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A shapes based geometric modeler for mesh++, API description
Get PDFOne of the purposes of the ViVa Project is the reconstruction of geometrical models from a suitable set of data provided by non invasive medical analyses like Computed Tomography (CT) or Magnetic Resonance Imaging (MRI). To do this, we first segment the vessel geometry from the data sets using techniques such as active snakes, and then reconstruct geometrical models using the XOX SHAPES geometric modeler, and in particular its MicroTopology features. In order to perform blood flow simulation on these models, we need to mesh them, and so we use the Mesh++ grid generator to process the models and create a two-dimensional grid for the surfaces and a three-dimensional one for the vessel lumen
Numerical simulation of premixed combustion flows: a comparative study
Get PDFIn this work four different commercial and research CFD codes have been compared for the simulation of two combustion test cases. The aim was to get an overview of the capabilities of these different tools to simulate combustion flows in premixed regimes. Codes tested were Fluent,
CFX, StarCD and Tanit. Three combustion models have been applied, namely the Eddy Break Up, the Eddy Dissipation Model and the Turbulent Flame Closure, the turbulence model used being the standard k-epsilon. Numerical results have been found to fairly fit experiments and helped to show some drawbacks of combustion models. In its theoretically correct range of applicability the TFC model has been found to give the better agreement with experiments
Multifractal modeling of anomalous scaling laws in rainfall
Get PDFThe coupling of hydrological distributed models to numerical weather
predictions outputs is an important issue for hydrological applications
such as forecasting of flood events. Downscaling meteorological predictions to the hydrological scales requires the resolution of two fundamental
issues regarding precipitation, namely: 1) understanding the statistical
properties and scaling laws of rainfall fields; 2) validation of downscaling
models that are able to preserve statistical characteristics observed in
real precipitation. In this paper we discuss the first issue by introducing
a new multifractal model that appears particularly suitable for random
generation of synthetic rainfall. We argue that the results presented in
this paper may be also useful for the solution of the second question.
Statistical behavior of rainfall in time is investigated through a high
resolution time series recorded in Genova (Italy). The multifractal analysis shows the presence of a temporal threshold, localized around 10÷20
hours, which separates two ranges of anomalous scaling laws. Synthetic
time series, characterized by very similar scaling laws to the observed one,
are generated with the multifractal model. The potential of the model
for extreme rainfall event distributions is also discussed. The multifractal analysis of GATE radar fields have shown that statistical properties
of rainfall in space depend on time durations over which precipitation
is accumulated. Further analysis of some rainfall fields produced with a
meteorological limited area model exhibited the same anomalous scaling
as the GATE fields
Metis: an object-oriented toolkit for constructing virtual reality applications
Get PDFVirtual reality systems provide realistic look and feel by seamlessly integrating three-dimensional input and output devices. One software architecture approach to constructing such systems is to distributethe application between a computation-intensive simulator back-end and a graphics-intensive viewer front-end which implements user interaction. Inthis paper we discuss Metis, a toolkit we have been developing based on such a software architecture, which can be used for building interactiveimmersive virtual reality systems with computationally intense components. The Metis toolkit defines an application programming interface on thesimulator side, which communicates via a network with a standalone viewer program that handles all immersive display and interactivity. Networkbandwidth and interaction latency are minimized, by use of constraint network on the viewer side that declaratively defines much of dynamic andinteractive behavior of the application.121-13
Thermo-mechanical stresses on the beam window
Get PDFThe Centre for Advanced Studies, Research and Development in Sardinia (CRS4) is
participating to an Italian R&D program, together with Ansaldo, ENEA and INFN, devoted to the design of a 80 MW prototype of the Energy Amplifier proposed by C. Rubbia. The use of advanced numerical tools has been of practical support in the design of critical elements of the machine such as the fuel element and the beam target. The aim of this work is to study the sensitivity of beam window stresses to the beam distribution, size and interruption. In order to compute thermal stresses, the heat deposition in the window and in the coolant generated by the interaction with the proton beam is calculated and used as input data for the fluid dynamic simulation of the natural convection flow of the target coolant
Integration of numerical tools for the combined thermal-hydraulics and structural analysis of energy amplifier components
Get PDFThe CRS4 R&D activity on the Energy Amplifier Demonstration Facility (EADF) [1]
concerns the thermal fluid-dynamic and structural computational analysis in support to the
design of some of the crucial components of the machine. We are currently studying the
operating conditions of the spallation target [2-3] and the sub-critical core [4-5], including
steady state, transient [31-32] and accidental conditions. The simulation activity also includes
the analysis of multi-phase (liquid-gas systems with high void fractions) [6-7] and free
surface Liquid Metal (LM) flows [8-9]. A parallel activity of benchmarking of numerical
codes on LM experiments is in progress [10-12, 33-34], joined with a critical theoretical
review of numerical models applied to LM flows [13-15]
Numerical studies related to the design of the beam target of the energy amplifier prototype
Get PDFThe Centre for Advanced Studies, Research and Development in Sardinia (CRS4) is participating in
an Italian R&D program, together with Ansaldo, ENEA and INFN, devoted to the design of a 80
MW prototype of the Energy Amplifier proposed by C. Rubbia et al.. The use of advanced
numerical tools has been of practical support in the design of critical elements of the machine such
as the fuel element and the beam target.
