Diagnosing subsynchronous vibrations in turbomachinery - stable or unstable /
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| Other Authors: | |
| Format: | Thesis eBook |
| Language: | English |
| Published: |
[College Station, Tex.] :
[Texas A&M University],
[2010]
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| Subjects: | |
| Online Access: | Link to OAK Trust copy |
| Abstract: | Rotordynamic instability, commonly observed as subsynchronous vibration, is a serious problem that can cause heavy damage to a turbomachine or make it incapable of operation because of high vibration levels. All subsynchronous vibrations, howver, are not necessarily unstable. If the amplitude of the subsynchronous vibration is large, it can cause damage to seals, bearings, or process wheels. If it is small, the question arises as to whether it has the potential to grow larger (“instability”) or whether it is benign and harmless. A way to know would be helpful. The objective of this study is to signal analyze subsynchronous vibrations in turbomachinery and distinguish benign subsynchronous vibration from the true potential instabilities. Effort is also made to identify unique signatures to a cause to aid in faster diagnosis. First, a computer simulation study is conducted on four rotors, including two gas-reinjection compressors that went unstable, to examine the possibility of using the change in the synchronous phase angle as a possible indicator of impending instability. Results indicate that, phase angle can be used as an indicator of potential instability, provided that a judicious approach is used, as the synchronous phase angle, by itself, cannot classify between benign and unstable motion. It can confirm, however, a true rotordynamic instability. Several causes of subsynchronous vibration in turbomachinery are studied experimentally. Signals are measured from a rotor having a dead-band clearance between the bearing outer race and the housing. It is studied as another example of a subsynchronous vibration arising because of a benign cause. The effect is studied with the rotor in the horizontal and vertical positions, and clear indicators are observed that confirm the subsynchronous vibration to be benign in nature. Dry friction whip is also experimentally produced on a test rig. The measurements show that dry friction whip defies the general rules of thumb for diagnosing a true instability and at the same time is a very violent one as well. The last phenomenon to be studied is coupled lateral-torsional vibrations. A special test rig was built to study this effect, and clear indicators have been identified to distinguish the response as resulting from torsional vibrations and also classify it as a benign source of subsynchronous vibration. The test rig is also mathematically modeled to predict its torsional natural frequencies. |
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| Item Description: | "Major Subject: Mechanical Engineering" Title from author supplied metadata (automated record created 2010-03-12 12:08:51). Electronic resource. |
| Physical Description: | 1 online resource. |
| Bibliography: | Includes bibliographical references. |