Engineering

Publication Search Results

Now showing 1 - 10 of 164
  • (2023) Chai, Qingmian
    Thesis
    Traditional passive distribution networks can not sufficiently handle the voltage stability issues brought by the increasingly integrated PV systems, while an active distribution network, which features active management of distributed energy resources, can flexibly utilise PV inverters to provide a volt/var control (VVC) function to regulate the network voltage. However, PV inverters are vulnerable power electronics devices and utilising them for additional VVC support can further degrade their reliability, leading to shortened inverter lifetime and impaired economic benefits. In this regard, the thesis focuses on addressing the PV inverter reliability issues in VVC methods, via assessing the PV inverter reliability in VVC and proposing advanced PV inverter based VVC methods considering inverter reliability enhancement. The thesis consists of four stages of my research. Firstly, a comprehensive PV inverter reliability assessment approach is developed to evaluate inverter lifetime when used for VVC functions, and the impacts of the PV inverter based VVC on inverter lifetime are successfully quantified. Secondly, a PV inverter reliability constrained VVC method is proposed in which the constraints to enhance inverter reliability are developed with a restriction factor to regulate inverter apparent power outputs. This method can efficiently minimise network power loss and curtailed PV power, while guaranteeing long inverter lifetime. Thirdly, a PV inverter reliability constrained VVC approach with power smoothing is proposed, in which an inverter power smoothing scheme with high control flexibility is developed by utilising a power smoothing factor to constrict variations of inverter apparent power outputs. Additionally, a penalty convex-concave procedure (CCP) solution method is developed to solve the non-convex optimisation problem with high computing efficiency. Fourthly, a multi-objective PV inverter based VVC method is proposed to simultaneously minimise network power loss and inverter apparent power output, and a Pareto front analysis method is developed to select a solution to achieve efficient power loss reduction with expected inverter lifetime. All the proposed methods apply advanced network operating models and optimisation methods to address uncertainties. These methods have been successfully demonstrated and tested through comprehensive case studies, and numerical simulation results verified the feasibility and high efficiency of the proposed methods.

  • (2023) Li, Qingya
    Thesis
    This age has witnessed a proliferation of technological advancements that affected all facets of civilisation. Driven by the joint force of the evolution of sophisticated design tools, tailored material characteristics, and robust mechanics-based analyses, smart composite materials are widely used in high-performance engineering applications. Meanwhile, there is a growing interest in micro/nanoscopic structures in academia and industry due to the overwhelming trend toward portability, miniaturisation and integration in engineering. Therefore, the theoretical, computational, and experimental research communities have developed various effective methodologies to understand the structural behaviour of smart small-scale structures comprehensively. This dissertation introduces two size-dependent continuum theories, modified strain gradient and nonlocal strain gradient theories, to build the analytical framework for exploring application-driven micro/nanoplates made of smart composite materials. As examples of promising candidates for power supply and nano/microelectromechanical systems, organic solar cells and thermo-magneto-elastic sandwich nanoplates are studied. Size-dependent continuum models combined with various shear deformation plate theories are adopted to derive the governing equations. The size-sensitive static and dynamic mechanical responses, including bending, buckling, and free vibration behaviours of these ultra-fine-size structures, are predicted by capturing the size effect with material length scale or nonlocal parameters. The numerical results underlying size-dependent theories pose a new insight into the structural analysis of functional micro/nanoscopic plate-like structures. Some typical size-involving mechanical characteristics are revealed by comparing the present estimation with those from size-independent models. Moreover, the simulation outcomes thoroughly investigate several practical factors, such as boundary conditions, geometric configuration, and elastic foundation modelling parameters. In this endeavour, taking advantage of the computational efficiency and accessible operation of nonclassical continuum-based theories, the current analytical framework is suitable for exploring the size-tendency of the smart micro-/nanosized structures. The present work may serve as a benchmark for following numerical simulations and as a guide for evolving new engineering tools for modelling relevant responses by designers and manufacturers.

