Coupled free vibration characteristics of rotating tuned bladed disk systems

A detailed qualitative study is presented of the coupled free vibration characteristics of rotating turbomachinery bladed disk systems having useful ranges of geometric parameters. The analysis is carried out by using a three noded triangular shell element having six degrees of freedom per node together with the cyclic symmetric nature of the problem. The blade and disk attachment is established by a set of constraint equations obtained by the Love-Kirchhoff hypothesis. The effects of rotation are included by using a stress smoothing technique while computing the geometric stiffness matrix. The contributions from membrane behaviour and transverse shear are included. The severely coupled systems are identified and an exhaustive parametric study is carried out for these systems to predict the influence of stagger and twist on natural frequencies for stationary as well as rotating systems. An assessment of Southwell's coefficients for these systems is made. Theoretical results agree closely with available experimental results.

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