Academic literature on the topic 'Demand-driven-Analysis – (PDA)'

The hydraulic analysis of water distribution networks (WDNs) is divided into two approaches: namely, a demand-driven analysis (DDA) and a pressure-driven analysis (PDA). In the DDA, the basic assumption is that the nodal demand is fully supplied irrespective of the nodal pressure, which is mainly suitable for normal operating conditions. However, in abnormal conditions, such as pipe failures or unexpected increase in demand, the DDA approach may cause unrealistic results, such as negative pressure. To address the shortcomings of DDA, PDA has been considered in a number of studies. For PDA, however, the head-outflow relation (HOR) should be given, which is known to contain a high degree of uncertainty. Here, the DDA-based simulator, EPANET2 was modified to develop a PDA model simulating pressure deficient conditions and a Monte Carlo simulation (MCS) was performed to consider the quantitative uncertainty in HOR. The developed PDA model was applied to two networks (a well-known benchmark system and a real-life WDN) and the results showed that the proposed model is superior to other reported models when dealing with negative pressure under abnormal conditions. In addition, the MCS-based sensitivity analysis presents the ranges of pressure and available discharge, quantifying service reliability of water networks.

The hydraulic analysis of water distribution systems (WDSs) is divided into two approaches, namely, a demand-driven analysis (DDA) and a pressure-driven analysis (PDA). In DDA, the basic assumption is that the nodal demand is fully supplied irrespective of the nodal pressure, which is mainly suitable for normal operating conditions. However, in abnormal conditions, such as pipe failures or unexpected increases in demand, the DDA approach may cause unrealistic results, such as negative pressure. However, despite these realistic hydraulic analysis approaches for WDSs being emphasized in the design process, this consideration was lacking in the design aspect. Therefore, in this study, the designs by the DDA-based design model and PDA-based design model are compared, and their design characteristics are analyzed to identify the efficiency of the WDSs design under abnormal system conditions. The developed PDA model was applied to three networks (a well-known benchmark system and a real-life WDN), and the results showed that the proposed model is superior to other reported models when dealing with negative pressure under abnormal conditions. In addition, the optimal design of WDN considered PDA is presented, and the optimal construction cost is decreased to increase the percentage of PDA.

This paper focuses on a methodology allowing to derive the pumping schedule in Water Distribution Networks (WDN), upon a time dependent water demand. The selected test case is a previously studied WDN. Two pumping algorithms give different pumping rules. By solving the nonlinear system of equations, consisting of energy balance equations, mass balance equations and pumping rules, one gets the pumps speed factors. Solutions attached to the Pressure Driven Analysis (PDA) correspond to energy and cost savings, with respect to the solutions given by the Demand Driven Analysis (DDA). The methodology described in this paper is simple and rapid, but the iterative numerical method used to solve the system of equations is highly dependent on the starting guess.

Patron Driven Acquisition (PDA) programs have been established in many libraries, but there is no agreed upon set of metrics to evaluate the programs’ performance. With that in mind, the University of Arizona (UA) formed the On-Demand Information Delivery (ODID) Metrics Team in January 2012 to establish metrics to evaluate their PDA program. This paper examines the results of the team’s findings and provides an extensive analysis of the purchases by Library of Congress (LC) classification, publisher, format, etc. The discussion includes an analysis of the process and challenges of measuring a PDA program based on UA’s experience. This paper also provides a list of key metrics that the authors argue that every library with a PDA program should monitor.

The correct management of Water Distribution Networks (WDNs) allows to obtain a reliable system. When a pipe failure occurs in a network and it is necessary to isolate a zone, it is possible that some nodes do not guarantee service for the users due to inadequate heads. In these conditions a Pressure Driven Analysis (PDA) is the correct approach to evaluate network behavior. This analysis is more appropriate than the Demand Driven Analysis (DDA) because it is known that the effective delivered flow at each node is influenced by the pressure value. In this case, it is important to identify a subset of isolation valves to limit disrupting services in the network. For a real network, additional valves must be added to existing ones. In this paper a new methodological analysis is proposed: it defines an objective function (OF) to provide a measure of the system correct functioning. The network analysis using the OF helps to choose the optimal number of additional valves to obtain an adequate system control. In emergency conditions, the OF takes into account the new network topology obtained excluding the zone where the broken pipe is located. OF values depend on the demand deficit caused by the head decrement in the network nodes for each pipe burst considered. The results obtained for a case study confirm the efficiency of the methodology.

