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(2021)ThesisNavigation is a technique for the determination of position and attitude of a moving platform with respect to a known reference. Global Navigation Satellite System (GNSS) has become a dominating navigation technology. However, GNSS signals are degraded or denied in indoor environments. It is necessary to develop alternative positioning techniques for indoor navigation to realize seamless navigation. Inertial Navigation System (INS) and Vision are both regarded to be highly promising because of their ubiquitous and self-contained nature. A new indoor navigation system with vision, INS and reality-based 3D maps are proposed. The main contributions of this thesis are summarized as follows: 1. A new strategy for the integration of vision with a low-cost INS has been developed based on a smartphone. This new approach solves the difficulty of precise calibration of INS errors in such a scenario and enables MEMS INS to generate stable position and attitude solutions. 2. Results show that improved accuracy and reliability of the geo-referenced solution can be achieved. Vision-based navigation with reality-based 3D maps (Vision)/INS integration improves the accuracy and robustness of a navigation solution compared with an INS only solution. 3. Aiding Optical Flow (OF) and Visual Odometry (VO) navigation solution to Vision/INS integrated system improved geo-referenced results during Vision outages. The results confirmed the effectiveness of integration for high accuracy positioning applications. 4. A novel geo-referenced system based on Vision/OF/VO/INS integration has been developed and tested for indoor navigation. Real experiments are conducted to evaluate the influence of different integrated configurations on the performance of the navigation system. 5. Integrated indoor navigation requires a robust outlier detection mechanism to ensure good performance. Outlier detection and identification are explored and researched on the integrated indoor navigation system. Besides, a multi-level outlier detection scheme for the navigation system has been proposed. 6. Analyzing the factors that influence the correlation coefficients between fault test statistics in Vision/INS measurements and the dynamic model is another essential contribution of this thesis. Reliability and separability analysis of outlier detection theory was extended by providing a more reliable estimation of MDB and MSB.
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(2021)ThesisDue to the large variety and unique physiochemical properties, such as high electrical conductivity, adjustable interlayer spacing, intercalation chemistry and so on, two-dimensional (2D) materials have attracted tremendous attention for their suitability in the development of high-performing supercapacitors. Despite that great progress has been made, there is still no single 2D material that can perfectly meet all the requirements to replace the existing material, mainly activated carbon, used in commercial supercapacitors. Therefore, continuing efforts for exploring novel, high-performing 2D materials with low cost are desirable. In this dissertation, the prior studies on the development of 2D materials ranging from layered inorganic materials to organic-inorganic hybrids for supercapacitors are first reviewed. As an emerging type of 2D material, layered organic-inorganic hybrids start to show promising results to be used to fabricate high-density, nonporous, and thick electrodes for compact capacitive energy storage. However, the studies in this area are still lacking. Thus, the goal here is to explore the opportunities of 2D organic-inorganic hybrids for applications in supercapacitors. The relevant techniques and methods used throughout the study are then outlined. Next, three research chapters supporting the main findings of the investigation are included. The first research chapter describes a facile mechanical strategy to improve the kinetics and rate performance of 2D organic-inorganic hybrid electrodes at ultrahigh mass loadings (up to 30 mg cm-2). The second research chapter reports the synthesis of a new layered organic-inorganic hybrid material with excellent volumetric and areal capacitances even at mass loadings reaching 50 mg cm-2, highlighting the good electrode kinetics. The third research chapter presents the wafer-scale electrochemical deposition synthesis of 2D organic-inorganic composite films with controlled size and thickness, which are promising for the development of flexible and transparent electrochemical energy storage devices. Finally, conclusions and recommendations are given at the end of this dissertation.
