Infrastructure Engineering - Theses

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Geotechnical Behaviour of Anchor Chains and Integrated Mooring System Analysis

Liu, Wenlong ( 2024-02)

Offshore floating facilities, such as the traditional oil and gas platforms and the more recent floating wind turbines, require mooring systems to restrain them at designated locations. A mooring system consists of an anchor embedded in the seabed soil, connected to an anchor chain (in soil) and mooring line (to the floating vessel or platform). The current practice of mooring system analysis usually only considers the mooring line segment suspended in water while the embedded chains and anchors are often simplified as fixed points or springs at mudline. There is a scarcity of approaches to model an entire mooring system, including the suspended mooring lines, embedded chains, and anchors. Furthermore, there are significant empiricism and limitations in the current studies of the embedded chains: 1) the chain links with complex geometry are mostly simplified as cylindrical bars; 2) normal and tangential soil resistances to embedded chain are expressed with empirical parameters; 3) the coupling nature of the normal and tangential soil resistances is largely neglected and they were simplistically related with a so-called friction coefficient; and 4) the analysis of the embedded chains is primarily limited to a two-dimensional plane. The aims of this thesis are to advance the understanding of the geotechnical behaviour of embedded chains and develop an integrated analysis approach for mooring systems. This thesis firstly investigates the soil resistances to anchor chains with consideration of their intricate geometry through three-dimensional finite element modelling. The chain-soil interaction is modelled by developing a new interface model, which is capable of accounting for the tangential resistance in tension. Uniaxial soil resistances along the normal N, lateral S and axial T directions of chain links are reported with consideration of the effect of the embedment depth, chain link type, link direction angle and interface roughness. Soil flow mechanisms are discussed, and equivalent bearing capacity factors are derived based on the finite element results. Then, a three-dimensional N-S-T soil resistance yield surface for chain links is established and a force-resultant model is developed with an associated flow rule, hardening law and elastic behaviour considered. Based on the developed force-resultant model, a new analytical solution comprising a system of governing equations is proposed and solved via an iterative scheme, which is capable of modelling the evolution of anchor chain configuration in a two-dimensional plane while considering the coupling of soil resistances. The results from this analytical solution show that the ratio of tangential soil resistance to normal soil resistance is not constant but varies depending on the loading condition. Lastly, this thesis proposes an integrated analysis approach for an entire mooring system in three-dimensional space by implementing the force-resultant models into a standard finite element program. An efficient integration algorithm is presented for the numerical implementation. A large rotation modelling scheme is adopted to address numerical challenges arising from large rotations of chain links and the anchor in three-dimensional space. Calculation results indicate that the restoring force and stiffness of the mooring system is overestimated if modelling the embedded chain and anchor is neglected, which can lead to unconservative design. This thesis contributes to the understanding of the geotechnical behaviour of embedded chains by providing insight to soil resistance mechanisms, developing a force-resultant model, and proposing a new analytical solution for estimating the embedded chain configuration. The proposed integrated modelling approach is expected to enhance the analysis of mooring systems in offshore engineering.
Beyond Conventional Space Cooling: A Structured Approach to Assessment of Thermally Activated Radiant Cooling Panels with Phase Change Materials

Mousavi, Seyedmostafa ( 2023-12)

The increasing demand for air-conditioning due to more extreme global temperatures has led to a rapid surge in energy consumption for space cooling over the past decade. This demand is projected to triple by mid-century under current business-as-usual practices, surpassing a quarter of the world's current electricity consumption. To address this challenge, there is an urgent need for innovative and sustainable space cooling alternatives. This PhD research aims to introduce and evaluate a novel solution integrating radiant chilled ceiling (RCC) panels with phase change material (PCM), termed PCM-RCC. This technology is designed for efficient energy use, substantial thermal energy storage, peak load-shifting capabilities, and enhanced thermal comfort. Although PCM-RCC is expected to progress from the “In Development” to the “Limited Availability” phase, ongoing debates about its design, implementation, and control methodologies contribute to hesitation among professionals. Addressing these concerns is crucial to accelerating the acceptance of PCM-RCC in the building and construction sector. This study employs a structured methodology combining both experimental and simulation-based approaches to advance the design and operation of PCM-RCC systems. Initially, a comprehensive review of the current state of PCM-RCC systems is conducted to identify key characteristics and practical aspects. This is followed by physical testing on a prototype PCM-RCC system in a full-scale test cabin, assessing its thermal and energy performance, including transient thermal behaviour of PCM panels during charging-discharging cycles, indoor comfort conditions, and the electricity peak demand reduction. A transient simulation model for PCM-RCC in then developed and validated using measured data from physical testing. This model is used to examine the design and operational performance of the system and to develop an advanced rule-based control strategy for enhanced efficiency. Based on the literature review, it is found that PCM-RCC exhibits higher energy efficiency compared to conventional all-air systems. This is primarily attributed to its ability to provide thermal comfort through direct radiant cooling, effectively managing daytime cooling loads and subsequently dissipating heat during nighttime. Experimental results reveal that overnight circulation of chilled water for 4–5 hours is sufficient to fully recharge PCM panels. Over 80% of the occupancy time conforms to ISO 7730 "Class B" thermal comfort standards. The system’s daily electricity usage predominantly occurs during off-peak hours, accounting for approximately 70% of total consumption. Validation results confirm the capability of the developed PCM-RCC model to simulate the transient behaviour of the system with an accuracy within a +/-10% margin of error. Furthermore, when compared to radiant cooling, PCM-RCC with the proposed advanced control shows high load flexibility, a 12% reduction in electricity usage, a 5% improvement in coefficient of performance, and a 30% decrease in operational costs. This research provides a deeper understanding of the benefits and challenges associated with PCM-RCC systems. The outcomes are expected to support the integration of PCM-RCC technology into mainstream building practices, promoting energy efficiency and sustainability in built environments.
Investigation of Mechanical Behaviour of Rockfill Materials

