The natural frequencies of a laminated orthatropic pipe and the closed form forced response t o 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 w i t h 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 Fliigge shell equations is shown for comparison purposes. It was found that the presence of the fluid substantially decreases the natural frequencies. a A. 1j Bij Dij C 911 Q22 912 a66 Nomenclature shell radius N k=l Qij (k) velocity o f sound in fluid Ex -Eewxe l-Vx*Uex 1-v v xe ex shear modulus G xe Ex,E8,Gxe = orthotropic elastic constants modified Bessel function shell length fluid pressure on the shell external surface loads time u1,u2,u3 = axial, circumferential and radial displacement, respectively, of midsurface axial, circumferential and radial coordinates, respectively, of midsurface -X a .'.2+g 22 c2 = major and minor Poisson's ratios of orthotropic material, respectively Kronecker delta mass density of fluid mass density of shell circular frequency -w2 PshaZ dimensionless circular frequency velocity potential -A66 a 2 A22 a a 2 ' 2 2 a 0 2 f--h = thickness of shell Hncl) = Rankel function of first kind L22 = --*66 a2 + a A22 aa2 ae