Dissertations / Theses on the topic 'Discrete numerical modelling (DEM)'
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Ochoa, Roman Jacqueline Vanessa. "Shaking table tests and DEM numerical modelling of a 3D-printed groin vault." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2019.
Sundström, Anton. "Numerical modelling for characterization of the granular flows impact on the gas flow in a packed-bed-reactor." Thesis, Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-79538.
Polwaththe, Gallage Hasitha Nayanajith. "Numerical modelling of deformation behaviour of red blood cells in microvessels using the coupled SPH-DEM method." Thesis, Queensland University of Technology, 2016. https://eprints.qut.edu.au/91719/1/Hasitha%20Nayanajith_Polwaththe%20Gallage_Thesis.pdf.
Al, Tfaily Bilal. "Capacité prévisionnelle de la modélisation discrète pour application aux ouvrages géotechniques complexes." Electronic Thesis or Diss., Université Grenoble Alpes, 2023. http://www.theses.fr/2023GRALI077.
Geotechnical engineering is a crucial field in the design and construction of foundations, embankments, tunnels, and other structures interacting with soil and rock. However, the description of the elastoplastic response of soil, with preponderant non-linear and non-reversible deformations together with a non-associative flow rule, is complex. The difficulty is even higher in the case of non-monotonous loading paths where phenomenological constitutive relations require ad-hoc history parameters and advanced experimental tests for their calibration.Discrete element method has been proved to be an effective method in predicting quantitatively the constitutive response of soils, even in the case of complex loadings (with rotation of principal stress directions, or loading/unloading cycles) where conventional elastoplastic constitutive relations may fail to simulate realistic responses. For granular soils with a narrow grading, a direct representation of soil grains by polyhedral particles or with the level set method is possible, whereas for finer soils, or soils with a wider grading, alternative solutions should be considered. Spherical particles with enriched contact laws (e.g. by introducing rolling resistance at the contact) or rather simplified clumps of spheres can be used to keep the model relatively light to tackle further boundary value problems with limited computational cost. However, even if the models provide satisfying results for direct shear tests or drained triaxial compression loading paths compared to experimental measurements, their validation with respect to more complex loading paths as the isochoric compression or the path at constant stress deviator still present difficulties, in particular for initially loose granular assemblies.First, this study aims to compare such different approaches in terms of the prediction abilities at the macroscopic scale of the constitutive responses of soils, particularly for complex loading paths. Two kinds of discrete models are considered: (i) spherical particles with rolling resistance, (ii) simple clumps made of 2 to 6 spheres. The models are calibrated from two drained triaxial compressions on dense and loose Hostun sand. They are then assessed, according to the macroscopic response, on loading paths significantly different from the calibration loading paths (isochoric compressions, circular stress paths in the deviatoric plane, constant deviatoric stress path, etc.).Then, we investigate the importance of the description of the anisotropy of the initial fabric and of the inter-particle friction law in the simulated responses of loose granular assembly to different kinds of loading paths. It shows how the combination of both can modify importantly the simulated responses to some kinds of loading paths. This investigation is carried out for a numerical discrete model made of spheres by comparison with experimental results on sand.Finally, the model is used to simulate the nonlinear interaction between a shallow foundation of building structure and the supporting soil during strong seismic loadings, as tested experimentally for the TRISEE project with a full scale physical model. An adaptative discretization technique is implemented to limit the number of particles in such a boundary value problem and make the computation possible with a conventional desktop computer. Numerical results are benchmarked against experimental measurements from the TRISEE project, and FEM numerical simulations or macro-element models
Kuruneru, Sahan Trushad Wickramasooriya. "A coupled finite-volume & discrete-element method to investigate particle-laden gas flows and particle deposition in metal foam heat exchangers." Thesis, Queensland University of Technology, 2019. https://eprints.qut.edu.au/125485/1/Sahan_Kuruneru_Thesis.pdf.
Javaid, Mehshan. "Numerical modelling of one-dimensional discrete source detonation." Thesis, McGill University, 2010. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=95251.
La détonation est une branche de la combustion qui est initiée par une réaction chimique exothermique duquel en résulte une onde de choc supersonique appelé «Detonation Wave". Généralement la détonation se produit dans une réaction homogène gazeuse, liquide ou solide. Mais parfois, la détonation est également observée en un milieu hautement non-uniforme qui contient des sources detonable (réaction gazeux, liquide ou solide ) dans un motif discret. Ce projet se concentre sur l'étude des effets des sources d'énergie discrets sur la vitesse de l'onde de détonation à l'aide de la modélisation numérique et des simulations. La libération d'énergie à la suite de la détonation est continue pour un mélange homogène de gaz et aboutit généralement à une vélocité de détonation appelé Chapman Jouguet (CJ). Toutefois, en présence de sources d'énergie distinctes, la vitesse de détonation sort d'être supérieure à la vitesse de détonation CJ observée théorique par A. Higgins (Proc. 20th ICDERS, Montréal, 2005). Ce projet vise à trouver des solutions numériques pour les systèmes de détonation très discrète afin de vérifier l'existance des résultats théoriques pour les systèmes de détonation discrets. Pour le calcul de vitesses des ondes de détonation pour les moyennes avec des sources discrètes, l'analyse numérique a été réalisée sur une maison d'une dimension de code Euler. Ces modifications du code ont été apportées à des fins de détonation continue . D'abord pour vérifier la vitesse de détonation CJ exacte dans lc code, puis à un stade ultérieur, d'autres modifications ont été apportées au code utiliser pour le phénomène de détonation discrets. Afin de pouvoir utiliser la maison en code numérique pour résoudre les problèmes d'écoulement supersoniques, le système continue de détonation a été modélisé et les résultats obtenus ont été de 0,05% de différence par rapport à la vitesse exacte d
Ngoma, Jeff. "Etude numérique et expérimentale de la déstabilisation des milieux granulaires immergés par fluidisation." Thesis, Aix-Marseille, 2015. http://www.theses.fr/2015AIXM4712/document.
The subject of this thesis is the numerical analysis and experimental investigation of the destabilization of submerged granular media caused by fluidization. This hydromechanical instability is one of the mechanisms that may trigger the regressive erosion, which is one of the main degradation phenomena driving the internal erosion of earthen hydraulic constructions. Such erosion mechanisms can only be understood through a rigorous description of the coupling and interaction between the eroding fluid and the soil particles. For this purpose, a 2D model has been used coupling two different numerical techniques, namely the discrete element method (DEM) for modelling the mechanical behaviour of the solid phase and the Lattice Boltzmann method (LBM) for the fluid phase. The experimental validation of this numerical 2D simulation has been carried out using two optical techniques for the internal visualization of a granular sample, namely the adjustment of the refraction index of the two phases and the laser-induced fluorescence
Brown, Nicholas John. "Discrete element modelling of cementitious materials." Thesis, University of Edinburgh, 2013. http://hdl.handle.net/1842/8011.
Durrani, Imran K. "Numerical modelling of discrete pile rows to stabilise slopes." Thesis, University of Nottingham, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.438556.
Wessling, Albin. "Towards Discrete Element Modelling of Rock Drilling." Licentiate thesis, Luleå tekniska universitet, Material- och solidmekanik, 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-83911.
