Dissertations / Theses on the topic 'Finite element and discrete element modelling'

An effective methodology for discrete fracture in quasi-brittle material is presented within an explicit finite discrete element framework. Simple pragmatic models are envisaged that reflect the data deficiency of the quasi-brittle material and recover the observed physical response within engineering accuracy. Phenomenological strain-softening constitutive models are adopted for the modelling of micromechanical processes in an average sense. An extensional basis for fracture is assumed in both tensile and compressive stress fields, with only the mechanism with which inelastic strain is realised differing between the two stress states. To overcome the mesh dependence introduced by local softening constitutive relationships, the socalled localisation limiters are adopted in the form of the tensile crack band, nonlocal and viscous smeared crack models. Effective localisation lengthscales introduced by these regularisation methods ensure mesh objective failure localisation a priori to discrete crack insertion. A nonlocal map of failure indicators initiates fracture, with discrete cracks inserted into the finite element continuum by the splitting of the discretisation. An isotropic, non-associative Mohr-Coulomb model is derived in principal stress space as a first order approximation to the quasi-brittle response in compression. A model for discrete fracture in tensile and compressive stress fields is proposed, defined by a composite yield surface consisting of the fully anisotropic rotating crack band model coupled with the isotropic, non-associative Mohr-Coulomb model. The novel inclusion of an explicit coupling between the extensional inelastic dilation strain accrued during compressive failure and tensile strength degradation in the dilation directions permits the realisation of discrete fracturing in purely compressive stress fields. The so-called continuum-discrete transition introduces additional degrees of freedom into quasi-brittle systems and permits large deformation to be realised through the process of cataclastic flow. This advancement is considered significant and necessary in the recovery of the observed quasi-brittle response. The effectiveness of the proposed constitutive fracture models is verified by application to a number of physical quasi-brittle fracture systems, including borehole breakout, fracturing around excavations, strip punch tests, dynamic spalling and anchor pullout tests, amongst others.

Dans l’industrie pharmaceutique, la granulation sèche par compactage à rouleaux est un procédé d’agglomération de poudres en granulés pour améliorer les propriétés d’écoulement nécessaire pour le procédé de compression en matrice. Comprendre le procédé de compactage à rouleaux et optimiser l’efficacité de production est limitée par l’utilisation de l’approche expérimentale à cause du coût élevé des poudres, le temps des essais et la complexité du procédé. Dans ce travail, une méthode d’éléments finis en 3D, est développée dans le but d’identifier les paramètres critiques du matériau et du procédé pour le contrôle de la qualité de la production. Le modèle de comportement de Drucker-Prager Cap est utilisé pour décrire le comportement en compression de poudres et sa calibration est déterminée à partir des essais standard. Pour surmonter la complexité liée à l’existence de deux mécanismes différents, l’alimentation en poudre par une vis sans fin et le compactage entre les rouleaux, une nouvelle méthode d’interfaçage entre la méthode des éléments discrets (DEM) employée pour décrire l’écoulement dans l’alimentation et la méthode des éléments finis (FEM) utilisée pour le compactage entre les rouleaux est développée. Enfin, pour une modélisation de compactage de rouleaux plus réaliste, prenant en compte la variation de l’entrefer entre les rouleaux, une nouvelle approche de couplage Euler-Lagrange est proposée. Les résultats de simulations par éléments finis montrent clairement l’effet des différents paramètres du procédé sur les distributions de pression et de densité dans la zone de compactage. En outre, les résultats montrent que l'utilisation de plaques de confinement de la poudre entre les rouleaux, développe une distribution de pression et de densité non homogène dans le compact, avec une densité plus élevée au centre et plus faible aux bords. D'autre part, l’utilisation de rouleaux dont l’un est surmonté d’une jante de confinement, a montré une distribution de propriétés globalement plus uniforme sur la largeur du compact avec des valeurs légèrement plus élevées aux bords qu’au centre. La méthodologie combinant les méthodes DEM & FEM montre clairement une corrélation directe entre la vitesse des particules entraînées par la vis dans la zone d’alimentation et la pression du rouleau. Tous les deux oscillent avec la même période. Cela se traduit par un compact anisotrope avec un profile de densité variant de manière sinusoïdale le long de sa largeur. Afin d'étudier la capacité du modèle à prédire les propriétés des compacts produits par compactage à rouleaux, les prédictions par simulations numériques sont comparées aux données de la littérature et validées par des mesures spécifiques
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

The expression “landslide from massive rock slope failure” (MRSF) is used to indicate large-scale landslides characterised by a variety of complex initial failure processes and unpredictable postfailure behaviour. In this context, deep-seated landslides are classified as “landslides from massive rock slope failure”. Typically, deep-seated landslides are slow mountain deformations which may involve movement along discrete shear surfaces and deep seated mass creep. The long-term development of deep-seated slope deformations creates suitable conditions for the subsequent occurrence of other slope deformations. Deep-seated landslides in mountain areas can be spatially interconnected with other types of slope deformations such as debris flows, debris slides, rock avalanches, topple, translational, rotational and compound sliding and complex type of mass movements. It is to be recognized that many aspects of large-scale landslides need be investigated in order to gain the necessary confidence in the understanding and prediction of their behaviour and in the associated risk assessment. The present thesis is to contribute to such understanding with specific reference to a number of mass movements which characterize large-scale landslides. An advanced numerical technique (FDEM) which combines finite elements with discrete elements has been applied in this thesis for improving such understanding. The open source research code, called Y2D, developed at the Queen Mary, University of London by Prof. Munjiza has been used. Considering that this code has not yet been applied to slope stability problems, a series of numerical tests have been carried out to assess its suitability to properly and efficiently simulate geomechanical problems. To this purpose standard rock failure mechanisms as well as laboratory tests have been modelled first and the results obtained have been compared with available analytical and numerical solutions. The advantages of the application of FDEM has been outlined by showing that both the simulation of failure initiation and progressive development to fragmentation of the rock mass is possible as this is deposited at the slope toe. The case study of interest for this thesis is the Beauregard massive landslide located in the Aosta Valley (Northwestern Italy). At this site the presence of an extensive deep-landslide insisting on the left abutment of an arch-gravity dam is well recognised. Based on detailed studies, the investigated area has been subdivided into zones which are characterised by different geomorphologic and geostructural features. Different landslide mechanics as well as different landslide activities upstream of the dam site have been identified and studied in detail. Such an area is thought to be at an intermediate stage of development of the deep seated landslide compared with the sector which insists on the dam. The observed failure mechanism has been ascribed to a large sliding on a compound surface. Some other failure mechanisms have been recognized, such as large flexural toppling and local block toppling instability. The final part of the thesis has been devoted to the FDEM numerical modelling of a large scale failure mechanism based on brittle behaviour of the rock mass. The aim is to apply the “total slope failure” approach through the application of FDEM. Such a technique has demonstrated the significant potential in predicting the development of possible slope instability phenomena.

Compressive residual stresses (CRS) are beneficial for enhancing the fatigue life of metal components. Shot Peening (SP) is an industrial cold working process that is applied to induce a field of CRS and modify the mechanical properties of the metal component. The SP process involves impacting a surface with tiny shots with forces sufficient to create plastic deformation. The process is governed by a number of important parameters such as the shot size, angle of attack, initial velocity, mass flow rate and the distance from the shot nozzle to the surface being peened. The relationship between the optimal peening outcome, particularly the residual stress distribution of the treated surface, and the peening parameters is still unknown and needs to be investigated further. Manufacturers are interested in producing a uniform peening process for complex geometries which optimises the SP parameters. Modelling the process is complex as it involves the interaction of a metallic surface with a large number of shots of very small diameter. Conventionally, such problems are solved using finite element software to predict stresses and strains of a single shot impact then applying superposition. At the moment there are no Finite Element Method (FEM) modelling solutions involving more than tens of shots. The number of shots and elements required for such a modelling process made the approach unfeasible prior to the work described herein. The objective of this work is to develop an appropriate numerical modelling approach that can better simulate the real SP process. The model will be provided by combining Discrete Element Method (DEM) with FEM. The DEM is employed to get a distribution of impact velocities over space and time which are then implemented into a FEM analysis. A discrete element model with randomly distributed steel shots bombarding a steel component at various velocities has been developed as benchmark example. With this model the SP shot - shot interaction, the shot - target interaction, the surface coverage, angle of impingement, shot size, impact velocity and the overall shot flow can be parametrically studied in details and with little computational effort. The novel approach also proposes a new method to dynamically change the coefficient of restitution for repeated impacts during the simulation and predicts the CRS more effectively. The effects of SP on different materials of relevance to gas turbine engine components will be investigated in order to improve the understanding of the interaction between the shots and the targeted material. Initially, an uncoupled analysis was peforned, in order to assess the capabilities of the two modelling systems, DEM and FEM, to delivery an improved solutuion when combining two commercially available codes. This parametric analysis is performed using the state-of-the-art Discrete Element (DE) application EDEM. In the subsequent part of this work, a dynamic Finite Element (FE) application Abaqus will be used to investigate single shot impacts and to obtain the residual stress distribution. This gives us a prescribed residual stress distribution and peening coverage. A Combined DEM/FEM tool (DEST) is proposed that eliminates any manual pre-processing required for linking/coupling, eliminating the use of two different applications and provide an integrated solution for the simulation of the Shot Peening process. In the subsequent chapter, the implementation of essential tools for the enchanced modelling of Shot Peening process functionalities, such as the nozzle, bounding box, coverage and intensity is described. A number of computational improvements are also implemented to reduce the computation time. The existing binary search is enhanced to self-balancing search tree and further improved to allow insertion and deletion of elements. A bounding box feature which removes shots that move out of the domain during the course of the simulation is also implemented. Experiments featuring single shot impacts are performed to gain better understanding the deformation process in the target material subjected to impact conditions to those occurring in the production peening. The single shot impacts are experimentally examined using SEM and EBSD. During final chapter, case studies are performed to compare the results of the simulations with large-scale experimental work. The coverage of peening of single and multiple nozzles with different angle of impingements are assessed. Finally, possible directions for further research concerning the accurate quantification of material responses to SP are identified in the report.

