Statistical investigation of the free vibration of mistuned blade system
Bah, M.T., Bhaskar, A. and Keane, A.J. (2001) Statistical investigation of the free vibration of mistuned blade system. In, Sixth US National Congress on Computational Mechanics, Dearborn, Michigan, 01  04 Aug 2001. U.S. Association for Computational Mechanics (USACM).
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Description/Abstract
A statistical investigation of the effects of uncertainty in root fixity on the free vibration of turbine blades is made. Emphasis is particularly placed on the statistical properties of the random eigenvalues and essentially on their standard deviations. These are evaluated using the direct product technique between matrices [1] and validated by Monte Carlo SImulations (MCS). The studied system is a simplified model of a shrouded blade assembly under the conditions of weak interblade coupling. It essentially consists of a cyclic chain of continuous beams with identical properties, fixed at one end via rotational springs with random stiffnesses representing the uncertain roots stiffnesses and coupled via linear springs at their tips.
Finite Element Method is used as a discretization technique to obtain the equations of motion of the tuned and mistuned systems and the corresponding random eigenvalue problem.
Numerical simulations show that small differences between the rotational springs stiffnesses spolit the natural frequencies that were in pairs, increase the width of each frequencycluster and strongly localizes the vibration around one blade. This strong localization has been shown to occur in a chain of singledegreeoffreedom, nearly identical, coupled oscillators if the coupling frequency between the subsystems is of order of, or smaller than the spread in the natural frequencies [2]
However, for the multidegreeoffreedom and randomly mistuned system considered her, multiple realizations are required to capture the behaviour of the eigenvalues appearing in frequencyclusters. It is found that for each frequencycluster, when the standard deviations of theeigenvalues are plotted against the mode number, they form a Ushaped curve. For the particular case when the coupling frequency line crosses a curve, this essentially shows that the vibration localization is stronger at the first and last modes than at the mid frequencies, which belong to one passband in the tuned system.
Item Type:  Conference or Workshop Item (Paper)  

Related URLs:  
Subjects:  Q Science > Q Science (General)  
Divisions :  University Structure  Pre August 2011 > School of Engineering Sciences > Computational Engineering and Design 

ePrint ID:  43645  
Accepted Date and Publication Date: 


Date Deposited:  30 Jan 2007  
Last Modified:  31 Mar 2016 12:17  
URI:  http://eprints.soton.ac.uk/id/eprint/43645 
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