Asadi, Reza ( 2023-11)

The study of the mechanical behaviour of rockfill material, an essential element in diverse geotechnical applications including dams, railway subgrades, and offshore structures, continues to be a critical area of exploration due to its complex testing requirements and limited comprehension. Comprised of rock aggregates spanning sizes from less than 1 cm to over 1 m, typically within the range of 10 cm to 80 cm, rockfill poses significant challenges for laboratory testing, primarily owing to its substantial particle sizes. In response to the scarcity of large-scale experimental equipment globally, numerous studies have turned to downscaled samples. However, it's crucial to acknowledge that the behaviour of rockfill is notably impacted by scale, predominantly attributed to rock particle breakage. Consequently, prevalent design methodologies lean heavily on historical large-scale studies, often neglecting vital micro and meso-scale parameters that significantly shape rockfill behaviour. At the microscale, rockfill behaviour is influenced by rock mineralogy, crack distribution, and grain breakage. In the mesoscale, particle shape, surface roughness, and the state of stress, particularly the confining stress, emerge as dominant factors. Additionally, in the macroscale, relative density, particle size distribution, maximum particle size, and humidity significantly contribute to rockfill behaviour. Particle breakage, a fundamental phenomenon, profoundly affects shear strength, deformability, and porosity under varying stress conditions. This phenomenon is influenced by factors such as rock mineralogy, particle shape, surface roughness, size distribution, and stress, albeit to varying degrees. While experimental studies traditionally focus on characterizing breakage post-testing, numerical methods offer a means to explore breakage evolution and its impact on the mechanical behaviour of rock particle assemblies. The discrete nature of rockfill, including phenomena like sliding, rolling, and interlocking, significantly shapes its behaviour. The Discrete Element Method (DEM) offers a promising avenue for modelling these intricate interactions, especially in granular materials like rockfill. DEM excels in modelling large deformations in granular materials, enabling in-depth micro and macro-mechanical analyses due to the discrete nature of particles. Its foundational framework is based on simple equations of motion, ensuring an uncomplicated modelling process. This thesis addresses the challenges associated with studying the mechanical behaviour of rockfill by proposing the Modified Particle Replacement Method (MPRM) through an advanced DEM model, combining replacement and bonded-particles methods, to delve into the effects of particle shape and breakage. The study examines stress and volumetric strain-related parameters affected by breakage, revealing critical findings about the concentration of broken particles in shear band zones and the impact of over-compaction on strength recovery. Additionally, a Tile-Based Flexible Membrane (TBFM) for triaxial test modelling is introduced, exploring parameters such as particle shape, confining stress, membrane resolution, and flexibility's influence on volumetric-related behaviour. The combined MPRM-TBFM approach sheds light on the significant impact of membrane flexibility on mechanical and particularly, volumetric-related behaviour. Furthermore, in this Ph.D. research project, the findings from six large-scale triaxial tests, utilizing sample sizes of 30 x 60 cm and 100 x 180 cm, are presented for the first time. They undergo thorough analysis and critical investigation to accurately calibrate and validate the fully developed DEM-based triaxial model. The developed and calibrated model was utilized to explore the effects of removing coarse fractions from rockfill, a common practice in experimental studies. This exploration delves into the influence of specimen size, parallel grading, and the coarse fraction on stress-strain behaviour, providing essential insights for more precise predictions and design in the construction of rockfill structures.
Advancing the representation of agricultural systems in Land Surface Models: systematic model evaluations and technical model developments

