(2005). The dynamic effect of pipe-wall viscoelasticity in hydraulic transients. Part II—model development, calibration and verification. Journal of Hydraulic Research: Vol. 43, No. 1, pp. 56-70.

The current paper aims at the assessment of the effectiveness of a popular transient-based technique—inverse transient analysis (ITA)—for leak detection in water pipe systems using physical data. Data were collected from two pipe systems made of polyethylene: a laboratory facility at Imperial College London and a quasi-field system at Thames Water Utilities. A hydraulic transient solver especially developed for viscoelastic pipes (typically made of polyethylene) and an optimization algorithm for the simultaneous creep calibration and leak location have been developed for the application of this technique. The evaluation of the presence, location, and size of leaks was carried out using collected data. ITA allowed for the identification of the approximate location of leaks as long as the physical characteristics of the pipeline are well known, the transient is generated by a fast change of flow conditions, the leak has a “reasonable size,” and the transient solver is accurate enough to describe the transient event.

The mechanical behaviour of the pipe material determines the pressure response of a fluid system during the occurrence of transient events. in viscoelastic pipes, typically made of polyethylene (pe), maximum or minimum transient pressures are rapidly attenuated and the overall pressure wave is delayed in time. this is a result of the retarded deformation of the pipe-wall. this effect has been observed in transient data collected in a high-density pe pipe-rig, at imperial college (london, uk). several transient tests were carried out to collect pressure and circumferential strain data. the pipe material presented a typical viscoelastic mechanical behaviour with a sudden pressure drop immediately after the fast valve closure, a major dissipation and dispersion of the pressure wave, and transient mechanical hysteresis. the creep-function of the pipe material was experimentally determined by creep tests, and, its order-of-magnitude was estimated based on pressure-strain data collected from the pipe-rig. a good agreement between the creep functions was observed. creep tests are important for the characterization of the viscoelastic behaviour of pe as a material; however, when pe is integrated in a pipe system, mechanical tests only provide an estimate of the actual mechanical behaviour of the pipe system. this is because creep depends on not only the molecular structure of the material and temperature but also on pipe axial and circumferential constraints and the stress-time history of the pipe system.

Pump operating as turbine (PAT) is an effective source of reducing the equipment cost in small hydropower plants. However, the manufacturers provide poor information on the PAT performance thus representing a limit for its wider diffusion. Additional implementation difficulties arise under variable operating conditions, characteristic of water distribution networks (WDNs). WDNs allow to obtain widespread and globally significant amount of produced energy by exploiting the head drop due to the network pressure control strategy for leak reductions. Thus a design procedure is proposed that couples a parallel hydraulic circuit with an overall plant efficiency criteria for the market pump selection within a WDN. The proposed design method allows to identify the performance curves of the PAT that maximizes the produced energy for an assigned flow and pressure-head distribution pattern. Finally, computational fluid dynamics (CFD) is shown as a suitable alternative for performance curve assessment covering the limited number of experimental data.

In the management of water distribution networks, large energy savings can be yielded by exploiting the head drop due to the network pressure control strategy, i.e., for leak reductions. Hydropower in small streams is already exploited, but technical solutions combining efficiency and economic convenience are still required. In water distribution networks, an additional design problem comes out from the necessity of ensuring a required head drop under variable operating conditions, i.e., head and discharge variations. Both a hydraulic regulation (HR)—via a series-parallel hydraulic circuit- and an electrical regulation (ER)—via inverter- are feasible solutions. A design procedure for the selection of a production device in a series-parallel hydraulic circuit has been recently proposed. The procedure, named VOS (Variable Operating Strategy), is based on the overall plant efficiency criteria and is applied to a water distribution network where a PAT (pump as a turbine) is used in order to produce energy. In the present paper the VOS design procedure has been extended to the electrical regulation and a comparison between HR and ER efficiency and flexibility within a water distribution network is shown: HR was found more flexible than ER and more efficient. Finally a preliminary economic study has been carried out in order to show the viability of both systems, and a shorter payback period of the electromechanical equipment was found for HR mode.