Rotating machinery is widely used in industries and, in practice, it faces inevitable faults because of the errors in manufacturing, assembling and operating conditions.
Mass unbalance is one of the most common faults encountered in rotating machinery.
Rotors are classified into two types: rigid and flexible rotors. Flexible rotors are served at speeds exceeding their critical speeds and rigid ones are not. In general, flexible rotors are balanced at service speed because their dynamical characteristics change with speeds. Balancing of flexible rotors is relatively complicated, expensive and dangerous because they have to run at high speeds around critical speeds.
Therefore, methods for low-speed balancing of high-speed rotors have been developed and presented.
Ri Yong Ho, a researcher at the Science Engineering Institute, has proposed a new low-speed balancing method for high-speed rotors by using Component Mode Synthesis (CMS).
The proposed method was tested numerically by simulating harmonic response of a rotor bearing system which is constructed of a steel shaft, three discs and two rolling elements bearings. The shaft was supported at two ends by bearings and worked at the maximum speed of 9 000r/min. The system was modeled by FEM. The shaft was divided into two dimensional finite beam elements with two translational and one rotational DOF at one node and the discs were modeled as concentrated masses and inertia moments at the corresponding nodes. And the support bearings were modeled as spring elements and proportional damping was supposed.
He confirmed by his method that a high speed flexible rotor can be exactly and effectively balanced without test runs at speeds higher than critical speed.
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