Analysis On Free Vibration Of Stiffened Cylindrical Shells And Dynamic Characteristics Of Drum Rubbing-impact

Cylindrical shells are widely used in many engineering applications, such asaircraft engines, space vehicles and ocean engineering, for their low weight, easeof fabrication and high flexural and torsional rigidity. To improve the performanceof the cylindrical shells, they are usually stiffened by stringers and rings. Inpractical engineering, those structures undertake many kinds of dynamic loads,which may lead to structure resonance, dynamic instability and stress fatigue.Hence it is of great importance to investigate the vibration characteristics ofring/string stiffened cylindrical shells.In this dissertation, free vibration of stationary and rotating stiffenedcylindrical shells with arbitrary boundary conditions is studied. Moreover,nonlinear dynamic characteristics are investigated for the drum in turbo-machineswhich can be seen as a practical application of cylindrical shells. The mainachievements derived in this dissertation are listed as follows.An efficient approach is proposed to analyze the free vibration of stiffenedcylindrical shells with arbitrary boundary conditions. Utilizing artificial springs tosimulate the constraints of the shell, the Rayleigh-Ritz method is employed toderive the frequency equations of the stiffened cylindrical shells by taking thecharacteristic orthogonal polynomial series constructed during Gram-Schmidtprocess as vibrational mode in longitudinal direction. The validation of theapproach proposed is examined by comparisons with those results from previousliterature in this dissertation. Convergence studies are also performed which showhigh rates of convergence for the approach. Based on the approach, the influencesof the changes of parameters (i.e. the stiffness of artificial springs, properties ofstiffeners and the rotating speed of cylinders) on the vibration characteristics arediscussed in detail.Dynamic model of drum-case rubbing contact is established. UsingLagrange’s equations and Rayleigh-Ritz method, the governing equations offorced vibration for drum are derived. For different kinds of rubbing contact mode,rub-impact forces are given and governing equations established are simplified bydimensionless method.Dynamic responses of the drum rubbing contact with case are derived. Bynumerical calculations, the effects of control parameters (i.e. contact stiffness,excitation frequency, damping coefficient and clearance between seal and case) arediscussed. The results show that vibrations of the drum rubbing contact with casecarry frequency doubling phenomenon; Central peak and side peaks can be observed in each cycle of vibration; Excitation frequencies and dampingcoefficients have significant influence on the drum’s response.