“The Effect of Bearing Support Flexibility on Critical Speed Prediction,”
Some vendors and many users of rotating machinery are arbitrarily reducing the bearing damping by as much as 75 percent in order to accurately predict the location of the first and second lateral critical speeds. This paper shows that if the bearing support flexibility is considered, accurate critical speed predictions are possible without reducing the bearing damping. The equations for-the equivalent support stiffness and damping are given for a flexible support spring, mass, and damper in series with the fluid film stiffness and damping properties of a tilting-pad bearing. These equations can easily be incorporated with any synchronous response and/ or stability computer program. Examples of test stand results for four production rotors are shown illustrating the accuracy of this method.