This thesis focuses on the development and implementation of an advanced numerical model to investigate complex fluid flow behaviour through novel metal foam heat exchangers used in various industrial applications such as computer heat sinks and air-conditioners. The developed numerical model permits engineers to better optimize heat exchanger designs. Moreover, the project delves into heat exchanger fouling which is a multifaceted issue in the industry. In this regard, a non-toxic and cost-effective anti-fouling heat exchanger fouling is proposed.

[ES] El principal objetivo de la presente tesis es el desarrollo de una completa metodología para el modelado numérico del UHPFRC desde el material hasta el elemento estructural. Se pretende contribuir al avance del conocimiento del comportamiento mecánico del UHPFRC obteniendo como resultado un procedimiento para la modelización numérica que permita el modelado y diseño estructural que permitiría hacer que este material fuera competitivo para ser utilizado en el mercado de la construcción. En la metodología de modelado propuesta, se considera un comportamiento constitutivo del UHPFRC optimizado por medio de un procedimiento directo y fiable con el que se aprovechan las ventajas del material, resultando en un diseño estructural eficiente desde el punto de vista mecánico y económico. ¿Es necesario producir SH-UHPFRC para conseguir grandes propiedades mecánicas? ¿Es posible generar SS-UHPFRC de manera que queden reducidos los costos iniciales y se mantengan unas propiedades mecánicas y de durabilidad competitivas que comporten un diseño estructural efectivo? El desarrollo de UHPFRC con bajo endurecimiento por deformación y de SS-UHPFRC puede reducir sus propiedades mecánicas, pero si son adecuadamente estudiadas y controladas, éstos podrían ser optimizados. La tesis aborda algunas de estas cuestiones a través del estudio del comportamiento a tracción que va desde SH-UHPFRC hasta SS-UHPFRC. Se pretende llevar a cabo una propuesta de procedimiento fiable para caracterizar el comportamiento constitutivo a tracción y definir un modelo numérico de elementos finitos fiable para modelar con precisión la respuesta de probetas y elementos estructurales armados de UHPFRC. Para definir el procedimiento directo para caracterizar a tracción tanto SH-UHPFRC como SS-UHPFRC, se ha llevado a cabo una campaña experimental y numérica en la que se ha analizado el resultado de ensayar 227 probetas sin armadura fabricadas con UHPFRC con cantidades de fibras cortas y lisas de acero de 120-130kg/m3 y 160kg/m3, ensayadas a flexión a través del ensayo a cuatro puntos (4PBT). El desarrollo y la validación de dicho proceso se respaldan mediante un modelo no lineal de elementos finitos (NLFEM) fiable. La validación numérica llevada a cabo ha sido decisiva para que este procedimiento sea preciso, simple y fiable. Utilizando esta campaña experimental, se ha desarrollado una aplicación predictiva para estimar los parámetros que definen el comportamiento constitutivo a tracción del UHPFRC. Esta aplicación es simple y directa y evita la posible variabilidad producida por malas interpretaciones en la aplicación del proceso. Además, se ha llevado a cabo una segunda campaña experimental constituida por vigas de UHPFRC armadas a flexión con diferentes escalas: 36 vigas cortas con 130 y 160kg/m3 de fibras y dos vigas largas. Esta campaña experimental se ha modelado con el NLFEM aquí desarrollado teniendo en cuenta efectos importantes debidos a la interacción del UHPFRC con las barras de armado. También se han modelado con el NLFEM tirantes de UHPFRC armados de una campaña experimental de otra investigación. El modelo considera efectos debidos a la retracción, al 3D y comportamiento tensión stiffening que generan resultados muy precisos cuando se comparan con los resultados experimentales. Como resultado de la presente tesis doctoral, se ha obtenido un modelo de elementos finitos capaz de modelar con precisión elementos estructurales de UHPFRC armados. Los resultados no sólo demuestran la fiabilidad del NLFEM llevado a cabo sino también la coherencia del procedimiento desarrollado para caracterizar el comportamiento constitutivo a tracción del UHPFRC para los dos casos, tanto SH-UHPFRC como SS-UHPFRC, tanto en elementos estructurales armados a flexión como en elementos estructurales armados a tracción directa. Consecuentemente se ha propuesto una metodología completa y efectiva para el modelado numérico del UHPFRC
[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

The microstructure of polycrystalline materials crucially determines their mechanical performance in engineering applications. A multi-scale modelling approach is capable of representing the microstructure and thus capturing the material performance for various resolution requirement at different scales. Besides, the application of multi-scale modelling effectively reduces expense and improves efficiency of computations without loss of accuracy at sensitive zones. A method of concurrent coupling of planar discrete dislocation plasticity (DDP) and a crystal plasticity finite element (CPFE) method was devised for simulating plastic deformation in large polycrystals with discrete dislocation resolution in a single grain or cluster of grains for computational efficiency; computation time using the coupling method can be reduced by an order of magnitude compared to DDP. The method is based on an iterative scheme initiated by a sub-model calculation, which ensures displacement and traction compatibility at all nodes at the interface between the DDP and CPFE domains. The proposed coupling approach is demonstrated using two plane strain problems: (i) uniaxial tension of a bi-crystal film and (ii) indentation of a thin film on a substrate. The latter demonstrated that the rigid substrate assumption used in earlier discrete dislocation plasticity studies is inadequate for indentation depths that are large compared to the film thickness, i.e. the effect of the polycrystalline plastic substrate modelled using CPFE becomes important. The coupling method can be used to study a wider range of indentation depths than previously possible using DDP alone, without sacrificing the indentation size effect regime captured by DDP. A comprehensive indentation pressure formula has been developed by applying the proposed multi-scale modelling approach on a polycrystalline coating system. Planar nano-sliding and fretting calculations have been performed on thin films modelling by CPFE and DDP at different scales. Results of CPFE simulations provide an understanding of the role of microstructure on the plasticity and crack initiation during a contact problem. Beside, a new DDP computational framework has been proposed for a nano-fretting problem which is able to capture the contact size effect, simulate the dislocation evolution and predict the surface profile variation of thin films. Calculations of DDP simulations potentially provide CPFE simulations with fatigue parameters that is of more physical significance. The method is general and can be applied to any problem where finer resolution of dislocation mediated plasticity is required to study the mechanical response of polycrystalline materials, e.g. to capture size effects locally within a larger elastic/plastic boundary value problem. Also, the model described here will provide further opportunities for directly coupled, three-tiered multi-scale models compromising an overall macroscopic continua having embedded crystal plasticity and discrete dislocation plasticity models, respectively, as the length scale decreases in the area of interest. Finally, the methodology of the proposed coupling method will shed light on archiving a general compatibility of sub-regions and thus benefit other researchers who are working on coupling methods among other scales.

