Engineer for DYNAMICS OF MACHINERY – Dynamics of Rotor-Bearing System

An engineer or masters student in mechanical engineering to complete a small project on machine dynamics.

Title: Lateral Vibrations and Stability Threshold of Rotors Supported On
Hydrodynamic Bearing and Ball Bearing.

The occurrence of instability in rotating machines is a very typical problem in high speed machines
and may be caused by fluid-structure interactions due to oil film forces presented in hydrodynamic
bearings or aerodynamic forces resulting from seals, among others. A machine designer normally
wants to know the range of angular velocity in which the machine will operate stable and without
vibration problems, i.e. maximum angular velocity and distance from the unstable operational range.
The aim of this second project in the discipline is to make you familiar with the prediction of critical
speeds in rotating machines, stability threshold and unbalance response and maximum vibration
amplitude while crossing critical speed ranges.
Aiming at dealing with a real rotor-bearing problem, the test rig illustrated in figure 1(a) will be
used as example of a rotating machine. It will facilitate the visualization of the problem and aid
the students to link the theoretical results to practical problems and experimental results. The test
rig shown in figure 1(a) simulates a large overhung centrifugal compressor. The scheme of a large
overhung centrifugal compressor can be seen in figure 1(b). The test rig as well as the overhung
centrifugal compressor is composed of one flexible shaft, discs or impellers positioned at the end
of the shaft. The shaft is laterally supported by two bearings. In the test rig the bearing closest
to the coupling will operate as thrust bearing as well. All technical information needed is given in
this project description. By using all theoretical and experimental tools related to Rotor Dynamics
obtained during the classes, you will win a solid overview and understanding about how real and
imaginary parts of eigenvalues - and consequently also eigenvectors - change as a function of the
operational speeds.
The steps of the project are summarized as follows:
- First, you have to obtain mechanical and mathematical models of the flexible shaft element using
Finite Element Method (FEM).
- Second, the disc (impeller) shall be mounted onto the shaft. Mechanical and mathematical models
shall be expanded to cope with the dynamics of the disc.
- Finally, the flexible shaft connected to the rigid disc is mounted onto a ball bearing and a journal
bearing, as it is shown in figure 1(a). The eigenvalues and eigenvectors will be calculated for the
global rotor-bearing-system. These calculations will serve as the basis for an elaborate analysis
involving mode shape visualization and stability. See the files below for the whole scope of the project.

Please ask for more detail on theory behind the project.
About the recuiter
Member since Mar 14, 2020
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from Oromia, Ethiopia

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