Mechanical Engineering - Theses

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    Trapping and manipulation of small particles using laser lights
    Bandara, P.M.T. (University of Melbourne, 2009)
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    Optimised sink trajectories for sensor networks
    Mendis, Champake. (University of Melbourne, 2008)
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    Clinically practical technology-assisted measures of upper limb spasticity
    GUO, Xinliang ( 2022)
    Spasticity is a motor disorder with high prevalence and important consequences following neurological injuries. Accurate measurement of spasticity is critical to direct management strategies and evaluate treatments' effectiveness. However, spasticity is commonly measured using clinical scales which lack specificity and reliability. Thus, technology-assisted measures have been developed as objective and accurate alternatives. Still, many of these methods have not been widely adopted in clinical settings, possibly due to their low feasibility and practicability. This work thus intends to identify and evaluate clinically practical technology-assisted measures of spasticity which have the potential and ability to be adopted into clinical practice. To achieve this objective, this work starts from systematically identifying and characterising existing technology-assisted measures of spasticity in the literature. An evaluation and comparison of psychometric properties and usability for each approach is then conducted. In addition, a validation of a potential practical robotic measure of elbow spasticity, using an upper limb rehabilitation device, is proposed. The discriminant validity and concurrent validity of this method is investigated. Finally, the possibility of using frequency information of neuromuscular signals to distinguish between spastic muscle reactions and voluntary muscle contractions is explored as a potential solution to overcome the limitations of existing muscle activity based measures. This work concludes that there is no ready-to-use valid and practical alternative to existing clinical scales. Still, among the promising methods, this work shows the possibility of using a robotic measure to evaluate elbow spasticity and provides future research directions for the use of frequency information to improve muscle activity measurements in spasticity detection.
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    The Effect of Crutch Usage on Human Walking with Lower Limb Exoskeleton
    Chen, Xin ( 2021)
    Lower limb exoskeleton robots allow patients with spinal cord injury (SCI) to perform overground gait. However, most lower-limb exoskeleton robots require users to use crutches to balance themselves during walking. It has been observed that long-term use of crutches will lead to potential harm to the shoulder joints due to the repetitive high load on the shoulder. Investigations of the shoulder reaction force experienced during exoskeleton use are needed to understand this effect better. Studies have shown that different crutch gaits can lead to the variation of shoulder reaction force. This study compares the effects of different gait patterns on the shoulder reaction force in an experiment involving six able-bodied individuals walking with the exoskeleton robot. Specifically, the shoulder reaction force during exoskeleton walking is studied with two commonly observed gait patterns: (1) the four-point parallel crutch gait (Gait-P) and (2) the four-point reciprocal crutch gait (Gait-R). Contact forces between the ground and crutches were recorded and indicated the shoulder reaction force. Three metrics (maximum rate-of-loading (MaxROL), maximum force (MaxForce), force- time-integral (FTI)) to evaluate the measured force have been adopted, and Wilcoxon signed-rank test has been used to check the difference significance. The results suggest a significant difference between FTI of different gait patterns, and Gait-R shows a higher accumulated force load on the shoulder joint. This difference in the accumulated load can be even larger with time, but current research results cannot estimate its effect on leading to shoulder injury. The result also indicates that there may be person to person variation in the metrics. The effect of changing the gait type on three metrics can be stronger, weaker, and sometimes are opposite to the effect shown at the population level. This difference may be caused by the subjects’ balance control ability or walking habits. In conclusion, the results suggest it is beneficial for SCI users to test the effect of each gait before using the exoskeleton robot in the long run. Otherwise, the parallel gait (Gait-P) was found to cause lower load on the shoulder at the population level.
