Dissertationen zum Thema „Dynamic cracking“
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Crump, Timothy. „Modelling dynamic cracking of graphite“. Thesis, University of Manchester, 2018. https://www.research.manchester.ac.uk/portal/en/theses/modelling-dynamic-cracking-of-graphite(71e81d6f-e712-458c-aa48-0a256749258a).html.
Der volle Inhalt der QuelleFejzo, R. „Dynamic behaviour of concrete structures with cracking“. Thesis, Swansea University, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.636965.
Der volle Inhalt der QuelleMarazzato, Frédéric. „Discrete element and time-integration methods forelasto-plasticity and dynamic cracking“. Thesis, Paris Est, 2020. http://www.theses.fr/2020PESC1001.
Der volle Inhalt der QuelleThe present Ph.D. dissertation proposes contributions to discrete element methods (DEM) and explicit time integration schemes with a view towards dynamic cracking for metallic materials under dynamic loading. DEM, which are usually used to simulate granular materials, are understood through the prism of gradient discretization methods in order to simulate continuous materials. The method has been extended from previous Voronoi meshes to support generalpolyhedral meshes. Material behaviours have been extended from elasto-dynamics to dynamic elasto-plasticity through the addition of a tensorial degree of freedom per mesh cell. The method is robust with respect to the incompressible limit and its parameters only depend on material parameters. Moreover, an explicit pseudo-energy conserving time integration method has been developed, even for nonlinear behaviours and variable time steps, so as to avoid thedissipation of energy available for plastic dissipation and cracking. The method has been coupled to the proposed DEM. Finally, Griffith crack propagation through the mesh facets has been adapted to the present DEM for linear elastic behaviours in two space dimensions. The energy release rate is computed for every cracking mode using the stress intensity factors approximated close to the crack. A criterion of maximization of elastic energy density is used tosimulate kinking
Beskari, Mohamed Ali. „Dynamic analysis of diffusion and convection in porous catalysts“. Thesis, University of Salford, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.244857.
Der volle Inhalt der QuelleIlles-Smith, Peter C. „A study of the modelling, dynamic simulation and control of the modern fluid catalytic cracking process“. Thesis, University of Leeds, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.330143.
Der volle Inhalt der QuelleAñez, Javier. „Modélisation de l'injection de pétrole pour les procédés FCC (Fluid Catalytic Cracking)“. Thesis, Normandie, 2018. http://www.theses.fr/2018NORMR132/document.
Der volle Inhalt der QuelleThis PhD is a joint venture between VINCI Technologies and the CNRS Laboratory CORIA. For its application, VINCI Technologies, developed mainly oil-related equipments and in particular injection/atomization systems. Some of these injectors are characterized by a very big geometrical dimensions (several meters long), that leads to very high Reynolds and Weber number. In addition, many injectors incorporate an internal mixing zone, in which liquid and gas phases are both present in a significant proportion. Consequently, this zone belongs to the dense two-phase flow category. To simulate the liquid dispersion and to characterize the spray formation special from these injectors, appropriate models are required. On its side, the CORIA team, has developed a suitable approach, so-called ELSA, based on the pioneering work of Borghi and Vallet [1, 2]. Key points of this approach are the liquid dispersion that can be associated to the turbulent liquid flux and the amount of liquid-gas surface that can be used to determine eventually the Sauter mean diameter (SMD) of the spray. During this PhD, the applications proposed by V INCI Technologies, have promoted a review of a large part of the multiphase flow approaches to find the more appropriate for each case. This has been the opportunity to clarify the range of application of each approach, and therefore stress the necessity to develop coupled approaches, in order to cover the proposed application in the most suitable way. In particular, this manuscript reports, in one hand, the theoretical development of the ELSA family models, and on the other hand, the corresponding industrial approximations. Since ELSA approaches are originally developed for RANS simulation of the dense zone, it has been extended to LES description. The link of this approach to the DNS¡ ICM approach, has been studied with a special care. The resulting proposed solver, switches dynamically from ICM to subgrid spray, through the ELSA concept, and thanks to resolution based indicator (IRQ). On the opposite side, once the dispersed spray is formed, the ELSA approach is coupled to multiphase flow method, that aims to determine the spray distribution through the WBE equation. This later equation, is solved with an original hybrid Euler-Lagrange method. The purpose is to solve the WBE equation with a Lagrange stochastic approach, and at the same time, preserving the compatibility to the Euler description of two-phase flow, based on ELSA, to benefit from both approaches. This coupled approach has been tested against academic experimental data coming from ECN research initiative, a combined DNS and experimental measurement of dispersed spray on a Diesel jet, and under an air-blast atomizer numerical test case, for which the mean liquid volume fraction has been measured. Eventually, these developed approaches have been applied to industrial application showing there robustness and their capacity to help in the process of design development of new injectors
Castelo, Branco Veronica Teixeira Franco. „A unified method for the analysis of nonlinear viscoelasticity and fatigue cracking of asphalt mixtures using the dynamic mechanical analyzer“. [College Station, Tex. : Texas A&M University, 2008. http://hdl.handle.net/1969.1/ETD-TAMU-3136.
Der volle Inhalt der QuellePelissari, Daniel Cícero 1989. „Estudo da influência dos bicos injetores sobre o escoamento gás-sólido e as reações em um riser de FCC via CFD“. [s.n.], 2015. http://repositorio.unicamp.br/jspui/handle/REPOSIP/266017.
