Engineering

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Now showing 1 - 10 of 124
  • (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.

  • (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) Holland, Sophie
    Thesis
    Anaerobic microbial metabolism of dichloromethane (DCM; CH2Cl2), quaternary amines, and methanol has important implications for carbon and nitrogen cycling in oligotrophic environments and the atmospheric flux of climate-active trace gasses. A novel, strictly anaerobic member of the Peptococcaceae family, strain DCMF, is the dominant organism in a DCM-fermenting enrichment culture (DFE) and one of very few known bacteria capable of fermenting DCM to the innocuous end product acetate. Long read, whole genome sequencing provided a single, circularised 6.44 Mb chromosome for strain DCMF, which contains 5,772 predicted protein-coding genes including an abundance of MttB superfamily methyltransferases. Genomic comparison of anaerobic, DCM-degrading bacteria provided a relatively small core genome, including the Wood-Ljungdahl pathway. Strain DCMF is the first non-obligate anaerobic DCM-degrading bacterium. Genomic, physiological and proteomic experiments confirmed that it is an anaerobic methylotroph, able to metabolise DCM, methanol, and methyl groups from quaternary amines via the Wood-Ljungdahl pathway. The quaternary amine choline was converted to glycine betaine, which was demethylated to sarcosine with a glycine betaine methyltransferase, then reductively cleaved to methylamine and acetate. Methanol (via a methanol methyltransferase) and DCM were fermented to acetate. Comparative proteomics revealed a methyltransferase system that was significantly more abundant in cells grown with DCM than glycine betaine. The novel, putative DCM methyltransferase genes are highly conserved between anaerobic DCM-degrading bacteria. Genomic and physiological evidence support placement of strain DCMF in a novel genus, for which we propose the name ‘Candidatus Formamonas warabiya’. Cohabiting bacteria in the DFE community have persisted despite repeated attempts to isolate strain DCMF, yet strain DCMF-free enrichments demonstrated that most are unable to utilise DCM, quaternary amines, or methanol. Five MAGs were generated from the long-read sequencing data and a metaproteogenomic approach suggested that the cohabiting organisms persist in the culture via necromass fermentation, i.e. oxidation of carbohydrates, proteins, and sugars released from expired strain DCMF cells. The DFE culture is a long-term stable-state community that highlights interactions between foundation species and supporting bacteria, as well as important pathways of carbon and nitrogen cycling.

  • (2020) Li, Mo
    Thesis
    The planetary boundaries (PB) concept has had a significant impact on global sustainability science and research agendas over the past decade. The challenge now is to operationalise the PB concept in order to render it relevant to human activities and decision-making at the local scale. The integration of PBs into existing sustainability frameworks and the translation of PBs into tangible targets remains underexplored. One unique evaluation is offered by environmental footprint accounting, which seeks to measure human demands on the natural environment from a consumption perspective. The overall aim of this thesis is to develop an absolute sustainability assessment framework that evaluates human consumption in the form of environmental footprints against localised PBs. The integration of footprints and local PBs via a global multi-regional input-output (GMRIO) model enabled a global assessment of how human consumption is transgressing PBs. Three specific assessments are explored with the PB-integrated footprint framework developed in this thesis. At the global level, a novel upstream emission footprint is developed to set emissions targets for indirect emissions of companies. The future level of allowable scope 3 emissions is defined and emission reduction pathways are derived using a scenario-based GMRIO model. At the national level, a novel exceedance footprint concept is developed to reflect the actual human demand and appropriation of the safe operating space. The phosphorus exceedance footprint captures sector-specific and global phosphorus PB transgression of countries. Results reveal a pattern of highly uneven distribution of phosphorus-compromised economies, with 76% of the worldwide exceeded phosphorus embodied in exports supplied by only four countries. At the sub-national level, the water exceedance footprint and surplus water footprint at Chinese provincial and city levels are developed, showing that nearly 72% of exceeded water withdrawal is exported to meet consumption elsewhere, and dominated by water transfers from the drier North to the wetter South. These new footprint indicators provide an alternative to conventional consumption-based responsibility attribution and enable the reconciliation of multi-scalar sustainability goals along the global supply chain. PB-integrated footprints are capable of informing policy solutions towards achieving absolute sustainability at various scales.

