This paper investigates the redesigning of existing steel piping hydraulic systems to control severe water hammer positive and negative surges. The applied control strategy is based on adding a branched polymeric short penstock at the transient sensitive regions of the existing system. Two types of polymeric materials used for the short penstock, high-density and low-density polyethylene (HDPE and LDPE), are investigated. The one-dimensional unconventional water-hammer model, based on the Vitkovsky and the Kelvin-Voigt formulations, is used for hydraulic transient analysis, along with the fixed-grid method of characteristics implemented for numerical computations. The numerical model is validated using comparison with experimental measurements available in the literature. The results demonstrate that such a strategy can significantly mitigate the pressure increase and decrease induced by water hammer waves. Moreover, it is found that the short penstock volume and material represent the key factors affecting the damping rate of the positive and negative pressure peaks. The branching strategy used herein induces a smaller increase of the period than does the inline strategy and produces a similar pressure-head damping.

This paper revisited the inline re-design strategy used for water-hammer control into an existing steel-piping water supply system to further promote a comprehensive exploration of the entire design driven parameters set, including pressure-head, circumferential-stress and radial-strain behaviors. This strategy consists of replacing a short-section of the transient sensitive region of the original piping system by another made of polymeric pipe-wall material. The 1-D unconventional water-hammer model embedding the Vitkovsky and the Kelvin–Voigt formulations was adopted to describe the flow behavior and solved by the Method of Characteristics (MOC). The model was used to investigate two critical scenarios, including water-hammer up- and down- surge events. The effectiveness of the proposed strategy was evaluated for the high- or low-density polyethylene (HDPE or LDPE) material used for the replaced short-section pipe-wall. Results suggested that the utilized strategy could be successfully employed to amortize pressure-head and circumferential-stress rise and drop. Moreover, the observed amortization rates were found to be strongly dependent upon the short-section material and size. However, two interesting characteristics of the control strategy at hand, not previously reported, also emerged from this study, including the amplification of the radial-strain peaks (and ridges) along with the spread-out of the wave oscillation period.