Ivan Stoianov

Imperial College London | Imperial · Department of Civil and Environmental Engineering

The localization of sources of pressure transients is essential for proactively managing and reducing the adverse effects of these transients in water supply networks (WSNs). This paper addresses the issue of localizing transient sources in a WSN where there is uncertainty about the network connectivity. If closed valves or blockages in the pipes a...

Significant financial resources are needed for the maintenance and rehabilitation of water supply networks (WSNs) to prevent pipe breaks. The causes and mechanisms for pipe breaks vary between different WSNs. However, it is commonly acknowledged that the operational management and water pressure influence significantly the frequency of pipe breaks....

This paper investigates an adaptive control strategy which takes advantage of remotely actuated pumps and valves to improve the performance of water distribution networks (WDN) during burst incidents. The proposed strategy relies on model predictive control (MPC) to switch between problem formulations corresponding to normal operating conditions an...

In this paper, we present a new control problem for optimizing pressure and water quality operations in water distribution networks. Our problem imposes a set of time-coupling constraints to manage temporal pressure variations, which are exacerbated by the transition between pressure and water quality controls. The resulting optimization problem is...

Cast iron pipes have been extensively utilised in water supply networks worldwide. Many of these pipes are either at the onset or within their wear-out phase, during which failure rates rapidly increase, and the pipes should be repaired or replaced. However, the replacement and rehabilitation of these pipes might require extensive resources and tim...

This paper investigates the problem of integrating optimal pressure management and self-cleaning controls in dynamically adaptive water distribution networks. We review existing single-objective valve placement and control problems for minimizing average zone pressure (AZP) and maximizing self-cleaning capacity (SCC). Since AZP and SCC are conflict...

The provision of self-cleaning velocities has been shown to reduce the risk of discolouration in water distribution networks (WDNs). Despite these findings, control implementations continue to be focused primarily on pressure and leakage management. This paper considers the control of diurnal flow velocities to maximize the self-cleaning capacity (...

The provision of self-cleaning velocities has been shown to reduce the risk of discolouration in water distribution networks (WDNs). Despite these findings, control implementations continue to be focused primarily on pressure and leakage management. This paper considers the control of diurnal flow velocities to maximize the self-cleaning capacity (...

The calibration and continuous maintenance of hydraulic models is essential for the optimisation, planning and management of water distribution networks (WDNs). This process requires model fitting against multiple hydraulic states. However, when extended time series of hydraulic data are considered, it is essential to know which hydraulic states to...

In the last decade, the increasing use of high frequency water pressure monitoring has shown that water distribution networks can be frequently affected by pressure transients. In some instances, thousands of high amplitude cyclic loadings per year have been exerted on pipes posing a risk of fatigue damage. However, despite this awareness of a poss...

This paper considers joint design-for-control problems in water distribution networks (WDNs), where locations and operational settings of control actuators are simultaneously optimized. We study two classes of optimal design-for-control problems, with the objectives of controlling pressure and managing drinking-water quality. First, we formulate th...

Novel methods for detecting and localising leaks in water distribution networks are being increasingly investigated as water utilities face unprecedented financial and environmental challenges in reducing water losses. A promising method includes the solution of the regularised inverse problem that minimises the difference between simulated and mea...

Optimal sensor placement in water networks has been traditionally formulated to maximize either hydraulic model accuracy or spatial coverage. Because a unique sensor configuration that optimizes both objectives may not exist, these approaches inevitably result in sub-optimal configurations with respect to one of the objectives. This paper presents...

This paper investigates control and design-for-control strategies to improve the resilience of sectorized water distribution networks (WDN), while minimizing pressure induced pipe stress and leakage. Both evolutionary algorithms (EA) and gradient-based mathematical optimization approaches are investigated for the solution of the resulting large-sca...

This manuscript investigates the design-for-control (DfC) problem of minimizing pressure induced leakage and maximizing resilience in existing water distribution networks. The problem consists in simultaneously selecting locations for the installation of new valves and/or pipes, and optimizing valve control settings. This results in a challenging o...

This paper investigates the problem of optimal placement and operation of valves and chlorine boosters in water networks. The objective is to minimize average zone pressure while penalizing deviations from target chlorine concentrations. The problem formulation includes nonconvex quadratic terms within constraints representing the energy conservati...

