Infrastructure Engineering - Theses
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ItemRigid Barrier with a Gabion Cushion Subjected to Boulder Impact( 2019)Protection against rockfalls occurring alongside landslides contribute to the major part of the disaster management budget in many counties like Switzerland, Japan and Hongkong. Protective structures are usually built over disaster trajectories to safeguard lives and properties. Reinforced concrete barriers that are fitted with gabions are one common form of installations to provide the protection. Few experimental investigations involving impact testings of a rigid reinforced concrete barrier which was fitted with a gabion cushion cover have been reported in the literature. But these investigations were limited to studying the localised actions of impact. The change of structural response behaviour of the barrier as a whole by the presence of a cushion layer is typically not within the scope of the reported investigations. Design methodologies that have been developed are typically limited to overly simplified calculations based on applying an equivalent static force to the barrier. To fill this knowledge gap full-scale pendulum tests have been conducted by the authors on a barrier that was fitted with a gabion cushion layer. The structural response behaviour of the barrier, contact force and tensile strains in the longitudinal reinforcement were of interests. Results recorded from the tests were compared with results from control experiments which were without the protection of any cushion materials. The introduction of a layer of cushion is shown to be able to have the deflection demand on the structure reduced by more than 70% when the amount of energy delivered by the impact is kept constant. An analytical procedure employing the Hunt and Crossley contact model, Swiss code model and two-degrees-of-freedom (2DOF) system modelling technique is presented for evaluating the flexural response demand behaviour of the cushioned barrier. The proposed analytical procedure is shown to be able to predict the reduced deflection demand with a reasonable degree of conservatism. At the end of the thesis, a simple hand calculation procedure featuring the use of design charts is presented for engineering applications. The procedure is illustrated by a worked example which is based on a realistic rockfall scenario.
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ItemAn integrated method for groundwater vulnerability assessment using a DRASTICL model and a green algae ecotoxicity test( 2019)The world population could reach 9.8 billion by the year 2050 (UN, 2019). The rising world population presents the challenge of water and food security for human development. As a result, excessive use of agricultural chemicals (both fertilisers and pesticides) which in most cases are toxic not only for the humankind but also for the environment, is putting significant stress on the groundwater levels and the water quality. Groundwater (GW) pollution from agriculture is particularly significant in partially and totally groundwater-dependent ecosystems, as these ecosystems provide habitat for various endangered flora and fauna. Even though the importance of GW systems is well recognised, groundwater pollution vulnerability assessment models and groundwater pollution quantification techniques have experienced slight changes over the last 10 years and in most cases, the use of agricultural chemicals is assumed to be safe in the absence of sufficient data and evidence. The existing models produce an annual GW Vulnerability map and there is little to no monitoring of groundwater for these chemicals due to difficulty with identifying the representative samples and the high analytical cost. Therefore, this thesis aims to develop a novel approach to understand the seasonal variations in groundwater vulnerability and used the modified model to identify the representative sampling bores and also explores an algal ecotoxicology test as for the pesticides in water, that can be used as a fast and inexpensive pre-screen to identify samples above a certain level of toxicity for detailed chemical analysis.
