Civil Engineering - Theses
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ItemNo Preview AvailableEffect of land surface heterogeneity on satellite near-surface soil moisture observations(University of Melbourne, 2009)This thesis develops a technique to reduce the error in near-surface soil moisture estimates from spacebome passive microwave sensors, by accounting for the heterogeneity of land surface conditions within the sensor field of view. Using experimental data collected in the course of this research, it is demonstrated that this technique will significantly reduce the error in satellite near-surface soil moisture retrieval. The technique has been developed specifically for the first dedicated passive microwave soil moisture satellite, the European Soil Moisture and Ocean Salinity Mission (SMOS), which will use L-band (1.4GHz) measurements to map nearsurface soil moisture globally at a near-daily time scale. The main steps taken to develop these techniques are the first evaluation of the core radiative transfer model of the SMOS soil moisture retrieval algorithm for the Australian conditions using airborne data, and an analysis of the land surface controls on near-surface soil moisture distribution at the satellite footprint scale. These initial steps provided the tools in order to test the accuracy of the soil moisture retrieval approach proposed for SMOS at the satellite footprint scale in the presence of spatial variability of the land surface, and to develop a new retrieval approach for SMOS which overcomes the shortfalls identified in the SMOS proposed approach.
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ItemAddressing uncertainties associated with water accounting(University of Melbourne, 2009)Water accounts provide information to a range of stakeholders who make decisions related to water. There are significant challenges in quantifying all of the information elements included in water accounts. Some information elements are measured while others are estimated. There is uncertainty associated with the information presented in water accounts, either due to measurement uncertainty or the assumptions made during the estimation process. The presence of uncertainties in water accounts poses two problems. Firstly, the decisions made based on information presented in the accounts may change if the associated uncertainties were disclosed. Secondly, due to the uncertainties associated with each element, the accounts rarely balance. At present the uncertainty in water accounts is not well understood and it is not systematically captured and reported in the accounts. This thesis identifies and quantifies the major sources of uncertainty in water accounts. Established techniques to quantify the uncertainties are only available for a few of the elements. A number of new techniques are developed to quantify the uncertainty associated with elements that include unmetered water use, net evaporation from storages, reservoir volumes and impacts of farm dams. A general framework to quantify uncertainties is developed and applied to a case study, the Werribee River basin (Victoria, Australia). The largest uncertainties in this catchment are associated with estimating rainfall runoff and surface water -groundwater interactions. A new method to constrain the uncertainty associated with each component of the water accounts and to create a balanced set of accounts, based on numerical data reconciliation, is presented. If the uncertainty surrounding each element is known, it is possible to improve the estimates and reduce the uncertainties by removing combinations of inflows and outflows that do not create a balanced set of accounts. Existing analytical techniques to perform the required calculations for data reconciliation are not suitable in water accounting because they assume that all uncertainties can be described using a Gaussian distribution. In order to incorporate other types of probability distributions, a numerical technique is developed. Overall, this thesis presents three new contributions: an identification of information elements which are useful to decision makers; a quantification of uncertainties associated with the elements reported in water accounts and methods are presented to quantify these uncertainties; a new numerical method, data reconciliation, to minimise the uncertainties by considering the joint probability of all inflows and outflows that create a balanced set of accounts.
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ItemA hybrid microsimulation model of freight transport demand(University of Melbourne, 2009)
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ItemA study of aerodynamic wind loads on tall buildings using wind tunnel tests and numerical simulations(University of Melbourne, 2009)
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ItemPricing carbon in power sector investment : a stochastic decision tree analysis(University of Melbourne, 2007)
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ItemIntersectoral water allocation : valuing water and the case for water property rights(University of Melbourne, 2006)
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ItemThe structure and strength of Victorian brown coals(University of Melbourne, 1961)A soil mechanics investigation into the structure and strength of Victorian brown coals has been performed and the results of consolidation and triaxial tests explained in terms of a proposed model of coal structure. Brown coal possesses a porous skeleton with aggregates of planar aromatic molecules cross-linked by aliphatic chain structures. The aggregates are effectively in contact with direct chemical linking at the points of contact. However, the bonding within the aggregates is much stronger than that between aggregates and the response of brown coal to stress is dominated by the inter-aggregate contact forces. Brown coal follows an effective stress law and a Hvorslev type law, with Ce/Je approximately 0.25 and �e approximately 35�, is applicable. A frictional type shear strength law is suggested and, good agreement is found between predicted and measured tensile strengths. Consolidation behaviour closely resembles that of a clay and the distribution of moisture contents in brown coal seams is shown to be a consolidation phenomenon. Other features in common with clays are the correlation of dimensionless parameters and the existence of a critical voids ratio line.
