The Dynamics of Aspirating Cantilevered Pipes and Pipes Conveying Variable Density Fluid

This thesis undertakes the investigation of the dynamics of two different cases of a slender, flexible pipe conveying fluid: (i) an aspirating cantilevered pipe, ingesting fluid at its free end and transporting it towards the clamped end, and (ii) a pipe conveying a fluid whose density varies axially along the length of the pipe. The general context of the research is first provided by broadly introducing the field of Fluid-Structure Interactions (FSI) and reviewing the basic theory regarding pipes conveying fluid. Subsequently, a numerical approach coupling Computational Fluid Dynamics (CFD) and Computational Structural Mechanics (CSM) to simulate each system is developed in ANSYS(TM). Lastly, the linear equation of motion is derived for each system and solved using a Galerkin approach; the numerical experiments are then combined with these analytical results to determine the stability characteristics of each system.;In the case of a pipe conveying variable density fluid, the analytical model is derived using a Hamiltonian approach, for (i) a pipe clamped at both ends and (ii) a cantilevered pipe. It is shown that these systems lose stability by buckling and flutter respectively, similarly to the constant-density case, but with two distinctions. First, it is the density at the discharging end which most significantly affects the critical flow velocities, and second, for (ii), the magnitude of the density change can strongly influence in which mode the system loses stability, as well as the critical flow velocities.;The problem of an aspirating cantilevered pipe is of both fundamental and practical interest, with applications, for example, in deep sea ocean mining. The motivation for a continued study of the system is demonstrated through a review of previous research on the topic -- spanning many years and yielding often contradictory results. The newly proposed analytical model, derived using a Newtonian approach and heavily influenced by CFD analysis, is different from previous ones, most notably because of the inclusion of a two-part fluid depressurization at the intake. In this case, the combined numerical and analytical approaches suggest a first-mode loss of stability by flutter -- albeit a very weak one -- at comparable but usually lower flow velocities than the discharging cantilever.