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    Inducing human movement pattern change
    Xu, Yangmengfei ( 2021)
    Human’s movement pattern shaping is widely used in neurorehabilitation and sports training. Recent studies have shown that robotic device has its potential to become an efficient tool for clinicians to induce this change. To understand human's movement, different computational models were proposed and studied to explain how human resolves their redundancy. Although some arguments are still existing, the general idea of optimization has been well accepted. Based on these computational models, the motor learning studies showed that through practice in the new environment, the reward-based optimization could drive human to search for a better movement pattern 1) to maximize the performance and 2) to minimize the motor cost. Leveraging this optimization idea in human motor learning, this work aims to induce the movement pattern changes in an experimental setup solely relying on the motor cost without any explicit kinematic error. In this strategy, the intervention space and adaptation space are decoupled: while the force field only applies to the hand linear velocity, the adaptation is expected to happen in the redundant arm joint space (\textit{i.e.} the swivel angle). This work, therefore, explores the following topics: * Investigating the feasibility of inducing human motor adaptation in the redundant space by providing a task space intervention without explicit error feedback or instruction; * Evaluating the contribution of a progressively changing goal in this implicit motor adaptation, assuming that this adaptation may be further promoted through subtle prompts to explore the cost space; * Demonstrating a motor cost analysis based on the upper limb kinematics and dynamics model to validate the relationship between observations and motor cost.
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    Balancing Performance of Haptic Physical Human-Robot Interaction
    Liu, Zheyu ( 2022)
    In the field of physical human-robot interaction (p-HRI), haptic interaction is one of the most popular features that can be applied to various applications such as rehabilitation for post-stroke patients, telemanipulation surgery, game-based training, and so on. On the one hand, stability or passivity is one of the basic requirements in designing p-HRI systems. On the other hand, other performance indices such as transparency are also needed in p-HRI. It is well-known that transparency and passivity are two conflicting performance requirements in p-HRI. This thesis focused on developing a data-driven strategy to address the performance trade-off between stability and desired dynamic behaviors of an admittance device for a physical human-robot interaction, which are known to be conflicting with each other. In this work, a novel concept of ultimate passivity is proposed to relax the requirement of passivity in transient response while keeping steady-state passivity to allow flexibility in improving other performance requirements. A new admittance-type passivity controller, consisting of a conservative controller to keep stability, a nominal controller to keep transparency, and a switching law between them to ensure the ultimate passivity, is proposed. The main result of this work provides sufficient conditions so that appropriately selected parameters can ensure the ultimate passivity. In order to illustrate the effectiveness of the proposed framework, a haptic simulation model is built in Matlab/Simulink. Simulation results support the theoretical findings.
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    Two Topics from Trajectory Planning and Formation Control
    Burke, Declan Thomas ( 2021)
    This thesis explores two topics: spline trajectory planning and rigidity-based formation control. The analyses presented in this thesis for each topic are self-contained and so this thesis is presented in two parts. The first chapter focuses on spline trajectory planning. We revisit a popular methodology from the quadrotor trajectory planning literature and address two roadblocks encountered in its practical implementation. Specifically, we consider the computational complexity of prototypical algorithms from the literature as well as their scalability. From this analysis, we propose two new algorithms: (i) Algorithm 1, which generates spline trajectories with linear computational complexity and (ii) Algorithm 2, an iterative algorithm that generates time-optimal spline trajectories with linear computational complexity in each iteration. Both methods are faster and plan larger trajectories than the state-of-the-art. We apply our methods to demonstrate their efficacy by conducting an experimental quadrotor flight and by proposing a novel rapidly-exploring random tree (RRT*) algorithm. The second chapter considers the use of rigidity theory for the formation control problem. We analyse a non-Euclidean norm and present a rigidity theory for frameworks under the 1-norm. We then use this rigidity theory to derive a distributed control law that, under a reasonable condition, comes with an exponentially stability result. The qualities of our new control law are investigated, particularly in comparison with other, related rigidity-based approaches.