In England and Wales, water utilities reduce hydraulic pressure to a minimum regulatory threshold in order to reduce leakage and avoid financial penalties. However, utilities are not legally bound to guarantee specific flow rates from fire hydrants, thus posing a risk for firefighting. We formulate a biobjective mixed-integer nonlinear program (MIN...

Hydraulic model-based leak (burst) localisation in water distribution networks is a challenging problem due to a limited number of hydraulic measurements, a wide range of leak properties, and model and data uncertainties. In this study, prior assumptions are investigated to improve the leak localisation in the presence of uncertainties. For example...

Hydraulic model-based leak (burst) localisation in water networks is a challenging problem due to uncertainties, the limited number of hydraulic measurements, and the wide range of leak properties. In this study, we investigate the use of prior assumptions to improve the leak localisation in the presence of model uncertainties. For example, 𝓁 2 -re...

In this paper, a new mixed integer nonlinear programming formulation is proposed for optimally placing and operating pressure reducing valves and chlorine booster stations in water distribution networks. The objective is the minimization of average zone pressure, while penalizing deviations from a target chlorine concentration. We propose a relax-t...

The deterioration and fracture of water supply pipes present a major threat for the continuous provision of drinking water. The hydraulic pressure in pipes is an influential factor for the occurrence of pipe breaks. However, little evidence has been provided so far for the quantitative assessment of the impact of pressure control on reducing the nu...

Water supply pipes age, deteriorate and break, which puts at risk the continuous provision of safe potable water endangering the public health in cities. Risk management methods are increasingly applied to optimise the capital investment for pipe replacement and rehabilitation, taking into account the probability and hydraulic impact of pipe breaks...

In this paper, a new mixed integer nonlinear programming formulation is proposed for optimally placing and operating pressure reducing valves and chlorine booster stations in water distribution networks. The objective is the minimisation of average zone pressure, while penalising deviations from a target chlorine concentration. We propose a tailore...

Unreported partially/fully closed valves or other types of pipe blockages in water distribution networks result in unexpected energy losses within the systems, which we also refer to as faults. We investigate the problem of detection and localization of such faults. We propose a novel optimization-based method, which relies on the solution of a non...

The ill-posed inverse problem for detecting and localizing leakage hotspots is solved using a novel optimization-based method that aims to minimize the difference between hydraulic measurement data and simulated steady states of a water distribution network. Regularization constrains the set of leak candidate nodes obtained from a solution to the o...

The resilience of a water distribution system is defined as its ability to maintain continuous customer supply, and can be improved by increasing its redundancy in energy and/or connectivity. This can, however, negatively impact other aspects of network performance, such as leakage management. In this article, we consider the design-for-control (Df...

The paper investigates the problem of optimal control of water distribution networks without storage capacity. Using mathematical optimization, we formulate and solve the problem as a non-convex NLP, in order to obtain optimal control curves for both variable speed pumps and pressure reducing valves of the network and thus propose a methodology for...

London Clay, which underlies the majority of Greater London, has a high shrink–swell potential that can result in damage to foundations and surface infrastructure due to seasonal expansion and contraction of the clay. Currently, surface movement as a result of shrink–swell is not monitored in London, meaning that the magnitude and cyclicity of thes...

This manuscript investigates the problem of optimal placement of control valves in water supply networks, where the objective is to minimize average zone pressure. The problem formulation results in a nonconvex mixed integer nonlinear program (MINLP). Due to its complex mathematical structure, previous literature has solved this nonconvex MINLP usi...

The implementation of robust hydraulic control in water supply networks relies upon the utilisation of redundant flow estimation methods. In this paper, we propose a novel model-based flow estimation method for diaphragm-actuated globe valves based on three pressure signals, namely the valve inlet pressure, valve outlet pressure and control chamber...

The optimal placement and operation of pressure control valves in water distribution networks is a challenging engineering problem. When formulated in a mathematical optimization framework, this problem results in a nonconvex mixed integer nonlinear program (MINLP), which has combinatorial computational complexity. As a result, the considered MINLP...