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(2021)ThesisNatural kidney filtration is a compact, multi-step filtration process which passes wastes and exceeded fluids via microscale vessels in glomerulus and tubules. The principal renal replacement therapy (RRT), commonly called dialysis, is a single-step filtration process based on diffusion to replace kidney failure. Conventional dialysis is limited in its effectiveness (not a continuous treatment), its impact on quality of life (typically requiring patients to spend several days per week in a clinic), and its cost (large systems, requiring frequent membrane replacement). This thesis is an investigation into the feasibility of using microfluidics and membrane technology to create portable alternatives to dialysis systems. It starts with a comprehensive review of the state-of-the-art in portable artificial kidneys, microfluidics, membrane science, and other related fields. An innovative, multi-step process was designed to mimic kidney filtration using two membranes; one to filter out large particles and one to remove urea and recycle water, thus mitigating the need for a dialysate system. The underlying physics (the mixing and shear stress) of the mechanisms which could enhance filtration performance at microscale was then studied. It was found that by adding microspacers into narrow-channel flows, it is possible to significantly enhance filtration. Optimized 3D-printed spacer designs (e.g., a ‘gyroid’ spacer) showed flux enhancement of up to 93% (compared to a plain channel) when using a plasma mimicking solution. The use of different blood and plasma mimicking solutions also suggested a prior step to separate large biological components (e.g., cells, proteins) is helpful to reduce cell contact and fouling in membrane filtration. The potential use of microfluidic diode valves and micropumps for pressure and flowrate regulation in the proposed small-format system was discussed. Membrane processes which mimic the filtration function of the tubules and have the potential for integration into portable systems (e.g., reverse osmosis and membrane distillation) are demonstrated to be useful potential alternatives to dialysis in toxin removal and in returning clean water to the blood stream.
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(2021)ThesisA pseudolite (PL) is a ground-based positioning system that offers flexible deployment and accurate “orbits”. The PL system can carry on the role of the GNSS to provide precise positioning for indoor users. However, there are some unusual challenges that seriously affect the performance of a PL system in precise indoor positioning. To raise PL-based positioning accuracy up to the centimeter level or higher, the use of the PL carrier phase measurement with ambiguity resolution is a unique consideration. The PL phase ambiguities are also contaminated by clock bias, multipath errors, and cycle clips. Their existence destroys the integer nature of ambiguity and impedes the pursuit of further accuracy improvement. The major contributions in this research for addressing the above-mentioned challenging issues are specified as follows: 1. The ground-based AR methods are discussed. The impact of ground-based geometry on indoor AR is researched, and the influence of linearization error is also investigated. An efficient PL-based AR method is studied and verified in the balance of gaining convenience and avoiding linearization impact. 2. The clock bias between PL transmitters can be properly handled in a way that time synchronization can be achieved with a transmitter-only PL system at low cost and simplicity. Therefore, the PL-based the ambiguities are able to be fixed to correct integers, and centimeter-level indoor precise positioning can be reliably achieved. In addition, the proposed way for time synchronization is also applicable for other ground-based systems for precise positioning purposes. 3. The stochastic model for mitigation of indoor multipath and NLOS is investigated. The experimental results demonstrate that the proposed stochastic model is superior to other existing models in indoor multipath mitigation as it is competent to suppress the multipath errors mainly caused by multipath to the smallest in both static and kinematic results, respectively. Moreover, it is also verified to be efficient for NLOS mitigation. With the proposed new stochastic model, precise point positioning is confidently expected indoors. 4. The methods for PL-based cycle slips are extensively studied and discussed. Numerical results indicate that the integer-cycle slips can be efficiently and accurately detected and corrected. The concern about PL-based cycle slip is minimized, the reliability and sustainability of PL-based precise indoor positioning can be promised.
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(2021)ThesisUnderwater sound can have a detrimental effect on marine animals due to the ever-increasing noise levels in their pristine habitat. It has also been commonly used to detect underwater floating objects via a sonar system. To absorb unwanted underwater sound, polymers (e.g., rubber), which have similar impedance to that of water, are widely used for sound absorption in water. Nanocomposites have attracted considerable attention due to their ability to improve sound absorption properties of polymer-based sound absorption materials. This project aims to develop a thin-layer nanocomposite with high underwater sound absorption at low frequency and high pressure. A water-filled impedance tube, an essential facility to test new materials developed in this PhD thesis, was designed and constructed. The established research facility consists of four main components: a stainless steel tube and its supporting devices, a sound source (a projector) and its associated electronics, an underwater sound pressure measurement system, and a water pressurized system. Subsequent calibrations and measurements showed that the established apparatus could be used to measure the underwater sound absorption coefficient in a frequency range of 1500 Hz to 7000 Hz and under hydrostatic pressure in a range of 0 to 1.5 MPa. Carbon nanotubes (CNTs) reinforced polydimethylsiloxane (PDMS) nanocomposites were designed, fabricated, and tested. This development comprised of two stages. In the first stage, PDMS was selected as the material matrix, surfactant and carboxyl functionalized multi-walled carbon nanotubes (MWCNT-COOH) as inclusions, and a new nanocomposite, namely PSM (PDMS/surfactant/MWCNT-COOH), was