Mechanical Engineering - Theses
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ItemComputational Design of Alternate Binders for Tungsten Carbide Hardmetals( 2023-11)Interest in the field of alternate binders for tungsten carbide (WC) hardmetals has increased due to the health implications surrounding the use of cobalt as a binder material. By incorporating the sinterability and mechanical properties of the system simultaneously, alternatives that are manufacturable using existing procedures can be determined. Here, an Integrated Computational Materials Engineering (ICME) approach was used to search for alternate binder compositions using a reduced-order model. The model was derived by combining the densification mechanisms present in cobalt-containing compacts with the rate enhancing factors governing early onset densification. The model incorporates thermodynamic and kinetic components coupled to a multi-objective genetic algorithm. It allows alloys with compositions optimized for sintering to be ranked against those optimized for mechanical properties to form Pareto sets. In this study, I present a computational methodology for the design of alternate binders based on multi-component alloys for the sintering of WC hardmetals. The current state-of-the-art binders used in the production of WC hardmetals have limited resistance to high temperature sintering and can result in unwanted side effects such as grain growth and decreased toughness. To address these limitations, I propose the use of multi-component alloys as binders in the sintering process. This methodology involves the use of first principles calculations to predict the thermodynamic stability and diffusion coefficients of different alloy systems. The results of these calculations are used to identify promising alloy systems for use as binders in the sintering process. Next, reduced-order models coupled with the CalPhaD method are used to speculate on the diffusive transport of the alloy components during sintering to predict the resulting phases of the final product. These simulations allow for the optimisation of the composition and processing conditions of the alternate binders for maximum densification and improved mechanical properties of the WC hardmetals. Finally, the results of the computational methodology are validated against experimental data and are shown to accurately predict the microstructure and mechanical properties of the sintered WC hardmetals. The results demonstrate that multi-component alloys have the potential to serve as effective and efficient binders for the sintering of WC hardmetals and can provide improved performance compared to current state-of-the-art binders. This thesis details the research plan that has been established for the development of a reduced-order design model for the discovery of alternate binders for the tungsten carbide system. The need for an alternate binder material has been highlighted due to health implications regarding the use of cobalt. A review of the literature focussing on the sintering of tungsten carbide was conducted. This led to the formation of three research questions that became the focus of this project. The design model uses an ICME-based approach and was validated using published data of the tungsten carbide cobalt system. The importance of this research in the development and deployment of a reduced-order design model has been highlighted. There have been efforts to find alternate binders for tungsten carbide (WC) hardmetals because of safety and ethical issues related to the continued use of cobalt. However, the process of identifying new binders is often performed using conventional prototype-and-test approaches. Additionally, these approaches are mostly focused on finding binders that result in acceptable mechanical properties, with limited investigation into their processability, particularly their sinterability. Here, I demonstrate a computational method for finding alternate binders for the sintering of WC hardmetals. The methodology involves new design models to describe the sintering performance of WC particles with different binder systems. It is implemented by using a multi-objective optimisation algorithm coupled with the design models. The thermodynamic and kinetic parameters necessary for the models are calculated by using the CalPhaD (Calculation of Phase Diagram) method, which allows the efficient search of the compositional space of alloys. The study presents validation of the developed design models using densification data from literature together with design exercises that resulted in potential alternate binder alloys. The developed method can help in the search for suitable binder metals by identifying alloys, which can facilitate the efficient sintering of WC particles.