Gram, Annika. "Numerical Modelling of Self-Compacting Concrete Flow : Discrete and Continuous Approach." Licentiate thesis, KTH, Civil and Architectural Engineering, 2009. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-10288.
With the advent of Self-Compacting Concrete (SCC) that flows freely, under the soleinfluence of gravity, the wish for hassle-free and predictable castings even in complexcases, spurged the simulation of concrete flow as a means to model and predictconcrete workability. To achieve complete and reliable form filling with smoothsurfaces of the concrete, the reinforced formwork geometry must be compatible withthe rheology of the fresh SCC. Predicting flow behavior in the formwork and linkingthe required rheological parameters to flow tests performed on the site will ensurean optimization of the casting process.In this thesis, numerical simulation of concrete flow is investigated, using both discreteas well as continuous approaches.The discrete particle model here serves as a means to simulate details and phenomenaconcerning aggregates modeled as individual objects. The here presented cases aresimulated with spherical particles. However, it is possible to make use of nonsphericalparticles as well. Aggregate surface roughness, size and aspect ratio maybe modeles by particle friction, size and clumping several spheres into forming thedesired particle shape.The continuous approach has been used to simulate large volumes of concrete. Theconcrete is modeled as a homogeneous material, particular effects of aggregates,such as blocking or segregation are not accounted for. Good correspondence wasachieved with a Bingham material model used to simulate concrete laboratory tests(e.g. slump flow, L-box) and form filling. Flow of concrete in a particularly congestedsection of a double-tee slab as well as two lifts of a multi-layered full scale wall castingwere simulated sucessfully.A large scale quantitative analysis is performed rather smoothly with the continuousapproach. Smaller scale details and phenomena are better captured qualitativelywith the discrete particle approach. As computer speed and capacity constantlyevolves, simulation detail and sample volume will be allowed to increase.A future merging of the homogeneous fluid model with the particle approach to formparticles in the fluid will feature the flow of concrete as the physical suspension thatit represents. One single ellipsoidal particle falling in a Newtonian fluid was studiedas a first step.
Med uppkomsten av självkompakterande betong (SKB) och dess möjligheter att flyta ut under inverkan av endast gravitation uppstod ett behov av att kunna förutsäga och kontrollera även mer komplicerade gjutningar. Numerisk simulering av SKBs flöde kan kommma att utgöra ett kraftfullt verktyg för att optimera gjutprocessen, ge möjlighet att förutsäga nödbvändig arbetbarhet och säkerställa kompatibilitet mellan den armerade formen och betongens reologi. I föreliggande avhandling undersöks betongens flöde med både diskreta och kontinuumbaserade simuleringsmetoder. Den diskreta partikelmodellen används för att simulera detaljer och fenomen hos t.ex. ballast i betong. I de här presenterade simuleringarna används sfäriska partiklar, men det är även möjligt att skapa ballastkorn av olika form. Ballastens ytråhet och storlek kan modelleras med parametrar för friktion och storlek medan sammanfogning av ett flertal partiklar kan ge ekvivalent form. Den kontinuumbaserade ansatsen används för att simulera större flödesmängder. Betongen modelleras som ett homogent material, eventuella effekter av ballastens inverkan, till exempel blockering eller separation, ingår ej. God överensstämmelse har uppnåtts med Binghams materialmodell som applicerats på några av SKBs provningsmetoder (bl a flytsättmått och L-låda) liksom även för större gjutningar. Formfyllnad av en hårt armerad sektion av ett STT-element, liksom två pumpade betongleveranser till en hög vägg, har framgångsrikt simulerats. En kvantitativ övergripande analys av betongflödet i formen kan göras med den kontinuumbaserade ansatsen för att upptäcka zoner med eventuella svårigheter. En högupplöst detaljstudie kompletterar sedan analysen på valda delar av och kring dessa zoner för att fånga partikelfenomen kvalitativt med hjälv av den diskreta modellen. Då datorkapaciteten ökar kommer även större volymer med högre detaljrikedom att kunna simuleras. En framtida modell simulerar med stor sannolikhet partiklar i flöde, vilket till fullo kan fånga betongens egenskaper som suspension. Som ett första steg på vägen har en fallande ellipsoid i en newtonsk vätska simulerats.
Zhang, Ting. "Numerical modelling of deformation within accretionary prisms." Thesis, Uppsala universitet, Institutionen för informationsteknologi, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-176502.
ESPOSITO, RICARDO GUREVITZ CUNHA. "NUMERICAL MODELLING OF PILE INSTALLATION AND PILE LOAD TEST USING DISCRETE ELEMENTS." PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 2015. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=26592@1.
COORDENAÇÃO DE APERFEIÇOAMENTO DO PESSOAL DE ENSINO SUPERIOR
PROGRAMA DE EXCELENCIA ACADEMICA
As alterações no solo decorrentes de um elemento de fundação profunda e seus desempenhos sob a aplicação de carga axial são processos há muito tempo estudados na engenharia civil. Diversos fatores como, método de instalação utilizado, formato da estaca, interações solo-estrutura, mecanismos de transferências de carga, movimentação do solo e alterações na compressibilidade e tensões do solo adjacente, apresentam desafios importantes que ainda não foram totalmente compreendidos nos fenômenos de penetração e capacidade de suporte em estacas. Diversos avanços foram realizados ao longo das últimas décadas para se investigar estes comportamentos, a partir procedimentos experimentais e novas formas de instrumentação, assim como ferramentas numéricas sofisticadas com o emprego de complexos modelos constitutivos em elementos finitos. Apesar destes avanços, a modelagem numérica dos processos citados, com todas as suas complexidades, ainda encontra alguns desafios. Devido a facilidade em lidar com simulações de grandes deformações e de captar o comportamento dilatante e nãolinear de solos granulares, o Método dos Elementos Discretos apresenta uma excelente ferramenta para investigar estes processos, sem grandes complicações. O presente trabalho procurou avaliar os comportamentos obtidos a partir de diferentes processos de instalação da estaca e seus efeitos nos resultados da prova de carga estática em solos granulares. As alterações de tensão e deslocamento foram avaliadas nos diferentes modelos e discutindo sobre uma metodologia básica para obter correspondências qualitativas e quantitativas com os diferentes comportamentos de campo e laboratório. Para este estudo foram utilizados os programas PFC, na versão 2D, e o programa UDEC, da Itasca co.
The disturbances experienced by the soil owing to the load applied to a deep foundation and its relative behavior consist of long time studied phenomena in civil engineering. Several factors such as the installation methods, the pile geometry, the interactions between soil and structure, the load-transfer mechanisms, the soil movements and the disturbances in the stress and compressibility fields present major challenges that have not yet been completely understood. Numerous advances have been observed throw-out the last decades, in order to investigate these behaviors starting from the different pile instrumentations, the use of calibration cameras and centrifuges and most recently the measurement of the stress and strain fields inside the soil mass in model tanks. Despite the advances the numerical modelling of those processes still faces major challenges. Due to simplified approach used by the Discrete Element Method to simulate large deformation and the dilant non-linear behavior of granular soils, it presents as an excellent tool to investigate these processes without further complications. The present work proposed to evaluate the different behaviors obtained with the variations of installation methods investigated as well as their effects in the results of the Pile Load Test. The disturbances were also evaluated in the different models considered and a basic method to achieve qualitative and quantitative comparisons was discussed. These studies were made possible with the help of the PFC2D and UDEC programs developed by Itasca co.