then developed. Effects of the added surfactant and MWCNT-COOH on the mechanical properties, chemical properties, and morphology were investigated, which indicated the nanocomposite’s potential for sound absorption improvement. Underwater acoustic tests showed high underwater sound absorption coefficients (>0.8) in the most frequency range 1500 Hz to 7000 Hz. However, it was observed that a significant drop in the underwater sound absorption performance under high hydrostatic pressure. It was found that the high compression of PSM was the cause of poor performance under high hydrostatic pressure. In the second stage, a core-shell structure was designed to maintain the high sound absorption coefficient of PSM under high hydrostatic pressure. A novel structure of a 2-mm-thick hard shell with a 2-mm-thick soft layer was developed to encapsulate the PSM sample so that its deformation can be minimized and its superior sound absorption property was improved under high pressure. Experimental results on the water-filled impedance tube demonstrated that the new structure offered a promising solution to the demand for advanced underwater materials, which are thin and have high sound absorption performance under high hydrostatic pressures. In summary, this study has developed a polymer-based nanocomposite. Mechanical properties, chemical properties, morphology, and underwater acoustic properties of the nanocomposite have been studied. The nanocomposite is thinner than existing underwater acoustic materials and has excellent underwater sound absorption performance in the frequency range of 1.5 to 7 kHz and under atmospheric pressure. For applications in high hydrostatic pressure up to 1.5 MPa, the proposed new structure with a total thickness of 14 mm, in comparison to 50 mm or more thickness of other developed materials for marine applications, showed good sound absorption results and potentially addressing the on-going technical challenge of poor sound absorption performance of acoustic materials under high hydrostatic pressure.
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(2021)ThesisCataracts are responsible for almost half of worldwide blindness, making it one of the biggest health challenges in this era. Cataracts are irreversible because of their pathology, which is controlled by the aging and biochemical change of eye tissues. As a result cataract surgery is currently the only effective treatment. The general procedure of cataract surgery includes separation and removal of the failed lens tissue from the surrounding soft tissue in the eye, followed by artificial lens implantation. Lens removal requires successful separation of lens tissues as a critical step that determines surgical success. However key parts of cataract separation affected by fluid mechanics and rheology are uncharacterised. This project aims to explain the behaviors of such separation phenomena and connect fundamentals with possible explanations and enhancements. A multi-layer bio-polymer injection model is developed to mimic the separation process in cataract surgeries. The separation can be considered peeling of a soft elastic tissue by a pressure-driven fluid flow, whose performance is closely related to properties such as flow rate and velocity as well as fluid viscosity, normal stress and yield stress. In our project, the separation physics is studied as a hydraulic fracture problem. Theories are proposed to discuss the effectiveness and safety of hydraulic fracture with different flow and fluid parameters. It is found both higher flow rate and viscosity will cause tissue to be deformed more, which may increase the risks of tissue damage. Yield stress fluids with significant elasticity are not suitable as in most cases they rupture the tissue. Normal stress fluids have the potential to provide safe and effective separation. It is found that with a small scale separation, however, the separation effectiveness is mainly affected by the flow rate, and the fluid properties play a more minor role. General ideas and potential improvements according to our results and theories are also proposed for cataract surgeries, which we hope will contribute to easier and safer separation.
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(2021)ThesisPolymer brushes are arrays of densely surface-tethered polymer chains, and are of interest for two reasons. Firstly, they possess interfacial characteristics, such as antifouling and lubrication, that are desirable in many applications. Secondly, they are model systems that can provide additional insight into polymer behaviour due to their unique geometry. Observing the interfacial structure of these brush layers is critically important for understanding both their properties and the mechanisms driving the polymer behaviour. To date, neutron reflectometry (NR) is the only technique that can demonstrably resolve the nanoscale structure of polymer brushes. However, these diffuse interfaces produce subtle features in the reflectometry data that challenge interpretation, with typical analyses failing to quantify the derived structure's uncertainty. Furthermore, the experimental potential of this technique for the study of brushes is only just being realised. This Thesis advances NR as a tool for studying polymer brush systems by establishing a robust analysis methodology that overcomes previous hurdles and demonstrating novel experimental techniques. In both cases, poly(N-isopropylacrylamide) (PNIPAM) brushes are used as model systems. First, the polymer system is characterised through the novel observation of surface-initiated ARGET ATRP using time-resolved NR, and a study of the dry brush as a function of humidity and temperature. Second, methodologies are developed that allow for robust determination of both solvated and confined brush structures. Lastly, NR is used to elucidate the behaviour of PNIPAM brushes in complex environments. A novel confinement apparatus is used to investigate the structure of a PNIPAM brush under mechanical confinement and contrast-variation provides unparalleled insight into PNIPAM–surfactant systems. In each case, complementary techniques are essential in guiding reflectometry experiments and fully understanding the polymer system. This work develops and demonstrates techniques that enhance the study of diffuse interfaces with the NR technique. Moreover, the holistic structural examination of PNIPAM undertaken sheds new light on the phase behaviour of this ostensibly well-understood polymer and highlights its rich interaction with surfactants.
