Giuseppe Pezzinga

Multiobjective Optimization of Pipe Replacements and Control Valve Installations for Leakage Attenuation in Water Distribution Networks

AbstractThis paper shows how pipe replacements and control valve installations can be optimized in water distribution networks to reduce leakage, under minimum nodal pressure constraints. To this end, a hybrid multiobjective algorithm, which has pipe diameters and valve positions and settings as decisional variables, was set up. The algorithm also enables identification of the isolation valves that have to be closed in order to improve effectiveness of the control valves installed. The algorithm is initially applied to the optimal valve location problem, where it explores the trade-off between the number of installed control valves and the daily leakage volume. In this context, the analysis of the results proves the new algorithm more effective than a multiobjective genetic algorithm widely adopted in the scientific literature. Furthermore, it shows that if some isolation valves identified ad hoc are closed in the network, the installation of control valves determines larger leakage volume reductions. In ...

Two-Dimensional Features of Viscoelastic Models of Pipe Transients

AbstractTransients in pressurized polymeric pipes are analyzed by means of a two-dimensional (2D) Kelvin-Voigt viscoelastic model, calibrated by means of a microgenetic algorithm on the basis of pressure traces. The reliability of the proposed model is then tested by comparing numerical and experimental profiles of the axial component of the local velocity, the latter measured by means of an ultrasonic Doppler velocimeter. Differences between transients in viscoelastic and elastic pipes are pointed out by considering a 2D model in which an elastic behavior is assumed for pipe material. The comparison between the two 2D models allows attribution of the faster decay of pressure oscillations and velocity profiles to viscoelasticity because of the time-shift between pressure oscillation and retarded circumferential strain. The 2D analysis shows that the viscoelastic model generally presents flatter velocity profiles with respect to the elastic model.

Second viscosity in transient cavitating pipe flows

The paper presents the results of a research on the use of distributed cavitation quasi-2D models to reproduce experimental runs of cavitating water hammer flow. Two effects due to presence of free gas are taken into account: the first is the dependence of the wavespeed on the pressure; the second is the presence of additional dissipations due to thermodynamic interactions between liquid and free gas or to dissolved gas release phenomena. For the latter aspects, different formulations of bulk viscosity (or second viscosity) coefficient are taken into account and verified by comparison with experimental results of cavitating water hammer flow. The comparison between computed and measured head oscillations show that the model allows a good reproduction of the observed phenomena if a proper calibration of the parameters is made.

Combined optimization of pipes and control valves in water distribution networks

An optimization model is presented for the combined design of pipes and control valves in water distribution networks. The model uses a genetic algorithm to select pipe diameters and location of control valves, and employs a non-linear programming algorithm to determine the valve settings. The optimal design includes minimization of both pipes and water leakage costs. The optimal valve regulation has the objective of reducing leakage with constraints on minimum pressure heads. The proposed methodology is applied to two networks, with results indicating that the optimal design is dependent on the unit cost of water. An analysis on this parameter shows that if water cost is low, the sizing of the diameters is not influenced by the pressure regulation policy to reduce leakage. As the cost of water increases, the combined optimization increases the pipe diameters, since this magnifies the possibility of pressure regulation by valves.

Analysis of Transient Vaporous Cavitation in Pipes by a Distributed 2D Model

AbstractThe features of an axial-symmetric two-dimensional (2D) model in a transient cavitating pipe flow are investigated. A distributed vaporous cavitation model is proposed, based on the mass and momentum balance equations for a liquid-vapor mixture. A conservation form of the continuity equation allows a simple numerical solution. Both one-dimensional (1D) and 2D models are considered to quantify the effect of friction in the simulation of experimental data. The axial-symmetric 2D model allows the evaluation of the velocity profile and a more accurate estimate of the wall shear stress. The comparison between the results of numerical runs and experimental data of pressure head oscillations in transient cavitating pipe flows shows that the errors on maximum head oscillations of 2D model are generally greatly reduced with respect to those of the 1D model. As expected, the quasi-steady 1D model does not adequately represent the experimental data, with exception of the first maximum oscillations, whereas t...

Mathematical models of blood flow in the arterial network

Mathematical models of blood circulation in the human arterial network are examined in the paper. In particular, a complete two–dimensional model is proposed in the hypothesis of gradually varied flow. Vessels are considered as elastic and blood is considered as a Newtonian fluid in laminar flow. The results are compared both with those of a two–dimensional model where the radial velocity component is neglected and with those of a one–dimensional model similar to others previously proposed. The comparisons show differences due to the effect of radial convection terms in the first case, and to the more correct evaluation of resistance and longitudinal convection terms in the second case.

On the choice of the demand and hydraulic modeling approach to WDN real‐time simulation

This paper aims to analyse two demand modelling approaches, i.e. top-down deterministic (TDA) and bottom-up stochastic (BUA), with particular reference to their impact on the hydraulic modelling of water distribution networks (WDNs). In the applications, the hydraulic modelling is carried out through the extended period simulation (EPS) and unsteady flow modelling (UFM). Taking as benchmark the modelling conditions that are closest to the WDNs real operation (UFM+BUA), the analysis showed that the traditional use of EPS+TDA produces large pressure head and water discharge errors, which can be attenuated only when large temporal steps (up to 1 hour in the case-study) are used inside EPS. The use of EPS+BUA always yields better results. Indeed, EPS+BUA already gives a good approximation of the WDNs real operation when intermediate temporal steps (larger than 2 min in the case-study) are used for the simulation. The trade-off between consistency of results and computational burden makes EPS+BUA the most suitable tool for real-time WDN simulation, while benefitting from data acquired through smart meters for the parameterization of demand generation models.