Vegh, Viktor. "Numerical modelling of industrial microwave heating." Thesis, Queensland University of Technology, 2003. https://eprints.qut.edu.au/37144/7/37144_Digitised%20Thesis.pdf.
Abbaspour-Fard, Mohammad Hossein. "Discrete element modelling of the dynamic behaviour of non-spherical particulate materials." Thesis, University of Newcastle Upon Tyne, 2000. http://hdl.handle.net/10443/970.
Cozens, Paul Dennis. "Numerical modelling of the roll damping of ships due to vortex shedding." Thesis, Imperial College London, 1987. http://hdl.handle.net/10044/1/38273.
Rorato, Riccardo. "Imaging and discrete modelling of sand shape." Doctoral thesis, Universitat Politècnica de Catalunya, 2019. http://hdl.handle.net/10803/668045.
Se sabe que la forma de las partículas juega un papel importante en el comportamiento del suelo, con efectos significativos de las respuestas mecánicas relevantes en ingeniería geotécnica. Por lo tanto, investigar cómo se puede medir y cuantificar la forma de las partículas se considera cada vez más importante en la mecánica del suelo moderna. Esto se acrecienta debido a las técnicas de análisis computacionales de imágenes y algoritmos de modelado discreto (DEM), que han abierto nuevas formas de abordar este problema. Este trabajo demuestra cómo se pueden hacer que estas dos técnicas funcionen juntas. Los análisis de imagen se realizan sobre micro-tomografías de rayos X (µ-CT) de muestras de arena en celdas triaxiales, centrándose en la caracterización y cuantificación de la forma de las partículas. Se estudian en detalle dos arenas con la forma de sus partículas muy diferentes: Caicos ooids (redondeados) y Hostun sand (angular). Luego se utiliza un algoritmo discreto de correlación de volumen digital (DVC) para rastrear la cinemática de granos individuales (alrededor de 50000 por cada muestra de arena) durante la prueba triaxial y medir, con buena precisión, sus desplazamientos y rotaciones acumulados. El análisis conjunto de la forma y las bases de datos cinemáticas adquiridas se realiza para encontrar cómo los descriptores de forma de partículas se relacionan con la cinemática observada a nivel de micro-escala. Resulta que la esfericidad verdadera predice bien el límite superior de rotación de una partícula. La modelización numérica se basa en el Método de Elementos Discretos (DEM). Los modelos que introducen resistencia a la rotación en el contacto se emplean ampliamente en simulaciones DEM, estos enfoques ofrecen beneficios computacionales sustanciales a costa de una mayor complejidad de calibración. En este trabajo, los valores de esfericidad verdadera (i.e., true sphericity) obtenidos mediante análisis de imagen de los granos, ya sea directamente por adquisición 3D o por correlación con medidas de forma 2D más simples, se utilizan para establecer restricciones de rotación mecánicamente equivalentes. Una relación empírica entre un parámetro de contacto (rolling friction) y un descriptor de forma de grano 3D (la esfericidad verdadera) se calibra primero, utilizando los resultados de la escala de muestras y de la escala de granos de dos pruebas triaxiales en las arenas de Hostun y de Caicos. Luego se valida simulando otras pruebas triaxiales (1) con las mismas arenas, pero en diferentes condiciones (2) con arena de Ottawa, para la que también estaban disponibles imágenes 3D de granos para su examen, y (3) con arena de Ticino, para la cual solo estaban disponibles imágenes 2D de los granos. Finalmente, se presentan resultados de simulaciones DEM a gran escala de la prueba de penetración de cono (CPT), aprovechando el nuevo modelo de contacto propuesto. Los datos experimentales del CPT realizado en una cámara de calibración (CC) sobre arena de Ticino se ajustan con éxito por las curvas de penetración numérica a diferentes presiones y condiciones de confinamiento. Un estudio paramétrico sobre la influencia de la forma de las partículas y la variabilidad de las formas de las partículas puso de manifiesto los efectos fuertemente acoplados de las resistencias rotacional y friccional en los contactos entre partículas. El trabajo descrito en esta tesis facilitará el uso de DEM para simulaciones a gran escala en problemas de ingeniería geotécnica.
Thakur, Subhash Chandra. "Mesoscopic discrete element modelling of cohesive powders for bulk handling applications." Thesis, University of Edinburgh, 2014. http://hdl.handle.net/1842/9777.
Li, Huiqi. "Discrete element method (DEM) modelling of rock flow and breakage within a cone crusher." Thesis, University of Nottingham, 2013. http://eprints.nottingham.ac.uk/14528/.
Kuruneru, Sahan Trushad Wickramasooriya. "Numerical modelling of particle deposition in idealized porous channels." Thesis, Queensland University of Technology, 2015. https://eprints.qut.edu.au/90555/1/Sahan_Kuruneru_Thesis.pdf.
Kanagasabai, Sasokanthan. "Three dimensional numerical modelling of rows of discrete piles used to stabilise large landslides." Thesis, University of Southampton, 2010. https://eprints.soton.ac.uk/210377/.
Murugaratnam, Kovthaman. "A refined numerical modelling technique for Shot Peening." Thesis, University of Oxford, 2014. http://ora.ox.ac.uk/objects/uuid:43e0fa12-bf49-425b-9ba6-6b93adaa8a7e.
Longshaw, Stephen Michael. "Numerical modelling and visualization of the evolution of extensional fault systems." Thesis, University of Manchester, 2011. https://www.research.manchester.ac.uk/portal/en/theses/numerical-modelling-and-visualization-of-the-evolution-of-extensional-fault-systems(51e33151-d9bd-4313-9251-6f55d4db4e15).html.
Morrissey, John Paul. "Discrete element modelling of iron ore pellets to include the effects of moisture and fines." Thesis, University of Edinburgh, 2013. http://hdl.handle.net/1842/8270.
Kulya, Chisenga. "Using discrete element modelling (DEM) and breakage experiments to model the comminution action in a tumbling mill." Master's thesis, University of Cape Town, 2008. http://hdl.handle.net/11427/5521.
Includes bibliographical references (leaves 147-153).
The Discrete Element Method (DEM) is a powerful modelling tool that characterises the system at the individual particle level. This makes it particularly well suited for simulating tumbling mills whose charge is principally individual particles (steel balls, rocks and fines). The use of DEM to simulate tumbling mills has proliferated since the early 1990s and been successfully employed to predict important milling parameters such as charge motion, power draw, liner wear and impact energy distribution. The ultimate aim of any model of the tumbling mill is to predict the product of the milling process. Current DEM simulations of the tumbling mill however do not simulate the breakage of the particles and as such can not directly predict the product. In order to predict the performance of industrial-scale tumbling mills, laboratory-scale mills are used to experimentally obtain data, which is then scaled up using black box mathematical models. In this thesis a tumbling mill model that utilises the power of DEM to provide the mechanical environment and the energies available for breakage is proposed. The incorporation of DEM eliminates the need to scale up because DEM is able to simulate the actual industrial-scale device. Data from breakage experiments on the ore being treated is also incorporated into the model to determine the breakage functions. Population balance techniques are applied in the mathematical framework of the model to predict the product of the comminution process. In order to test the proposed tumbling mill model, DEM simulations of a 1.695m diameter pilot SAG mill using charge based on actual operation data were performed and analysed. Results from the DEM simulation and Drop Weight Tester breakage experiments were then used in the proposed tumbling mill model to predict the evolution of the product size distribution.
