عنوان مقاله [English]
The research investigates a fluid filled pipeline that is connected to a tank at its upstream and to a valve in the downstream and undergoes forces of water hammer due to sudden closure of the valve. The aim is to study the possibility of instability in this pipeline when there are large lateral displacements with small strains. As conventional dynamic analysis models of beams which are based on the infinitesimal strain theory (ε=∂u⁄∂x) cannot reflect the effect of large lateral displacements, in this study axial stresses are modeled as linear stresses and strains are modeled by so called von Karman nonlinear strains. The resulting partial differential equations are solved in the time domain by the finite elements method. The linearized equation of lateral vibration is made dimensionless and then it is solved in the frequency domain so as to plot dimensionless frequencies versus the dimensionless fluid velocities which represent the stability of the pipeline. The results provides useful diagrams to anticipate possible pipeline instability induced by fluid velocity.