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The successful industrial applications of pinch analysis techniques in energy optimisation and wastewater minimisation have resulted in the recent studies of combined mass and heat integration. Kim and Smith (2001) have demonstrated that operation of cooling water networks in series, rather than the conventional parallel arrangement improve cooling tower and cooling water network performance in new and retrofit design. In this work, utilising a superstructure to determine the mathematical formulation that characterises a cooling water network supplied by multiple cooling water sources, which often occurs in practice, extends this methodology. It is further demonstrated that the optimum cooling water supply to a network of cooling-water-using operations supplied by multiple sources is determined by considering the entire framework of sources and cooling-water-using operations, that is, unified targeting. This optimum is better than that obtained from considering individual subsets of cooling-water-using operations and its respective source, that is, single source targeting. Relevant practical constraints were included in the formulations to enhance robustness and applicability to real life situations. Practical constraints consisted of maximum return temperatures to cooling water sources, as wells as dedicated water sources and sinks of cooling-water-using operations. This concept was applied to an illustrative example and a case study of the Sasol Synfuels (Pty) Limited cooling water system that consisted of individual networks supplied by separate water sources. For the case with maximum water reuse the single source targeting method yielded an improvement of 11.6% over the parallel target for the illustrative example. In comparison, superior results were obtained with the developed unified targeting method, which yielded an improvement of 18.4%. Likewise, for the case with the aforementioned practical constraints 6.8% and 7.6% improvements were forecasted for the single source and unified targeting methods respectively. For the maximum reuse scenario of the case study, improvements of 37.9% and 41.0% over the parallel target were obtained using the single source and unified targeting methods, respectively. Similarly, considering practical constraints improvements of 20.3% and 31.1% were obtained. In both the illustrative example and case study the unified targeting method resulted in superior results than the single source targeting methods. / Dissertation (MEng (Chemical Engineering))--University of Pretoria, 2008. / Chemical Engineering / unrestricted

Access to clean drinking water is very important to the health and well-being of the population. Mathematical modeling, optimization, and online estimation are needed to solve challenging problems in water network applications such as the requirement to meet the new dynamic regulations in the Safe Drinking Water Act and the Clean Water Act. This includes providing sufficient capacity to satisfy uncertain and changing water demands, maintaining consistent water quality, and identifying and responding to abnormal events. In most of these applications, reliable knowledge of the water flow velocity is necessary. However, in practice, few measurements are usually available. This work uses a nonlinear optimization framework to estimate the unknown water demands and velocities from limited measurements. The problem is formulated as a constrained nonlinear least squares estimation problem. The constraints represent the basic governing mass and energy conservation laws as well as some operational constraints. Given the limited number of flow measurements, the estimation problem is ill-posed. Non-unique solutions may exist in which many demand profiles can match the limited number of measurements. Offline estimates of the demand patterns based on historical data are used to regularize the problem and force a unique solution. In the first phase of this project, a hydraulic model was developed for water distribution systems. This model showed very good agreement when it was validated against the simulator EPANET using 3 case studies. In the second phase, the estimation formulation was tested using the same 3 case studies with different sensor configurations. In each of the case studies, estimation results are reasonable with fewer sensors than the available degrees of freedom.

Arid regions tend to take careful measures to ensure water supplies are secured to consumers, to help provide the basis for further development. The distribution network is the most expensive part of the water supply infrastructure and it must maintain performance during unexpected incidents. Many aspects of performance have previously been discussed separately, including reliability, vulnerability, flexibility and resilience. This study aimed to develop a framework to bring together these aspects as found in the literature and industry practice, and bridge the gap between them. Semi-structured interviews with water industry experts were used to examine the presence and understanding of robustness factors. Thematic analysis was applied to investigate these and inform a conceptual framework including the component and topological levels. Robustness was described by incorporating network reliability and resiliency. The research focused on resiliency as a network-level concept derived from flexibility and vulnerability. To utilise this new framework, the study explored graph theory to formulate metrics for flexibility and vulnerability that combine network topology and hydraulics. The flexibility metric combines hydraulic edge betweenness centrality, representing hydraulic connectivity, and hydraulic edge load, measuring utilised capacity. Vulnerability captures the impact of failures on the ability of the network to supply consumers, and their sensitivity to disruptions, by utilising node characteristics, such as demand, population and alternative supplies. These measures together cover both edge (pipe) centric and node (demand) centric perspectives. The resiliency assessment was applied to several literature benchmark networks prior to using a real case network. The results show the benefits of combining hydraulics with topology in robustness analysis. The assessment helps to identify components or sections of importance for future expansion plans or maintenance purposes. The study provides a novel viewpoint overarching the gap between literature and practice, incorporating different critical factors for robust performance.

