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Elaborazione di modelli matematico-numerici per la simulazione di flusso e trasporto per problemi dipendenti dalla densità
Get PDFIl presente rapporto descrive lo stato di avanzamento dell’attività 1 del sottoprogetto al termine del primo anno del progetto MURST/CIPE , ovvero la descrizione della modellazione di fenomeni di flusso e trasporto nel caso di fenomeni dipendenti dalla densità (cioè la presenza stessa dell’inquinante è in grado di influenzare fortemente il campo di moto), con particolare riferimento al caso di dispersione di inquinanti immiscibili in acqua detti NAPL (liquidi organici in fase non acquosa, quali idrocarburi, solventi organici, liquidi oleosi, sostanze bitumose, etc.) possibili di biodegradazione ad opera della flora batterica naturalmente presente , di trasporto di inquinanti chimicamente reattivi nel sottosuolo (NaOH, e altri contaminanti in grado di influenzare il pH dell’ambiente sottostante) e del caso di intrusione dell’acqua marina nel sottosuolo. L’elaborato descrive dunque l’insieme delle equazioni e la formalizzazione degli algoritmi risolutivi dei modelli matematici e delle integrazioni modellistiche e numeriche dei modelli dei seguenti processi: inquinanti immiscibili in acqua; biodegradazione; intrusione di acqua marina; trasporto in non-equilibrio
Comparison of a 3-D Richards equation-based model with the hillslope-storage Boussinesq model: A test case for nine characteristic hillslopes
Get PDFIn this study, a numerical simulation for these nine characteristic hillslopes is carried out using the three-dimensional, distributed model CATHY: a coupled model describing both subsurface flow and surface runoff. The model is capable of accurately describing flow characteristic, and thus provides us with the opportunity of studying spatially distributed phenomena like water table or storage dynamics in detail. The objective of the study is to compare the CATHY simulations with a recently developed extensions to the Boussinesq model that uses the width function to account for hillslopes shape
Development of a partially premixed combustion model
Get PDFIn this work, a possible extensions of the TFC model to imperfectly premixed cases has been introduced and validated, even if in a purely qualitative way. The proposed IPM model has given results physically consistent and it seems able to describe in more correct terms actual combustor, in which it is far from real any assumption of having perfectly premixed mixtures feeding the combustion chamber. Nevertheless, a proper validation of the proposed IPM model and of the TFC model over a realistic industrial case is still to come and it will be an essential part of the future work. Finally, the quite general lines of how to get a partially premixed model (premixed plus diffusion) have been drawn, showing that, in principle, no new modeling is needed and that it would be probably enough to assembly already existent premixed and diffusion models. The actual implementation of the idea above into ARES could be also a future development of this work
Development and implementation of turbulence models in the combustion code Ares
Get PDFThis report describes the R&D activities carried out under the ENEA-MURST programme , objective 4. Three more turbulence models (the RNG K – ε, the one-equation Spalart & Allmaras and the Wilcox K – ω) have been implemented into the Ares combustion code. They represent state-of-the-art models that have demonstrated over the past decade their superior accuracy , robustness as well as ease of implementation with respect to the class of K – ε models. The first chapter describes the models formulations. In chapter 2 the three models have been validated against three well known test cases. Particular attention has been dedicated to coupling the one-equation turbulence model by Spalart & Allmaras to the TFC premixed combustion model, for two computed turbulence scales are needed to evaluate the turbulent flame velocity and one-equation models provide one turbulent scale only. For validating the correct models implementations, two simple cold test cases have been chosen, namely the turbulent boundary layer over a flat plate, and a well documented turbulent flow over a backward facing step. Finally the Moreau combustor test case have been used for the validation of the models for premixed combustion flow. The state-of-the-art turbulence models implemented should allow the combustion code Ares to increase its ability to correctly compute complex turbulent premixed reactive flows in real combustors, which is the objective of the next project tasks
Creating and presenting real and artificial visual stimuli for the neurophysiological investigation of the observation/execution matching system
Get PDFRecent neurophysiological experiments have shown that the visual stimuli that trigger a particular kind of neurons located in the ventral premotor cortex of monkeys and humans are very selective. These textitmirror neurons are activated when the hand of another individual interacts with an objects but are not activated when the actions, identical in purpose, are made by manipulated mechanical tools. A Human Frontiers Science Program project is investigating which are the parameters of the external stimuli that mirror neurons visually extract and match on their movement related activity. The planned neurophysiological experiments will require the presentation of digital stimuli of different kinds, including video sequences showing meaningful actions made by human hands, synthetic reproductions of the same actions made by realistic virtual hands, as well as variations of the same actions by controlled modifications of hand geometry and/or action kinematics. This paper presents the specialized animation system we have developed for the project
CFD simulation of a heated round jet of sodium in forced flow regime (TEFLU benchmark)
Get PDFThe results of the simulation of the forced-flow case of the TEFLU benchmark [1], obtained at
CRS4 with the Star-CD code, are reported. First, a comparison among different k-ε turbulence models implemented in Star-CD was carried out. The Chen k-ε model [4], [5] gave the best agreement with experimental results.