  • (2020) Mahmood, Aziz Hasan
    Thesis
    With anticipated changes to the coastal wave climate due to climate change scenarios, coastal breakwaters are predicted to be exposed to greater wave energy and, thus, higher rates of damage. Breakwater armour unit design equations and most literature reveal that higher material density results in better stability to breakwater structures in such changed conditions. In this research, alkali-activated materials were studied extensively for their fresh properties and microstructure and a high-density geopolymer concrete mix with steel furnace slag (SFS) aggregate was developed and material properties were evaluated for on-site applications under ambient curing conditions. Moreover, the unique, sustainable high-density geopolymer concrete mix developed in the laboratory was upscaled for field applications in upgrading existing coastal breakwaters. The system is being tested at the Northern breakwater of NSW Ports’ Port Kembla harbour. The concrete uses steel furnace slag (SFS) aggregate in a blended fly ash-blast furnace slag binder (65/35 by mass proportions) proportioned to facilitate the elimination of delayed expansion of the aggregate. The concrete properties were measured, and microstructural analysis was undertaken. The geopolymer concrete developed offers higher bulk density to concrete on account of using SFS aggregates, with satisfactory workability and setting time. Most importantly, the fly ash- blast furnace slag blended binder used in this study leads to good strength gain in ambient curing and allows the diffusion of the free lime associated with the SFS aggregate into the geopolymer matrix to eliminate delayed hydration and expansion of the aggregate. The high-density allows the armour units to be smaller resulting in reduced armour mass requirements and material savings. This research provides a novel approach to both repairs of existing structures and construction of new structures with reductions to both cost and carbon footprint.

  • (2021) Cheng, Zesheng
    Thesis
    The development of science and technology brings novel directions, data sources and methods to deal with transport issues. In the past few decades, especially, a large amount of researches in the transport field have been undertaken based on applying emerging data sources or methods. In light of their findings, emerging data sources are considered to have relatively easier accessibility, larger user coverage and richer information. Meanwhile, novel modelling methodologies are better at mining the latent relationship between the various aspects of the data. Therefore, combining emerging data sources and novel large-scale data analysis methodologies is considered to be valuable for improving existing models and solving emerging problems in transport research. This thesis will mainly concentrate on three related problems. The first is to apply these models to a traditional problem – travel demand estimation. This study demonstrates that social media is an appropriate data source for improving the travel demand estimation model. It also presents the factors which may affect the usage of social media data in the existing models. The second problem addressed is an emerging problem – carsharing system design and demand forecasting. The aim is to estimate the latent demand by spatio-temporal autocorrelation model using historical big data. The last problem is potentially a future problem called a ‘Network Inferring Problem’ which is helpful in sketch network designing. This problem is defined as finding the number of links which can feasibly carry all the point-to-point demand. Meanwhile the travel time on those links is closest to what is actually observed. Following the ‘storyline’ of ‘traditional-emerging-future’, we aim to demonstrate that novel data sources and the analysis methods to enable them are appropriate for the different requirements of various transport research problems. Even though gaps could still be found in both quantity and quality between emerging data sources and traditional data sources, there is enough evidence to believe that with the improvement of information technology and analysis methods, they will have promising prospects for different studies in the future.

  • (2021) Siripanich, Amarin
    Thesis
    Transport modelling is an essential tool for policy makers to make informed transport planning decisions for the wellbeing of the society. However, most strategic transport models do not accurately incorporate the dynamics of population and households and their interactions, resulting in inaccurate forecasts of travel and land use demands. While it is highly crucial that strategic transport models provide accurate long-term forecasts that are vital for the appraisal of large transport infrastructure projects, short-term and medium-term forecasts are also integral for enhancing the efficiency of transport systems. Furthermore, in the modern, fast-paced world, emerging data sources are integral in both transport research and practice. For instance, data collected from smartphone travel surveys and electronic ticketing systems can be used to derive deep insights into people’s travel behaviour. Therefore, this thesis is set out to investigate how population evolution modelling can be improved in transport models, and also how emerging data sources can be leveraged to fill existing knowledge gaps. This thesis focuses on two main themes: (1) to explore new opportunities from emerging technologies and data sources and (2) to develop a dynamic microsimulation model that can provide a more accurate population input for a transport demand model and also to enhance the model development process. Using transit smart card data, The first main chapter explores the impacts of transit ridership and reliability on residential property values in Brisbane, Australia. Three frequently used spatial regression techniques in hedonic studies are used along with a simple linear regression model. The second main chapter presents the first analysis on how social media offers a cost effective means to recruit and engage smartphone travel survey participants. On top of that, recommendations on recruitment, marketing, sample representativeness, incentivisation, and deployment of the study are discussed. The third main chapter introduces an open source dynamic microsimulation toolbox for integrated urban modelling. This toolbox allows microsimulation models to be more easily developed and enables several well-known modelling packages in R to be integrated with the models. Finally, the last main chapter presents a demographic microsimulation model, built with the toolbox, that not only simulates the lifecycle of individuals but also the integration of new migrants into the population using a novel household alignment method.

