CONTACT:
Harold Simmons, P.E.
 Machinery Vibration
   Services
 (210) 522-2557
 E-mail: hsimmons@swri.org

KEY TERMS:
rotating machinery
compressor failure
machinery rotor
systems
bearing stiffness
vibration amplitudes
turbomachinery rotor
systems
aircraft gas engine
turbines
bearings and dampers
failure analysis 
unbalanced rotor

Since the 1960s, Southwest Research Institute (SwRI) has developed and applied rotordynamics tools to predict and rectify problems with rotating machinery and to allow design of new equipment.

Lateral Analysis

SwRI engineers use computer models, such as this mass-elastic model, to predict system performance.

Critical speed map guides assessment of rotordynamic characteristics.

To predict the lateral critical speeds of rotors and to determine sensitivity to unbalance, SwRI calculates:

• Undamped critical speeds

• Bearing performance

• Stiffness and damping coefficients 

• Damped unbalance response amplitudes and frequencies 

• Rotor stability

• Mode shapes

Torsional Vibration

To predict the torsional critical speeds of the entire train, including the effects of gear boxes, couplings, etc., SwRI engineers calculate:

• Undamped critical speeds 

• Transient critical speeds, including synchronous motor start-ups

• Mode shapes 

• Cumulative fatigue criteria, such as maximum starts

Stability Analysis

As part of a torsional analysis, SwRI predicts the steady-state critical speeds of rotor trains.

SwRI evaluates designs to determine system stability and sensitivity to instability mechanisms. These analyses involve:

• Aerodynamic cross coupling

• Logarithmic decrement predictions

Rotordynamic Modeling

SwRI engineers develop mass-elastic models, as this diagram shows, for rotating components (e.g., compressors, turbines, pumps, motors, and gearbox shafts), accounting where appropriate for the lateral stiffening effect of interference fits. The resultant model enables prediction of rotor system dynamic characteristics, such as:

• Lateral critical speeds

• Torsional critical speeds

• Response to unbalance excitation

• Stability

Critical Speed Map

Critical speed maps, such as this one, help SwRI engineers evaluate a machinery rotor system. Combined with bearing stiffness curves, the critical speed map shows where critical speeds will likely occur. The map indicates the effectiveness of bearing damping in controlling vibration amplitudes. The critical speed map also reveals the likely effectiveness of the changing stiffness of bearings or bearing supports in changing a critical speed.

Bearings

Fluid film, tilting pad bearings influence the dynamics of turbomachinery rotor systems. Plain fluid film bearings act as highly loaded dynamic elements in reciprocating engines. Rolling element bearings carry the high-speed rotors of modern aircraft gas turbine engines and their derivatives in power generating and mechanical drive service. Squeeze film dampers help moderate resonant vibration levels in gas turbine engines, and some manufacturers use them to stabilize high-performance centrifugal compressors. For bearings and dampers, SwRI has capabilities that include:

• Modeling

• Application

• Vibration and temperature measurement

• Condition monitoring

• Failure analysis of bearings and dampers

For more information about machinery vibration services or rotordynamic analysis capabilities at SwRI, or how you can contract with SwRI, please contact  Harold Simmons, P.E. at hsimmons@swri.org or (210) 522-2557.

Mechanical and Fluids Engineering Department
  Mechanical & Materials Engineering Division SwRI Home

Southwest Research Institute^® (SwRI^®), headquartered in San Antonio, Texas, is a multidisciplinary, independent, nonprofit, applied engineering and physical sciences research and development organization with 11 technical divisions.