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(2021)ThesisFunctionally graded material (FGM) with the volumetric fraction of ceramic and metal changing gradually along the thickness is a prospective armour material with attractive properties. The gradually changing composition of FGM allows a relatively smooth transition from the ceramic rich zone to the metal to be achieved replacing the obvious interface in the bi-layered armour. This smooth transition theoretically leads to the improved ballistic performance of the armour. However, not many studies were reported on revealing the gradually varying microstructure and mechanical response under dynamic loading conditions of FGMs. This limits the practical application of FGM armour. Thus, this thesis aims to inspect the microstructures and mechanical responses of the single composition materials (SCMs) at different locations of an FGM under different loading conditions and understand the reinforcement and failure mechanisms of the SCMs. Ti-Ni-C metal matrix composites (MMCs) including FGMs and SCMs were fabricated with Ti-6Al-4V (Ti64) and Ni coated graphite (NCG) powders using LENS additive manufacturing system. The phase compositions and microstructures of SCMs and FGMs were examined by X-ray diffraction, optical microscopy and scanning electron microscopy. The results showed that Ti2Ni and TiCx phases were in situ synthesized with different quantity correlated to the chemical compositions. The variations of micro-hardness along the direction of composition variation were investigated using hardness tests. It was found that the hardness of the composite was enhanced by the higher content of TiCx and Ti2Ni. The quasi-static and dynamic compression tests were performed on SCMs with different NCG contents using universal testing machine and split Hopkinson pressure bar (SHPB) at various strain rates from 10-3 to 6×102 s-1. The larger amount of NCG in SCM resulted in the increase of strength and the reduction of ductility. The strain rate effect was negligible when the strain rate was lower than 10-1 s-1. However, SCM with higher NCG content exhibited decreased strain rate hardening effect and better resistance to shear fracture at a higher strain rate of approximately 6×102 s-1. The dynamic responses of SCMs with different NCG contents under shock loading were investigated using flyer plate impact experiments conducted with a gas gun. The SCMs containing more NCG exhibited lower spall strength and tended to break into larger number of fragments with smaller size.
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(2021)ThesisIn this thesis, we aim to generalize the negative imaginary systems theory to a broad class of nonlinear systems. A formal definition will be given for the negative imaginary property in the nonlinear domain by invoking a new dissipativity notion with an appropriate work rate. This formula is considerably more general than the existing classical dissipativity framework. Flexible structures with colocated force actuators and position sensors are dissipative according to this new definition. Having defined the nonlinear negative imaginary property in a time-domain dissipativity framework, we are able to extend some of the main existing results on negative imaginary systems from the linear to nonlinear domain. First, a Lyapunov-based approach will be used to establish the stability robustness of a positive feedback interconnection of negative imaginary systems in the linear case under a set of theoretical assumptions. Then, these assumptions will be adapted in the nonlinear setup to establish the stability robustness analysis of a positive feedback interconnection of nonlinear negative imaginary systems by making use of Lyapunov stability theory and dissipativity techniques. The applicability of this nonlinear stability result will be illustrated through an example of nonlinear mass spring damper system. Furthermore, the nonlinear negative imaginary systems theory will be extended to the case of free motion. It will be shown that, under suitable assumptions, a cascade connection of an affine nonlinear system and single integrator will lead to a nonlinear negative imaginary system (with integrator). Finally, this thesis is concluded by a summary of current progress and a discussion of possible future developments of the nonlinear negative imaginary systems theory.