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ItemShallow geothermal systems: individual and district applications( 2019)Worldwide energy use is expected to rise due to an increase in population and global warming. About half of this energy use is for space heating and cooling for buildings, where electricity (mostly derived from fossil fuels) and natural gas are the most common sources of energy. To achieve long term energy sustainability, electricity and natural gas consumption needs to be reduced. One way to achieve this reduction is by utilising shallow geothermal system or ground source heat pump (GSHP) system technology. This technology utilises the ground as a heat source or a heat sink to provide sustainable heating and cooling for buildings. The use of this technology has been growing worldwide. However, information and high-quality datasets of GSHP systems are still rare in Australia, leading to installations with low efficiency and high installation costs. This research aims to contribute to the understanding of GSHP systems under Australian climatic, cost and emission conditions, including how to improve their viability and uptake. The first part of this research aims to address this lack of availability of quality datasets. To do this, a full-scale monitoring project was undertaken. This thesis presents the performance data from 10 monitored residential and small commercial GSHP system installations in the greater Melbourne area. The measured data reveals that a GSHP system can perform well under Melbourne climatic condition, with an estimated coefficient of performance between 2 and 4.9. One common trend in all of the monitored properties is that they are used only around 10 to 20% of the year, which is much smaller compared to the expected usage based on typical design methods. For this reason, a more detailed comparison was conducted for two properties with the lowest and highest system usage. The comparison indicates that the differences in the usage patterns imposed by the occupiers can significantly impact the potential cost-effectiveness and environmental benefits of the GSHP system. This suggests that in general, a GSHP system can be an alternative heating and cooling options under Melbourne climatic and geological conditions, but they have to be designed, installed and used appropriately. Otherwise, this may lead to an inefficient system with a long payback period. One potential explanation behind the moderate GSHP system usage described above is the temperate climatic conditions of Melbourne, which requires only moderate heating and cooling. For these conditions, a hybrid combination between GSHP and conventional systems may be preferred to maximise the benefits from both systems. A hybrid GSHP (HGSHP) system means a GSHP system that is sized to provide the baseload thermal energy for a building and this system is supported by a conventional system during the hottest and coldest days of the year. This leads to the next part of this research where an HGSHP system design method is proposed with the objective that considers both costs and emissions by using a Pareto optimum approach. This analytical study is extended to cover different climatic, cost and emission conditions across several Australian cities. The results reveal that HGSHP systems can have a lower lifetime cost than GSHP or conventional systems. However, this hybrid system mix with the lowest lifetime cost is not necessarily the same as the one with the lowest lifetime emission. Overall, this research may provide a basis on which decisions about whether to install an HGSHP system with the objective to minimise their lifetime costs or emissions. A solution which considers both factors with equal weight is also provided herein. The last part of this research considers the possibility to combining several individual HGSHP systems into a district arrangement. This is called a district HGSHP system and this is possible because buildings are located close to each other in the urban area. The results indicate that district HGSHP systems can reduce capital and operational costs compared to individual HGSHP systems. The highest financial savings occur when buildings with significantly contrasting thermal load patterns are combined together, for example, combining heating dominant with cooling dominant buildings. Combining more buildings lead to higher financial savings, but this follows the law of diminishing returns. Altogether, the findings from each chapter are expected to contribute incrementally to improving our knowledge of GSHP system technology as well as providing more real-life performance data. The insights from this research may also be applicable to other locations with similar climatic, cost and emission conditions. Further, based on the outcomes of the work covered in this thesis, stakeholders may be able to make more informed decisions on design, installation and operation of GSHP systems. These should also allow the development of more appropriate public policy to encourage the growth of the shallow geothermal industry.
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ItemDevelopment of Advanced Timber-based Prefabricated Panelised Systems( 2019)This thesis aims to develop advanced timber-based panelised prefabrication in an impactful manner. The research approach involved the establishment of close collaborative industry-partnerships which were then leveraged to best satisfy the critical needs faced in industry, resulting in targeted in-depth advancements across a range of areas. Five core areas for detailed advancement were identified, namely: manufacturing processes, waterproofing, wall systems, design methods (including optimal configuration selection) and floor systems. Within each core area, the pressing limitations of most immediate commercial need were investigated and addressed in detail. Consequently, the original contributions to knowledge are as follows: - Full evaluation and assessment of advanced automated manufacturing technologies and processes available for complete timber-based panelised systems; - Development and successful commercial adoption of a purpose specific prefabricated panel to panel waterproofing solution to replace on-site work; - Development and implementation of a significantly more material and cost-efficient panelised timber-based wall system for mid-rise buildings, namely stiffened engineering timber walls with post-tensioning; - Corresponding mathematical modelling via the computationally efficient exact finite strip method based upon the Wittrick-Williams algorithm with appropriate orthotropic material models and strength limits; - Development of associated design curves, configuration specific post-tensioned strength reduction factors and optimal configuration selection methods; - Development of a panelised stressed-skin timber floor system through reductive-design with increasing material efficiency whilst also reducing the number of manufacturing processes required for competitive commercial adoption. As a result, this development of knowledge, process and product innovations, is spurring and enabling the growth of research in, and industry adoption of, advanced timber-based panelised prefabrication.
