On-line damage detection in rotating machinery

Keywords

Finite element method; Modal analysis; Vibration

Abstract

Monitoring techniques to detect defects in turbon1achinery units during operation are highly desirable, since conventional NDT techniques such as magnetic particles, dye penetratnts or ultrasonic require the equipment to be taken out of service for some period of time. Thus, detecting of defects in the structural con1ponents and determining their locations without the need of ren1oving any part is an in1portant issue in minimizing the cost to industry. This work is concerned with a set of techniques to detect internal defects in uniform circular discs (rotors). An internal defect is intentionally manufactured in stereolithographic discs by a rapid prototyping process using cured resin SL 51 70 material. The analysis and results presented here are limited to a uniform circular disc, with internal defects, mounted on a uniform flexible circular shaft. The setup is comprised of a Bently Nevada rotor kit connected to a data acquisition system. The rotor consists of a disc and shaft that is supported by journal bearings and is coupled to a motor by a rubber joint. Damage produces localized changes in the strain energy, which is quantified to characterize the damage. Based on previous research, the Strain Energy Damage Index (SEDI) is utilized to localize the damage due to strain energy differences between damaged and undamaged modes.  To accomplish the objective, this work covers three types of analysis: finite element analysis, vibration analysis, and experimental modal analysis. Finite element analysis (using SDRC Ideas software) is perfom1ed to develop a multi-degree-of-freedom (MDOF) rotor system with internal damage, and its dynan1ic characteristics are investigated. The analysis is performed for two different types damage cases: radial damage and circular damage. Parametric study for radial da1nage and random noise to undamaged disc have been investigated to predict the effect of noise in the damage detection. The developed on-line damage detection technique for rotating equipment incorporates and couples both vibration analysis and experimental modal analysis. The dynamic investigation of the rotating discs (with and without defect) is conducted by vibration signal analysis (using proximity sensors, data acquisition and Lab View). The vibration analysis provides a unique vibration signature for the damaged disc, which indicates the existence of the damage. The vibration data are acquired at different running speeds (1000, 2500, 5000 ·rpm). Then the dynamic investigation of non-rotating discs (with and without defect) is conducted by experimental modal analysis (using ST AR software). While the vibration analysis detects and indicates the existence of damage while the disc is rotating, experimental modal analysis (using STAR and MATLAB software) provides the localization of damage through the modal parameters for a non-rotating disc. Both of the experimental diagnostic algorithms are based on measurement of the dynamic behavior of the damaged disc. The results are compared with the reference, or baseline, one, obtained initially for an undamaged disc. The vibration signature for a rotating disc clearly indicates the existence of the damage compared with the non-damaged spectrum, while the experimental modal analysis results for a static disc indicate the location of the dan1age in stereo lithographic disc.

Notes

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Graduation Date

2003

Advisor

Moslehy, Faissal

Degree

Doctor of Philosophy (Ph.D.)

College

College of Engineering

Department

Mechanical, Materials, and Aerospace Engineering

Format

PDF

Pages

202 p.

Language

English

Length of Campus-only Access

None

Access Status

Doctoral Dissertation (Open Access)

Identifier

DP0029117

Subjects

Dissertations, Academic -- Engineering; Engineering -- Dissertations, Academic

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