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	SwRI engineers use computer models, such as this mass-elastic model, to predict system performance.
	Critical speed map guides assessment of rotordynamic characteristics.

Rotordynamics tools have been developed and applied by Southwest Research Institute (SwRI) since the 1960s to predict and rectify problems with rotating machinery and to allow design of new equipment.

Lateral Analysis

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

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

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:

• Modelings

• Application

• Vibration and temperature measurement

• Condition monitoring

• Failure analysis of bearings and dampers

For more information about our machinery vibration services or rotordynamic analysis capabilities, or how you can contract with SwRI, please contact Jeff Moore, Ph.D., at jmoore@swri.org or call (210) 522-5812.

machinery.swri.org

| Fluids and Machinery Engineering Department | Mechanical 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.

January 03, 2013