Vibration of non-homogeneous rectangular membranes with arbitrary interfaces

The study deals with the generalized solution of the title problem. The free vibration problem of a rectangular membrane with partial domains each of uniform density and arbitrary interface is tackled. Previous studies by other researchers include straight parallel to the borders and oblique interfaces, and bent ones. The solution is found by means of a direct variational method with a series composed with a complete set of functions. Two alternative sets are explored: trigonometric and power series. Such series are uniformly convergent to the exact solution. The approach is straightforward and very efficient from the computational viewpoint. A determinant-factorization method is employed to automatically eliminate eventual spurious frequencies. The well-known analogy between plates and membranes does not hold in this problem and a demonstration is included. Diverse illustrations are worked out as the cases of an oblique straight line interface and an open curve line which divides the membrane in two domains each of different density are first presented. Also a rectangular membrane with an interior closed domain is stated and the numerical example of a circular interior zone is included. Comparison between the two alternatives and with other authors’ results show excellent agreement. In all cases the computational cost is very low.