Transient Energy Analysis in Water-Filled Viscoelastic Pipelines

The transient flow phenomenon in a pipeline accounts for the flow variations with time and space. The transient energy analysis (TEA) overlooks the process as it sums the energy of the entire pipe domain and reports it at each moment. The current research takes advantage of this approach to investigate different influential factors in water pipelines, including steady friction, unsteady friction, and pipe wall viscoelasticity, to figure out the energy conversion and dissipation during a transient flow process. To this end, energy expressions are derived and compared for both elastic and viscoelastic pipeline systems. Two different viscoelastic materials - oriented polyvinyl chloride (PVC-O) and high-density polyethylene (HDPE) - are applied in the analysis to compare the proportions of the energy dissipation by different influential factors. The results reveal that at small transient perturbations, the influence of the steady friction is dominant in the energy dissipation, and the impact of viscoelasticity grows with the excitation intensity and valve's oscillation frequency. Besides, spatial variations of energy dissipation (per unit of length) along the pipeline have been investigated in single and branched systems, demonstrating significant deviations by distance from the excitation source.