  • (2023) Afzal, Hafiz
    Thesis
    Sensory signals informing about frictional properties of a surface are used both for perception to experience material properties and for motor control to be able to handle objects using adequate manipulative forces. There are fundamental differences between these two purposes and scenarios, how sensory information typically is obtained. This thesis aims to explore the mechanisms involved in the perception of frictional properties of the touched surfaces under conditions relevant for object manipulation. Firstly, I show that in the passive touch condition, when the surface is brought in contact with immobilised finger, humans are unable to use existing friction-related mechanical cues and perceptually associate them with frictional properties. However, a submillimeter range lateral movement significantly improved the subject's ability to evaluate the frictional properties of two otherwise identical surfaces. It is demonstrated that partial slips within the contact area and fingertip tissue deformation create very potent sensory stimuli, enabling tactile afferents to signal friction-dependent mechanical effects translating into slipperiness (friction) perception. Further, I demonstrate that natural movement kinematics facilitate the development of such small skin displacements within the contact area and may play a central role in enabling the perception of surface slipperiness and adjusting grip force to friction when manipulating objects. This demonstrates intimate interdependence between the motor and sensory systems. This work significantly extends our understanding of fundamental tactile sensory processes involved in friction signaling in the context of motor control and dexterous object manipulation tasks. This knowledge and discovered friction sensing principles may assist in designing haptic rendering devices and artificial tactile sensors as well as associated control algorithms to be used in robotic grippers and hand prostheses.

  • (2023) Kilani, Mohamed
    Thesis
    Nanowire-based sensors offer extraordinary performance to accurately detect and quantify chemical and biological analytes relevant to industrial safety, medical diagnosis, food quality, and defense applications. Their superior performance originates from their small size and ultrahigh surface-to-volume ratio, which allows higher sensitivity, selectivity, faster response, and lower power consumption compared to their traditional counterparts. Yet, despite hundreds of published studies on nanosensors each year, very few reached the market. The translation of the nanosensors from the proof-of-concept stage to mass production has proven to be problematic. This thesis presents potential solutions to overcome the nanowire device manufacturing scalability problem. The studies presented here focus on the controlled electrodeposition of Charge-Transfer Complex (CTC) nanowires on electronic substrates to reduce the complexity in nanosensor fabrication. First, a simple method is reported to control the growth and assembly of electrodeposited tetrathiafulvalene bromide ((TTF)Br) nanowires using microelectrodes. The controlled mass transport on microdisk electrodes produced more uniform nanowires with higher aspect ratios and controlled density compared to those electrodeposited on planar electrodes. This was extended by electrochemically depositing (TTF)Br nanowires across interdigitated photolithographic microelectrodes to make gas sensing devices. The sensitivity and selectivity of the sensors were tuned by varying the nanowire chemical composition, which can be controlled by the applied potential and precursor concentration. Finally, the effects of the potential, concentration, and electrode geometry on the early stages of the CTC electrodeposition were investigated. By lowering the electrochemical potential, new insights were revealed into the nucleation and crystallization process from the initial pre-critical nanoclusters to the final 1D hollow crystals. Customized nanopatterned electrodes were used to spatially adjust the nucleation and growth rates in a controlled process predictable by mass-transport modelling. Collectively, this work presents simple systematic methodologies for the controlled electrodeposition of CTC nanowires by tuning the electrochemical parameters. The outcomes of this thesis provide new technological solutions to the nanowire sensor manufacturing scalability, which can potentially lower the barrier towards the commercialization of nanodevices.

