The effect of pipe viscoelasticity on the optimal design of pressurized irrigation network under water hammer conditions (Case study of Ismail Abad Lorestan pressurized irrigation network)

The present study focuses on the effect of viscoelastic properties on the optimal design of pressurized irrigation system taking into account the impact of water hammer. For this purpose, the three models, the optimizer, the hydraulic steady solver (HSS), and hydraulic transient solver (HTS) were coded together in the form of a computer model. In the optimizer model, the initial population is created from the available diameters. Then, for each member of this population, in the HSS, the values of pressure in the nodes and velocity in the pipes are calculated. These values are sent to HTS as an initial condition. In the HTS, by applying a water hammer condition on the system, the maximum overpressure in each node is calculated and the results are sent to the optimizer model. Here the value of the objective function is calculated by observing the constraints for each member of the initial population and relative compatibility is obtained for all members. By applying the operation of mutation, intersection, replacement with the elitist approach, the next generation is finally calculated and the mentioned steps are repeated until the condition of stopping the calculations and determining the optimal answer is reached. Validation of the HTS in viscoelastic pipes using data measured at the Imperial College (London, UK) and considering three Kelvin–Voigt elements and retardation times of 0.05, 1.5 and 5 seconds for these three elements are done. The results showed that for wave speed of 390 m / s, the measured pressure fluctuations are in good agreement with the calculations. After confirming the model results, water hammer simulation of Ismailabad network in the current situation, which is composed of GRP and HDPE pipes, was performed with and without considering the viscoelastic properties for polyethylene pipes.