Boas, Theresa Sophie ( 2023-10)

Global climate change, with its projected increase in weather extremes and drought risk, presents global and regional agriculture with vulnerability and new challenges. It is crucial to gain a comprehensive understanding and accurate quantification of the intricate dynamics of agricultural land cover and its role within the terrestrial system, especially in the context of climate change. Land surface models play a central role for the research on climate change effects on the Earth's surface and hold particular value in examining the influence of weather patterns on agricultural land at larger spatial scales. The incorporation of a comprehensive crop module in land surface models offers the possibility to study the effect of agricultural land use and land management changes on the terrestrial water, energy and biogeochemical cycles. It may help to improve the simulation of biogeophysical and biogeochemical processes on regional and global scales and thus to study climate change impacts on terrestrial ecosystem as well as the significance of human land cover changes for climate change. Land surface models simulate the complex interactions at the terrestrial land surface in response to atmospheric states, based on land cover and soil type information. In combination with data from different sources, like seasonal weather forecasts, land surface models can potentially provide useful information for water resources or agricultural planning. In this thesis, a systematic evaluation of the state-of-the-art land surface model, the Community Land Model version 5.0 (CLM5), was conducted from point to regional scales in combination with data from a multitude of sources, e.g. from remote sensing, numerical predictions and field observations. A special focus was placed on the representation of arable land and its feedback to weather related factors in the context of climate change. In the first part of this thesis, the performance of the crop module of CLM5 was evaluated at point scale with site specific field data focussing on the simulation of seasonal and inter-annual variations in crop growth, planting and harvesting cycles, and crop yields as well as water, energy and carbon fluxes. In order to better represent agricultural sites, the model was modified by (1) implementing the winter wheat subroutines after Lu et al. (2017) in CLM5; (2) implementing plant specific parameters for sugar beet, potatoes and winter wheat, thereby adding the two crop functional types (CFT) for sugar beet and potatoes to the list of actively managed crops in CLM5; (3) introducing a cover cropping subroutine that allows multiple crop types on the same column within one year. The latter modification allows the simulation of cropping during winter months before usual cash crop planting begins in spring, which is an agricultural management technique with a long history that is regaining popularity to reduce erosion, improve soil health and carbon storage, and is commonly used in the regions evaluated in this study. In comparison with field data, the crop specific parameterizations, as well as the winter wheat subroutines, led to a significant simulation improvement in terms of energy fluxes (RMSE reduction for latent and sensible heat by up to 57 % and 59 %, respectively), leaf area index (LAI), net ecosystem exchange and crop yield (up to 87 % improvement in winter wheat yield prediction) compared with default model results. The cover cropping subroutine yielded a substantial improvement in representing field conditions after harvest of the main cash crop (winter season) in terms of LAI magnitudes and seasonal cycle of LAI, and latent heat flux (reduction of winter time RMSE for latent heat flux by 42 %). Our modifications significantly improved model simulations and should therefore be applied in future studies with CLM5 to improve regional yield predictions and to better understand large-scale impacts of agricultural management on carbon, water and energy fluxes. These model improvements were then ported to the regional scale and tested in combination with sub-seasonal and seasonal weather forecasts in the second part of this thesis. Long-range weather forecasts provide predictions of atmospheric, ocean and land surface conditions that can potentially be used in land surface and hydrological models to predict the water and energy status of the land surface or in crop growth models to predict yield for water resources or agricultural planning. However, the coarse spatial and temporal resolutions of available forecast products have hindered their widespread use in such modelling applications, which usually require high-resolution input data. In