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ItemA scenario analysis approach to distributed energy system optimisation( 2016)Distributed Energy Systems (DESs) can provide less carbon-intensive, more resilient and highly efficient alternatives to centralised electricity generation for growing urban populations. Their successful planning depends on the selection of technologies and capacities, which are heavily reliant on an unknown future energy landscape. Furthermore, precinct development, electricity and natural gas price changes, future advances in DESs efficiencies and costs and government interventions can all influence the financial performance of installations. Existing DES optimisation methods typically assess a single year of representative data and yield a single immediate investment solution without capturing or adapting for future shifts in influencing factors. Accordingly, to address the need to include these future changes, this thesis developed a framework that facilitates the selection of optimal DES investment strategies over the lifespan of a project for a range of scenarios at the precinct scale. This approach enables a more representative assessment of DES performance by considering future forecasts as well as providing the additional freedom to defer investment to later during the project life. Building energy performance simulation software (DOE 2.2) with the addition of available measured data was used in conjunction with a bottom-up archetype approach to determine precinct scale electricity and heat load profiles for an analysis period of up to 20 years. Existing hourly intermittent supply models and long-term representative meteorological years were used to estimate solar photovoltaic (PV) and small-scale wind turbine outputs. When adjoined with a combined heat and power dispatch logic formed the electricity and heat supply model. The objective of the optimisation is to minimise the net present value of costs (NPVC) associated with the supply of heat and electricity to the precinct. Optimisation decision variables pertained to investment capacity and technology for each year of assessment. Solar PV installation capacities were approximated as continuous variables and wind turbine and gas generators consisted of integer variables for type and number of units leading to a total of 80 decision variables for a 20-year assessment period. Review and testing of a variety of optimisation algorithms showed the inability of genetic algorithms (GAs) to converge within a reasonable computer run-time. An iterative hybrid approach was therefore developed where GAs were initially employed due to their ability to handle integers and global search strengths after which particle swarm optimisation (PSO) was implemented to optimise continuous variables and the process repeated. The scenario analysis approach developed was tested for the Parkville Campus, the primary precinct of The University of Melbourne between 2016 and 2036. Four scenarios were developed, capturing a range of gross floor area (GFA) growth from 11% to 65% based on the Universities strategic plan as well as future electricity and gas prices, DES investment costs and government interventions. The buildings within the Parkville Campus were categorised based on their use and construction era, resulting in a total of 16 archetypes, where each were assigned an hourly representative electricity and heat demand profile. Electricity demand was estimated based on existing measured data where average annual demand was found to vary from 95 kWh m-2 a-1 for modern office space archetypes up to 266 kWh m-2 a-1 for traditional laboratory archetypes. Heating demand was estimated using building energy simulations for hot water and space heating which were scaled to match monthly measured natural gas demand data. This resulted in modern teaching space archetypes requiring an average of 25 and 99 MJ m-2 a-1 for hot water and space heating respectively whereas traditional cafés and restaurants were found to require 201 MJ m-2 a-1 for hot water and 119 MJ m-2 a-1 for space heating. Different trial runs were conducted for each Parkville Campus scenario, (1) no DES investment, (2) the traditional optimisation approach where DES investment was ‘now or never’ or only considering a single year solution and (3) the long-term optimisation approach with DES investment was allowed at the beginning of each analysis year. Constrained optimal DES investment strategies for all scenarios selected the upper bound of 6.7 MWp of solar PV installations whilst the selection of combined heat and power (CHP) systems ranged from none to 9.3 MWp depending upon the trial case and the scenario in assessment. Scenarios with high GFA growth and the inclusion of nearby residential apartment development provided the best business case