Proper performance of water distribution networks (WDNs) plays a vital role in customer satisfaction. The aim of this study is to conduct a sensitivity analysis to evaluate the behavior of WDNs analyzed by a pressure-driven analysis (PDA) approach and the classification technique by using an appropriate artificial neural network, namely the Group Method of Data Handling (GMDH). For this purpose, this study is divided into four distinct steps. In the first and second steps, a real network has been analyzed by using a Pressure-Driven Analysis approach (PDA) to obtain the pressure, and α coefficient, the percentage of supplied flow. The analysis has been performed by using three different values of the design peak coefficient k*. In the third step, the Group Method of Data Handling (GMDH) has been applied and several binary models have been constructed. The analysis has been carried out by using input data, including the real topology of the network and the base demand necessary to satisfy requests of users in average conditions and by assuming that the demand in each single one-hour time step depends on a peak coefficient. Finally, the results obtained from the PDA hydraulic analysis and those obtained by using them in the GMDH algorithm have been compared and sensitivity analysis has been carried out. The innovation of the study is to demonstrate that the input parameters adopted in the design are correct. The analysis confirms that the GMDH algorithm gives proper results for this case study and the results are stable also when the value of each k*, characteristic of a different time hour step, varies in an admissible technical range. It was confirmed that the results obtained by using the PDA approach, analyzed by using a GMDH-type neural network, can provide higher performance sufficiency in the evaluation of WDNs.

Abstract. Pressure-driven analysis (PDA) of water distribution networks necessitates an assessment of the supplying capacity of a network within the minimum and required pressure ranges. Pressure-deficient conditions happen due to the uncertainty of nodal demands, failure of electromechanical components, diversion of water, aging of pipes, permanent increase in the demand at certain supply nodes, fire demand, etc. As the demand-driven analysis (DDA) solves the governing equations without any bound on pressure head, it fails to replicate the real scenario, particularly when the network experiences pressure-deficient situations. Numerous researchers formulated different head–discharge relations and used them iteratively with demand-driven software, while some other approaches solve them by incorporating this relation within the analysis algorithms. Several attempts have been made by adding fictitious network elements like reservoirs, check valves (CVs), flow control valves (FCVs), emitters, dummy nodes and pipes of negligible length (i.e., negligible pressure loss) to assess the supplying capability of a network under pressure-deficient conditions using demand-driven simulation software. This paper illustrates a simple way of assessing the supplying capacity of demand nodes (DNs) under pressure-deficient conditions by assigning the respective emitter coefficient only for those nodes facing a pressure-deficit condition. The proposed method is tested with three benchmark networks, and it is able to simulate the network without addition of any fictitious network elements or changing the source code of the software like EPANET. Though the proposed approach is an iterative one, the computational burden of adding artificial elements in the other methods is avoided and is hence useful for analyzing large networks.

In the analysis of drinking Water Distribution Networks (WDNs), performance indices are widely used tools for obtaining synthetic information about the WDN operating regime (pressures and flows). This paper presents applications of a series of local surplus indices that act in a new mathematical framework. This framework allows reworking many well-known performance and energetic indices and simultaneously allowing analysis of specific aspects of the WDN. The analyses are carried out using different resolutive hydraulic approaches: the Demand-Driven Analysis (DDA) and the Pressure-Driven Analysis (PDA), typical of software such as EPANET and WaterNetGen. The authors analyse the hypotheses necessary for the application of these models, and how these influence the results of both the hydraulic modeling and the resilience indices assessment. In particular, two resilience indices are reformulated through the new local surplus indices and all of them are then simulated in different conditions for a water network known in literature as the Kang and Lansey WDN. The solving model assumption effects are deepen, reporting graphical and numerical results for different consumption scenarios and the different hydraulic approaches used.

Demand-driven acquisitions (DDA) programs have become a well-established approach toward integrating user involvement in the process of building academic library collections. However, these programs are in a constant state of evolution. A recent iteration in this evolution of ebook availability is the advent of large ebook collections whose contents libraries can lease, but not own only if they choose to do so. This study includes an investigation of patron usage and librarian ebook selection by comparing call number data generated by usage of three entities: (1) an ebrary PDA; (2) Academic Complete, which is a leased collection of ebooks; and (3) subject librarian selections based on the YPB approval plan at Iowa State University. The context is provided through a description of the development and evolution of demand driven acquisitions programs with an analysis of where libraries have been and where they are going with enhancing the collection development in academic libraries.

