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Torsional & Lateral Vibration analysis

Safe rotating machinery operation requires
smart rotor-dynamic, torsional & lateral vibration analyses

Rotating machinery (compressors, pumps, turbines, etc.) is subject to cyclic forces along the shaft line mainly due to load fluctuations, unbalancing, instability, misalignment etc. The variable conditions of pressure, handled capacity and speed as well as the geometry of some components produce exciting forces and therefore vibrations, torsional and lateral. Vibration can be very harmful for the whole machinery, in particular when one or more harmonics are close to one or more natural frequencies, or the shaft line is in a resonant condition.
To avoid resonances and damage to machinery a Torsional and /or Lateral Vibration Analysis is strongly recommended.

CST experience and solution

CST developed a proprietary software CSTors to perform very accurate torsional and lateral analysis. CSTors is kept continuously up-to-date to the best of breed available technology. In addition, CST has long-standing experience gained by troubleshooting machines of various types. CST can deliver the most appropriate torsional and lateral vibration analysis to prevent vibrational issues on rotating equipment, both for new and existing units.
CST calculation methodology focuses on:

  • Equivalent shaft calculation by FEM analysis
  • Optimum flywheel and coupling selection
  • Exciting harmonics by CST SW ReciPerf
  • Electric motor air-gap effect evaluation

CST proprietary software CSTors allows to supply API 618/684 studies with:

  • Modal Analysis to find possible resonances
  • Steady-state & Transient Forced Response Analysis
  • Post process evaluation of torsional shaft stresses and endurance limits and induction motor current pulsations

Some examples of cst torsional/lateral vibration study


Change of the driver of a reciprocating compressor required an accurate torsional analysis to assess the proper operation of the new machine train


Impeller destroyed twice at first start-up. Lateral analysis revealed wrong clearance on bearings being the cause. Clearance correction was the solution


High vibrations were encountered during the commissioning of a permanent-magnet electric motor detected with the detailed lateral analysis. The rotor had to be re-designed to avoid the first critical speed within the operating range.