Vibrations in rotating machinery are normally the consequence of mechanical faults such as mass unbalance, manufacturing, mechanical looseness, assembly, installed machines, coupling misalignment, and many other causes. However, unbalance is the most popular reason of machine vibration. An unbalanced rotor always causes more vibration and generates excessive force in the bearing area and reduces the life of the machine. In this paper, experimental studies were performed on a rotor with two mounted disks to identify the unbalance in rotor using order tracking technique based on one key phasor. After calculation of the coefficients of influence α of each experimental test, the matrix of influence coefficient [C] and the global matrix of coefficients [H] can be obtained. Finally, the two suitable masses are identified in order to reduce the unbalance of the rotor systems.
The dynamics of rotating machinery have been extensively investigated during the past century. To date, longer rotating shafts, higher rotating velocity, higher fluid pressure, and generally high performances are required. For this purpose, a deep understanding and a more accurate modelling of the rotating machinery dynamical behaviour is needed, especially in terms of the resultant vibrations and stability issues. In this paper, a mathematical model was developed for a simple rigid rotor-bearing system using finite element method. Several natural frequencies and corresponding mode shapes of the systems were presented. In order to validate the model, some experimental tests were performed using a small test rig. The response of the system in the frequency domain and the direct orbit of the shaft were plotted as well.
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