Investigation of the dynamic behaviour of hydraulic fluid lines under different end conditions

An investigation of dynamic characteristics of hydraulic transmissionlines has been carried out in order to develop a simple mathematical modelcapable of representing the dynamics of these lines accurately. Dynamicsof lines connecting different components of hydraulic control systems are,so far, considered by taking into account either the lines compressibilityeffects or their inertial resistances. In many cases, such a treatment wouldnot predict the dynamic characteristics properly, and in order to improvethe theoretical predictions, Navier - Stokes’ equations together with thelines boundary conditions are to be solved. The resulting mathematicalmodel in the latter case, however, is generally very difficult to be solved,specially when large hydraulic control systems incorporating lines withcomplex terminations are dealt with.In this work, the partial differential equations governing thedynamics of closed and open end lines have been solved under theassumptions of ideal flow, a linear friction term is added to compensate forthe viscous effects, and a viscous flow which is governed by Navier -Stokes’ equations. Comparing the theoretically obtained results withpublished experimental results showed that the first two treatments fail topredict the dynamics of the lines, while the third yields good agreementwith the experimental results. When the lines frictional resistance isassumed to be linear, but dependent on the exciting frequency in a certainway, this model showed to predict the dynamic characteristics with goodaccuracy ..