This thesis contains three separate yet closely related topics: fracture, friction and simulation of mechanical response of a confined granular medium. The first two are experimental investigations and the last one is a numerical study. In the fracture part, I will describe how to break a piece of silicon in a controlled way such that the atomic nature of the fracture process can be revealed in a macroscopic experiment. In the friction part, I will present another experiment using almost exactly the same setup as for the low temperature fracture experiment to study the properties of static friction and explore ideas concerning the origin of friction. In the last part, I will construct a confined granular packing and study how pulses and continuous waves propagate through it. All these three topics are relevant to geophysical science. I sincerely hope that my study can ignite some fresh thinking in that area and help other researchers to design models that can make more precise earthquake predictions. / text

Εισάγουμε σταθερή εισροή υλικού στο πρώτο δοχείο με σκοπό να περιγράψουμε τις συνθήκες κάτω από τις οποίες η ροή θα είναι ομαλή και συνεχής μέχρι και το τελευταίο δοχείο. Σε αντίθεση με τα κανονικά ρευστά, τα κοκκώδη υλικά έχουν την τάση να δημιουργούν συσσωματώματα (λόγω της μη-ελαστικής σύγκρουσης των σωματιδίων τους [Goldhirsch and Zanetti, 1993]). Όταν συμβαίνει αυτό η ροή σταματά και η εκροή από το τελευταίο δοχείο μηδενίζεται. Δεδομένης της δύναμης ανατάραξης και των διαστάσεων του διαδρόμου, καθορίζουμε την οριακή τιμή της εισροής πέρα από την οποία η δημιουργία συσσωματωμάτων είναι αναπόφευκτη. Δείχνουμε ότι η κρίσιμη αυτή κατάσταση αναγγέλλεται εκ των προτέρων (ήδη πριν από την οριακή τιμή της εισροής) από την εμφάνιση ενός κυματιστού προφίλ πυκνότητας υλικού κατά μήκος του διαδρόμου. Η οριακή ροή καθώς και το κυματιστό προφίλ εξηγούνται σ΄αυτή την εργασία, τόσο ποιοτικά όσο και ποσοτικά, μέσω ενός μαθηματικού μοντέλου ροής [Eggers 1999, Van der Weele et al., 2001]. Τέλος, βασιζόμενοι σε αυτό το μοντέλο προτείνουμε πρακτικές λύσεις ώστε να βελτιωθεί σημαντικά η παροχή του διαδρόμου. / We study the flow of granular material on a conveyor belt consisting of K connected, vertically vibrated compartments. A steady inflow is applied to the top compartment and our goal is to describe the conditions that ensure a continuous flow all the way down to the Kth compartment. In contrast to normal fluids, flowing granular matter has a tendency to form clusters (due to the inelasticity of the particle collisions [Goldhirsch and Zanetti, 1993]); when this happens the flow stops and the outflow from the Kth compartment vanishes. Given the dimensions of the conveyor belt and the vibration strength, we determine the critical value of the inflow beyond which cluster formation is inevitable. Fortunately, the clusters are announced in advance (already below the critical value of the inflow) by the appearance of a wavy density profile along the K compartments. The critical flow and the associated wavy profile are explained quantitatively in terms of a dynamical flux model [Eggers, 1999; Van der Weele et al., 2001]. This same model enables us to formulate a method to greatly increase the critical value of the inflow, improving the capacity of the conveyor belt by a factor two or even more.

An experimental study of the drying of sand using an induction heated double-screw conveyor (screw shaft radius 0.0381 m, blade radius 0.0883 m, thread pitch 0.0869 m, heated length 1.96 m) is presented. The main aim was to improve the understanding of the operating characteristics of the dryer and obtain data for testing and refining future mathematical models. In the drying tests, power to the induction coils was controlled to obtain uniform screw shaft temperatures between 150 to 250°C. The angular rotation speed of the screws ranged between 2.5 to 15 rpm; and inlet moisture content (mass fraction of water) was varied between 0.1 to 10 %. The sand used had a mean effective diameter of 0.38 mm, particle density of 2743.7 kg/m3, and uncompacted dry bulk density of 1508.2 kg/m3. The results of sand characterization tests, conveying tests without induction heating, and drying tests are presented and discussed.