Pan, Deng. "Numerical modelling of rows of discrete piles used to stabilise landslides under long-term conditions in clays." Thesis, University of Southampton, 2013. https://eprints.soton.ac.uk/359749/.
Jasevičius, Raimondas. "The Numerical Modelling of Normal Interaction of Ultrafine Particles." Doctoral thesis, Lithuanian Academic Libraries Network (LABT), 2011. http://vddb.laba.lt/obj/LT-eLABa-0001:E.02~2010~D_20110224_161120-06365.
Ultrasmulkios dalelės yra šiuolaikinės chemijos, farmacijos, maisto ir kitų pramonės šakų produktų sudėtinė dalis. Tiriant pramoninius technologinius procesus, neišvengiamai reikalingos teorinės žinios apie ultrasmulkių dalelių elgseną. Išsamus supratimas įmanomas tik atlikus įvairius tyrimus. Pastaruoju metu milteliai, klasifikuojami kaip ultrasmulkios (0,1 < d < 10 μm) dalelės, imti plačiai naudoti pramoniniuose procesuose, todėl suprasti ultrasmulkių dalelių elgsenos fundamentalumą miltelių technologijoje yra labai svarbu. Ultrasmulki dalelė yra itin maža, todėl su ja atlikti fizinį eksperimentą, kuris reikalauja specialios įrangos bei žinių, labai sunku. Tokiu atveju dažniausiai naudojamas skaitinis eksperimentas, kurį galima atlikti virtualiai. Skaitinio eksperimento metu yra tiriamos dinaminės ultrasmulkios dalelės savybės bei sprendžiamas dinaminis uždavinys. Taikant skaitinius modelius bei dalelės judėjimą aprašančias jėgų lygtis, naudojami sąveikos modeliai, apimantys adhezinę, klampią, tamprią bei tampriai plastinę sąveikas. Mikroskopinis adhezinės sąveikos modeliavimas – aktualus mechanikos mokslo uždavinys. Taikant sąveikos modelius, svarbu pritaikyti ir diskrečiųjų elementų metodą, kadangi, norint aprašyti dalelių elgseną, visų pirma reikia su-vokti ir aprašyti dalelės modelį. Dalelės elgsenos skaitiniam modeliavimui siūlomi teoriniai modeliai leidžia tirti dalelės sąveiką su dalele ar tampria puserdve bei sąveikos dinamiką. Šie modeliai galėtų būti pritaikyti... [toliau žr. visą tekstą]
Kasina, Veera Pratap Reddy. "DEM modelling and quantitative validation of flow characteristics and blending of pellets in a planar silo." Thesis, University of Edinburgh, 2016. http://hdl.handle.net/1842/25525.
Green, Daniel. "Understanding urban rainfall-runoff responses using physical and numerical modelling approaches." Thesis, Loughborough University, 2018. https://dspace.lboro.ac.uk/2134/33530.
Lajevardi, Seyed Hamid. "Comportement des géosynthétiques en ancrage : Modélisation physique et numérique." Phd thesis, INSA de Lyon, 2013. http://tel.archives-ouvertes.fr/tel-00995109.
Adams, Ethan. "PATHWAY CONNECTIVITY IN AN EPIGENETIC FLUVIOKARST SYSTEM: INSIGHT FROM A NUMERICAL MODELLING STUDY IN KENTUCKY USA." UKnowledge, 2019. https://uknowledge.uky.edu/ce_etds/88.
Panton, Brad. "Numerical modelling of rock anchor pullout and the influence of discrete fracture networks on the capacity of foundation tiedown anchors." Thesis, University of British Columbia, 2016. http://hdl.handle.net/2429/57464.
Applied Science, Faculty of
Mining Engineering, Keevil Institute of
Graduate
Rodella, Andrea. "Analytical and numerical modelling of undulatory locomotion for limbless organisms in granular/viscous media." Doctoral thesis, Università degli studi di Trento, 2020. http://hdl.handle.net/11572/273235.
Rodella, Andrea. "Analytical and numerical modelling of undulatory locomotion for limbless organisms in granular/viscous media." Doctoral thesis, Università degli studi di Trento, 2020. http://hdl.handle.net/11572/273235.
PIOVANO, GIOVANNA. "Combined finite-discrete element modelling of key instabilities which characterise deep-seated landslides from massive rock slope failure." Doctoral thesis, Politecnico di Torino, 2012. http://hdl.handle.net/11583/2502740.
Volk, Annette. "Quantification and Assessment of Numerical Error in Coupled Computational Fluid Dynamics - Discrete Element Method Simulations of Gas Flow through Granular Solids." University of Cincinnati / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1543139366302536.
Mezquida, Alcaraz Eduardo José. "Numerical Modelling of UHPFRC: from the Material to the Structural Element." Doctoral thesis, Universitat Politècnica de València, 2021. http://hdl.handle.net/10251/167017.
