Whirling and Vibration of Rotating Machinery Critical Speeds and Modes

  • Kadim Karim Mohsen Alturshan Mechanical Engineering Department College of engineering /Thi-Qar University
Keywords: Rotating shafts, Whirling, Inhomogeneities structure, Critical speed


The paper investigate the vibration of the rotating shafts and whirling were theoretically by
dealing with only the shaft bending without torsion. It is shown that the shaft whirling result
from vibration consider for this particular system will have critical whirling speed which
increases as the inertia forces of the rotor. Whirling is associated with fast-rotating shafts. When
a shaft rotates it is subjected to radial or centrifugal forces, which cause the shaft to deflect from
its rest position. These centrifugal forces are unavoidable, since material inhomogeneities and
assembly difficulties ensure that the center of gravity of the shaft or its attached masses cannot
coincide with the axis of rotation. The centrifugal forces involved and determined that the only
destabilizing or restoring force was that due to the elastic properties or stiffness of the shaft.
Hence, to deduce the critical speed caused an infinite deflection of shaft due to whirling.
Loading response analysis can simulate the response of the rotor using Ansys program, which
can help to identify the main modal frequency. To a rotating shaft, the modal analysis can give
a serial of Eigen frequency, but only some of them are just the right modal frequency value we
need. The harmonic analysis can extract the eigenvector of the modal analysis result, integrate
them together, and show the amplitude frequency response, deformation and stress distribution
characteristics of some special place of the rotating shaft.