Image based simulation of one-dimensional compression tests on carbonate sand

High factors of safety and conservative methods are commonly used on foundation design on shelly carbonate soils. A better understanding of the behavior of this material is, thus, critical for more sustainable approaches for the design of a number of offshore structures and submarine pipelines. In particular, understanding the physical phenomena taking place at the microscale has the potential to spur the development of robust computational methods. In this study, a one-dimensional compression test was performed inside an X-ray scanner to obtain 3D images of the evolving internal structure of a shelly carbonate sand. A preliminary inspection of the images through five loading increments has shown that the grains rearrange under loading and in some cases cracks develop at the contacts. In order to replicate of the experiments in the numerical domain, the 3D image of the soil prior to loading was imported into a micro Finite Element (µFE) framework. This image-based modelling tool enables measurements of the contact force and stress map inside the grains while making use of the real microstructure of the soil. The potential of the µFE model to contribute insights into yield initiation within the grain is demonstrated here. This is of particular interest to better understand the breakage of shelly grains underpinning their highly compressive behavior

Master of Science

thesisTight shale reservoirs have recently emerged as potential game changers in oil and gas and energy sectors worldwide. Consequently, exploration and exploitation of unconventional reservoirs has significantly increased over the last decade. Currently used stimulation designs are based on conventional planar fracture models that cannot realistically simulate the geometry and the extent of hydraulically induced fractures. For that reason, developing models that can thoroughly and accurately describe fracture network initiation and propagation plays a significant role in evaluating well production. The main goal of this work is to evaluate the utility of the peridynamic theory (PD) in modeling the process of hydraulic fracturing. Peridynamics is a nonlocal theory of continuum media that can facilitate a direct coupling between classical continuum mechanics and molecular dynamics. A linear-viscoelastic PD model was applied to a three-dimensional domain that was discretized with cubic lattices of particles. Damage in the model is represented by the bond breakage; as the stretch between two lattices reaches its critical limit, s_0, the bond breaks. The validity of the peridynamic simulation was tested by comparing results obtained in this project against the results obtained in a study performed by Zhou et al. Therefore, six sets of experimental tests were conducted to simulate hydraulic fracturing based on the peridynamic method. Five sets of the simulation results produced in this work were in good agreement with the experimental results. The investigation examined the influences of the differential horizontal stress and preexisting fracture, along with different approach angles, on the geometry of the hydraulic fracture. Different injection rates were applied to the model in order to compare the fractured area that resulted from different injection rates. The simulation showed that the maximum dilatation and fractured zone occurred at the injection rate of 0.61 m3?min. The 0.61 m3/min injection rate caused the highest complete damage (0.9-1) with 5.24 % of the total number of atoms. As a result, the peridynamic approach presents promising results in predicting fracture propagation and damage area

Enhancing Consultants' IT Skills: A Reverse Mentoring Project

13-16 July 2002 Many medical students arrive with excellent IT skills and experience of mentoring their peers in secondary school. Senior clinicians, by contrast, did not grow up with the technology and often feel left behind by the IT revolution. This generation gap is often seen as a threat to the authority of clinical tutors. We have set up a reverse mentoring scheme to help consultants develop their IT skills. With a grant from the post graduate dean, we have recruited thirty medical students to act as personal trainers to thirty consultants and specialist registrars. Each participant is issued with a set of learning vouchers which enables them to purchase four hours of training and a password to access the learning resources from the project website. This paper will describe the methods used, and report on the results of this unique reverse mentoring scheme

Being Gender/Doing Gender, in Alice Munro and Pedro Almadovar

In this thesis, I compare the short stories, “Boys and Girls” and “The Albanian Virgin”, by Alice Munro, with two films, La Mala Educación and La Piel Que Habito, by Pedro Almodóvar. This comparison analyzes how these authors conceive gender as a doing and a performance, and as culturally constructed rather than biologically determined. My main theoretical framework is Judith Butler’s theory of gender performativity as developed in Gender Trouble: Feminism and the Subversion of Identity. In my first chapter, I compare “Boys and Girls” with La Mala Educación, and in the second chapter, I compare “The Albanian Virgin” with La Piel Que Habito, to illustrate the multiple ways in which gender is constructed according to Munro and Almodóvar. I argue that both Alice Munro and Pedro Almodóvar not only perceive gender as non-essential, but they also locate various possibilities of resistance through gender performance, drag, impersonation and masquerade

A laboratory-based technique for grain size and shape characterisation

The significance of grain shape dependent behaviour is widely reported in the literature. Quantification of grain shape is, however, not part of routine laboratory characterisation and this can be in part attributed to the lack to accessible equipment. In this paper, we discuss the potential of a novel imaging technique to capture the three-dimensional outline of grains. This technique enables the volumetric description of the grain to be obtained by reconstructing the planar projections of the grain acquired at different angles of rotation using a standard camera. The imaging setup is very simple and can be easily implemented in any laboratory. It includes a camera, a lens (optional) and a stepper motor to rotate the object in controllable and precise increments. The greater the number of acquired projections, the better the detail of the reconstructed volume will be. Results from single grain compression tests on Leighton Buzzard sand and a shelly carbonate sand from the Persian Gulf are presented to demonstrate the dependency of the tensile strength on the grain shape. The simplicity and easy access to this laboratory-based technique have the potential to enhance laboratory and physical experiments of geomaterials