[CA] El principal objectiu de la present tesi es el desenvolupament d'una completa metodologia per al modelat numèric de l'UHPFRC des del nivell material fins arribar als elements estructurals. Es pretén contribuir a l'avanç del coneixement del comportament mecànic de l'UHPFRC per mitjà d'un procediment per al modelat numèric útil per al modelat i disseny estructural que permeta fer que aquest material siga competitiu al mercat de la construcció. En la metodologia de modelat proposta, es considera un comportament constitutiu de l'UHPFRC optimitzat per mitjà d'un procediment directe i fiable amb el qual s'aprofiten els avantatges del material, resultant en un disseny estructural eficient des del punt de vista mecànic i econòmic. És necessari produir SH-UHPFRC per a aconseguir grans propietats mecàniques? És possible generar SS-UHPFRC amb el qual queden reduïts els costs inicials mantenint unes propietats mecàniques i de durabilitat competitives que comporten un disseny estructural efectiu? El desenvolupament d'UHPFRC amb baix enduriment per deformació i de SS-UHPFRC pot reduir les seues propietats mecàniques però, si són adequadament estudiades i controlades, aquests podrien ser optimitzats. La tesi aborda algunes d'aquestes qüestions per mitjà de l'estudi del comportament a tracció de l'UHPFRC que va des de SH-UHPFRC fins SS-UHPFRC. Es pretén dur a terme una proposta de procediment fiable per a caracteritzar el comportament constitutiu a tracció i definir un model numèric d'elements finits fiable per a modelar amb precisió la resposta de provetes i elements estructurals armats d'UHPFRC. Per a definir el procediment directe per a caracteritzar a tracció tant SH-UHPFRC com SS-UHPFRC, s'ha dut a terme una campanya experimental i numèrica en la que s'ha analitzat el resultat d'assajar 227 provetes sense armadura fabricades amb UHPFRC amb quantitats de fibres curtes i llises d'acer de 120-130kg/m3 i 160kg/m3, assajades a flexió per mitjà de l'assaig a quatre punts (4PBT). El desenvolupament i la validació de l'esmentat procés són assegurats per mitjà d'un model no lineal d'elements finits (NLFEM) fiable. La validació numèrica duta a terme ha estat decisiva per a que aquest procediment siga precís, simple i fiable. Utilitzant aquesta campanya experimental, s'ha desenvolupat una aplicació predictiva per a estimar els paràmetres que defineixen el comportament constitutiu a tracció de l'UHPFRC. Aquesta aplicació és simple i directa i evita la possible variabilitat produïda per males interpretacions en l'aplicació del procés. A més a més, també s'ha dut a terme una segon campanya experimental constituïda per bigues d'UHPFRC armades a flexió amb diferents escales: 36 bigues curtes amb 130 i 160kg/m3 de fibres i dos bigues llargues de gran escala. Aquesta campanya s'ha modelat amb el NLFEM ací desenvolupat incloent efectes importants deguts a la interacció de l'UHPFRC amb les barres d'armat. Addicionalment, també s'han modelat amb el NLFEM tirants d'UHPFRC armats a tracció provinents d'una campanya experimental d'altra investigació. El model considera efectes deguts a la retracció, al 3D i comportament tensió stiffening que generen resultats molt precisos quan es comparen amb els resultats experimentals. Per tant, com a resultat de la present tesi doctoral, s'ha obtingut un model d'elements finits capaç de modelar amb precisió elements estructurals d'UHPFRC armats. Els resultats del model comparats amb els resultats experimentals no sols demostren la fiabilitat del NLFEM dut a terme sinó que també la coherència del procediment directe desenvolupat per a caracteritzar el comportament constitutiu a tracció de l'UHPFRC als dos casos, tant per a SH-UHPFRC com SS-UHPFRC, tant en elements estructurals armats a flexió com amb elements estructurals armats a tracció directa. Conseqüentment, s'ha proposat una metodologia completa i efectiva per al modelat numèric de l'UHPFRC des del niv
[EN] The main objective of the present PhD thesis is to develop a complete methodology for the numerical modelling of UHPFRC from the material level to structural elements. It intends to contribute to advanced knowledge of mechanical UHPFRC behaviour to lead to a numerically modelling proposal that is useful for structural modelling and design that allows options for this material to be competitive in the construction market. Optimised UHPFRC material constitutive behaviour, characterised by a direct reliable defined procedure, is considered in the proposed modelling methodology to take advantage of these properties, and to lead to an efficient structural design from the mechanical and economical points of view. Is it necessary to produce SH-UHPFRC to obtain excellent properties? Is it possible to develop SS-UHPFRC that leads to lower initial costs and to maintain competitive mechanical and durability properties that result in an effective structural design? The development of low strain-hardening and SS-UHPFRC would lead to reduce its mechanical properties, but they can be optimised if they are studied and controlled. The thesis addresses some of these questions by studying tensile UHPFRC behaviour to cover a wide range of tensile constitutive behaviours from SH-UHPFRC to SS-UHPFRC. It intends to propose a reliable tensile characterisation process and a reliable finite element model capable of accurately simulating the response of UHPFRC specimens and reinforced structural elements. An extensive experimental and numerical campaign with 227 unreinforced four-point bending test (4PBT) specimens with amounts of smooth-straight (13/0.20) steel fibres of 1.53-1.66% (120-130kg/m3) in volume and with 2.00% (160kg/m3), which represents SS-UHPFRC and SH-UHPFRC tensile behaviours, was carried out to set up a direct tensile characterisation procedure involving SS-UHPFRC and SH-UHPFRC. The direct procedure's development and validity are ensured by a reliable non-linear finite element model (NLFEM). Numerical validation was carried out and is decisive for performing the direct procedure to characterise the tensile behaviour of both SS and SH-UHPFRC herein developed accurately, simply and reliably. With the experimental programme herein, a predictive application for estimating tensile UHPFRC parameters was developed. The prediction offers reliable results. The application is simple and direct, and avoids variability in the characterisation procedure due to possible misinterpretations in its application. In addition, a second experimental programme, which includes reinforced concrete flexural beams on different scales, with 36 UHPFRC reinforced short beams with 130 and 160kg/m3 of steel fibres and two full-scale long beams, was carried out and modelled with the NLFEM herein developed including major effects due to the interaction between UHPFRC and reinforcement bars. Additionally, reinforced UHPFRC tensile bars from a recent experimental campaign performed by other researchers were modelled with the NLFEM. The model considers shrinkage effects, tension stiffening behaviour and 3D effects due to the particularities of the test, which provide very accurate results compared to those obtained with the experimental tests. As a result of this PhD thesis, an accurate NLFEM was obtained to model reinforced UHPFRC structural elements. The results of the model compared to the experimental ones demonstrate not only the reliability of the developed NLFEM, but also the coherence of the developed direct procedure to characterise tensile UHPFRC behaviour in both strain-softening and strain-hardening in reinforced flexural and direct tensile structural elements. Consequently, a complete and effective methodology for numerical UHPFRC modelling from the material level to structural elements is proposed.
Mezquida Alcaraz, EJ. (2021). Numerical Modelling of UHPFRC: from the Material to the Structural Element [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/167017
TESIS
Min, Ki-Bok. "Fractured Rock Masses as Equivalent Continua - A Numerical Study." Doctoral thesis, KTH, Land and Water Resources Engineering, 2004. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-3742.
In this thesis, fractured rock masses are treated asequivalent continua for large-scale analyses of rockengineering projects. Systematic developments are made for thedetermination of equivalent mechanical and hydraulic propertiesof fractured rock masses using a hybrid discrete fracturenetwork - distinct element method (DFN-DEM) approach. Thedetermined equivalent properties are then used for a far-fieldfinite element analysis of the thermo-mechanical impacts on thestress, deformation and permeability of fractured rockssurrounding a hypothetical geological repository of nuclearwaste. The geological data were extracted from the results ofan extensive site investigation programme at Sellafield, UK,conducted by Nirex UK Ltd.
The scale dependencies of the hydraulic and mechanicalproperties were investigated by using multiple realizations ofthe fracture system geometry with increasing model sizes untilproperly defined hydraulic and mechanical representativeelementary volumes (REVs) were reached. The validity of thesecond order permeability tensor and the fourth-ordermechanical compliance tensor were tested for continuum analysesat larger scales. The REV was determined to be around 5 m formechanical and hydraulic data in this study.
Analysis of the stress-dependent mechanical and hydraulicproperties shows that the effect of rock stresses is crucial.The elastic moduli increase significantly with the increase ofstress and an empirical equation of stress-dependent elasticmodulus is suggested based on results of numerical experiments.Calculations of the Poisson's ratios suggest greater valuesthan are normally assumed in practice. Depending on the stateof stress, permeability decreases or increases with increasingcompressive stress. Stress-induced flow channeling effect iscaptured by numerical modeling for the first time and detailedmechanisms of shear dilation of fractures are provided. Basedon the numerical experiments, a set of empirical equations wassuggested for the stress-dependent permeability, consideringboth normal deformation and shear dilation of fractures.
