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Entropy parameter estimation in large-scale roughness open channel
Full text linkThe entropy model allows estimating, in an expeditive way, both water discharge and flow velocity field in open channels. In fact, such model presents an almost simple analytical structure, based on the evaluation of a single parameter calculated through the ratio between the mean and maximum flow velocities in the cross section. Recent studies have demonstrated that, for large-scale roughness, the evaluation of the entropy parameter seems to be affected by the local conditions near the bed. In order to investigate such influence, the present work proposes an explicit relationship between the entropy parameter and the relative submergence. This relation was validated using data collected in a rectangular tilting flume of laboratory, where the bed roughness was composed by elements of regular shape such as spheres. Several tests were performed in conditions of large-scale roughness (1.9<D/d<6.4) and for different values of slope (0.05%<i<1%) and water discharge (7l/s<Q<76l/s). The method shows a good agreement between the observed and calculated data for both the velocity profiles and water discharges
Experimental analysis for the entropy parameter evaluation
No full textIn the last years the target of optimal management of the surface water resources has
characterized the needed to effectively estimate the rate of water discharge to maintain in
perennial way a stream to the aim to guarantee the continuity of biological and physical
dynamics of the fluvial system.
Water, like sanctioned from the Rio conference and the Aia forum, is the unavoidable good
through which allowing the survival of the planet and, like such, it must be protected and
defended. At the same time, because the total and local climatic variations, water assumes the
role of element of risk for the human health and for the ecosystems in a generalized way both
in terms of quantity in the catastrophic events and quality like privileged path of polluting and
of triggering in the alimentary chain.
The extreme conditions represent anomalous situations to avoid whenever generated by
anthropic activities, generally consequence of recovery requirements of water resource or
management of the resources available.
One of the aspects of particular relief, deriving from the pressing requirement to generate
surface water storages for drinkable or pluribus purposes, is the evaluation of the minimum
life instream that, even if for some aspects is an administrative technical parameter, represents
the tool through which contributing for the balance of the water budget and guaranteeing the
continuity of the river environmental systems.
Present study applies, in a feedback process, the concept of informational entropy for river
velocity profiles, giving the evaluation of the entropy parameter imposing the boundary
conditions of the local velocity gradient dictated by the satisfaction of dynamic and biological
equilibriums.
Generally the common used methodologies require the estimation of a relevant number of
coefficients and parameters related to meticulous and sometimes difficult field measures
2nd International Conference
New Trends in Water and Environmental Engineering for Safety and Life: Eco-compatible Solutions for Aquatic Environments
Capri (Italy), June 24-28, 2002
internet: www.capri2002.com
M. Greco, D. Mirauda
Experimental Analysis for the Entropy Parameter Evaluation Page 2
addressing the researchers in the use of abacuses or logical similitude in order to closing
mathematically the flow problems.
In alternative it is possible to employ new methodologies based on the concept of
informational entropy and maximization of the same one, derived through the statistical
observation of the variable in examination. The entropy velocity profile is a result of such
theory that leads back its applicability to the evaluation of the single parameter depending on
macroscopic variables of easy esteem and acquisition.
In detail the value of the entropy coefficient can be obtained through several analytical
relationship and mainly by the knowledge of the ratio between the average and the maximum
cross section velocity or the local shear stress.
