Effects of Imperfections on the Instability of a Pipe Conveying Fluid: Data-Driven Modeling and Instability Transition

This paper studies the instability of a non-ideal pipe system conveying fluid. Unlike ideal modeling, three types of possible non-ideal factors have been considered in the present analysis. The pipe has a crack and is subjected to boundary relaxation, and the fluid in the pipe is viscous. It is an interesting instability problem of a fluid-structure system with multiple forms of imperfections. It gains motivation from our previous study and aims at further essential results for comprehensively understanding the nature of such a problem. In order to incorporate multiple imperfections, a new data-driven approach is developed to model the non-ideal pipe-fluid system. Then the influences of the support stiffness, fluid-solid mass ratio, crack, and fluid viscosity on the pipe instability are systematically discussed. Results show that the pipe exhibits flutter-divergence conversion at low mass ratios and flutter-mode transition at high mass ratios. Due to the two types of instability transitions, the critical flow speed could experience multiple sudden jumps as the support stiffness changes. With the imperfections of crack and viscous flow, the pipe's instability behavior tends to be more complicated, but the inducing mechanisms for the sudden changes are straightforward. They are instability-type conversion, instability-mode transition, and laminar-turbulent flow transition.