Engineering: Theses and Dissertations

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Open Access
Enhancing non-expert rescuers’ emotional experience in cardiac arrest emergencies : a demonstrative design of an emergency care device.
(2024) Chen, Zhen
Global ageing is leading to an increase in cardiac arrest incidents among senior citizens, posing a significant societal challenge. Most out-of-hospital cardiac arrest (OHCA) incidents occur at patient’s domestic residences, limiting their immediate access to professional help and Automated External Defibrillators (AEDs). In such instances, Cardiopulmonary Resuscitation (CPR) performed by caregivers, often the patient's family with no expert knowledge of emergency care, becomes crucial. Compared to professional rescuers, non-expert rescuers such as caregivers could face challenges in executing effective CPR due to skill gaps and potential emotional barriers in performing such procedures on family members. This study investigates the experience of caregivers in cardiac arrest scenarios, a critical but often overlooked aspect in the design of emergency care devices. We aim to understand 1) how emotions affect caregivers' performance and experience during domestic cardiac arrest incidents and 2) how design can support their practical and emotional needs, enhancing their performance. Semi-structured interviews with professional rescuers and caregivers reveal both emotional and skill-related challenges that caregivers might confront before, during, and after cardiac arrest incidents, such as unfamiliarity with rescue procedures, unskilled in CPR, physical strain, fear of approaching a collapsed person, anxiety about causing harm, lack of confidence, and moral pressure from social ties. These challenges can lead to adverse reactions that further hinder their CPR performance. The study highlights the importance of including emotional support for non-expert rescuers in OHCA incidents. By incorporating human-centred design principles, we propose an inclusive design guideline for emergency care devices and practical design recommendations to mitigate emotional barriers and assist operational performance for non-expert rescuers. Under these design guidelines, we conducted two follow-up interviews to engage non-expert rescuers in co-design sessions to propose an emergency care device concept. With the co-design results, this study established the final design concept for this device and created a digital prototype demonstration of our final design concept. Finally, we invited two non-expert participants to evaluate the demonstration through an experiential evaluation. This study contributes to the field by presenting a design demonstration of an emergency care device, emphasising the emotional and practical support to enhance the experience of non-expert rescuers in domestic OHCA incidents.
Open Access
Inference of effective rheological laws for shallow lava flow models from free-surface measurements.
(2024) Muchiri, David Kibe
To understand, describe, simulate, and predict the dynamics of geophysical lava flows for hazard mitigation, this research work presents mathematical modelling and simulations of three-dimensional shallow free-surface flows of Herschel–Bulkley viscoplastic fluids down an inclined non-flat topography with varying basal conditions. Starting from a systematic perturbation analysis, lower-order models of the Navier–Stokes equations are derived by employing the multi-regime approach, which allows to model different flow regimes originating from the variation of the mean-slope and/or the basal conditions. In particular, the lubrication model, the shallow water equations, and the depth-averaged heat equation are derived for multi-regime viscoplastic flows applicable to a natural setting consisting of an irregular topography with perturbations in basal slipperiness. Two flow regimes (Regime A, the basic/classical one, and Regime B, the enriched one with a corrective pressure term) corresponding to different balances between shear and pressure forces are defined and investigated. Flow models corresponding to these regimes are calculated as perturbations of the zeroth-order solutions. The classical reference models in the literature are recovered by considering their respective cases on a flat-inclined surface. The flow solutions of the two regimes are compared; the difference appears, in particular, in the vicinity of sharp changes of slopes. Nonetheless, both regime models are compared with experiments and are found to be in good agreement. Moreover, the derived shallow water equations and the lubrication approximation are compared to test their validity limits in different flow regimes in terms of the inclination angle, aspect ratio, basal perturbations, and Reynolds numbers. In the limit of low Reynolds numbers, both models are observed to agree well with viscoplastic experiments on a flat topography. The significant difference is observed at early times of dam-break, where the lubrication approximation overestimates the speed of the front position compared to the experiments. Also, it is shown that the flow dynamics over a perturbed topography are well predicted by the shallow water equations compared to the lubrication model. Generally, the shallow water equations are observed to have a wider predictive limit (e.g., in terms of the slope angle and Reynolds numbers) than the lubrication approximation. Furthermore, to investigate the effects of rheological parameters: power-law index (n), consistency