Vibration characteristics of reinforced plastic pipes in a fluid medium

The natural frequencies of a laminated orthotropic pipe and the closed form forced response to bending forces, have been obtained by using Fourier series expansion in conjunction with Galerkin´s method. Numerical results for the dimensionless frequencies are presented for the case of an empty pipe, one that is filled with a fluid, one that is surrounded by a fluid, and one that is filled and surrounded by a fluid. The isotropic case based on the Flügge shell equations is shown for comparison purposes. It was found that the presence of the fluid substantially decreases the natural frequencies.