Mechanical Vibration » Stability Analysis

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Stability Analysis

The rotor stability analysis is used to estimate the high amplification factor of first critical speed for sensitive machine, and it is composed with simplified Level I and detailed Level II analysis. Stability study has two (2) purposes: first, it provides an initial screening to identify rotors that do not required a more detailed study. Second, this stability study specifies a standardized procedure applied to equipment manufacturers. This analysis is one of procedure of lateral study (rotordynamics), and damping and instability factor is calculated.

Bearing Type for Stability
Bearing Type for Stability

Stability Study

Stability analysis includes below kinds of procedure;

  • Estimate the anticipated cross coupling coefficients
  • For centrifugal and axial compressors
  • Damping and log decrement
  • Stability experience plot
  • Gas density and critical speed ratio
  • Level 1 analysis (Level I)
  • Level 2 analysis (Level II)
  • For labyrinth seals, damper seals, impeller/blade flow aerodynamic effects
  • Acceptance criteria for stability study
  • Assessment of instability factor

Lateral Study

After lateral study completed, Level 1 analysis shall be performed the rotating equpment that meet the following;

  • Rotors whose maximum continuous speed is greater than the first undamped critical speed on rigid support condition.
  • Rotor with fixed gometry bearings
Lateral-study (Mode-shape)
Lateral-study (Mode-shape)

Damping & Instability

As results of Level 1 analysis, the damping and instability factor is lower than 0.1, Level 2 stability analysis shall be performed. Final log decrement shall be greater than 0.1.

Level II-Stability-for-Damping-and-Instability
Level II-Stability-for-Damping-and-Instability

These analysis shall be calculated at the defined maximum continuous speed of rotating equipment.

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