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(2021)ThesisPlasmonic is an emerging technology used to increase the performance of thin-film devices via light-trapping mechanisms. Recently, plasmonic devices have been used due to their nanoscale fabrication abilities. Metamaterials are promising candidates for improving the light absorption of plasmonic devices. The extraordinary properties of metamaterial-plasmonic devices (such as the perfect absorption of light) open up applications such as solar energy harvesting, photo-detecting and making batteries. This thesis focuses on the theoretical design and experimental studies of metamaterial-based perfect absorbers (MMPA) to improve their optical properties and applications (e.g., energy harvesting). I also design a high-power MMPA for high-power laser applications. First, I present the design and analysis of a high-power broadband perfect absorber. An array of rectangular patterns was placed to broaden the bandwidth so that the array can function between 950 nm and 1400 nm. Here, I propose a tungsten boride (a refractory ceramic) broadband metamaterial absorber and characterize its optical properties numerically and experimentally. I have also analyzed the damage characteristics of this absorber using a femtosecond laser and compared these with an ordinary gold metamaterial absorber. Second, a multilayer-based perfect absorber for omnidirectional capabilities is theoretically and experimentally analyzed. The device provides a reasonable amount of light absorption and thermal stability has been checked. Applying this device to high-temperature solar cell applications is discussed. I demonstrate a thermally stable broadband absorber based on an ultrathin layer of refractory ceramic, tungsten boride. I experimentally analyze and compare the performance of the absorber with an aluminum-based absorber. The multilayer perfect absorber has absorption higher than 85% in the wavelength range between 500 and 1600 nm over a large range of incident angles (up to 60 degrees). I show that a tungsten boride absorber has significantly better temperature stability compared to its aluminum counterpart, achieving stable operation at temperatures up to 270 ℃. These absorbers may have applications in solar thermophotovoltaic energy conversion. Third, a square hole structure is proposed, where a lossless silica dielectric material is combined with MnO2 materials. Then, the geometric parameters of this structure are numerically optimized at the desired application. An adequate choice of parameters, shape and the proper combination of materials can lead to an electrically tuneable metasurface. The structure can produce a 25% change of transmission with the applied electric power. Finally, I numerically analyzed and experimentally characterized Kevlar fabrics for the application of personal heat management. Heat management is essential for human comfort. In recent years, passive radiative cooling through heat transfer to outer space has been extensively studied. Personal temperature control is used to control the temperature of objects beyond the local environmental temperature. I show that Kevlar fabrics are transparent to mid-infrared human body radiation but opaque to visible light. Here, I have experimentally investigated the optical and thermal properties of Kevlar fabrics, which can have 90% emissivity in the mid-infrared region and produce a 2.6 ℃ temperature drop. I processed a Kevlar textile that promotes effective radiative cooling while retaining sufficient air permeability, water-wicking rate, and mechanical strength for wearability. The Kevlar fabric is an effective and scalable textile for personal thermal management.
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(2021)ThesisA handful of technologies have had a profound influence on the course of human history. The most influential have transformed society by recasting the social, political, economic and military norms of the age. Another transformation is presently underway, driven by the influence of computation, artificial intelligence, biotechnologies and nanotechnologies behaving as General Purpose Technologies. This change constitutes a Fourth Industrial Revolution with enduring consequences for all aspects of modern society. Anticipating transformational change is a prerequisite for adequate preparation. The Australian Army is preparing for an increasingly uncertain future in which emerging technologies, domain fusion and accelerating rates of change will produce disruptive discontinuities in military power. While the Army is aware of the magnitude of change it faces, it remains poorly positioned to adapt, let alone thrive. The Australian Army needs to prepare for a future where successive waves of technology influence society. This influence will change societal expectations governing how military power is applied, while concurrently disrupting the methods available to apply military force. This study assesses organisational adaption to these change pressures through the lens of military transformation theory. Military Revolutions theory describes transformational societal conditions alongside the potential for one or many Revolutions in Military Affairs to profoundly influence military power. The Australian Army is not prepared for either, preferring traditional approaches to modernisation that replace existing equipment with expensive upgrades. This approach to modernisation is conservative, avoiding the risk of uncertain conditions, but in doing so sets the conditions for a future crisis. The Australian Army can adequately prepare for the conditions ahead, but it must be willing to challenge long held beliefs. Balancing sustaining and disruptive forms of innovation is key to competitiveness in the present and future. New structures and a culture that supports all forms of innovation will allow the Army to thrive in the design competition which will characterise military preparedness in the Fourth Industrial Age.
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(2021)ThesisDemocratic transitions in multinational countries can be problematic when ethnic minorities are excluded from a dominant majority group’s vision of the nation. This is the case in Myanmar where, since independence was granted in 1948, ethnic people’s aspirations have clashed with the military’s vision of a centralised state and a national identity based on the Bamar majority group. Consequently, civil war has been raging for more than 70 years, and discrimination of ethnic groups has been gradually institutionalised. Thus, in order to support peace, one of the main challenges of state building in Myanmar will be to develop institutions that reflect the multinational character of the country. In this thesis, I argue that more attention should be paid to the perceptions of the broader ethnic population. Employing a political ethnographic design, I seek to reveal people’s lived experiences of ethnicity in the current democratic transition to suggest state building strategies promoting national belonging. Focusing on the perceptions of two groups, the Mon and the Pa-O, my findings suggest: First, that they experience the institutional dominance of the Bamar group as a number of cultural, economic, social and political insecurities; second, while Mon and Pa-O attitudes indicate a tendency towards rigid ethnic identification, Bamar chauvinism appears to be the main obstacle to inclusiveness; third, Mon and Pa-O aspirations show that redressing Bamar privilege through institutional reforms bringing about equality of status and greater autonomy would positively support a sense of belonging to the national identity; and finally, I found that among the existing institutional models advanced by the ethnic conflict management literature, the state-nation model reflects most closely Mon and Pa-O aspirations because its policies aim to protect ethnic identities while also promoting national membership. The state-nation model is not a perfect fit, however because its proposed policy sequence prioritises constitutional amendments that do not appear politically feasible in present day Myanmar. I therefore recommend the prioritisation of policies that support a sense of belonging such as symbolic recognition, access to opportunities or cultural autonomy. I argue that since these policies do not directly challenge the political order and the existence of Bamar privilege, they would positively support trust building and thus peace.
