Impact of monotonic valve closure strategies on water hammer: numerical investigation including splines and cavitation effects

ABSTRACT

Valve-induced water hammer remains a major concern in fluid systems because it can generate severe pressure surges and cause system damage. However, valve closure times and closure policies are often evaluated separately, which limits a deeper understanding of their combined effects. This study treats monotonic valve closure as a curve-design problem for water hammer control in a reservoir pipe valve system. Conventional one-stage, multistage linear, and classical power-law closures are compared with smooth monotonic spline closures, namely piecewise cubic Hermite interpolating polynomial and Bézier, together with a modified power law incorporating a timing parameter. The method of characteristics is applied under single-phase flow and cavitating flow conditions for different closure durations, initial velocities, and pipe configurations. The results show that closure policy ranking is not universal but depends on the hydraulic state. At lower initial velocities, one-stage linear closures can produce lower transient heads, whereas at higher velocities and shorter closure durations, smoother and more aggressive profiles like the Bézier splines become preferable. The gas-cavity cavitation framework showed marked sensitivity to closure policy in the transition from the wave-dominated regime to the valve-dominated regime, underscoring the need for system-dependent valve closure design.