Focusing the attention on the last condition it has been possible to formulate a general
methodology, based on the sustainability of the local river ecosystem, through which impose
boundary conditions for the local velocity gradient with respect to the selected biocenosis
community and thus derive the value of the entropy parameter
Vibrazioni trasversali di una sfera investita da una corrente in moto stazionario
No full textIl lavoro focalizza l’attenzione su alcuni aspetti di rilievo relativi allo studio dell’interazione ostacolo-corrente in termini di effetto del campo di moto, ed in particolare dell’assetto delle strutture vorticose generate a valle del flusso, sulla risposta in ampiezza e frequenza del corpo. L’analisi propone il regime di vibrazioni indotto su un sistema vincolato, spiccatamente tridimensionale, immerso in una corrente a superficie libera, in moto stazionario, attraverso la caratterizzazione dei parametri critici che intervengono nella formulazione analitica del processo. Le attività di laboratorio sono state indirizzate verso la misura diretta dello spostamento trasversale, della frequenza di oscillazione e del campo di moto di un sistema caratterizzato da bassi valori del rapporto di massa (m*<10), alti valori del parametro combinato massa-smorzamento, m*, piccole ampiezze di oscillazione e bassi valori di sommergenza relativa (rapporto tra profondità della corrente e grandezza caratteristica del corpo)
Valutazione globale del parametro entropico di velocità
No full textE’ fornito un ulteriore contributo alla verifica dell’applicabilità del modello entropico e probabilistico di Chiu (1987) alle correnti naturali ed alla caratterizzazione alla macroscala, del parametro entropico M. In sintesi lo studio ha interessato lo sviluppo di una sperimentazione di laboratorio su deflussi regolari a pelo libero in sezioni di geometria nota e prefissata. Le misure hanno consentito la determinazione accurata del coefficiente M, sia alla scala della sezione trasversale sia a quella di verticale, valutandone comparativamente l’ordine di grandezza. Infine la variabilità della portata, pendenza e sezione ha indirizzato la leggibilità del parametro entropico come variabile dipendente da tali grandezze e dai gruppi adimensionali significativi delle correnti a pelo libero
Assessment of rating curve through entropy-based Manning’s equation
No full textThe rating curve is the most used methodology for river flow quality and quantity monitoring and control. Nevertheless, it is still difficult to obtain a reliable rating curve because it takes a long time and involves high costs, especially if the measurement cross-section is unstable. Besides, the difficulties faced by operators who carry out the measurements lead to water discharge values being calculated on a statistical basis or with numerical models, which could involve significant errors in rating curves. To overcome these difficulties, the use of a modified form of the Manning’s equation, which contains information about the geometric development of the cross-section and the hydraulic behaviour, is suggested here. This formulation, derived from the entropy velocity theory, allows assessing water discharge in an expeditive way, maintaining a sufficient level of reliability, through the use of global parameters which consider the geometric information and the roughness of the river or, more extensively, of the areas of fluvial pertinence. In a first step, the procedure is validated on four river sections in the Grand-Duchy of Luxembourg and in the Basilicata region of Southern Italy. The results seem to demonstrate the validity and potential of the proposed approach
Downward and upward approach for entropy velocity profile
No full textThe use of the entropy velocity profile in the field of Applied Hydraulics allows describing the local flow condition through the use of simple parameters easily to derive. The features of the law, based on the mean and maximum velocity, as well as the recent results concerning the relationship between the mean and the maximum cross section velocity, suggest employing the velocity profile at both local and global scale. That is, downward and upward approaches are proposed in order to describe the flow energy budget at the small scale and the morphological river characteristics at the high scale respectively
Expeditive models for river water discharge evaluation
No full textThe forecasting of flows in rivers represents a relevant element within the actions addressed to individualize a correct management policy concerning the water resources, connected to exigencies of prevention and defence from the environmental degradation.
Recently the European directive 2000/60/CEE confirms the importance of the monitoring and control activities supporting the phases addressed to individualize the protection measures suitable to reach the “good state” of the water body.
The quantitative monitoring of rivers is essential for a correct planning of the interventions in a middle and long term in relation to the control activity and environmental protection; besides it is useful to plan civil protection interventions in a short term in relation to the forecasting and prevention of flood events.
In this last case a crucial element is represented by the constant updating of depth/discharge scales in control sections. This updating needs for large field activities not easily realizable both for the climatic conditions not always favourable both for the notable costs. All this encourages the development and implementation of expeditive models for water discharge evaluation in order to reduce the data acquisition time and processing without losing measurement precision.
Studies of the literature (Greco & Mirauda 2002, 2004; Moramarco et al 2002, 2004, 2006 and Xia 1997), demonstrated a perfectly linear dependence between the maximum and the mean velocities in the regular and irregular cross section where the proportional coefficient is constant in all the investigated sections.
