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Solid particle transport behavior and the effect of aerosol mass loading on performance of a slit virtual impactorSeshadri, Satyanarayanan 30 September 2004 (has links)
Transport of solid particles in a slit virtual impactor has been analyzed using visualization techniques. Particle trajectories were observed using laser-induced fluorescence of monodisperse particles seeded in the virtual impactor flow. It was observed from these trajectories that for smaller inertia particles essentially followed the flow streamlines, whereas higher inertia particles tend to deflect from their initial streamlines. These transport characteristics were used to determine particle collection efficiency curves, and the percentage of defect particle transmission, particles transmitted to the major flow that are well beyond the experimentally determined 50% cutoff. Defect percentages were found to be in good agreement with those based on a local stokes number approach, an analytical model using a converging flow velocity profile. It was hypothesized that these defects occur by virtue of larger particles passing through the near wall flow region and consequently transported to the major flow. The trajectories of such defect occurrences clearly show that these particles originated in the near wall region. Performance at higher mass loadings was evaluated using a background dust matrix generated by a turntable aerosol generator. At high mass loadings, clogging of the slit led to the deterioration of the impactor's performance. The time taken to clog the silt was estimated by modeling the slit edge as a single filter fiber of rectangular cross section with the primary mechanism of filtration being interception and was found to be in good agreement with the experimental data. Elimination of defect transmission and clogging would be possible by the provision of a sheath airflow, which ensures that the near wall regions are free of particles.
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Using Conservative and Biological Tracers to Better Understand the Transport of Agricultural Contaminants from Soil Water through the Epikarstic ZoneHam, Brian 01 December 2009 (has links)
Agriculture contamination is very common in karst systems due to the vulnerability of these aquifers. Animal waste is often spread across crop land to enrich the soil with nitrates and phosphates. Herbicides and pesticides are also applied to the crops. The transport of these pollutants through the soil and epikarst is a difficult process to monitor due to the complex, heterogeneous behavior of the groundwater as it makes its way down to the aquifer below.
An experimental site at Crumps Cave lended a unique opportunity to monitor the vadose zone at a waterfall in the cave below. A previous dye trace established the connection between an 11.15 m2 grass plot and this underground waterfall. The field design used here, utilizing a rainfall simulator, allowed control of the input of precipitation and tracers to understand more about the movement of stormwater infiltrating the soil and the differences in transport of solute particles and bacteria in the epikarstic zone. Two particle transport experiments were used to better understand these processes. The first trace involved injection of fluorescein dye and sodium chloride. The 2,650 liters of solution were injected over a period of 3.6 hours at a rate of 6.6 cm/hr. An electrical resistivity traverse, perpendicular to the hypothesized straight-line path of the established dye trace connection, showed a peak in lower resistance at the upper epikarst layers 4 hours and 15 minutes after the beginning of the injection. Dye concentrations reached a peak of 1,600 ppb 3 hours and 15 minutes after the beginning of the injection. The conductivity also peaked at this time with a value of 814 µS. This first trace showed that rapid transportation of solutes happened in localized conduits causing a peak of both solutes in the cave before the widespread mobilization of sodium chloride was seen in the epikarst by the resistivity images an hour later.
In the second trace, 2,605 liters of a sulphorhodamine dye solution was injected over 180 kg of dairy cattle manure spread on the 11.15 m2 plot of grass for a period of 3.6 hours at a rate of 6.6 cm/hr. Dye concentrations reached a peak of 27 ppm 4 hours and 15 minutes after the beginning of the injection. Fecal coliform reached its first peak of 2,755 MPN (most probable number of viable cells per 100 mL of water) 90 minutes prior to the dye peak and a second peak of 2,481 MPN occurred 15 minutes prior to the dye peak. These results showed that solutes travelling through the soil and epikarst follow similar paths while bacteria prefer conduits that offer more rapid transmission to the underground waterfall.