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ItemDirect geothermal energy: reducing the poultry industries’ carbon footprint( 2019)A Ground Source Heat Pump (GSHP) system is a type of highly efficient renewable energy system which utilizes the ground as the heat source when heating and as the heat sink when cooling. Since the initial installation cost of GSHP systems can be relatively high, hybrid GSHP systems can be designed to reduce the initial cost by coupling with other energy technologies, including solar technology. One promising area where hybrid GSHP systems can be applied to is in the rural industries which has high requirement for heating and lack of reticulated gas infrastructure and land availability. This research aims to contribute to the development of hybrid GSHP system with horizontal ground heat exchangers (GHEs) suitable for the rural industry, with poultry sheds in Australia investigated as cases studies. A full-scale instrumented hybrid geothermal system for the poultry shed in Peats Ridge was then designed and built to verify, demonstrate the performance. Providing 80 kW heating, the ground heat exchanger field consists of 12 horizontal trenches at the depth of 1.5 m totalling 4,800 m of ground loop and 400 m of pond loop in a nearby pond submerged at a depth of 4 to 6 m. This work then investigated energy efficient solutions for poultry sheds in Australia. The space heating and cooling demand cycles of a typical poultry sheds in Peats Ridge, NSW, Australia have been simulated in detail, using TRNSYS 18. It is found that heating systems, operational schedule (raising batches of chicks) and ventilation strategies have a great impact on energy consumption. An optimum scheduling strategy was developed, and energy demands were minimised. Furthermore, this work contributed to the improvement of the design of hybrid geothermal system with horizontal GHEs. As hourly simulation of GSHP with horizontal GHEs is not yet available in major commercial software packages, Artificial Neural Network (ANN) models were proposed, which can potentially be generally applied to similar sheds at different locations and under different climate conditions, with readily available and limited types of input data, hourly heating loads, accumulated heating loads and ambient air temperature. Trained with simulated data from a verified TRNSYS model, the ANNs can predict the performance of GSHPs systems with identical GHEs even under climatic conditions (and locations) that has not been specifically trained for. This represents a major advance in this area. With only limited input data and showing a high accuracy (no more than 5% error in most cases tested), the presented ANN is 100 times computationally faster than TRNSYS model and 10,000 times faster than comparable Finite Element models. Finally, to reduce the lifecycle cost and greenhouse gas (GHG) emissions of heating the shed, multi-objective optimisation regarding hybrid geothermal-solar-gas heating systems are investigated. In these systems, the baseload heating demand is satisfied by GSHPs, with solar photovoltaic panels providing the electricity needed to drive the pumps and LPG gas boilers toping up the balance of the heating. This study investigated and optimised lifecycle cost along with GHG emissions arising from the three components of these hybrid systems, considering three different electricity offsetting scenarios. The results indicated that a considerable reduction in the lifecycle heating costs (up to 55%) and GHG emissions (up to 50%) can be achieved when optimised hybrid systems are used for heating. The Pareto front solutions for this hybrid geothermal-solar-gas heating system were also determined. By comparing the Pareto front solutions in different scenarios, it has been identified that the shave factor, a measure of the proportion of GSHP to the overall heating system, has the highest impact when to comes to reducing the lifecycle cost, while the size and utilisation of solar PV panels contributes more to the lifecycle GHG emissions. The findings obtained from this study can contribute to the design and optimisation of hybrid geothermal systems to reduce its lifecycle cost and carbon footprint as well as assist in wide spreading the application of GSHPs for the rural industry.