Der volle Inhalt der QuelleDissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Química
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Resumo: A aplicação de fluidodinâmica computacional (CFD) em estudos de otimização e projeto de novos equipamentos de processos industriais vem aumentando significativamente, uma vez que apresenta custo reduzido e possibilidade de avaliar equipamentos complexos e de extremas condições de operação. Dentre os processos mais estudados via CFD está o processo de craqueamento catalítico fluidizado (FCC), onde as frações pesadas do petróleo de baixo valor são convertidas em produtos de maior valor agregado, sendo uma das aplicações de fluidização gás-sólido mais importante na indústria de petróleo. O presente trabalho avaliou especificamente a zona de injeção do FCC, na qual a matéria-prima, alimentada por bicos injetores, se mistura a sólidos quentes (catalisador) e a vapor de fluidização. A performance desses dispersores de carga para garantir uma boa distribuição das gotículas de gasóleo com o catalisador é a chave para melhorar a eficiência do riser de FCC. Desta forma, o principal objetivo deste trabalho foi avaliar o efeito de diferentes designs, ângulos (30°, 45° e 60°) e configurações dos injetores sobre o escoamento gás-sólido e o desempenho do riser. Para tal, simulou-se um escoamento gás-sólido reativo tridimensional baseado em uma abordagem Eulerian-Eulerian. Nas simulações foram utilizados o modelo cinético de 12-lumps de Wu et al. (2009), modelo de turbulência k-? e modelo de arraste de Gidaspow. Foi observado que o design, o ângulo e a configuração dos bicos injetores exercem uma forte influência sobre a fluidodinâmica e a performance do riser, sendo o ângulo a variável que apresentou maior influência. Pôde-se observar que o design de bico tipo multi-orifícios (Caso 3) foi o que apresentou os melhores resultados, sendo a partir deste avaliados os ângulos, onde notou-se que o aumento do ângulo de 30° para 60° melhorou a mistura entre as fases e o rendimento. A análise dos arranjos foi realizada utilizando o design de bico do Caso 3 e o ângulo de 45°, e observou-se que o arranjo com bicos intercalados (Arranjo 2) apresentou uma mistura mais homogênea entre as fases e, consequentemente, uma melhor conversão e rendimento de produtos desejados. Em geral, os resultados obtidos no presente trabalho salientam a importância da utilização de geometrias mais detalhadas para os bicos, uma vez que influenciam a mistura entre as fases, a qual afeta o desempenho do riser
Abstract: The Computational Fluid Dynamic (CFD) application in industrial process optimization and new equipments design studies has increased significantly, once it presents low cost and the possibility of evaluating complex and extreme operating conditions equipments . Among the most widely studied processes via CFD is the fluidized catalytic cracking process (FCC), where the oil heavy fractions of low-value are converted into higher value-added products and which is one of the most important gas-solid fluidization applications in the oil industry . The present study specifically evaluated the FCC injection zone, in which the feedstock fed by nozzles, is mixed with hot solids (catalyst) and fluidization steam. The nozzles performance to guarantee a good gas oil droplets distribution with the catalyst is the key to improve the efficiency of FCC riser. Thus, the study main objective was to evaluate the different nozzles designs, angles (30 °, 45 ° and 60 °) and arrangements effect on the gas-solid flow and the riser performance. For this purpose, it was simulated a three-dimensional reactive gas-solid flow based on an Eulerian-Eulerian approach. In the simulations it was used the 12 lumps kinetic model by Wu et al. (2009), turbulence model k- ? and drag model Gidaspow. It was observed that the nozzle design, angle and configuration have a strong influence on fluid dynamics and on the riser performance, and the angle was the variable with the greatest influence. It can be observed that the nozzle design of multi-orifice type (Case 3) showed the best results, and that¿s why it was used to evaluate the angle, in which was noted that the angle increase of 30 ° to 60 ° improved phases mixing and the yield. The arrangement analysis was performed using Case 3 nozzle design and the design angle of 45 °, and it was observed that the arrangement with intercalated nozzles (Arrangement 2) showed a more homogeneous phases mixture and therefore a better conversion and desired product yield. In general, the results obtained in this work highlighted the importance of using more detailed geometries for the nozzles, since they influence the mixing of the phases, which affects the riser performance
Mestrado
Engenharia Química
Mestre em Engenharia Química
Wade, James. „Contact damage of ceramics and ceramic nanocomposites“. Thesis, Loughborough University, 2017. https://dspace.lboro.ac.uk/2134/24932.
Der volle Inhalt der QuelleEksi, Murat. „Optimization Of Mechanical And Microstructural Properties Of Weld Joints Between Aluminium-magnesium And Aluminium-magnesium-silicon Alloys With Different Thicknesses“. Master's thesis, METU, 2013. http://etd.lib.metu.edu.tr/upload/12615649/index.pdf.
Der volle Inhalt der Quellesuccessful welding of aluminium alloys gains importance. In this study a research is carried out on eldability of plates having different thicknesses of composition 5754 aluminium and 6063 aluminium in T-fillet geometry using Gas-metal Arc Welding technique. It was aimed to have a successful joint without using pre-weld and post-weld heat treatments. During tests welding current and voltage were the varying parameters as welding speed was held constant. Macro-examinations were performed to see the penetration of the weld metal. It was seen that the type of filler wire greatly effects weld penetration. Hardness tests, tensile tests were done to compare the mechanical properties of the welded joints with different filler wires. Despite having better penetration in 4043 filler wire used weld joints, 5356 filler wire used weld joints had higher tensile strength and ductility. In the second part of the study, a dynamic loading machine was designed and manufactured to see the behavior of the fillet welds under dynamic loading. The amount of stress and strain given to the specimen on this machine was adjustable but can&rsquo
t be measured. The tests that were made with this machine aimed only to compare the number of cycles of specimens before fracture. For dynamic loading tests two groups of specimens were prepared with filler wire 4043
each group having been welded with different heat inputs. It was aimed to see the effect of welding heat input on service lifes but no significant difference between cycle numbers of specimen groups having been welded with different heat inputs was observed. Microstructure examinations of these specimens revealed that coarsening the grains, grain boundaries, particles in PMZ and HAZ regions between Al 6063 base metal and weld zone made these areas more susceptible and favorable for crack propogation than Al 6063 base metal.
Sjöström, Julia, und Helena Åkesson. „Investigation of Ductility Dip at 1000˚C in Alloy 617“. Thesis, KTH, Materialvetenskap, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-209823.
Der volle Inhalt der QuelleNickelbaslegeringen 617 uppvisar en minskning i duktilitet under Gleeble-dragprovning vid exakt 1000˚C vilket leder till sprött brott. En plötslig sänkning av duktiliteten vid varmdragning av Ni-baserade superlegeringar är ett välkänt fenomen, dock är orsaken inte fastställd. Många mekanismer har bekräftats som bidrag till problemet och under de senaste åren har den simultana närvaron av fler av dessa mekanismer bekräftats som orsaken. Sänkningen i duktilitet leder till sprickbildning i fast fas och en specifik typ av sprickbildning känd som ”ductility dip cracking” är speciellt förekommande i Ni-bas legeringar. Denna identifieras bland annat genom intergranulära sprickor och närvaron av specifika utskiljningar. Detta arbete undersöker möjligheten att duktilitetssänkningen beror på ”ductility dip cracking”. Dessutom undersöks fler tänkbara förklaringar. Visuell granskning genomfördes via LOM och SEM och analys av sammansättningar via EDS-analys. I kombination med termodynamiska simuleringar blev förekomsten av Cr-rika M23C6 karbider, Ti(N,C) och Mo-rika partiklar, troligtvis M3B2, bekräftad. Fortsatt är det bekräftat att duktilitetssänkningen är relaterat till avsaknaden av rekristallisation vid 1000˚C. Det är inte bekräftat i detta arbete att duktilitetssänkningen i legering 617 beror av ”ductility dip cracking”.
Darestani, Mostafa Yousefi. „Response of concrete pavements under moving vehicular loads and environmental effects“. Thesis, Queensland University of Technology, 2007. https://eprints.qut.edu.au/16662/1/Mostafa_Yousefi_Darestani_Thesis.pdf.
Der volle Inhalt der QuelleDarestani, Mostafa Yousefi. „Response of concrete pavements under moving vehicular loads and environmental effects“. Queensland University of Technology, 2007. http://eprints.qut.edu.au/16662/.
Der volle Inhalt der QuelleÀlvarez, Castro Helver Crispiniano 1984. „Análise de variáveis de processo via CFD visando aperfeiçoamento de performance em riser de FCC“. [s.n.], 2014. http://repositorio.unicamp.br/jspui/handle/REPOSIP/266067.
