Dynamic Effects Caused by the Non-Linear Behavior of Oil-Film Journal Bearings in Rotating Machines

2012 ◽  
Author(s):  
A. Vania ◽  
P. Pennacchi ◽  
S. Chatterton
Keyword(s):  
Dynamic Behavior ◽  
Journal Bearings ◽  
Rotating Machines ◽  
Dynamic Effects ◽  
Oil Film ◽  
Linear Behavior ◽  
Non Linear ◽  
Linear Effects ◽  
Harmonic Components ◽  
Very High

Many common faults and malfunctions in rotating machines mainly cause synchronous vibrations (1X). Very high 1X vibration levels can occur, in case of severe faults. Large journal orbits inside oil-film journal bearings may generate non-linear effects in the oil-film forces, whose presence can be detected by means of the appearance of not negligible super-synchronous vibrations of the shafts. In this paper, a model-based method has been used to study the effects of non-linear oil-film forces on the machine dynamic behavior that may occur during runups and rundowns. In general, it is possible to suppose that the importance of the non-linear behavior of oil-film journal bearings, and then the level of the super-synchronous vibrations, increases with the amplitude of the 1X vibrations caused by the primary fault. However, the numerical results of this study and the experimental evidences found in the monitoring data of a real machine have shown that the super-synchronous harmonic components of the oil-film forces may excite resonances of the shaft-train causing unexpected amplifications of the super-synchronous vibrations. This may make difficult the recognition of the presence of non-linear effects in the machine dynamic behavior and the identification of the actual cause of abnormal vibrations.

scholarly journals A Novel Ultrasonic Technique to Detect Damage Evolution in Quasi-Brittle Materials

2007 ◽  
Vol 347 ◽  
pp. 633-638 ◽  
Author(s):  
Paola Antonaci ◽  
Pietro G. Bocca ◽  
Davide Masera ◽  
Nicola Maria Pugno ◽  
Marco Scalerandi ◽  
...  
Keyword(s):  
Signal Analysis ◽  
Plain Concrete ◽  
Theoretical Models ◽  
Processing Technique ◽  
Signal Processing Technique ◽  
Signal Model ◽  
Multiple Signal Classification ◽  
Linear Behavior ◽  
Non Linear ◽  
Harmonic Components

The results of an experimental research on plain concrete are presented. The non-linear behavior of both virgin and damaged samples is investigated by means of ultrasonic tests: recent theoretical models, indeed, have pointed out that mono-frequency ultrasonic excitations bring to light such phenomena as harmonic generation and sidebands production, which are essentially due to the material classical or hysteretic non-linearity. The estimation of the harmonic components parameters (amplitudes and phases) is achieved through a signal processing technique based on MUltiple SIgnal Classification (MUSIC) system, which reveals to be optimal for the specific signal model here considered. The experiments described in this paper show that the material non-linear features increase with increasing level of internal micro-cracking, thus suggesting the possibility to use the ultrasonic signal analysis in the frequency domain as a valuable tool for damage assessment.

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