The filling of pipelines must be made in conditions of maximum safety, since it is a delicate operation that can generate important system overpressures. The need, therefore, arises to design a filling protocol for big pipelines, which requires the use of a mathematical simulation model. The model is able to predict the evolution of pressure and flow during operation, as well as the filling time with enough precision, having compared the results with experimental data obtained on the field and those that the Allievi model provides, which uses the piston model as well as the method of characteristics. A restriction of this method is the application to a section of constant slope with a maximum of five suction cups distributed along the pipeline.

La resolución de ejercicios por parte del alumno y la evaluación individual de estos ejercicios resulta compleja cuando se trabaja con asignaturas técnicas con un elevado número de alumnos. La dificultad de generar gran número de ejercicios y al mismo tiempo mantener al alumno motivado durante todo el proceso de resolución, hace que pocas veces estas actividades sean adecuadamente aceptadas por los alumnos. Sin embargo, el potencial de estas actividades no es nada despreciable, la posibilidad de aportar un feedback en tiempo real al alumno cuando éste resuelve sus ejercicios favorece la asimilación de conceptos teóricos vistos en clase. En este trabajo se presenta los resultados obtenidos con una herramienta informática diseñada exclusivamente para el entrenamiento de alumnos en un determinado tipo de ejercicios y su posterior evaluación. La herramienta se ha utilizado durante 4 cursos académicos consecutivos, en la asignatura de Mecánica de Fluidos de Grado en Ingeniería en Tecnologías Industriales de la UPV, y ha permitido evaluar a un total de 1.622 alumnos. Palabras clave: evaluación, ejercicio práctico, entrenamiento, ingeniería, automatización

This paper consists of an experimental and numerical study into transient behaviour in a residential building. The analysed effects occur by centrifugal pumps when they start with a direct supply (fixed-speed pumps are connected to the service pipe without an atmospheric tank). Direct supply increases the transient effect and places higher demands on the water main. The properties of such an installation were analysed using a hydraulic model in order to detect the most unfavourable scenario. The results were compared to experimental data. Basic hydraulics demonstrates that a pressure drop occurs during the start-up. The magnitude mainly depends on the pump capacity. But, numerical and field results show that other variables related to service pipe design could also negatively affect the pressure surge. The study provides water utilities with information about the influence of the different variables on pressure surge magnitude and basic design criteria to minimize these effects.

This paper presents three new indicators for assessing the energy efficiency of a pressurized water system and the potential energy savings relative to the available technology and economic framework. The first two indicators are the ideal and real efficiencies of the system and reflect the values of the minimum energy required by users-the minimum amount of energy to be supplied to the system (because of its ideal behavior) and the actual energy consumed. The third indicator is the energy performance target, and it is estimated by setting an ambitious but achievable level of energy loss attributable to inefficiencies in the system (e.g., pumping stations, leakage, friction loss). The information provided by these three key performance indicators can make a significant contribution towards increasing system efficiency. The real efficiency indicator shows the actual performance of the system; the energy performance target provides a realistic goal on how the system should be performing; and finally, the ideal efficiency provides the maximum and unachievable level of efficiency (limited by the topographic energy linked to the network topography). The applicability and usefulness of these metrics will be demonstrated with an application in a real case study. This work is made available under the terms of the Creative Commons Attribution 4.0 International license, http://creativecommons.org/licenses/by/4.0/.

The paper under discussion is of great interest, for it simultaneously 20 presents three relevant topics by themselves: (1) the optimal loca-21 tion of valves for pressure management, (2) the importance of pres-22 sure management in reducing leakage levels, and (3) the possibility 23 to recover energy using pumps as turbines (PATs).The authors 24 present a complete cost-benefit analysis aiming to determine the 25 convenience of a certain investment.This methodology is applied 26 in a real case, a sector of Naples' water distribution network making 27 the work even more interesting, for although there are many theo-28 retical studies on the topic, real applications are certainly much 29 harder to find in the literature, especially with a holistic approach 30 as the one shown in the paper.The discussers therefore believe that 31 this paper is certainly relevant and the topic well approached.32 However, it must be mentioned that some of the presented re-33 sults are difficult to replicate, as some key data are not provided.34 This is understandable, as summarizing in a single paper the char-35 acteristics of a large network is almost impossible.For this reason, 36 the first part of the paper cannot be fully assessed [e.g., the optimal 37 location of the pressure reduction valves (PRVs)] and the discus-38 sion is focused on the water audit and the energy recovery potential 39 from the use of PATs.40 More specifically, the discussion deals with two key issues: On 41 one hand the water audit presented by the authors and the ratio be-42 tween real and apparent losses.This ratio is presented as a fixed 43 figure in the paper, and yet, even the results provided in the paper 44 clearly show that such relationship is variable.This issue has im-45 plications in the cost-benefit analysis presented later.On the other 46 hand, the calculations leading to the energy recovery figures can be 47 improved in the discussers' opinion.The use of Suter curves to 48 characterize the PATs and modeling the behavior of the PRV de-49 rives in energy saving figures significantly different from the ones 50 obtained by the authors.51 Water Audit 52 The water balance presented by the authors shows a significant 53 amount of water loss (66.8%).This figure, and the other compo-54 nents of the water balance are key to the cost-benefit analysis 55 presented in the paper, and given their importance they deserve 56 some comments: 57

