DYNAMIC ANALYSIS OF HIGH SPEED ROTOR SUPPORTED ON BALL BEARING

Abstract

Different malfunctions i.e. defects including cracks induce nonlinear vibrations. Multiple catastrophic failures of machines, caused by cracked rotors, have increased the interest in early detection of rotor cracks. Modal and Harmonic analysis of high speed rotor supported on ball bearing is done using linear finite element model of the uncracked and cracked rotor in FEM software ANSYS 11. In modal analysis, Campbell diagram has been plotted for transverse cracked and uncracked rotor which gives natural frequencies at different rotational speed and also gives critical speeds of rotor. Orbital plots, mode shape, and nodal solution are also plotted. In harmonic analysis, steady-state response (frequency verses displacement diagram) has been plotted for an unbalance excitation for cracked and uncracked rotor which gives displacement amplitude at a particular node at the different critical speeds. The meshed shaft specimen has been considered fixed and the load rotating, instead of fixed load acting on rotating shaft. Bending moment load have been applied to one end of the un-cracked and cracked specimen clamped at its other end, and the breathing mechanism and the deflections according to the six degrees of freedom in space have been evaluated for the different angular positions of the loads with respect to the crack, by means of a 3D fmite element model in which the non-linear contact conditions on the cracked surface are taken into account. At each• increment (load rotation angle), a fmite element analysis is performed and contact conditions on the crack surfaces are updated. This method predicts effectively the contact and evaluates local flexibilities and stiffnesses due breathing crack with the crack rotation angle. This technique form the basis for the nonlinear dynamic response of rotors associated with crack breathing effects.