La mauvaise qualité de la couche de fondation est un défi important dans la construction de routes non revêtues. Les géosynthétiques (GSY) sont des solutions innovantes développés à partir des années 70. Selon le type de GSY utilisé, ils peuvent assurer un ou plusieurs rôles, notamment la séparation, le renforcement par les effets membrane et la stabilisation par l'imbrication des grains de sol dans les ouverture de la géogrille et/ou le frottement à l'interface sol-GSY. Il existe dans la littérature peu de méthodes de dimensionnement pour quantifier ces mécanismes, et elles présentent des limites en raison de leur calibration sur des paramètres spécifiques aux GSY et au sol utilisé et, parfois, dans des conditions de charge statique plutôt que cyclique. La complexité des mécanismes et le nombre importants de paramètres qui interviennent dans leur mise en place requirent une analyse plus poussée dans ce domaine.Pour répondre à ce problème persistant, une série d'études expérimentales et numériques a été menée. Le volet expérimental a étudié la performance du renforcement sous des charges cycliques verticales et de circulation en testant deux GTX tissés avec deux rigidités de traction différentes et deux épaisseurs de plateformes granulaires. En parallèle à l'expérimentation, un modèle numérique couplant couplant la méthode des éléments discrets et la méthode des éléments finis (à l'aide du logiciel SDEC) a été utilisé. Ce modèle visait à mettre en évidence l'impact du GSY et des paramètres du sol sur le rôle du renforcement et à fournir des données sur des phénomènes difficiles à mesurer expérimentalement.Les plots expérimentaux sont formés d'une couche de sol de fondation avec un CBR d'environ 1 %, recouverte par une plateforme granulaire compactée d'une épaisseur de 300 mm ou 500 mm. Le GTX est placé à l'interface entre la couche de fondation et la couche de base. Les résultats ont montré que, sous des charges verticales cycliques, le GTX n’apportaient pas de gain d’efficacité des plateformes de 500 mm d’épaisseur. Pour une plateforme de 300 mm d’épaisseur, les deux GTXs ont réduit de manière significative le tassement par rapport à une plateforme non renforcée de la même épaisseur (300 mm) et à une plateforme plus épaisse (500 mm). L'amélioration la plus importante a été observée avec le GTX le plus rigide. Trois essais ont été réalisés avec une charge de trafic appliquée par le Simulateur Accélérateur de Trafic (SAT). Il a été démontré que la charge de circulation exerçait une plus grande déformation dans la plateforme par rapport à la charge verticale, mais il était difficile d'arriver à une conclusion définitive sur la comparaison entre une plateforme renforcée et non renforcée.Dans le modèle numérique, une loi de comportement (1D) a été intégrée prenant en compte les variations du module de réaction du sol pendant les phases de chargement et de déchargement ainsi qu’avec les cycles, et décrivant la transition d'un comportement plastique à un comportement quasi-élastique du sol compressible. Par ailleurs, la plateforme granulaire purement frottant a montré son incapacité à supporter la charge cyclique verticale appliquée sur une plaque circulaire placée au centre du modèle. Cette limitation « numérique » a nécessité l’ajout d’une cohésion entre les particules de sol. Une fois calibré, le modèle numérique s'est avéré capable de reproduire le comportement des plates-formes renforcées par GSYs sur sol mou au cours du premier cycle et au fur et à mesure des cycles. Initialement, les efforts de frottement dépassaient l'effet membrane, mais à mesure que la déflexion augmentait avec les cycles, l'effet membrane devenait plus important. En plus, une étude paramétrique sur la compressibilité de la couche de fondation, la rigidité du GSY, le frottement à l’interface sol granulaire-GTX et les paramètres mécaniques de la couche a permis de mettre en évidence l’influence de ces différents paramètres sur les mécanismes
Poor subgrade quality is a pervasive challenge in the construction of unpaved roads. Geosynthetics (GSYs) have emerged as innovative solutions since their initial usage in the late 1970s. Depending on the type of GSY employed, they can fulfil one or several roles, including separation, reinforcement by tensioned membrane effects, and stabilization by interlocking and/or friction at the soil-GSY interface. Few design methods exist in the literature to quantify these mechanisms, but they have limitations due to their calibration on specific GSY and soil parameters and, at times, under static rather than cyclic loading conditions. The various factors and parameters that influence the dominant mechanism and its corresponding contribution to platform enhancement underscore the necessity for further exploration in this area.To address this persistent issue, a series of experimental and numerical studies were conducted. The experimental part studied the performance of reinforcement under cyclic vertical and traffic loadings using two woven geotextiles (GTXs) with two different tensile stiffness and two base course thicknesses. Additionally, alongside the experimentation, a numerical model coupling the discrete element method and the finite element method (using Software-Defined Edge Computing) was employed. This model aimed to showcase the impact of GSY and soil parameters on reinforcement performance and provide insights into aspects challenging to measure through experimentation.The tested unpaved road sections are composed of a subgrade layer with a CBR around 1% covered by a compacted base course layer with thickness of 300 mm or 500 mm. The GTXs are placed at the interface between the subgrade and the base course layers. The results showed that the 500 mm base course reinforced platform did not exhibit reinforcement effects under vertical cyclic loading. However, the use of a 300 mm base course with GTX significantly reduced settlement compared to an unreinforced base course of the same thickness (300 mm) and to the thicker base course (500 mm). The most important improvement was observed with the highest-stiffness GTX. Moreover, three tests were performed under traffic loading applying by the Simulator Accelerator of Traffic (SAT). It was shown that traffic loading exerted greater deformation in the base course layer compared to vertical loading, but definitive conclusion can hardly be reached about the comparison between reinforced and unreinforced platform.In the numerical model, a behavioural law (1D) was integrated, considering the variation of the soil reaction modulus during loading and unloading phases and with cycles, and describing the transition of the soil from plastic to quasi-elastic behavior. In addition, the purely frictional base course layer revealed its incapacity to sustain the loading applied in the experimental. This inherent limitation prompted the incorporation of adhesion between soil particles to rectify this shortcoming in load-bearing capacity. Once calibrated the numerical model proved capable of accurately replicating the behavior of GTX-reinforced platforms in the first cycle and with cycles. It facilitated a quantification of the GTX friction effort and GTX tension effort with cycles. Initially, frictional forces outweighed the tensioned membrane effect, but as deflection increased with cycles, the latter became more prominent. This dynamic highlighted a diminishing dominance of the soil confinement mechanism with cycles, giving way to the increasing significance of the membrane effect. Furthermore, the subgrade softness, the GTX rigidity, the mattress-GTX interface parameters and the base course mechanical parameters influenced the behavior of the model

The objective of this thesis is the establishment of an objective comparison between the Finite Element Method and the Discrete Element Method when modelling the mechanical behaviour of the continuum, both for quasi-static and dynamic response. These two very different approaches to the same problem have increasingly gained popularity during the last years, becoming the distinction between the fields of application of each method each time more difficult. This research aims the assessment of the accuracy of the Discrete Element Method to solve problems that traditionally belong to the field of the Finite Element Method. This comparison has the ultimate purpose of determining the applicability of the first method to problems that involve a first stage when the material is elastic or elasto-plastic, followed by a second stage where actual physical separation of portions of the material occurs. The first part of this work comprises a review of the theoretical background and numerical techniques used to solve continuum mechanics problems using the Finite Element Method, both for quasi-static and dynamic loading. A description of the Discrete Element Method, encompassing its insights and the numerical strategies involved in its implementation constitute the second part of this work. The establishment of a methodology to model the continua using a Discrete Element Method based approach, namely the development of techniques to simulate elasto-plastic behaviour and crack path modelling, accompanied by illustrative benchmark examples, are the main pylons over which the third part of this research lays.

Brittle fracture is a large problem for steel structures in the arctic region. It is thus important to qualify materials and welds so they do not behave in a brittle manner. Since fracture testing of the heat affected zone (HAZ) around a weld gives a lot of scatter, doing weld simulated testing is proposed as an alternative method. In this thesis cracks in weld simulated HAZ specimens are compared to cracks in real welds, by use of finite element simulations. A weld simulated specimen is usually more brittle than a real weld. The goal of this thesis is thus to find a general rule for how much more brittle a weld simulated test specimen is, compared to a real weld on a structure. It would then be possible to establish how brittle a real weld is based on the result from the weld simulated testing. As a fracture criterion the Weibull stress is used, which is a statistical criterion. Crack tip opening displacement (CTOD) is used as a measure on how brittle a specimen is. To compare weld simulated specimens with real welds, two 2D modified boundary layer (MBL) models are used. One homogeneous model to represent weld simulated specimens, and one with three different materials to represent a real weld. The three materials in the weld model are base material, welded material and heat affected zone. On the two models a large parameter study is performed. The variables investigated are: - Position of the crack relative to the HAZ. - Size of the HAZ. - Geometry constraint. - Mismatch in WM. - Mismatch in HAZ. - Hardening. - The Weibull exponent m. There have also been made 3D models to investigate the size effect on the weld simulated specimen. This is because a weld simulated specimen is limited to a cross-section of $10$x$10$~mm. The parameter study concludes that it is mainly the size of the HAZ, the yield stress mismatch and the geometry constraint, that make weld simulated specimens more brittle than welds. The 3D simulations are however concluding that the geometry constraint effect can not be included, due to the size of the small test specimen. Based on these results a general relationship is proposed between the critical CTOD for a weld simulated specimen, and the critical CTOD for a real weld. There are three requirements for this relationship to be valid: - At least 10% overmatch in HAZ compared to base material. - No more than 10% undermatch in HAZ compared to welded material. - Maximal brittle HAZ thickness of 0.5 mm.

