Engineering

Publication Search Results

Now showing 1 - 10 of 577
  • (2021) Chen, Kai
    Thesis
    Navigation 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. 

  • (2021) Liu, Huabo
    Thesis
    Due 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.

  • (2021) Dang, Bac
    Thesis
    Natural 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.

  • (2021) Sun, Yu
    Thesis
    A 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.

  • (2021) Fu, Yifeng
    Thesis
    Underwater 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.

  • (2021) Li, Zhiwei
    Thesis
    Cataracts 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.

  • (2020) Cho, Yongyoon
    Thesis
    The power conversion efficiency (PCE) of metal halide perovskite solar cells (PSCs) has increased from 3.8 to 25.2% in the last decade, making perovskite the most promising material for future solar cells. However, further PCE and stability improvement are important for successful commercialization. Therefore, the aim of this thesis is to investigate ways of increasing PCE and addressing instability of PSCs. Initial PCE increase has been observed during ambient storage for many PSCs. Through a series of experiments, the origin of the storage effect was attributed to a combination of i) defect reduction in perovskite, ii) conductivity increase, and iii) evolution of the highest occupied molecular orbital (HOMO) in spiro-OMeTAD. In particular, the HOMO level change was revealed to play a significant role in PCE improvement. In terms of strategy for improving PCE, a novel passivation technique was developed by forming 2D/3D perovskite thin layer using a mixture of formamidinium iodide and iso-butylammonium iodide on the perovskite layer. This technique achieved a maximum PCE of 21.7%, while simultaneously enhancing device light and moisture stability. The defect density reduction, the uniform surface coverage of the passivation material and the suppressed ion migration by bulky organic cation were found to be the key parameters for PCE and stability improvement. Storage effect was also studied for these passivated PSCs. It is found that the changed conduction band of passivated perovskite influenced the initial temporal change of PCE, suggesting the importance of interface band alignment by passivation and conductive materials. Also, despite significantly suppressed non-ideal recombination at the surface/interface by passivation, analysis of the dominant recombination revealed the need for defect reduction in bulk perovskite. Consequently, by engineering the composition of bulk perovskite layers to decrease defects, PCE of 22.2% was achieved. Finally, the effects of removing one of hole transport material (HTM) additives, 4-tert-butylpyridine (tBP) (via HTM solvent engineering) on device performance and thermal stability were investigated. The suppressed morphological change at high temperature for tBP-free HTM was the reason for thermal stability improvement. This work shows that comparable efficiencies can still be achieved without the use of the thermally unstable HTM dopant.

  • (2021) Gresham, Isaac
    Thesis
    Polymer 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.

  • (2020) Sarmiento, Czar Jakiri
    Thesis
    The Philippine Height System (PHS) modernisation is driven by recent advances in geodetic technology and the Philippines’ need to be geodetically responsive to natural disasters. Aspects of the shift from a levelling-based system to a GNSS and gravimetric geoid-based system, being a cost-effective modernisation strategy for developing countries, were investigated. This thesis expands available scientific literature for the International Height Reference System/Frame (IHRS/F) development of the International Association of Geodesy (IAG), and the PHS modernisation efforts of the National Mapping and Resource Information Authority (NAMRIA). Three elements of a modern PHS were studied. 1. The engineering implications of the new Philippine Geoid Model (PGM). 2. The temporal variability of the geoid and benchmarks with focus on the effects of tropical hydrology. 3. The PHS relationship to the IHRS/F. An evaluation of the new Technical University of Denmark (DTU-Space) and NAMRIA-developed PGM, was done to provide a quality baseline for managing the progression and limitations of a gravimetric geoid-based height system for the country. Statistical measures show that points clustered in the southern latitudes and eastern longitudes have relatively higher residuals due to geodynamic and hydrologic activity. It is concluded that a localised PGM can be used for third order applications. Tropical effects on the reference frame and the geoid were examined. Displacements were analysed by estimating tidal and non-tidal loading for selected Philippine active geodetic stations using rain sensor data, local geologic information and ground validation. The mean dynamic topography (MDT) was also investigated. DTU10, VM500-ph and RADS-ph were compared with GNSS-geoid MDTs (GNSS-PGM2016.66, GNSS-EIGENGL05C). A nationwide scale, low-resolution Philippine vertical ground motion map inferred from Sentinel-1A scenes from January 2015 to December 2019 was also produced. Estimations confirm the intensity of land motion in the eastern and southern part of the country. Using Gravity Recovery and Climate Experiment (GRACE) temporal models, large variations for two IHRS/F-proposed Philippine stations were computed and show coincidence with high rainfall records. A causality relationship between high rainfall and geoid variation, however, is inconclusive. Lastly, a novel way of characterising local height systems relationship for the IHRS/F that takes into account the non-homogenous states of geodetic development within a developing, archipelagic country is introduced. Recommendations for a modernised Philippine Height System were made as a result of this study.

  • (2020) Morsalin, Sayidul
    Thesis
    Electrical insulation of high voltage (HV) power equipment plays essential roles in sound functioning and reliability of power systems. Examining the insulation condition through various diagnostic testings such as dielectric response (DR) and partial discharge (PD) measurements may be able to reveal the presence of defects and degradations in the insulation. Very low frequency (VLF- 1 Hz or lower) applied voltage has emerged as a promising diagnostic tool as it significantly reduces the required reactive power from the test supply. However, the existing interpretation knowledge at conventional power frequency (PF) 50 Hz cannot be directly applied to understand test results in the VLF range. This is the main motivation of the research which explores the dielectric behaviours and associated physical processes under VLF excitation. For dielectric response, experimental studies were carried out on short sections of medium voltage service-aged cross-linked polyethylene (XLPE) cables to diagnose the bulk insulation condition, such as the measurement of dissipation factor, polarisation and depolarisation current, frequency domain spectroscopy, activation energy etc. Experimental results show that dielectric behaviours of electric insulation are influenced by several factors including the excitation frequency, voltage amplitude, ambient temperature, dipolar processes (e.g. conduction and polarisation) etc. An empirical physical model describing the loss-factor measurement based on well-known dipolar theories is developed and verified by experimental results. Different partial discharge processes (e.g. cavity, surface and corona) are also investigated at both VLF (0.1 Hz) and 50 Hz applied voltage. Measurement results are presented with the phase-resolved image and show that discharge characteristics (inception voltage, magnitude and repetition rate) are strongly dependent on the applied frequency. Based on the finite element analysis (FEA) method, a dynamic model to simulate the discharge behaviours in the cavity or on the degraded surface is developed to examine the frequency dependence. The main contributions of this research include the measurement and modelling of both the dielectric response and partial discharge in electrical insulation. The research findings provide valuable information to understand the diagnostic characteristics at very low frequency excitation.