Conclusion
In this paper, a dynamic model based on the shell theory was developed to investigate the vibration characteristics of a rotating composite laminated blade. The natural frequencies of a rotating pretwisted composite laminated blade were obtained by the Rayleigh-Ritz method. The convergence and comparison studies demonstrated the accuracy and validity of the present modeling method. The effects of the rotation velocity on the natural frequencies and the corresponding mode shapes of the blade were discussed. Due to the effects of the Coriolis and centrifugal forces, variation of different natural frequencies with rotation velocity was diverse, resulting in the phenomena of frequency loci veering and crossing. Two ways of frequency loci veer can be observed. For the first one, the nodal line patterns of the mode shapes switch their shapes to each other continuously. For the other one, the nodal line patterns vary in abrupt and discontinuously. A comprehensive parameter investigation of the effects of the aspect ratio, pre-twisted angle, stagger angle and hub radius on the variations of modal characteristics was conducted. Numerical results demonstrated that the natural frequencies of the rotating blade increase as the pre-twisted angle, stagger angle and the hub radius increase, while decrease as the thickness ratio increases. It was demonstrated through the results of this paper that the proposed model is an efficient tool for predicting the dynamic behavior of blades with arbitrary geometry dimension, stagger angle and pretwisted angle, which will provide useful information for the design and optimization of the blades. Based on the results of this paper, further investigations will extend to the internal resonances and nonlinear dynamics of the composite laminated blades rotating at high rotation velocity.
