The influence of three elastic contact models on the dynamics of the drilling module is studied by representing the percussive drilling process as a drifting oscillator. The Kelvin-Voigt, Hertz stiffness and nonlinear stiffness and damping models were considered. The local dynamics of the system were found to be almost identical for the three models. Hence the Kelvin-Voigt system adequately describes the local dynamics of the system. However, for larger frequency and higher damping the behaviour of the three models differed. Experimental indentation studies were carried out on sandstones samples using static and dynamic loading. A force penetration relation was obtained for the loading and unloading phases of the indentation using a conical and spherical indenter under quasi-static conditions. Conical indentation tests were carried out in dynamic conditions. Both experiments showed that the force penetration relationship that could describe the contact model were closer to that obtained for the elastic-plastic indentation of ductile materials. The dynamic model for the drilling module was developed using an elastic plastic model for conical and spherical indenter. In addition, the model’s parameters were modified to those obtained from the experiments and used for the comparison with the results obtained for the elastic plastic model. The result obtained suggested a topological similarity between the experimental and theoretical parameters. It was also noted that the results suggested that the conical indenter appeared to be more efficient of the two indenter types considered. Finally, the rock fracture as a result of its contact with the drill-bit insert was investigated. For simplicity, the inserts are considered as flat punch and the contact problem is treated as a plane strain problem. Experimental studies were also carried out to determine the crack initiation angle in sandstone.

Thesis (M.Sc.)--University of the Witwatersrand, Faculty of Engineering, 1996 / One of the major impediments in the field of numerical modelling in rock mechanics is limited knowledge of the mechanisms of fracture and failure of brittle rock. One important tool for improving the understanding of rock behaviour is the use of laboratory experiments under controlled conditions. The Displacement Discontinuity Method, capable of fracture growth simulation (DIGS), has been used to model fracturing in samples under punch loading. A Finite Difference Method, capable of plastic deformations due to its explicit time marching scheme (FLAC), has also been used to model the punch tests. By comparing numerical simulations with results from laboratory experiments of punch tests, it has been possible to define the basic failure mechanism for pillar foundation failure. Two different test set-ups were used namely, steel jacketed axisymmetric punch tests and long strip punch tests in the triaxial cell which is built for these specific tests. The layered structure of the test specimens and in the test procedure had significant effects on the fracture pattern as well as the failure load. When the layer is near to the punch area, then both the layer and the layer conditions had a strong effect on the failure load. When the layer was frictionless, the failure stress dropped by about 20 percent. The same result occurred in both the axisymmetry and strip loading tests. When shear fractures intersect a layer with either low or high friction it terminates. This is not the case for the tensile fractures, which can pass through the layer media. However, it is important to note that the tensile fractures which originate from near the cone area can not pass through the layers. They stop at the interface.

University of Macau / Faculty of Science and Technology. / Department of Civil and Environmental Engineering

The cell impedance analysis technique is a label-free, non-invasive method, which simplifies sample preparation and allows applications requiring unmodified cell retrieval. However, traditional impedance measurement methods suffer from various problems (speed, bandwidth, accuracy) for extracting the cellular impedance information. This thesis proposes an improved system for extracting precise cellular impedance in real-time, with a wide bandwidth and satisfactory accuracy. The system hardware consists of five main parts: a microelectrode array (MEA), a stimulation circuit, a sensing circuit, a multi-function card and a computer. The development of system hardware is explored. Accordingly, a novel bioimpedance measurement method coined digital auto balancing bridge method, which is improved from the traditional analogue auto balancing bridge circuitry, is realized for real-time cellular impedance measurement. Two different digital bridge balancing algorithms are proposed and realized, which are based on least mean squares (LMS) algorithm and fast block LMS (FBLMS) algorithm for single- and multi-frequency measurements respectively. Details on their implementation in FPGA are discussed. The test results prove that the LMS-based algorithm is suitable for accelerating the measurement speed in single-frequency situation, whilst the FBLMS-based algorithm has advantages in stable convergence in multi-frequency applications. A novel algorithm, called the All Phase Fast Fourier Transform (APFFT), is applied for post-processing of bioimpedance measurement results. Compared with the classical FFT algorithm, the APFFT significantly reduces spectral leakage caused by truncation error. Compared to the traditional FFT and Digital Quadrature Demodulation (DQD) methods, the APFFT shows excellent performance for extracting accurate phase and amplitude in the frequency spectrum. Additionally, testing and evaluation of the realized system has been performed. The results show that our system achieved a satisfactory accuracy within a wide bandwidth, a fast measurement speed and a good repeatability. Furthermore, our system is compared with a commercial impedance analyzer (Agilent 4294A) in biological experiments. The results reveal that our system achieved a comparable accuracy to the commercial instrument in the biological experiments. Finally, conclusions are given and the future work is proposed.

The purpose of this research is to reduce the amount of waste generated in Department of Energy nuclear cleanup efforts currently underway. Due to the highly radioactive nature of the waste, any fluid that contacts the waste must then be treated and processed as waste. To minimize the fluids contaminated during flushing, this research aims to provide a basis for the flushing of High Level Waste (HLW) pipelines. Edgar Plastic Kaolin (EPK) with solid particles of a nominal diameter of 1 micron was used as a simulacrum for HLW. An Eulerian-Eulerian simulation built in StarCCM+ software, with a k-ω turbulence model, and a drag coefficient to connect the solid EPK phase with the liquid phase, was used to simulate the flushing of pipelines. Velocities from 3 ft/s to 10 ft/s were investigated to find the highest volumetric efficiency, and it was determined that 10 ft/s was the optimal flushing velocity.