this study, we applied sub-seasonal (up to 4 months) and seasonal (7 months) weather forecasts from the latest European Centre for Medium-Range Weather Forecasts (ECMWF) seasonal forecasting system (SEAS5) in a land surface modelling approach using the Community Land Model version 5.0 (CLM5). Simulations were conducted for 2017-2020 forced with sub-seasonal and seasonal weather forecasts over two different domains with contrasting climate and cropping conditions: the German state of North Rhine-Westphalia (DE-NRW) and the Australian state of Victoria (AUS-VIC). We found that, after pre-processing of the forecast products (i.e. temporal downscaling of precipitation and incoming short-wave radiation), the simulations forced with seasonal and sub-seasonal forecasts were able to provide a model output that was very close to the reference simulation results forced by reanalysis data (the mean annual crop yield showed maximum differences of 0.28 and 0.36 t/ha for AUS-VIC and DE-NRW, respectively). Differences between seasonal and sub-seasonal experiments were insignificant. The forecast experiments were able to satisfactorily capture recorded inter-annual variations of crop yield. In addition, they also reproduced the generally higher inter-annual differences in crop yield across the AUS-VIC domain (approximately 50 % inter-annual differences in recorded yields and up to 17 % inter-annual differences in simulated yields) compared to the DE-NRW domain (approximately 15 % inter-annual differences in recorded yields and up to 5 % in simulated yields). The high- and low-yield seasons (2020 and 2018) among the 4 simulated years were clearly reproduced in the forecast simulation results. Furthermore, sub-seasonal and seasonal simulations reflected the early harvest in the drought year of 2018 in the DE-NRW domain. However, simulated inter-annual yield variability was lower in all simulations compared to the official statistics. While general soil moisture trends, such as the European drought in 2018, were captured by the seasonal experiments, we found systematic overestimations and underestimations in both the forecast and reference simulations compared to the Soil Moisture Active Passive Level-3 soil moisture product (SMAP L3) and the Soil Moisture Climate Change Initiative Combined dataset from the European Space Agency (ESA-CCI). These observed biases of soil moisture and the low inter-annual differences in simulated crop yield indicate the need to improve the representation of these variables in CLM5 to increase the model sensitivity to drought stress and other crop stressors. While extensive research is dedicated to investigating the impacts of changing climate conditions on global food security, the specific implications for regional inter-annual yield variability remain largely uncertain. In the final part of this thesis, the model’s ability to represent the inter-annual variability of crop yield in comparison to recorded yield variability was evaluated in multi-decadal simulations (1999-2019) that were forced with the WFDE5 reanalysis. Additionally, synthetic experiments were performed for both regional domains, AUS-VIC and DE-NRW, and forced with a reduced precipitation rate (50% of the reanalysis precipitation), allowing for a more detailed analysis of crop water stress regimes and correlations between seasonal rainfall and crop yields. Overall, the simulation results were able to reproduce the total annual crop yields of certain crops, with RMSE values between 0.52 t/ha to 1.76 t/ha in AUS-VIC and 0.61 t/ha and 1.58 t/ha in DE-NRW, while also capturing the differences in total yield magnitudes between the domains. However, the simulations showed limitations in correctly capturing inter-annual differences of crop yield compared to official yield records, in particular for winter crops, which resulted in relatively low correlations (maximum correlation coefficients of 0.39 in AUS-VIC and 0.42 in DE-NRW). Specifically, the mean absolute anomaly of simulated winter wheat yields was up to 4.6 times lower compared to state-wide records from 1999 to 2019. Our results suggest the following limitations of CLM5 in predicting inter-annual variability in crop yields: (1) limitations in simulating yield responses from plant hydraulic stress; (2) errors in simulating soil moisture contents compared to satellite-derived data; and (3) errors in the representation of cropland in general, e.g. crop parameterizations, differentiations of crop varieties, and human influences (such as management decisions, fertilizer types, and application techniques).
Hydrological changes under multi-year drought: exploring the roles of vegetation and evapotranspiration dynamics

