Includes bibliographical references (p. 239-255).

Thesis (Ph. D.)--Ohio State University, 2006. / Available online via OhioLINK's ETD Center; full text release delayed at author's request until 2007 Mar 24

Thesis (M. S.)--Mechanical Engineering, Georgia Institute of Technology, 2007. / Jeffrey Streator, Committee Member ; Richard Neu, Committee Member ; Itzhak Green, Committee Chair.

Thesis (Ph.D.)--University of Delaware, 2007. / Principal faculty advisor: Robert Gilbert, Dept. of Mathematical Sciences. Includes bibliographical references.

This thesis aims to model the uniaxial deformation of a class of materials consisting of microscopic spherical shells embedded in a rubber matrix. These shells are assumed to buckle as the stress on the material increases. To motivate the analysis we consider the paradigm problem of the debonding of a distribution of cylindrical inclusions in an elastic material undergoing antiplane shear, with bonded and debonded inclusions playing the role of unbuckled and buckled shells respectively. We begin the modelling of the microsphere-containing material by considering the buckling of an isolated embedded shell inclusion with a uniaxial stress field at infinity, using Koiter's theory of shallow shells. The resulting energy functional is solved as an eigenvalue problem by the Rayleigh-Ritz method. Subsequently, we analyse the buckling criterion asymptotically in the limit as the thickness ratio tends to zero by analogy with the WKB analysis of a beam on a variable-stiffness substrate. To model the shell after buckling we consider the simplified case of an embedded shell with a crack around its equator. The system is solved by expressing the displacements in the shell and matrix as series of Love stress functions, with the resulting infinite system of equations solved numerically with the aid of a convergence acceleration method. Finally we consider a composite material consisting of a homogenised dilute distribution of buckled and unbuckled shells, with the proportion of each type of shell dependent on the stress applied to the material, according to an asymptotic formula relating the size of the inclusions and the critical buckling stress that was obtained previously.

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In this thesis, the Smoothed Particle Hydrodynamics (SPH) method is applied to elastic dynamics and fracture. More specifically, two coupling methods are presented which make use of both the Eulerian and Total Lagrangian formulations. These coupling methods are intended for problems whereby SPH particles, which constitute the domain, are required to convert from a Total Lagrangian kernel to an Eulerian kernel once a damage criterion is activated. The conservation equations are derived for the Eulerian and Total Lagrangian formulations, in a consistent manner which naturally presents the conditions required for the conservation of momentum and energy. These derivations are written such that they make no use of the symmetrical nature of the kernel function or the anti-symmetrical nature of the kernel function gradient. The conservation of momentum and energy is then enforced, along with improving the consistency of the formulations, by implementing the mixed kernel-and-gradient correction. This mixed correction can be applied to both the Eulerian and Total Lagrangian formulations without detracting from the energy and momentum preserving properties provided that the kernel gradient anti-symmetry property is not exploited. The symmetry terms, which are often found in SPH, are included in the derivation of the conservation equations. This is done both to reduce the number of calculations required and to simplify the first coupling procedure. Both coupled formulations are further expanded by highlighting how artificial viscosity can be introduced. A disadvantage of the first coupling method, this being the incompatibility with artificial stress, is also detailed. The equations of state and the plasticity and damage models used in this work are outlined. Additionally, a number of practical details concerning numerical implementation are given. These include the coupled implementations of ghost particle boundary conditions, memory storage, OpenMP implementation, and the Predict, Evaluate, Correct (PEC) form of leapfrog time integration used. Lastly, the proposed formulations and models are verified and validated. This is done by modelling progressively more complex simulations that verify individual aspects of the formulations. Either analytical or experimental results are used for validation where possible. The final simulations highlight how high velocity impacts can be modelled using the proposed coupled mixed correction Eulerian Total Lagrangian SPH method.

