Significance of Creep Behavior of the Pipe Wall on Optimal Sizing of an Air Chamber in Long-Distance Viscoelastic Pipes

Viscoelastic pipes have lower wave speeds than typical rigid materials, but they also display a lag in their strain response when subject to the stresses associated with transient loadings. Although many transient solvers (including most commercial ones) neglect the wall’s lagging behavior, this work assesses the significance of viscoelastic behavior on air chamber design. To this end, crucial design parameters, namely, the chamber’s orifice coefficient, its total volume, and the ratio of water volume to the total capacity, are explored for their sensitivity to the wall’s creep response. Several alternative wave speeds, steady-state flow rates, and pipe lengths are explored, and an appropriate air vessel is designed for each using genetic algorithm (GA) optimization. The significance of a viscoelastic solver in designing an air chamber is particularly pronounced in pipes that are longer than a characteristic length LC=0.5a0τkm, where a0 is the initial wave speed and τkm is the longest lagging time, as well as in thin pipes with a smaller elastic moduli and lower static heads. The results demonstrated that accounting for the wall’s creep behavior in transient simulations permits a reduction in the size of the air chamber, in some cases by up to 82%, thus permitting more economically sized air chambers for the transient protection of pressurized flow systems.