Flow-Induced Vibration And Instability Of Pipes Conveying Fluid And Plates In Axial Flow

Fluid-structure interactions of pipes conveying fluid and plates in axial flow are studied theoretically, numerically and experimentally. The focus is on the behaviours of the structures in flow-induced vibration and instability, and the effects of various factors and parameters on their dynamical behaviours. Following are the main contents and results of this study:1. Considering the non-uniformity of the flow velocity distribution in real fluids, the centrifugal force term in the equation of motion of pipes conveying fluid is modified. The flow-profile-modification factors are obtained for different flow profiles. The critical flow velocities in the cases of laminar and turbulent flow profiles are found to be lower to different extent than that with plug flow. Flow profiles have greater effects on the critical flow velocity for flutter than on that for divergence. By introducing the concepts of equivalent flow velocity and equivalent mass, the equation of motion of pipes conveying fluid with different flow profiles can be converted to the same form as that with plug flow.2. Based on Pflüger column model and that of a fluid-conveying pipe, the dynamical behaviours of pipes under coaction of distributed follower force and flowing fluid are studied. The effects of the distributed follower force and mass ratio on the dynamical behaviours of both simply-supported and cantilevered pipes are analyzed. The distributed follower force is found to have remarkable effects on types of instability and the critical flow velocities.3. The dynamical behaviours of rectangular plates with free side-edges in channel flow are studied with a two-dimensional fluid model. The Galerkin method and Fourier transform technique are employed to solve the plate and fluid equations. A new approach is introduced to treat the mixed boundary condition of perturbed velocity and pressure on the plate plane, which leads to a singular integral equation. Different types of instability, such as divergence, single-mode flutter, and coupled-mode flutter are found for plates supported differently at the leading and trailing edges. Mass ratio and channel-height-to-plate-length ratio have significant effects on types of instability and the critical flow velocities.4. The dynamical behaviours of rectangular plates with clamped side-edges and free leading and trailing edges in channel flow are studied with a three-dimensional fluid model. The effects of mass ratio, plate aspect ratio, channel-height-to-plate- width ratio, and damping on types of instability and the critical flow velocities are investigated.5. The in-vacuo and in-fluid dynamical behaviours of parallel-plate assemblies are studied theoretically and experimentally. A model of multi-parallel beams joined with a single beam is formulated in the theoretical analysis. The in-vacuo and in-fluid natural frequencies and mode shapes are obtained, as well as the variation of the in-fluid natural frequencies with varying flow velocity. An electro-magnetic method is employed in measuring flow-induced vibrations in narrow channels. The theoretical and experimental results are in fairly good agreement with each other.6. The in-vacuo and in-fluid natural frequencies and mode shapes of an aliform stay vane of a hydraulic turbine are calculated numerically with FEM software. The results and analyses show that the aliform stay vane is good in avoiding flow-induced resonance.