Abstract Water Distribution Networks (WDN) are complex and highly interconnected systems. To maintain operation under failure conditions, WDNs should have built-in resilience based on topological and energy redundancy. There are various methods for analysing the resilience of WDNs based on either hydraulic models or surrogate network measures; howe...

In this paper, a new mathematical framework is proposed for maximizing the self-cleaning capacity (SCC) of drinking water distribution systems by controlling the diurnal peak flow velocities in the pipes under normal operation. This is achieved through an optimal change of the network connectivity (topology). This paper proposes an efficient algori...

Chlorination is necessary to prevent epidemics of waterborne disease however excess chlorination is wasteful, produces harmful disinfection byproducts, exacerbates corrosion and causes deterioration in aesthetic qualities, leading to consumer complaints. Residual chlorine must be continuously monitored to prevent both under- and over-chlorination a...

In this paper, we consider the proactive control of flow velocities to maximise the self-cleaning capacity of the drinking water distribution systems under normal operations both through a change of the network topology and through an optimal control of pressure reducing valve (PRV) settings. Inspired by line outage flow distribution in electrical...

Changes in power generation and supply and changes in water distribution systems are creating new opportunities for water utilities to enhance operational efficiency and income through the use of advanced control and optimisation. First, the increase in renewables penetration into the grid is causing a growth in energy storage schemes. Second, vari...

The sectorisation of water supply networks (WSNs) includes the permanent closure of valves in order to achieve a cost-effective leakage management and simplify pressure control. The impact of networks sectorisation, also known as district metered areas (DMAs), on water quality and discolouration has not been extensively studied and it remains unkno...

In the present manuscript, we investigate and demonstrate the use of outer approximation methods for simultaneously optimising the placement and operation of control valves in water distribution networks. The problem definition results in a mixed-integer nonlinear program with nonconvex constraints. We simplify the formulation, compared to previous...

For electricity grids with an increasing share of intermittent renewables, the power generation mix can have significant daily variations. This leads to time-dependent emission intensities and volatile electricity prices in the day-ahead and spot market tariffs that can be better utilised by energy intensive industries such as water supply utilitie...

In this paper, we investigate the application of penalty and relaxation methods to the problem of optimal placement and operation of control valves in water supply networks, where the minimization of average zone pressure is the objective. The optimization framework considers both the location and settings of control valves as decision variables. H...

This paper presents a novel analysis of the accuracy of quadratic approximations for the Hazen–Williams (HW) head loss formula, which enables the control of constraint violations in optimisation problems for water supply networks. The two smooth polynomial approximations considered here minimise the absolute and relative errors, respectively, from...

In this paper, we study the multiobjective co-design problem of optimal valve placement and operation in water distribution networks, addressing the minimization of average pressure and pressure variability indices. The presented formulation considers nodal pressures, pipe flows and valve locations as decision variables, where binary variables are...

Biofouling presents a significant obstacle to the long-term use of electrochemical sensors in complex media. Drinking water biofilms reduce performance of sensors by insulating electrode surfaces by inter alia inhibiting mass transport. Boron-doped diamond (BDD) electrodes are relatively resistant to biofouling and inert at high potentials. These q...

Increasingly more variable speed drive pumps are installed in water distribution systems worldwide. However, the modeling of variable speed drives in such networks remains difficult, especially in the context of mathematical optimization for pump scheduling. For the problem of energy usage minimization, formulated as a mixed integer program, we pro...

Water utilities face a challenge in maintaining a good quality of service under a wide range of operational management and failure conditions. Tools for assessing the resilience of water distribution networks are therefore essential for both operational and maintenance optimization. In this paper, a novel graph-theoretic approach for the assessment...

Significant changes in the power generation mix are posing new challenges for the balancing systems of the grid. Many of these challenges are in the secondary electricity grid regulation services and could be met through demand response (DR) services. We explore the opportunities for a water distribution system (WDS) to provide balancing services w...

Null space Newton algorithms are efficient in solving the nonlinear equations arising in hydraulic analysis of water distribution networks. In this article, we propose and evaluate an inexact Newton method that relies on partial updates of the network pipes' frictional headloss computations to solve the linear systems more efficiently and with nume...