Gardiya Weligamage, Hansini Anuththara Chandrasiri ( 2024-03)

Climate-induced, prolonged hydrological droughts have been observed worldwide, and more are expected in future years due to rapid drying trends in climate. Significant reductions in streamflow generation, relative to rainfall reductions, are generally termed ‘hydrological shifts’ in the literature and have been observed in many regions around the world. This scenario is challenging and requires a thorough understanding for projecting and managing future water availability under a future drying climate. Investigating past prolonged drought scenarios aids in comprehending how catchment hydrology responded to drought, facilitating insights into potential responses to similar future scenarios. Many studies have investigated the influences of climate and catchment characteristics on streamflow generation under multiyear drought. They revealed that catchment characteristics are more prominent in hydrological shifts than climate characteristics. However, investigating factors driving hydrological shifts under prolonged drought conditions is still ongoing. In terms of hydrological predictions, conceptual rainfall-runoff models are often used to predict runoff in hydrology. However, studies show that rainfall-runoff models overestimate runoff compared to observations during prolonged droughts, implying the need to adapt hydrological models under future drying climates. This research is mainly structured to investigate drought-induced changes in terrestrial water balance components and vegetation, along with their impacts on hydrological shifts, and assessment of the modelling of water balance components in conceptual rainfall-runoff models under multiyear drought. Therefore, three main research questions were formulated to address the above-mentioned aims and objectives: 1. How did reductions in rainfall partition into other terrestrial water balance components during the Millennium Drought? 2. Did vegetation dynamics cause hydrological shifts during and after Australia’s Millennium Drought? 3. Do commonly used rainfall-runoff models match actual evapotranspiration (AET) signatures indicated by flux towers and remotely sensed AET products? The first research question (RQ1) aimed to investigate how terrestrial water balance components, such as evapotranspiration and soil moisture, vary under prolonged drought and their impacts on runoff generation. The Millennium Drought in Victoria, Australia, was selected as the case study as many catchments in Victoria were found to be hydrologically shifted, and about one-third of them have not recovered after the Millennium Drought. The results showed approximately unchanged actual evapotranspiration between the pre-drought and Millennium Drought periods. The water balance derived change in storage showed a decline over the Millennium Drought, which is in line with findings from the literature. Overall, precipitation reduction during the Millennium Drought was found to be partitioned into a reduction in streamflow and subsurface storage, whereas evapotranspiration was approximately constant over the whole period. The second research question (RQ2) aimed to investigate the impact of vegetation changes on hydrological shifts in catchments in Victoria during and after the Millennium Drought. First, this study investigated how vegetation responded during and after the Millennium Drought and their response based on the land cover types using multiple remotely sensed vegetation indices. Then, the correlation between vegetation and hydrological shifts was investigated by quantifying vegetation shifts during and after the Millennium Drought compared to pre-drought. The findings from remotely sensed vegetation indices indicated that vegetation tended to maintain or increase its properties rather than decrease during and after the Millennium Drought. The analysis of the correlation between vegetation and hydrological shifts produced nuanced results. In the broader context, the findings indicated that while hydrologically shifted catchments generally maintained their vegetation properties, in absolute terms (mostly grass/pasture or mixed vegetation dominant), they actually exhibited higher levels than expected, given the weather conditions during and after the Millennium Drought. This implies a prioritization of precipitation for vegetation survival, consequently leaving less rainfall available for streamflow. Therefore, it can be inferred that vegetation may be a causal factor in hydrological shifts in those catchments during and after the Millennium Drought. The third research question (RQ3) aimed to investigate the realism of simulated actual evapotranspiration (AET) from conceptual rainfall-runoff models. To achieve this, AET signatures were defined and evaluated at different temporal scales, using observed and remotely sensed AET products. Then, employing AET signatures, the study evaluated the simulated AET estimates obtained from models calibrated with streamflow only and those calibrated with both streamflow and observed AET. Overall, this study confirms that conceptual rainfall-runoff models poorly represent some characteristics in AET when calibrated traditionally with streamflow only. However, incorporating AET information into the model calibration can only improve the representation of monthly AET characteristics. Therefore, this study underscores the need for improvements in model calibrations and structures to represent hydrological components more realistically for improved predictions. The case studies and methods presented in this PhD thesis contribute to advancing the progression of the current understanding of hydrological processes such as AET, other catchment characteristics such as vegetation dynamics, and their impacts on hydrological shifts during and after multiyear droughts. Additionally, this research highlights deficiencies in AET representation in rainfall-runoff models. These findings, insights, and methods offer valuable applications for future studies, such as explaining hydrological shifts and non-recovery behaviour under future drying climates, both locally and globally, addressing gaps in the field of hydrology.
Sustainable Shared Automated Fleets: Strategies for Integrated Operations with Public Transport

Tiwari, Sapan ( 2024-02)