  • (2023) Broadbent, Gail
    Thesis
    To obviate significant and growing road vehicle greenhouse gas (GHG) emissions contributing to climate change, transitioning to battery electric vehicles (BEV) is urgently required to maximise fleet emissions reductions soonest, deploying the most suitable available technology. Many countries have implemented policies to incentivise electric vehicle (EV) uptake, which have been well studied. This thesis undertakes novel research by employing a case study of New Zealand to examine consumer responses to EV policies implemented in 2016, plus two mooted policies. Questionnaires and interviews surveyed private motorists from a demand perspective, capturing quantitative and qualitative data to assess attitudes, values, and perceptions of EVs, awareness of government policies, and to reveal those most popular. Employing a unique innovation, four motorist groups (segmented by attitude to EVs, which influences adoption rates) were compared. As additional novelty the role of communication channels, including print media, in influencing consumer behaviour was investigated. Results revealed New Zealand’s conventional motorists, in contrast with EV owners, had low policy awareness, confirming international findings. EV Positives, the next-most ‘EV ready’ segment, favoured policies designed to reduce EV purchase price and increase nationwide charger deployment. Concordant with social marketing research, governments should focus on such buyers’ preferences. Furthermore, to improve BEV readiness, disseminating updated information about EVs via multiple communication channels could shift perceptions of EVs from ‘expensive and inconvenient’ to ‘fun and economical’. Thus, two key concepts namely purchase price-parity and charging infrastructure availability, were incorporated into models specifically for Australia, where policies are limited, to investigate the feasibility of transitioning Australia’s road vehicle fleet to electromobility to achieve net-zero emissions by 2050. A national scale, integrated, macro-economic, system dynamics model (iSDG Australia) was used innovatively to project Australia’s future road transport demand, vehicle mix, energy consumption and GHG emissions. Firstly, the model applied numerous ‘adoption target’ scenarios comparing them to Business-as-Usual; secondly, various combinations of policy options were modelled to project potential outcomes and implementation costs. Based on the assumptions, results suggest emissions reductions are maximised by the fastest passenger vehicle fleet transition to BEVs, entailing declining but ongoing transformational government policy support to achieve net-zero by 2050.

  • (2023) Ding, Yuchen
    Thesis
    The flow that forms in the junction region between a wing and a wall is associated with a horseshoe vortex (HSV) structure, potential trailing edge (TE) flow separation and low-frequency flow-induced noise. To characterize the turbulent junction flow as well as the unsteady loading and the induced-noise generation, a combined experimental and numerical study is presented in this thesis. Acoustic beamforming results demonstrate that junction noise dominates over other wing noise sources in the low-frequency range. Most of the junction noise originates at the leading edge (LE)-wall junction region, and its magnitude primarily depends on the LE bluntness, while variations in camber have little influence on the junction noise spectra. Mean total wall pressure measurements exhibit variations of the flow structure at different streamwise locations around the wing, indicating that increasing junction noise level with angle of attack (AoA) is due to stronger interaction of the lowmomentum flow with wing-wall junction. Additionally, lowering the wing aspect ratio (AR) enhances the effect of the tip vortex which modifies the junction vortex structure and the shear layer on the wing surface. The junction flow environment challenges traditional turbulence closure models in even the mean wall pressure predictions. The γ-Reθ SST model, due to its transition predictor, slightly outperforms other turbulence models including two second closure models in pressure predictions. The unsteady wall pressure results reveal that the fluctuating wall pressure is a function of the wing AoA and AR, particularly in the LE stagnation region and on the suction side. The pressure fluctuations are most energised around the LE due to intense LE-flow interaction which coincides with the junction noise source location. The LE pressure fluctuations are significantly increased at higher AoA, only displaying a slight reduction in the pressure level in a deep stall condition, which coincides with the observations in the far-field acoustic analysis. To complement the experimental findings, a Large Eddy Simulation (LES)study of the wall-mounted wing was performed to visualize the junction flow structure. The observed rapid variation of the mean strain rate in the LE-junction separation region is contradictory with the Boussinesq assumption and explains the failure of traditional turbulence models in capturing the LE flow physics. The streamwise pressure spectral level in the flow upstream is greatly enhanced at all frequencies as the boundary layer approaches the LE. The HSV formation is primarily responsible for the generation of the low frequency content below a chord-based Strouhal number of Stc = 3.5. As the frequency increases, likely due to the multimode oscillation of the HSV, the local peak of unsteady pressure splits into several distinct cores. Further increasing the frequency to Stc = 28 weakens the dominance of the pressure fluctuations in the HSV region and enhances the contribution of the downwash region attached the LE likely as a result of the Kelvin-Helmholtz convective instabilities.

