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Experimenting with a new calibration method for current meters
No full textThe necessity of a simple way to control the reliability of laboratory’s current meters
brought to develop a method that allows to calibrate the instruments in their usual working conditions, as it happens, for example, in a river or in a sewer, using an equipment simpler than the traditional method: the current meter is still, hung by a support, and the propeller is put in rotation by flow through totally submerged outflows, exploiting the main characteristic of these outflows, that is a uniform velocity profile on all the cross-section.
Since current meter is a local velocity gauger, the influence of current meter’s position, respect to the outflow, on velocity measurements reliability, has been investigated. In fact, the current must be linear to obtain satisfying discharge measurements.
Two different kinds of submerged outflows has been analyzed: a flow nozzle and an orifice plate. The problem about the orifice plate is to localize with accuracy where the contracted section A_c is located, that is to say where current is linear, and which is the contraction ratio C_c . Usually, the contracted section is considered to be D_OP /2 far from the outflow.
On the contrary, the flow nozzle doesn’t cause a contracted section, because of its well-connected entrance; nevertheless, there is a lot of turbulence around it, because of liquid jet expansion, but, near the outflow, current may be considered linear, assuming, as reference piezometric line, that of the axial flow pattern.
To confirm the hypothesis at the basis of the method, that is a uniform velocity distribution on all the cross section, velocity profiles along two directions, horizontal and vertical, have been studied, showing results matching with theory.
A calibration method consists in putting into relationship the number of propeller’s rates in a fixed time interval with current velocity, determining instrument’s characteristic calibration curve; in this case, two reference current velocities have been adopted for calibration: the one is the ratio between discharge (indicated by an electromagnetic flow meter) circulating in the system and outflow’s area; the other is obtained by the Torricelli’s formula, measuring the difference between upstream and downstream reservoirs’ levels. In particular, the propellers of two current meters, different in dimension and typtology, have been calibrated by the new method.
In the end, since a measurement is complete only if associated to its uncertainty, the uncertainty of measurements carried out has been calculated, in particular about Torricelli’s velocity
Evaluation of the Feasibility of Irrigation Storage in a Flood Detention Pond in an Agricultural Catchment in Northern Italy
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Experimental data on the reliability of flowmetrs for pressure pipes
No full textThis paper summarizes the results of a large number of tests carried out about the reliability of discharge measurements given by flowmeters for pressure pipes of different kinds (electromagnetic, ultrasonic and turbine flowmeters), on the basis of the experimental data collected at Laboratorio di Idraulica “G. Fantoli” of Politecnico di Milano.
In fact, since 2002, this laboratory is the seat of the Settore Portate of Centro SIT n. 104, that is a structure of Politecnico di Milano accredited for flowmeters calibration in the discharge range from 3 l/s to 80 l/s, with a so-called “best measurement capability” (BMC) equal to 0.2 %.
During these years, a lot of calibrations of different flowmeters have been carried out (61 flowmeters were tested so far: 44 electromagnetic, 9 ultrasonic, 8 turbine flowmeters). So, the tested flowmeters are supposed to give a relevant sample of experimental data, and therefore it seems interesting to carry out some statistical analyses about their performances and reliability. Of course no general consideration can be inferred about the general performances and reliability of other similar instruments not tested
Experimental study of velocity fields in rectangular shallow reservoirs
Full text linkVelocity fields in rectangular shallow reservoirs with different length-to-width and expansion ratios were investigated in an experimental study, to evaluate the effect of geometry on the flow field. A wide range of combinations of these two non-dimensional geometric parameters were tested at constant hydraulic conditions. Ultrasound velocity profilers were used to measure the horizontal velocity components across the entire reservoir surface, allowing for the visualization of streamlines and of the instantaneous and average velocities. Five different types offlow patterns were identified, depending on the values of the length-to-width ratio and expansion ratio of the reservoir. Asymmetrical flow patterns were found to develop for certain combinations of these geometric parameters despite the perfect reservoir symmetry. A critical comparison of these new experimental results with those of other works is provided.PL-LCH[799
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Investigation of flow patterns and sedimentation in rectangular shallow reservoirs
Full text linkQuesta tesi riguarda la classificazione dei diversi tipi di campi di moto che possono svilupparsi in un serbatoio rettangolare di acque basse. Dopo una ricerca bibliografica, avente lo scopo di acquisire la conoscenza dello stato dell’arte su questo argomento, la prima parte del lavoro è stata una attività sperimentale condotta nel Laboratorio di Costruzioni Idrauliche presso l’Ecole Polytechnique fédérale di Losanna. Tramite questa ricerca, è stato possibile ottenere un ampio sguardo sui tipi di campo di moto che possono svilupparsi in differenti configurazioni geometriche del serbatoio a condizioni idrauliche fissate. L’interesse in questo studio è generato dalla forte influenza che la fluido dinamica del serbatoio esercita sui processi di sedimentazione all’interno del serbatoio stesso. L’idea è che, se conosciamo meglio la fluidodinamica del serbatoio, possiamo anche trattare in modo più efficiente i depositi di sedimenti nel serbatoio. A questo proposito, per quanto concerne i sedimenti, sono anche stati condotti esperimenti per osservare a scala di laboratorio l’influenza che il campo di moto esercita sulla deposizione di solidi sospesi entranti nel serbatoio.