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Solid particle transport behavior and the effect of aerosol mass loading on performance of a slit virtual impactorSeshadri, Satyanarayanan 30 September 2004 (has links)
Transport of solid particles in a slit virtual impactor has been analyzed using visualization techniques. Particle trajectories were observed using laser-induced fluorescence of monodisperse particles seeded in the virtual impactor flow. It was observed from these trajectories that for smaller inertia particles essentially followed the flow streamlines, whereas higher inertia particles tend to deflect from their initial streamlines. These transport characteristics were used to determine particle collection efficiency curves, and the percentage of defect particle transmission, particles transmitted to the major flow that are well beyond the experimentally determined 50% cutoff. Defect percentages were found to be in good agreement with those based on a local stokes number approach, an analytical model using a converging flow velocity profile. It was hypothesized that these defects occur by virtue of larger particles passing through the near wall flow region and consequently transported to the major flow. The trajectories of such defect occurrences clearly show that these particles originated in the near wall region. Performance at higher mass loadings was evaluated using a background dust matrix generated by a turntable aerosol generator. At high mass loadings, clogging of the slit led to the deterioration of the impactor's performance. The time taken to clog the silt was estimated by modeling the slit edge as a single filter fiber of rectangular cross section with the primary mechanism of filtration being interception and was found to be in good agreement with the experimental data. Elimination of defect transmission and clogging would be possible by the provision of a sheath airflow, which ensures that the near wall regions are free of particles.
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Rapid numerical simulation and inversion of nuclear borehole measurements acquired in vertical and deviated wellsMendoza Chávez, Alberto 10 August 2012 (has links)
The conventional approach for estimation of in-situ porosity is the combined use of neutron and density logs. These nuclear borehole measurements are influenced by fundamental petrophysical, fluid, and geometrical properties of the probed formation including saturating fluids, matrix composition, mud-filtrate invasion and shoulder beds. Advanced interpretation methods that include numerical modeling and inversion are necessary to reduce environmental effects and non-uniqueness in the estimation of porosity. The objective of this dissertation is two-fold: (1) to develop a numerical procedure to rapidly and accurately simulate nuclear borehole measurements, and (2) to simulate nuclear borehole measurements in conjunction with inversion techniques. Of special interest is the case of composite rock formations of sand-shale laminations penetrated by high-angle and horizontal (HA/HZ) wells. In order to quantify shoulder-bed effects on neutron and density borehole measurements, we perform Monte Carlo simulations across formations of various thicknesses and borehole deviation angles with the multiple-particle transport code MCNP. In so doing, we assume dual-detector tool configurations that are analogous to those of commercial neutron and density wireline measuring devices. Simulations indicate significant variations of vertical (axial) resolution of neutron and density measurements acquired in HA/HZ wells. In addition, combined azimuthal- and dip-angle effects can originate biases on porosity estimation and bed boundary detection, which are critical for the assessment of hydrocarbon reserves. To enable inversion and more quantitative integration with other borehole measurements, we develop and successfully test a linear iterative refinement approximation to rapidly simulate neutron, density, and passive gamma-ray borehole measurements. Linear iterative refinement accounts for spatial variations of Monte Carlo-derived flux sensitivity functions (FSFs) used to simulate nuclear measurements acquired in non-homogeneous formations. We use first-order Born approximations to simulate variations of a detector response due to spatial variations of formation energy-dependent cross-section. The method incorporates two- (2D) and three-dimensional (3D) capabilities of FSFs to simulate neutron and density measurements acquired in vertical and HA/HZ wells, respectively. We calculate FSFs for a wide range of formation cross-section variations and for borehole environmental effects to quantify the spatial sensitivity and resolution of neutron and density measurements. Results confirm that the spatial resolution limits of neutron measurements can be significantly influenced by the proximity of layers with large contrasts in porosity. Finally, we implement 2D sector-based inversion of azimuthal logging-while-drilling (LWD) density field measurements with the fast simulation technique. Results indicate that inversion improves the petrophysical interpretation of density measurements acquired in HA/HZ wells. Density images constructed with inversion yield improved porosity-feet estimations compared to standard and enhanced compensation techniques used commercially to post-process mono-sensor densities. / text
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Direct numerical simulation of particle-laden turbulence in a straight square ductSharma, Gaurav 30 September 2004 (has links)
Particle-laden turbulent flow through a straight square duct at Reτ = 300 is studied using direct numerical simulation (DNS) and Lagrangian particle tracking. A parallelized 3-D particle tracking direct numerical simulation code has been developed to perform the large-scale turbulent particle transport computations reported in this thesis. The DNS code is validated after demonstrating good agreement with the published DNS results for the same flow and Reynolds number. Lagrangian particle transport computations are carried out using a large ensemble of passive tracers and finite-inertia particles and the assumption of one-way fluid-particle coupling. Using four different types of initial particle distributions, Lagrangian particle dispersion, concentration and deposition are studied in the turbulent straight square duct. Particles are released in a uniform distribution on a cross-sectional plane at the duct inlet, released as particle pairs in the core region of the duct, distributed randomly in the domain or distributed uniformly in planes at certain heights above the walls. One- and two-particle dispersion statistics are computed and discussed for the low Reynolds number inhomogeneous turbulence present in a straight square duct. New detailed statistics on particle number concentration and deposition are also obtained and discussed.
