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Research Papers: Gas Turbines: Oil and Gas Applications

Rotordynamic Analysis of a Large Industrial Turbocompressor Including Finite Element Substructure Modeling

[+] Author and Article Information
J. Jeffrey Moore

Mechanical and Materials Engineering Division, Southwest Research Institute, Post Office Drawer 28510, San Antonio, TX 78228-0510jeff.moore@swri.org

Giuseppe Vannini

 GE Oil & Gas, Nuovo Pignone, Via Felice Matteucci, 2, 50127 Florence, Italygiuseppe.vannini@np.ge.com

Massimo Camatti

 GE Oil & Gas, Nuovo Pignone, Via Felice Matteucci, 2, 50127 Florence, Italymassimo.camatti@np.ge.com

Paolo Bianchi

 GE Oil & Gas, Nuovo Pignone, Via Felice Matteucci, 2, 50127 Florence, Italypaolo.bianchi.ing@np.ge.com

J. Eng. Gas Turbines Power 132(8), 082401 (May 18, 2010) (9 pages) doi:10.1115/1.2938272 History: Received June 01, 2006; Revised October 08, 2007; Published May 18, 2010

A rotordynamic analysis of a large turbocompressor that models both the casing and supports along with the rotor-bearing system was performed. A 3D finite element model of the casing captures the intricate details of the casing and support structure. Two approaches are presented, including development of transfer functions of the casing and foundation, as well as a fully coupled rotor-casing-foundation model. The effect of bearing support compliance is captured, as well as the influence of casing modes on the rotor response. The first approach generates frequency response functions (FRFs) from the finite element case model at the bearing support locations. A high-order polynomial in numerator-denominator transfer function format is generated from a curve fit of the FRF. These transfer functions are then incorporated into the rotordynamics model. The second approach is a fully coupled rotor and casing model that is solved together. An unbalance response calculation is performed in both cases to predict the resulting rotor critical speeds and response of the casing modes. The effect of the compressor case and supports caused the second critical speed to drop to a value close to the operating speed and not compliant with the requirements of the American Petroleum Institute (API) specification 617 7th edition. A combination of rotor, journal bearing, casing, and support modifications resulted in a satisfactory and API compliant solution. The results of the fully coupled model validated the transfer function approach.

Copyright © 2010 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Back-to-back compressor arrangement

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Figure 2

Rotordynamic shaft model

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Figure 3

Bearing 1 response unbalance at each quarter-span location (1× API)

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Figure 4

Solid model assembly—original casing geometry

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Figure 5

FE mesh—original casing geometry

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Figure 6

Boundary conditions

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Figure 7

Location of applied force for harmonic analysis

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Figure 8

Calculated mode shapes and natural frequencies—original casing model

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Figure 9

Forced response prediction—Bearing 1-vertical—original casing model

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Figure 10

Dynamic stiffness prediction—Bearing 1-vertical—original casing model

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Figure 11

Curve-fit of FRFs—original casing model

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Figure 12

Bearing 1 response unbalance at quarter-span location (1× API)—original casing model

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Figure 13

Modified casing with cradle support

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Figure 14

Modified casing with forward pedestal supports

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Dynamic stiffness comparison

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Figure 16

Bearing 1 response to API unbalance at quarter-span location for alternate Design 1

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Figure 17

Bearing 1 response to API unbalance at quarter-span location for alternate Design 2

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Figure 18

Bearing 1 response to API unbalance at quarter-span location for alternate Design 2 with modified bearings, minimum and maximum clearance

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Figure 19

Coupled rotor-casing model—alternate Design 1

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Figure 20

Unbalance response comparison—Bearing 1 vertical response

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