Then, a study of the influence of the turbulent Prandtl number Prt was carried out. The first step
was the comparison between the molecular conductivity and the turbulent heat diffusion
coefficients, calculated using the turbulent Prandtl number approach (Reynolds analogy). It was
found that that the two contributions are of the same order of magnitude. This result implies that
there is a strong interaction between the molecular and turbulent heat transfer, which could have a
strong effect on the scaling coefficient between the turbulent transfer of momentum and heat,
namely on Prt. In order to study the effect of the variation of Prt on the temperature profiles, the inlet turbulence kinetic energy profile was scaled in order to obtain a good agreement between calculated and experimental velocity profiles. Then, the value of Prt was changed from the standard value of 0.9 to 10 (on the basis of the considerations of Jisha and Rieche [6]) and to 104 (to exclude the
contribution of the turbulent heat transfer). A very good agreement with experimental
measurements was found in both cases (the best being the case of no turbulent heat transfer).
The above results indicate that the heat conduction is predominant in the forced-flow case. In this
situation, the standard value 0.9 of Prt yields an overestimation of the thermal diffusion rate
A volumetric virtual environment for catheter insertion simulation
Get PDFWe present an experimental catheter insertion simulation system that provides users co-registered haptic and head-tracked stereoscopic visual feedback. The system works on patient-specific volumetric data acquired using standard medical imaging modalities. The actual needle insertion operation is simulated for individual patients, rather than being an example of a model surgical procedure on standard anatomy. Patient specific features may thus be studied in detail by the trainees, overcoming one of the major limitations of current training techniques.125-13
Sardinian natural clinoptilolites for heavy metals and ammonia removal: experimental and modeling
No full textSardinian natural clinoptilolites are examined to evaluate their performance for
metals, i.e. copper, cadmium, lead and zinc, as well as ammonium removal. The natural
material is either used as received or once converted into the sodium form. Equilibrium data
for each species and the natural material are obtained. The corresponding behavior is
quantitatively correlated using classical isotherms, whose parameters are estimated by fitting
the equilibrium data. Breakthrough experiments of lead solutions are also performed. Fixed-bed runs are simulated using a mathematical model which includes axial dispersion as well as
a new approximate rate law for non-linear adsorption and diffusion in spherical adsorbent
particle based on an equivalent film resistance model
A thermal fluid-dynamic steady state analysis of the EADF downcomer channel
Get PDFIn this work a numerical simulation of the Energy Amplifier Demonstration Facility (EADF) [1, 2] downcomer channel is presented. The simulation is fully three-dimensional (3D) and is focused on a Steady-State Analysis. All relevant
heat transfer phenomena are taken into account.
The Intermediate Heat eXchangers (IHX) of the EADF reference configuration are immersed in the lead-bismuth eutectic of the downcomer and no physical barrier separates the hot and cold collectors.
As expected, the simulation shows a thermal stratification outside the IHX, whose characteristics mainly depend on the IHX pressure loss. A parametric
study of the effects of the IHX pressure loss coeficient on the thermal stratification pattern is presented
Sistema informativo per l'individuazione di zone a rischio ambientale in un'area a sud della Sardegna
Get PDFIl presente studio si inquadra nel più vasto progetto europeo del CRS4 ADAPT VISION. Esso prevede la realizzazione di un prototipo di sistema informativo territoriale che consenta di verificare se l'azione antropica, nell'area scelta per lo studio, ha determinato una trasformazione dell'ambiente dal punto di vista idrogeologico e forestale.
L'area oggetto di studio si trova a cavallo dei comuni di Pula e Domus De Maria in Provincia di Cagliari (sud Sardegna). Tale area è caratterizzata da 3 zone differenti dal punto di vista morfologico, idrogeologico e forestale ma da una situazione analoga dal punto di vista vincolistico. La zona costiera e’ caratterizzata da un’alta concentrazione di insediamenti turistici.
Lo studio ambientale dell'area ha messo in evidenza che l'aspetto predominante è il rischio di erosione; è stato quindi inserito nel sistema un modello empirico di individuazione di zone a rischio. Nella zona costiera ci si è preoccupati di verificare la possibilità di intrusione salina nelle acque sotterranee attraverso la misura della conducibilità elettrica in alcuni pozzi opportunamente scelti.
Per verificare lo stato di salute della vegetazione sono state effettuate, in ognuna delle tre zone, misure dendrometriche.
Inoltre, per la zona residenziale è stata prodotta una mappa di rischio di evacuazione, ottenuta tenendo conto dello stato della viabilità e della distribuzione della popolazione.The present study is part of CRS4’s European Project “ADAPT VISION”, and its purpose is to develop a GIS-based prototype that allows the user to evaluate the consequences of human activities on the landscape.
The study area is located in the South-Western coast of Sardinia and it consists of three zones that are characterizated by the same legislative restriction, but that differ in morphology, hydrography and land use. An empirical model has been applied to the whole area in order to define erosion risk zones; in situ conductivity measurements in coastal wells have been taken to check the presence of saltwater intrusion; a spatial evacuation model has been used to achieve an escape route vulnerability map for the edified zone