Discrete element modelling has been used to capture the essential mechanical features of railway ballast and gain a better understanding of the mechanical behaviour and mechanisms of degradation under monotonic and cyclic loading. A simple procedure has been developed to generate clumps which resemble real ballast particles. The influence of clump shape on the heterogeneous stresses within an aggregate was investigated in box test simulations. More angular clumps lead to greater homogeneity and the interlocking provides a much more realistic load-deformation response. A simple two-ball clump was used with two additional small balls (asperities) bonded at the surface, to represent a single particle; it is shown that particle abrasion gives the correct settlement response. A clump formed from ten balls in a tetrahedral shape was used in monotonic and cyclic triaxial test simulations and found to produce the correct response. The interlocking and breaking of very small asperities which find their way into the voids and carry no load was modelled using weak parallel bonds. The interlocking and fracture of larger asperities was modelled by bonding eight small balls to the ten-ball clump. Monotonic tests were performed on triaxial samples under different confining pressures and the results compared with existing experimental data. Tests were also simulated using uncrushable clumps to highlight the important role of asperity abrasion. Cyclic triaxial tests were then simulated on the same aggregates under a range of stress conditions and the results compared to existing experimental data for the same simulated ballast. The clumps are able to capture the behaviour of ballast under different conditions, and asperity abrasion plays an important role in governing strength and volumetric strain under monotonic loading, and on permanent strains under cyclic loading. The contribution of this thesis is therefore to show that it is possible to model a real granular material under static and cyclic conditions, providing much micro mechanical insight.

This thesis presents a new bonded particle model that accurately predicts the wideranging behaviour of cementitious materials. There is an increasing use of the Discrete Element Method (DEM) to study the behaviour of cementitious materials such as concrete and rock; the chief advantage of the DEM over continuum-based techniques is that it does not predetermine where cracking and fragmentation initiate and propagate, since the system is naturally discontinuous. The DEM’s ability to produce realistic representations of cementitious materials depends largely on the implementation of an inter-particle bonded-contact model. A new bonded-contact model is proposed, based on the Timoshenko beam theory which considers axial, shear and bending behaviour of inter-particle bonds. The developed model was implemented in the commercial EDEM code, in which a thorough verification procedure was conducted. A full parametric study then considered the uni-axial loading of a concrete cylinder; the influence of the input parameters on the bulk response was used to produce a calibrated model that has been shown to be capable of producing realistic predictions of a wide range of behaviour seen in cementitious materials. The model provides useful insights into the microscopic phenomena that result in the bulk loading responses observed for cementitious materials such as concrete. The new model was used to simulate the loading of a number of deformable structural elements including beams, frames, plates and rings; the numerical results produced by the model provided a close match to theoretical solutions.

This work presents the study of a three-dimensional (3D) simulation of the concrete behaviour in a uni-axial compressive test and flexural test using discrete element modelling (DEM). The proposed numerical models are namely, unreinforced cylindrical concrete under a uni-axial compressive test, unreinforced concrete beam under three-point flexural test and lastly, steel reinforced concrete beam under four-point flexural test. Those models were built up with fish programming language and python programming language (see Appendix A1 for the code created) and run into a computer program namely Particle flow code (PFC 3D). The main aim of this paper is to validate those numerical models developed and to study the cracking initiation and failure process in order to understand the fracture behaviour of concrete. The particles were distributed using an algorithm that is based on the sieve test analysis. The parameters were set up in order to validate the numerical model with the experimental result. It was observed that all the three models developed show a strong correlation with the laboratory experiment in term of stress-strain response, load-displacement response, crack pattern and macroscopic cracks development. Once, the bond between the spheres is broken, it leads to the formation of microscopic cracks which is not visible in laboratory experiment. DEM can help to identify which part is more prone to the evolution of microscopic cracks to macroscopic cracks under the discrete fracture network. In addition to, the rosette plot allows identifying the orientation that leads to a significant amount of micro cracks which is essential for designing structures. From the observation recorded in this research, it was observed that DEM is capable to reproduce concrete behaviour both quantitatively and qualitatively. It is also possible to measure the strain energy stored in the linear contact bond and parallel bond. At yield point which corresponds to the maximum amount of microcracks recorded, that strain energy is released in the form of kinetic energy, frictional slip energy, energy of dashpot, local damping. This can be extended further to compute fracture energy in the future work. Hence, it can be concluded DEM can be used to study the heterogeneous nature of concrete and as well as randomness nature of the fracturing of concrete structure.

In contrast to concrete, masonry is a complex inhomogenous material, which exhibits distinct directional properties due to the presence of mortar joints. In the past, both finite element and discrete element techniques have been used for modelling of masonry structures. However, no comparison of these two different approaches has been made. In this study, to achieve a fundamental insight into the behaviour of masonry structures, a series of numerical analyses have been carried out using Finite and Discrete Element methods for structures such as shear walls with/out opening, masonry panel under point load, and masonry arches. In Discrete Element analyses, bricks were modelled as conventional continuum elements, while an interface contact law (instead of mortar joints) was used to capture masonry failure mechanisms in the 2D plane-strain analyses. The contact law included softening in tension, shear and compression modes. In Finite Element modelling of the same structures, separate continuum elements were used for both constituents, i.e. the brick and mortar. The results were compared with experimental data. Both methods were able to reproduce the complete deformation pattern of the structures up to and beyond the peak until total degradation of strength, without major numerical difficulties. Parametric studies of the above problems have also been carried out to demonstrate the crucial role of some of the parameters. Comparative studies using the Finite Element and Discrete Element methods have shown that collapse load as well as mechanisms of failure are significantly influenced by the choice of interface parameters used in the Discrete Element method. These parameters are also difficult to determine from experiments. On the other hand, Finite Element analyses indicate lesser influence of parameters of the constituents and no anomalies arise in their choice from experimental data.

Aspects of constitutive modelling and numerical prediction of failure in finitely straining ductile metals are investigated in this thesis. Attention is focused on the construction of a framework for prediction of failure. The development of a model for finite strain elasto-(visco)plastic damage; a low order finite element for the numerical treatment of incompressibility and an adaptive mesh refinement strategy for this class of problems, constitute the building blocks of the overall approach. Emphasis is given to the efficient numerical simulation of the proposed theories in large scale problems. The characterisation of material response has to account for the interaction between the different phenomena that precede fracture initiation. The derivation of constitutive models is addressed within Continuum Damage Mechanics theory. Particular, the effect of micro-crack closure which may dramatically decrease the rate of damage growth under compression is emphasised. With regard to the computational treatment of incompressibility, a new technique which allows the use of simplex finite elements in the large strain analysis of nearly incompressible solids is proposed. It is based on relaxation of the excessive volumetric constrain by the enforcement of near-incompressibility over a patch of elements. The new elements are implemented within an implicit quasi-static and an explicit transient dynamic finite element environment. The algorithms for numerical integration of the corresponding path dependent constitutive equations are discussed in detail. The strategy for numerical simulation of the associated incremental boundary value problems relies on fully implicit and explicit displacement based finite element procedures.

The aim of this thesis is to determine the ground deformation and stress distribution around highway tunnels at various stages of excavation and for several support conditions using finite element modelling techniques. When ground is excavated and material removed the subsequent redistribution of stress in the remaining surrounding material needs to be treated by one of three methods. These are the gravity difference method, the stress reversal technique and the relaxation approach. The first two methods were chosen for the simulation of excavation in this study. The tunnel data are in the form of the dimensions of the tunnel, heights of the rock layers, details of the shotcrete lining and tunnel support systems. A pre-processing program was written to transform this information into a finite element mesh in a format suitable for use by PAFEC-FE software. This enables different tunnel models and meshes to be produced with minimum error and time. The lack of adequate post-processing facilities available in PAFEC-FE dictated that computer programs needed to be written in order to reformat the textual output files and process the mesh stress and displacement outputs for graphical display using UNIRAS. In this way repeated use could be made of PAFEC-FE without time-consuming and error-prone manual retrieval of data. The tunnels were modelled at various stages of excavation and with such support provided at those stages as to allow the computed displacements to be compared with measurements made on highway tunnels in Turkey. The stresses generated in the tunnel supports and surrounding ground were also calculated to enable the possibility of damage or failure of the support structure or ground to be assessed and the selection of an optimal support system. Insertion of a support system into the model has a marginal effect on the development of rock strength around an excavation boundary.