In seguito, un’attività numerica è stata condotta in collaborazione con l’università di Liegi, con lo scopo di ottenere un modello numerico capace di riprodurre i campi di moto trovati sperimentalmente. I dati sperimentali raccolti precedentemente sono stati la base con cui validare il modello numerico WOLF2D, che si è rivelato essere in grado di riprodurre in modo abbastanza accurato, e in numerose configurazioni geometriche, i risultati sperimentali. Così, grazie al modello numerico validato, è stato possibile testare nuove configurazioni del serbatoio, cambiando le condizioni al contorno del problema. In particolare, è stato possibile modificare non solo la geometria del serbatoio, ma anche le condizioni idrauliche, in modo da estendere la classificazione dei campi di moto non solo in funzione della geometria ma anche sulla base delle condizioni idrauliche del sistema, raggiungendo una visione più completa del fenomeno.
Il cambiamento delle condizioni idrauliche apre un ampio spettro di possibili combinazioni dei parametri adimensionali del sistema (il numero di Reynolds e il numero di Froude), che possono portare a diversi tipi di campi di moto e a una futura classificazione dei campi di moto basata non solo sulla geometria del serbatoio ma anche in funzione delle condizioni idrauliche.
Per il momento, la modifica del numero di Foude del canale di ingresso ha mostrato l’esistenza di un nuovo tipo di campo di moto, non registrato negli altri esperimenti oggetto di questa tesi: esso è il meandering flow , le cui caratteristiche sono state parzialmente investigate in questa tesi tramite simulazioni numeriche. Lo scopo è, in futuro, collezionare dati sperimentali quantitativi in modo da confermare i risultati del modello numerico, anche se l’esistenza di questo tipo di campo di moto è stata già appurata anche dal punto di vista sperimentale.
Il modello numerico WOFL2D è stato anche dotato di un modulo di trasporto solido in sospensione, per mezzo del quale il processo di deposizione dei solidi sospesi può essere modellato; lo scopo è riprodurre lo spessore dei depositi di sedimenti e la trapping efficiency delle configurazioni di serbatoio testate sperimentalmente, in modo da sviluppare un modello di trasporto solido dei solidi sospesi che sia disponibile per simulare altre configurazioni di serbatoio, cambiando le caratteristiche dei sedimenti o i parametri idraulici, e valutare così la loro influenza sul processo di sedimentazione.This thesis deals with the classification of the different types of flow patterns that can develop in a rectangular shallow reservoir. After a bibliographic research, with the aim to get knowledge on the state of the art on the subject, the first part of the work has been an experimental activity carried out in the Laboratory of Hydraulic Construction at the Ecole Polytechnique fédérale de Lausanne. From this research, a wide overview has been obtained on the types of flow patterns that can develop in different reservoir configurations depending on reservoir geometry, at fixed hydraulic conditions.
The interest in the investigation of flow patterns types is generated by the strong influence that the fluid-dynamic of the reservoir exerts on the sedimentation processes inside the reservoir. The idea is that, if we better know the fluid-dynamics of the reservoir, then we could also manage in a more effective and efficient way the sediments deposits in the reservoir. So, as far as concerns sediments, experiments were also carried out in order to observe at laboratory scale the influence that the velocity field exerts on sediments deposition of suspended solids entering in the reservoir.
Then, a numerical activity has been carried out in collaboration with Liège University, with the aim to have a numerical model able to reproduce the velocity fields experimentally found. The experimental data previously collected have been the basis to validate the numerical model WOLF2D, which revealed to be able to reproduce in a quite accurate way and in numerous reservoir configuration, the experimental results. So, thanks to the validated numerical model, it has been possible to test new reservoir configurations, changing the boundary conditions of the problem. In particular not only the geometry of the reservoir could be easily modified, but also the hydraulic condition were varied, in order to extend the classification of the developing flow patterns not only as a function of reservoir geometry but also on the basis of the hydraulic conditions of the system, reaching a more complete view of the phenomenon.
The change of the hydraulic conditions opens a wide range of possible combinations of the non-dimensional hydraulic parameters of the system (mainly the Reynolds and Froude numbers), which could lead to different types of flow patterns and to a future flow patterns classification not only based on the geometry of the reservoir but also as a function of the hydraulics of the reservoir.
For the moment, the change of the inlet Froude number, that is to say the Froude number of the inlet channel, has shown the existence of a new type of flow pattern, not registered in the previous experiments object of this thesis: it is the meandering flow, whose characteristics have been partially investigated in this thesis by numerical simulations. The aim is, in future, to collect quantitative experimental data in order to confirm the numerical model results, even if the existence of this type of flow pattern has been already assessed also from the experimental point of view.
The numerical model WOLF2D has been also endowed with a suspended sediments transport module, by which the deposition process of suspended load can be modelled; the aim is to reproduce the sediments deposits thickness and the global trapping efficiency of the reservoirs configurations experimentally tested, in order to develop a suspended sediment transport model available to simulate other reservoir configurations, changing sediments characteristics or hydraulics parameters, and evaluating their influence on the sedimentation processes.DIPARTIMENTO DI INGEGNERIA IDRAULICA, AMBIENTALE, INFRASTRUTTURE VIARIE, RILEVAMENTO24GUADAGNINI, ALBERTOSANSO', FERNAND
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