for CHP, however the long-term investment strategy recommended deferring this investment until 2022. Both the long-term approach and traditional DES investment strategies provided benefits to the university over the do-nothing approach, with different scenarios yielding: (1) a reduction of the NPVC between 3% and 18%; and (2) greenhouse gas (GHG) emission reductions between 7% and 40%. Compared to traditional optimisation approaches, it was found that the long-term scenario analysis approach resulted in greater reductions in NPVC of between 0.34% for low growth scenarios and 3.76% for high growth scenarios. This translated into a saving of between A$0.9m for low growth and A$14.6m for high growth scenarios for a twenty year NPVC of A$241.7m and A$332.7m respectively. The scenario analysis approach did not consistently yield reductions in GHG emissions compared to traditional optimisation approaches, due to the deferral of DES investment. By allowing deferral of DES investment, the long-term scenario optimisation framework was shown to have several key advantages over traditional ‘now or never’ optimisation approaches, including: reduction in upfront capital expenditure by allowing step wise investment in DES in line with projected precinct electricity and heating demand growth; provision of installation lead time for planning, approval acquisition and allocation of plant area; reduced overall NPVC particularly for high growth scenarios; lower risk of oversized DES as investments are made when required. The long-term scenario optimisation framework requires significantly more data collection and simulation than traditional approaches and is therefore only warranted where precincts are expected to undergo meaningful change over the assessment period. A more detailed heat network loss model and optimal dispatch logic algorithm would be required if this framework is to be used at the functional design stage. Finally, the inclusion of GHG emissions as a second objective and the use of multi-objective optimisation could provide decision makers with an assessment of the trade-offs between NPVC and GHG emission reduction.
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ItemDevelopment of fabric-reinforced polyurea structures for ballistic protection( 2016)Textile-reinforced structures have been increasingly applied in personal protective armours due to their blast and impact resisting capabilities. Their enhancement in energy absorption, lightweight, flexibility, and fragments capturing capabilities when subjected to ballistic impact made them the preferable alternative options to traditional metallic materials. However, the recently developed multi-laminate structures with rate-dependent and non-homogeneous materials have substantially increased the complexity in analysing the behaviour of such systems, which renders the traditional experimental-reliant development approach less capable. This research aims at establishing a new development approach for multi-material laminate structures using finite-element modelling, supported by the experimental testing of basic material properties and structural performance. A new polymer-textile laminate structure was investigated by constructing virtual composite laminate models using LS-DYNA® package. Using the third-party software commanded via the custom-developed python code, the ballistic model of the meso-scale single layer Kevlar® 29 woven fabrics was first constructed and validated to study the evolution of kinetic, strain, and frictional energy components of the fabric during the ballistic impact, as well as its damage mechanism. An improved meso-scale solid element model was then developed to resemble the Twaron® fabric properties, in order to study the influence of the woven structures and projectile impact resistance. The results have shown superior performance from the plain weave structure in comparing to other architectures. To simulate the multi-layer fabric structures, further studies using various mesh sizes have led to the development of a hybrid-mesh finite element model, which simulates the inter-yarn and inter-layer contacts of the multi-layer fabrics with enhanced computational efficiency of over 500%. The numerical models of the textile-reinforced polyurea structures were eventually constructed by combining the meso-scale hybrid-mesh Twaron® fabric model with the nonlinear polyurea model. Ballistic impact on the three-section layup structures consist of polyurea sheets and fabric piles of similar areal density was then simulated. Comparison between various multi-material structures provided insights into the criticality of the material layup arrangements. Energy absorption mechanism was compared among all structural arrangements to reveal the contribution and energy absorption capacity (EAC) of each structure.