The ability to predict the wave climate has a great impact on a wide range of sectors, including coastal and offshore engineering, marine renewable energy and shipping. The state of the art in wave prediction is called spectral wave modelling and is based on a phase-averaged, spectral description of the sea-surface elevation. The governing equation, called the action balance equation, is five-dimensional and describes the generation, propagation and evolution of action density in geographic space, spectral space and time. Due to the multidimensional nature of the equation the feasible resolutions are restricted by the computational costs. The aim of this work is to propose schemes which can increase the range of possible resolutions in spectral wave modelling, with the use of adaptivity in space and angle. Thus, this work focuses on the development of an unstructured, adaptive finite element spectral wave model (Fluidity-SW). A sub-grid scale model for the spatial discretisation is used, which retains the stability of discontinuous systems, with continuous degrees of freedom. Then, a new framework for angular adaptivity is developed, with results in dynamic angular and spatial anisotropy of the angular mesh. Finally a spatially h−adaptive scheme is implemented, which can dynamically treat the spatial gradients of the solution fields. The resulting framework is thoroughly verified and validated in a wide range of test cases and realistic scenarios, against analytical solutions, wave measurements and the results obtained with the widely used SWAN model. Thus, the overall ability of the code to simulate surface gravity wind-waves in fixed and adaptive spatial and angular meshes is demonstrated.

Flood inundation phenomena typically occur over reach lengths of 5- 30 km and incorporate a number of complex flow mechanisms. These include a momentum transfer between the main channel and floodplain and turbulent mixing caused by the delivery of water to the floodplain from the channela nd its subsequenrte turn. However, currently available one dimensional schemes applicable at scales appropriate to floodplain inundation processes cannot effectively simulate such processes. This is due to both an incomplete description of the flow physics and a failure to treat floodplain areas in realistic fashion. More complex two and three dimensional models, which have these capabilities, have only been applied over very short reach lengths (c. 0.5 -2 km) and rarely to compound meandering channels. This thesis reports on the further development of a generalized two dimensional, finite element code (RMA-2) to meet this research need. This is achieved via a series of modifications to the numerical model and to the physical representation by finite elements that enable river channel/floodplain flow at the long reach scale to be effectively simulated. Evaluationo f the enhancedR MA-2 schemef ollows a three stages trategy. Firstly, the assumptions underlying the scheme are examined to identify possible inconsistencies. Secondly, tests are undertaken to assess whether the specified physical model has been correctly transferred into computer code. This is achieved via sensitivity analysis, examination of numerical stability issues and investigation of model response to abnormal parameterization. Thirdly, model predictions of flow field information are compared to observed field data in the context of an application of the enhanced model to an 11 km reach of the River Culm, Devon, UK. Results from this evaluation process indicate that the enhanced RMA-2 model is capable of simulating main channel/floodplain momentum transfer and the two dimensionale ffects associatedw ith compoundm eanderingc hannelsa t this scale. Model simulations compare favourably to field data, both for specific cross sections and over the entire mesh. Finally, extension of this core modelling capability is begun via the development of two model application scenarios. These demonstrate the likely utility of the enhanceds chemef or the assessmenotf flood risk and the investigationo f sediment depositionp rocessesin floodplain systems.

This thesis investigates the use of Discrete Element Modelling (DEM) to simulate the behaviour of a highly idealised bituminous mixture under uniaxial and triaxial compressive creep tests. The idealised mixture comprises single-sized spherical (sand-sized) particles mixed with bitumen and was chosen so that the packing characteristics are known (dense random packing) and the behaviour of the mixture will e dominated by the bitumen and complex aggregate interlock effects will be minimised. In this type of approach the effect of the bitumen is represented as shear and normal contact stiffnesses. A numerical sample preparation procedure has been developed to ensure that the final specimen is isotropic and has the correct volumetrics. Elastic contact properties have been used to investigate the effect of the shear and normal contact stiffnesses on bulk material properties. The bulk modulus was found to be linearly dependent on the normal contact stiffness and independent of the shear contact stiffness. Poisson's ratio was found to be dependent on only the ratio of the shear contact stiffness to the normal contact stiffness. An elastic contact has been assumed for the compressive normal contact stiffness and a viscoelastic contact for shear and tensile normal contact stiffness to represent the contact behaviour in idealised mixture. The idealised mixture is found to dilate when the ratio of compressive to tensile contact stiffness increases as a function of loading time. Uniaxial and triaxial viscoelastic simulations have been performed to investigate the effect of stress ratio on the rate of dilation with shear strain for the sand asphalt. The numerical results have been validated with experimental data. The geometric factors that influence asphalt dilation are investigated. The level of dilation was found to be dominated by the proportion of frictional contacts in the sample. Simulations have been performed to investigate the effect of particle shape on asphalt dilation. Greater dilation was found in the sample with clumps under loading.

This document describes research into the development of software to allow the visualisation of finite and discrete element simulations within a virtual environment. The particular requirements of rendering deep level mining simulations are given precedence, but the resulting techniques apply in general to all finite element problems. In particular, a new rendering method based upon incremental frame updating is presented, and this provides the basis for two new rendering optimisations: Priority Ordering predicts the visibility of objects within the scene from the current viewpoint. This mapping of objects to a scalar value allows the incremental rendering step to process geometry in order such that the objects contributing the largest amount to the scene quality are rendered first. This is shown to provide an improvement in the quality of the rendered image as the incremental update step proceeds, when compared to conventional algorithms; Z Occlusion using Priority Ordering uses the coverage information obtained from the generation of priority values to allow the lazy evaluation of Z buffer area for occlusion culling. This is shown to decrease the time taken to render an entire frame to completion where sufficient depth complexity is present to outweigh the Z buffer access overhead, and to provide little or no performance penalty where little depth complexity is present, or Z buffer access is disproportionately high. The design of a highly threaded rendering system which allows the asynchronous operation of multiple parts of the system is also documented.

Pulp lifter assembly is one of the important components at the discharge ends of grate-discharge grinding mills. It discharges grinded materials out through the discharge trunnion like a centrifugal pump running in the reverse direction to that required by a pump. Though it is widely known conventional pulp lifter design associates with drawbacks that cause inefficient discharge operation, little has been done to understand the causes of this particular happening. With the aim to better understand the effects of different pulp lifter designs on the discharge performance and also establish strategies for future design and operation of such equipment, this work is initiated.Three types of industry scaled pulp lifter designs, including two conventional designs and a new design, were comparably studied using Discrete Element Method (DEM) modeling technique. The discharge performances of these designs were evaluated against three criteria which include discharge rate, power consumption, and flow-back/carry-over. The results have shown that pulp lifter assembly with spiral designed radial arms possesses better discharge performance than that with straight radial arms. The discharge performances of three types of designs are also found to be sensitive to some specific design and operating parameters, such as number of vanes, mill rotational speed, the size of particle, and the coefficients of friction. Based on the results, five guidelines on future design and operation of pulp lifter assembly were established.
L'assemblage du releveur de pates est l'une des composantes importantes à la sortie de grille termine-décharge des broyeurs. Il décharge des matériaux broyés à travers le tourillon de la décharge comme une pompe centrifuge fonctionnant en sens inverse à celui requis par une pompe. Bien qu'il soit largement connu conventionnels associés de pâte de conception lifter avec des inconvénients qui causent opération de décharge inefficaces, peu de travaux ont été fait pour comprendre les causes de cet événement particulier. Dans le but de mieux comprendre les effets des différentes conceptions du releveur pates sur la performance de décharge et également établir des stratégies pour la conception et l'exploitation futures d'un tel équipement, ce travail est lancé.Trois types de conceptions de releveur de pates d'industrie à l'échelle ont été étudiés, y compris deux conceptions classiques et un nouveau design, à l'aide de technique de modélisation méthode des éléments discrets (MED). Les performances de décharge de ces dessins ont été évalués en fonction de trois critères, qui comprennent le taux de décharge, la consommation d'énergie, et flow-back/carry-over. Les résultats ont montré que l'assemblage de pâte-lève comprenant des bras radiaux conçus en spirale possède une meilleure performance que celle de décharge avec des bras radiaux droits. Les performances de décharge de trois types de conceptions sont également trouvés à être sensibles à certains paramètres spécifiques de conception et d'exploitation, telles que le nombre d'aubes, la vitesse de rotation moulin, la taille des particules, et les coefficients de frottement. Basé sur les résultats, cinq lignes directrices sur la conception et le fonctionnement futurs de l'assemblage pâte-lève ont été établis.