The aim of this work is to show the design and optimization of the Liquid Metal Spallation
Target, which consists in an axial-symmetric vertical cylinder, where a Pb-Bi eutectic, in a natural
convection driven flow regime, works at the same time as spallation material and coolant for the
target and the beam window. The most critical part of the target is the window itself, where the
highest temperatures and thermal stresses are reached. The minimization of such temperatures and
stresses is the goal of the optimization.
The main geometrical dimensions of the target (i.e. beam pipe, beam window and external
container) are somehow fixed since they are related to the proton beam distribution and to the EA
core design. The optimization therefore acts on the suitable design of the flow guide which
separates the hot rising flow from the cold one. In the region where the flow is heated by the
proton beam the flow guide has a funnel shape which accelerates the liquid metal.
The numerical simulations are performed by using three different tools. The FLUKA Montecarlo
code is used to calculate the heat source distribution in the window and in the coolant generated by
the interaction with the proton beam. The results of these calculations are used as input data for the
thermal fluid dynamic simulations performed with the STAR-CD commercial software. The
resulting temperature and pressure fields are finally introduced in the NASTRAN code used for the
structural analysis of the solid components
Model for heterogeneous catalysis on metal surfaces with application to hypersonic flows
Get PDFA model for heterogeneous catalysis for Copper, Nickel, and Platinum has been devised. The model simulates the heterogeneous chemical kinetics of dissociated air flow impinging metal surfaces. Elementary phenomena such as, atomic and molecular adsorption, Eley-Rideal and Langmuir-Hinshelwood recombinations, and thermal desorptions have been accounted for. Comparisons with experimental results for Nitrogen and Oxygen recombination show good agreement. In the second part of this work, the finite rate catalysis model has been used to analyzed numerically the problems of the heterogeneous catalysis similarity between hypersonic ground testing and reentry flight. Therefore the flow around a blunt cone under these conditions has been calculated and results for heat fluxes and for a suggested similarity parameter have been compared and discussed
On the limits of industrial premixed combustion simulation
Get PDFThis work analyses the simulation potential of two premixed turbulent combustion models based on different combustion mechanism concepts: the Eddy Dissipation Concept based on the volume combustion mechanism, and the Turbulent Flame-speed Closure based on the thickened-wrinkled amelets combustion mechanism.
Ability of simulating numerically a standard experimental test case (premixed methane-air combustion in a plane channel at high flow velocity) and the influence of flow parameters variation on the combustion process have been tested.
The paper shows that the flamelets model describes the standard experimental data more accurately. Furthermore, comparisons of the two models results obtained varying combustion flow parameters show the presence of quantitatively, and in one case even qualitatively
different trends. These results are explained, and potentialities and limits of these models are discussed from an industrial premixed burner applications standpoint
Phenomenology of liquid metal thermal-hydraulics
Get PDFThe cooling system of the Energy Amplifier (EA) is based on a Lead flow driven by natural circulation [1]. In the Energy Amplifier Demonstration Facility (EADF) a Lead-Bismuth eutectic is used and natural circulation, although enhanced through a gas injection system, is the pumping force for the cooling of both the target (only in the case of the window-type target) and the primary circuit[2].
Numerical simulation is extensively used for the design and analysis of these flows, using both commercial and in-house codes. However, liquid metals properties are very different from that of common fluids, so the physical models to be used in the simulations should be carefully assessed.
In general the numerical simulation of any kind of flow requires: (i) the thermodynamic modelling of the fluid; (ii) the fluid dynamics governing equations; (iii) the turbulence modelling.
In this work the thermodynamic model for heavy liquid metals is presented, starting with the derivation of the equations of state for a general fluid from the basic laws of thermodynamics. This thermodynamic model is then used for the analysis of a one-dimensional natural convection
loop, in order to put in evidence the main physical mechanisms governing this particular kind of flow and the simplifications that can be applied to the one dimensional governing equations.
An extensive analysis of the tree-dimensional fluid dynamic governing equations and of the turbulence models for liquid metal flows can be found in [7] and [8] respectively