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ItemInvestigation of hyporheic flow through meandering rivers: Implications for nitrogen processing( 2019)Increased nitrogen loads have significant negative consequences in streams. The hyporheic zone of streams, where surface-subsurface water exchange happens, provides significant attenuation for nitrogen compounds from the fluvial system. From many geomorphic features that contribute to hyporheic flow, meanders are particularly important for these biogeochemical reactions. Meanders provide longer residence times to allow complete denitrification of various nitrate to nitrogen gas, which can support more significant improvements in water quality compared to other channel features that only allow for partial denitrification due to short residence time. From the published literature, it is evident that there is not enough understanding about the extent of temporal variation of meander driven hyporheic flow except for few theoretical studies that have been performed to investigate the physical behavior of water and solute movement. Therefore, this research aims to investigate how meandering morphology impacts on transport characteristics of water and dissolved solutes in the hyporheic zone and to identify primary mechanisms controlling the flow. This was achieved through a set of laboratory experiments and a three-dimensional numerical model developed for meandering stream. Laboratory experiments were conducted in a recirculating flume with a set of river discharges and meandering morphologies. Residence time distribution and downwelling water flux were determined by continuously monitoring the exchange of a conservative tracer (Rhodamine WT) introduced into the surface flow. The experimental results show that both; stream discharge and meander wavelength affect the residence time and water flux into the sediment bed, hence affecting the rates of biogeochemical reactions. Most importantly, change in stream discharge affects residence times in the hyporheic zone, but the importance of considering river flow conditions in modeling hyporheic flow through meanders has been neglected in previous studies. The three-dimensional model developed in this study is based on the combination of surface flow modeled with Reynold average Navier-Stokes equation and subsurface flow modeled with the Continuity equation for groundwater flow and Darcy’s law equation. This mathematical model was solved using COMSOL Multiphysics Modelling Software (will be referred to as COMSOL henceforth), and water transport characteristics in the hyporheic zone were estimated using a numerical particle tracing technique in COMSOL. The model predicted the observed residence time distributions of laboratory tracer experiments with an R2 of 0.95. Results show that there are two primary mechanisms driving hyporheic flow through meanders; 1) Lateral flow caused by channel slope at the scale of meander wavelength (Floodplain HE) and 2) vertical flow caused by surface water acceleration due to the curvature of the channel at the scale of channel width (Fluvial HE). This three-dimensional model was then used to study the effect of meander morphology on the hyporheic residence time distribution and water flux complemented by Taguchi orthogonal array design. Channel sizes considered in the simulations range from 1m to1000m in widths. We propose three empirical relationships to predict downwelling water flux and characteristics of residence time distribution (mean and standard deviation). Also, we found that the hyporheic residence time distribution induced by three-dimensional meanders follows a log-normal distribution. Meander wavelength has a significant effect on the hyporheic residence time as well as the downwelling water flux, demonstrating the importance of channel size on the hyporheic flow processes. However, the sinuosity of the river does not affect much on the time that water spends in the hyporheic zone but alters the volume of water entering the hyporheic zone. Most importantly, meanders produce significant vertical hyporheic flow in addition to lateral flow. Increasing the channel curvature (increased sinuosity or decreased wavelength) increases the vertical flow, hence higher downwelling water flux but the reduction in the residence time. Finally, we looked at how meander induced hyporheic flow influences on nitrogen processing. We consider a dimensionless number (Da, Damkohler number), defined as the ratio between the median residence time and the critical concentration of dissolved oxygen below which nitrogen removal reactions occur (reaching anaerobic conditions). Meanders, being large morphologic features, observed to provide high Da values (>20) suggest the availability of hyporheic regions with prevailing anaerobic conditions for nitrogen removal reactions. In recent decades, fate and transport of nitrogen in hyporheic zones have been significantly influenced by flow modifications, increased water pollution, and channel straightening. Increased straight channels and impervious surfaces confine the hydrological flow paths and residence times in the hyporheic zone, which may limit sufficient treatment. In order to support this important ecological service, implementing restoration solutions is vital. Understanding the underlying mechanisms and effects of urbanization on nitrogen transformation is a prerequisite for minimizing stream degradation and achieving restoration goals. Therefore, our findings can potentially be incorporated in river restoration practices and to design rivers as natural nitrogen filters. This study represents a step forward for the analysis of large-scale channel features and their residence times, which are less understood in previous literature but are very important for biogeochemical cycling in rivers.
