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Preliminary study on density-dependent flow and transport in the Lake Karachai area (UE RaCoS project): adequacy of CODESA-3D to model a plume of contaminant brine
Get PDFOne of the main objectives in this preliminary study was to implement CODESA-3D (COupled variable DEnsity and SAturation) code for the Lake Karachai site and to run preliminary simulations under a variety of conditions, but with density ratio coeffcient no larger than 0.07 (density variations of maximum 7%).
Because CODESA-3D is a finite element numerical code for coupled flow and transport that is normally used for problems of seawater intrusion, where density variations are around 3%, part of our work has been devoted to determine the limit of applicability of the code
Simulazione numerica del flusso e trasporto di contaminanti in mezzi porosi a saturazione e densità variabile
Get PDFLa legislazione riguardante la salvaguardia e la tutela delle risorse idriche, e tra queste le acque sotterranee, è in continua crescita in tutti i paesi industrializzati. La protezione delle acque di falda dal sovrasfruttamento e dalla contaminazione di origine diversa (rifiuti urbani e industriali, pesticidi e fertilizzanti, scorie nucleari, ecc...) richiede la previsione degli effetti indotti dalle attività umane sulla quantità e qualità delle risorse sotterranee, previsione che si può conseguire solo attraverso l'impiego di idonei modelli matematico-numerici. Un problema di stringente attualità in tutti i paesi che si affacciano sul Mediterraneo è l'inquinamento degli acquiferi costieri per intrusione di acqua di mare. La simulazione della penetrazione del cuneo salino comporta lo sviluppo di modelli accoppiati di flusso e trasporto che possono essere accuratamente ed efficientemente risolti col metodo degli elementi finiti (FEM) che viene qui implementato in un mezzo poroso tridimensionale a saturazione variabile, e che è quindi in grado di simulare sia la zona insatura (suoli superficiali) che quella satura (falde in pressione).
Le non linearità che scaturiscono dall'accoppiamento e dalle leggi costitutive della permeabilità e del coefficiente di immagazzinamento nella zona insatura sono risolte con le tecniche di Picard e di Newton parziale. I modelli discreti finali linearizzati sono trattati col metodo dei gradienti coniugati opportunamente precondizionati per le matrici simmetriche di flusso (PGC) e quelle non simmetriche di trasporto (GMRES, Bi-CGSTAB, TFQMR). Le procedure descritte sono implementate nel codice FEM CODESA-3D (COupled variable DEnsity and SAturation) di cui è offerto un esempio applicativo.In the industrialized countries subsurface water resources are increasingly subject to regulations for protection from over-exploitation and from contamination arising from urban, industrial, nuclear, military, and agricultural activities. Prediction of the effects of anthropogenic impacts on water quantity and quality is an important part of proper aquifer management, and can be achieved through the use of mathematical models. As an example, seawater intrusion in coastal aquifers represents a serious environmental problem, especially in the countries of the Mediterranean basin, and can be simulated using coupled models of water flow and solute transport. Sophisticated groundwater models such as these can be accurately and effciently solved numerically via finite element discretizations of the three-dimensional porous medium. Both saturated (groundwater) and unsaturated (soil water) zones can be represented, and nonlinearities arising from storage-pressure head and conductivity-pressure head dependencies in the
unsaturated zone and from coupling of the two equations can be resolved using Picard, Newton, or partial Newton methods. The resulting linearized systems of equations can be solved using a variety of preconditioned conjugate gradient-like methods applicable to symmetric and non-symmetric systems. The mathematical formulation and numerical procedures to be described form the basis of the CODESA-3D (COupled variable DEnsity and SAturation) model
PSPI: streamlining 3D echo-reconstructive imaging
Get PDFEchoreconstruction techniques for subsurface imaging, widely
used in oil exploration, are based on experiments in which short acoustic impulses, emitted at the surface, illuminate a certain volume and are backscattered by inhomogeneities of the medium. The inhomogeneities act as reflecting surfaces which cause signal echoing; the echoes are then recorded at the surface and processed through a propagation model (which acts as a “computational lens”) to yield an image of those very inhomogeneities.