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    Effect of solidity on momentum and heat transfer of rough-wall turbulent flows
    Saurav, Tanvir Mahmud ( 2020)
    A major area of interest in engineering is the skin-friction drag and convective heat transfer of surfaces in turbulent flow, such as turbine blades, marine vehicles, and airplanes. While these surfaces may appear smooth, they almost always have some form of roughness, for example, pitting on the surface of a turbine blade, barnacles on the hull of a marine vehicle, or rivets on the wings of an airplane. For a given roughness and flow speed, the Moody diagram can be used to find the frictional drag or pressure drop. A similar diagram can be constructed to find heat transfer. Although widely used, the biggest limitation of the Moody diagram is that the Nikuradse equivalent sand grain roughness has to be known for the rough surface in question. Another limitation of the Moody diagram is in predicting skin friction for transitionally rough surfaces, owing to the unrepresentative Colebrook fit. Also, while the effects of varying key roughness topographical parameters on momentum transfer have been studied extensively, relatively little is known on heat transfer. Over the years, researchers have used computational and experimental methods to investigate the flows over a number of roughness types. This thesis expands on the computational works on sinusoidal roughness by systematically investigating the effect of varying roughness solidity on both momentum and heat transfer in turbulent air flow, and the underlying flow physics that give rise to the observed behaviour. Rough-wall flows transfer more momentum and heat when compared to smooth-wall flows, and it is found that an increase in solidity for a matched equivalent sand-grain roughness height causes a greater increase in heat transfer than the increase in momentum transfer due to increased wetted area and increased recirculation region that facilitates mixing.
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    Investigation of mixing in gravity currents using high-resolution molecular tagging techniques
    Agrawal, Tanmay ( 2020)
    Gravity currents are horizontal flows of fluid of a higher density into an ambient fluid of slightly lower density. They occur frequently in the atmosphere as sea-breeze fronts, thunderstorm outflows, katabatic flows etc., and are also encountered in industrial applications. The initial density difference between the two fluids can either be due to the presence of a salt or a temperature difference. While a majority of the studies employ a salinity based stratification, this work focuses on the flow dynamics of a gravity current generated as a result of an initial temperature difference. In the laboratory environment, a gravity current can be produced using a lock-exchange experiment in which the two fluids, initially at rest, are separated by a vertical barrier (or lock gate). At time $t$ = 0, a rapid removal of the lock gate results in the formation of a gravity current. The present gravity currents were produced in a Perspex tank of 2.0 m x 0.2 m x 0.2 m where the lock was located mid-way. The present flows were first visualized by mixing a dye in the heavier (cold) side to evaluate the bulk properties of the flow e.g. Froude number, $Fr$. Subsequently, simultaneous measurements of streamwise velocity and temperature field were conducted using the single-component molecular tagging velocimetry (1c-MTV) and molecular tagging thermometry (MTT) respectively. These experiments were focused at the interface between the hot and cold fluid to estimate the resultant mixing across the interface. The measurements were acquired using a 1024 x 1024 pixel Princeton Instruments PI: MAX4 camera and were shown to resolve the Kolmogorov (velocity) and Batchelor (scalar) length scales. To the author's knowledge, to date no previous experimental study has documented lock-exchange mixing at this level of resolution. The obtained density (temperature) distribution allows an estimation of the background potential energy of the flow which was used to quantify the diapycnal mixing. Specifically, mixing is attributed to the irreversible changes in fluid properties associated with fluid motions [1] and therefore differentiated from buoyancy induced reversible stirring. These measurements yield a mixing efficiency of 0.13 for the Reynolds number range considered ($Re \leq \mathcal{O}(10^4)$). Flow analysis revealed that the locally high values of mixing efficiency occur \textit{after} the occurrence of certain dissipative stirring events in the flow. These events, largely associated with vortical overturns, are commonly observed at the interface between the two fluids and are shown to lead the locally efficient mixing.
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    Assembly line sequencing for product-mix
    Cother, R. F. ( 1971)
    This thesis is concerned with the sequencing of various models of a product when these are manufactured on one assembly line using product-mix. A simplified model of the assembly line is postulated. Four heuristic algorithms are developed which aim at minimizing assembly line length while avoiding operator interference. Two of these algorithms are used in a factorial experiment to determine the relationship between assembly line length and five factors. These factors are characteristics of the production requirement and workload balance. From the experimental results, empirical equations are developed which are a useful aid in the design of new assembly lines or the balancing of existing assembly lines. The experimental results are also analyzed to determine a range of sequencing problems for which near optimal sequences can be expected using the two algorithms.