In biomolecules, the relationship among the sequence, molecular structure, and biological function are of very importance in the development of nanotechnology such as drug discovery. Previous studies involving multiple sequence alignment of biomolecules have demonstrated that interdependent or associated sites are indicative of the structural and functional characteristics of biomolecules, as an extension to methods such as consensus sequences analysis. In this thesis, a new method to detect associated sites in aligned sequence ensembles is proposed. It involves the use of multiple sub-tables (or levels) of two-dimensional contingency table analysis. The idea is to incorporate analysis by following an approach known as granular computing, which represents information at different levels of granularity or resolution. When associations of multiple sites in the sequence alignment converge, they reflect points of interrelatedness among the sites in the biomolecules. The study involves two different phases of analysis. The first phase includes labeling of the molecular sites in the p53 protein multiple sequence alignment according to the detected patterns. The sites are consequently labeled into three different types based on their site characteristics - conserved sites, associated sites, and hypervariate sites. To identify and label the associated sites, the proposed method is employed. In the second phase, the significance of the extracted site patterns is evaluated with respect to some of the structural and functional characteristics of the p53 protein. The results indicate that the extracted site patterns in combination with conserved sites are significantly associated with some of the known functionalities of p53 such as post translational modifications and the mutation frequency of the sites, hence establishing the link between these identified sites and the defined functionality. Furthermore, when these sites are aligned with p63 and p73, the homologs of p53, based on the common domains, the sites significantly discriminate between the human sequences of the p53 family. Therefore, the study confirms the importance of these detected sites that could indicate their differences in cancer suppressing property.

No description available.

No description available.

The Discrete Element Method (DEM) has been applied to numerical modelling of the bulk compression of low modulus particulates. An existing DE code for modelling the contact mechanics of high modulus particles using a linear elastic contact law was modified to incorporate non-linear viscoelastic contact, real containing walls and particle deformation. The new model was validated against experimental data from the literature and physical experiments using synthetic spherical particles, apple and rapeseed. It was then used to predict particle deformation, optimum padding thickness in a handling line and bulk compression parameters during oilseed expression. The application of DEM has previously been limited to systems of hard particles of high compressive and shear modulii with relatively low failure strain. Material interactions have therefore commonly been modelled using linear contact law. For high modulus particles, particle shape change resulting from deformation is a not a significant factor. Most agricultural particulates however deform substantially before failure and their interaction is better represented with non-linear hysteretic viscoelastic contact relationship. Deformation of geometrically shaped particles in DEM is usually treated as "virtual" deformation, which means that particles are allowed to overlap rather than deform due to contact force. Change to particle shape has not previously been possible other than in the case of particles modelled as 2-D polygons or where each particle is also modelled concurrently with an FE mesh. In this work a new approach has been developed which incorporates a non-linear deformation dependent contact damping relationship and a shape change while maintaining sufficient geometrical symmetry to allow the problem to be handled by the same DE algorithms as used for true spheres. The method was validated with available experimental results on impact behaviour of rubber and the variations with different damping coefficients were simulated for a selected fruit. A fruit handling process dependent on the impact process was then simulated to obtain data required in the design of a fruit processing line. Changes in shape of spherical synthetic rubber particles and rapeseeds under compression were predicted and validated with physical experiments. Images were taken and analysed using image processing techniques with 1: 1 scaling. The method on shape change entails a number of simplifying assumptions such as uniform stress distribution and homogeneous material properties and uniform material distribution when deformed, which are not observed in real agricultural materials and will tend to overestimate the true contact area between particles. In reality for fruits and vegetables, material redistribution is a complex process involving a combination of compaction and movement. However with the new method a better approximation of bed voidage (which standard DEM approaches underestimate) and stress were obtained in the compression of a synthetic material. This is a significant improvement on existing methods particularly with respect to stress distribution within a bulk particulate system comprising deforming elements where the size and orientation of contact surface between particles has a strong influence on the bulk modulus. The new model was used for prediction of mechanical oil expression in four oilseed beds. Similar patterns in the variation of the characteristic parameters were obtained as observed in existing experimental data. The data could not be matched exactly as the quantity and arrangement of seeds in the initial seedbeds were not the same as those used in the experimental work. However the DE model gave approximate oil point data for seedbeds with the same physical properties and initial conditions as in the experiment. This suggests that the new model may be a useful tool in the study of mechanical seed-oil expression and other agricultural particulate compression processes.

No description available.

No description available.

A study of the constitutive equations of the flow of cohesionless granular materials at large rates of deformation and low stress levels is presented. The interstitial fluid effects are assumed negligible and the particles approximately incompressible. / Dimensional arguments and experimental observations suggest that two different regimes of flow may occur. At low rates of deformation, the Coulomb friction gives rise to stresses that are rate independent (of the plastic type). At large rates of deformation, momentum transfer arises from particles collisions and the resulting stresses become rate dependent (of the viscous type). A continuum model that includes both types of behaviour is proposed. The equilibrium part of the stress tensor satisfies the Mohr-Coulomb yield criterion and a non-coaxial flow rule. The viscous part is assumed to have a form corresponding to an isotropic Reiner-Rivlin fluid. / Experiments of simple shear flow flow in an annular shear cell were performed on several types of dry granular materials. The purpose of the tests was to obtain the information needed for the continuum description of the material behaviour. At lower solids concentrations and high shear rates where the inter-particle collisions are dominant, both shear and normal stresses were proportional to the square of the shear rate. At higher concentrations and lower shear rates, Coulomb friction between particles became increasingly important and the stresses were proportional to the shear rate raised to a power less than two. All tests showed a strong dependence upon solids concentration.