Thermo-mechanical impact on the performance of ahypothetical repository at a far-field scale (5 km by 1 km) wasinvestigated with the stress-dependent equivalent propertiesdetermined at the REV scale. This analysis shows thatmechanical responses vary significantly depending on how themechanical properties were determined. The change ofpermeability due to the thermal loading is, however, notsignificant in this particular case.
The thesis provides a framework for systematic analysis oflarge-scale engineering applications in fractured rock masses,such as geological repositories of nuclear wastes.
Keyword:Fractured rock masses, Equivalent Continuum,Discrete Fracture Network (DFN), Distinct Element Method (DEM),Finite Element Method (FEM), Nuclear Waste Disposal, CoupledThermo-Hydro-Mechanical Processes
Volk, Annette. "Quantification of Numerical and Modeling Errors in Simulation of Fluid Flow through a Fixed Particle Bed." University of Cincinnati / OhioLINK, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1448275079.
Wilke, Charel Daniel. "Experimental measurement of graphite wear in helium at elevated temperatures and the discrete element modelling of graphite dust production inside the Pebble Bed Modular Reactor." Thesis, Stellenbosch : Stellenbosch University, 2013. http://hdl.handle.net/10019.1/80211.
ENGLISH ABSTRACT: Production of graphite dust inside the Pebble Bed Modular Reactor (PBMR) influences the reactor operation negatively. Graphite is used as a moderator in the reactor core and the formation and transportation of graphite dust away from the reactor core decreases the amount of moderator which in turn has a negative impact on the reactor operation. High levels of radioactive dust may also contaminate reactor components which may pose a health risk to maintenance personnel. In this study a pressure vessel was designed and used to measure the wear of a graphite pebble in helium at elevated temperatures. By means of a multi-linear regression analysis a proper mathematical function was established in order to relate graphite wear to certain tribological parameters. These parameters were identified through a literature study. Discrete Element Modelling (DEM) was used to simulate the gravitational flow of graphite pebbles through the reactor core. The experimentally determined mathematical function was incorporated into the DEM simulation to estimate the annual mass of graphite dust to be produced by the PBMR pebble bed as a result of pebble-pebble interaction and pebble-wall interaction during refuelling.
AFRIKAANSE OPSOMMING: Die vorming van grafiet stof binne die korrelbed-modulêre reaktor (PBMR) beïnvloed die werking daarvan negatief. Grafiet word gebruik as 'n moderator in die reaktor kern en die vorming en vervoer van grafietstof weg van die reaktor kern lei tot 'n afname in die hoeveelheid moderator en dit het 'n negatiewe impak op die werking van die reaktor. Hoë vlakke van radioaktiewe grafietstof kontamineer ook reaktorkomponente wat 'n gesondheidsrisiko vir onderhoudspersoneel inhou. In hierdie studie was 'n drukvat ontwerp en gebruik om die slytasie van 'n grafietkorrel in helium by verhoogde temperature te meet. 'n Multi-lineêre regressie analise is dan gebruik om 'n wiskundige funksie daar te stel wat die verband tussen grafietslytasie en die eksperimentele parameters vas stel. Hierdie parameters was met behulp van 'n literatuurstudie geïdentifiseer. Diskrete Element Modellering (DEM) was gebruik om die gravitasionele vloei van grafietkorrels in die reaktor te modelleer. Die eksperimenteel bepaalde wiskundige funksie word in die DEM simulasie ge-inkorporeer om 'n skatting te maak van die jaarlikse massa grafietstof wat gevorm sal word in die PBMR korrelbed as 'n gevolg van korrel-korrel interaksie en korrel-wand interaksie gedurende hersirkulasie.
MARCHELLI, MADDALENA. "Debris flow interaction with open rigid barriers A DEM-LBM approach for trapping efficiency and impact force analysis." Doctoral thesis, Politecnico di Torino, 2018. http://hdl.handle.net/11583/2702811.
Louati, Haithem. "Experimental and numerical study of humid granular material : influence of liquid content in quasi-static regime." Thesis, Ecole nationale des Mines d'Albi-Carmaux, 2016. http://www.theses.fr/2016EMAC0008/document.
We study experimentally and numerically the shear behaviour of wet granular material. We investigate the effect of the liquid content and the applied normal stresses to this behaviour. An annular shear cell was used to carry out the experiments, for a large range of applied normal stress from about 0.3 kPa to 12 kPa. The results give the variation of the shear stress at steady-state as a function of the normal stress for a wide range of liquid fraction. The incorporated liquid goes from forming bridges at the contact point to completely filling the space between grains. The shear resistance and the voidage fraction variations with the liquid fraction were analysed. Depending on the applied normal stress and the liquid fraction, different regimes of the shear resistance were identified. The discrete element method (DEM) was used to gain a microscopic understanding of the shear behaviour of dry and partially wet granular material in the shear cell. Large size glass beads were used to speed up the computational time and to facilitate characterisation at the particle scale. First, the influence of the microscopic properties of the particle (The Young’s modulus and the sliding friction) on the macroscopic properties of dry and wet granular materials (the coordination number, the voidage fraction, the shear ratio and the velocity of particles) was investigated. Secondly, the shear behaviour of the partially wet granular material for different liquid fractions and normal stresses was studied. The capillary forces and the number of liquid bridges were quantitatively analysed
Carvalho, Marcelo de Rezende. "Computational Framework for Fracture Simulation of Concrete Structures until Failure." Thesis, University of Sydney, 2019. https://hdl.handle.net/2123/23283.
Mazor, Alon. "Modelling of roll compaction process by finiite element method." Thesis, Ecole nationale des Mines d'Albi-Carmaux, 2017. http://www.theses.fr/2017EMAC0009/document.
In the pharmaceutical industry, dry granulation by roll compaction is a process of size enlargement of powder into granules with good flowability for subsequent die compaction process. Understanding the roll compaction process and optimizing manufacturing efficiency is limited using the experimental approach due to the high cost of powder, time-consuming and the complexity of the process. In this work, a 3D Finite Element Method (FEM) model was developed to identify the critical material properties, roll press designs and process parameters controlling the quality of the product. The Drucker-Prager Cap (DPC) model was used to describe the powder compaction behavior and was determined based on standard calibration method. To overcome the complexity involving two different mechanisms of powder feeding by the screw and powder compaction between rolls, a novel combined approach of Discrete Element Method (DEM), used to predict the granular material flow in the feed zone and the Finite Elements Method (FEM) employed for roll compaction, was developed. Lastly, for a more realistic roll compaction modelling, allowing the fluctuation of the gap between rolls, a Coupled-Eulerian Lagrangian (CEL) approach was developed. FEM simulation results clearly show the effect of different process parameters on roll pressure and density distribution in the compaction zone of powder between the rolls. Moreover, results show that using a cheek-plates sealing system causes a nonuniform roll pressure and density distribution with the highest values in the middle and the lowest at the edges. On the other hand, the resultant pressure and density distributions with the rimmed-roll obtained higher values in the edges than in the middle and overall a more uniform distribution. The combined DEM-FEM methodology clearly shows a direct correlation between the particle velocity driven by the screw conveyor to the feed zone and the roll pressure, both oscillating in the same period. This translates into an anisotropic ribbon with a density profile varying sinusoidally along its length. To validate the results, the simulations are compared with literature and experimentally measured values in order to assess the ability of the model to predict the properties of the produced ribbons
Argilaga, Claramunt Albert. "FEMxDEM double scale approach with second gradient regularization applied to granular materials modelization." Thesis, Université Grenoble Alpes (ComUE), 2016. http://www.theses.fr/2016GREAI066/document.
