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Research Papers: Gas Turbines: Structures and Dynamics

Structural Change Quantification in Rotor Systems Based on Measured Resonance and Antiresonance Frequencies

[+] Author and Article Information
Adam C. Wroblewski

e-mail: a.wroblewski@csuohio.edu

Alexander H. Pesch

e-mail: a.pesch@csuohio.edu

Jerzy T. Sawicki

e-mail: j.sawicki@csuohio.edu
Center for Rotating Machinery Dynamics
and Control (RoMaDyC),
Cleveland State University,
Cleveland, OH 44115-2214

Contributed by the Structures and Dynamics Committee of ASME for publication in the Journal of Engineering for Gas Turbines and Power. Manuscript received August 19, 2013; final manuscript received September 6, 2013; published online November 1, 2013. Editor: David Wisler.

J. Eng. Gas Turbines Power 136(2), 022506 (Nov 01, 2013) (6 pages) Paper No: GTP-13-1314; doi: 10.1115/1.4025484 History: Received August 19, 2013; Revised September 06, 2013

A structural change quantification methodology is proposed in which the magnitude and location of a structural alteration is identified experimentally in a rotor system. The resonance and antiresonance frequencies are captured from multiple frequency response functions and are compared with baseline data to extract frequency shifts due to these features. The resulting expression contains sufficient information to identify the dynamic characteristics of the rotor in both the frequency and spatial domains. A finite element model with carefully selected tunable parameters is iteratively adjusted using a numerical optimization algorithm to determine the source of the structural change. The methodology is experimentally demonstrated on a test rig with a laterally damaged rotor and the frequency response functions are acquired through utilization of magnetic actuators positioned near the ball bearings.

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Figures

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Fig. 1

The rotor test rig photo is pictured (top) with the description of the layout (bottom)

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Fig. 2

Rotor model cross section illustrating components as well as I/OS for the TF calculations and measurements

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Fig. 3

The updated baseline model is plotted against baseline experimental data showing good agreement

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Fig. 4

Photo of the circumferential cut inducing a stiffness reduction of the shaft. Three cut depth cases are progressively implemented, 1.8 mm, 2.8 mm, and 4.0 mm.

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Fig. 5

The stiffness of a single element from the FE rotor model was investigated as a function of cut depth. (a) A side view of element; (b) A FE model of selected rotor element.

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Fig. 6

The predicted stiffness reduction of a single finite element of the rotor model as a function of cut depth

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Fig. 7

The element sensitivity study illustrates which elements are sensitive to the objective function in the model updating routine. Element number 28 was chosen to host the stiffness reduction in the test rig.

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Fig. 8

Experimental FRFS for use in the model updating routines for the baseline and three stiffness reduction cases

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Fig. 9

The updated FE rotor models illustrating normalized detected structural change

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Fig. 10

Graphical representation of stiffness reduction prediction values are present in other finite elements

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