This research developed novel methodologies to achieve cost effective solutions to overcome many of the difficulties associated with unsteady state material recovery network synthesis. The work focuses on the development of three different methodologies: the first is a hierarchical multi-step methodology developed for the design and scheduling of batch water (material of interest) recycle networks. A new source- double tank-sink arrangement is introduced to overcome the limitation of samecycle assignment by permitting sources to be optimally recycled within the same batch cycle and/or storing and recycling sources to sinks in the following batch cycle. The problem is solved in interconnected stages. First, network targets such as minimum fresh water consumption and minimum waste water discharge are identified ahead of network design. Once design targets have been identified, an iterative procedure is followed to tradeoff fixed and operating cost to achieve a network design which has the minimum total annualized cost (TAC). The second developed methodology is a one-step simultaneous approach to design and schedule cost-effective batch water recycle networks. A new source-tank-sink representation is developed to embed potential configurations of interest for design and scheduling. As a result, water may be assigned from sources to sinks within the same cycle (with or without a storage tank) and in two subsequent cycles using a double tank arrangement. A mathematical formulation is developed to determine the network design and sufficient information on the scheduling of the network with the minimum TAC in one step. The third methodolgy this research developed is a systematic procedure to schedule the operation of an unsteady state material recovery network. The network has a set design and receives a number of feedstocks (sources) that are to be processed into higher value/quality products. The sources may be stored in tanks, mixed, and/or intercepted in separation devices to produce the desired products while maximizing profits and meeting all process constraints. The developed systematic procedure includes mathematical formulations that allow available sources to be stored, mixed, intercepted and determine the optimal scheduling scheme over time period ??with the objective of maximizing total annualized profit of the network.

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Management and supply of water in an urban water distribution system is a complex process, which include various complexities like pressure variations across the network depending on topography, demand variations depending on customers’ requirement and unaccounted water etc. Applying automatic control methods to water distribution systems is a way to improve the management of water distribution. There have been some attempts in recent years to develop optimal control algorithms to assist in the operation of complex water distribution systems. The difficulties involved by these hydraulic systems such as non-linearity, and diurnal demand patterns make the choice of a suitable automatic control method a challenge. For this purpose, this study intends to investigate the applicability of different controllers which would be able to meet the targets as quickly as possible and without creating undue transients. As a first step towards application of different controllers, PD and PID linear controllers have been designed for pump control and valve control in water distribution systems. Then a Dynamic Inversion based nonlinear controller has been designed by considering the non-linearities in the system. Here, different cases considering the effects of initial conditions used, linearization methods used, time step used for integration and selection of gains etc., have been studied before arriving at best controller. These controllers have been designed for both the flow control problems and level control problems. It is found that Dynamic Inversion-based nonlinear controller outperforms other controllers. It is well known that the performance of controllers is much dependent on the tuning of the gains (parameters). Thus in this study various alternative techniques such as Ziegler--Nichols rules (ZNPID), Genetic algorithms (GAPID) and fuzzy algorithms (FZPID) have been studied and a comparative study has been made Although with all the three gain tuning methods, required states have reached their target values, but the responses vary much in reaching to final targets. The self-tuned FZPID controller outperforms other two controllers, especially with regard to overshoots and the time taken to tune the gains for each problem. Further, an optimal DI controller is developed for the over determined case with more controls and less targets. Energy loss is considered as an objective function and normal DI controller equations are considered as constraints. Hence, an attempt is made to reduce the energy minimization in water distribution system by formulating an optimal control problem using optimal Dynamic Inversion concept. Finally, leakage reduction model is developed based on excessive pressure minimization problem by locating valves optimally as well as by setting valves optimally. For this purpose, optimization problem is solved using Pattern search algorithms and hydraulic analysis is carried out using EPANET program.

