Engineering

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Now showing 1 - 6 of 6
  • (2022) Zhao, Runqing
    Thesis
    Emerging modes of air transport such as autonomous airport shuttle and air taxi are potentially efficient alternatives to current transport practices such as bus and train. This thesis examines bus shuttle service within an airport and air metro as two examples of network design. Within an airport, the bus shuttle serves passengers between the terminals, train stations, parking lots, hotels, and shopping areas. Air metro is a type of pre-planned service in urban air mobility that accommodates passengers for intra- or inter-city trips. The problems are to optimise the service, and the outputs including the optimal fleet size, dispatch pattern and schedule. Based on the proposed time-space networks, the service network design problems are formulated as mixed integer linear programs. The heterogeneous multi-type bus fleet case and stochastic demand case are extended for the airport shuttle case, while a rolling horizon optimisation is adopted for the air metro case. In the autonomous airport inter-terminal bus shuttle case, a Monte Carlo simulation-based approach is proposed to solve the case with demand stochasticity, which is then further embedded into an "effective" passenger demand framework. The "effective" demand is the summation of mean demand value and a safety margin. By comparing the proposed airport shuttle service to the current one, it is found that the proposed service can save approximately 27% of the total system cost. The results for stochastic problem suggest estimating the safety margin to be 0.3675 times of the standard deviation brings the best performance. For the second case, the service network design is extended with a pilot scheduling layer and simulation is undertaken to compare the autonomous (pilot-less) and piloted service design. The results suggest that an autonomous air metro service would be preferable if the price of an autonomous aircraft is less than 1.6 times the price of a human-driven one. The results for rolling horizon optimisation suggest to confirm the actual demand at least 45 minutes prior to departure. Based on data from the Sydney (Australia) region, the thesis provides information directly relevant for the service network design of emerging modes of air transport in the city.

  • (2021) Alohali, Ruaa Tawfiq A
    Thesis
    The Arabian basin was subject to several tectonic events, including Lower Cambrian Najd rifting, the Carboniferous Hercynian Orogeny, Triassic Zagros rifting, and the Early/Cretaceous and Late/Tertiary Alpine orogenic events. These events reactivated Precambrian basement structures and affected the structural configuration of the overlying Paleozoic cover succession. In addition to a 2D seismic array and several drill well logs, a newly acquired, processed 3D seismic image of the subsurface in part of the basin covering an area of approximately 1051 km2 has been provided to improve the understanding of the regional tectonic evolution associated with these deformation events. In this study, a manual interpretation is presented of six main horizons from the Late Ordovician to the Middle Triassic. Faults and folds were also mapped to further constrain the stratigraphic and structural framework. Collectively, this data is used to build a geological model of the region and develop a timeline of geological events. Results show that a lower Paleozoic sedimentary succession between the Late Silurian to the Early Permian was subject to localised tilting, uplift, and erosion during the Carboniferous Hercynian Orogeny, forming a regional unconformity. Subsequent deposition occurred from the Paleozoic to the Mesozoic, producing a relatively thick, conformable, upper succession. The juxtaposition of the Silurian rocks and Permian formations allows a direct fluid flow between the two intervals. Seismic analysis also indicated two major fault generations. A younger NNW-striking fault set with a component of reverse, east-side-up displacement affected the Lower Triassic succession and is most likely related to the Cretaceous and Tertiary Alpine Events that reactivated the Najd fault system. These fault structures allow vertical migration that could act as conduits to form structural traps. Manual mapping of fault structures in the study area required significant time and effort. To simplify and accelerate the manual faults interpretation in the study area, a fault segmentation method was developed using a Convolutional Neural Network. This method was implemented using the 3D seismic data acquired from the Arabian Basin. The network was trained, validated, and tested with samples that included a seismic cube and fault images that were labelled manually corresponding to the seismic cube. The model successfully identified faults with an accuracy of 96% and an error rate of 0.12 on the training dataset. To achieve a more robust model, the prediction results were further enhanced using postprocessing by linking discontinued segments of the same fault and thus, reducing the number of detected faults. This method improved the accuracy of the prediction results of the proposed model using the test dataset by 77.5%. Additionally, an efficient framework was introduced to correlate the predictions and the ground truth by measuring their average distance value. This technique was also applied to the F3 Netherlands survey, which showed promising results in another region with complex fault geometries. As a result of the automated technique developed here, fault detection and diagnosis were achieved efficiently with structures similar to the trained dataset and has a huge potential in improving exploration targets that are structurally controlled by faults.