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ItemHigh performance concrete railway sleepers( 2016)Rail transport is the safest and one of the most efficient transportation modes to move both passengers and goods. It has a range of advantages such as low travel time, high capacity, energy efficiency and low impact on the environment. The demand for rail transport is expected to keep its continuously increasing trend over the next decade. Conventional track or ballasted track is still widely used in a large number of newly established lines, even those constructed for high-speed or heavy-haul trains. Sleepers are an essential component of ballasted tracks and play a significant role in track safety and performance. While timber, steel and concrete have been used to make sleepers since the establishment of railways, nowadays, prestressed concrete sleepers (PCSs) are most commonly used as a solution to the increasing rail demand around the world. Although PCSs are a small structural element, their behaviour is very complicated due to different loading conditions, small dimensional tolerances, prestressing, steam curing, subjected to cyclic and high-magnitude dynamic loads and exposure to various environmental conditions. In addition, several reports show premature damage and early failure of PCSs that require unplanned replacement. Therefore, over the last few decades, many research projects have been aimed at identifying key behaviours, responses and interactions with other components, as well as main issues of PCSs in the track. These projects have shed some light on several aspects such as loading conditions, interactions with other components, dynamic responses and load carrying mechanisms of PCSs. The most critical problems of PCSs also have been identified globally, namely, cracking, especially from dynamic loads. However, the literature on performance of materials, particularly under dynamic loading, is still very limited. High performance concrete (HPC) is believed to be an appropriate solution to the most critical problems and unresolved issues of PCSs and is a subject of interest to the railway industry. In this regard, recently, a few research projects have been conducted to apply specific kinds of HPC as a material of PCSs in order to address their cracking or durability issues. Nevertheless, the cracking behaviour of PCSs made of HPC under dynamic loading is still lacking. Furthermore, some issues of PCSs are attributed to the inadequacy of current analysis (quasi-static) and design (permissible stress) methodology of the current standard codes of PCSs. This has motivated few researchers and organisations to shift the current design concept to a rational limit states format code. Nonetheless, establishment of a new code needs further investigation to recognise the behaviour of material under railway loads; for example, to identify the influence of dynamic loading on strength enhancement of PCS material due to strain rate effects. This study was mainly aimed at proposing the most appropriate types of HPC in order to make durable PCSs that possess sufficient resistance to cracking from high-magnitude dynamic loads. To achieve this main aim, a few specific objectives were proposed: (a) identify the level of strain rates in PCSs and their effects on material enhancement; (b) recognise the effectiveness of concrete grade on controlling PCS cracking; (c) identify the properties of concrete that effectively influence PCS cracking; and (d) identify the most appropriate types of HPC based on the findings in the previous objective. The current study was divided into five parts: (a) a comprehensive review of behaviour of PCSs; (b) an overview of specific behaviour and properties of HPC types that potentially can be suitable to make PCSs; (c) development and validation of an elaborated finite element model to simulate the behaviour of a PCS in track conditions; (d) a parametric study to investigate the influence of various factors on structural behaviour, especially cracking behaviour, of PCSs; and (e) propose the most appropriate types of HPC to produce durable PCSs. An elaborated finite element model was developed using the LS-DYNA package. The model consists of a full-scale PCS and its surrounding components. The model was calibrated using results of an experimental study, an analytical computer program, and a numerical track model. The finite element model is capable of simulating loading conditions of the track as well as all key behaviours of concrete materials under high-magnitude dynamic loads. Structural behaviour and severity of sleeper cracking were investigated using the model for a number of parameters, such as strain rate effects, concrete grade, key mechanical properties of concrete material, different levels of prestressing force, and specific combinations of these parameters. The results of this study suggest that the model developed may be used to analyse the structural behaviour of PCSs made of different materials. The effects of strain rates are recommended to be taken into consideration during the analysis and design process of PCSs. It was found that using higher grades of concrete is not an effective way to control PCS cracking from dynamic loads. The results proved that fracture energy of concrete is the most effective property of concrete to enhance the crack resistance of PCSs. It is revealed that including fibres in the concrete material is the most practical way to increase concrete fracture energy. Finally, it is recommended that using appropriate combinations of fibres and silica fume in concrete material may be the best option to make durable sleepers with adequate resistance to cracking from dynamic loads. This thesis also provides a framework to investigate the performance of different materials to make PCSs, which can be used in future studies. The thesis is expected to pave the design path to select the most appropriate types of HPC to make PCSs in various conditions and to contribute in the establishment of a new design approach.