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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)
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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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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 / O tratamento de câncer possui diversas modalidades. Uma delas é a utilização de fontes de radiação como principal protagonista do tratamento. A radioterapia e a medicina nuclear são exemplos desse tipo de tratamento. Por utilizarem a radiação ionizante como principal ferramenta para a terapia, há a necessidade de se efetuar diversas simulações do tratamento a fim de maximizar a dose nos tecidos tumorais sem ultrapassar os limites de dose nos tecidos sadios circunvizinhos. Os sistemas utilizados na simulação desses tipos de terapia recebem o nome de Sistemas de Planejamento Dosimétrico. A medicina nuclear e a radioterapia possuem seus próprios sistemas de planejamento dosimétricos devido a grande diversidade das informações necessárias às suas simulações. Os sistemas de planejamento em radioterapia são mais consolidados do que os de medicina nuclear e por tal motivo um sistema que aborde tanto os casos de radioterapia como de medicina nuclear contribuiria para significativos avanços na área de medicina nuclear. Dessa forma, o objetivo do trabalho foi modelar um Sistema de Planejamento Dosimétrico com o uso do código de Monte Carlo MCNP6 Monte Carlo N-Particle Transport Code que permitisse incorporar os casos de radioterapia e medicina nuclear e que fosse extensível a novos tipos de tratamentos. A modelagem desse sistema resultou na construção de um Framework, orientado a objetos, nomeado IBMC o qual auxilia no desenvolvimento de sistemas de planejamento que necessitam interpretar grandes quantidades de informações com o objetivo de escrever o arquivo base do MCNP6. O IBMC permitiu desenvolver de maneira rápida e prática sistemas de planejamento para radioterapia e medicina nuclear e os resultados foram validados com sistemas já consolidados. Ele também mostrou alto potencial para desenvolver sistemas de planejamento de novos tipos de tratamentos que utilizam a radiação ionizante. / Tese (Doutorado em Tecnologia Nuclear) / IPEN/T / Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP
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Aerodynamic, infrared extinction and tribocharing properties of nanostructured and conventional particlesPjesky, Susana Castro January 1900 (has links)
Doctor of Philosophy / Department of Biological & Agricultural Engineering / Ronaldo G. Maghirang / Nanostructured particles possess unique chemical and physical properties, making them
excellent candidates for air purification, smoke clearing, and obscuration. This research was
conducted to investigate the aerodynamic, charging, and infrared (IR) extinction properties of
nanostructured particles. Specific objectives were to: (1) measure the size distribution and
concentration of aerosolized nanostructured particles; (2) evaluate their IR extinction properties;
(3) determine their relative chargeability; and (4) numerically model their transport in enclosed
rooms.
The size distribution and concentration of two nanostructured particles (NanoActive®
MgO and MgO plus) were measured in an enclosed room. The particles differed in size
distribution and concentration; for example, the geometric mean diameters of NanoActive®
MgO and MgO plus were 3.12 and 11.1 [Mu]m, respectively.
The potential of nanostructured particles as IR obscurants was determined and compared
with other particles. Four groups of particles were considered: nanostructured particles
(NanoActive® MgO plus, MgO, TiO[subscript2]); nanorods (MgO, TiO[subscript2]); conventional particles (NaHCO[subscript3]
and ISO fine test dust); and common obscurants (brass, graphite, carbon black). The extinction
coefficients of the nanostructured particles were generally significantly smaller than those of the
other particles. Graphite flakes had the greatest mass extinction coefficient (3.22 m[superscript2]/g), followed
by carbon black (1.72 m[superscript2]/g), and brass flakes (1.57 m[superscript2]/g). Brass flakes had the greatest volume
extinction coefficient (1.64 m[superscript2]/cc), followed by NaHCO[subscript3] (0.93 m[superscript2]/cc), and ISO fine test dust
(0.91 m[superscript2]/cc).
The relative chargeability of nanostructured particles was also investigated. Selected
particles were passed through a Teflon tribocharger and their net charge-to-mass ratios were
measured. Tribocharging was able to charge the particles; however, the resulting charge was
generally small. NanoActive® TiO[subscript2] gained the highest net charge-to-mass ratio (1.21 mC/kg)
followed by NanoActive® MgO (0.81 mC/kg) and ISO fine test dust (0.66 mC/kg).
The transport of NanoActive® MgO plus and hollow glass spheres in an enclosed room
was simulated by implementing the discrete phase model of FLUENT. In terms of mass
concentrations, there was reasonable agreement between predicted and measured values for
hollow glass spheres but not for NanoActive® MgO plus. In terms of number concentration,
there was large discrepancy between predicted and measured values for both particles.
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Development of an adaptive variance reduction technique for Monte Carlo particle transport / Développement d'une méthode de réduction de variance adaptative pour le transport Monte Carlo de particulesLouvin, Henri 12 October 2017 (has links)
L’algorithme Adaptive Multilevel Splitting (AMS) a récemment fait son apparition dans la littérature de mathématiques appliquées, en tant que méthode de réduction de variance pour la simulation Monte Carlo de chaı̂nes de Markov. Ce travail de thèse se propose d’implémenter cette méthode de réduction de variance adaptative dans le code Monte-Carlo de transport de particules TRIPOLI-4,dédié entre autres aux études de radioprotection et d’instrumentation nucléaire. Caractérisées par de fortes atténuations des rayonnements dans la matière, ces études entrent dans la problématique du traitement d’évènements rares. Outre son implémentation inédite dans ce domaine d’application, deux nouvelles fonctionnalités ont été développées pour l’AMS, testées puis validées. La première est une procédure d’encaissement au vol permettant d’optimiser plusieurs scores en une seule simulation AMS. La seconde est une extension de l’AMS aux processus branchants, courants dans les simulations de radioprotection, par exemple lors du transport couplé de neutrons et des photons induits par ces derniers. L’efficacité et la robustesse de l’AMS dans ce nouveau cadre applicatif ont été démontrées dans des configurations physiquement très sévères (atténuations du flux de particules de plus de 10 ordres de grandeur), mettant ainsi en évidence les avantages prometteurs de l’AMS par rapport aux méthodes de réduction de variance existantes. / The Adaptive Multilevel Splitting algorithm (AMS) has recently been introduced to the field of applied mathematics as a variance reduction scheme for Monte Carlo Markov chains simulation. This Ph.D. work intends to implement this adaptative variance reduction method in the particle transport Monte Carlo code TRIPOLI-4, dedicated among others to radiation shielding and nuclear instrumentation studies. Those studies are characterized by strong radiation attenuation in matter, so that they fall within the scope of rare events analysis. In addition to its unprecedented implementation in the field of particle transport, two new features were developed for the AMS. The first is an on-the-fly scoring procedure, designed to optimize the estimation of multiple scores in a single AMS simulation. The second is an extension of the AMS to branching processes, which are common in radiation shielding simulations. For example, in coupled neutron-photon simulations, the neutrons have to be transported alongside the photons they produce. The efficiency and robustness of AMS in this new framework have been demonstrated in physically challenging configurations (particle flux attenuations larger than 10 orders of magnitude), which highlights the promising advantages of the AMS algorithm over existing variance reduction techniques.
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