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Nonlinear dynamics of rotating shaft with a breathing crack - CHINA SCHOLARSHIP COUNCIL PhD for 2017

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Because of the increasing need of energy, the plants installed by electricity supply utilities throughout the world are becoming larger and more highly stressed. Thus, the risk of turbogenerator shaft cracking is increasing also. The development and propagation of a crack represents the most common and trivial beginning of integrity losses in engineering structures. For rotating shafts, a propagating fatigue crack can have detrimental effects on the reliability of a process or utility plant where theses vital parts are subjected to very arduous working conditions in harsh environment. It is one of the most serious causes of accidents and, an early warning is essential to extend the durability and increase the reliability of these machines. The vibration analysis and modeling of the shaft and cracks are necessary for a reliable identification of the crack location and depth to avoid catastrophic failures. In fact, cracks can develop and propagate to relevant depths without affecting consistently the normal operating conditions of the shaft. Another feature related to the problem of modeling cracked rotating shafts is the consideration of the opening−closing phenomenon of the crack during the shaft rotation.

An elegant, simple and comprehensive model has been suggested for the nonlinear dynamics and stability analysis of a cracked rotating shaft. It is known that the gap between the lips of a fatigue-induced crack are very small and that closure of the crack occurs when the shaft rotates. Accordingly, the breathing mechanism of the crack is taken into account by considering a more realistic function describing the periodic variation of the global stiffness of the shaft. In particular, a partial opening−closing of the crack in both directions is allowed since a switching crack model is not adequate to examine the stability of shafts with deep cracks. Moreover, the breathing mechanism is depending not only but substantially on the shaft dynamics response and, thus, the obtained equilibrium equations are nonlinear. Additional work is required for deeper exploration of this complex mechanical system and to establish quantitative results and diagrams that could be useful for engineers in power stations industry.

This program is open to highly qualified Chinese students interested in carrying on doctoral training at ParisTech with financial support of the CSC.

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