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Métodos espectronodais para cálculos de transporte de partículas neutras com fonte fixa na formulação de ordenadas discretas e multigrupo de energia / Spectral nodal methods for multigroup fixed-source neutral particle transport calculations in the discrete ordinates formulationWelton Alves de Menezes 22 August 2012 (has links)
Conselho Nacional de Desenvolvimento Científico e Tecnológico / Um método espectronodal é desenvolvido para problemas de transporte de
partículas neutras de fonte fixa, multigrupo de energia em geometria cartesiana na
formulação de ordenadas discretas (SN). Para geometria unidimensional o método
espectronodal multigrupo denomina-se método spectral Greens function (SGF) com
o esquema de inversão nodal (NBI) que converge solução numérica para problemas
SN multigrupo em geometria unidimensional, que são completamente livre de erros
de truncamento espacial para ordem L de anisotropia de espalhamento desde que
L < N. Para geometria X; Y o método espectronodal multigrupo baseia-se em integrações
transversais das equações SN no interior dos nodos de discretização espacial,
separadamente nas direções coordenadas x e y. Já que os termos de fuga transversal
são aproximados por constantes, o método nodal resultante denomina-se SGF-constant
nodal (SGF-CN), que é aplicado a problemas SN multigrupo de fonte fixa em geometria
X; Y com espalhamento isotrópico. Resultados numéricos são apresentados para
ilustrar a eficiência dos códigos SGF e SGF-CN e a precisão das soluções numéricas
convergidas em cálculos de malha grossa. / A spectral nodal method is described for neutral particle energy multigroup
fixed-source transport problems in cartesian geometry in the discrete ordinates (SN)
formulation. For slab geometry the offered multigroup spectral nodal method is referred
to as the spectral Greens function (SGF) method with the one-node block inversion
(NBI) iterative scheme, which converges numerical solutions to multigroup
slab-geometry SN problems, that are completely free from spatial truncation errors for
scattering anisotropy of order L, provided L < N. For X; Y-geometry, the offered multigroup
spectral nodal method is based on transverse integrations of the SN equations
inside the discretization nodes, separately in x- and y- coordinate directions. Since the
transverse-leakage terms are approximated by constants, the resulting nodal method
is referred to as the multigroup SGF-contant nodal (SGF-CN) method, which is applied
for multigroup X; Y-geometry fixed-source SN problems with isotropic scattering. Numerical
results are presented to illustrate the efficiency of the SGF and SGF-CN codes
and the accuracy of the converged numerical solutions in coarse-mesh calculations.
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Modelos aproximados para o calculo do transporte de particulas neutras em dutosONO, SHIZUCA 09 October 2014 (has links)
Made available in DSpace on 2014-10-09T12:44:01Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:07:20Z (GMT). No. of bitstreams: 1
06913.pdf: 2715369 bytes, checksum: 9d927e16226a25d1d362ba0ebc83502c (MD5) / Tese (Doutoramento) / IPEN/T / Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP
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Modelagem de um sistema de planejamento em radioterapia e medicina nuclear com o uso do código MCNP6 / Modeling of a planning system in Radiotherapy and Nuclear Medicine using the MCNP6 codeMASSICANO, FELIPE 22 June 2016 (has links)
Submitted by Claudinei Pracidelli (cpracide@ipen.br) on 2016-06-22T11:21:31Z
No. of bitstreams: 0 / Made available in DSpace on 2016-06-22T11:21:31Z (GMT). No. of bitstreams: 0 / Tese (Doutorado em Tecnologia Nuclear) / IPEN/T / Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP
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Um método sintético de difusão para aceleração do esquema de fonte de espalhamento em cálculos SN unidimensionais de fonte fixa / A diffusion synthetic acceleration method for the scattering source iteration scheme in fixed source slab-geometry SN calculationsFrederico Pereira Santos 09 September 2011 (has links)
Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / O esquema iterativo de fonte de espalhamento (SI) é tradicionalmente aplicado para a
convergência da solução numérica de malha fina para problemas de transporte de nêutrons
monoenergéticos na formulação de ordenadas discretas com fonte fixa. O esquema SI é muito
simples de se implementar sob o ponto de vista computacional; porém, o esquema SI pode
apresentar taxa de convergência muito lenta, principalmente para meios difusivos (baixa
absorção) com vários livres caminhos médios de extensão. Nesta dissertação descrevemos
uma técnica de aceleração baseada na melhoria da estimativa inicial para a distribuição da
fonte de espalhamento no interior do domínio de solução. Em outras palavras, usamos como
estimativa inicial para o fluxo escalar médio na grade de discretização de malha fina,
presentes nos termos da fonte de espalhamento das equações discretizadas SN usadas nas
varreduras de transporte, a solução numérica da equação da difusão de nêutrons em grade
espacial de malha grossa com condições de contorno especiais, que aproximam as condições
de contorno prescritas que são clássicas em cálculos SN, incluindo condições de contorno do
tipo vácuo. Para aplicarmos esta solução gerada pela equação da difusão em grade de
discretização de malha grossa nas equações discretizadas SN de transporte na grade de
discretização de malha fina, primeiro implementamos uma reconstrução espacial dentro de
cada nodo de discretização, e então determinamos o fluxo escalar médio em grade de
discretização de malha fina para usá-lo nos termos da fonte de espalhamento. Consideramos
um número de experimentos numéricos para ilustrar a eficiência oferecida pela presente
técnica (DSA) de aceleração sintética de difusão. / The scattering source iterative (SI) scheme is traditionally applied to converge finemesh
numerical solutions to fixed-source discrete ordinates neutron transport problems.