Der volle Inhalt der QuelleTese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Química
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Resumo: Conversão de matéria-prima e rendimento são estudados através de um modelo 3D que simula o principal reator do processo de craqueamento catalítico fluidizado (FCC). Fluidodinâmica computacional (CFD) é usada como técnica com abordagem Euleriana-Euleriana para prever o comportamento do riser da FCC. O modelo considera 12 grupos com desativação do catalisador dada por coque e envenenamento por nitritos alcalinas e adsorção aromático policíclico para estimar o comportamento cinético, o qual partindo de uma determinada matéria prima, se craquea a diversos produtos. Composições diferentes para matérias-primas foram consideradas. Para validação o modelo foi comparado com dados experimentais em condições de operação industrial. O modelo é capaz de representar com precisão a geração de produtos para as diferentes condições de operação consideradas. Todas as condições consideradas foram resolvidos usando o solver Ansys CFX 14.0. As diferentes variáveis do processo de operação e efeitos hidrodinâmicos do riser industrial de craqueamento catalítico fluidizado (FCC) foram avaliadas. As previsões do modelo são apresentados e comparadas; conversão e produtos são apresentados. Recomendações para criar condições para obter maior rendimento do produto no processo industrial foram dadas
Abstract: Feedstock conversion and yield products are studied through a 3D model simulating the main reactor of the fluid catalytic cracking (FCC) process. Computational Fluid Dynamic (CFD) is used with Eulerian-Eulerian approach to predict the fluid catalytic cracking behavior. The model considers 12 lumps with catalyst deactivation by coke and poisoning by alkaline nitrides and polycyclic aromatic adsorption to estimate the kinetic behavior which, starting from a given feedstock, produces several cracking products. Different feedstock compositions are considered. The model is compared with sampling data at industrial operation conditions. The simulation model is able to represent accurately the products behavior for the different operating conditions considered. All the conditions considered were solved using a solver Ansys CFX 14.0. The different operation process variables and hydrodynamic effects of the industrial riser of a fluid catalytic cracking (FCC) are evaluated. Predictions from the model are shown and comparison with experimental conversion and yields products are presented; recommendations are drawn to establish the conditions to obtain higher product yields in the industrial process
Doutorado
Engenharia de Processos
Doutor em Engenharia Química
Yao, Lan. „Experimental and numerical study of dynamic crack propagation in ice under impact loading“. Thesis, Lyon, 2016. http://www.theses.fr/2016LYSEI043/document.
Der volle Inhalt der QuelleThe phenomena relating to the fracture behaviour of ice under impact loading are common in civil engineering, for offshore structures, and de-ice processes. To reduce the damage caused by ice impact and to optimize the design of structures or machines, the investigation on the dynamic fracture behaviour of ice under impact loading is needed. This work focuses on the dynamic crack propagation in ice under impact loading. A series of impact experiments is conducted with the Split Hopkinson Pressure Bar. The temperature is controlled by a cooling chamber. The dynamic process of the ice fracture is recorded with a high speed camera and then analysed by image methods. The extended finite element method is complementary to evaluate dynamic fracture toughness at the onset and during the propagation. The dynamic behaviour of ice under impact loading is firstly investigated with cylindrical specimen in order to obtain the dynamic stress-strain relation which will be used in later simulation. We observed multiple cracks in the experiments on the cylindrical specimens but their study is too complicated. To better understand the crack propagation in ice, a rectangular specimen with a pre-crack is employed. By controlling the impact velocity, the specimen fractures with a main crack starting from the pre-crack. The crack propagation history and velocity are evaluated by image analysis based on grey-scale and digital image correlation. The main crack propagation velocity is identified in the range of 450 to 610 m/s which confirms the previous results. It slightly varies during the propagation, first increases and keeps constant and then decreases. The experimentally obtained parameters, such as impact velocity and crack propagation velocity, are used for simulations with the extended finite element method. The dynamic crack initiation toughness and dynamic crack growth toughness are determined when the simulation fits the experiments. The results indicate that the dynamic crack growth toughness is linearly associated with crack propagation velocity and seems temperature independent in the range -15 to -1 degrees
Novák, Jan. „Měření dynamických charakteristik zpětných armatur“. Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2017. http://www.nusl.cz/ntk/nusl-318147.
Der volle Inhalt der QuelleMarchenko, Arina. „Analyse multi-échelles de la viscoplasticité à froid et de la rupture différée du titane en relation avec ses teneurs en hydrogène et oxygène“. Thesis, Paris, ENMP, 2015. http://www.theses.fr/2015ENMP0030/document.
Der volle Inhalt der QuelleWidely used for aircraft or rocket engine manufacturing titanium and its alloys are prone to the room-temperature creep that leads to the phenomenon of sustained load subcritical crack growth. One of the major cause of such unusual viscoplastic behavior of titanium is the phenomena of static and dynamic strain aging which represents an interaction between dislocations and interstitial atoms of oxygen and hydrogen. The aim of the present experimental and numerical multiscale study is to investigate the influence of the interstitial hydrogen and oxygen on the viscoplastic behavior and the resistance to sustained load cracking in commercially pure titanium of phase alpha.In a first step, a scenario of static and dynamic strain aging was proposed. The presence of the stress peak was attributed to the segregation of interstitial atoms of oxygen on the edge dislocations. In case of dynamic strain aging, the observed instabilities, typical for the Portevin-Le Chatelier effect, were associated with the non-planar core of screw -type dislocations. The crystal plasticity was introduced into the phenomenological model in order to capture the strain aging phenomena and the anisotropy of the mechanical properties. The modeling approach for strain aging suggested by Kubin-Estrin-McCormick is based on the internal variable called the aging time which corresponds to the waiting time of a dislocation in a pinned state. Finite element simulations were then performed on the polycrystalline aggregates for different number of grains. At the next step, fracture toughness and sustained load cracking tests were performed on the material with different levels of hydrogen. Finally, numerical simulations of toughness and sustained load cracking tests using the identified viscoplastic model were carried out for all experimental conditions. A cohesive zone model was then introduced ahead of the crack tip to simulate crack propagation
Chantrait, Teddy. „Approche multiéchelle en espace et en temps pour la prévision des endommagements dans les structures composites soumises à un impact de faible énergie“. Thesis, Lyon, INSA, 2014. http://www.theses.fr/2014ISAL0129/document.
Der volle Inhalt der QuelleThe composite laminates are increasingly used in aircraft structural parts which lead to new issues such as the Low Energy Impacts (LEI). Indeed, although they have well mechanical properties relative to their mass, small shocks may be very harmfull for laminates. Controlling such situations is essential for manufacturers that why lot of testing campaigns are currently performed. Yet, they are time consuming and expensive considering the many influential parameters (energy, speed, layup...). Numerical simulations of this phenomenon by practicing the so called “virtual testing” process could be really helpfull to rationalize testing campaigns in order to save money. Yet, this practice remain currently hard to do at the industrial scale due to the excessive CPU time required for fine simulation of damages induced by the LEI. Based on this observation, this work has consisted in taking advantage of the spatial and temporal location of delamination, matrix cracking and fiber breakage that can occur during impact in order to reduce the computational cost. Thus, a space and time multiscale method has been put in place. The impacted structure is split into two areas. One is located around the impacted point, it contains all the non-regularities of the problem (contact, softening law, cohesive zone model). This domain is treated with the explicit dynamics code Europlexus. The other one corresponds to the complementary part. The mechanical problem is much more regular and it is treated with the implicit dynamics code Zset / Zebulon. A low intrusive coupling based on the GC method is carried out between these two codes. It allows to use an adapted model in both regions different time step are in particular used. A time step ratio upper to 1000 can be reach between the one of the explicit code set by the stability condition and the one used in the complementary part. As a results, significant CPU time is saved. This is confirmed by the simulation of a stiffened composite panel impacted. It is also shown that the implicit / explicit allocation can change over the calculation. To do that, a switch mechanism has been established. It thus makes it possible to transit the resolution of a portion of the structure initially solved in the code Zebulon to Europlexus. As a results, further gain is obtained
Rey, Jérôme. „Mechanisms and kinetics of alkenes isomerization and cracking in chabazite zeolite quantified by constrained ab initio molecular dynamics“. Thesis, Lyon, 2019. http://www.theses.fr/2019LYSEN049.
