Flow-Induced Vibration of a Flexible Rod Subjected to Axial Leakage Flow. Stability Analysis by using F. E. M. on the Axisymmetric Rod.

Recently, the leakage-flow inside the mechanical structures such as rods in the cylinders, valves, seals and orifices, so on for controlling the flow volume and the fluid pressure tends to become larger aiming to increse the plant efficiency, which lead to the occurrence of the fluid-elastic instability of these structures. In this study, the fluid-elastic instability analysis procedure is proposed in order to establish the design criteria on protecting the key components from the flow-induced instability. The unsteady fluid force is derived theoretically for the simple segment and the equation of motion for the axisymmetric rods is conducted by the finite element method. Using these formulation the coupled equation of motion between fluid and structures is derived. The stability evaluation is performed using the Argand diagram obtained by plotting the real part and the imaginary part of the eigen value λ. Comparing the numerical values with the experimental values, this evaluation method is very efficient as the design criteria for the flow-induced instability.