Cette thèse cherche à renouveler les cadres d’interprétation sur la conflictualité autour de la ressource en eau au Mexique, en adoptant une approche constructiviste des conflits hydriques. A travers l’analyse détaillée de deux situations de conflit sur l’eau liées à l’urbanisation dans l’Etat du Morelos, et l’étude de la façon dont les groupes mobilisés formulent le problème, nous mettons en évidence que les conflits sur l’eau n’expriment pas uniquement une demande d’accès à l’eau, mais aussi des revendications d’ordre patrimonial : les communautés paysannes se mobilisent pour préserver certains points d’eau, certaines infrastructures (réseaux d’eau, réservoirs), qui ont pour eux une signification particulière. Même si dans le Morelos, les réseaux d’eau sont le support d’une culture hydraulique singulière, le projet patrimonial ne répond pas seulement à la volonté de conserver certaines traces qui se trouvent menacées de disparition et revêt des enjeux politiques et identitaires pour les communautés agraires, qui ont subi de profonds bouleversements à la suite des réformes du statut des terres ejidales. Cependant, la dimension patrimoniale n’est pas prise en compte par les acteurs publics de l’eau, et la conflictualité reste latente. / This dissertation aims at renewing interpretations on water conflicts in Mexico, by adopting a constructivist approach. Through the detailed study of two water conflicts linked to urbanization in the State of Morelos and the analysis of the way the actors formulate the problem, we show that water conflicts don’t only express demands on water access, but also patrimonial claims: peasant communities mobilize because they want to preserve some water points, some hydraulic infrastructure (water networks, water tanks) that have a special meaning for them. Although in Morelos, water networks have given rise to a specific hydraulic culture, the patrimonial project is not only linked to the will of preserving a cultural heritage that may disappear and has a political and identity relevance for peasant communities that have been deeply shaken up by the land reforms of the nineties. Nevertheless, water public actors do not take patrimonial claims into account, and conflicts are latent.