Der volle Inhalt der QuelleHydrocracking and hydroisomerization catalysts are bifunctional, with a hydro-dehydrogenation function and an acidic function, typically an acid zeolite, to isomerize and crack alkenes. With advanced ab initio molecular dynamics approach, and explicit simulation of the effects of temperature (300 – 500 K), we investigate the mechanisms of isomerization and cracking reactions of C7 alkenes within the chabazite zeolite in order to provide reliable rate constants and explain the observed products distribution. By blue moon sampling, we established for the first time, the free energy profiles for the isomerization of C7 alkenes in zeolites, with carbenium ions as intermediates (and protonated cyclopropane (PCP) as transition states), connecting di- to tri-branched, and mono- to di-branched alkene isomers (Sections III and IV). We demonstrate that the dynamic effects with the correct sampling of rotational conformers play an important role to quantify the stability of the key intermediates and transition states. These effects could not be captured by previous static DFT simulations. The much lower barriers for type A isomerization mechanisms are thus recovered, and assigned to a loose transition state, while the transition state of type B isomerization is tighter, due to the formation of an edge PCP. The study of cracking reactions (Section V) with the same methods, unravel the role of secondary cations. For the first time, we identify the structures of transition states involved in the β-scission mechanisms. From this analysis, we deduce the ab initio- rate constants that could be used in future kinetic modeling to predict activity and selectivity of the catalyst
Shim, Sang-Hea. „The effect of fluid flow on the stress corrosion cracking of sensitized type 304 stainless steel in 0.01 M Na₂SO₄ solution at 250⁰C /“. The Ohio State University, 1985. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487264603216315.
Der volle Inhalt der QuelleAlvarez, Guevara Kervin Alexander, und Chumpitaz Marco Fabricio Medina. „Análisis de la influencia de las secciones agrietadas en la respuesta a una solicitud sísmica en edificios regulares e irregulares multifamiliares de 5, 10 y 15 pisos en la ciudad de Lima“. Bachelor's thesis, Universidad Peruana de Ciencias Aplicadas (UPC), 2020. http://hdl.handle.net/10757/653473.
Der volle Inhalt der QuelleThis research addresses the real influence of the cracking of structural elements in the reduction of rigidity when a seismic event occurs. To do this, first, he described the problematic reality, the background and previous generalities about the topic to determine what type of building to use. Secondly, the theoretical framework exposed a set of fundamental concepts necessary to understand the cracking of concrete, the obtaining of effective inertia, the irregularity of buildings and a review of the considerations of foreign standards. In the third place, it was determined to work with 6 multifamily housing plans, of which 3 were regular structures and 3 were irregular. Likewise, the structures were subdivided into heights of 5, 10 and 15 floors, since they are the type of building that is most constructed in Lima. Afterwards, the geographic, use and geometrical parameters were found from the E-030 standard, to then perform the linear seismic analysis (static and dynamic). Then, the moment diagrams - curvature (beams, columns and plates) were made, so that from them, obtain a reduction factor of the gross inertia and perform a new seismic analysis considering this value as an effect of cracking. Finally, a comparative analysis was made between the results obtained according to the height in regular and irregular buildings.
Tesis
Lammens, Bastien. „Caractérisation de la décohésion dynamique des matériaux composites à matrice organique (CMO)“. Electronic Thesis or Diss., Ecole centrale de Nantes, 2024. http://www.theses.fr/2024ECDN0007.
Der volle Inhalt der QuelleOrganic matrix laminated composites are increasingly used in the aeronautical field to reduce the weight of structures. However, during an impact on this type of material, various damage mechanism can occur, such as delamination. This is a process of macroscopic decohesion of the interlaminar environment, which can be characterised by GIC (or KIC ). The literature shows a wide disparity in measurements due to incomplete decoupling of the effects of resin confinement by fibers, nonlinearitiesbehaviour and/or velocity effects. This work proposes to develop an experimental protocol to characterise pure resin usingfullfields measurements to methodically study these couplings. The goal is to evaluate the impact of the crack propagation speed and the structural effects on the fracture behaviour and in particular to extend Griffith's theory to laminated composites. Different specimen geometries are used to reproduce structural effects. Crack propagation speeds ranging from quasi-static to dynamic are studied and all the tests are analysed using linear elastic fracture mechanics and the fracture surfaces. Finally, this work proposes a model to describe the evolution of KIC for the resin HexplyM21 used in aeronautics field, from the non-singularterms of the stress field T-stress, B-stress and also the speed ȧ in the ranges [0 - 15] MPa, [- 200 - 10] MPa.m-0.5 et [10-6, 600] m.s-1 respectively
Jaafari, Chaimaa. „Effect of early age drying shrinkage on the seismic response of RC Structures“. Thesis, Lyon, 2020. http://www.theses.fr/2020LYSEI113.
Der volle Inhalt der QuelleReinforced Concrete (RC) structures get damaged over time due to many factors: thermal conditions, chemical attacks, shrinkage, creep, carbonation, corrosion, etc. This damaging process starts at early-age and continues with structure aging. Early age damage can have a significant impact on the dynamic behavior of reinforced concrete structures. In fact, the natural frequency of a structure, which is a design parameter can be highly reduced due to this damage. In order to quantify the impact of early-age damage (0 to 28 days) on the seismic response of a reinforced concrete structure, this thesis combined both numerical modeling and pseudo-dynamic tests on two types of RC portal frames. The first one was kept in endogenous conditions (water exchange with the surrounding environment was prevented) during its early age period in a way to limit drying effects leading to cracks. As for the second one, it was kept in non-endogenous conditions (possibility of water exchange with the surrounding environment) similar to construction site conditions, which induced an initial damage (cracks apparition) due to a more important drying shrinkage. Both types of RC portal frames were subjected after their early age period to the same seismic loading using pseudodynamic tests. On the one hand, this manuscript presents the experimental results obtained through the use of pseudodynamic tests in order to evaluate the behavior of the two types of RC structures under a moderate intensity earthquake. The structures were instrumented using optical fiber sensors, displacement and load sensors, velocimeters and monitored using Digital Image Correlation. On the other hand, the enhanced multifiber beam model that was developed for the portal frames in order to follow their early age damage and to determine their static and dynamic behavior while accounting for their early age effects is presented. In this numerical model, shrinkage and concrete thermal deformations are calculated and then introduced as inputs of a coupled damage model accounting for creep and mechanical deformations. Such model was validated by comparing its results to the ones obtained experimentally, which made it possible to evaluate the evolution of frequency content of the two types of structures during early age and to quantify their difference of behavior in the non-linear domain. Work conducted within this thesis thus allowed proposing a complete model for reinforced concrete structures that can be used in order to follow their damage evolution from casting until being subjected to a seismic load and to quantify their seismic vulnerability
Lopes, Gabriela Cantarelli. „Estudo computacional da dinâmica do escoamento reativo em risers industriais de FCC“. [s.n.], 2012. http://repositorio.unicamp.br/jspui/handle/REPOSIP/266768.