Migration, based on the scalar wave equation, is the standard imaging technique for seismic applications [1]. In the migration process, the recorded pressure waves(called the seismic traces or the seismic section) are used as initial conditions for a wave field governed by the scalar wave equation in an inhomogeneous medium
Mixing influence on ε-caprolactam quality: an industrial application of CFD simulation
No full textCPL production is a mixing sensitive system and for this reason it is used as test case for a CFD code including micromixing phenomena description. The code CFX-4 is used for simulating the behaviour of a rotor-stator mixer, considered as a reactor. Specific properties like kinetic laws and viscosity functions have been experimentally estimated and here reported. The preliminary results of fluid dynamic validation are here reported
Transient time in unidirectional synchronization
Get PDFWe consider here the behaviour of a dynamical system consisting
of unidirectionally coupled Duffing oscillators. Under certain conditions the subsystems may become synchronised corresponding to a stable invariant subset of the full dimensional phase space. The distribution for the transient time that trajectories take to converge onto the synchronised state is investigated via numerical simulations. Some initial conditions undergo a very long transient motion distinct from the drive, before synchronisation occurrs. The dependence of this time on the governing system parameters and on the initial conditions of the driving system is discussed
Kolmogorov methodology as a practical way to answer to the challenge of turbulent combustion
Get PDFThis paper analyses possible practical answer to so-called challenge of turbulent combustion (i. e. inability of combustion models predict accurately at real Reynolds and Damkohler
numbers combustion rates) using Kolmogorov idea of equilibrium small-scale states. As this challenge is connected with inability to resolve at combustion modeling small space and time scales where takes place coupling between chemistry and turbulence, controlling the rates, our propose is based on assumption some equilibrium small-scale structures of reaction zones at flamelet combustion mechanism, whose properties could be expressed in terms of large-scale parameters. In other words the combustion rates enter in the combustion equation through a physical model similar to the molecular dissipation in the Kolmogorov "k - ε" turbulence model.
The concrete analyzed premixed combustion problem refers to the case of strong turbulence and flames with increasing brush width (this combustion regime is preceded to the traditional stationary flames). Two main equilibrium states are assumed for quantitative description of this coupling: equilibrium fine-scale turbulence, which controls thickened flamelet parameters and equilibrium small-scale structure of strongly wrinkled amelet sheet that controls the flamelet
area. We examined integral turbulent ame speed Ut and the local combustion rates across the flame ρW. It has been shown that at the same Ut, the possibility of accurate prediction of the ρW distribution is closely connected with the possibility to describe the counter-gradient transport phenomenon.
Finally we generalize the premixed combustion model equation in terms of the progress variable to the general case of partially premixed combustion. These more general equations are in terms of PDF of a passive concentration and a conditional progress variable, the transport terms are controlled only by physical gradient diffusion, equations contain only the dissipation of the passive concentration. At equilibrium products (fast chemistry) the coupling between chemistry and turbulence is described similar to the premixed case by a model source term. All coupling effects contains only in the equation in the terms of the conditional progress variable and enter in the source term through the physical model
Misura di variabili meteoclimatiche su scala di grigliato modellistico-numerico mediante radar CASSINI. Definizione di una procedura di assimilazione della velocità verticale nei modelli meteorologici idrostatici e sviluppo della diagnostica della instabilità simmetrica su grigliato numerico
Get PDFLo studio presentato in queste note si inquadra nell'ambito del progetto finanziato dall'ASI per la messa a punto e la sperimentazione di un radar
(CASSINI) per la stima da satellite di parametri meteorologici, ed ha come
obiettivo, a lunga scadenza, l'approfondimento delle procedure per valutare
l'impatto potenziale, sul forecast dei fenomeni di precipitazione intensa, dovuto alla assimilazione di misure telerilevate nella condizione iniziale di un
modello meteorologico ad area limitata.
Tenendo presente quest'obiettivo generale, è stato effettuato lo studio di
fattibilità di un processo di assimilazione della velocità verticale nei modelli
meteorologici idrostatici, e realizzato un codice numerico per la diagnostica
della instabilità condizionale simmetrica umida che si pensa sia uno degli
elementi che concorrono agli eventi di precipitazione intensa a bande. Dopo
aver applicato tale strumento alle analisi meteorologiche dei mesi di Gennaio
e Febbraio dell'anno 1991, si è studiato mediante un modello di circolazione atmosferica ad area limitata (BOLAM) un caso di precipitazione intensa localizzato nella zona del canale di Sardegna alla risoluzione spaziale di ∼
30 km
CASTEM 2000 interfacing capabilities
Get PDFIn this set of examples we want to show the CASTEM 2000 capabilities to interface with other finite element analysis or physical simulation software.
CASTEM2000 is a computer code for the analysis of structures by the finite
element method (FEM). The program was developed by the Department of Mechanics and Tecnology (DMT) of the French Atomic Energy Commission (CEA), it is an high level instrument, that can be used as a support in the design and analysis of components in the nuclear field as in the traditional industrial sector.
CASTEM 2000 is a complete system integrating not only the functions of calculation (processing), but also for the construction of the model (proprocessing) and for the evaluation of the results (post-processing). CASTEM 2000 can analyze linear or non-linear, static or dynamic problems in structural mechanics, heat trasfer and so on
Multifractal analysis and simulation of rainfall fields in space
Get PDFStatistical downscaling of precipitation from the large scales of meteorological models to the characteristic response scales of small catchment basins needs to correctly preserve the anomalous scaling laws observed in real rainfall. Multifractal behaviour of precipitation in space is investigated on a set of rainfall fields obtained by a high resolution simulation with a limited area model for numerical weather prediction and on two sets of radar measures of it rainfall during the GATE campaign. Some sets of synthetic rainfall fields were generated applying a multifractal model based on a wavelet expansion with coefficients extracted by a log-Poisson random cascade, and results of comparisons with the GATE rainfall fields are presented.73-78Pubblicat