The mechanical model of the system representing a ribbed pipe of ring like profile, formed by two surfaces of the coaxial cylindrical shells interacting with viscous incompressible liquid, the outer of which is geometrically irregular, and inner one is an absolutely rigid cylinder under the effect of the harmonic pressure 3526 D. V. Kondratov et al. pulsation at pipe ends is considered. The mathematical model of this system, consisting of differential equations in partial derivatives presenting dynamics of viscous incompressible liquid and an elastic ribbed shell together with boundary conditions is constructed. Expressions for amplitude frequency characteristics of outer geometrically irregular shell are discovered.