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(2021)ThesisThis thesis is focused on analysis the behaviours of two forms of protective panels, namely (i) steel built-up panel formed by welding of standard beam sections and plates and (ii) steel-concrete sandwich panel (SCS), subjected to combined blast and fragment loadings (CBFL) experimentally and numerically. Three explosion trials, including a bare charge of 2.7 kg TNT and two cased charges of 15 kg of TNT encased in a mild steel pipes, were performed. After the explosion trials, static bending tests of the damaged panels were carried out to estimate the residual capacity of the damaged panels. In addition, in order to investigate the behaviours of both steel and SCS sandwich panels against fragment loading under laboratory conditions, high velocity impact tests were carried out on both panel which have the similar cross-sectional design and dimensions as blast tests. Numerical models were developed for both steel and SCS sandwich panel to simulate experimental test cases using LS-DYNA finite element software package to further investigate the effects of different loading components (fragment and blast) on structural response. After FE model development, it was validated and compared with the experimental results. It was found that FE model can simulate dynamic responses with reasonable accuracy. The validated FE models were then utilised to conduct comprehensive parametric study to further analyse the panels under different loading and geometric conditions for both steel and SCS sandwich panel. The three types of simplified modelling techniques namely (a) Single degree of freedom (SDOF) model, (b) multiple degree of freedom (MDOF) model, and (c) simplified finite element model (SFEM) were developed to predict the responses of the steel and SCS sandwich panels under CBFL generated from cylindrical cased charge. It was found that the responses matched with reasonable accuracy when compared with experimental and detailed FE model results considering its simplicity of the modelling as well as significantly reduced analysis time required. After development and validation of simplified models, comparative investigations were carried out to evaluate the performance of the simplified models.
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(2021)ThesisThis dissertation sets out to examine the claims of policymakers and scholars that middle powers act as system-stabilisers during times of hegemony or not. By investigating the role perception and policy responses of three pivotal middle powers - Australia, Indonesia, and South Korea - to the changing regional dynamics in the Asia-Pacific between 2009 and 2020, the research tests the extent to which middle power diplomacy and collectivism can mitigate the destabilising impact of US-China power transition. The original contribution to knowledge in this research is that middle powers are more likely to resort to pragmatism over principle in role conception under the pressures of great power competition. However, middle powers can become significant regional stabilisers by asserting a degree of autonomy in relations with great powers, defending the rule of law in maritime Asia and deepen collaboration between them to consolidate the regional architecture. This dissertation also develops a three-level role-based approach to understand the impact of middle powers during power transition, which helps to add theoretical rigour to middle power theory. The findings from this research will provide new insights about how middle powers navigate the uncertainties in the Asia-Pacific, as well as their pattern of behaviours. Moreover, an empirically-based understanding of the effectiveness of middle power diplomacy and the factors that are shaping it will have practical implications for policymaking.
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(2021)ThesisUnmanned Aerial Vehicles (UAVs) have played an essential role in military and civilian domains. The research in this thesis contributes to the field of Intelligent Control Systems (ICSs) and especially achieving reliable and convenient autonomous control for Rotary Wing UAVs (RUAVs). In particular, the challenge of adapting to unmodelled dynamics and disturbances such as changing payloads in mid-air is tackled. UAVs can carry extra weights such as sensors, cargo and even underslung loads which are known as the payload. Many strategies have been developed to stabilize the drone with changing payload but they all assume the payload to be rigid and the Centre of Gravity (CoG) to be static and known. Variations in the payload mass and its type during flight, can dramatically affect the dynamics of the drone, requiring a controller to adapt to maintain satisfactory closed loop performance. A scenario where a fleet of delivery drones could be launched from a larger aircraft (like a weather balloon) in mid-air with random pose attitude is also not yet explored. Finally, uncertainties such as unmodelled dynamics and wind gusts pose challenges to flight operations, so ICSs are essential to deal with these uncertainties but not enough attention is given to the design and development of non-model-based ICSs. Motivated by these research gaps, this thesis tackles the control problem of handling payload with changing CoG and pose independent launch in mid-air. To address these problems and to achieve the desired trajectory tracking control, a novel non-model based ICS called the Bidirectional Fuzzy Brain Emotional Learning (BFBEL) control system is presented. The proposed control system merges fuzzy inference, neural networks and a novel Bidirectional Brain Emotional learning (BBEL) algorithm based on reinforcement learning. The proposed BFBEL controller is capable of adapting rapidly from scratch and it is introduced to control all the Six Degrees of Freedom (6DOF) of the RUAVs. To expand the applicability of the proposed controller, both Single-Input-Single-Output (SISO) and Multi-Input-Multi-Output (MIMO) architecture are developed. The two RUAV models considered for this research are the Quadcopter UAV (QUAV) and the Helicopter UAV (HUAV). The SISO version of BFBEL control system is applied to QUAV to address the problem of handling external payload with varying CoG and weight. The MIMO version of the BFBEL control system is applied to a HUAV to address the problem of pose independent launch in mid-air. Both systems are evaluated with simulations and the problem of handling external payload with uncertain CoG is verified with experiments. Finally, the flight capabilities and control performance are compared with a conventional Proportional Integral Derivative (PID) controller scheme under the same control scenarios.