As the world undergoes rapid urbanization, with predictions that 68% of the world's population will be urban residents by 2050, the dynamics of urban transportation are undergoing a significant transformation. Transportation network companies (TNCs) and shared autonomous vehicles (SAVs) are two important technological advancements within this transformation. One of the most significant disadvantages of these technological services is their potential competing role with more sustainable modes, such as Public Transport (PT), walking, and cycling. While PT is likely to remain one of the most essential modes of travel because of its affordability and efficiency in transporting a large number of users in dense urban areas, SAVs may eventually lead to a decline in PT ridership and escalate urban congestion. However, if the operations of SAV fleets are planned with the network, services, and ridership of PT in mind, these modes have the potential to work complementarily and increase the overall transport level of service experienced by users. This thesis presents an in-depth exploration of strategies to integrate the operation of SAV fleets with PT systems. The research critically examines the rise of SAVs and their role in addressing inefficiencies in PT, such as long wait times and the demand for on-demand services. Furthermore, it underscores the importance of developing SAV dispatching strategies that are not only efficient for the operation of this mode in isolation but are also integrated with the PT system to maximize user access, equity, and sustainability. The thesis identifies significant knowledge gaps, including the need for a broader classification of dynamic dial-a-ride problem (DDARP) objectives under the Triple Bottom Line (3BL) approach of sustainability, including social, economic, and environmental dimensions. It also underscores an opportunity to enhance urban mobility by leveraging PT schedules for more efficient ride-matching of SAVs. Therefore, this thesis identifies four primary objectives: 1) Categorizing DDARP objectives under the 3BL sustainability model, 2) Developing prioritization strategies for SAV ride-matching that enhance PT integration, 3) Formulating PT accessibility-based rebalancing strategies, and 4) Developing prioritized-based insertion strategies to improve both SAV and PT service quality through strategic ride-matching. To achieve these objectives, this thesis first developed a novel framework categorizing DDARP objectives across the 3BL dimensions. Then, the thesis developed innovative ride-matching strategies for SAVs, prioritizing mobility-impaired trips and those without feasible PT alternatives. It introduced rebalancing strategies that enhanced PT reach by relocating vehicles to areas with high potential for First/Last-Mile (FMLM) requests and lower PT accessibility. Finally, it developed various insertion strategies prioritizing rides to improve the overall SAV service quality and accessibility in areas with limited PT options. This thesis utilized the MATSim simulation tool to evaluate these operational strategies within the Melbourne Metropolitan Area (Victoria, Australia), focusing on enhancing SAV operations. Implementing the proposed strategies in a simulated urban environment yielded promising results from a 3BL perspective. Economically, there was an observed increase in served rides and enhanced fleet utilization, particularly noticeable in the scenarios of undersupply of SAVs. Socially, these strategies significantly improved service efficiency and accessibility, especially in regions with limited PT access, thereby enhancing the equity of the transportation network and ensuring a more balanced distribution of services. Environmentally, implementing these strategies reduced empty vehicle kilometers and overall vehicle travel, which are key indicators of a transportation system’s environmental impact and emissions, underscoring the strategies’ alignment with broader sustainable urban development goals. Among the key findings, one of the most significant was the substantial increase in PT ridership and service efficiency in areas previously underserved by PT. The strategies developed in this thesis have significant implications for various stakeholders in urban transportation: For users, they show enhanced service accessibility and quality, especially in areas traditionally underserved by PT. SAVs can integrate these strategies to evolve from competitors to collaborators within the urban transport ecosystem and leverage these strategies to attract more users by improving service rates and eventually increasing their revenue. PT operators, through alignment with these strategies, can optimize their schedules and services for better alignment with SAVs, enhancing the entire transportation network's efficiency and PT’s reach. Governments and policymakers could leverage these insights to develop regulations and frameworks that facilitate SAV-PT integration, emphasizing sustainability, equity, and efficient resource utilization. In conclusion, the findings of this thesis highlight the practicality and effectiveness of integrating SAVs with PT in achieving sustainable, efficient, and equitable urban mobility, guided by the principles of the 3BL approach.
Representing contemporary water allocation frameworks and climate change impacts on storage-reliability-yield relationships for carry-over reservoirs across scales

Ren, Peizhen ( 2023-07)

Freshwater resources are widely regarded as one of the most virtual natural resources. Many freshwater systems have been regulated (e.g. by multiple reservoirs) to maximize the water withdrawn for human use. However, the highly regulated water systems are currently experiencing water scarcity problems (where water demand exceeds water availability for human use) due to climate change and increased human water demands (e.g. population growth and related economic activities). How to strengthen water security over a broad range of scales, from local to global, is a complex and common challenge across the world. To ensure water security, it is important to adopt integrated and sustainable water management practices that take into account the advanced water allocation frameworks (e.g. political water policies, and meet the needs of all stakeholders, including households, industries, and ecosystems). Hydrological simulation models can be valuable tools for this kind of water resources management and planning, however, the complexity of these methods means that they can be only achieved when sufficient resources (e.g. high computation and data resources) are available, even at single specific water systems. To achieve integrated and sustainable water management practices, the current literature is calling for rapid water management technologies to be applied in the context of climate change, especially at multiple scales (from local to global). Thus, this thesis develops several novel and relatively simple water management technologies to fill the research gaps based on the Gould-Dincer method (a rapid and efficient storage-reliability-yield relationship for water resources management in carryover systems). The major contributions of this thesis include: (1) the development of a rapid method to assess the yield of carry-over reservoirs subject to environmental water requirements; (2) the development of a rapid analytical method to represent multiple-priority water allocation system (e.g. ‘dual-priority’ water rights); and (3) the development of the Equivalent Reservoir Model (ERM) to model the storage-reliability-yield relationship for multiple parallel carry-over reservoirs as a single equivalent reservoir. In addition, the thesis develops a spill correction model to extend the range of the Gould-Dincer method. The original Gould-Dincer method performs well over the ideal carryover reservoir with less or little spill volume, but its performance will be worse if spills happen often. Thus, this spill correction model could help adjust the water yield estimate from the Gould-Dincer method for a more realistic condition. Moreover, the thesis develops an empirical equation to estimate the covariance of annual flows in parallel tributary rivers using the mean of annual inflows (rather than flow series data), which provides an easier way for ERM application over ungauged and less-data regions. These advanced water management techniques developed in this thesis are relatively simple and less-data demanding. Their simplicity facilitates the rapid assessment of contemporary integrated water management that can be implemented by stakeholders and decision-makers easily and effectively at multiple scales, considering multiple historic and future climate conditions simultaneously.
Developing and Implementing Collaborative Urban Distribution Networks to Improve the Sustainability of Last-mile Logistics