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(2021)ThesisThis thesis investigated the ecology and metabolism of microorganisms, especially yeasts, during the wet fermentation of Australian coffee beans, and their contribution to coffee quality. Pulped coffee beans were fermented underwater for 36 h where yeast growth was suppressed by the addition of Natamycin at 300 mg/L. Spontaneous fermentation without the addition of Natamycin was conducted as control. The growth and diversity of microorganisms during fermentation were monitored by both culture dependent and independent methods. Major non-volatile metabolites during fermentation were monitored by high performance liquid chromatography (HPLC) and volatiles in the green and roasted beans were measured by solid phase microextraction coupled with gas chromatography tandem mass spectrometry (SPME GC-MS). Both bacteria and yeasts grew significantly during spontaneous fermentation while yeast growth was restricted in the Natamycin treated fermentation without significant impact on bacterial growth. The bacterial community was dominated by Citrobacter sp., Gluconobacter cerinus, Leuconostoc mesenteroides and Lactococcus lactis with maximum populations between 4-7.2 log CFU/g, while Hanseniaspora uvarum and Pichia kudriavzevii were the predominant yeasts at 4.5-5 CFU/g. During fermentation, the microflora utilized sugars in the mucilage and produced mannitol, glycerol and essential volatiles, mainly alcohols, esters, aldehydes and organic acids, with their concentrations generally lower in beans fermented with yeast suppression. Coffee produced from yeast suppressed fermentation received lower sensory scores in flavour and aroma and overall quality by 3 Q-Grade coffee masters. When H. uvarum and P. kudriavzevii were inoculated individually and in combination, they dominated the fermentation by growing to 9-10 log CFU/ml, and produced greater amounts of glycerol and flavour volatiles in the green beans which remained in higher levels after roasting compared with the control. Coffee brewed from these beans received significantly high scores of flavour, aroma, acidity and overall quality. Mucilage degradation seems to be initiated by endogenous enzymes and microbial contributions to the process occurred subsequently either enzymatically or by acidification. These findings demonstrated the crucial contribution of yeasts to successful coffee fermentation and high-quality coffee, and the potential of developing the two yeasts into starter cultures for coffee fermentation.
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(2021)ThesisRural electrification demands the use of inexpensive technologies such as single wire earth return (SWER) networks. There is a steadily growing energy demand from remote consumers, and the capacity of existing lines may become inadequate soon. Besides, the existing SWER networks are very inefficient and experience poor voltage regulation. Furthermore, high-impedance arcing faults (HIF) from SWER lines can ignite bushfires such as the catastrophic 2009 Black Saturday bushfires in Victoria (Australia). Replacing SWER lines by cables as recommended by the Victorian Royal Commission comes at an astronomical cost and service providers are not able to comply with. As a solution, reliable remote electricity networks can be established through splitting the existing system into microgrids, and existing SWER lines can be utilised to interconnect those microgrids. The development of such reliable networks with better energy demand management will rely on having an integrated network-wide condition monitoring system. As the first contribution of this thesis, a distributed online monitoring platform is developed that incorporates power quality monitoring, real-time HIF identification and transient classification in SWER network. Characteristic features are extracted from the current and voltage signals, and Artificial Intelligence (AI) based classification techniques are developed to classify the faults and transients. The proposed approach demonstrates higher HIF detection accuracy (98.67%) and reduced detection latency (115.2 ms). Secondly, to facilitate electricity demand management, a remote consumer load identification methodology is developed to detect the load type from its turn-on transients. An edge computing-based architecture is proposed to facilitate the high-frequency analysis for load identification with minimum data transmission. Computationally efficient load identification methodologies are developed to enable their real-time deployment on resource constrained devices. The proposed approach is evaluated in real-time, and it achieves an average accuracy of 98% in identifying different loads. Finally, a deep neural network-based energy disaggregation framework is developed to separate the load specific energy usage from an aggregated signal. A generative approach is applied to model energy usage patterns. The proposed framework is evaluated using a real-world data set. It improves the signal aggregate error by 44% and mean aggregate error by 19% in comparison with other state-of-the-art techniques.