  • (2023) Lee, Minwoo
    Thesis
    Due to the unique photovoltaic properties and ease of fabrication, organic-inorganic halide perovskites have generated considerable research interest. The perovskite solar cell can be applied to many applications, by tuning the bandgap. Inter of Things (IoT) devices and tandem solar cell applications, in particular, have been required for the wide bandgap perovskite solar cells. However, wide bandgap perovskite solar cells have band alignment mismatch problems, leading to charge recombination at the interface of perovskite, resulting in encouraging low device performance and decrease device stability. The first part of this thesis includes the study of the structure and working mechanism of perovskite solar cells. In addition, the defect of the perovskite was explained about how the majority of defects formed. This is caused by shallow defect energies within the bandgap, low density of deep traps, and low trap-charge interaction cross-sections which are occurred during the interaction between traps and charges. After that, the explanation of the reason how wide bandgap is applied for the indoor application. There is previous work on the tuning of the band alignment between perovskite and hole transfer layer which improved the efficiency of hole transfer, resulting in high device performance under the low light intensity condition. Lastly, the experiment of the thesis is focused on the address of the band alignment mismatch by adding two dimensional (2D) BA2PbBr4 perovskite layer for the tunnelling effect between the electron transport layer (ETL) and perovskite layer. The tunnelling layer of 2D perovskite improved the 3D perovskite crystal quality and charge transport from the 3D perovskite to ETL. As a result, the power conversion efficiency under the 200 lux white light emitting diodes (LED) light for the IoT devices was 43.70% with around 1 V of open circuit voltage and improved the device stability under the 1000 lux of white LED up to 1200 hrs.

  • (2023) Selvadoss, Samuel
    Thesis
    Hollow fibre (HF) membrane modules implemented in submerged membrane bioreactors (MBR) and pressurised applications have been widely accepted for both wastewater treatment and polishing wastewater treatment plant (WWTP) effluents. Further innovations in membrane technologies and wastewater treatment market competitiveness, however, are restricted by high manufacturing and operational costs, where a trade-off exists between membrane system design and filtration performance. In the current work, the effects of HF lengths, physical characteristics and system fouling mitigation techniques were investigated to further optimize filtration performance. The following experimental approaches were considered, (1) small-scale filtration experiments with various HF membrane lengths and fibre dimensions, (2) the development of theoretical filtration models and the assessment of filtration simulations, and (3) pilot-scale filtration performance of prototype large-scale membrane modules in wastewater. Two mathematical models for constant TMP filtration using dead-end HF membranes were developed using firstly the Darcy friction factor, and secondly, the Hagen–Poiseuille model. The models allowed for the overall theoretical lumen pressure drop values, local flux distributions and overall filtration performance to be extensively studied. Laboratory-scale filtration experiments using HF membranes of different lengths (0.5 – 2.0 m) were undertaken with the objective of demonstrating the influence of lumen pressure drop in overall filtration performance. Though greater permeate volumes were obtained when using modules prepared with longer HF membranes, such systems experienced greater lumen pressure loss. These losses reduced the operating TMPs effectiveness, resulting in greater non-uniformity in local fluxes across the length of the HF membranes. The magnitude of losses and degree of non-uniformity in such longer systems were extensively studied, allowing for the identification of effective loss reduction techniques, such as the incorporation of HF membranes with larger inner diameters (ID) in the membrane modules. Pilot scale investigations were undertaken to evaluate the influence of HF length on overall performance in real wastewater feeds. Prototype full-scale modules were prepared with HF membrane of different lengths (1.6 – 2.0 m) and ID. Longer modules demonstrated greater filtration performance as the influence of increased lumen pressure drop due to longer fibre lengths was effectively offset by the enhanced fibre dimensions. Overall, the results presented in this study reveal that a significant interplay exists between module design (including length, packing density, slack, and fibre size), filtration process design (feedwater quality, biomass concentration, aeration rate, aeration/shear efficiency) and the critical flux (of threshold flux) conditions. In conclusion, the incorporation of longer length HF membranes in pressurised and submerged MBR modules has been proven to be a promising innovation which offers enhanced filtration capabilities.