Der volle Inhalt der QuelleTese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Química
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Resumo: O craqueamento catalítico fluido (FCC) é um dos processos de maior importância da indústria do refino de petróleo, já que converte as frações pesadas de baixo valor comercial provenientes de outros processos de refino, em produtos comercialmente mais importantes, como gasolina, GLP e diesel. Atualmente, com o aumento da demanda por combustíveis fósseis e a redução na extração de óleos convencionais, o aperfeiçoamento do processo de FCC tem se tornado essencial para as refinarias. Estudos empíricos sobre a dinâmica do escoamento em reatores industriais de FCC são raros, em parte devido às altas temperaturas e pressões presentes no interior desses reatores, o que dificulta a obtenção de dados, e em parte por causa da complexidade da operação, que envolve uma série de fenômenos simultâneos, como a vaporizacão da carga, reações heterogêneas, a expansão do leito devido ao craqueamento e a desativação das partículas de catalisador, por exemplo. Contudo, para que se possa melhorar a performance do processo, é necessário conhecer a dinâmica desse escoamento. Foi proposto então, neste estudo a simulação computacional de risers industriais de FCC, usando ferramentas de CFD. O nível de complexidade das simulações realizadas foi aumentado gradativamente e fenômenos como a adsorção das moléculas reagentes nos sítios ativos do catalisador e a vaporizacão da carga líquida, foram estudados separadamente, possibilitando a avaliação individual de sua influência sobre o processo em termos de variáveis globais. Para uma análise detalhada do escoamento, foram usados modelos tridimensionais e foram propostas configurações geométricas similares às encontradas em unidades típicas de FCC. Além disso, um estudo da sensibilidade das variáveis do escoamento ao uso de diferentes geometrias de saída para o reator foi realizado, tornando possível determinar as configurações que propiciam melhor rendimento para o processo. Em geral, os resultados fluidodinâmicos obtidos neste estudo ressaltam a importância da aplicação de modelos que representem os complexos fenômenos presentes no riser de FCC, já que estes influenciam consideravelmente as reações
Abstract: The fluid catalytic cracking (FCC) is one of the most important process in the oil refining industry. It converts heavy distillation fractions with low commercial value into lighter and valuable hydrocarbon products such as gasoline, diesel and LPG. With the increase in the fossil fuels demand and the reduction in the conventional oil extraction, the improvement of the FCC process has become essential for the refineries. Empirical studies on the dynamics of the flow in industrial FCC reactors are rarely found, partly due to high temperatures and pressures present in these reactors, which difficult the data obtaining, and in part because of the complexity of the operation, which involves several simultaneous phenomena, such as the feedstock vaporization, heterogeneous reactions, the bed expansion due to cracking and deactivation of the catalyst particles, for example. However, it is necessary to understand the flow in order to improve the performance of the process. Then, a numerical study of industrial FCC riser reactors using CFD tools was proposed in this work. The level of complexity of the simulations was increased gradually and phenomena such as the adsorption of reactant molecules in catalyst active sites and the vaporization of liquid feedstock, were studied individually, allowing the evaluation of each phenomena on the process. For a detailed analysis of the flow, three-dimensional models were used in these simulations and geometric configurations similar to those found in typical FCC units have been applied. Furthermore, a study of the sensitivity of the variables of the flow to the use of different geometries for the reactor outlet was developed, enabling the determination of the output configuration that provides a better yield for the process. Overall, the fluid dynamic results obtained in this study emphasize the importance of application of models that represent the complex phenomena present in the FCC riser, since they substantially influence the reactions
Doutorado
Desenvolvimento de Processos Químicos
Doutor em Engenharia Química
OLIVEIRA, Talles Caio Linhares de. „Modelagem e simulação de um reator de craqueamento térmico do 1,2-Dicloroetano“. Universidade Federal de Campina Grande, 2014. http://dspace.sti.ufcg.edu.br:8080/jspui/handle/riufcg/526.
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CNPq
O monômero cloreto de vinila (MVC), matéria prima usada para a obtenção do policloreto de vinila (PVC), é produzido comercialmente em larga escala através da decomposição térmica do 1,2-dicloroetano (EDC) em um reator tubular inserido em um forno industrial. O PVC possui aplicações que vão desde produtos médico-hospitalares e embalagens para alimentos até peças de alta tecnologia como as usadas em equipamentos espaciais. O principal problema enfrentado na operação é a formação de uma camada de coque no interior do reator que limita o tempo de operação. O presente trabalho consiste no desenvolvimento de modelos matemáticos para a previsão do comportamento de um reator de craqueamento térmico de EDC. Um total de três modelos foram formulados, o primeiro modelo serviu para estruturação do algoritmo e para a análise geral da metodologia usada. No segundo modelo uma cinética reacional mais complexa envolvendo composto estáveis e radicais foi implementada, a deposição de coque foi considerada o que possibilitou estimar o seu impacto no tempo de produção e nas variáveis do processo como: pressão, temperatura e conversão. O último modelo foi desenvolvido utilizando técnicas de fluidodinâmica computacional (CFD) e forneceu as distribuições na direção radial e ao longo do reator para as variáveis do processo. Os resultados obtidos de todos os modelos estão em concordância com dados industriais disponíveis. Os modelos I e II podem ser usados para realização de testes no processo sem a necessidade de utilização de unidade piloto e como ponto de partida para a otimização nos fornos de craqueamento, enquanto o modelo em CFD pode contribuir para estudo de melhorias de projeto deste tipo de reator.
The vinyl chloride monomer (MVC) raw material used to obtain the polyvinyl chloride (PVC), is commercially produced on a large scale by thermal decomposition of 1,2dichloroethane (EDC) inserted into a tubular reactor in an oven industrial. PVC has applications ranging from medical products and food containers to high-tech parts like those used in space equipment. The main problem faced in the operation is the formation of a layer of coke inside the reactor which limits the time of operation. The present work is the development of mathematical models for predicting the behavior of reactor thermal cracking of EDC. A total of three models were formulated, the first model was used to structure the algorithm and the overall analysis of the methodology used. In the second model a more complex reaction kinetics involving radicals and stable compound was implemented, coke deposition was found which allowed to estimate their impact on production time and the process variables such as pressure, temperature and conversion. The last model was developed using computational fluid dynamics (CFD) and provided the distributions in the radial direction and along the reactor for the process variables. The results of all the models are in agreement with industrial data available. Models I and II can be used for testing the process without the need of using pilot unit and as a starting point to optimize the cracking furnaces while the CFD model study can contribute to improvements in the design of this type reactor.
Lucar, Monzón Edgar Manuel. „Estudo da dinâmica do escoamento gás-sólido em resfriadores de catalisador de FCC usando fluidodinâmica computacional (CFD)“. Universidade Federal de São Carlos, 2017. https://repositorio.ufscar.br/handle/ufscar/8834.
