The influence of structural damping on the internal fluid pressure during a fluid transient pipe flow

The traditional approximation made in the analysis of fluid-structure interaction for a reach of pipe is to view the transient behavior as a modified one-dimensional fluid wave. The major problem with this type of analysis is that the fluid model assumes the pipe structure is rigid. Therefore, the trend in analysis of fluid transients is to use a model which couples the equations for the fluid and structure, then solves them simultaneously. A four equation model concerned with only axial wave propagation and Poisson coupling to account for the fluid-structure interaction is evaluated in this study. The developed model includes viscous damping, and a fluid shear stress term to account for the structural and liquid energy dissipation.; Based on the comparison of the predictions with experimental data, the model can satisfactorily predict the wave speed, the fluid pressure, and the structural velocity. The results also show that the viscous damping of the pipe material reduces the pressure peaks caused during a transient event by eliminating the high frequency structural components from the pressure response. External supports also contribute to the structural damping. A typical saddle type support can be expected to increase the damping, and this can be modeled as either additional distributed damping or as an external damper.; In addition to the axial study, this report also includes an experimental study of a piping system to describe the influence of structural damping when transverse bending is present. It was discovered that when damping bending motion created by a valve closure, the effect of a properly sized pipe/damper system is to greatly accelerate the decay of the fluid pressure transient compared to a fixed case. The damper in effect absorbs some strain energy of the structure, reducing the resulting rebound fluid pressure.; The steady state vibration of a piping system also produces a fluid pressure response. These pressures can be reduced by installing an external damper: the stiffer the damper the more effective it is in reducing the dynamic pressure.