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ItemUnderstanding the Co-evolution of Land, Water, and Environmental Governance in Victoria during 1860 - 2016( 2019)There are many cases where the changes in government interventions have resulted in considerable negative consequences to social-ecological systems (SESs) instead of promoting improvement. Difficulties occur in guiding governance change to steer SESs onto desirable pathways. However, the linkage between the degradation of SESs and governance failure remains unclear. To address this gap, this research aims to understand the co-evolution of land, water, and environmental governance through the integration of policy into social-ecological system frameworks (SESFs). This research is presented into three chapters to answer the following three research questions: Research Question 1: How does land, water, and environmental governance steer the SES condition? Research Question 2: How have policy instruments for land, water, and environmental governance developed from 1860 to 2016 in Victoria, Australia? Research Question 3: How have the policy instruments for land, water, and environmental governance co-evolved? Is there any association with biophysical changes? Chapter 3 developed an SES framework by extending the SES frameworks proposed by Ostrom and Anderies. In the proposed framework, SES condition is viewed as the product of the accumulation of policy instruments used in land, water, and environmental governance to rule the interaction between and among components of biophysical and social systems. Policy instruments can help policy analysts explain the linkages between resources, resource users, and public infrastructure providers and which has a significant role in enhancing the robustness of SES. The framework provides a new way to develop a wider recognition and appreciation of dynamic, site-specific biophysical and social system conditions in influencing the government intervention, and in turn, have been shaped by them. In particular, the framework can help policymakers elucidate: 1. how the biophysical system has been understood in SES governance as represented by the relevant policy instruments; 2. how the social system has been set up in SES governance; and 3. how the synergies and trade-offs between the biophysical and social systems have been managed in the governance of the SES. It can help for systematically analyzing SES governance through the configuration of policy instruments. Chapter 4 used the proposed framework to investigate the evolution of policy instruments used in the land, water, and environmental governance in Victoria, Australia. The content analysis of Victorian Acts related to land, water, and environment practices between 1860 to 2016 was conducted. The investigation found that policy instruments to manage the behavior in resource utilization (substantive and procedural policy instruments) did not vary. However, they were differences in the circumstances in which they were implemented, in this case, differing interactions among components of the biophysical and social systems. The policy instruments held a particular focus in managing components of SESs in different periods and the evolution of each policy instrument has its pathway. Four regimes were identified in the evolution of policy instruments used in water governance: reserve, authority, information, and integration regimes. Whilst, policy instruments used in land governance experienced three regimes (authority, information, and integration regimes) and policy instruments used in environmental governance experienced two regimes (information and integration regimes). Chapter 5 associated the co-evolution of land, water, and environmental governance and biophysical changes. The co-evolution was analyzed by unpacking the integration of policy instruments used in land, water, and environmental governance. The integration was analyzed by examining the relationships between SES components covered in policy instruments. Represented by the subtle changes in their integration, the analysis showed the Victorian government’s learning process in adapting and accommodating the natural system and its desire to avoid significant negative impacts on the land, water, and environmental conditions have resulted in the inclusion of the dynamic interaction within SES as the consideration in formulating its policy instruments. Comparing the co-evolution of policy instruments used in land, water, and environmental governance with state-wide changes within the biophysical system, it is found that there is a strong association between the integration of land, water, and environmental governance and the change in SES condition in Victoria from 1860 to 2016. This longitudinal study of Victoria land, water, and environmental governance developed a new way to explain the linkage between natural resources governance and SES condition. Re-constructing government intervention through policy instruments implemented in the land, water, and environmental governance, the study found the way policy instruments were designed and implemented varied with the state of understanding of the dynamic interactions within the SESs. Looking back over Victoria’s history in developing policy instruments used in land, water, and environmental governance, the study suggests that policy instruments should be formulated to address the interactions among components within SES, in this case, policy instruments as managers of interaction within SES. This is crucial to steer SES conditions onto desirable conditions.