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ItemCharacterisation of micro-scale flows and devices for high strain rate applications( 2023-10)Since the early 2000s, pursuing single-cell experiments has been crucial for comprehending cell mechanoresponses. Various measurement techniques, such as micropipette aspiration, optical tweezers, and atomic force microscopy, have been extensively employed to assess cell properties. However, these methods risk damaging cell structures due to their intrusive nature. Therefore, microfluidics offers a platform for replicating cell dynamics in vivo using hydrodynamic forces exclusively, employing non-intrusive measurement techniques involving imaging and optics. In this context, two distinct micro-scale devices have been examined for screening blood cells, specifically platelets and red blood cells. In this comprehensive investigation, microfluidic devices were characterised through micro-PIV measurements to understand their performance in high-strain rate applications, particularly in blood handling and hydrodynamic particle trapping. The study employed micropump devices with varying actuation frequencies to mimic pulsatile flow profiles. Interestingly, only one specific channel operating at 3 Hz proved optimal for platelet-based assays, successfully managing small fluid volumes while achieving the critical shear gradient required for platelet activation. Notably, fabrication tolerance variations among devices underscored the importance of device uniformity. Furthermore, the micro-PIV measurements were extended to cross-slot channels to estimate strain rates at different Reynolds numbers. This multifaceted approach enhanced the understanding of microfluidic devices, aiding in the selection of appropriate platforms for applications demanding high strain rates. For the motivation of single-cell experiments, real-time imaging control experiments were conducted for hydrodynamic particle trapping in microfluidic cross-slot channels. Through detailed characterisation in channels of varying widths (0.4 mm and 0.1 mm), the study employed an image-based linear feedback control algorithm implemented in Python-OpenCV to assess the stability of particle confinement. The investigation revealed a distinct interplay between algorithmic delay, particle resolution, and achievable strain rates. Specifically, reductions in algorithmic delay led to notable increases in the maximum attainable strain rates, particularly evident in the 0.1 mm channel, where controlled high strain rates of 250 (1/s) ever achieved in the cross-slot channels. Moreover, the study expanded its scope to investigate the feasibility of trapping individual red blood cells (RBCs) under high strain rates, elucidating the challenges posed by the asymmetrical nature of biological specimens. These investigations underscored the critical need for robust image processing techniques, especially for asymmetric entities like RBCs, to ensure accurate measurements at elevated strain rates. Overall, this research lays a solid foundation for advancing high-strain rate applications in microfluidics, offering insights that extend beyond blood handling to various precision-controlled hydrodynamic scenarios.
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ItemPhysical modelling of riblet performance in yawed and non-yawed flows( 2023-11)We introduce a viscous vortex model to predict the drag and heat transfer of riblets, eliminating the need for expensive direct numerical simulations (DNS) or experiments. The footprint of a typical quasi-streamwise vortex, in terms of the spanwise and wall-normal velocities, is extracted from smooth-wall DNS flow fields in close proximity to the surface. The extracted velocities are then averaged and used as boundary conditions in a Stokes-flow problem, wherein riblets with various cross-sectional shapes are embedded. Here, the same smooth-wall based boundary conditions can be used for riblets, as we observe from the DNSs that the quasi-streamwise vortices remain unmodified apart from an offset. In particular, the position of these vortices remain unpinned above small riblets. This smooth-wall-like behaviour persists up to the optimal size of riblets, and also up to a yaw angle of 15 degrees, enabling us to predict the riblet drag and heat transfer within these size and yaw-angle constraints. The present approach is compared with the protrusion height model of Luchini et al. (J. Fluid Mech., vol. 228, 1991, pp. 87–109), which is also based on a Stokes calculation, but represents the vortex with only a uniform spanwise velocity boundary condition. The key novelty of the viscous vortex model is the introduction of a non-zero wall-normal velocity component into the boundary condition. This approach induces transpiration at the riblet crests, as transpiration becomes relevant at increasing riblet sizes. Consequently, we show that the drag and heat-transfer prediction of the present model agree with our DNS data, as well as published data.
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ItemComputational wake acoustics : effects of freestream disturbances on wake structure and sound emission(University of Melbourne, 2010)
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ItemAnalysis of numerical error on unstructured meshes: with applications to fluid dynamics(University of Melbourne, 2010)
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ItemSensor scheduling for target tracking in sensor networks(University of Melbourne, 2009)
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ItemTrapping and manipulation of small particles using laser lights(University of Melbourne, 2009)
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ItemHybrid methods for the detection of regulatory signals in genomic sequences(University of Melbourne, 2008)
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ItemBiomechanics of the anatomical and reverse shoulder(University of Melbourne, 2008)
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ItemFlame propagation and knock in a HAJI engine(University of Melbourne, 2008)