  • (2020) Nury, Ahmad Hasan
    Thesis
    The Tibetan Plateau (TP) plays a critical role in modulating the hydrology for a number of prominent river basins. Despite its importance, changes in hydrological processes of the region are not closely monitored. It is now well known that rising temperatures are impacting the water cycle in the Plateau. The Upper Brahmaputra Basin, originating from the TP, provides fresh water for a large population downstream and its likely change in reference to future water availability is the focus of this thesis. One possible way to ascertain and project such changes is to formulate hydrological models and use simulations from General Circulation Models (GCMs) and Regional Climate Models (RCMs) as inputs. This thesis seeks to investigate climate change impacts on snowpack and streamflow as its two key aims. The first part of the thesis explores snowpack changes in terms of within-year accumulation and depletion across the Northern Hemisphere using measured spatially distributed snow water equivalent (SWE) information. Following this, a catchment-scale investigation of uncertainties in precipitation downscaling across the TP is then presented. Such uncertainties affect future projections of precipitation, which in turn influence streamflow simulations. Next, an evaluation of GCM and RCM-derived SWE is reported, which reveals that both GCM and RCM products suffer from significant uncertainties and biases. Such uncertainties and biases in SWE and other climatic variables are reduced significantly using a multivariate bias correction approach. In the second part of the thesis, a conceptual hydrological model is proposed to assess the impact of temperature-driven changes in snowpack attributes on the streamflow, considering the lack of data available for the upper Brahmaputra basin. The model simulates snow cover fraction, SWE and streamflow using temperature and precipitation information. The results show that SWE is likely to decrease in the near future (2041 to 2064) as well as in the far future (2071 to 2094), which will impact streamflow, and hence water availability for a significant portion of the global population that depends on the water supplied by the Brahmaputra as well as the other major rivers originating from the Tibetan Plateau.

  • (2020) Lu, Xiao
    Thesis
    Coal is considered as a dual-porosity rock that is highly heterogeneous and hosts complex and unique gas flow mechanisms. Coalbed methane can be stored in coal as free gas and in adsorbed state. The gas flow mechanisms with deformability of coal due to the change of stress during production from coalbed methane reservoirs have an extensive impact on reservoir characteristics. Because of the complexity of coupled pressure change and sorption phenomena, the understanding of the coal structure and gas flow in it is still limited. In this Thesis, X-ray micro-computed tomography (micro-CT) and gas flooding experiments are conducted to study flow mechanisms in the complex structure of coal. The properties that are discussed include fracture aperture, permeability and effective gas diffusivity using methane, helium and krypton. Our results show how imposing stress affects fracture aperture and coal permeability. There exists a difference between helium and methane permeability due to the adsorptive nature of methane gas. Effective diffusivity is analysed at different scales: pore-scale (micrometres) from the micro-CT images, particle-scale (millimetres) in crushed coal adsorption experiments and core-scale (centimetres) in bulk diffusion experiments. The results demonstrate that the diffusivities obtained at different scales are in the range of 10-9 to 10-11 m2/s, with the particle-scale diffusivity being the highest and pore-scale diffusivity being the lowest. The mechanisms associated with diffusion at these scales are discussed and compared. Overall, results of this Thesis provide insights into the complex gas flow mechanisms occurring in coalbed methane reservoirs specifically in terms of impact of sorption, gas pressure, stress and gas type on fracture aperture, permeability and effective diffusivity.

  • (2020) Wu, Xia
    Thesis
    Despite improvements in data collection and observing technologies, observation error in environmental data is still considerable and its precise quantification is important for improved environmental model calibration and simulation. Its statistical features (e.g. probability distribution) are generally independent of the model processes and can be estimated a priori by analysis of the data acquisition instruments and procedures. Simulating total suspended solids (TSS) via a build-up/wash-off model (BwMod) is a typical example to demonstrate this situation, whose input is streamflow and output is TSS concentration. These variables are often surrogated by the measurement of river stage or turbidity to make up for the lack of high-resolution data. The use of such proxy data can introduce significant observation uncertainty, outside of existing model structural or parameter errors. In the context of Bayesian inference, this thesis develops an improved approach to model calibration by specifically targeting the observation uncertainty. First, an iterative approach to likelihood specification is proposed, based on data transformations that acknowledge the heteroscedasticity in the total residual error. Next, a new method, referred to as Bayesian Error Analysis with Reshuffling (BEAR), is developed to decompose individual observation errors from the total residual error in the calibration mode. Unlike directly calibrating time-varying error values via the current methods, the BEAR method first samples the proposed errors from an assumed error distribution and then reshuffles them with the estimated ranks via an optimisation method. This sampling and reshuffling strategy improves the efficiency and accuracy of error identification and is developed for four different case studies: (1) response observation errors for BwMod; (2) input errors for BwMod with an instantaneous response; (3) input errors for a hydrologic model which exhibits persistence; (4) multiple observation errors for BwMod. Collectively, these case studies show that the BEAR method is robust, flexible, and can be adapted to a wide variety of environmental modelling scenarios to improve model specification under uncertainty.