The SI scheme is very simple to implement under a computational viewpoint. However, the
SI scheme may show very slow convergence rate, mainly for diffusive media (low absorption)
with several mean free paths in extent. In this work we describe an acceleration technique
based on an improved initial guess for the scattering source distribution within the slab. In
other words, we use as initial guess for the fine-mesh average scalar flux in the scattering
source terms of the SN discretized equations used in the transport sweeps, the coarse-mesh
solution of the neutron diffusion equation with special boundary conditions to account for the
classical SN prescribed boundary conditions, including vacuum boundary conditions. To
apply this coarse-mesh diffusion solution into the fine-mesh SN transport sweep discretized
equations, we first perform within-node spatial reconstruction, and then we determine the
fine-mesh average scalar flux for use in the scattering source terms. We consider a number of
numerical experiments to illustrate the efficiency of the offered diffusion synthetic
acceleration (DSA) technique.
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Métodos espectronodais para cálculos de transporte de partículas neutras com fonte fixa na formulação de ordenadas discretas e multigrupo de energia / Spectral nodal methods for multigroup fixed-source neutral particle transport calculations in the discrete ordinates formulationWelton Alves de Menezes 22 August 2012 (has links)
Conselho Nacional de Desenvolvimento Científico e Tecnológico / Um método espectronodal é desenvolvido para problemas de transporte de
partículas neutras de fonte fixa, multigrupo de energia em geometria cartesiana na
formulação de ordenadas discretas (SN). Para geometria unidimensional o método
espectronodal multigrupo denomina-se método spectral Greens function (SGF) com
o esquema de inversão nodal (NBI) que converge solução numérica para problemas
SN multigrupo em geometria unidimensional, que são completamente livre de erros
de truncamento espacial para ordem L de anisotropia de espalhamento desde que
L < N. Para geometria X; Y o método espectronodal multigrupo baseia-se em integrações
transversais das equações SN no interior dos nodos de discretização espacial,
separadamente nas direções coordenadas x e y. Já que os termos de fuga transversal
são aproximados por constantes, o método nodal resultante denomina-se SGF-constant
nodal (SGF-CN), que é aplicado a problemas SN multigrupo de fonte fixa em geometria
X; Y com espalhamento isotrópico. Resultados numéricos são apresentados para
ilustrar a eficiência dos códigos SGF e SGF-CN e a precisão das soluções numéricas
convergidas em cálculos de malha grossa. / A spectral nodal method is described for neutral particle energy multigroup
fixed-source transport problems in cartesian geometry in the discrete ordinates (SN)
formulation. For slab geometry the offered multigroup spectral nodal method is referred
to as the spectral Greens function (SGF) method with the one-node block inversion
(NBI) iterative scheme, which converges numerical solutions to multigroup
slab-geometry SN problems, that are completely free from spatial truncation errors for
scattering anisotropy of order L, provided L < N. For X; Y-geometry, the offered multigroup
spectral nodal method is based on transverse integrations of the SN equations
inside the discretization nodes, separately in x- and y- coordinate directions. Since the
transverse-leakage terms are approximated by constants, the resulting nodal method
is referred to as the multigroup SGF-contant nodal (SGF-CN) method, which is applied
for multigroup X; Y-geometry fixed-source SN problems with isotropic scattering. Numerical
results are presented to illustrate the efficiency of the SGF and SGF-CN codes
and the accuracy of the converged numerical solutions in coarse-mesh calculations.
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