Made available in DSpace on 2015-01-26T13:21:26Z (GMT). No. of bitstreams: 0 Previous issue date: 2014-01-24Bitstream added on 2015-01-26T13:30:27Z : No. of bitstreams: 1 000802929.pdf: 1592999 bytes, checksum: 52f3dfc2dc242335eb92bff83a73a0a4 (MD5) / Objetivou-se avaliar a melhor diluição para dejetos de suínos, aves de postura, ovinos, caprinos, bovinos de corte e bovinos de leite para o abastecimento de biodigestores, bem como a influência da separação de sólidos desses mesmos dejetos na produção e qualidade do biogás, no potencial de produção de biogás e redução de sólidos. Para o teste de diluições os dejetos foram diluídos em água nas proporções: 1:4, 1:5, 1:6, 1:7 e 1:8 (kg de dejeto por kg de água) e adotado o processo físico de peneiramento (peneiras com malhas quadradas de 0,75, 1,00 e 1,50 mm) para separação dos sólidos. Para o ensaio de biodigestão anaeróbia (biodigestores tipo batelada e semi-contínuos) a separação dos sólidos foi feita com peneira de malha de 1mm e substratos com cerca de 4% de sólidos totais. Teste de diluição: embora os resultados tenham variado entre os tipos de dejeto, de modo geral a peneira de malha 1,50 mm permitiu a maior passagem de sólidos. Mas em relação a diluição cada tipo de dejeto apresentou uma resposta. Ensaio de biodigestão anaeróbia (biodigestores tipo batelada): embora para cada dejeto o processo de biodigestão anaeróbia tenha tido uma resposta diferente, de modo geral a separação de sólidos proporcionou melhor qualidade de biogás, porém não foi eficiente para aumentar o potencial de produção de biogás e reduzir sólidos do substrato. Ensaio de biodigestão anaeróbia (biodigestores do tipo semi-contínuo): para os dejetos utilizados (aves de postura e bovinos de leite) a separação de sólidos proporcionou melhor qualidade de biogás, menor produção de biogás, maior redução de sólidos e, para os potenciais de produção de biogás os resultados foram quase sempre positivos. Conclui-se que para o teste de diluição e peneiras os resultados não permitiram uma conclusão geral para todos os dejetos avaliados, pois cada um apresentou características individuais e, para a ... / This trial aimed to evaluate the best dilution for pig, laying hens, sheep, goats, beef cattle and dairy cattle manure to supply digesters, as well as the influence of the solids separation in those same wastes on the production and quality of biogas, on the potential of biogas production and solids reduction. For the dilution test the wastes were diluted with water in the proportions 1:4, 1:5, 1:6, 1:7 and 1:8 (kg of manure per kg of water) and adopted the physical process of screening (sieve with square meshes of 0.75, 1.00 and 1.50 mm) for separation of solids. When tested for anaerobic digestion (batch and semi-continuous digesters) separation of solids was made with 1 mm mesh sieve and substrates of about 4% total solids. Dilution test: although the results varied among the types of manure, generally a 1.50 mm mesh sieve allowed greater flow of solids. But in relation to the dilution used each type of waste had a different response. Testing of anaerobic digestion (batch digesters): although for each manure the process of anaerobic digestion has had a different result, generally solids separation provided better biogas quality, but it was not efficient to increase the potential of biogas production and reduce solids of substrate. Testing of anaerobic digestion (semi-continuous digesters): for the wastes (laying hens and dairy cattle) used the solids separation provided better quality of biogas, lower biogas production, greater reduction of solids and in regards to the potential of biogas production the results were almost always positive. It was concluded that for dilution and sieves test results did not allow a general conclusion for all waste reviews, because each one had individual characteristics and, the separation of solids is an efficient method to enhance the quality of the biogas produced, but in relation to the potential of biogas production and solids reduction of the substrate ...

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M.Ing. (Engineering Management) / In a tender bid to energy and chemical company Sasol, a request to offer a technical solution for a two-flight overland conveyor system whose function is to transport coal from a 15 000 tonne bunker into an external stockpile storage facility in the plant was made. This conveyor consisted of two conveyor flight sections of lengths 18 423m and 8 537m each. The prospect of combining the two flights of conveyors to form one, super-efficient conveyor structure with additional cost saving benefits was identified. It was found that this occurrence was not unique to the individual project as other researching engineers have been faced with similar problems before [18]. This then lead the researcher into believing that there could be some advantage in investigating the possible benefits to the overall cost, maintainability and scheduling of the fabrication and erection activities for the entire project of combining the multiple flight conveyors into a single-flight conveyor. It is also the conviction of the researcher that the achieved outcomes will prove beneficial to the bulk materials handling industry as a whole. The problem is traditionally short, multiple flight conveyors have always been used for performing the function of transporting bulk material from one location in a mining plant to another hence; long, single-flight overland conveyors of lengths exceeding 26 km have not been commonly installed. In this dissertation the possibility of employing a single-flight overland as opposed to a two-flight conveyor in the Sasol Impumelelo coal plant is investigated. This is done against the work of other researchers who have conducted similar studies in the field as well as by utilizing project-specific data using applicable industry standards as well as Engineering Management course theory. By employing actual project procurement and engineering design data; the investigation is done by calculating and comparing the individual capital and operational costs that encompass the total cost of ownership (TCO) for both conveyor systems as well as the two systems’ reliability, availability and maintainability to establish each system’s complete life cycle costs. It is the opinion of the researcher that the investigation method is valid as it is in line with the guidelines given by The Miami University of Ohio [24] as well as J Hanek [25] and thus provides the researcher with a plausible technique for establishing which between the single-flight overland conveyor and two-flight overland conveyor configurations is overall the more superior system to install. It was found that even though its initial capital and operational costs are higher; the single-flight conveyor system is more reliable, readily available and cheaper to run and sustain over the 30 year expected life-span of the plant. It also is less labour intensive to perform maintenance on, yields less material degradation and results in less material spillage because of the elimination of additional transfer points and transfer towers. These results can be taken as valid on a global scale, for any mining plant, not restricted to any specific material as they are not subject to South African temperature, altitude or seismic conditions nor are they constrained to the type of bulk material being mined.