391 research outputs found
Vulnerability assessment to trihalomethane exposure in water distribution system.
Chlorination is an effective and cheap disinfectant for preventing waterborne diseases-causing microorganisms, but its compounds tend to react with the natural organic matter (NOM), forming potentially harmful and unwanted disinfection by-products (DBPs) such as trihalomethanes (THMs), haloacetic acids (HAAs), and others. The present paper proposes a methodology for estimating the vulnerability with respect to users' exposure to DPBs in water distribution systems (WDSs). The presented application considers total THMs (TTHMs) concentration, but the methodology can be used also for other types of DPBs. Five vulnerability indexes are adopted that furnish different kinds of information about the exposure. The methodology is applied to five case studies, and the results suggest that the introduced indexes identify different critical areas in respect to elevated concentrations of TTHMs. In this way, the use of the proposed methodology allows identifying the higher risk nodes with respect to the different kinds of exposure, whether it is a short period of exposure to high TTHMs values, or chronic exposure to low concentrations. The application of the methodology furnishes useful information for an optimal WDS management, for planning system modifications and district sectorization taking into account water quality
A Pre-screening Procedure for Pollution Source Identification in Sewer Systems
Illicit intrusions in Sewer Systems (SSs), modifying the wastewater characteristics, may create problems to the treatment plant
and/or to the final recipient water body. For this reason, the source identification (SI) problem is becoming an important issue
also in SSs. For large real systems, the computational burden might make the SI methodologies impractical. In this paper a prescreening
procedure, based on the pollution matrix concept, is introduced and applied before the SI methodology. Selecting a
group of possible candidate nodes and cutting consequently the scheme, a significant improvement both in terms of time and the
accuracy is obtained
Analysis of the isolation valve system in water distribution networks using the segment graph
The mechanical reliability of Water Distribution Networks (WDNs) is a relevant technical and scientific issue. During planned maintenance or unplanned interruptions, the affected area must be isolated by valves shutdown. This operation involves the alteration of the network structure, i.e., the domain of the hydraulic system, and for this reason the isolation valve system plays a central role. Some studies started to consider the presence of the isolation valve system in WDNs reliability analysis.
Accordingly, this work uses the Complex Network Theory to analyse the isolation valve system performance and to assess the importance of the segments generated by valves shutdown. Differently from the classic complex network theory approach, in this work the recently proposed WDN-relevance-based betweenness centrality is applied to the segment graph to introduce information about the relevance of the different elements into the network, considering geometric and hydraulic parameters, such as length, demand, risk of disconnection, etc. The proposed strategy also suggests an improvement in the representation of the segment graph with respect to the presence of parallel edges.
The strategy is presented using a small network, while it is demonstrated and discussed using a real WDN. The results indicate that the WDN-relevance-based betweenness centrality allows to effectively assess the importance of the segments generated by valves shutdowns, also providing indications to improve the isolation valve system design
Applicability of Kinematic and Diffusive models for mud-flows: a steady state analysis
The paper investigates the applicability of Kinematic and Diffusive Wave models for mud-flows with a
power-law shear-thinning rheology. In analogy with a well-known approach for turbulent clear-water
flows, the study compares the steady flow depth profiles predicted by approximated models with those
of the Full Dynamic Wave one. For all the models and assuming an infinitely wide channel, the analytical
solution of the flow depth profiles, in terms of hypergeometric functions, is derived. The accuracy of the
approximated models is assessed by computing the average, along the channel length, of the errors, for
several values of the Froude and kinematic wave numbers. Assuming the threshold value of the error
equal to 5%, the applicability conditions of the two approximations have been individuated for several
values of the power-law exponent, showing a crucial role of the rheology. The comparison with the
clear-water results indicates that applicability criteria for clear-water flows do not apply to shearthinning
fluids, potentially leading to an incorrect use of approximated models if the rheology is not
properly accounted for
Impact dynamics of mud flows against rigid walls
Mud flows represent one of the major causes of natural hazards in mountain regions. Similarly to
debris flows, they consist of a hyper-concentrated mixture of water and sediments flowing down a
slope and may cause serious damages to people and structures. The present paper investigates the
force produced by a dam-break wave of mud impacting against a rigid wall. A power-law shearthinning
model is used to describe the rheology of the hyper-concentrated mixture. A onedimensional
shallow water model is adopted and a second-order Finite Volume scheme is employed
to numerically solve the governing equations. The results indicate that depending on the fluid
rheological parameters and on the bottom slope, there exists a minimum value of the wall distance
above which the peak force does not exceed the asymptotic value of the hydrostatic final condition.
