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Torsional Dynamics

Torque fluctuations within machine trains can yield torsional vibrations and stresses sufficient to cause undetected and catastrophic shafting failures.

BRG conducts several different types of analysis to help ensure such torsional failures are avoided:

Potential interferences between train natural frequencies and torque excitation sources are identified. In addition, the influences of torque distribution and coupling design can be assessed using the resulting mode shapes.
Small torsional damping within many trains causes some interferences to be well amplified resulting in large torsional vibrations. To determine the stresses caused by such vibrations, this analysis applies steady state oscillating torques. Locations with high stress concentration factors, such as keyways, are examined for their safety factor against high cycle fatigue failure.
Train startups and electrical events, such as short circuit and recloser faults, require analysis in the time domain. Such events and their resulting motions can also be nonlinear due to the presence of gear backlash, elastomeric or torque-limited couplings. Transient analysis, in conjunction with cumulative fatigue damage analysis, provides a vital tool for evaluating components' life when subjected to these events.

 

Campbell diagram for compressor train driven by a 9 MW synchronous motor


Campbell diagram for compressor train driven
by a 9 MW synchronous motor
Mode shape for an integrally geared compressor train that experienced a catastrophic torsional fatigue failure after 125 starts Mode shape for an integrally geared compressor train that experienced a catastrophic torsional fatigue failure after 125 starts
In some cases, resolving a problem may require measurement of the machine's torsional vibrations using special instrumentation. BRG performs such vibration analysis when clients need these specialized field measurements.

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