Luigi Cimorelli

Optimal design of urban drainage networks

In this paper, a general procedure for the optimal design of urban drainage networks is proposed taking into account realistic technical constraints and the management cost of the automatic flushing devices. The procedure, which is based on the utilisation of a standard genetic algorithm, is first tested with reference to a urban drainage network taken from the literature, while a second test case is considered in order to evaluate the impact of different input parameters and constraints on the optimisation problem. In particular, we evaluate: (i) the effect of considering the crown elevation of the network outlet not fixed a priori but variable in a given range; (ii) the effect of imposing that the size of the conduit downstream a node should be not smaller than the sizes of the conduits upstream; and (iii) the effect of modifying input parameters such as the peak wastewater discharge or the management unit costs.

Optimal Design of Rural Drainage Networks

Abstract In this paper, a novel procedure is presented and demonstrated for the optimal design of rural drainage networks, based on the coupling of a genetic algorithm with suitable hydrologic and hydraulic models. The models, which allow the evaluation of water depth and discharge through the network, differ for the levels of simplification introduced into the representation of physical phenomena (rainfall-runoff transformation and flood wave propagation through channels). Their applications are shown and the use of oversimplified approaches is discussed: although very popular in practice, they can adversely affect the characteristics of the optimal network.

Optimal Location and Setting of PRVs in WDS for Leakage Minimization

Water loss is an issue that affect Water Distribution Systems (WDSs) very often, especially when aged and high pressure occurs. Pressure reduction valves (PRVs) can be used as devices to reduce as much as possible the water losses within the network. Indeed, for a given number of PRVs, the daily volume of water lost from the network can be reduced minimizing the pressure through a proper choice of valve positions as well as their settings. In this paper, a methodology for the optimal number, positioning and setting of PRVs is presented. In the proposed methodology, a genetic algorithm is coupled with a physical modelling of leakage from joints and a simplified and yet realistic hydraulic simulation of the WDS. The proposed methodology is demonstrated using two WDSs examples. Comparisons with a more extreme and complicated hydraulic modelling, already proposed by authors in previous work, are also performed in the first case study in order to validate the proposed methodology. These comparisons demonstrate that the methodology proposed in this work performs fairly well when compared to similar approach that uses a more sophisticated hydraulic model. As a consequence, it revealed to be a good tool for the optimal positioning and sizing of PRVs within WDS aimed at reducing the background leakages even when the WDS is characterized by complex geometry and topology.

Enhancing the Efficiency of the Automatic Design of Rural Drainage Networks

AbstractThe discharges flowing through rural drainage networks depend not only on the local climatic and hydrologic characteristics, but also on the geometric characteristics of the channels constituting the network. For this reason, the evaluation of the design discharges should be accomplished during the search of the optimal network. This leads to time-consuming optimization procedures, and it is desirable to devise efficient numerical alternatives. Two novel models, EGA and EGA-f, are proposed in order to increase the numerical efficiency of genetic algorithms (GAs) for the solution of the optimal rural drainage network problem. Both EGA and EGA-f procedures are based on the use of the nodal excavation depths at the channel ends as decision variables. Moreover, the EGA-f procedure improves EGA by freezing temporarily the design discharges during the optimization process in the case where uniform flows through the channels can be assumed. The application of the two models is demonstrated by means of nu...

Novel Numerical Approach for 1D Variable Density Shallow Flows over Uneven Rigid and Erodible Beds

AbstractThe numerical modeling of hyperconcentrated shallow flows is a challenging task because they exhibit special features, such as propagation over dry beds, profound bed elevation modifications owing to erosion or deposition phenomena, and flow discontinuities. In this paper, a novel depth-positivity preserving Harten, Lax, and van Leer—contact (HLLC) Riemann solver is devised in order to approximate the solution of the Riemann problem for the 1D (one-dimensional) hyperconcentrated shallow flows equations over horizontal beds. The solver is used as a building block for the construction of hyperconcentrated shallow flows (HCSF), a well-balanced finite-volume scheme for the solution of the hyperconcentrated shallow flows equations with variable elevation. HCSF is able to handle the case of dry beds, to take into account the variability of the topography also in the presence of bed discontinuities, considering the flow resistance and the mass exchange between the flowing mixture and the mobile bed. The ...