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(2021)ThesisThe focus of this research is the development of a suitable optical material for multilevel optical data storage and demonstration of multiple bit optical data storage in samarium activated nanocrystalline mixed alkaline earth fluoro halides using persistent spectral hole-burning (PSHB) at room temperature. Samarium-ion-activated nanocrystalline alkaline earth fluorohalides MFX (M = Ba, Sr ; X = Cl, Br, I) are efficient X-ray and UV storage phosphors. The optical spectroscopic properties of nanocrystalline BaFCl:Sm3+ and SrFCl:Sm3+ prepared at room temperature by ball milling and co-precipitated method were studied under UV-C and X-ray irradiation. The Sm3+ in BaFCl/SrFCl is reduced to Sm2+ upon exposure to ionising radiation. The Sm2+ centres can be efficiently readout by photoexcitation of the narrow intraconfigurational 5D0-7F0 f-f luminescence lines at around 687 nm, after excitation into the very intense 4f6-4f55d1 transition at ~425 nm. The photoluminescence properties before and after UV-C exposure were investigated in both ball milled and co-precipitated samples. The UV-C induced reduction of Sm3+ to Sm2+ and photobleaching of Sm2+ to Sm3+ were monitored by tracking the photoluminescence intensity of Sm2+ and Sm3+. Results were modelled by dispersive first-order kinetics. X-ray induced reductions were also studied in ball milled nanocrystalline BaFCl/ SrFCl:Sm3+ samples. A variety of mixed alkaline earth fluorohalides with the general formula M1x M21−x FX1yX21−y (M1 and M2 = Ba, Sr, Ca; X1, X2 = Cl, Br, I) and doped with Sm3+ ions were synthesized by ball milling at room temperature. The reduction of Sm3+ to Sm2+ by either UV-C exposure or X-ray irradiation was investigated using photoluminescence measurements. Strategic mixing of different mixed systems allowed engineering of luminescence line shapes with flat top profiles. A broadening of the inhomogeneous width of the 5D0-7F0 f-f transition to 70 cm−1 was achieved at room temperature compared to the previously reported best value of 43 cm−1. The room temperature spectral hole- burning was demonstrated in the 5D0-7F0 transition of Sm2+ ions generated by UV-C light in these mixed nanocrystalline MFX host. The presence of oxide impurities in these alkaline earth fluorohalides plays a major role in the storage mechanism. The presence of EPR active oxygen ions was also explored through room temperature electron paramagnetic resonance (EPR).
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(2021)ThesisIn the current world, online retailing accounts for the major share of retailing due to the unique benefits it provides to customers. However, its success is highly dependent on how it manages its operations. Compared to traditional retailing, online retailing requires new decision-making models to support its operations. In this thesis, the E-SMART framework is proposed which assists e-tailers in operations management in the three areas of the sourcing, distribution, and personalization of an assortment. The E-SMART framework consists of three modules. The first module manages sourcing decisions and develops a framework to assist the e-tailer to decide if it should interact with a powerful main brand supplier or instead, procure items from an alternate supplier. The framework determines the best strategy, taking into consideration selling price, assortment size and the inventory level of the item to be procured. It also considers the importance of considering customers as shopping basket consumers in sourcing decisions in different scenarios. The second module manages distribution decisions and develops a decision-making model to determine the most profitable strategy from drop shipping and batch ordering. The interaction of the supplier and the e-tailer is modeled using the game-theory approach. Another important aspect that needs to be considered carefully in the drop-shipping model is the profit-sharing ratio between the supplier and the e-tailer. By analyzing different scenarios, the model shows which strategy is more profitable for the e-tailer. The third module of the E-SMART framework assists the e-tailer in dynamic assortment personalization to improve its sales. The problem is modeled as a Markov decision process to mitigate customers' churn rate in the case of demand uncertainty and limited inventory. Customer choice and customer lifetime are modeled using the multinomial logit model and survival analysis techniques respectively, and are estimated using historical sales data. Following this, personalized assortment planning to increase the e-tailer’s profit and reduce customer churn is proposed. The results of each module of E-SMART are demonstrated in different scenarios to show how the proposed model is applicable in real-world practice.
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