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ItemAn Integrated Framework to Optimise Consolidating the Last Leg of Deliveries in the Inner-City( 2019)Efficient and reliable freight delivery and pickup services are important for the functioning of retailers and businesses in the inner-city area as well as the consumption of products for residents, visitors and workers. Furthermore, the limited availability of affordable industrial land for logistics facilities and inefficient loading infrastructure in the inner-city coupled with the increasing demand for express and fragmented deliveries make it operationally difficult and economically cost-prohibitive for freight carriers to maintain offering reliable and low-cost delivery services to inner-city receivers. Policymakers and transport researchers have considered freight consolidation delivery solutions to address negative externalities caused by growth in last mile deliveries. However, there has been an imbalance of focus in previous initiatives towards freight carriers, with far less emphasis placed on goods receivers. This is a critical oversight given that the success of consolidation schemes is inextricably linked to the willingness of receivers to accept and respond positively to the consolidation scheme. Moreover, the lack of focus on financial viability of consolidation solutions early in the planning process often results in making these schemes highly dependent on government incentives. Site selection of consolidation facilities is mainly evaluated using decision support models that are performed by numerical computations or multi-criteria analysis without inputs from spatial analysis. These issues and shortcomings of previous consolidation policies have adversely impacted their efficacy and suitability. An effective and properly planned consolidation policy could offer an alternative solution for freight carriers to cope with increasing activities of express deliveries in the highly congested inner-city. Accordingly, the objective of this research is to develop an integrated framework to optimise the design and set-up of a suitable, sustainable and financially viable freight consolidation facility in the inner-city based on operational, social, environmental and economic objectives of all stakeholders. The integrated framework developed in this research consists of five stages. In the 1st stage (Chapter 4), direct insights from freight carriers describe their delivery trips specifically inside the inner-city and subsequently the proposed design of the consolidation facility incorporates operational requirements, sustainable freight land-use polies and business value propositions. Analysis of operational parameters from freight carriers revealed that their delivery trips in the inner-city include higher use of delivery vans, higher number of delivery stops and lower vehicle fill-in rate compared to deliveries in other parts of the urban area. Then, the 2nd stage (Chapter 5) applies a multi-stakeholder decision-support approach to evaluate the suitability of four consolidated delivery fleet configurations in addressing the requirements of six stakeholder groups involved in last mile delivery. The multi-criteria analysis of the alternatives is performed using the PROMETHEE method based on the priority weights of 30 decision criteria. The multi-actor analysis reveals that the combined use of battery-electric delivery vans and electricity-assisted cargobikes addresses the concerns of societal stakeholders and operational requirements of business stakeholders in a balanced approach. The mono-actor analysis of the alternatives underlines the clashing views of each stakeholder group regarding the optimal delivery fleet. Moreover, the 3rd stage (Chapter 6) of the integrated framework applies econometric models to examine the willingness of receivers to request their freight carriers to transfer the parcels to the proposed consolidation facility for subsequent consolidated delivery to their businesses. Behavioural responses were collected using a stated-preference survey from 255 retailers and businesses representing 13 different sub-industries in Melbourne CBD. The study findings reveal a general potential willingness to participate in the proposed consolidated delivery. The ordered logit model estimations illustrate that the receivers’ willingness to participate is significantly influenced by the intensity of their delivery activities. Furthermore, the mixed logit model estimations highlight that the consolidated delivery time-window and availability of relevant value-added services hold the greatest potential to sway receivers’ support or opposition to delivery consolidation. Subsequently, the 4th stage (Chapter 7) presents a GIS-based Multi-Criteria Decision-Making (GIS-MCDM) approach to locate and rank optimal sites for the proposed consolidation facility in the inner-city. Real geographic datasets from Inner Melbourne, Australia, are applied to identify 20 candidate sites using geoprocessing tools in ArcGIS that are then evaluated and ranked using the TOPSIS method based on 11 weighted decision criteria. The spatial suitability analysis confirms that the most suitable candidate sites are in zones with affordable industrial land with excellent accessibility to major roads and receivers. A sensitivity analysis was performed to examine the influence of changing the criteria weight on the stability of candidate sites’ rankings and test the robustness of the process and the confidence in the outcomes. Finally, the 5th stage (Chapter 8) presents a two-phase ex-ante profitability assessment approach to analyse the business case of the proposed consolidation policy in the upper-phase and a mixed integer linear programming model is formulated in the lower-phase to optimise the facility profitability. The holistic cost model incorporates a stochastic approach in the profitability estimation by accounting for the uncertainty of the interest of freight carriers to transfer their inner-city parcels to the consolidation facility. The genetic algorithm solution of the MILP model estimates that personnel costs contribute to the largest share of total costs and that the profit margin could be very tight. Unlike other studies in the literature that question the viability of a consolidation facility to be self-sustaining, this study provides evidence that these facilities could be profitable without government subsidies. Based on the optimisation solution, it is recommended that a successful consolidation facility should focus on i) ensuring a minimum daily throughput; ii) employing a strategy to effectively manage critical staffing resources – primarily drivers; iii) ensuring vehicle fill-in rates are optimised. The data-adjusted decision-support framework presented in this thesis incorporates the freight industry operational requirements as well as social and environmental concerns to optimally and sustainability establish a suitable consolidation facility in the inner-city. The modelling results of the integrated framework enable decision-makers and transport researchers to not only apply value-decisions at the onset of the process, but also allow for understanding and visualisation of the results and of the importance of chosen criteria in the decision-making process. The findings of the econometric models provide valuable insights into the type and size of receivers that might be useful in formulating an effective consolidated delivery policy that is tailored for most willing receivers. The acquired knowledge from freight carriers facilitate an enhanced understanding and depict an accurate picture of the current state of the last leg of delivery in the inner-city. Hence, appropriate and practical solutions could be proposed to enhance the efficiency of freight carriers and alleviate the negative impacts of their operations in the inner-city area.