Calculating the optimum replacement period of meters has always been a major concern for water utility managers. Its determination is time-consuming and requires multiple calculations. This note presents a graphical method to obtain, in a simple but accurate manner, the optimum replacement period of installed meters. For this purpose, a chart has been produced, in which the most influencing variables are considered. These variables include the degradation rate of the weighted error of the meters, the selling price of water, the acquisition and installation cost of the meters, the volume consumed by the users and the discount rate. The chart also allows for a quick sensitivity analysis of different options. For example, by plotting straight lines it is possible to determine by how much the optimum replacement frequency of a meter would change if it degrades at a different rate than expected or if the selling price of water increases.

As has been recently recognised by the European Water Framework Directive (WFD), an adequate urban water management demands a correct water-pricing policy. In particular, the article 9 of the WFD suggests a full cost recovery, mainly as far as urban and industrial uses are concerned. This is a request that, due to historical reasons and vested interests, most of the south European countries (like Spain) are far from being able to fulfil. Developed countries certainly find themselves in an even worse situation, and with complicated socio-economic circumstances, they find serious difficulties to even recover partially the costs. Politicians most frequently establish urban water pricing policies. Since they are usually more concerned about their short-term popularity than for the long-term technical results, urban water supply systems are poorly managed. The real fact is that water prices respond mainly to socio-economic and political factors than to any other rational criteria. However a sustainable water supply management requires the inverse approach: the standards to be fulfilled must be initially defined while the water tariff should be such that it would allow satisfying the established goals.

This paper presents the sensitivity analysis developed with a mathematical model for Dissolved Oxygen over an irrigation channel in Valencian Community, Spain. This channel transports water from agricultural irrigation, wastewater and industrial discharges, and the processes of dispersion, transport and interaction between the water constituents have been studied.The Dissolved Oxygen (DO) model, developed in finite differences, integrates the Nitrogen cycle and the BOD study within the DO equations. As a result, we can evaluate the concentration of every constituent in the system. We can make also an estimation of the influence of each parameter in the comparison between the data given by the model and the collected data in the real channel. The results have been contrasted with other mathematical surface water model such as QUAL2E.The results have been calibrated with data collected in the channel during a measurement campaign, and in the process of calibration, the sensitivity analysis has been used as a tool for optimising this verification process. The study has pointed out the more influencing parameters in the concentrations over the whole system, and the optimum methodology for calibrating the model, which can be used also in unsteady state pollution situations and in branched systems. As a conclusion we show the results of the sensitivity analysis comparing the more important factors influencing the concentration of DO, BOD, Organic Nitrogen, Nitrite and Nitrate and the calibration methodology for this case.

From a hydrological perspective, to speak of drought management in Spain while we are still in this excessively generous autumn of 1997 might appear a topic of scarce relevance. Especially since it has been preceded by two years of rainfall whose mean is very superior to the average annual values. Consequently, the current circumstances allow us to consider concluded the extraordinary dry period that was existent in Spain between 1991 and 1995. However it is now a timely moment, without any sense of hurry or need for agitation, to reflect on what happened in order to avoid the repetition of those events.

This paper presents a study about atmospheric dispersion of the pollutant SO, over the Comunidad Valenciana, in Est Spain, which occupies an area of 23200 km(2) approximately. The emission data come from a previous source inventory for the year 1987. The computational model uses the turbulent transport equation with some simplifications; the equation is solved using the finite difference method along the 2904 rectangles of 5 x 5 km(2) in which the space domain (220 x 330 km) has been divided, giving as a result the averaged concentration of the pollutant SO2 in every grid node. To validate the results we have used the yearly averaged concentration data from an air monitoring network. The results obtained with the model have been used to study the atmospheric dispersion capacity of different terrain zones in order to locate future industrial installations with pollutant emissions. The conclusions of this study are to be used as preliminar studies of land use regulations.

In this paper, a generalized treatment of the equations describing the behavior of a pumping station is presented. It enables the simulation of many reasonable combinations of elements within a pumping station, by using a single routine and one set of state data suitably maintained. Thus, it represents a unified algorithm massively solved that easily accommodates to virtually every condition in a pumping station. Besides, the interpolating method it uses allows to incorporate manufacturers information into dimensionless curves helping plausibly to produce more real results. The interest of the paper is mainly computational. Nevertheless, the scheme we propose enables the joint consideration of a wide range of elements in a pumping station without the need of including short reaches between them. In this way, it is claimed to represent a good improvement for existing packages to model transient analysis in networks.