Informatics Publishing Limited

B. Gurudatt ¹, S. Seetharamu ², P. Sampathkumaran ³, Vikram Krishna ⁴

Affiliations
1 Professor, Dept of Mechanical Engg., Bangalore Institute of Technology, Bangalore-560004, IN
2 Additional Director, MTD, Central Power Research Institute, Bangalore-560080, IN
3 Joint Director, MTD, Central Power Research Institute, Bangalore-560080, IN
4 Research Associate, RSOP Project of CPRI (Govt. of India), Bangalore-560004, IN

Abstract

Vibration is the default state of all mechanical systems that causes them to possess a natural frequency. The significance of natural frequency cannot be emphasised enough, considering the fact that its study is essential in averting resonance which causes violent swaying motions and catastrophic failures in improperly constructed structures. In case of rotating structures, the study of natural frequency is incomplete without the understanding of spin softening. This paper presents an ANSYS based analysis to study natural frequency variation due to spin softening, but in a faster and more accurate way than conventional GUI-based ANSYS analysis. The conventional GUI based ANSYS procedure is a laborious time consuming process, with the user having to perform multiple iterations of model analysis involving different rotational velocities to examine the variation of natural frequencies of the system. Through this paper, a novel way has been suggested to bring down the time and effort involved in such a study by using an advanced ANSYS feature called ANSYS Parametric Design Language (APDL). The results obtained have been found to validate spin softening.

Keywords

Finite Element Method, ANSYS Parametric Design Language, Natural Frequency, Spin Softening, Vibrations, Nelson Rotor.

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B. Gurudatt ¹, S Seetharamu ², P. Sampathkumaran ², Vikram Krishna ³

Affiliations
1 Department of Mechanical Engineering, Bangalore Institute of Technology, Bangalore-560004, IN
2 Central Power Research Institute, Bangalore-560080, IN
3 M S Ramaiah Institute of Advanced Studies, Bangalore, IN

Abstract

Resonance is a common thread that runs through almost every branch of engineering. Yet, this phenomenon often goes unnoticed, silently resulting in inconveniences, such as causing a bridge to collapse or a helicopter to fl y apart, to name a few. It is, therefore, of utmost importance to avert resonance, for which determining the frequency of the system becomes indispensible. In complex rotating structures, as one considered in this paper, theoretical determination of frequency is as diffi cult and laborious as a task can be. Finite element analysis has proven to be an effective tool to handle such a task. Resonant vibrations incited by the running speed harmonic excitations, steam impinging frequency, engine order excitations are fundamental causes for failure of turbine components. The mainstream discipline that is encompassed by this paper is the modal analysis. Modal analysis is performed to estimate the critical speeds and study the mode shapes of the bladed rotor disc under prestressed condition.

Keywords

Resonance, Steam turbines, Blade vibration, Disc vibration, Finite Element Analysis (FEA).

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