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Implementation and testing of the CODESA-3D model for density-dependent flow and transport problems in porous media
Get PDFThe report describes the implementation and the test phases of the computer code CODESA-3D (Coupled variable Density and Saturation 3-Dimensional model), whose mathematical and numerical models are described in all details in the ten chapter of the book. CODESA-3D is a three-dimensional finite element simulator for flow and solute transport in variably saturated porous media on unstructured domains. The flow and solute transport processes are coupled through the variable density of the filtrating mixture made of water and dissolved matter (salt, pollutants). The flow module simulates the water movement in the porous medium , taking into account different forcing inputs: infiltration/evaporation, recharge/discharge, withdrawal/injection, etc., while the transport module computes the migration of the salty plume due to advection and diffusion processes
Time-critical multiresolution rendering of large complex models
Get PDFVery large and geometrically complex scenes, exceeding millions of polygons and hundreds of objects, arise naturally in many areas of interactive computer graphics. Time-critical rendering of such scenes requires the ability to trade visual quality with speed. Previous work has shown that this can be done by representing individual scene components as multiresolution triangle meshes, and performing at each frame a convex constrained optimization to choose the mesh resolutions that maximize image quality while meeting timing constraints. In this paper we demonstrate that the nonlinear optimization problem with linear constraints associated to a large class of quality estimation heuristics is efficiently solved using an active-set strategy. By exploiting the problem structure, Lagrange multipliers estimates and equality constrained problem solutions are computed in linear time. Results show that our algorithms and data structures provide low memory overhead, smooth level-of-detail control, and guarantee, within acceptable limits, a uniform, bounded frame rate even for widely changing viewing conditions. Implementation details are presented along with the results of tests for memory needs, algorithm timing, and efficacy.785-803Pubblicat
Physically-based distributed model for coupled surface runoff and subsurface flow simulation at the catchment scale
Get PDFThe interactions between surface and subsurface hydrologic processes are important in many water
resource applications and require modeling approaches capable of treating these processes in an integrated manner.
We describe a distributed, physically-based model that couples a three-dimensional subsurface flow module to a DEM-based one-dimensional surface routing module and resolves in a detailed manner the exchange of flux and head information between the two regimes. The coupled model can treat flow in saturated and variably saturated porous media, surface runoff, channel flow, and storage in lakes and other topographic depressions. The algorithm that handles the exchange between the surface and subsurface components is described in detail, and an illustrative test case is presented.1115-112
Guidelines for validation and verification of groundwater mathematical studies (GULLIVER): a case study
No full textThe goal of this work is to define a set of guidelines for “validating" mathematical models that are to be used in real-world problems of subsurface flow and contaminant transport. Groundwater models today are being used to study increasingly complex problems involving large temporal and spatial scales and with many uncertainties inherent in the data and in the
models themselves. It becomes important therefore to establish procedures
and benchmark tests with which to assess a given model's adequacy for
simulating a specific groundwater problem. In the GULLIVER project we
propose to create a public library of phenomenological schemes (PS), each
one satisfactorily solved by an established model. A user with a specific
application and model at hand can select the PS that most closely corresponds to his application, and corroborate his model against the established solution. The user's model is considered validated when the two numerical solutions match according to specified criteria. In this paper we describe this methodology and present its application to a 2D saturated flow and transport test case based on data from a field study site in Calabria, Italy.281-29
Studio del comportamento idroelastico di contenitori galleggianti
No full textMaster in Tecniche informatiche avanzate per la progettazione e la simulazione numerica.Il progetto di tesi svolto durante lo stage conclusivo del “Master in Tecniche informatiche avanzate per la progettazione e la simulazione numerica” si proponeva di studiare il comportamento idroelastico delle strutture galleggianti.Inedit
Eiha?!?: XML per l'organizzazione di URL con distribuzione multimodale
