Limarchenko V. Oscillations of pipelines with liquid on a vibrating base

The thesis deals with study of oscillations of pipelines on a moving foundation with high-speed fluid flow for different types of excitation of foundation. For studying this class of problems we constructed nonlinear model, which considers great number of normal modes, on the basis of variational principles, methods of nonlinear mechanics and variational methods of mathematical physics. Investigation of straight cantilevered pipeline with flowing liquid was performed. We consider vibrational transversal and longitudinal given motions of foundation as well as the case of impulse motion of pipeline foundation. Effect of variation of liquid velocity and frequency of vibration of foundation on character of system motion was analyzed. It was discovered that for high velocities of fluid flow the system may lose stability of rectilinear state and pass to the state of oscillations near alternative equilibrium, and that on increase of frequency of vibration of foundation modulation of oscillations is manifested. Several cases, when liquid flow has stabilizing effect on pipeline oscillations, were found. Keywords: pipeline oscillations, moving base, fluid flow, transition process, critical velocity, loss of stability.