  • (2023) Tahir, Muhammad Naeem
    Thesis
    Metal-faced insulating sandwich panels (MFISPs) typically consist of two cold-formed thin metal face sheets which may be flat, lightly, or heavily profiled with an intermediate thick insulating layer made from rigid or flexible polymer foam core. This thesis investigates the thermo-mechanical structural response of such panels under typical summer conditions that incorporate the effects of high temperatures, thermal cycles, and lateral loading with a particular emphasis on their local buckling (wrinkling) behaviour. In the first phase of the thesis, the effects of sustained high temperatures and thermal cycles on the mechanical properties of expanded polystyrene (EPS) foam core were examined through a comprehensive experimental investigation on small-scale sandwich specimens. A total of 117 specimens were cut from metal-faced sandwich panels with EPS core and were exposed to different numbers of thermal cycles and/or sustained high temperatures. The specimens were then loaded under compression, tension, and four-point bending for evaluating the degradation of the mechanical properties of the foam. The thermal cycles reflect typical surface temperature during daily summer conditions in Australia, with a cycle period of 24 hours each and with a temperature varying between 24°C to 80°C. Although the ambient temperature in most hot summer conditions is around 40°C, the temperature of metal surface exposed to sunlight depends on its color and reflectivity and can reach up to 80°C. The results show that the modulus of elasticity of EPS foam in compression reduced by about 38% after exposure to thermal cycles for 45 days, whereas the tensile and shear moduli reduced by about 5.7% and 13.8%, respectively. Exposure to sustained high temperature after thermal cycles led to larger degradation of the elastic and shear moduli in the range of 38%-50%. These degradations can lead to early failures in applications that rely on the EPS foam as a structural component like in MFISPs. In the second phase, an experimental and numerical investigation of the influence of sustained and cyclic temperatures on the thermo-mechanical response of MFISPs under lateral pressure was carried out. A total of 20 full-scale panels made with two different thicknesses were tested under instantaneous loading at ambient conditions as well as under various combinations of sustained high temperatures, thermal cycles, and loading. The panels were 3.25 m long by one meter wide with a core thickness of 50 mm or 75 mm. The load was applied through a vacuum chamber whereas thermal blankets were used for sustained and cyclic thermal exposure of the panels. Each thermal cycle entails 24 hours of time duration with a temperature range between 20⁰C to 80⁰C. The results show a consistent reduction in the initial stiffness, local buckling pressure, and strength of the panels when they were loaded at high temperatures. These reductions were more substantial (up to 24%) under the combined effects of high temperature (80⁰C), 45 thermal cycles, and loading. The study also shows that the thickness of the foam core can play an important role in controlling the local buckling capacity and strength of MFISPs. The numerical investigation is based on the development of a nonlinear 3D finite element (FE) model using the commercially available software ABAQUS. The FE results are in relatively good agreement with the test results. The numerical results provide further insights into the structural response and explain certain aspects that could not be obtained from the test results. Numerical investigation of the structural response of continuous panels is also conducted. The results show that the critical failure mode of continuous profiled MFISPs when subjected to uplifting (suction) wind pressure is local buckling at intermediate supports followed by steel yielding. Moreover, the thermal exposures combined with a wind load significantly affect the structural performance of the continuous sandwich panels. The strength of these panels is reduced by about 17.5% under the combined effects of high temperature (80⁰C), 45 thermal cycles, and uplifting pressure. Finally, a simplified FE modeling approach is proposed to estimate the local buckling pressure of MFISPs. Within the proposed approach, only the face sheet under compression is modeled; thus avoiding the need to perform a full 3D structural analysis. The working assumption is that the relative deflection of the buckled face against the face under tension (unbuckled face) can be modeled by the use of a two-parameter elastic foundation approach. The elastic foundation is simulated by closely spaced horizontal and vertical springs that model the rigidities of the foam core. Two models are used to determine the elastic foundation properties. The simplified approach is validated through comparison with 3D analyses of full sandwich panels, and through comparison with available experimental results from the literature and the test results generated in this study. The results reveal that the proposed approach can be applied to all types of MFISPs (flat or heavily profiled) with a variety of foam cores and thicknesses of the face sheet. This modeling approach is also applied to investigate the effects of various parameters including the height of the profiling region, spacing of profiling ribs, length of the panel, thickness and modulus of the foam core, and thickness of the profiled face sheet, on the local buckling capacity of profiled MFISPs. It was found that all the above-mentioned parameters play important roles in controlling the buckling capacity of the panel. However, the slenderness ratio of the panel is the most dominant parameter among all. Furthermore, the influence of debonding at the face-core interface was investigated numerically and showed a substantial reduction in the local buckling pressure and strength of profiled MFISPs. Based on the results presented in this thesis, it can be concluded that typical environmental conditions like sustained and cyclic temperatures combined with wind load can significantly affect the strength of profiled MFISPs. Given that such panels are typically used for roofing in the construction industry, where the combination of the above-mentioned loads are inevitable at certain regions, the results presented in this thesis are recommended for consideration in their design. The simplified FE approach presented in this work, as well as, the full FE analysis provide the numerical tools required to predict the local buckling and strength of such panels.