This thesis presents goal-based error measures and applies them, via appropriate metric tensors, to the adaptation of three dimensional anisotropic tetrahedral finite element meshes for a range of oceanographic modelling problems. The overall aim of this work is to produce error measures which are able to resolve the flow features of an ocean over a wide range of spatial and temporal scales simultaneously. For example, western boundary currents, the Antarctic Circumpolar Current (ACC), equatorial jets, meddies (mid-latitude eddies) and Open Ocean Deep Convection. Conventional numerical ocean models generally use static meshes. The use of dynamically-adaptive meshes has many potential advantages but needs to be guided by an error measure. Mesh quality is gauged with respect to the metric tensor which embodies the error measure, such that an ideal element has sides of unit length when measured with respect to this metric tensor. The result is meshes in which each finite element node has approximately equal (subject to certain boundary conforming constraints and the performance of the mesh optimization procedure)'error contribution. Error measures are formulated which measure the error contribution of each solution variable to an overall goal, which encompasses important features of the flow structure and is embodied in an integral form, e.g. the integral of the solution in a small region of the domain of interest. The sensitivity of the functional, taken with respect to the solution variables, is used as the basis from which error measures are derived. The error measures then act to predict those areas of the domain where resolution should be changed and lead to the solution of so-called forward and adjoint (backward) problems. Focus is given to developing relatively simple methods that refer to information readily accessible from the discretized equation sets and do not explicitly use equation residuals.

Numerical modelling of Bed Dynamics in 1-D and 2-D poblems using the Two-Step Taylor Galerkin Finite Element scheme has been proposed. It has been shown that the scheme is capable of handling the coupled system that exists between unsteady hydrodynamics and a mobile bed. Fully coupled codes have been developed with an option to semi-couple the system while maintaining numerical accuracy for both the hydrodynamics and the bed level change. The semi-coupled extension enables the modelling of the hydrodynamics and the bed level change with different time steps. Coupling is maintained at common time terminals and, or, with separate computational meshes, where coupling is achieved by means of interpolation between the meshes. The Two-Step Taylor Galerkin scheme has been verified extensively for hydraulic problems related to bed dynamics, especially the interaction of progressive waves and the development of steady state flow in channels. Treatment of the boundary condition allowing waves to leave the computational domain both for the fluid and the bed have been proposed and work well. For the hydrodynamic equations, it is also demonstrated that the boundary treatment is capable of absorbing outgoing waves while incoming waves are simultaneously prescribed. These treatments are based on an examination of the characteristics of the bed dynamic system. The results of the analysis can be used to approximate the Reimann invariant vector of the bed dynamic system and this is especially useful when the fully coupled method is applied. A Von Neumann linear stability analysis of the 1-D Taylor-Galerkin scheme for a system including a source term is presented. The anlaysis is based on the graphical interpretation of an Argand Diagram representation for the amplification factor. It is found that the presence of a strong source term may reduce the time step limit.

Photonic crystal fibre (PCF), a new kind of optical fibre, has many air-holes in their cross-section and has potential applications to new optical communication systems. The main objective of this research is the modelling of photonic crystal fibre to identify the fundamental and higher order quasi-TE and TM modes with square, ,rectangular and circular air holes in a square and hexagonal matrix, by using a rigorous full-vectorial H-field based finite element method (FEM). Besides the modal solutions of the effective indices, mode field profiles, spot sizes, modal hybridness, polarization beat length and group velocity dispersion values for equal and unequal air holes; research was carried out to optimize and design highly birefringent PCF. The variation of modal birefringence is shown through the effect of hole diameters, air hole arrangement, structural asymmetry, operating wavelength, and pitch-distance. Birefringence was enhanced by breaking the structural symmetry and this was verified by using unequal air holes. The diameter of two air holes and four air holes in the first ring was changed to break the rotational symmetry and a comparison between the two designs is made in this work. In this work, highly birefringent PCF is designed with higher operating wavelength, larger d2/A value, lower pitch length for a given structural asymmetry. It is identified that birefringence value increases rapidly when d2 is much larger than d. At lower pitch value, one of the highest birefringence values reported so far at wavelertgth of 1.55 J.Jm for an asymmetric PCF using circular air holes. A single polarization guide PCF structure is also achieved. In this study, it has been identified that for fixed d/A and d2/A value, as operating wavelength is increased, birefringence increases significantly. It can also be identified that for higher d/A values, birefringence changes rapidly with A as their corresponding cutoff condition also approaches. One important validation of this work is the existence of modal birefringence for PCF with six-fold rotational symmetry. It is shown that birefringence value of a simple PCF incorporating circular holes but of different diameters is high compared to polarization maintaining Panda or Bow-tie fibres. This research also aims to investigate the modal leakage losses of PCF, by using a semi-vectorial beam propagation method (BPM) based on the versatile FEM. The robust perfectly matched layer (PML) boundary condition has been introduced to the modal solution approach. The effects of d2/A, operating wavelength and number of air holes have been thoroughly detailed and explained. In this study, it has been identified that the confinement loss decreases significantly with the increased number of rings, lower operating wavelength and lower d2/A value. For special case, PCF with large spot-size provides higher leakage loss.

The general aim of this study is to develop a 3-D FE model for multi-point forming dies using ABAQUS software and use this to study the effect of process parameters related to tool geometry such as radius of curvature of deformed parts, pin size, elastic cushion thickness and coefficient of friction. Doubly curved parts will be investigated in this research. The material properties for two blanks were determined for use as required parameters for the simulation analysis. Finite element models of the doubly curved forming process were developed and validated for two materials: DC05 steel sheet and 5251-0 aluminium sheet. The mesh sensitivity, reliability of the numerical model, suitable blank holder force, effect of gap distance between punch and blank holder on the thickness distribution, and the comer defect were studied. A parametric study was carried to investigate the effect of certain parameters on the deviation from target shape, wrinkling, and thickness variation. A test rig for the experimental work was designed and manufactured. In parallel, experiments with the forming of doubly curved parts were conducted to validate the simulation results. The numerical analysis results were compared with the experimental results and good agreement was generally found. The methodology developed in this research could help to build a reliable numerical model to predict the common defects in sheet forming using the multi-point forming process.

The movement of cohesive sediment is of great importance in many coastal and estuarine engineering problems. Navigation channels often used to be dredged to maintain navigable depths, allowing for the effect of a harbour or wharf on the local sediment transport regime. Contaminants are readily absorbed by silt and clay particles, causing a range of water quality problems. This thesis describes the development and testing of a finite element program to model cohesive sediment transport. The program solves the coupled Navier-Stokes and scalar-transport equations along with several complex numerical algorithms for settling velocity, flocculation, non-Newtonian flow and turbulence. The program also uses h-adaptivity and unstructured mesh generation to capture important flow features. The program is benchmarked against the thermally driven cavity problem, producing results that compare well with existing solutions without any special scheme for advection dominated flow. This is possible by modelling the transient problem using h-adaptivity. The programme is also applied to realistic cohesive sediment transport problems. It predicts the formation of a hindered settling layer and uses h-adaptivity to capture sharp density interfaces. It also solves settling of dredged material onto a inclined bed and non-Newtonian flow in a race-track flume. The program produces results that compare well with experimental data. The h-adaptive finite element method is found to be a very successful in modelling the transport of cohesive sediment and its associated physical processes.

Most tyre models developed to date require a fair amount of data before an accurate representation of the tyre can be obtained. This study entails the development of a simplified, yet accurate, non-linear Finite Element (FE) model of an “off-road” tyre to study the behaviour of the tyre due to radial loading conditions. The study aims to develop a FE tyre model that can solve fast and be accurate enough to be used in multibody dynamic vehicle simulations. A model that is less complex than conventional detailed FE models is developed. The work explores the use of superimposed finite elements to model the varying stiffness in the respective orthogonal directions of the sidewall and tread of the tyre. Non-linear elements defined by Neo-Hookean or Ogden models and elements with different linear orthogonal stiffnesses are superimposed onto each other to simulate the global material properties of the tread and the sidewall of the tyre investigated. The geometry of the tyre studied was measured experimentally using laser displacement transducers and digital image correlation techniques. Material properties of segments of the tyre were obtained by performing tensile tests on samples. Since the rubber slipped against the clamps during the experiment, deformation of the segments was also measured using digital image correlation. These geometrical and material properties were used as input to develop a finite element model of an “off-road” tyre. Measurements were conducted using laser displacement transducers, load cells mounted to actuators, etc. to obtain accurate sidewall deformation profiles and global radial load vs. displacement curves for different radial loading conditions. The data obtained from the results was used to validate the tyre model developed. Numerous analyses are performed with different combinations of moduli of elasticity in the respective orthogonal directions of the sidewall stiffness and the tread to investigate its influence on the global behaviour of the tyre model. The main focus of the project was to develop a tyre model from data obtained from laser and photogrammetry measurements in a laboratory that accurately represents tyre behaviour due to radial forces. A finite element model that can simulate the effect of radial forced and obstacles on a tyre was developed. The use of two subsets of elements, superimposed onto each other to simulate global material properties of the rubbers, steel wires, polyester and nylon threads, was investigated. The combination of material properties that gave the best fit for all the load cases investigated were determined. The finite element model correlated well with the load vs. displacement graphs and sidewall displacement profiles determined experimentally. The solving time is still fairly high and is still not quite suitable for real-time dynamic simulation. However, it solves faster than more complex tyre models where details of steel wires, etc. are included in the model. For future studies it is recommended that different element types be investigated in the tyre model. The study proves that equivalent material properties can be used to simulate the composite properties of the materials in tyres. Most tyres can be divided into a few regions that each has its own material structure right through the region. These regions can be characterized by simple tests and the input can be used as a first estimation of the tyre’s material properties for the model. Accurate validation criteria should be used to validate the tyre model if time does not allow for excessive testing of the material properties of all the rubber, steel wires, polyester threads, etc. Geometric displacement data at various loading conditions can be used for validation of the tyre model. The model developed can be used to investigate the effect of different stiffnesses and other material changes in the sidewall or tread of a tyre. Useful insight can be obtained from the finite element model developed for dynamic simulation where the force vs. global displacement data is important.
Dissertation (MEng)--University of Pretoria, 2014.
tm2015
Mechanical and Aeronautical Engineering
MEng
Unrestricted

