Lateral Vibration Analysis

Rotordynamics, Critical Speed, and Stability Analysis

Lateral vibration of a shaft rotor is due to instability, unbalance, or other forces acting on the rotor. Lateral Analysis (also called Rotordynamics Analysis) simulates the rotating system, calculates the critical speeds, predicts vibration amplitudes, and provides recommendations to reduce vibration risks.

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1 Scope: Analysis Features

The scope is API Compliant (including but not limited to 610, 617, 619, and RP 684).The modeling and analysis include these activities:

Undamped Critical Speed Analysis

• Prepare the rotor dynamic model to simulate the entire system
• Determine critical speeds over a range of bearing stiffnesses
• Calculate the mode shapes, eigenvalues, and critical speeds

Damped Eigenvalue (Critical Speed) Analysis

• Calculate modes across the speed range
• Damped eigenvalue analysis of critical speeds of the rotor with the actual bearing stiffness and damping coefficients; damping evaluated using several methods
• Separation margins evaluated per API requirements

Forced Response Analysis

• Calculate the unbalanced vibration response amplitudes and critical speed locations based on API recommended unbalanced guideline
• Evaluate the separation margins for a range of bearing clearances.

Unbalanced response calculated using API recommended approach

Stability Analysis

• Evaluate oil whirl and shaft whip to avoid self-excited instabilities
• Calculate damped eigenvalues

Transient and Nonlinear Analysis

• Using the Time Domain solver, evaluate blade-loss, rubs, and other events as the system decelerates through critical speeds

Quality Checks and Reporting

• Perform technical review to ensure validity of model and inputs
• Issue report containing detailed results of the Lateral Analysis, separation margins, design acceptance (or not), and recommendations if required 

2 Wood Advantages

• Integrated engineering capabilities to support all vibration-related design and field engineering for compressors, pumps, and piping systems
• Large torsional and lateral vibration analysis team – including field engineers
• Global support for OEMs, end users, and engineering consulting firms
• Accurate software for Lateral Analysis 

3 Related Services

• Torsional Vibration Analysis (TVA) 
• Surge Control Dynamic Analysis for Centrifugal Compressor Systems
• Flow-Induced Vibration Analysis
• Flow-Induced Turbulence Analysis
• Acoustic Induced Vibration Analysis

4 Related Information

• The Influence of Tilting Pad Bearing Clearance on Rotor Response of a Steam Turbine, Howes and Leung 1984 (pdf)
• Simplified Prediction of Balance Sensitivity, Howes and Masterson, 1990 (pdf)
• A Centrifugal Compressor Synchronous Motor Case History, Howes, 2000 (pdf)
• Lateral and Torsional Vibration Problems in Systems Equipped with Variable Frequency Drives, Howes and De la Roche 2005 (pdf)

Example of 1st forward whirl mode with damped eigenvalue mode
Example of 2nd forward whirl mode with damped eigenvalue mode

5 Key Words

• Rotordynamics 
• Critical Speed
• Stability Analysis
• Lateral Analysis