טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
Ph.D Thesis
Ph.D StudentTresser Shachar
SubjectBalancing High-Speed Flexible Rotors at Low Speed using
Parametric Excitation
DepartmentDepartment of Mechanical Engineering
Supervisor Professor Izhak Bucher


Abstract

The research deals with the dynamics and vibration of rotating structures and with methods to detect the projection of imbalance on high speed modes via externally tuned excitation signals. Within this research analytical and experimental methods utilizing nonlinear, parametrically excited systems of differential equations are used. These equations describe the dynamics of flexible rotating systems and their interaction with externally applied tunable forces geared towards obtaining hidden data that cannot be retrieved otherwise.

High-speed machinery is often designed to pass several “critical speeds”, where vibration levels can be very high. To reduce vibrations, rotors usually undergo a mass balancing process, where the machine is rotated at its full speed range, during which the dynamic response near critical speeds can be measured. High sensitivity, which is required for a successful balancing process, is achieved near the critical speeds, where a single deflection mode shape becomes dominant, and is excited by the projection of the imbalance on it.

This research proposes a novel approach to the balancing of high-speed flexible rotors, without the need to rotate them at high speeds. The method proposes to rotate the rotor at low speeds and to induce a set of tuned parametric excitations, which will cause enough excitation of the flexible modes to be detected and will permit a way to identify the projection of imbalance, using two actuators and several sensors. Analytical, numerical and experimental results are shown to validate and demonstrate successfully the proposed method.