In details, the knowledge of the relation between mean and maximum velocities of a cross section of river allows to concentrate the velocity measures only along the verticals where the possibility that the maximum or mean velocity of the section occurs is higher.
The choice of those verticals is linked to the implementation of simple analytical methods (Moramarco et al. 2002, 2004, 2006) able to individuate the position of the maximum and mean velocity in the section investigated in different flow regimes.
Such analysis has been restricted to few gauged river sites located in Central Italy.
The aim of this work has been to extend the analysis to river sites with different hydraulic and geometric characteristics from tested ones in Central Italy.
At the purpose, different stream flow stations located along natural channels in Basilicata region, South Italy, have been used as case studies. Results were found in good agreement with observed water discharges with errors not exceeding 20%
Flow-induced vibration of an elastically sphere at high combined mass-damping parameter
No full textThe paper reports the results of the experimental analysis on the transverse flow-induced vibration of an elastically
mounted rigid sphere in a free surface flow. Simultaneous displacement and velocity measurements have been used to
describe the free vibrations. Experiments have been performed referring to low mass ratio value (m*), high combined massdamping
parameter (m*ζ), small amplitude (A/D<1) and low values of relative submergence (ratio between water depth and
sphere diameter). Preliminary results compared to the literature case studies suggest a different behaviour between the test
case of the sphere and those referred to the cylinder mainly concerning the lock-in and hysteresis phenomena
Influence of hydraulic geometry ratios on the entropy parameter in open channel flow
Full text linkThe knowledge of flow velocity distribution is an essential requirement in dealing with stage–discharge relationships, sediments transport processes and prediction of morphological behaviour in alluvial streams, design of stable channels, flood control works and mathematical and physical modelling of flows. Due to the limitations of classical hydraulic methods, Chiu (1987) derived the velocity distribution law basing on the concept of informational entropy introduced by Shannon (1948) and Tsallis (1988). Such velocity profile has been widely employed in many different flow cases and improved by relevant and meaningful both theoretical and applied contributions derived from robust experimental knowledge. Main aspect of such model is related to the need of one parameter M said as entropy parameter. Such parameter is depending on the ratio between the mean cross section velocity over maximum velocity, Φ(M).
The way to evaluate the entropy parameter M through the ratio Φ(M), still represents a relevant issue nourishing a reach discussion among researchers mainly addressed to the reasonable ground about the invariance of Φ(M) for sections along the same river only at high flow while for low stage the ratio Φ(M) can be affected by the influence of roughness, through the relative submergence, the ratio between water depth and roughness height (D/d) as well as by the aspect ratio related to the cross section geometry, the ratio between flow width and flow depth (B/D). Therefore M should be assumed as a peculiar characteristic not only of the monitored site but also of the river reach where sites are located and the observed flow stage. Moving from these bases, using laboratory and field data, the classical hydraulic relationships on entropy velocity profile, the uniform flow and regime theory, a predictor for entropy parameter is proposed for open channel flow. The work proposes a general logarithmic relationship existing between the parameter Φ(M), the relative submergence and the aspect ratio of the flow. The [Φ(M)-(D/d)-(B/D)] relationships have been applied to a set of experimental velocity data collected both in laboratory and in field, showing a good response of the theoretical model but selecting different behaviour depending on the roughness scale. In fact, Φ(M) is strongly depending on the ratio depth/roughness for values of D/d less than 4 when large and intermediate roughness scale occurs, while it might be assumed almost constant to 0.66 for small roughness scale (D/d>4) according to literature for high flow stage. On the other hand, the relationship among Φ(M) and B/D seems to be depending on whether or not the flow is confined, like artificial channel, instead of natural cross section. The comparison between the two set of data, laboratory versus field, enlighten the effect of the aspect ratio which is strongly related to Φ(M) for flume velocity data while it results not depending on Φ(M) for river measurements. Further, even this last issue enforce the difference between the Φ(M) ratio behaviours for high roughness flow and low roughness one, remaking the value of D/d=4 as operative threshold
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