The problem of cavity expansion in unsaturated soils is investigated. A unified constitutive model for unsaturated soils is presented in a critical state framework using the concepts of effective stress and bounding surface plasticity theory. Consideration is given to the effects of suction and particle crushing in the definition of the critical state. A simple isotropic elastic rule is adopted. A loading surface and bounding surface of the same shape are defined using simple and versatile functions. A limiting isotropic compression line exists, towards which the stress trajectories of all isotropic compression load paths approach. A non-associated flow rule is assumed for all soil types. Isotropic hardening/softening occurs due to changes in plastic volumetric strains as well as suction for some unsaturated soils, enabling account of the phenomenon of volumetric collapse upon wetting. Results of isotropic compression tests, oedometric compression tests and drained and undrained triaxial compression tests performed on Kurnell (quartz) sand in saturated and unsaturated states and subjected to stresses sufficient to cause particle crushing are presented and used to calibrate the model. The model is also calibrated using results reported in the literature for triaxial tests performed on saturated and unsaturated speswhite kaolin and three load paths. For both soils the model leads to a much improved fit between simulation and experiment compared to that for models based on conventional plasticity theory. The model is implemented into a cavity expansion analysis using the similarity technique, extended for application to unsaturated soils. Cylindrical and spherical cavities are considered, as are drained and undrained conditions. Cavity expansion results for the bounding surface model and conventional plasticity models are compared for saturated conditions. Substantial differences highlight the importance of adopting a model that accurately describes stress-strain behaviour. Cavity expansion results for the bounding surface model and saturated and unsaturated conditions are also compared. Substantial differences, particularly in the limit pressure, highlight the major influence of suction and the importance of accounting for this when using cavity expansion theory to interpret results of the cone penetration and pressuremeter tests.

L'étude des sols latéritiques de la région de l'Agnéby en Côte d'Ivoire a été effectuée sur les données géotechniques des rapports d'étude de dix sections de routes construites en utilisant des graveleux latéritiques dans la structure de chaussée. Ces données comportaient des courbes granulométriques, des limites de consistance pour la fraction fine, des résultats d'essais Proctor modifié et d'essais CBR. Ces données ont fait l'objet de traitements statistiques classiques (caractérisation de la variabilité de chaque paramètre géotechnique, recherche de corrélations entre paramètres) et d'une analyse factorielle en composantes principales de l'ensemble des données (188 prélèvements). L'étude conclut que les échantillons de sols latéritiques analysés ont des propriétés assez voisines pour que l'on ne puisse pas les différencier clairement par analyse statistique. Elle conclut qu'il serait utile de prolonger l'étude en couvrant un territoire suffisamment grand (pays, partie du continent africain) pour qu'on y trouve les différents types de sols latéritiques décrits dans la littérature, notamment des latérites de forêt comme celles de l'Agnéby, des latérites de savane et des latérites de cuirasses anciennes. Le mémoire propose une méthodologie pour cette étude plus générale. Le mémoire comprend six chapitres, une introduction et une conclusion générales et donne en annexe l'ensemble des valeurs des données géotechniques utilisées.

Dans le cadre du dimensionnement à la fatigue thermomécanique des culasses automobiles, nous proposons une méthode de simulation des structures soumises à des chargements cycliques. Cette méthode, alternative aux méthodes classiques (comme la méthode incrémentale) permet de résoudre des problèmes thermomécaniques cycliques non-linéaires. Il s'agit d'une Méthode Cyclique Directe qui consiste à rechercher directement la solution asymptotique d'une structure anélastique soumise à un chargement thermomécanique périodique, sans suivre l'histoire du chargement. Elle est fondée sur les techniques de grand incrément de temps [Ladevèze et al.], en prenant en compte la périodicité de l'état limite [Nguyen et al.] et la transformation de Fourier. Cette méthode permet des gains de temps importants pour les structures comprenant un grand nombre de degrés de liberté. Un développement de cette méthode dans une version commerciale d'Abaqus, a permis de montrer la faisabilité de cette approche dans le cas de la simulation d'une culasse.

Even though the elastic deformations that occur during the impact of colliding bodies may be small in comparison to their actual dimensions, they play an important role in mechanical collisions. During the time the bodies are in contact, elastic, friction, and inertia properties combine to produce a complex variation of sliding and sticking throughout the contact surface. Detailed analysis of this interaction is quite tedious, but would seem to be necessary for accurately predicting the impulse and velocity changes that occur during contact. However, a considerably-simplified model captures the essential characteristics of the elastic-friction interaction during contact, leading to predictions of impulse and velocity changes that agree well with those of more detailed analyses of a number of different collisions. The model's simplicity enables an examination of parameters that affect a general class of collisions. For planar collisions, the model contains five dimensionless parameters; the effects of four of these on the rebound velocity are examined here. In addition, comparisons are made with a previously-used, somewhat simpler model, which neglects the tangential compliance in the region of contact. / Graduation date: 1993

Thesis (Ph. D.)--University of Rhode Island, 2005. / Typescript. Includes bibliographical references (leaves 126-134).