Get PDFLa crescita esponenziale di risorse presenti in rete ed il largo sviluppo di strumenti per l'accesso multimodale ad internet fanno sorgere nuovi problemi di gestione dell'informazione quali la ricerca di contenuti e la formattazione dei contenitori. In questo contesto ed all'interno del progetto europeo Vision abbiamo costruito un manuale telematico interattivo della cultura e del territorio della Sardegna. Questa raccolta di dati e stata progettata anche come piattaforma di sperimentazione di nuove tecnologie quali l'XML e le sue applicazioni. Il risultato ottenuto e un servizio multimodale, denominato Eiha?!?, fruibile attraverso PC, cellulari e PDA
HPF to OpenMP on the Origin2000: a case study
Get PDFThe geophysics group at CRS4 has long developed echo reconstruction codes in HPF on distributed-memory machines. Now, however, with the arrival of shared-memory machines and their native OpenMP compilers, the transfer to OpenMP would seem to present the logical next step in our code development strategy. Recent experience with porting one of our important HPF codes to OpenMP does not bear this out—at least not on the Origin2000. The OpenMP code suffers from the immaturity of the standard, and the operating system's handling of UNIX threads seems to severely penalize OpenMP performance. On the other hand, the HPF code on the Origin2000 is fast, scalable and not disproportionately sensitive to load on the machine.1147–1154Pubblicat
Soil moisture mapping from ASAR imagery for the Flumendosa and Meuse river basins
Get PDFSP-461 (CD)Soil moisture monitoring and the characterization of the spatial and temporal variability of this hydrologic parameter at scales from small catchments to large river basins continues to receive much attention, reflecting its critical role in subsurface – land surface – atmosphere interactions and its importance to drought analysis, crop yield forecasting, irrigation planning, flood protection, and forest fire prevention.
We will describe the objectives and methodologies of an Envisat project that will aim to produce maps of seasonal soil moisture patterns at the regional scale based on ASAR imagery. The work will be carried out for two river basins that have significantly different climatic, geologic, and land use characteristics: the Flumendosa basin in Sardinia (Italy) and the larger Meuse basin that drains a good part of Belgium and the Netherlands as well as portions of France, Germany, and Luxembourg. High resolution ASAR data will be acquired over selected catchment scale test sites within each of these study regions, whereas medium resolution images will be acquired over the entire river basin (or extended region in the case of the smaller basin). A statistical analysis of the information from the processed images at these two different scales will be used to develop an aggregation methodology to generate large scale soil moisture maps. Data assimilation
techniques will also be developed for dynamically integrating the high resolution satellite data into catchment scale hydrological simulation models. The work being planned will be placed in the context of recent efforts at validating and applying SAR soil moisture data, which we will briefly review
Rapporto di ricerca bibliografica (Stato dell'arte dei modelli di flusso e trasporto in mezzi porosi)
Get PDFIn questo primo rapporto vengono presentate le equazioni fondamentali che reggono i fenomeni di flusso e trasporto in mezzi porosi insieme ai metodi numerici che verranno utilizzati per la soluzione di tali equazioni. I modelli matematici in questione sono basati su equazioni differenziali a derivate parziali che impongono il bilancio di massa sia per il fluido che per il soluto (inquinante disciolto in acqua). Queste equazioni vengono scritte in forma generale per un mezzo poroso tridimensionale; in dipendenza dal tipo di applicazione è possibile adottare modelli mono o bidimensionali che portano a semplificazioni notevoli. L'equazione di flusso è sviluppata per il caso di mezzi porosi a saturazione variabile e può essere quindi utilizzata contemporaneamente nella zona insatura (suoli superficiali) e satura (falde freatiche e artesiane). Nell'equazione di trasporto si considerano i processi di dispersione, diffusione e avvezione, insieme ad alcune fenomenologie di interazione chimico-fisica tra il soluto e la matrice porosa. Accanto a queste equazione, si descrive anche un modello, a scala di bacino, di afflussi-deflussi superficiali accoppiato con un modello di infiltrazione. Questo approccio viene tiene conto di fenomeni importanti qualora vi sia una stretta correlazione tra il moto dell'acqua in superficie e il moto dell'acqua nella zona insatura
Parallel spectral elements for applications to linear elastodynamics
Get PDFWe present a parallel implementation of a fully unstructured spectral element method for elastic wave propagation problems. Our target is to merge the high accuracy of spectral methods with the flexibility of finite elements in dealing with complex geometries. The spectral algorithms we propose is based on a domain decomposition approach, implemented into a multiprocessor environment. Parallelism is exploited at the algebraic level: the global linear system is distributed among processors, and then solved by iterative techniques