Kahalimoghadam, Masoud ( 2024-03)

Initiatives targeting global climate change, for example the 2015 Paris Agreement and the United Nations’ Sustainable Development Goals (SDGs), have underscored the importance of environmentally friendly transportation. Despite efforts to fulfil these commitments, projections indicate a potential 16% increase in carbon dioxide (CO2) emissions from transport vehicles of all kinds, by 2050, underscoring the urgent need for transformative action within the transport sector. Urban areas are particularly significant, contributing approximately 70% of global emissions, with one-third coming from transportation. Challenges within last-mile logistics (LML) are further compounded by factors like rapid urbanisation, ongoing stresses such as pandemics, and emerging trends influenced by the dynamic nature of the LML environment. In recent years, electronic commerce (e-commerce) has experienced remarkable expansion, fundamentally transforming consumer shopping habits and business strategies. While offering numerous advantages, this surge has led to a significant increase in business-to-consumer (B2C) parcel deliveries, primarily through home delivery. This has resulted in a measurable rise in vehicle kilometres travelled (VKT) and CO2 emissions in metropolitan areas, usually due to failed delivery and poorer vehicle consolidation efficiencies, posing a significant challenge to achieving sustainability. The recent COVID-19 pandemic has further boosted e-commerce growth, with consumers increasingly opting for online shopping to avoid physical stores and reduce their exposure to viruses or other air-borne diseases. This unexpected surge has strained e-commerce providers and logistics services, altering the geographical pattern of goods demands and delivery routes and relocating freight vehicles to local roads. In this complex environment, optimising LML relies on strategically locating innovative collaborative logistics hubs, as well as efficiently deploying urban delivery vehicles. An integrated, Operations Research-based methodology is devised for tackling LML challenges, providing decision-makers with structured optimisation methods and mathematical problem-solving techniques or strategies. This research first conducts two thorough literature reviews on LML. The first review identifies four key unsustainable trends: urbanisation, e-commerce growth, rapid delivery demands, and disruptive events. Meanwhile the second review reveals key LML stakeholders, including residents, customers, carriers, shippers, governments, and proposes integrating Physical Internet managers (PI-Managers) to oversee shared and collaborative logistics hubs. Stakeholders’ objectives are determined, and their interactions within the LML are mapped. Utilising data from Australia's largest B2C carrier, the impact of COVID-19 on business-to-business (B2B) and B2C parcel delivery in Sydney is explored. It reveals there has been a shift from CBD deliveries to outer metropolitan areas and identifies employment, population, and internet access as key factors determining this demand pattern change. At the strategic level, a spatial approach is developed to address the uncapacitated single allocation hub covering problem (USAHCP) by incorporating the spatial features and strategic legislation of Sydney. This location-based methodology minimises VKT by establishing a collaborative last-mile distribution network through the optimised placement of micro-consolidation centres (MCCs). Simultaneously, it maximises the coverage of parcel lockers serviced by MCCs, assuming parcels are collected from parcel lockers by end customers. A sensitivity analysis assesses how the distribution network design (number and location of MCCs) varies according to different driving time constraints and traffic patterns, exemplified by various times of day. At the operational level, a new collaborative multi-depot green vehicle routing problem is introduced, utilising MCCs as shared hubs and linking emission rates to vehicle and route characteristics through a microscopic approach. An innovative self-adaptive metaheuristic algorithm is developed, combining intelligent water drops and simulated annealing with a feedback control system actively monitoring the algorithm's performance and convergence towards the global minimum solution. Through continuous adjustments to algorithm parameters via feedback, this methodology balances exploitation and exploration. The algorithm is tested first on the Cordeau benchmark, compared with previous state-of-the-art methods, and then in a case study comparing the collaborative network to an independent one. By focusing on stakeholders' interactions, an intelligent multi-agent system (iMAS) is developed where carriers, shippers, and PI-Managers are deemed to be learning agents. Each agent's objectives, actions, and roles are meticulously defined for simulation. iMAS employs Q-learning, a machine learning method aiding optimal actions based on environmental rewards, within a distribution network and vehicle routing problem environment to evaluate interactions among agents. Seven simulations, varying agent combinations undergoing learning, demonstrate improved objective achievement when agents learn. iMAS acts as a decision support system, evaluating policies and actions for policymakers to enhance LML efficiency.
Skin temperature and air-sea heat fluxes in the Antarctic marginal ice zone: A field observation perspective