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Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)
The fluid catalytic cracking (FCC) is an important process in oil industry, since it converts heavier fractions in lighter ones, which are more valuable. The catalyst particles (typically m) are deactivated during the reacting process and need to be regenerated before returning to the reactor. Temperature is a key factor that promotes coke formation and deactivation inside the reactor. As a consequence, it is necessary to cool down the solid catalyst particles before returning them to the reactor. The cooling system is usually outside the regenerator in a specific designed heat exchanger, that uses water as cold fluid. The catalyst cooler was not much studied before and many contributions can be made for improvements and intensification. The goal of this work was to contribute with this topic, using Computational Fluid Dynamics (CFD) to evaluate the gas-solid flow behavior in characteristic geometries of the catalyst cooler. Commercial package Fluent by ANSYS v14.5 was used during simulation and Eulerian model was applied for the solid phase. The volume fraction phase for the solid phase, solid and gas velocities were evaluated and described. The results were compared in terms of gas-solids flow in different geometries and showed a hydrodynamic explanation different from that currently used by the authors to justify the intensification of thermal exchange in this type of equipment. In short, longer solid-wall contact time will be primarily responsible for efficient heat transfer.
O craqueamento catalítico fluidizado é um processo amplamente utilizado no campo do refino de petróleo. Na unidade de craqueamento, frações pesadas são transformadas em outras mais leves e com maior valor de mercado (gasolina, diesel, naftas). Após o craqueamento, o catalisador é regenerado e retorna ao reator. A temperatura do catalisador é um parâmetro que possui forte influência sobre o processo. O resfriamento de catalisador é feito em unidades externas a fim de controlar a temperatura de entrada do catalisador no reator. O funcionamento deste sistema ainda foi pouco explorado e o objetivo deste trabalho foi o de simular o escoamento gás-sólido em geometrias características de colunas para resfriamento de catalisador com diferentes condições de operação, assim tentando contribuir com o conhecimento sobre este processo. Técnicas de Fluidodinâmica Computacional foram usadas para a simulação de diferentes geometrias com o programa comercial FLUENT do pacote ANSYS v14.5. As distribuições fração volumétrica dos sólidos e de velocidades do gás e fase particulada foram analisados como parâmetros de interesse hidrodinâmico. Os resultados foram comparados em termos de escoamento gás-sólido em diferentes geometrias e mostraram uma explicação hidrodinâmica diferente da atualmente utilizada pelos autores para justificar a intensificação de troca térmica em este tipo de equipamentos. Em suma, maior contato sólido-parede seria o principal responsável pela transferência eficiente de calor.
González, Silva Germán. „Metodologia para aplicar LES ao craqueamento catalítico fluido em um reator riser industrial“. [s.n.], 2012. http://repositorio.unicamp.br/jspui/handle/REPOSIP/266671.
Der volle Inhalt der QuelleTese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Química
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Resumo: O objetivo principal desta tese é propor uma metodologia para aplicar simulação de grandes escalas (LES) em uma unidade de craqueamento catalítico industrial. Para atingir este objetivo, iniciou-se propondo uma metodologia para a construção da malha, sendo uma malha quase-uniforme. As malhas propostas foram implementadas para minimizar o esforço computacional e procedimento para a refinação uniforme no domínio do sistema. Inicialmente, foi estudada a fluidodinâmica de um leito fluidizado gás-sólido na escala de laboratório sem reação química, utilizando Simulação de Grandes Escalas. Com base nos resultados numéricos obtidos a partir de resultados da escala de laboratório foi aplicado o modelo cinético de 4 lump em uma simulação CFD tridimensional para um reator industrial FCC, utilizando LES para a fase gasosa, e considerando o catalisador como uma fase contínua (Euleriana). Os pacotes de simulação utilizados foram Ansys ICEM versão 13 para a construção da malha e Ansys CFX versão 13 para o pós-processamento dos resultados. No pós-processamento dos resultados foi proposta uma metodologia para determinar as médias azimutais das variáveis em planos perpendiculares ao escoamento e finalmente foram validadas as simulações com dados reportados na literatura. As principais conclusões do trabalho foram que foi possível diminuir o tamanho da malha e o tempo de processamento. Notou-se também que, ao usar malhas com discretização quase-uniforme não foi necessário fazer um refinamento de malha elevado, nem refinar perto da parede para o sistema gás-sólido
Abstract: The main objective of this thesis is to propose a methodology in how to apply Large Eddy Simulation (LES) on a unit of catalytic cracking. In order to achieve this, it was proposed an alternative way of constructing the computational mesh, by using quasi-uniform meshes. The proposed meshes were implemented to minimize the computational effort and procedure for refining them in the entire domain of the system. Initially it was studied the fluid dynamics of a lab scale gas-solid system without chemical reaction, using Large Eddy Simulation. Based on the numerical results obtained from lab scale results it was implemented the 4 lump kinetic model in a three dimensional CFD simulation of an FCC industrial reactor, using LES for the gas phase and considering the catalyst as a continuous phase (Eulerian). The simulation packages used were Ansys ICEM, version 13 for mesh construction and Ansys CFX 13 for computation and post-processing of the results. In the data post-processing it was proposed a methodology for calculating average values of fluctuating variables between two circular sections in the azimuthal direction. The results were compared with data reported in literature. The main conclusions of the results showed that it was possible to decrease the mesh size and the computational time. It was also noticed that by using quasi-uniform discretization it was not necessary to make a high mesh refinement near the wall for a gas-solid system
Doutorado
Desenvolvimento de Processos Químicos
Doutor em Engenharia Química
Cuadros, Bohórquez José Fernando. „Estratégia alternativa de otimização em duas camadas de uma unidade de craqueamento catalítico-FCC : implementação de algoritmos genéticos e metodologia híbrida de otimização“. [s.n.], 2012. http://repositorio.unicamp.br/jspui/handle/REPOSIP/266651.