  • (2022) Al-Farsi, Mo
    Thesis
    Multijunction solar cells based on silicon are predicted to achieve an efficiency of 40-45% for a top cell with a band gap of 1.6-1.9 eV. However, there are currently no known materials with suitable band gaps able to deliver high efficiencies. Two classes of materials that have been proposed for top cells are alloys of CuGaSe2 and alloyed oxide perovskites. CuGaSe2 has a suitable band gap (1.68 eV) for a top cell on silicon, but the maximum efficiency achieved is only 11%, while that of the closely-related CuInGaSe2 (band gap 1.14 eV) is 23.35%. The low efficiency of CuGaSe2 has been attributed to anti-site defects. Therefore, suppressing this defect formation is critical to achieving higher efficiencies. On the other hand, most oxide perovskites have band gaps that are too high (>2 eV) to be used as top cells on silicon, hence strategies such as alloying are required to lower their band gaps. In this work, the effects of alloying CuGaSe2 with Ag, Na, K, Al, In, La and S were investigated using Density Functional Theory (DFT) calculations. The band gaps of the alloyed compounds and formation energies of anti-site defects were calculated to find alloying elements that can increase the defect formation energy but maintain the band gap. CuGaSe2 alloyed with Al at 50at% showed the highest increase (compared to unalloyed CuGaSe2) in the defect formation energy (by ~0.20 eV) followed by Na (~0.15 eV) and S (~0.10 eV), both at 50at%. However, the band gap of the Al alloy (~2.15 eV) is too high for a top cell, while those of Na (~1.95 eV) and S (~1.91 eV) are slightly above the upper limit. Thus, alloying with these elements is not an ideal route towards significantly increasing the formation energy of anti-site defects while maintaining the band gap of CuGaSe2. However, some of the factors that influence the defect formation energy are identified, potentially leading to design rules for future work. Defect formation energies were found to be higher in structures with more positively charged Ga and negatively charged Se atoms. Analysis of bond lengths revealed a positive correlation between shorter Ga and Se bonds and higher defect formation energies. Band gaps of various alloyed oxide perovskites were calculated using DFT. BiFeO3 was alloyed with Y and Sb; LaFeO3 with Cr and Sb and YFeO3 with Bi and Sb. YFeO3 alloyed with Sb at 50at%, was found to have a band gap of 1.4-2.1 eV (depending on the basis set used) which is in the range for a top cell.

  • (2023) Baker, Mackenzie
    Thesis
    The Australian continent provides an excellent canvas to study the impacts of dynamic topography due to the flat nature of the continent. Previous work into Australian studies of biota have mainly focused on climate being the main contributor to biotic distribution and evolution. This study will investigate the influence dynamic topography contributes to this evolution of the landscape and biota through implementing three landscape evolution models (AuM1, AuM2 and AuM3), created using Badlands software. These models will establish the impacts dynamic topography has to the evolution of the Australian landscape and biota over the last 40 million years. All three models possessed the same inputs of elevation, precipitation, sea-level and erodibility regions, however differed in their dynamic topography input. The first of these models (AuM1) involves a best fit model of the Australian continent with a dynamic topography input that was an accurate depiction of the dynamic topography within the Australian continent. The second model acted as a control model, with the subtraction of a dynamic topography input. Lastly the third model (AuM3) involved the input of a varying dynamic topography inconsistent with AuM1. The comparison of these models exhibits that changes to the Australian landscape have taken place. The main finding was the deposition rate of sediment changes between AuM1 and AuM2, where AuM2 possess lower rates of deposition in the northern region. With these lower rates of sediment deposition, there was an accompanying narrower confluence angle of river channels in the northeastern region, indicating a more arid environment for those simulations without dynamic topography (AuM2). With these new findings through the numerical modelling of the Australian continent new constraints to the evolution of the Australian landscape and biota have been gained.