Many sequential mathematical optimization methods and simulation-based heuristics for optimal control and design of water distribution networks rely on a large number of hydraulic simulations. In this paper, we propose an efficient inexact subspace Newton method for hydraulic analysis of water distribution networks. By using sparse and well-conditi...

Cost-effective management of leakage has driven the sectorization of water supply networks into discrete areas that are referred to as District Metered Areas (DMAs). The resulting change in network topology has a major impact on the hydrodynamic conditions and consequently changes in water quality. This paper investigates the impact of DMAs on the...

In this paper, we consider the use of an efficient null space algorithm for hydraulic analysis that employs preconditioned conjugate gradient (PCG) methods for solving the Newton linear equations. Since large water network models are inherently badly conditioned, a Jacobian regularization is employed to improve the condition number to some degree,...

An extensive experimental investigation into the pressure management and resilience of three water distribution network configurations is conducted including: fixed topology zones with fixed outlet pressure reducing valves (PRV), fixed topology zones with flow modulating PRVs, and a dynamic topology. Hydraulic data (128S/s) captures the network beh...

A novel hydraulic resilience index for the analysis of water distribution networks (WDN) is presented based on the reserve capacity, a concept extensively studied in transportation network literature. The reserve capacity is defined as a demand multiplier that represents how close a WDN is operating to a minimum service level. A method for calculat...

Hydraulic resilience can be formulated as a measure of the ability of a water distribution network to maintain a minimum level of service under operational and failure conditions. This paper explores a hybrid approach to bridge the gap between graph-theoretic and hydraulic measures of resilience. We extend the concept of geodesic distance of a pipe...

Water pipe failures are associated with pipe characteristics, material properties, environmental and loading conditions. Understanding the impact of individual factors, their dynamics and interactions is extremely complex. The steady and unsteady state hydraulic conditions may impose excessive loading on assets. The resulting cyclic loadings when a...

The operation of water distribution networks (WDN) with a dynamic topology is a recently pioneered approach for the advanced management of District Metered Areas (DMAs) that integrates novel developments in hydraulic modeling, monitoring, optimization, and control. A common practice for leakage management is the sectorization of WDNs into small zon...

Reducing discolouration events in aging water supply networks is a major challenge facing water utilities worldwide as they are required to comply with increasingly stringent water quality regulations in a proactive and cost-effective manner. Emerging control methods for dynamic reconfiguration of network topologies could reduce the risk of discolo...

In this article, a comprehensive review of existing methods is presented and computationally efficient sparse null space algorithms are proposed for the hydraulic analysis of water distribution networks. The linear systems at each iteration of the Newton method for nonlinear equations are solved using a null space algorithm. The sparsity structure...

The operation of pump systems in water distribution systems (WDS) is commonly the most expensive task for utilities with up to 70% of the operating cost of a pump system attributed to electricity consumption. Optimisation of pump scheduling could save 10-20% by improving efficiency or shifting consumption to periods with low tariffs. Due to the com...

In this paper, we survey mathematical programming methods for the management of pressure in water distribution systems through optimal placement and operation of control valves. The optimization framework addresses the minimization of average zone pressure under multiple demand scenarios, enforcing hydraulic equations as nonlinear constraints. Bina...

A dynamic topology aggregates zones in water distribution networks (WDNs) for improved pressure management and resilience to failure. Based on a sequential convex programming (SCP) approach, we propose an optimization method for the control of pressure reducing valves (PRV) in WDNs with dynamic topology. By restricting the SCP iterations to the fea...

A new approach for the operational management of water distribution networks is herein presented, which introduces district metered areas (DMA) with dynamic topology. The approach facilitates the operation of an open and adaptive network that reverts back to the original DMA structure only at night for leakage detection purposes, therefore eliminat...

This paper describes a simulation framework for the scale-adaptive hydraulic and chlorine decay modelling under steady and unsteady-state flows. Bulk flow and pipe wall reaction coefficients are replaced with steady and unsteady-state reaction coefficients. An unsteady decay coefficient is defined which depends upon the absolute value of shear stre...

This paper describes a novel approach for the continuous monitoring and analysis of the dynamic hydraulic conditions in water transmission and distribution systems. The developed InfraSense data logging and management technology extracts static and dynamic indicators which characterise the occurrence of hydraulic instabilities and unsteady-state fl...