  • (2023) Pirzada, Muhammad
    Thesis
    Understanding the frictional behaviour of rock joints and its associated fluid flow is critical in numerous subsurface engineering applications. Development of underground projects and mitigating their associated hazards, in fact, require a full understanding and accurate modelling of joint shearing processes. Characterising the joint frictional behaviour during shearing, however, offers significant experimental and theoretical challenges. This dissertation, therefore, aims to understand the shearing and fluid flow behaviour of rock joint systems with complex void geometries through assessing the joint contact area evolution both experimentally and numerically. To achieve this aim, first, a large number of direct shear tests at varying normal stresses on dry, and saturated natural and synthetic rock joints are performed. The effect of joint contact area and its influence on actual stresses acting on joint asperities in these tests are then investigated. Furthermore, a novel experimental system coupled with time-lapse X-ray micro-computed tomography (XRCT) is used to measure the contact area and joint aperture evolution during shearing process of several natural joints. The time-lapse XRCT measurements are then extended to synthetic rock joints with varying roughness while joint conductivity is measured under both normal deformability and direct shear testing. Finally, the Discrete Element Modelling (DEM) tool, PFC, is used to model the contact area evolution during shearing of synthetic joints and understand whether the physical processes have been suitably captured. The most important contributions of this dissertation are: i) understanding the effect of joint contact area evolution on joint frictional behaviour and its associated fluid flow, ii) implementing the effect of contact area in hydraulic aperture prediction for more accurate modelling of fluid flow behaviour in joints, and iii) showing that the identified micro-to-macro scale processes involved in contact area evolution can be adequately captured numerically using DEM modelling. These findings provide great insight into the significance of contact area evolution in determining the joint frictional characteristics that influence the hydraulic behaviour of rock joints during complex shearing processes.

