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TECHNICAL PAPERS: Gas Turbines: Structures and Dynamics

Dynamic Behavior of Spherical Friction Dampers and Its Implication to Damper Contact Stiffness

[+] Author and Article Information
K-H. Koh

Mechanical Engineering Department, Carnegie Mellon University, 5000 Forbes Avenue, Pittsburgh, PA 15213kkoh@andrew.cmu.edu

J. H. Griffin

Mechanical Engineering Department, Carnegie Mellon University, 5000 Forbes Avenue, Pittsburgh, PA 15213

Note that the displacements at only three points are relevant in this study, points 1, 2, and 3, i.e., the point where the damper contacts the blade, the point where the blade is excited, and the point where the accelerometer is attached. The damper contacts the blade at two points on one side and a single point on the other. Because of the geometry and the types of modes that participate in the response, it was found that all three points have essentially the same modal deflections. As a result, a single value of modal deflection could be used to represent their response.

Appropriate boundary conditions were applied to the finite element model shown in Fig. 4 so that only anti-symmetric modes were generated for use in the receptance calculation, i.e., modes in which the tips of the blades move in opposite directions.

This might mean using an extremely small mesh in the finite element model or possibly using a substructuring technique to capture the local contact behavior.

J. Eng. Gas Turbines Power 129(2), 511-521 (Jul 06, 2006) (11 pages) doi:10.1115/1.2436547 History: Received June 14, 2006; Revised July 06, 2006

A model that predicts the quasi-static behavior of a friction damper that has spherical contacts was developed using Mindlin’s theory. The model was integrated into a dynamic analysis that predicts the vibratory response of frictionally damped blades. The analytical approach was corroborated through a set of benchmark experiments using a blades/damper test fixture. There was good agreement between the theoretical predictions of amplitude and the values that were measured experimentally over a wide range of test conditions. It is concluded that it is possible to predict the vibratory response of frictionally damped vibrating systems using continuum mechanics, provided that the contact geometry is clearly defined and the local nonlinear contact is correctly taken into account.

Copyright © 2007 by American Society of Mechanical Engineers
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Figures

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Figure 1

Test apparatus used for vibration measurements

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Figure 2

Damper specimen for a vibration test

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Figure 3

Comparison between experiments and Mindlin’s prediction

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Figure 4

A quarter model of FEM

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Figure 5

Peak voltage input versus excitation force graph

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Figure 6

Spring and damper in parallel

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Figure 7

Friction joints replaced with equivalent nonlinear elements

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Figure 8

Application of springs-in-series concept

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Figure 9

Combined effective stiffness and damping through all joints

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Figure 10

One blade with external forces

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Figure 11

Amplitude comparison for 0.44N and 0.89N

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Figure 12

Amplitude comparison for 1.78N and 3.56N

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Figure 13

Peak frequency comparison for 0.44N and 0.899N

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Figure 14

Peak frequency comparison for 1.78N and 3.56N

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Figure 15

Amplitude comparison between experiment and analysis for 0.89N normal load

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Figure 16

Padé rational function approximation

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