Numerical Simulation of Dynamic Phenomena of Unsteady Friction and Viscoelastic Effects in Pipeline under the Transient Flow

Abstract

Plastic pipes are widely used in pressurized water systems. The analysis of transient flow and estimation of maximum and minimum pressure wave propagation in pipeline and pipe networks is required for design and practice of piping systems, pumping stations, and dam water conveyance tunnels. The viscoelastic properties of the polyethylene pipes have significant effect on the estimation of pressure wave speed and attenuation in transient flow. The use of polymeric pipes such as polyethylene and polyvinyl chloride has recently increased due to their technical and economic advantages over steel and concrete pipes. Due to viscoelastic behavior, polymeric pipes have a significant impact on transient flows (Pezzinga, 2002). In a fast transient flow event like water hammer, viscoelastic properties of polymeric materials cause a residual stress in the pipe wall. These deformations will not return to their original state immediately after unloading (Covas, 2003). This viscoelastic behavior also affects the intensity, shape, and dampening of pressure oscillation in transient flows. Covas (2003) developed a numerical model to simulate the viscoelastic behavior of the pipe wall in transient flow events. In this study, the results of a linear viscoelastic model were compared with experimental results in the presence and absence of unsteady friction loss. Soares et al., (2008) also considered transient flow in PVC pipes, and their results were in good agreement with those obtained by Ramos et al. (2004). Evangelista et al., (2015) studied water hammer phenomenon in a Y-shaped system both experimentally and numerically. According to their results, the linear viscoelastic model was able to simulate the water hammer phenomenon in this system. The present research deals with the introduction and simulation of dynamic effects, including unsteady friction and pipe-wall viscoelastic in transient flows in polymeric pipes that widely used in water works. Accordingly, the governing equations are rewritten and manipulated for considering the unsteady friction and viscoelastic properties. The equations are then solved using the method of characteristics coupled with the finite difference method. Appling the inverse transient analysis method and with the aid of a genetic algorithm, the unknown parameters are determined. Steady state friction coefficients have to be estimated based on steady state data and other unknown parameters were calibrated based on the transient flow.

Keywords

• transient flow
• viscoelastic pipeline
• unsteady friction
• numerical model
• invers solution