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ItemA Study on the Behavior of Vehicle Platoons and Platoon Formation and Dissolution Strategies( 2019)Vehicle platooning, a coordinated movement strategy, has been proposed to address a range of current transport challenges such as traffic congestion, road safety, energy consumption and pollution. The current literature and on-road platooning trials typically assume a planned formation at the source and dissolution at the destination. In contrast, this research considers platoons that can be formed in an ad-hoc manner, on the fly, opportunistically. To form platoons in an ad-hoc manner the vehicles have to `speak the same language', which is in current practice limited to vehicles of particular manufacturers. There is no standard language yet. This thesis aims to fill this fundamental gap of standardization by developing a formal model of platooning concepts. The research proposes an ontological model of platooning objects and properties and abstracts the basic building blocks of platoon operations that can then be aggregated to complex platooning behavior. Also, the current literature considered platoon formation by tail merge which is sufficient only for the formation on a ramp or at a ramp-highway junction. In ad-hoc formation, a vehicle can express a merge request when approaching the platoon on the highway from the back, front or the side of the platoon. This thesis studies the impact of these three different merge operations, namely front merge, middle merge, and tail merge. The efficiency of these operations is analyzed under different scenarios, varying the vehicles’ speed adjustment strategy, traffic density, and the density of mergeable vehicles. The impact of the merge operations is represented in terms of merge time, merge distance, average traffic speed, and merge success rate. Our experiments show that in an ideal no traffic scenario, the middle merge is costlier in terms of merge time for the same merge distance whereas in the presence of traffic middle merge helps is quick platoon formation on an average in a higher traffic density in particular. This insight should provide a more flexible toolkit for planning a platoon formation. As this research considers ad-hoc formations of platoons, the question arises whether the original benefits of platooning can be preserved for the ad-hoc formations. The formation is not desirable if the time the vehicles move as a platoon is too short to realize the fuel efficiency. Hence, for a vehicle, it is crucial to decide whether or not to platoon in a given traffic situation. This thesis aims to solve this decision-making problem by analyzing the situation-aware fuel efficiency of platoon formation, and building a cost prediction model. The model provides a guideline of efficient ad-hoc platoon formation. The proposed model is evaluated using prediction accuracy, i.e. the percentage of correct prediction to form fuel-efficient platoons, out of all predictions. The experimental result shows 89.2% prediction accuracy of the proposed model. At the final stage, this research investigates two different types of ad-hoc platoon formation and corresponding platoon dissolution strategies on multi-lane highway. Multi-lane allows the vehicle to overtake. Hence, a platoon can be formed in many different ways. The first approach forms a platoon greedily without considering the order of destinations of the platoon members. This approach enables a quick formation but imposes an overhead of platoon rebuilding, and consequently, additional fuel cost when platoon members leave. An alternative approach forms a platoon in the order of the destinations of its platoon members. This ordered approach incurs a comparatively higher formation time due to vehicles' reorganization but does not lead to further overhead of platoon rebuilding. The research investigates these two ad-hoc formation and dissolution strategies. The prediction model shows 90.4% prediction accuracy for the greedy approach and 82.2% prediction accuracy for the ordered approach on average for platoon size two to six. The experiment determines greedy formation of platoon is more fuel-efficient for multi-lane highway.