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(2021)ThesisIn recent years, electric power generation using renewable energy sources has experienced an exponential growth in the world energy market. Their unprecedented large scale penetration foresees a 100% renewable based power generation in near future. These sources require power electronic converters at various levels for power conversion and grid integration. The converters are fast acting devices and use advance control techniques in a hierarchical manner. With the retirement of the conventional synchronous generators, the modern power electronics based power system lacks the inertia property. Hence, they are more vulnerable to several grid transient events; for instance grid faults. Control functionalities classify these converters as grid-forming and grid-following. Both these types can act as grid supporting devices during grid fault. In contrast to grid-forming type, grid-following type converters are mostly used to support the grid. The act of supporting the grid with reactive power instead of tripping during a fault for a pre-defined duration is known as fault ride-through. These converters rely on a separate synchronization unit to inject grid current during both normal and fault condition. Recent grid fault events across the globe have revealed the inefficiency of such synchronization units. This is attributed to the delayed grid parameter estimation that eventually leads to the tripping of the converters rather ride-through. It indicates that the performance robustness of the synchronizing unit while considering the fault ride-through of converter needs to be further investigated thoroughly. In lieu of the above, accurate and fast grid voltage parameter estimation is essential for grid-connected converters. To achieve this objective, the contributions of this thesis are classified into two parts. The first part of the thesis deals with the fault detection for converters during a grid fault using digital signal processing (DSP) techniques. Faster fault detection is vital to safeguard the power converter as they have limited fault current carrying capacity. Hence a hybrid fault detection technique is proposed. The technique combines the features of two DSP techniques, Hilbert-Huang Transform (HHT) and Teager Energy Operator (TEO). This is called Teager-Huang in this thesis. With this proposed technique, several grid faults, balanced and unbalanced, in both the grid voltage magnitude and phase-angle jumps are detected. Further, comparisons of the fault energies are presented, which provides a benchmark for the severity of the grid faults. In the second part of the thesis, the synchronization aspect of the converter is investigated. For the purpose of analysis, the synchronization using the classical synchronous reference frame phase-locked loop (SRFPLL) is considered. Initially, the synchronization inefficiency of SRFPLL during the grid fault is explained in regards to the loss of synchronization (LOS) instability. It is shown that the cause for LOS during a fault may be initiated as results of very low grid voltage magnitude, high grid impedance or high current injection. The analysis emphasises on the occurrence of phase-angle jump (PAJ) during a fault. The thesis indicates that the conventional SRFPLL design parameters result in synchronization delay and insufficient damping to ride-through such PAJs. The decrease in the SRFPLL synchronization robustness highly affects the grid-connected converters. To enhance the grid synchronization performance during a grid fault with PAJ, a hybrid grid synchronization concept is proposed. It consists of both hybrid phase-angle estimators and hybrid frequency estimators. The hybrid frequency estimators contain several improved adaptive and PLL independent frequency estimation techniques. The proposed technique is designed to be compatible with both the three-phase and single-phase grid synchronization. To avoid voltage transients during the transition between the estimators, a transition scheme is presented. This is controlled based on the instantaneous phase-angle error measured by the estimators. The three-phase grid-connected converter is modelled using the proposed hybrid grid synchronization technique. The current controller of the converter is designed both in stationary and synchronous reference frame. Further, the fault ride-through (FRT) strategy is embedded in the converter controller. With the developed model, the FRT of the converter is tested during a fault. Both symmetrical and asymmetrical grid faults with PAJs are considered. The efficacy of the proposed technique is evaluated using both simulation and experimental validations. The last part of the thesis explores the FRT of single-phase power converters employing the proposed hybrid grid synchronization transition. The synchronization performance along with the current controller robustness during FRT is investigated.