Preface

De formigó blanc, ceràmica, acer inoxidable i arbres, mesura 7,02 x 5,13 x 4,44 metres.Bergeron, Valérie (dissenyadora)Pla general de l'obra. consistia en la plantació de tres espècies vegetals al voltant d'una talla mètrica de formigó enrajolada, de set metres d'alçada, que havia de servir per mesurar els diferents ritmes de creixement dels arbres triats

Developments in unsteady pipe flow friction modelling

This paper reviews a number of unsteady friction models for transient pipe flow. Two distinct unsteady friction models, the Zielke and the Brunone models, are investigated in detail. The Zielke model, originally developed for transient laminar flow, has been selected to verify its effectiveness for "low Reynolds number" transient turbulent flow. The Brunone model combines local inertia and wall friction unsteadiness. This model is verified using the Vardy's analytically deduced shear decay coefficient C* to predict the Brunone's friction coefficient k rather than use the traditional trial and error method for estimating k. The two unsteady friction models have been incorporated into the method of characteristics water hammer algorithm. Numerical results from the quasi-steady friction model and the Zielke and the Brunone unsteady friction models are compared with results of laboratory measurements for water hammer cases with laminar and low Reynolds number turbulent flows. Conclusions about the range of validity for the three friction models are drawn. In addition, the convergence and stability of these models are addressed.Anton Bergant, Angus Ross Simpson, John Vìtkovsk

groundwater supply and climate change management by means of global atmospheric datasets preliminary results

Abstract Climate change influences hydrological cycle with a direct effect on groundwater resources, one of the most important supply sources for human consumption and irrigation. In a scenario where General Circulation Models do not represent yet a usual tool for water industry managers, potentially the use of global atmospheric datasets is of great interest for evaluating groundwater resources. In this paper data from the European Centre for Medium-Range Weather Forecasts (ECMWF) are compared to local water table measurements. With particular regard to unconfined aquifers, the good correlation between the trend of soil moisture and local water table data is pointed out. Such a promising result authorizes further insights in order to refine reliable tools for evaluating available groundwater resources in a climate change scenario

Editorial

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Leak Detection in a Real Transmission Main Through Transient Tests: Deeds and Misdeeds

AbstractThis paper concerns the use of Transient Test‐Based Techniques (TTBTs) for fault detection in a long transmission main. It reports the results of two series of transient tests executed in a real and operating pipe system. Because of the complexity of the investigated pipeline that includes several stubs, different pressure wave generators were used at both the end sections. Precisely, transients were caused by a pump shut‐down and the Portable Pressure Wave Maker device. The analysis of the results shows that, according to the characteristics of the transient tests and the investigated system, only a part of the system can be explored properly from a given generation point. The proposed test procedure allows overcoming the negative effect of a change in the initial and boundary conditions. In fact, contrary to laboratory, in a real system, it is quite impossible to repeat tests in the same flow conditions. The success of the survey—with two leaks detected with a good precision—confirms the potential of the TTBTs for fault detection in real systems

Numerical and experimental investigation of leaks in viscoelastic pressurized pipe flow

Abstract. This paper extends the analysis concerning the importance in numerical models of unsteady friction and viscoelasticity to transients in plastic pipes with an external flow due to a leak. In fact recently such a benchmarking analysis has been executed for the cases of a constant diameter pipe (Duan et al., 2010), a pipe with a partially closed in-line valve (Meniconi et al., 2012a), and a pipe with cross-section changes in series (Meniconi et al., 2012b). Tests are based on laboratory experiments carried out at the Water Engineering Laboratory (WEL) of the University of Perugia, Italy, and the use of different numerical models. The results show that it is crucial to take into account the viscoelasticity to simulate the main characteristics of the examined transients

Transient-Flow Induced Compressed Air Energy Storage (TI-CAES) System towards New Energy Concept

In recent years, interest has increased in new renewable energy solutions for climate change mitigation and increasing the efficiency and sustainability of water systems. Hydropower still has the biggest share due to its compatibility, reliability and flexibility. This study presents one such technology recently examined at Instituto Superior Técnico based on a transient-flow induced compressed air energy storage (TI-CAES) system, which takes advantage of a compressed air vessel (CAV). The CAV can produce extra required pressure head, by compressing air, to be used for either hydropower generation using a water turbine in a gravity system or to be exploited in a pumping system. The results show a controlled behaviour of the system in storing the pressure surge as compressed air inside a vessel. Considerable power values are achieved as well, while the input work is practically neglected. Higher power values are attained for bigger air volumes. The TI-CAES offers an efficient and flexible solution that can be exploited in exiting water systems without putting the system at risk. The induced transients in the compressed air allow a constant outflow discharge characteristic, making the energy storage available in the CAV to be used as a pump storage hydropower solution

Systematic evaluation of one-dimensional unsteady friction models in simple pipelines

In this paper, basic unsteady flow types and transient event types are categorized, and then unsteady friction models are tested for each type of transient event. One important feature of any unsteady friction model is its ability to correctly model frictional dissipation in unsteady flow conditions under a wide a range of possible transient event types. This is of importance to the simulation of transients in pipe networks or pipelines with various devices in which a complex series of unsteady flow types are common. Two common one-dimensional unsteady friction models are considered, namely, the constant coefficient instantaneous acceleration-based model and the convolution-based model. The modified instantaneous acceleration-based model, although an improvement, is shown to fail for certain transient event types. Additionally, numerical errors arising from the approximate implementation of the instantaneous acceleration-based model are determined, suggesting some previous good fits with experimental data are due to numerical error rather than the unsteady friction model. The convolution-based model is successful for all transient event types. Both approaches are tested against experimental data from a laboratory pipeline.John P. Vítkovský, Anton Bergant, Angus R. Simpson and Martin F. Lamber