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ItemInfluence of bioturbation and fine sediment clogging on hyporheic exchange in streams( 2019)Sediment permeability and its heterogeneity exert strong control on the hyporheic exchange which underpins several hydrological, biogeochemical and ecological services provided by streams. Streambed permeability has been observed to vary over several orders of magnitude, both in space and time. This thesis argues that a definitive explanation for this observed variability has not been provided due to limited fundamental understanding of three critical in-stream processes- bioturbation, fine sediment clogging, and bioclogging. Feedback mechanisms exist between these processes which collectively influence the structure, composition and hydraulic properties of streambeds. This PhD is directed to advance our current understanding of bioturbation and fine sediment clogging on modifying the streambed permeability and consequently the hyporheic flow regime in fluvial ecosystems. A conceptual model is presented which identifies the causal pathways through which bioturbation process could alter small-scale hyporheic exchange in lotic environments. To support the arguments presented in this model, experiments in re-circulating flumes are conducted to study the effects of bioturbating organisms (Lumbriculus variegatus) on dune-induced hyporheic exchange. Results showed that macroinvertebrate bioturbation has complex effects on the hyporheic flow regime which resulted in modification of hyporheic flux, residence time distributions and penetration depth in treatment flumes. The observed variability in these characteristics of hyporheic exchange is attributed to the generation of a heterogeneous & anisotropic permeability field in sediment beds and alteration of bed morphology due to the bioturbation by model organisms. The experimental results also indicated that sediment re-working time and size of bioturbating organisms are dominant controls on the extent to which hyporheic exchange is moderated. To advance the understanding of fine sediment clogging in streams, experiments were conducted in re-circulating flumes to study the distribution of clay-sized sediments in streambeds comprising of different grain sizes. The results suggested that the infiltration pattern of clay-sized particles depends on the relative size of fine particles & bed grains and the initial concentration of fine particles in the surface water. The observed profiles of deposition/infiltration of clay particles also highlighted that fine sediments are preferentially transported with downwelling hyporheic flow paths into the streambed. The clogging by fine sediments is expected to reduce bed permeability and subsequently hamper the hyporheic exchange. Fine sediment deposition in streambeds reduced hyporheic flux, inhibit deeper penetration and increase median residence times. These results also indicated that clogging by clay-sized particles can have a larger influence on the hyporheic flow regime in coarse-bedded streams compared to fine-bedded streams. Finally, the impact of macroinvertebrate bioturbation on modifying hyporheic exchange in clogged streams was assessed by conducting experiments in re-circulating flumes using a control (clogged flumes) and treatment (clogged flumes + Lumbriculus variegatus) design. The observations from treatment flumes provided evidence of mitigation of clogging by the activities of model bioturbating organisms. The invertebrates infiltrated the top layer of deposited fine sediments, mixed them with underlying bed grains and disturbed the clay deposits in interstitial regions within a sediment bed. The bioturbation of the clogging layer improved the vertical connectivity in treatment flumes producing shorter residence times, greater penetration depths and higher hyporheic flux than the control flumes. These experiments illustrated that the extent to which the characteristics of hyporheic exchange are modified depends on the overall streambed composition i.e., the size of both fine sediments and underlying grains, and the size of bioturbating organisms. Primarily, the findings from this study suggested that the interacting in-stream abiotic and biotic processes could potentially induce spatio-temporal variability in streambed permeability and modify the hyporheic exchange in streams. This holds direct implications for modeling strategies that aim to predict hyporheic exchange in stream networks but consider streambed as a homogenous porous medium with non-transient hydraulic properties for simplicity. These critical processes and their mutual interaction could also influence biogeochemistry in hyporheic zones and must not be overlooked in stream management and restoration programs. Thus, it is argued that more interdisciplinary research must be conducted to comprehend the role of these processes in modifying streambed properties and associated ecosystem functions.