Dynamics of Branched Pipelines Conveying Internal Unsteady Flow

초록

The pipeline system conveying high pressurized unsteady internal flow may experience severe transient vibrations under the time-varying conditions imposed by the pump and valve operations. In the present work, a set of partial differential equations of motion developed by the author in his previous work to achieve the complete modeling of the fully coupled fluid-pipe interaction mechanism, is briefly reviewed and modified to include the effect of the circumferential strain due to the internal fluid pressure based on the shell theory. The finite element formulation for the modified fully coupled pipe dynamic equations is developed and applied to several sample pipeline systems. Numerical fluid and structural dynamic responses of the same pipeline system considered in a previous reference work are first compared with those given in the reference work so as to ensure the validity and accuracy of the present numerical analysis methodology. And then a new series pipeline system with high reservoir head is analyzed to investigate the effect of the additional coupling and nonlinear terms taken into account in modified pipe dynamic equations. To complete the present study, a simple branched pipeline system with a junction is investigated. The connectivity conditions for both fluid and pipe at the junction of a branched pipeline system are developed and properly incorporated in the finite-element formulation. Even these exist very little experimental investigations on the fully coupled fluid-pipe interaction problem, the author convinces that the numerical results obtained in this study are quite reliable. Furthermore, the present study shows that the additional linear and nonlinear coupling terms of fluid-pipe interaction can become significant at high fluid pressure or velocity.