Investigation of Water Distribution Networks (WDNs) is considered a challenging task due to the unpredicted and uncertain conditions in water engineering. When in a WDN, a pipe failure occurs, and shut-off valves to isolate the broken pipe to allow repairing works are activated. In these new conditions, the hydraulic parameters in the network are modified because the topology of the entire system changes. If the head becomes inadequate, the Pressure Driven Analysis (PDA) is the correct approach to evaluate the performance of water networks. Hence, in the present study, the water distribution system was evaluated in pressure-driven conditions for 100 different scenarios and then using a type of neural network called Group Method of Data Handling (GMDH) as a stochastic technique. For this purpose, several most notable parameters including the base demand, pressure, and alpha (the percentage of effective supplied flow) were calculated using simulations based on a PDA approach and applied to the water distribution network of Praia a Mare in Southern Italy. In the second stage, the output parameters were used in a developed binary classification model. Finally, the obtained results showed that the GMDH algorithm can be applied as a powerful tool for modeling water distribution networks.

Dissertação de Mestrado Integrado em Engenharia Civil apresentada à Faculdade de Ciências e Tecnologia
Em Portugal, a Entidade Reguladora dos Serviços de Água e Resíduos (ERSAR) estima que, em média, cerca de 30% do volume de água captado, tratado e distribuído pelos sistemas de abastecimento não é faturado, chegando este valor, em casos mais graves a rondar os 70%. O combate às fugas e perdas é, portanto, imperativo tanto do ponto de vista de gestão dos recursos hídricos, como do ponto de vista económico-financeiro, social e ambiental. Assim, uma gestão eficiente e sustentável dos recursos hídricos torna-se, cada vez mais um desafio importante para as Entidades Gestoras de água.Perante esta temática, a presente dissertação aborda os conceitos de perdas reais e aparentes, balanço hídrico, zonas de medição e controlo – ZMC, métodos de deteção de fugas e simulação hidraúlica em sistemas de abastecimento. No Capítulo de revisão bibliográfica procura-se apresentar todos estes conceitos fundamentais para a compreensão do tema. A presente dissertação tem como principal objetivo a modelação hidráulica de sistemas de abastecimento, com recurso ao EPANET e à extensão WaterNetGen. Para tal, considerou-se como caso de estudo a ZMC de Chão do Bispo, sendo esta uma ZMC que pertence ao sistema de abastecimento da cidade de Coimbra e é gerida pela empresa Águas de Coimbra. Faz-se a comparação da modelação com base nos consumos da rede demand driven analysis- DDA e com base nas pressões da rede pressure driven analysis -PDA. Em primeiro optou-se por fazer a simulação para o dia de maior consumo, de acordo com os dados conhecidos e comparou-se os resultados obtidos com as duas simulações, DDA e PDA. Em seguida, para a mesma rede e para as mesmas condições simulou-se a ocorrência de um incêndio e comparou-se novamente os resultados obtidos com as simulações. Por último, com vista a redução de pressão na rede, instalou-se válvulas redutoras de pressão. Com este caso de estudo, procurou-se comparar os resultados obtidos pelas simulações DDA e PDA e perceber quais as principais diferenças e vantagens de cada simulação. Pretendeu-se também sensibilizar para a importância do combate de fugas e perdas, assim como, reforçar a importância da gestão da pressão numa rede.
In Portugal, the Water and Waste Services Regulatory Authority (ERSAR) estimates that, on average, around 30% of the volume of water collected, treated and distributed by the supply systems is not billed, with this figure, in some serious cases, standing at around 70%.The battle against leaks and losses is therefore imperative, both from the point both of view of the management of hydric resources and from an economic, financial, social and environmental point of view. Thus, an efficient and sustainable management of water resources increasingly becomes an important challenge for the Water Management Entities.In this context, this dissertation addresses the concepts of real and apparent losses, water balances, measurement and control zones - ZMC, leaks detection methods and hydraulic simulation in water supply systems. In the literature review chapter, the aim was to present all these fundamental concepts in order to understand the subject.The main goal of this dissertation is the hydraulic modelling of supply systems, using EPANET and the WaterNetGen extension. For this effect, the ZMC of Chão do Bispo was considered as a case study, being this a ZMC that belongs to the supply system of the city of Coimbra and is under the management of Águas de Coimbra company.The modelling was compared based on demand driven analysis (DDA) network consumption and pressure driven analysis (PDA) network pressures.In the first place, it was decided to perform the simulation for the day with the highest consumption, according to the known data and to compare the results obtained with the two simulations, DDA and PDA. Then, for the same network and for the same conditions the occurrence of a wildfire was simulated and the results obtained with the simulations were compared again. At last, in order to reduce the pressure in the network, pressure reducing valves were installed.With this case study, we tried to compare the results obtained by the DDA and PDA simulations and realize the main differences and advantages of each simulation. It was also intended to raise awareness of the importance of tackling leaks and losses, as well as to reinforce the importance of pressure management in a network.