Tersigni, Ippolita ( 2023-09)

The Southern Ocean stores and releases more energy than any other latitude band on the planet and, hence, it is a major contributor to global climate. At high latitudes, energy fluxes are mediated by a strong seasonal sea ice cycle, which forms an unsteady composite interface of different types of sea ice and open water fractions, separating the upper ocean from the lower atmosphere. The general lack of in-situ observations in the sea ice region hampers the understanding of relevant mechanical and thermodynamic processes, resulting in uncertainties of satellite observations, prediction models, and reanalysis products. An analysis of air-sea heat fluxes in the Antarctic marginal ice zone (MIZ), with a focus on the Weddell Sea region spanning from 1970 to 2023 is presented in this dissertation. Key parameters such as air and skin temperatures (TA and Tsk, respectively), and sea ice concentration (Ci) exhibited notable trends, revealing a warming trend in temperatures alongside a significant decline in sea ice concentration, particularly accentuated in the last decade. The Ph.D. project encompassed three distinct field measurement campaigns conducted within the Antarctic MIZ aboard the icebreaker S.A. Agulhas II. Data has been acquired through novel instruments such as the high-resolution thermal camera and other onboard sensors. These campaigns facilitated comprehensive data acquisition about the physical variables governing the thermodynamic processes occurring within the marginal band of the Antarctic sea ice. Field data collection allowed comparison with satellite observations and model estimations. The analysis brought to light challenges in extracting accurate Tsk and Ci data from satellite products with biases up to 7 Celsius degrees for the Tsk and up to 50% for the Ci, attributable to atmospheric interferences and the considerable dynamism of ice within the MIZ. The model comparison allowed us to understand the source of discrepancies in the estimations of the surface energy fluxes that govern the seasonality cycle of the sea ice.
Improving the structural and mechanical performance of engineered wood products through inclusion of plantation hardwood timber

Nero, Richard Anthony ( 2023-11)

The mounting pressures of a changing climate are necessitating a drastic shift in the way we approach energy production, consumption, and conservation. In the building and construction industry this has resulted in a growing push for structures with low operational energy requirements built from materials with low embodied carbon emissions. Increasing population density means mid- and high-rise structures make up a growing portion of our global residential and office building stock. These buildings conventionally employ concrete and steel which both have high carbon-dioxide emissions associated with their manufacture, unlike timber which naturally sequesters carbon during its growth cycle. The focus of this thesis is on the potential for sustainably sourced plantation hardwood timber, traditionally grown for the pulp industry, to be valorised in high-performance and novel engineered wood products (EWPs). Softwood timber varieties such as pine, spruce, and fir are well established in EWPs such as cross-laminated timber (CLT), glue-laminated timber (GLT), and laminated veneer lumber (LVL). However, there is a knowledge gap regarding the structural suitability and performance of similar EWPs built from hardwood timber varieties. Additionally, these conventional EWPs are less suited than traditional steel and concrete systems to achieve the long floor spans and wide column grids preferred by developers and architects for mid- and high-rise buildings. Another barrier to such EWPs seeing greater use in the construction industry is the complex, inhomogeneous nature of the timber material. This feature increases perceived risks, as predicted performance can vary quite drastically from actual performance. Statistical approaches are necessary to capture the performance uncertainties imposed by the natural variabilities of the timber material. Although past studies have reported reliability assessments of individual timber elements, the impact on the reliability assessment when combining these elements into an EWP such as CLT has not been previously addressed. In this thesis the material and mechanical properties of common plantation hardwoods were determined through a series of experimental studies. These properties include rolling shear strength and stiffness crucial to CLT performance as well as longitudinal bending strength, stiffness, and ductility. These material properties were used to inform analytical and numerical models that demonstrate the suitability and performance-enhancing characteristics of hardwood timber in conventional EWPs like CLT. A novel statistical capacity prediction model for CLT in out-of-plane bending was developed to reflect the variable performance of timber structural products. This prediction model was then leveraged in developing a reliability framework to inform design codes and enable safe structural timber products. Overall, this thesis presents evidence to support the utilisation of hardwoods in existing and novel EWPs to improve their structural and mechanical performance. The culmination of this work is a novel adhesive-free timber-steel composite system that valorises plantation hardwoods while contributing a long-span prefabricated EWP with strong sustainability credentials to the toolbox of design engineers.

Infrastructure Engineering - Theses

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