Der volle Inhalt der QuelleTese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Química
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Resumo: Esta pesquisa teve por finalidade o desenvolvimento de uma metodologia de otimização em duas camadas. A otimização preliminar foi baseada na técnica de planejamento de experimentos junto com a metodologia por superfície de resposta com a finalidade de identificar uma possível região de busca do ponto de operação ótimo, o qual foi obtido através da implementação de métodos híbridos de otimização desenvolvidos mediante associação do modelo determinístico de otimização por programação quadrática sucessiva (SQP) com a técnica dos algoritmos genéticos (GA) no modelo do processo de craqueamento catalítico fluidizado- FCC. Este processo é caracterizado por ser um sistema heterogêneo e não isotérmico, cuja modelagem detalhada engloba as equações de balanço de massa e energia das partículas do catalisador, como também para a fase líquida e gasosa, sendo um dos casos de estudo para a aplicação da metodologia de otimização desenvolvida. Como caso de estudo principal foi considerado o modelo do conversor do processo de FCC desenvolvido por Moro e Odloak (1995). Mediante a metodologia de otimização do processo baseado no uso do modelo determinístico da planta, foram definidas estratégias e políticas operacionais para a operação da unidade de FCC em estudo. Procurou-se alto nível de desempenho e segurança operacional, através da integração das etapas de operação, otimização e controle no contexto de otimização em tempo real do processo. As otimizações foram divididas em quatro etapas: 1) Análises preliminares dos fatores e das variáveis de resposta do modelo do conversor foram realizadas usando a técnica de planejamento de experimentos, com o objetivo de compreender a interação entre elas, assim como obter modelos simplificados das variáveis de resposta. A geração dos modelos simplificados é devido à necessidade de ganho no tempo computacional permitindo o conhecimento prévio da região de otimização já que em casos industriais pode não ser possível representar adequadamente o processo por modelos determinísticos; 2) Otimização usando algoritmos genéticos implementados no modelo simplificado da conversão, e no modelo determinístico com e sem restrições; 3) Otimização considerando o método de otimização SQP implementado no modelo simplificado da conversão e no modelo determinístico com restrições; e 4) otimização multi-objetivo do conversor usando x a técnica dos algoritmos genéticos, com o objetivo de maximizar a conversão, assim como a minimização da vazão dos gases de combustão, especificamente o monóxido de carbono (CO). Das otimizações foram obtidos ganhos em torno de 8% na conversão quando comparado com os valores de conversão sem otimização. Finalmente, foi realizada a integração do modelo do processo, com a otimização e o controle, dando como resultado a otimização em tempo real do conversor de FCC. A variável de otimização foi a conversão e, através da implementação do controle por matriz dinâmica com restrições (QDMC), aplicando a metodologia de controle inferencial. As variáveis escolhidas como variável controlada foi a temperatura de reação e como variável manipulada foi a temperatura da alimentação, com perturbações na vazão de alimentação do ar de regeneração. Valores de conversão da ordem de 88% foram atingidos para o esquema de otimização em tempo real, o método de otimização por algoritmo genético apresentou um desempenho satisfatório, com tempos e cargas computacionais razoáveis para implementação desta metodologia, em nível industrial
Abstract: The purpose of this research was the develop of an optimization methodology. Experimental design technique along with a hybrid optimization methodology obtained by association of sequential quadratic programming (SQP) with genetic algorithms (GA), were implemented in the model of a Fluid Catalytic Cracking process (FCC) developed by Moro and Odloak (1995). This process is described for a heterogeneous, non isothermal system, in which a detailed modeling comprises mass and energy balance equations for catalyst particles, liquid and gaseous phases that makes this process model, a case study for implementing the optimization methodology developed. The process optimization methodology developed; along with the deterministic model of the plant were applied to define operational strategies and policies for the operation of the FCC unit studied aiming to obtain high performance and operational safety, through the integration of control, operation and optimization stages in the context of real-time optimization (RTO) process. Optimizations were divided into four stages: 1) Preliminary analysis of factors and response variables of converter modeling were performed using experimental design technique aiming to understand the factors and response variables interaction, as well as to obtain response variables simplified models to be used as objective function in optimization stages, 2) a optimization using genetic algorithms was implemented in the simplified conversion model, in the deterministic modeling and the deterministic model considering factors restrictions, 3) a optimization considering a local search methodology like sequential quadratic programming (SPQ) was implemented in the simplified model of process conversion and also it was consided the deterministic model with restrictions. As initial estimative, the optimum factor values obtained with genetic algorithms were considered as well as two random points in the search space, and 4) a multi objective optimization considering genetic algorithms technique in order to maximize conversion and minimize combustion gases emissions, specifically carbon monoxide was developed. Applying this optimization methodology was obtained increments of around 8% in the feed conversion when compared with conversion values without optimization. xii Finally, it was developed the integration of optimization, control and process modeling giving as result the real time optimization (RTO) of FCC converter. The variable maximized by genetic algorithms was the feed conversion and the control technique implemented was based on the matrix named (QDMC) in conjunction with inferential control methodology. It was considered as controlled variable the reaction temperature adjusting the feed temperature (manipulated variable), for disturbances in the feed flow of the regeneration air. Feed conversion in the order of 88% were achieved for the real time optimization scheme considered, in which, the genetic algorithm showed an excellent performance in reasonable computational times and computational loads for implementation at industrial level
Doutorado
Desenvolvimento de Processos Químicos
Doutor em Engenharia Química
Akiki, Rana. „Développement d'un outil numérique pour la prévision de la fissuration d’une structure en béton de fibres sous impact“. Thesis, Université Paris-Saclay (ComUE), 2017. http://www.theses.fr/2017SACLN056/document.
Der volle Inhalt der QuelleThe research work falls within the framework of the transportation and handling safety of radioactive waste containment packages. The goal is to develop a numerical tool capable of simulating the overall behaviour of a fiber concrete structure subject to a dynamic loading. It also gives access to more local information such as cracking, both in terms of path and opening. To do this, a set of mechanical tests is carried out in order to better understand the mechanisms of damage and cracking of the material under quasi-static and dynamic loading. The model capable of capturing on a global scale the non-linearities related to the cracking of the structure in a continuous framework is detailed. The parameters associated with the material constitutive law are identified via an identification procedure based on the experimental data of the conducted tests. The determination of dynamic cracking energy is investigated and the structural inertial part of this is underlined. Two numerical methods used to post-process the results of the global numerical simulations, giving access to finer information at the local scale, in terms of path and crack opening, are detailed. The study of a fiber-reinforced concrete beam subjected to a dynamic 1-point bending loading, post-processed with the two approaches, is presented. The results of the numerical post-processing are compared with those obtained experimentally by correlation of digital images
Almeida, Alexandre Barros de. „Análise e modelagem termodinâmica de um modelo de gás de rede para pontes líquidas“. Universidade de São Paulo, 2012. http://www.teses.usp.br/teses/disponiveis/43/43134/tde-14032013-153056/.
Der volle Inhalt der QuelleThis work studied a three dimension lattice gas model to simulate macroscopic liquid systems. We used the model to study the energy and the forces involved during the process of liquid bridge formation and rupture between two parallel planes. The motivarion of this study was a physiological processes which occur inside the mammals lungs. Furthermore, a study was made to elucidate thermodynamic properties of the model. Concerning to physiological application, it was observed that the free energy of liquid bridge is smaller than the free energy of the droplet, for different liquid systems. With this observation, was proposed that this energy is dissipated as an acoustic energy. This sound should also exist in the rupture of liquid bridge. Comparing the free energy of liquid bridge in the formation and rupture process was observed a hysteresis curve. It was also found an effect of finite size in the formation of small size of the liquid bridge. In the numerical model, the liquid bridge is always formed earlier than expected from the analytical model. In the thermodynamic study, the model was simplified removing both parallel planes. First, the simplest case of this model was studied, only two liquid particles in a large gas lattice. In this case, the specific heat and internal energy was numerically studied and the results was compared with analytical calculation. Subsequently, we carried out a study of the phase transition of this system. Then, the free energy and the force generated between two parallel planes due the presence of the liquid bridge. This studied was performed using two different temperatures and two distinct methods. In the first method the entropy was neglected, and in the second method not. The second method was the ``Overlapping Distribution\'\'. It was concluded that the entropy has a very small effect in the studied conditions. The model is viable for modeling fluids at macroscopic level and therefore can be used to quantify not only the internal forces of the lung structures, but evaluate the energies released after the rupture process of the formation of these bridges.
Jan, Yannick. „Modélisation de la propagation de fissure sur des structures minces, soumises à des sollicitations intenses et rapides, par la méthode X-FEM“. Thesis, Lyon, 2016. http://www.theses.fr/2016LYSEI066/document.
