Misalignment in turbomachinery has been commonly known to produce twotimes-
running-speed (2N) response. This project aimed to investigate the source of the
2N vibration response seen in misaligned vibrating machinery by simulating
misalignment through a coupling. Three flexible disc-pack couplings (4-bolt, 6-bolt, and
8-bolt coupling) were modeled, and parallel and angular misalignments were simulated
using a finite element program. The stiffness terms obtained from the coupling
simulations had 1N, 2N, and 3N harmonic components. The 4-bolt coupling had large
1N reaction components under angular and parallel misalignment. The 6-bolt coupling
model only had a 1N reaction component under angular misalignment, and both cases of
parallel misalignment showed a strong 2N reaction component, larger than both the 1N
and 3N components. The 8-bolt coupling model under angular misalignment produced
large 1N reaction components. Under parallel misalignment, it produced 1N, 2N, and 3N
components that were similar in magnitude. All the couplings behaved linearly in the
range studied.
A simple model predicted that the 2N frequency seen in the response is caused
by the harmonic (1N) term in the stiffness. The amplitude of the 2N component in the
response depends on the amplitude of the 1N term in the stiffness compared to the
average value of the stiffness and the frequency ratio.
The rotordynamic response of a parallel and angular misaligned system was
completed in XLTRC2. When the frequency ratio was 0.5, the system response with the
4-bolt and 6-bolt coupling had a synchronous 1N component that was much larger than
the 2N component. The response did not have a 2N component when the 8-bolt
coupling was used but the response did have a 1.6N component that was considerably
larger than the 1N component. When the frequency ratio was 2, the system response
with the 4-bolt and 6-bolt coupling had a synchronous 1N component and a relatively
small ½ frequency component. The response with the 8-bolt coupling had a 0.4N
component that was larger than the 1N component.
A 5-tilting pad journal bearing was also tested to better understand its behavior
under misalignment because some experts attribute the 2N response to the nonlinear
forces produced by bearings with high unit loads. The response of the 5-tilting pad
bearing did not produce any 2N components while the bearing was subjected to unit
loads of up to 34.5 bars.
| Identifer | oai:union.ndltd.org:tamu.edu/oai:repository.tamu.edu:1969.1/ETD-TAMU-2010-08-8315 |
| Date | 2010 August 1900 |
| Creators | Avendano Ovalle, Raul David |
| Contributors | Childs, Dara W. |
| Source Sets | Texas A and M University |
| Language | en_US |
| Detected Language | English |
| Type | thesis, text |
| Format | application/pdf |
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