turbomachinery."
Norway.
@misc{etde_10120676,
title = {Nonlinear analysis of rotordynamic instabilities in high-speed turbomachinery}
author = {Hung, Chan Siu}
abstractNote = {Unstable lateral vibrations caused by hydrodynamic journal bearings, seals or other fluid-mechanical interactions, are the most common types of rotordynamic instabilities in high-speed turbomachinery. Mechanically, high-speed turbomachines are often modeled as rotorbearing systems. The rotor can usually be assumed as a linear system consisting of shaft and disk elements, whereas the bearings and seals are sources of fluid forces which are highly nonlinear in nature. When large vibration amplitudes occur, e.g. due to unbalance, the linearized coefficient approach may not be accurate enough and the concept of quasi-linear bearing dynamic coefficients is introduced. Studies of the stability of typical rotor-bearing systems are carried out by means of linear, quasi-linear (method of averaging), and nonlinear (direct numerical integration) methods. Results obtained from these methods are compared. The most important finding of this study is that the stability threshold can be favorably or adversely affected by nonlinearity due to unbalance, depending mainly on the shaft flexibility and the type of instability. In the case of bearing induced instability, the addition of unbalance tends to improve the stability of the system. However, for very flexible rotors supported on tilting-pad journal bearings and subjected to aerodynamic cross-coupling, increasing the unbalance lowers the instability threshold. The numerical integration results confirm the predictions of the quasi-linear method. Other results such as the whirl/speed ratio, eigenvalue sensitivity to speed change, etc, can be useful information for turbomachinery design and diagnosis purposes. 106 refs., 72 figs.}
place = {Norway}
year = {1992}
month = {Dec}
}
title = {Nonlinear analysis of rotordynamic instabilities in high-speed turbomachinery}
author = {Hung, Chan Siu}
abstractNote = {Unstable lateral vibrations caused by hydrodynamic journal bearings, seals or other fluid-mechanical interactions, are the most common types of rotordynamic instabilities in high-speed turbomachinery. Mechanically, high-speed turbomachines are often modeled as rotorbearing systems. The rotor can usually be assumed as a linear system consisting of shaft and disk elements, whereas the bearings and seals are sources of fluid forces which are highly nonlinear in nature. When large vibration amplitudes occur, e.g. due to unbalance, the linearized coefficient approach may not be accurate enough and the concept of quasi-linear bearing dynamic coefficients is introduced. Studies of the stability of typical rotor-bearing systems are carried out by means of linear, quasi-linear (method of averaging), and nonlinear (direct numerical integration) methods. Results obtained from these methods are compared. The most important finding of this study is that the stability threshold can be favorably or adversely affected by nonlinearity due to unbalance, depending mainly on the shaft flexibility and the type of instability. In the case of bearing induced instability, the addition of unbalance tends to improve the stability of the system. However, for very flexible rotors supported on tilting-pad journal bearings and subjected to aerodynamic cross-coupling, increasing the unbalance lowers the instability threshold. The numerical integration results confirm the predictions of the quasi-linear method. Other results such as the whirl/speed ratio, eigenvalue sensitivity to speed change, etc, can be useful information for turbomachinery design and diagnosis purposes. 106 refs., 72 figs.}
place = {Norway}
year = {1992}
month = {Dec}
}