Dynamic analysis of a pipe conveying a twophase fluid considering parametric and non parametric uncertainties

Abstract

This thesis is interested in the dynamic system of a simply-supported horizontal pipe conveying a two-phase fluid. The fluid is modelled considering the hypothesis called “plug-flow”, it considers a uniform profile for the flow velocity. The pipe is represented considering two different structural models. The prior considers the linear Euler-Bernoulli beam hypothesis, while the latter considers nonlinear terms for the beam stiffness. The dynamic system final equation is obtained using the extended Hamilton’s principle. Next, the system is discretized by means of the finite element method. The flow velocity acts in the structure as a compression load, and it can cause the dynamic system bifurcation (buckling) when the flow reaches critical velocities. Parametric and non-parametric uncertainties are introduced in the system, where the two-phase flow parameters and the fluid finite element matrices are modelled considering probabilistic distributions, it results in a stochastic dynamic model which the final result is approximated by the Monte Carlo method. The multiphase flow parameters: void fraction, vapour quality and slip ratio may be introduced into coefficients being modification factors of the terms of the singlephase fluid. Therefore, the unique difference between pipes conveying a single-phase or a multiphase flow is these coefficients values. This way, it is possible to understand and evaluate the influence of the multiphase flow parameters in the system structural response.