Crystallographic texture and its evolution are known to be major sources of anisotropy in polycrystalline metals. Highly simplified phenomenological models cannot usually provide reliable predictions of the materials anisotropy under complex deformation paths, and lack the fidelity needed to optimize the microstructure and mechanical properties during the production process. On the other hand, physics-based models such as crystal plasticity theories have demonstrated remarkable success in predicting the anisotropic mechanical response in polycrystalline metals and the evolution of underlying texture in finite plastic deformation. However, the integration of crystal plasticity models with finite element (FE) simulations tools (called CPFEM) is extremely computationally expensive, and has not been adopted broadly by the advanced materials development community. The current dissertation has mainly focused on addressing the challenges associated with integrating the recently developed spectral database approach with a commercial FE tool to permit computationally efficient simulations of heterogeneous deformations using crystal plasticity theories. More specifically, the spectral database approach to crystal plasticity solutions was successfully integrated with the implicit version of the FE package ABAQUS through a user materials subroutine, UMAT, to conduct more efficient CPFEM simulations on both fcc and bcc polycrystalline materials. It is observed that implementing the crystal plasticity spectral database in a FE code produced excellent predictions similar to the classical CPFEM, but at a significantly faster computational speed. Furthermore, an important application of the CPFEM for the extraction of crystal level plasticity parameters in multiphase materials has been demonstrated in this dissertation. More specifically, CPFEM along with a recently developed data analysis approach for spherical nanoindentation and Orientation Imaging Microscopy (OIM) have been used to extract the critical resolved shear stress of the ferrite phase in dual phase steels. This new methodology offers a novel efficient tool for the extraction of crystal level hardening parameters in any single or multiphase materials.

This works encompasses a broad review of the basic aspects of the Discrete Element Method for its application to general granular material handling problems with special emphasis on the topics of particle-structure interaction and the modelling of cohesive materials. On the one hand, a special contact detection algorithm has been developed for the case of spherical particles representing the granular media in contact with the finite elements that discretize the surface of rigid structures. The method, named Double Hierarchy Method, improves the existing state of the art in the field by solving the problems that non-smooth contact regions and multi contact situations present. This topic is later extended to the contact with deformable structures by means of a coupled DE-FE method. To do so, a special procedure is described aiming to consistently transfer the contact forces, which are first calculated on the particles, to the nodes of the FE representing the solids or structures. On the other hand, a model developed by Oñate et al. for the modelling of cohesive materials with the DEM is numerically analysed to draw some conclusions about its capabilities and limitations. In parallel to the theoretical developments, one of the objectives of the thesis is to provide the industrial partner of the doctoral programme, CITECHSA, a computer software called DEMPack (www.cimne.com/dem/) that can apply the coupled DE-FE procedure to real engineering projects. One of the remarkable applications of the developments in the framework of the thesis has been a project with the company Weatherford Ltd. involving the simulation of concrete-like material testing. The thesis is framed within the first graduation (2012-2013) of the Industrial Doctorate program of the Generalitat de Catalunya. The thesis proposal comes out from the agreement between the company CITECHSA and the research centre CIMNE from the Polytechnical University of Catalonia (UPC).
Aquest treball comprèn una àmplia revisió dels aspectes bàsics del Mètode dels Elements Discrets (DEM) per a la seva aplicació genèrica en problemes que involucren la manipulació i transport de material granular posant èmfasi en els temes de la interacció partícula-estructura i la simulació de materials cohesius. Per una banda, s'ha desenvolupat un algoritme especialitzat en la detecció de contactes entre partícules esfèriques que representen el medi granular i els elements finits que conformen una malla de superfície en el modelatge d'estructures rígides. El mètode, anomenat "Double Hierarchy Method", suposa una millora en l'estat de l'art existent al solucionar els problemes que deriven del contacte en regions de transició no suau i en casos amb múltiples contactes. Aquest tema és posteriorment estès al contacte amb estructures deformables per mitjà de l'acoblament entre el DEM i el Mètode dels Elements Finits (FEM) el qual governa la solució de mecànica de sòlids en l'estructura. Per a fer-ho, es descriu un procediment pel qual les forces de contacte, que es calculen en les partícules, es transfereixen de forma consistent als nodes que formen part de l'estructura o sòlid en qüestió. Per altra banda, un model desenvolupat per Oñate et al. per a modelar materials cohesius mitjançant el DEM és analitzat numèricament per tal d'extreure conclusions sobre les seves capacitats i limitacions. En paral·lel als desenvolupaments teòrics, un dels objectius de la tesi és proveir al partner industrial del programa doctoral, CITECHSA, d'un software anomenat DEMpack (http://www.cimne.com/dem/) que permeti aplicar l'acoblament DEM-FEM en projectes d'enginyeria reals. Una de les aplicacions remarcables dels desenvolupaments en el marc de la tesis ha estat un projecte per l'empresa Weatherford Ltd. que involucra la simulació de tests en provetes de materials cimentosos tipus formigó. Aquesta tesis doctoral s'emmarca en la primera promoció (2012-2013) del programa de Doctorats Industrials de la Generalitat de Catalunya. La proposta de tesi prové de l'acord entre l'empresa CITECHSA i el centre de recerca CIMNE de la Universitat Politècnica de Catalunya (UPC).

A granular material is usually an irregular packing of particles and its constitutive relationship is very complex. Previous researches have shown that the discrete element method is an effective tool for fundamental research of the behaviour of granular materials. In this research, discrete element modelling was used to obtain the macroscopic stress-strain behaviour of granular material in cavity expansion. The micro mechanical features and the mechanical behaviour of granular material at particle level have been investigated. A simple procedure was used to generate the samples with spherical particles and two-ball clumps. The influence of particle properties on the stress strain behaviour within an aggregate was investigated in biaxial test simulations. It was found that more angular clumps lead to sample more homogeneous and that the interlocking provided by the angular clumps induces a higher strength and dilation in the sample response. Interparticle friction was also found to have significant effect on the strength and dilation of the sample. The sample macromechanical properties can be obtained from these biaxial simulations. For investigating the effect of particle shape, the spherical or non-spherical(two-ball clump) particle shapes were used in the cavity expansion simulations. Monotonic loading was performed on a fan-shaped sample with various particle properties under a range of initial cavity pressures. The results were compared with calculated analytical solutions and existing experimental data in order to optimise the micro mechanical parameters governing the behaviour. The pressuremeter test data were adapted for this comparison since the theory of cavity expansion has been used to describe the pressuremeter tests in soil and rocks by many geotechnical researchers and engineers. This research showed that particle properties play an important role in soil behaviour of cavity expansion under monotonic loading. The contribution of this research is to present that it is possible to model a granular material of boundary value problem (cavity expansion) under static conditions, providing micro mechanical insight into the behaviour.

An effective methodology for modelling particulate systems is presented within an explicit finite/discrete element framework. Issues related to contact resolution of the contact constitutive laws and kinematics relationship of particle of various geometry complexities (circular disk, ellipse particle, sphere, clumped or bonded disk and sphere particle) are presented and investigated. Particular emphasis is given to the specification of contact parameters of particle such as normal and tangential damping, cohesion and adhesion force, rotational damping and rolling resistance. Preliminary numerical test for simple particulate problem are carried out to support the validity of the contact algorithms implemented. The develop discrete contact algorithms are implemented to the numerical tool in order to simulate the particulate systems problem in industrial applications. Since there is a lack of theoretical and experimental solutions for some of the challenging problems of particulate system in industrial applications, the numerical contact scheme provides an alternative solution. The numerical simulation based on the developed contact algorithms is demonstrated on three main different industrial applications. The bucket filling process in mining operation, silo filling, hopper discharging, tumbling mills and screw feeder discharging in mineral processing and vibrating beds in chemical engineering. The particulate system for these industrial applications shows a good agreement in comparison with the qualitative and some quantitative results from the experiment.

