Abstract
The main goal of this work is to carry out a numerical modal analysis of a Quill shaft of turbo-generator unitaffiliate to Mosul gas turbine station, using a trail version of popular finite element analysis software SolidWorks. The main function of Quill shaft is to protect the turbo-generator unit against overloads due to electrical network faults. The high flexibility of this shaft makes it capable of absorbing high displacements of resonance phenomena. This analysis is essentially needed to study the effect of transient loads applied to Quill shaft of turbo-generator unit under severe loading conditions such as electric network disturbances. The first five values of critical frequencies and mode shapes of axial, bending, and torsional vibrations were studied and analyzed. Each mode has been isolated separately by applying a special type of boundary conditions (restraints) available in program. The three types of natural frequencies have been found and reported. It was observed that the fundamental values of each three types of natural frequencies are relatively high and out of the range of Quill shaft operating speed. Finally, it has been concluded from all analyses that Quill shaft under consideration is safe from the stand point of modal analysis. The results show that the Quill shaft is not running at any of each three types critical speeds. Therefore, the resonance phenomenon for all three types of vibrations can not be happened no matter how high the amount of transient load applied.
Highlights
The main goal of the present work is to find the values of resonate natural frequencies of the Quill shaft for three conditions: axial, bending and torsional and its corresponding mode shapes, by using numerical method (Finite element method) and compare them with the forced frequency.If one or more of these natural frequencies is located within the value of operated speed of the shaft, it is said that the shaft is in resonance condition, the case that should be avoided in the initial or early design stages.in this case, a redesign or improved design of Quill shaft should be introduced
Final Results The eventual results of analysis can be acquired by running the program including critical speeds and inherent mode shapes for three types of vibrations
The vibration characteristics of Quill shaft in turbo-generator unit was obtained with modal analysis
Summary
Qing He and Dongmei Du [2] showed that the coupling interaction between electrical network faults and torsional vibrations makesshaft of turbine-generator unitvibrate. Torsional vibrations of shaft occur, alternate shear stresses due to these vibrations decrease the shaft life, and may be break the shaft. For this reason, it becomes important to compute and analyze the natural or resonatefrequencies and their corresponding mode shapes of all three types of vibrations(axial, bending, and torsional) agitated by the faults of electrical network, in order to obviate and stop disastrous accidents. The high axial, bending, and torsional flexibility owned by Quill shaft material make it deformed or brake before any other part of the unit because of its high capacity to absorb the induced large axial, bending, and torsional displacements
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