| Main purpose of this dissertation is to examine the effects of asymmetry on the vibration of disk/spindle systems.; Through numerical simulation and perturbation analysis, first part studies how ball bearing stiffness asymmetry affects natural frequencies and mode shapes of the rotating disk/spindle system. Numerical simulation shows that ball bearing asymmetry splits a pair of repeated (0,1) unbalanced modes into two modes with distinct frequencies when spindle is stationary. As the rotational speed increases, the (0,1) unbalanced mode with lower and high frequencies evolve into backward and forward precessions, respectively. Moreover, the precession orbits are elliptical. For low rotational speed, contraction iteration predicts the effects of bearing asymmetry on the natural frequencies and mode shapes. For high rotational speed, Lindsted-Poincaré approach predicts the effects of bearing asymmetry on the natural frequencies and mode shapes.; Second part presents new experimental setup for fluid-dynamic bearing (FDB) spindles. The cross coupling of FDB destroys bearing axisymmetry resulting in half-speed whirls and traditional (0,1) unbalanced modes. In this new experimental setup, an impact hammer generates an input excitation near the inner rim to improve signal-to-noise ratio. Frequency response functions (FRFs) are measured using a capacitance probe, a laser Doppler vibrometer, and an edge probe. With the experimental setup presented, it is possible to measure up to three pairs of (0,1) unbalanced modes.; Third part examines two or more nodal diameter disk modes that are coupled by the surrounding air and structural flexibility. FRFs are measured in air and in vacuum to determine the natural frequencies of co-rotating disks. In vacuum, the experimental measurements depict a single natural frequency for each traveling wave associated with disk modes. In air, however, each traveling wave splits into a group of N waves with distinct frequencies, where N is the number of disks. Finite element analysis and experimental measurements indicate that the flexibility of the clamp and spacers also couples the disk vibration in the same manner. Aerodynamic coupling is more significant for high disk modes like four-nodal-diameter modes; whereas, structural coupling through spacer flexibility is more pronounced for low disk modes like two-nodal-diameter modes. |