Optimal Positioning and Sizing of Detention Tanks within Urban Drainage Networks

AbstractThe present work describes a procedure for the evaluation of the optimal number, position, configuration, and sizes of detention tanks in urban drainage networks, to decrease the maximum flow depths and velocities for an assigned return period and to comply with the local design requirements. Each candidate solution of the optimization problem is evaluated by means of a semidistributed hydrological model in which the kinematic wave is used as flood routing model, whereas the variational approach is used to evaluate the critical flow characteristics corresponding to a given return period. The procedure, which makes use of a genetic algorithm to search for the optimal solution among the candidates, is applied to a case study drainage network, considering superpipe-based detention tanks as detention systems. The results indicate that these tanks are effective in the rehabilitation of the drainage network and that the cost of this intervention is substantially lower than that corresponding to the upgr...

A numerical model for the simulation of debris flow triggering, propagation and arrest

In this paper, it is described the development and the assessment of a 1D numerical procedure for the simulation of debris flow phenomena. The procedure focuses on: (1) the rainfall triggering, and the effects induced on slope stability by both rainfall infiltration and groundwater dynamics; (2) the possible inception of debris flows during the propagation phenomenon itself, due to the actions exerted on the slope by the already triggered flowing masses; (3) the propagation phenomenon over complex topographies; (4) the non-Newtonian internal dissipative processes that develop within the sediment–water mixture; (5) the effects induced by the evolution of the boundaries where the propagation phenomenon occurs; (6) the run-out and arrest phenomena. In order to show the performance and capabilities of the model, the results of its application to an analytic test and to laboratory experimental tests are first analyzed, and finally, the application to a plausible debris flow scenario, taken from a real case study, is discussed.

Exact Solution of the Dam-Break Problem for Constrictions and Obstructions in Constant Width Rectangular Channels

AbstractIn hydraulic engineering, it is common to find geometric transitions where a channel is not prismatic. Among these geometric transitions, constrictions and obstructions are channel reaches ...

Comparison Among Resilience and Entropy Index in the Optimal Rehabilitation of Water Distribution Networks Under Limited-Budgets

The replacement of existing pipes is a strategy for the rehabilitation of water distribution networks that is frequently adopted by water companies. Usually, the optimal choice of the pipes diameter is a difficult optimization task, because limited budgets are available. In order to support the selection of a rehabilitation strategy, surrogate reliability measures are often used as an indirect measure of the water distribution system hydraulic performance. Among others, the resilience and entropy indices have attracted considerable interest because they both represent a measure of the network robustness. In the present work, a comparison between these indices is provided in the framework of the optimal rehabilitation of an existing network under limited budget constraint. The resilience and entropy indices are applied to the case of a realistic water distribution network in an extended period simulation framework. Several values of the maximum budget allocable for rehabilitation are considered, and hydraulic calculations are undertaken by means of a pressure driven approach within a modified EPANET 2 environment. The effectiveness of the two surrogate reliability measures is demonstrated by an a-posteriori reliability assessment.

A Derivative Free Non-Linear Programming Method for the Optimal Setting of PATs to Be Used in a Hybrid Genetic Algorithm: A Preliminary Work

In recent years, recovering energy while managing excessive pressure in water distribution networks (WDNs) has gradually taken hold through the use of Pumps as Turbines (PATs). Therefore, algorithms commonly used for the optimizations of WDNs require modifications to incorporate these devices. Within this study, an intermediate step toward a new Hybrid Genetic Algorithm (HGA) for the optimal placement and setting of PATs within WDNs is proposed. The described methodology is based on a non-linear optimization algorithm, the Powell Direction Set (PDS) method. For each WDN configuration with PATs, a non-linear univariate function, namely the energy production subjected to pressure and technical constraints, is maximized by the PDS method. The promising capabilities of the algorithm are demonstrated with a case study.