Low-density fibre networks are a fundamental structural framework of everyday hygiene products, such as baby diapers, incontinence and feminine care products, bathroom tissue and kitchen towels. These networks are a random assembly of fibres, loosely bonded and oriented in the plane direction. Designing such a complex network structure for better performance, better use of materials and lower cost is a constant challenge for product designers, requiring in-depth knowledge and understanding of the structure and properties on the particle (fibre) level. This thesis concerns the development of a computational design platform that will generate low-density fibre networks and test their properties, seamlessly, with the aim to deepening the fundamental understanding of the micromechanics of this class of fibre networks. To achieve this goal, we have used a particle-based method, the Discrete Element Method (DEM), to model the fibres and fibre networks. A fibre is modelled as a series of linked beads, so that one can consider both its axial properties (stretching and bending) and transverse properties (shearing,twisting and transverse compression). For manufacturing simulations, we developed the models for depositing fibres to form a fibre network, consolidating the fibre network, compressing to make a 3D-structured network, and creating creping. For testing the end-use performance, we have developed two models and investigated the micromechanics of the fibre network in uniaxial compression in the thickness direction (ZD) and in uniaxial tension in the in-plane direction. In the ZD-uniaxial compression of entangled (unbonded) fibrenetworks, the compression stress exhibits a power-law relationship with density, with a threshold density. During compression, the fibre deformation mode changed from fibre bending to the transverse compression of fibre. Accordingly, the transverse properties of the fibreshad a large impact on the constitutive relation. By considering a realistic value for the transverse fibre property, we were able to predict the valuesof the exponent widely observed in the experimental literature. We havefound that the deviation of the experimental values from those predictions by the earlier theoretical studies is due to the neglect of the transverse fibre property. For tensile properties of bonded networks, we have investigated scaling of network strength with density and fibre–fibre bond strength. The network strength showed beautiful scaling behaviour with both density and bond strength, with exponents 1.88 and 1.08 respectively. The elastic modulus of the network, on the other hand, showed a changing exponent(from 2.16 to 1.69) with density in accordance with previous results in the literature. We have also reconfirmed that, with increasing density, the deformation mode changes from bending to stretching. The predicted results for both elastic modulus and strength agreed very well with experimental data of fibre networks of varying densities reported in the literature. We have developed a computational platform, based on DEM, for accurately modelling a fibre network from its manufacturing process to product properties. This is a tool that allows a versatile design of materials and products used for hygiene products, providing a promising venue for exploring the parameter space of new material and process design.

Vid tidpunkten för framläggningen av avhandlingen var följande delarbeten opublicerade: delarbete 2 och 3 (manuskript).

At the time of the defence the following papers were unpublished: paper 2 and 3 (manuscript).

Hearing loss is the third leading chronic disability after arthritis and hypertension, and the most frequent birth defect. Non-invasive diagnoses and middle-ear prostheses are often unsatisfactory, partly because of a lack of understanding of middle-ear mechanics. The focus of this thesis is to develop a 3-D finite-element model to quantify the mechanics of the gerbil middle ear. An MRM dataset with a voxel size of 45 &mgr;m, and an x-ray micro-CT dataset with a voxel size of 5 um, supplemented by histological images, are the basis for 3-D reconstruction and finite-element mesh generation. The eardrum model is based on moire shape measurements. The material properties of all the structures in the model are based on a priori estimates from the literature.
The behaviour of the finite-element model in response to a static pressure of 1 Pa is analyzed. Overall, the model demonstrates good agreement with low-frequency experimental data. For example, (1) the ossicular ratio is found to be about 3.5; (2) maximum footplate displacements are about 34.2 run +/- 0.04 nm; (3) the motion of the stapes is predominantly piston-like; (4) the displacement pattern of the eardrum shows two points of maximum displacements, one in the posterior region and one in the anterior region. The results also include a series of sensitivity tests to evaluate the significance of the different parameters in the finite-element model. Finally, in an attempt to understand how the overall middle-ear mechanics is influenced by the anterior mallear ligament and the posterior incudal ligament, results are shown for cutting or stiffening the ligaments.

Most models of the middle ear are based on oversimplified geometries and iterative material-property fitting to experimental data which may yield physiologically incorrect estimates.
The aim of our work was to build an accurate human middle-ear finite-element model that is based on accurate geometry and a priori material-property estimates.
A human temporal-bone specimen was obtained for which the middle-ear response had been measured by means of laser Doppler vibrometry. High-resolution micro-computed tomography data for the specimen were used for accurately defining structure geometry. This model comprises the tympanic membrane, the ossicles, two joints, and four ligaments. We assigned estimated material-property values derived from the literature.
We compared the response of our model with those of other human middle-ear models, and with experimental measurements including those from the same ear. Sensitivity of the model to several of its parameters was also investigated.

The aim of this research was to produce a generic rockbolt model for inclusion in two and three dimensional explicit finite element analyses of mining problems. Installation of rockbolts is completely automated. Algorithms for the automatic placement of rockbolt nodes within continuum elements are developed and described. The rockbolts are described independently of the continuum degrees of freedom. Continuum elements and the rockbolt elements are connected through bond elements. Displacements from the continuum are transferred to the rockbolt system through these elements, and the resultant reactions passed to the continuum as external loads. In this way, the solution procedures for the continuum and the rockbolts are separated, thus creating an explicit-explicit subcycle. Using this form or nodal partitioning, rockbolts may have much higher stiffness than the parent continuum without effecting the overall timestep for the problem. Rockbolt systems are constructed of interconnected layers of bond elements and axial structural elements. The constitutive models for both these types of elements are effectively one-dimensional and therefore may be expressed algebraically. The most appropriate bond models from the literature are discussed and implemented. In addition, there is the capacity for elements crossing discontinuities to generate reactions consistent with transverse shearing of rockbolts. The model is tested by performing numerical pull-tests, based on experimental data from the literature. The sensitivity of rockbolt system to the relative bond and axial stiffness is demonstrated. The numerical axial and bond stress distributions were consistent with the experimental results. The model is applied to an excavation problem, with various rockbolt types and support patterns being analysed. The capacity of rockbolts to reduce the occurrence and depth of fracturing around the excavation is demonstrated. The model is also used to represent reinforcing bars in a concrete beam.

In the modelling of powder compaction, the behaviour of powders is assumed to be rate-independent elastoplastic, and the process may be described by a large displacement based finite element formulation. Three constitutive relationships to describe the mechanical behaviour of the powders were examined, namely a Mohr-Coulomb yield surface, an elliptical cap yield surface and a combined yield surface model. Of all the models tested, an elliptical cap was shown to be the most appropriate for the compaction phase. An incremental elastoplastic material model was used to simulate the relaxation phase and a plasticity theory for friction was employed in the treatment of the powder-tooling interface for the ejection phase. The model was extended to provide a decoupled thermal solution where the plastic and friction work during the compaction process was considered as sources of energy and the consequent temperature fields were calculated. In parallel, a series of experimental studies were carried out in the laboratory and factory for a plain bush and multi-level component. The parameters which were measured were force, displacement and density. The friction coefficient was derived from the plain bush compaction and shear yield tests were conducted to establish the shear behaviour of the powders. The powders tested are typical of those used in industrial applications. The results detailed information concerning the behaviour of the powders in terms of their material parameters for modelling and in validation of the numerical simulation work. Finally the numerical simulation results were validated against the experimental data to gain confidence in the model developed. The comparisons showed good agreement. The versatility of the simulation allows the complete representation of the green compact generation cycle.

A Finite Element Model is developed and implemented in order to study the hydrodynamics of coastal zones. The Shallow Water Equations for well mixed waters are derived integrating the Reynolds Equations along the water depth, using the surface and bottom stress laws, and taking into account the geostrophic acceleration. The system of equations is derived in conservation form. The Euler-Taylor-Galerkin scheme is used to discretize the system of equations, with the temporal discretization preceding the spatial discretization. In the process, triangular elements are used, taking advantage of exact quadrature laws and of the meshing flexibility that such elements provide. Marching in time is done explicitly and stability controlled by the smallest element present in the grid. Analytical solutions for the linearized shallow water equations are revisited and used to assess the model's performance. A rectangular and a polar basin with constant bathymetry and closed at one end are used to test the model. Two algorithms are presented for mesh generation, one generates unstructured meshes and the other structured meshes. A methodology is devised in order to blend both types of meshes to produce an unstructured-structured hybrid mesh and the final connectivity matrix from the contribution of each individual mesh. Particular emphasis is put on the bathymetry modelling process. A new methodology is developed to obtain the information from hydrographic charts converting it into digital format using a digitizer device driver, written with the specific needs of the problem at hand. A Delaunay triangular irregular network is used to encode bathymetric information. The bathymetric information is then automatically transferred, superimposing the computational grid to the triangular irregular network, solving a point-in-triangulation query and interpolating linearly from the background grid. Two case studies are presented simulating tidal flow.