El control i supervisió de processos es basa generalment en la utilització de models. Models que han de ser tan acurats com sigui possible. Processos complexes com les xarxes de distribució d'aigua no escapen d'aquesta situació. Una bona gestió d'aquest element tan necessari i cada cop més escàs en les condicions adequades és una necessitat vital.Aquesta tesi ha estat realitzada amb la col·laboració de dos grups de recerca, un més orientat a l'aplicació -xarxes d'aigua- i l'altre ala metodologia -control i supervisió -. L'experiència d'ambdós grups va generar la necessitat de la calibració de models de xarxes per tal de poder realitzar bones simulacions, optimitzacions, supervisió, detecció de fuites, etc. L'objectiu principal d'aquesta tesi és desenvolupar una metodologia per aquesta calibració.L'originalitat d'aquest treball rau tan en l'abast del problema com les tècniques emprades. Una xarxa inclou elements diversos (nodes, dipòsits, canonades, vàlvules i bombes) i la calibració requereix l'estudi detallat de cada element així com l'aplicació a sistemes immensos. S'ha parat especial atenció a als tres passos principals de la calibració: estudi d'identificabilitat, macrocalibració i microcalibració. Cada un d'aquests passos requereix tècniques específiques. En aquesta tesi s'ha aplicat tècniques poc o gens conegudes en l'àmbit de les xarxes d'aigua.L'estudi d'identificabilitat s'ha desenvolupat per diferents escenaris, des del cas simple i il·lustratiu fins a xarxes reals i grans. Els experiments més simples es van fer amb xarxes lineals i estàtiques. En general les xarxes són no lineals i l'ús de més d'un instant en el temps en les mesures millora les condicions d'dentificabilitat. La metodologia proposada permet la determinació de la identificabilitat per xarxes en general (no lineals). L'eina obtinguda ajuda en el disseny dels problemes d'identificació fent servir informació topològica de la xarxa.Quan el model es genera, s'introdueixen grans errors. Aquests errors són detectats en un primer esforç de calibració, macrocalibració. Aquest procés es realitza manualment i l'objectiu d'aquesta tesi és donar suport a aquesta feina. La metodologia emprada pels experts s'ha analitzat. S'han fet servir algorismes específics per cada tipus d'error. Per tal de detectar errors en un conjunt gran d'elements s'han fet servir algorismes de classificació. Aquests algorismes permeten la generació de coneixement a partir d'experiments simulats i l'optimització de funcions de versemblança.La sintonia de paràmetres, es tractada com un problema d'optimització. La no convexitat del problema es determina en una caracterització acurada del problema. Aquesta no convexitat mostra els problemes que els optimitzadors locals tindran per resoldre'l. Les possibilitats d'alguns optimitzadors globals s'han explorat. El cost computacional dels optimitzadors globals, especialment quan les xarxes creixen, representa una gran limitació. El filtre de Kalman estès s'ha fet servir amb resultats prometedors.Els resultats d'aquesta tesi s'han presentat en tres congressos [Per-01a], [Per-01b], [Per-03] i s'està redactant un article per a revista abans de final d'any.Process control and supervision is based mainly in the use of models, which have to be as accurate as possible. Complex processes, like water distribution networks, fall into such a situation too. Water is a necessary element and its shortage in good conditions is a major problem. Therefore, a good management of water distribution is vital. / This thesis has been carried out with the collaboration of two research groups. One is more oriented to the application -water networks- and the other one is more oriented to the technology -control and supervision-. Experience of both groups has generated the necessity of calibration of water network models in order to be able to do good simulations, optimisations, supervisions, leak detections, etc. For this reason, the main objective of this thesis is to develop a closed methodology for the calibration process of water distribution network models.The originality of this work comes both from the magnitude of the problem and the techniques used. On the one hand, a water network includes different elements (nodes, reservoirs, pipes, valves, and pumps), and its calibration requires the study of those elements in detail. On the other hand it has to be applied to huge systems. Special attention has been paid to the three main parts of calibration: identifiability study, macrocalibration and microcalibration. Each of those steps needs specific techniques. Some of the techniques used in this thesis are little known or unknown at all in the water industry.The identifiability study has been developed for different case studies, ranging from simple, illustrating case to real huge networks. The simplest experiments were performed with linear and static networks. In general, networks are non-linear and the use of more than one time-step in the measurements provides better identifiability conditions. The methodology proposed allows the determination of the extended-period identifiability for general networks (non-linear). The obtained tool helps in the design of identification problems using topological information of the network.When the model is generated, large errors are introduced. These errors are detected in a first calibration effort, macrocalibration. This process is done manually and the objective in this thesis is to give support to such work. The methodology followed by the experts has been analysed. Specific algorithms have been used in this thesis for each kind of error. In order to detect errors in huge amount of elements classification algorithms have been used. Those algorithms allow the generation of knowledge from simulation experiments and optimisation of likelihood functions.The parameter tuning, microcalibration, is treated as an optimisation problem. The non-convexity of the problem is detected by a detailed characterisation. This non-convexity shows to be a problem for the local optimisers. The capabilities of some global optimisation algorithms have been explored. The computing cost for the global optimisers, especially when huge networks are identified, represents a major limitation. The Extended Kalman Filter has been used with promising results.Results of this thesis have been presented in three Conferences [Per-01a], [Per-01b], [Per-03] and a paper is will be finished before the end of the year.

京都大学 / 0048 / 新制・論文博士 / 博士(農学) / 乙第13021号 / 論農博第2831号 / 新制||農||1042(附属図書館) / 学位論文||H28||N4967(農学部図書室) / 32949 / 京都大学大学院農学研究科地域環境科学専攻 / (主査)教授 藤原 正幸, 教授 村上 章, 准教授 宇波 耕一 / 学位規則第4条第2項該当 / Doctor of Agricultural Science / Kyoto University / DFAM