Der volle Inhalt der QuelleIn shipbuilding industry, classical methods to analyze the behavior of structures under extreme loadings are very dependent on the size of the mesh. Moreover, propagation over long lengths with volumetric models requires huge processing power, often inaccessible within this framework. In order to manage these issues and due to the geometry to be considered, a coupling between shell finite element and the extended finite element method (X-FEM) using an adapted propagation criterion is proposed. The developments are made in the fast explicit dynamic finite element code EUROPLEXUS, CEA Saclay. For shell structures involving significant thickness such as submarines, Mindlin-Reissner theory is needed to enable shear strain. Therefore, locking-free element are used to avoid the numerical issue of shear-locking that appears when the shell becomes too thin. The fracture of Mindlin-Reissner plates based on the X-FEM discrete approximation framework is studied by Dolbow and Belytschko with the MITC4. A four node shell element using the same formulation is here only enriched with a step function along the crack line to take into consideration the discontinuity of the displacement field across the crack. The calculation remains accurate without the asymptotic enrichment functions near the crack-tip, as long as the mesh is refined near the crack tip. The numerical integration issue for elements cut by the crack is solved by a partitioning strategy developed by Elguedj. Since the crack is contained in the shell for which the mid plane's position is entirely known, only one information left is needed to locate it. Therefore, a crack is represented by several line segments on the three-dimensional mesh. Only through thickness cracks are considered so far. As regards to the crack propagation, a local criteria proposed by Haboussa is used based on the calculation of mechanical equivalent quantities in the vicinity of the crack tip. The maximum of the equivalent stress tensor near the crack tip is used to decide if the crack propagates as well as its propagation direction, and the Kaninen equation gives the crack velocity
Cavalcanti, De Sousa Pedro. „Automated Protocol for the Analysis of Dynamic Mechanical Analyzer Date from Fine Aggregate Asphalt Mixes“. 2010. http://hdl.handle.net/1969.1/ETD-TAMU-2010-08-8463.
Der volle Inhalt der QuelleYang, Chi, und 楊基. „Structural Evolution and Cracking Dynamics in 2D Cold Dusty Plasma Liquids“. Thesis, 2015. http://ndltd.ncl.edu.tw/handle/86v396.
Der volle Inhalt der Quelle國立中央大學
物理學系
103
Microscopically, unlike intuitive expectation, the cold liquid around freezing is not completely disordered. The competition between the strong particle interaction and weak thermal agitation leads to the heterogeneous structure with coexisting crystalline ordered domains and surrounding defect clusters, and heterogeneous dynamics with alternating particle rattling in the caging wells of nearest neighbor particles and cooperative particle hopping which induces structural rearrangements. Namely, the cold liquid can be viewed as a patchwork of crystalline ordered domains, which partially possesses solid like behavior but can still be rearranged under thermal agitation or external stress. In this work, through direct experimental microscopic visualization of cold dusty plasma liquid and numerical simulation of cold Yukawa liquids, we address the following important unexplored fundamental issues. (1) What is the cooperative motion existing in cold liquids, (2) How is structure rearranged through the cooperative motion, (3) whether the growth of crystalline ordered domains in crystallization and cold liquids are similar, (4) what is the generic flow behavior of cold liquids under various applied stresses, and (5) what is the avalanche dynamics of cracking of crystalline ordered domains in the weakly stressed cold liquid? It is found, using a novel bond-dynamics analysis, the cooperative motion in cold liquids can be categorized into static patches, rotating patches, drifting patches, and shear strips located at the interface of co-rotating patches, beyond the earlier findings of the cooperative hopping strings and bands. The structural evolution is thereby accomplished by the drifting, rotation, rupture, and healing of crystalline ordered domains. In addition, the similar domain rotation, regarded as the kinetic origins of grain coalescence, is found in the crystallization of quenched two dimensional Yukawa liquids. Furthermore, suffering to the external stress which provides local force and torque, the above cooperative processes are enhanced persistently. Strong applied stress can cause the formation of the shear band with a higher averaged forward displacement and coherent vortical excitations. However, under weak stress, crystalline ordered domains either crack and heal in the loading zone, or temporally sustain and propagate stress to remote regions for avalanche cracking. The spatiotemporal behaviors of the avalanche cracking are discussed through the collision of dislocations with mismatched Burgers vectors, which is the key to generate the large crack clusters inside a crystalline ordered domain.
Pham, Hieu. „Environmetally Assisted Cracking in Metals under Extreme Conditions“. Thesis, 2011. http://hdl.handle.net/1969.1/ETD-TAMU-2011-08-9671.
Der volle Inhalt der QuelleWang, Wen, und 王彣. „Avalanche Cracking-Healing and Defect dynamics in Weakly Stressed Cold Dusty Plasma Liquids“. Thesis, 2017. http://ndltd.ncl.edu.tw/handle/3tkq68.
Der volle Inhalt der Quelle國立中央大學
物理學系
105
Under weak external stress, intermittent emergent responses in the form of avalanche type spatiotemporal clusters are ubiquitous phenomena in strongly coupled systems, such as granular systems, stressed solids, and seismic systems. The strong coupling not only sustains the structure from structural rearrangement but also spreads the local strain energy to remote regions inducing spatiotemporally correlated clusters once the accumulated local strain energy goes beyond a certain threshold. Unlike solids, under weak external stress, liquids exhibit plastic deformation. The local strain energy cannot accumulate and is rapidly relaxed through structural rearrangement. However, unlike the intuitive expectation, a cold liquid around freezing under weaker thermal agitations is not completely disordered. It possesses a patchwork of crystalline ordered domains (CODs), which not only sustains the local strain energy but also releases the energy through structural rearrangement. Recent studies showed that the thermal-excited structural rearrangement exhibits cooperative excitation hopping in the form of co-rotating CODs, which ruptures the large CODs into small CODs followed by healing back to large CODs, and that, under weak external stress, CODs can temporarily sustain and propagate the local stress to remote regions that further initiates the bond cracking near defects. Nevertheless, the generic spatiotemporal dynamics, the scaling behaviors and the kinetic classification of the cracking, and the alarms for warning the short quiescent period between cracking bursts, are still unexplored issues. In this work, we experimentally investigate spatiotemporal dynamical behaviors of the avalanche type structural rearrangement through cracking-healing processes in a weakly stressed dusty plasma cold liquid. It is found that the cracking cluster size in xyt space follows power law distribution. The histograms of the cracking burst and quiescent time periods between cracking, and the persistent times maintaining ordered and disordered structures all follow power law scaling behaviors. The temporal cracking behavior can be classified into single burst and successive cracking burst fluctuation. Kinetically, a COD is ruptured by cracking lines through co-rotating domains, which induce dislocation propagation into the region. If the directions of the Burgers vectors of incoming dislocations allow dislocation annihilation, deteriorated structure anneals into a large COD. If the directions of Burgers vectors forbid the annihilation process, the structure needs successive cracking behavior to resume a better structural order. The low regional structural order at the end of a cracking burst can be regarded as an alarm for predicting a short quiescent time period before the next cracking burst.
Kreuzer, Steven Michael. „On the mechanical response of helical domains of biomolecular machines : computational exploration of the kinetics and pathways of cracking“. Thesis, 2013. http://hdl.handle.net/2152/25156.
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