  • (2023) Merhebi, Salma
    Thesis
    Liquid metals are fast becoming a new class of materials and additives for composites synthesis. In particular, gallium (Ga) and Ga-based liquid metal and alloys exhibit fluidity and frictionless behaviours along with metallic conductivity properties. Liquid metals based on Ga also present low-toxicity and can be readily formed into micro and nanodroplets or utilised in the bulk as conductive liquid substrates. The resulting Ga-based composites present novel physio-chemical behaviours and multifunctional properties that remain to be explored for a range of applications. In this PhD thesis, the author investigates three liquid metal/polymer composite systems synthesised with low toxicity input materials for remote magnetic actuation, ionic sensing and separation, and cell electrostimulation capabilities. In the first project, the author aims to develop conductive and magnetic liquid metal polymeric gels. Electrically and magnetic conductive nanodroplets of Ga-based alloys are in-situ synthesised in a polyvinyl alcohol (PVA) solution using mild mechanical agitation methods. The resulting conductive and magnetic gels show additional self-healing properties and demonstrate great potential for the design of soft electronic systems and robotics. For the second project, Ga-based composites are investigated for the sensing and separation of alkali metal ions. Nanodroplets of Ga-based alloys embedded into a crosslinked PVA flat-sheet composite provide selectivity and sensing capability and stability in mixed ionic alkali metal solutions. The Ga-based flat-sheet composite has implications for the efficient and low-energy recovery of lithium ions from brines. In the third project, conductive liquid metal polymer composites are prepared for cell culture and electrostimulation. The composite substrates are composed of bulk Ga coated with polydopamine (PDA) to enhance cell adhesion capability. The Ga/PDA composites surfaces show high biocompatibility for cell culture. With added electrical stimulation protocols, the proliferation of mouse embryonic fibroblast cells is promoted. The conductive and biocompatible substrates lead to the use of liquid metals in regenerative medicine and tissue engineering. Collectively, the findings presented in this thesis provide deep insights and scientific findings for future research directions in the field of liquid metal-based composites for multifunctional materials in soft electronics, separation and sensing, and biomaterials.

  • (2023) Wang, Yifang
    Thesis
    The enigmatic surface of gallium-based liquid metals that is ultra-active and smooth, offering opportunities for synthesising and templating two-dimensional (2D) films. When the reactive surface is in contact with an appropriate aqueous solution, the built-in potential at the aqueous solution-liquid metal interface can induce an interfacial reaction and lead to the deposition of desired 2D materials onto the liquid metal surface. In this thesis, the author is involved in research on molybdenum-based 2D materials synthesis at an aqueous solution-liquid metal interface. In the first stage of this Ph.D. research, the author develops a technique of 2D molybdenum sulfide synthesis at the surface of liquid metals. Utilising an aqueous solution of ammonium tetrathiomolybdate as a precursor, 2D molybdenum sulfide layers of large area are deposited on the surface of liquid metals, which are transferrable onto silicon wafers with a touch-transfer technique. Upon annealing, the resultant 2D molybdenum sulfide is of unit-cell thickness and highly crystalline. In the second stage, this Ph.D. research extends this technique to the deposition of molybdenum oxide patterns. Uniform layer of molybdenum oxides, which are hydrated and amorphous, are templated onto liquid metal droplets and later transferred. The as-synthesised molybdenum oxide layers can be selectively dehydrated and crystalised via laser exposure, transforming them into conductive molybdenum dioxide patterns. The resultant conductive patterns show optical and electronic responses to bio-stimuli, which can be used for bio-sensing. In the third stage of this thesis, the liquid metal-aqueous solution interfacial reactions are applied for surface decoration and band structure modulation of liquid metal-based particles. Utilising the built-in potential at the interfaces, a secondary layer of molybdenum-based semiconductor is deposited on the surface of liquid metal particles, leading to core-shell structures with different optical properties and band structures. Collectively, the author demonstrates a new method for synthesising 2D materials utilising aqueous solution-liquid metal interfacial reactions, which potentially establishes a new route for the room temperature deposition of 2D materials at large lateral dimensions. The outcomes of this Ph.D. research offer significant possibilities for future industrial uptakes.