Evaluation of Vibrational Characteristics of Laminated FRP Circular Cylindrical Shells Including Damping Effect.

Abstract

Evaluation method of vibrational characteristics of laminated FRP shells including damping is examined. Natural frequencies and loss factors of FRP circular cylindrical shells subjected to three kinds of prestresses are obtained on the ground of the first-order shear deformation shell theory by applying the modified Galerkin method. The results show that natural frequencies generally decrease, whereas loss factors increase for such the prestresses as external pressure, axial compression stress and torsional shear stress. Besides, it turned out through parametric studies that it is fairly difficult to find appropriate constructions of anisotropic laminated layers for which the both of natural frequency and loss factor become concurrently large. Considering the above, the following criterion optimizing vibrational characteristics of such structures as shells with the fairly large damping and the high frequency distribution density is proposed, i.e., that the least value of the product of frequency and loss factor for all vibrational modes should be maximized from the viewpoint of optimizing the free vibration reduction characteristics, in stead of the criterion to maximize the fundamental frequency which is one of the conventional concepts.