The multi-scale FEMxDEM approach is an innovative numerical method for geotechnical problems involving granular materials. The Finite Element Method (FEM) and the Discrete Element Method (DEM) are simultaneously applied to solve, respectively, the structural problem at the macro-scale and the material microstructure at the micro-scale. The advantage of using such a double scale configuration is that it allows to study an engineering problem without the need of standard constitutive laws, thus capturing the essence of the material properties. The link between scales is obtained via numerical homogenization, so that, the continuum numerical constitutive law and the corresponding tangent matrix are obtained directly from the discrete response of the microstructure.Typically, the FEMxDEM approach presents some drawbacks; the convergence velocity and robustness of the method are not as efficient as in classical FEM models. Furthermore, the computational cost of the microscale integration and the typical mesh-dependency at the macro-scale, make the multi-scale FEMxDEM approach questionable for practical uses. The aim of this work is to focus on these theoretical and numerical issues with the objective of making the multiscale FEMxDEM approach robust and applicable to real-scale configurations. A variety of operators is proposed in order to improve the convergence and robustness of the method in a quasi-Newton framework. The independence of the Gauss point integrations and the element intensive characteristics of the code are exploited by the use of parallelization using an OpenMP paradigm. At the macro level, a second gradient constitutive relation is implemented in order to enrich the first gradient Cauchy relation bringing mesh-independency to the model.The aforementioned improvements makes the FEMxDEM approach competitive with classical FEM models in terms of computational cost thus allowing to perform robust and mesh-independent multi-scale FEMxDEM simulations, from the laboratory scale (e.g. biaxial test) to the engineering-scale problem, (e.g. gallery excavation).Keywords:Double scale, numerical homogenization, numerical constitutive law, elasto-plasticity, second gradient, microstructured materials, large strain, finite elements, discrete elements, Newton method, parallelization, uniqueness
Moukadiri, Dounia. "Développement d'une approche numérique par la MED pour la prédiction des propriétés mécaniques des matériaux hétérogènes avec prise en compte de leur variabilité : application aux matériaux composites biosourcés." Electronic Thesis or Diss., Amiens, 2019. http://www.theses.fr/2019AMIE0061.
Natural fiber composites are attracting growing interest. However, pieces made from this type of material exhibit a high variability in terms of mechanical properties, which makes them less competitive compared to conventional materials. In this work, a numerical approach, based on Discrete Element Method (DEM) and the probabilistic method Certain Generalized Stress Method (CGSM) is proposed, in order to take into account the different sources of variability. For validation purposes, a unidirectional bio-based composite material based on flax fibers is considered. The first part of this work describes the material's manufacturing, the elastic properties experimental characterization and the quantification of their variability. The DEM is then introduced to simulate the macroscopic behaviour of the material. Since the stress field obtained using DEM modelling is heterogeneous, an approach named Halo is introduced to control this dispersion. The proposed approach is tested and validated in homogeneous and heterogeneous media. Finally, the variability of elastic properties is introduced into the discrete model via a coupling approach with the probabilistic method CGSM
Noorian-Bidgoli, Majid. "Strength and deformability of fractured rocks." Doctoral thesis, KTH, Mark- och vattenteknik, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-155719.
QC 20141111
Peña, Monferrer Carlos. "Computational fluid dynamics multiscale modelling of bubbly flow. A critical study and new developments on volume of fluid, discrete element and two-fluid methods." Doctoral thesis, Universitat Politècnica de València, 2017. http://hdl.handle.net/10251/90493.
El estudio y modelado de flujos bifásicos, incluso los más simples como el bubbly flow, sigue siendo un reto que conlleva aproximarse a los fenómenos físicos que lo rigen desde diferentes niveles de resolución espacial y temporal. El uso de códigos CFD (Computational Fluid Dynamics) como herramienta de modelado está muy extendida y resulta prometedora, pero hoy por hoy, no existe una única aproximación o técnica de resolución que permita predecir la dinámica de estos sistemas en los diferentes niveles de resolución, y que ofrezca suficiente precisión en sus resultados. La dificultad intrínseca de los fenómenos que allí ocurren, sobre todo los ligados a la interfase entre ambas fases, hace que los códigos de bajo o medio nivel de resolución, como pueden ser los códigos de sistema (RELAP, TRACE, etc.) o los basados en aproximaciones 3D TFM (Two-Fluid Model) tengan serios problemas para ofrecer resultados aceptables, a no ser que se trate de escenarios muy conocidos y se busquen resultados globales. En cambio, códigos basados en alto nivel de resolución, como los que utilizan VOF (Volume Of Fluid), requirieren de un esfuerzo computacional tan elevado que no pueden ser aplicados a sistemas complejos. En esta tesis, mediante el uso de la librería OpenFOAM se ha creado un marco de simulación de código abierto para analizar los escenarios desde niveles de resolución de microescala a macroescala, analizando las diferentes aproximaciones, así como la información que es necesaria aportar en cada una de ellas, para el estudio del régimen de bubbly flow. En la primera parte se estudia la dinámica de burbujas individuales a un alto nivel de resolución mediante el uso del método VOF (Volume Of Fluid). Esta técnica ha permitido obtener resultados precisos como la formación de la burbuja, velocidad terminal, camino recorrido, estela producida por la burbuja e inestabilidades que produce en su camino. Pero esta aproximación resulta inviable para entornos reales con la participación de más de unas pocas decenas de burbujas. Como alternativa, se propone el uso de técnicas CFD-DEM (Discrete Element Methods) en la que se representa a las burbujas como partículas discretas. En esta tesis se ha desarrollado un nuevo solver para bubbly flow en el que se han añadido un gran número de nuevos modelos, como los necesarios para contemplar los choques entre burbujas o con las paredes, la turbulencia, la velocidad vista por las burbujas, la distribución del intercambio de momento y masas con el fluido en las diferentes celdas por cada una de las burbujas o la expansión de la fase gaseosa entre otros. Pero también se han tenido que incluir nuevos algoritmos como el necesario para inyectar de forma adecuada la fase gaseosa en el sistema. Este nuevo solver ofrece resultados con un nivel de resolución superior a los desarrollados hasta la fecha. Siguiendo con la reducción del nivel de resolución, y por tanto los recursos computacionales necesarios, se efectúa el desarrollo de un solver tridimensional de TFM en el que se ha implementado el método QMOM (Quadrature Method Of Moments) para resolver la ecuación de balance poblacional. El solver se desarrolla con los mismos modelos de cierre que el CFD-DEM para analizar los efectos relacionados con la pérdida de información debido al promediado de las ecuaciones instantáneas de Navier-Stokes. El análisis de resultados de CFD-DEM permite determinar las discrepancias encontradas por considerar los valores promediados y el flujo homogéneo de los modelos clásicos de TFM. Por último, como aproximación de nivel de resolución más bajo, se investiga el uso uso de códigos de sistema, utilizando el código RELAP5/MOD3 para analizar el modelado del flujo en condiciones de bubbly flow. El código es modificado para reproducir correctamente el flujo bifásico en tuberías verticales, comparando el comportamiento de aproximaciones para el cálculo del término d
