Numerical study of the effect of the nonlinear gain compression on the dynamic behavior of directly modulated semiconductor lasers

1996 ◽  
Author(s):  
Guillermo Carpintero ◽  
Horacio Lamela
Keyword(s):  
Semiconductor Lasers ◽  
Dynamic Behavior ◽  
Numerical Study ◽  
Nonlinear Gain ◽  
Gain Compression

On Instability of Overhung Centrifugal Compressors

1999 ◽  
Author(s):  
François Berot ◽  
Hervé Dourlens
Keyword(s):  
Thermal Effect ◽  
Dynamic Behavior ◽  
Numerical Study ◽  
Technical Solution ◽  
Test Results ◽  
Centrifugal Compressors ◽  
The Third ◽  
Instability Problem ◽  
Angle Rotation ◽  
Bearing Design

This paper describes the synchronous vibration instability problem that occurred on a series of large overhung centrifugal compressors. The first part of this paper deals with the identification and display of the instability phenomenon: cyclic vibration amplitude variations and phase angle rotation occuring during testing of overhung centrifugal compressors. After numerical simulations and analysis of the test results, the bearing design has been identified as the cause of the problem. The second part describes the numerical study of the instability of the compressor. This problem is related to the eccentricity of the shaft in the bearing and to the shape of its orbit. We have investigated and propose different solutions to avoid this unstable dynamic behavior. These solutions have been tested on different compressors and have confirmed the results of the numerical analysis. The third part reminds a link between the thermal effect occurring in the bearings, the numerical results and the tested dynamic behavior of the compressor. Recently, some authors such as Keogh et al. (1994) and Liebich et al. (1994) have noticed and studied this unstable behavior. Althougth the nature of the phenomenon seems to be known (de Jongh et al., 1984) (Faulkner et al., 1997a, 1997b), no universal technical solution to this important problem has been found. The contribution of this work is to present another case of the influence of the thermal effect on the dynamic behavior of an overhung compressor. We present the typical symptoms of the phenomenon, explain it, and propose the solutions we have used to avoid the problem.

scholarly journals Numerical Study on the Dynamic Behavior of a Francis Turbine Runner Model with a Crack

Energies ◽  
2018 ◽  
Vol 11 (7) ◽  
pp. 1630 ◽  
Author(s):  
Ming Zhang ◽  
David Valentin ◽  
Carme Valero ◽  
Mònica Egusquiza ◽  
Weiqiang Zhao
Keyword(s):  
Dynamic Behavior ◽  
Numerical Study ◽  
Francis Turbine ◽  
Turbine Runner
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