83 research outputs found
Bioturbation experiments in the Venice Lagoon
Short experiments (14â21 days) were carried out during autumn 1998 and spring 1999 at one selected site of the
Venice Lagoon to measure bioturbation activities and mixing rates, as well as to obtain quantitative information on
benthos functionality. Fluorescent sediment particles (luminophores, 63â350 ÎŒm) were introduced as pulse inputs
at the sediment surface. The concentrationâdepth profiles of the tracer were simulated with a new advectionâ
diffusionânon local model applied under non-steady state conditions. This allowed the quantification of the mixing
parameters associated with different mechanisms: biodiffusion (Db), bioadvection (W) and non-local mixing (Ke,z1, z2). A parameter RS (removed sediment) was also calculated to account for the flux of sediment due to nonlocal transport. Results show that bioturbation was dominated by biodiffusion in autumn and by bioadvection in
spring. Mean mixing parameters Db, W, and RS changed from 3.09 to 0.87 cm2 yâ1, from 0.93 to 15.50 yâ1 and from 5.85 to 7.79 g cmâ2 yâ1, respectively
Numerical methodologies for the simulation of liquid metal flows
The fluid-dynamic modelling for the simulation of the Lead-Bismuth flow in the EADF was reviewed. The general form of the non-dimensional governing equation was derived, and the analysis of the orders of magnitude of the different terms in the case of a the liquid metal flows in the EADF was performed, through a flow-Mach number asymptotic analysis. It was found that the resulting form of the equations is the one commonly used in commercial CFD codes for the simulation of liquid flows, which can then be used for our applications.
The most common numerical methods for flow-Mach number applications were also presented.
These methods are general and can be applied to liquid metal flows without any modification.
The peculiarity of the numerical simulation of liquid metal flows lies in the modelling of the turbulent heat transfer, due to the flow Prandtl number of this type of fluids. This subject is discussed in [21]
Integration of numerical tools for the combined thermal-hydraulics and structural analysis of energy amplifier components
The 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]
Phenomenology of liquid metal thermal-hydraulics
The 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
Thermo-mechanical stresses on the beam window
The 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
Structural response of the EADF target beam window to beam interruptions: transient thermo-mechanical computation
The operability of a high power proton beam target in an Accelerator Driven System (ADS) is
strictly connected to the structural integrity of the beam window, which is undoubtedly the most
delicate component in such devices, being exposed to the combined effects of high intensity proton
and neutron irradiation, liquid metal corrosion and high thermal stresses induced by the interaction
with the beam. It has also recently been highlighted that beam trips may frequently occur in current
high power accelerators [1]. Clearly, the definition of the requirements of future accelerators depends
on the behaviour of the window under such conditions. For this purpose a numerical study of typical
transients has been carried out on the 600 MeV proton beam target that drives the 80 MW
Demonstration Facility of the Energy Amplifier proposed by C. Rubbia, [2] presently under
development in Italy by Ansaldo, CRS4, ENEA and INFN [3]
Numerical studies related to the design of the beam target of the energy amplifier prototype
The 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
Dataset of analyzes performed to determine the level and timing of selected organic pollutantsâ inputs in sediments of the Lake of Cavazzo (Italy)
This data article presents the dataset collected for selected organic pollutants in the framework of a larger research project aimed at assessing the effects of different environmental stressors (natural and anthropogenic) in sediments of the Lake of Cavazzo, a basin of glacial origin located in a seismically active region of the Italian Eastern Alps. Information relative to sampling strategy and operations, location of sampling sites, sedimentary chronological benchmarks, and profiles of RGB (Red-Green-Blue) color code determined from high resolution photos taken at cores CAV-04 and CAV-06 are reported, together with analytical data for 15 polycyclic aromatic hydrocarbons, 21 polychlorinated biphenylsâ congeners (including the non-Aroclor CB-11), 14 polybrominated diphenyl ethersâ congeners, and 22 organochlorine pesticides, whose concentrations were determined by Gas Chromatography coupled both to Low-Resolution and High-Resolution Mass Spectrometry. Interpretation of this dataset is fully discussed in the companion article by Pizzini et al. (2022) and relys on the multi-proxy analysis of sediment samples presented in Polonia et al. (2021) that highlighted lake stratigraphy and major changes occurring at a decadal scale since the 1950s
Advances in virtual archaeology. Research, preservation, and dissemination
The archaeological and palaeontological record (including human skeletal remains) often bears crack, damage and deformations. The recent rapid development of the diagnostic potentials of âvirtual archaeologyâ has provided innovative tools to manage, study and preserve cultural and natural heritage. These tools include, among others, CT-scans, Laser-scanning, photogrammetry, 3D imaging and rapid
prototyping. This approach can contribute to any archaeological context from its discovery to research, preservation, and dissemination. 3D imaging techniques, for instance, substitute physical intervention with a virtual protocol aimed at restoring the original shape of an archaeological item or a fossil specimen. In a similar way, the recovery of digital morphological information can be gathered using data preserved even on a deficient finding through the use of 3D comparative samples. Here we present an extended and updated review about the most innovative protocols applied in virtual archaeology and palaeontology
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