A micro finite-element model for soil behaviour

This paper describes a numerical model that virtualises the fabric of a natural sand obtained from micro computed tomography (μCT) to simulate the mechanical response of the material, termed here a micro finite-element (μFE) model. The grain-to-grain interactions under loading are modelled in a framework of combined discrete–finite-element method. The basis of this approach is that using a true representation of soil fabric and deformable grains will enable a more realistic representation of the physics of granular behaviour. Each individual grain is represented in a numerical mesh and modelled as a continuum body allowed to deform according to a prescribed constitutive model with appropriate friction contact conditions. An important feature of this model is the ability to compute the map of stress distribution inside the grains. A case study of an intact sand subjected to oedometer compression is presented to demonstrate the insights that can be gained into the stress transmission mechanisms and yield initiation within the grains. The displacement field, inertia tensor and active contact number are used to quantify grain kinematics as the virtual fabric deforms. By coupling contact dynamics with contact topology, this approach provides a robust numerical tool to infer important grain scale parameters that link the micro phenomena to the macro response of soil

A micro finite element model for soil behaviour: Numerical validation

A micro finite-element (μFE) model capable of handling arbitrary shapes and deformable grains has been developed by the authors. The basis of this μFE model is to use a virtualised soil fabric obtained from micro computed tomography (μCT) of real sand to simulate grain-to-grain interaction in a framework of combined discrete–finite-element method. By incorporating grain deformation into the model, the contact response emerges from the interaction of contacting bodies and each irregular contact area will produce a unique response. A detailed numerical description of grain morphology and contact topology of a natural sand and the subsequent simulation are presented in the original paper. The present study focuses on the numerical validation of the constitutive contact behaviour against existent theories, for a single sphere and an assembly of spheres. The ability of the model to simulate elastic–plastic behaviour making use of the deformability of the grains is demonstrated. The unloading–reloading behaviour associated with the geometrical arrangement of the grains for a granular assembly under triaxial compression is examined in terms of energy dissipation quantities

Prime-based method for interactive mining of frequent patterns

Over the past decade, an increasing number of efficient mining algorithms have been proposed to mine the frequent patterns by satisfying a user specified threshold called minimum support (minsup). However, determining an appropriate value for minsup to find proper frequent patterns in different applications is extremely difficult. Since rerunning the mining algorithms from scratch can be very time consuming, researchers have introduced interactive mining to find proper patterns by using the current mining model with various minsup. Thus far, a few efficient interactive mining algorithms have been proposed. However, their runtime do not fulfill the need of short runtime in real time applications especially where data is sparse and proper frequent patterns are mined with very low values of minsup. As response to the above-mentioned challenges, this study is devoted towards developing an interactive mining method based on prime number and its special characteristic “uniqueness” by which the content of the relevant data is transformed into a compact layout. At first, a general architecture for interactive mining is proposed consisting of two isolated components: mining model and mining process. Then, the proposed method is developed based on the architecture such that the mining model is constructed once, and it can be frequently mined by various minsup. In the mining model construction, the content of relevant data is captured by a novel tree structure called PC-tree with one database scan and mining materials are consequently formed. The PC-tree is a well-organized tree structure, which is systematically built based on descendant making introduced in this study. Moreover, this study introduces a mining algorithm called PC-miner to mine the mining model frequently with various values of minsup. It grows an effective candidate head set introduced in this study starting from the longest candidate patterns by using the Apriori principle. Meanwhile, during the growing of the candidate head set in each round, the longest candidate patterns are used to find maximal frequent patterns from which the frequent patterns can be derived. Moreover, the PC-miner reduces the number of candidate patterns and comparisons by using several pruning techniques. A comprehensive experimental analysis is conducted by several experiments and scenarios to evaluate the correctness and effectiveness of the proposed method especially for interactive mining. The experimental results verify that the proposed method constructs the mining model independent of minsup once and this enable the model to be frequently mined. The results also show that the proposed method mines frequent patterns correctly and efficiently. Moreover, the results verify that the proposed method speeds up interactive mining of frequent patterns over both sparse and dense datasets with more scalable total runtime for very low values of minsup over sparse datasets as compared to results from the previous work

A Large-scale Distributed Video Parsing and Evaluation Platform

Visual surveillance systems have become one of the largest data sources of Big Visual Data in real world. However, existing systems for video analysis still lack the ability to handle the problems of scalability, expansibility and error-prone, though great advances have been achieved in a number of visual recognition tasks and surveillance applications, e.g., pedestrian/vehicle detection, people/vehicle counting. Moreover, few algorithms explore the specific values/characteristics in large-scale surveillance videos. To address these problems in large-scale video analysis, we develop a scalable video parsing and evaluation platform through combining some advanced techniques for Big Data processing, including Spark Streaming, Kafka and Hadoop Distributed Filesystem (HDFS). Also, a Web User Interface is designed in the system, to collect users' degrees of satisfaction on the recognition tasks so as to evaluate the performance of the whole system. Furthermore, the highly extensible platform running on the long-term surveillance videos makes it possible to develop more intelligent incremental algorithms to enhance the performance of various visual recognition tasks.Comment: Accepted by Chinese Conference on Intelligent Visual Surveillance 201