L'estudi i modelatge de fluxos bifàsics, fins i tot els més simples com bubbly flow, segueix sent un repte que comporta aproximar-se als fenòmens físics que ho regeixen des de diferents nivells de resolució espacial i temporal. L'ús de codis CFD (Computational Fluid Dynamics) com a eina de modelatge està molt estesa i resulta prometedora, però ara per ara, no existeix una única aproximació o tècnica de resolució que permeta predir la dinàmica d'aquests sistemes en els diferents nivells de resolució, i que oferisca suficient precisió en els seus resultats. Les dificultat intrínseques dels fenòmens que allí ocorren, sobre tots els lligats a la interfase entre les dues fases, fa que els codis de baix o mig nivell de resolució, com poden ser els codis de sistema (RELAP,TRACE, etc.) o els basats en aproximacions 3D TFM (Two-Fluid Model) tinguen seriosos problemes per a oferir resultats acceptables , llevat que es tracte d'escenaris molt coneguts i se persegueixen resultats globals. En canvi, codis basats en alt nivell de resolució, com els que utilitzen VOF (Volume Of Fluid), requereixen d'un esforç computacional tan elevat que no poden ser aplicats a sistemes complexos. En aquesta tesi, mitjançant l'ús de la llibreria OpenFOAM s'ha creat un marc de simulació de codi obert per a analitzar els escenaris des de nivells de resolució de microescala a macroescala, analitzant les diferents aproximacions, així com la informació que és necessària aportar en cadascuna d'elles, per a l'estudi del règim de bubbly flow. En la primera part s'estudia la dinàmica de bambolles individuals a un alt nivell de resolució mitjançant l'ús del mètode VOF. Aquesta tècnica ha permès obtenir resultats precisos com la formació de la bambolla, velocitat terminal, camí recorregut, estela produida per la bambolla i inestabilitats que produeix en el seu camí. Però aquesta aproximació resulta inviable per a entorns reals amb la participació de més d'unes poques desenes de bambolles. Com a alternativa en aqueix cas es proposa l'ús de tècniques CFD-DEM (Discrete Element Methods) en la qual es representa a les bambolles com a partícules discretes. En aquesta tesi s'ha desenvolupat un nou solver per a bubbly flow en el qual s'han afegit un gran nombre de nous models, com els necessaris per a contemplar els xocs entre bambolles o amb les parets, la turbulència, la velocitat vista per les bambolles, la distribució de l'intercanvi de moment i masses amb el fluid en les diferents cel·les per cadascuna de les bambolles o els models d'expansió de la fase gasosa entre uns altres. Però també s'ha hagut d'incloure nous algoritmes com el necessari per a injectar de forma adequada la fase gasosa en el sistema. Aquest nou solver ofereix resultats amb un nivell de resolució superior als desenvolupat fins la data. Seguint amb la reducció del nivell de resolució, i per tant els recursos computacionals necessaris, s'efectua el desenvolupament d'un solver tridimensional de TFM en el qual s'ha implementat el mètode QMOM (Quadrature Method Of Moments) per a resoldre l'equació de balanç poblacional. El solver es desenvolupa amb els mateixos models de tancament que el CFD-DEM per a analitzar els efectes relacionats amb la pèrdua d'informació a causa del promitjat de les equacions instantànies de Navier-Stokes. L'anàlisi de resultats de CFD-DEM permet determinar les discrepàncies ocasionades per considerar els valors promitjats i el flux homogeni dels models clàssics de TFM. Finalment, com a aproximació de nivell de resolució més baix, s'analitza l'ús de codis de sistema, utilitzant el codi RELAP5/MOD3 per a analitzar el modelatge del fluxos en règim de bubbly flow. El codi és modificat per a reproduir correctament les característiques del flux bifàsic en canonades verticals, comparant el comportament d'aproximacions per al càlcul del terme de drag basades en velocitat de drift flux model i de les basades en coe
Peña Monferrer, C. (2017). Computational fluid dynamics multiscale modelling of bubbly flow. A critical study and new developments on volume of fluid, discrete element and two-fluid methods [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/90493
TESIS
Peerun, Mohammud Irfaan. "Characteristics and 3D Behaviour of Granular Geomaterials due to Shear." Thesis, Griffith University, 2022. http://hdl.handle.net/10072/419081.
Thesis (PhD Doctorate)
Doctor of Philosophy (PhD)
School of Eng & Built Env
Science, Environment, Engineering and Technology
Full Text
Bonilla, Sierra Viviana. "De la photogrammétrie à la modélisation 3D : évaluation quantitative du risque d'éboulement rocheux." Thesis, Université Grenoble Alpes (ComUE), 2015. http://www.theses.fr/2015GREAI072/document.
Structural and mechanical analyses of rock mass are key components for rock slope stability assessment. The complementary use of photogrammetric techniques and numerical models coupling discrete fracture networks (DFN) with the discrete element method (DEM) provides a methodology that can be applied to assess the mechanical behaviour of realistic three-dimensional (3D) configurations for which fracture persistence cannot be assumed. The stability of the rock mass is generally assumed to be controlled by the shear strength along discontinuity planes present within the slope. If the discontinuities are non–persistent with their continuity being interrupted by the presence of intact rock bridges, their apparent strength increases considerably. In this case, the contribution of the rock bridges located in-between these discontinuities have to be accounted for in the stability analysis. The progressive failure of rock slope involving non–persistent discontinuities can be numerically investigated based upon simulations performed using a DEM approach. The intact material is represented as an assembly of bonded particles interacting through dedicated contact laws that can be calibrated to properly represent the behaviour of the rock material. The advantage of the method is that it enables to simulate fracture initiation and propagation inside the rock matrix as a result of inter-particle bond breakage. In addition, pre–existing discontinuities can be explicitly included in the model by using a modified contact logic that ensures an explicit and constitutive mechanical behaviour of the discontinuity planes. Stability analyses were carried out with emphasis on the contribution of rock bridges failure through a mixed shear-tensile failure process, leading to the generation of new failure surfaces. Jennings' formulation being considered to be one of the first rock slope stability analysis that evaluates the resistance to sliding as a weighted combination of both, intact rock bridges and discontinuity planes strengths, its validity was discussed and systematically compared to results obtained from numerical simulations. We demonstrate that the validity of Jennings' formulation is limited as soon as tensile failure becomes predominant and an alternative formulation is proposed to assess the resulting equivalent strength. Regarding field slope stability, we show that the combination of high resolution photogrammetric data and DFN-DEM modelling can be used to identify valid model scenarios of unstable wedges and blocks daylighting at the surface of both natural and engineered rock slopes. Back analysis of a real case study confirmed that failure surfaces can be simulated as a result of both fracture propagation across rock bridges and sliding along pre-existing discontinuities. An identified wedge failure that occurred in an Australian coal mine was used to validate the methodology. Numerical simulations were undertaken to determine in what scenarios the measured and predicted failure surfaces can be used to calibrate strength parameters in the model. The work presented here is part of a more global need to improve natural and mining hazards management related to unstable rock masses. We believe that the proposed methodology can strengthen the basis for a more comprehensive stability analysis of complex fractured rock slopes