Natural frequencies of circular annular plates with variable thickness by a new method

A new method using the limited finite element method (FEM) for the analysis of the natural frequencies of circular annular plates of polar orthotropy and variable thickness is presented. Three-node annular elements of variable thickness are used. The stiffness matrix and mass matrix of the annular elements are obtained by combining analytical and numerical methods. Computations show that the results obtained by the present method are very accurate.