This paper investigates the impact of the dynamic hydraulic conditions on the kinetics of chlorine decay in water supply systems. A simulation framework has been developed for the scale-adaptive hydraulic and chlorine decay modelling under steady- and unsteady-state flows. An unsteady decay coefficient is defined which depends upon the absolute val...

This paper presents a novel concept of adaptive water distribution networks with dynamically reconfigurable topology for optimal pressure control, leakage management and improved system resilience. The implementation of District Meter Areas (DMAs) has greatly assisted water utilities in reducing leakage. DMAs segregate water networks into small are...

When a piezoelectric energy harvester is connected to a simple load circuit, the damping force which the piezoelectric element is able to generate is often below the optimal value to maximize electrical power generation. Circuits that aim to increase the power output of a piezoelectric energy harvester do so by modifying the voltage onto which the...

The occurrence of hydraulic transients in water transmission and distribution systems and their impact on the deterioration of water quality is a topic which is beginning to attract a significant interest among scientists and system operators. Hydraulic transients are traditionally associated with large scale system failures. However, experimental...

The occurrence of hydraulic transient events in water supply systems may adversely affect the quality of drinking water. Sudden changes in the flow and pressure may cause sediment and biofilm detachment leading to discoloration and loss of residual chlorine. This paper presents the development and evaluation of a 1-D model that describes the chlori...

Monitoring the quality of drinking water from the treatment plant to the consumers tap is critical to ensure compliance with national standards and/or WHO guideline levels. There are a number of processes and factors affecting the water quality during transmission and distribution which are little understood. A significant obstacle for gaining a de...

Wireless sensor networks are deployed to monitor real-world phenomena, and are seeing growing demand in commerce and industry. These networks can benefit from time synchronized clocks on distributed nodes. The precision of time synchronization depends on error elimination or reliable estimation of errors associated with synchronization message dela...

The deterioration of civil infrastructure is a significant issue throughout the world. To manage infrastructure in a way that ensures safe and efficient operation, managers and engineers require data about its short-and long-term performance. This paper reports on the trial installations of wireless sensor networks in a suspension bridge, slab brid...

In recent years, research in wireless sensor networks (WSN) has been undergoing a quiet revolution, promising to have significant impact on a broad range of applications relating to environmental monitoring, structural health monitoring, security and water safety. The convergence of the Internet, telecommunications, and novel information technologi...

This paper describes the development and deployment of a modular, remote wireless sensor monitoring system and its initial deployment for monitoring railway track performance on a busy high speed Amtrak Northeast Corridor line. The monitoring platform addresses some of the challenges faced by remote system applications; cost factor, power consumpti...

US water utilities are faced with mounting operational and maintenance costs as a result of aging pipeline infrastructures. Leaks and ruptures in water supply pipelines and blockages and overflow events in sewer collectors cost millions of dollars a year, and monitoring and repairing this underground infrastructure presents a severe challenge. In t...

A state-of-the-art mathematical model has been developed to calculate hydraulic transients in pressurized polyethylene (PE) pipe systems. This hydraulic transient solver (HTS) incorporates additional terms to take into account unsteady friction and pipe-wall viscoelasticity. Numerical results obtained were compared with the classic waterhammer solu...

This paper analyzes the dynamic effects of pipe wall viscoelasticity on hydraulic transients. These effects have been observed in transient data collected from two polyethylene (PE) pipe systems. The first is a 270 m pipeline, 50 mm diameter, at Imperial College London, and the second is the world's longest experimental PE pipeline, 1.3 km long, 11...

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 defor...

In recent years there has been a decline in water quality in many urban lakes and ponds. We have developed a practical management and planning modelling framework, linking park land use with resulting pond water quality. This framework has a map-centric management structure, in which Geographic Information Systems (GIS) interact with the developed...

This paper presents, for the first time, experimental results demonstrating a new approach to increasing the power output of piezoelectric energy harvesters by applying a bias charge at the beginning of each half cycle of motion. Ultimate power limits of inertial energy harvesters depend only on the device size and nature of the excitation, rather...