For two different values of the channel slope, the dimensionless value of this lower bound is
individuated for several values of the power-law exponent and of a dimensionless Basal Drag
coefficient. An estimation of the maximum peak force for wall distance smaller than the minimum
value is also provided
Potentialities of Complex Network Theory Tools for Urban Drainage Networks Analysis
Urban drainage networks (UDNs) represent important infrastructures to protect and maintain community health and safety. For these reasons, technicians and researcher are focusing more and more on topics related to vulnerability, resilience and monitoring for controlling illicit intrusions, contaminant and pathogenic spread. In the last years the complex network theory (CNT) is attracting attention as a new, useful and structured approach to analyze urban systems. The aim of this work is to evaluate potentialities of CNT approaches for UDNs vulnerability assessment and monitoring system planning. Limits and potentialities of applicability of CNT tools to UDNs are first provided evaluating the performances of standard centrality metrics. Then, it is proposed the use of tailored metrics embedding prior information, as intrinsic relevance of each node and pipe flow direction, which derive from the Horton's hierarchy and geometric data (pipe slope), respectively, without performing hydraulic simulations. The analysis is applied on two schematic literature networks of different complexity and to a real case-study. The results suggest that vulnerability/resilience, monitoring design, contaminant and pathogenic spreads can be effectively analyzed using tailored metrics. Therefore, the proposed approach represents a complementary tool respect the more complex and computationally expensive methodologies and it is particular useful for large complex networks
A Strategy for Passive Control of Natural Roll-Waves in Power-Law Fluids through Inlet Boundary Conditions
The paper investigates the influence of the inlet boundary condition on the spatial evolution of natural roll-waves in a power-law fluid flowing in steep slope channels. The analysis is carried out numerically, by solving the von Kármán depth-integrated mass and momentum conservation equations, in the long-wave approximation. A second-order accurate scheme is adopted and a small random white-noise is superposed to the discharge at the channel inlet to generate the natural roll-waves train. Both shear-thinning and shear-thickening power-law fluids are investigated, considering uniform, accelerated and decelerated hypercritical profiles as the unperturbed condition. Independently of the unperturbed profile and of the fluid rheology, numerical simulations clearly enlighten the presence of coalescence, coarsening and overtaking processes, as experimentally observed. All the considered statistical parameters indicate that the natural roll-waves spatial evolution is strongly affected by the unperturbed profile. Compared with the uniform condition, at the beginning of roll-waves development an accelerated profile reduces the growth of the roll-waves with a downstream shift of the non-linear wave interaction. The opposite behavior is observed if the roll wave train develops over a decelerated profile. The comparison with the theoretical outcomes of the linearized near wave-front analysis allows the interpretation of this result in terms of stability of the base flow. It is shown that once the coarsening process starts to take place, the roll-waves spatial growth rate is independent of the unperturbed profile. Present results suggest that an appropriate selection of the flow depth at the channel inlet may contribute to control, either enhancing or inhibiting, the formation of a roll-waves train in power-law fluids
Optimal Placement of Water Quality Monitoring Stations in Sewer Systems: An Information Theory Approach
A core problem associated with the water quality monitoring in the sewer system is the optimal placement of a limited number of
monitoring sites. A methodology is provided for optimally design water quality monitoring stations in sewer networks. The
methodology is based on information theory, formulated as a multi-objective optimization problem and solved using NSGA-II.
Computer code is written to estimate two entropy quantities, namely Joint Entropy, a measure of information content, and Total
Correlation, a measure of redundancy, which are maximized and minimized, respectively. The test on a real sewer network
suggests the effectiveness of the proposed methodology
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