Angelo Leopardi

A two-phase model for fast geomorphic shallow flows

The paper introduces a 2D shallow water model based on a two-phase formulation for the analysis of fast geomorphic transients occurring in the context of river morphodynamics. Mass and momentum conservation principles are separately imposed for both phases. The model naturally accounts for non-equilibrium solid transport, since neither instantaneous adaptation hypothesis nor any lag equation is employed to represent sediment dynamics. The hyperbolic character of the proposed model is shown to be preserved independently on the flow conditions. Results from numerical simulations of both 1D and 2D test-cases are compared with literature experimental data and with available numerical solutions.

Modelling trihalomethanes formation in water supply systems

Chlorination is the most widely used method for disinfection of drinking water, but there are concerns about the formation of by-products, such as trihalomethanes (THMs), since the chronic exposure to them may pose risks to human health. For these reasons regulations fix maximum acceptable THMs levels throughout distribution networks, so it is very important to be able to correctly reproduce their formation. In the literature many models for predicting THMs formation have been developed, both based on empirical relationships and on kinetics involved during chlorine reactions. In this work the use of some of these models and their reliability in real situations is investigated through the application to the Aurunci-Valcanneto Water Supply System in Southern Lazio (Italy). The comparison of the performances of 18 selected literature empirical models furnishes interesting observations, indicating that the formula, developed using field data, results in being more suitable for reproducing THMs formation for the presented case study. Other considerations are also offered from the comparison with the results obtained using a simple first order kinetic model, calibrated using measured data.

Hydraulic Transients in Viscoelastic Branched Pipelines

AbstractPlastic pipes are widely used in pressurized water systems. Their viscoelastic behavior has to be taken into account in the design phase as well as in the interpretation of water-hammer signals for diagnostic purposes. The aim of the present paper is to experimentally investigate the transient waves’ transmission and reflection in branched networks of high density polyethylene (HDPE) pipes and to test the efficacy of a viscoelastic model for the interpretation of the results. Two laboratory Y-shaped systems were built in the Water Engineering Lab of the University of Cassino and Southern Lazio (Italy) and a set of water-hammer tests was conducted on them. A significant variation of transmission and reflection coefficients at the pipe junction is observed in comparison with the values suggested in classical textbooks. The strong agreement between the experimental pressure values and those obtained using the viscoelastic model suggests that the differences from the classical theory are due to the vi...

Creep functions for transients in HDPE pipes

New experimental results obtained from a high density polyethylene (HDPE) pipeline for transient conditions are presented and discussed. Transient pressure data at different pipe sections were collected. Peculiar features were observed, which are typical of viscoelastic pipes, in particular, a significant damping of extreme pressures was observed in comparison to what is typically obtained for metal pipes. Physical constraints of the pipe are important to describe some vibrations observed in the system. The viscoelastic transient solver developed by Covas et al. (2005) was used to carry out numerical simulations of experimental tests. The comparison of numerical results with experimental data has shown that the viscoelastic model accurately predicts observed transient pressures. Additional considerations are carried out about the calibrated creep function for this test case in comparison with the ones obtained in previous researches.

Simulation of dam-break waves on movable beds using a multi-stage centered scheme

Abstract This paper presents the application of the multi-stage first-order centered scheme GMUSTA to solve a two-phase flow model with four equations for simulating dam-break floods without and with sediment transport. Computation of generalized Riemann invariants can be particularly complex and costly in simulating dam-break floods with sediment transport. GMUSTA numerical scheme, which does not require complete knowledge of the eigenstructure of the hyperbolic mathematical model, offers a suitable and attractive option. The quality of the dam-break flood simulations with GMUSTA scheme is verified by comparing the results against laboratory tests and some experimental data available in the literature, on fixed and mobile bed conditions, with different bed materials and flush or stepped bottoms. The numerical results reproduce quite well the experimental evidence, proving that the model is capable of predicting the temporal evolution of the free-surface and the bed. The GMUSTA scheme, which is not only simple to implement but also both accurate and computationally efficient, is proposed as an appropriate tool for integrating non-equilibrium sediment-transport models.

Evaluation of Different Formulations to Optimally Locate Sensors in Sewer Systems

AbstractEfficient management of a sewer system includes the control of the conveyed wastewater quality to adequately operate treatment plants and protect the receiving water bodies. Moreover, these...

Illicit intrusion characterization in sewer systems

Abstract A very important aspect in sewer systems management is represented by the detection of illicit intrusions, which recently supported the development of online sensors for wastewater quality monitoring. The present paper proposes a new methodology for characterizing an illicit intrusion in a sanitary or combined sewer system, using on-line pollutant concentration measurements. The source identification is formulated as an optimization problem, solved combining the hydraulic and quality simulation tool storm water management model (SWMM) with the GALib code. The methodology, which includes a pre-screening procedure useful for complex and large systems, is applied to a literature scheme and a real test-case, showing promising results. An uncertainty analysis is also performed for checking its robustness with respect to inflow uncertainty and in the presence of measurement errors.

Simulation of Chlorine Decay in Drinking Water Distribution Systems: Case Study of Santa Sofia Network (Southern Italy)

Drinking water treatment is needed for providing water that is safe from disease-causing pathogenic microorganisms. Chlorine is widely used as a disinfectant in drinking water systems, although the main disadvantages are the decay of its concentration along the pipes and the formation of undesirable by-products (DBPs). In this research work, the chlorine decay process has been investigated along a real water distribution system, the Santa Sofia aqueduct (Campania, Southern Italy), by an innovative modeling approach. The adopted hydraulic and water quality models have been calibrated on live data (the physical/chemical characteristics of the drinking water) and gathered continuously by a wireless network of multi-parametric probes distributed along the Santa Sofia aqueduct. The residual chlorine concentrations throughout the Santa Sofia network, predicted by hydraulic and water quality models calibrated on the same aqueduct, may be considered reliable.

Dam-break waves over an erodible embankment: experiments and simulations

ABSTRACT The impact of a dam-break wave on an erodible embankment with a steep slope is studied in the paper using both experimental and numerical approaches. The laboratory experiments have been specifically designed and performed for a range of the storage water levels and the embankment elevations and slopes. The simulations were carried out using a recently-developed two-phase depth-integrated model, supplemented with a geofailure operator to account for the possible occurrence of geotechnical collapses. A comparison between numerical and experimental results indicates that the two-phase model reproduces the experimental free surface elevation well, with or without the geofailure operator. On the other hand, especially for high embankment slopes, this operator appears to be important for predicting the observed morphological evolution. The results also show that, due to the geotechnical collapses, water and sediment velocities may have opposite signs. While the models based on equal direction of the liquid and the solid motions cannot reproduce this effect, the proposed two-phase approach easily accounts for such a peculiarity of the investigated process.

Water Infrastructure Protection Against Intentional Attacks: The Experience of Two European Research Projects

In the last years many interesting studies were devoted to the development of technologies and methodologies for the protection of water supply systems against intentional attacks. However, the application to real systems is still limited for different economical and technical reasons. The Water Engineering Lab (L.I.A.) of the University of Cassino (Italy) was involved in two research projects financed by the European Commission in the framework of the European Programme for Critical Infrastructure Protection (E.P.C.I.P.). Both projects, developed in partnership with a large Italian water company, have the common objective of providing guidelines for enhancing security in water supply systems with respect to the intentional contamination risk. The final product is represented by the arrangement of a general procedure for protection systems design of water networks. In particular, the procedure is described through the application to two real water systems, characterized by different size and behavior.