index (K), and yield stress (τc), on flow height and velocity of Herschel– Bulkley fluids over different topographies, three practical examples of dam-break flow cases are studied: a dam-break on an inclined flat surface, a dam-break over a nonflat topography, and a dam-break over a wet bed. The effects of bed slopes and depth ratios between upstream and downstream fluid levels on flow dynamics are also analyzed. The numerical results are compared with experimental data from the literature and are found to be in good agreement. Results show that increasing any of the three rheological parameters decreases the fluid front position, peak height, and mean velocity, for both dry and wet bed conditions. Lastly, by formulating an inverse problem, we can infer the rheological parameters (K, τc, n) from free-surface measurements based on experimental data of flows around an occlusion. The rheological identification problem is formulated to minimize an objective function that measures the discrepancy between the elevation hydrographs from the model output and experimental data. The inverse solver is tested on both synthetic and laboratory data. The set of rheological parameters inferred is compared with the values measured on a rheometer for the fluid used in the experiments. The results have shown that hydrograph measurements at the wetted solid-fluid interface contain information of the fluid flow, which can be used to retrieve the unknown rheology for hazard mitigation and/or aid prediction of the wetting dynamics. Novel results include the derivation and validation of the shallow water models for 3D Herschel–Bulkley flows that account for basal elevation and basal slipperiness, a formal comparison of the lubrication and shallow water equations with experiments, numerical simulations of viscoplastic dam-break flows over a dry non-flat bed and over a wet bed, and the inference of rheological parameters for viscoplastic flows using elevation hydrographs around an occlusion.
Open Access
Characterization of fluid and thermal flows through 3D printed triply periodic minimal surfaces.
(2024) Hawken, Mathew Burnett
Porous materials are prevalent in both nature and industry. In industry, heat and mass transfer processes often require porous materials. Characterizing the flow and heat transfer facilitates the design of optimal geometries to meet the required performance, such as pressure drop, heat transfer or mass transfer rates. The often-random nature of porous materials hinders control of the geometry. Experiments or simulations can be employed to understand the fluid flow through porous structures. Magnetic resonance imaging (MRI) offers a range of techniques to determine flow and heat transfer and provide validation of simulations. This thesis aims to develop methods to characterize flow and heat transfer through an ordered porous material based on triply periodic minimal surfaces (TPMS). Additive manufacturing was used to generate a range of different TPMS structures. Initial investigations focused on determining the ability to produce the desired structure accurately and the effects of changing structure on the pressure drop. The pressure drop showed that for aspect ratios as small as 2.1, no wall effects were present, and the transition between laminar and turbulent flow occurred between Reynolds numbers of 60 and 600. Then, the validation of MRI sequences to investigate both velocity and temperature was conducted. First, a sequence to measure spatially resolved velocities was implemented on a commercially available low-field MRI machine. Furthermore, the flow field mapped by the sequence was validated inside a straight tube and later TPMS with volumetric flow rate discrepancies of 6% in both. Second, temperature measurements based on the proton resonance frequency method (PRF) were validated for a high-field MRI machine. The implementation involved a flow compensated spin echo sequence, which sampled both positive and negative times relative to the spin echo centre and detected temperature changes of less than 1°C. Finally, by combining velocity and temperature maps on a high-field MRI machine, the heat transfer and fluid flow were measured for the first time inside a TPMS structure. From the velocity and temperature maps, the local geometry was shown to cause variations in local temperatures and velocity. Comparison with an available numerical simulation highlighted the consistency between flow fields while isolating a potential discrepancy in thermal flow. These maps demonstrated the potential for MRI to characterize both the heat and flow inside a TPMS structure and the potential to discover previously unknown features.
Open Access
Triplet Matroids and Closure in Phylogenetics
(2024) Levy, Maayan
This thesis examines a meeting point of two combinatorial structures: matroids and phylogenetic trees. Matroids are a tool for generalising the notion of independence, with areas of application including graph theory, linear algebra, and coding theory among others. Meanwhile, phylogenetic trees are representations of ancestral relationships, with common applications in computational biology including hypothesising evolutionary histories, modelling disease transmission, and classifying species. These trees can be broken down into sets of rooted triples, which serve as a list of lineage constraints that encode a phylogenetic tree. Rooted triples are useful for determining tree compatibility and constructing supertrees from overlapping datasets. In this thesis, we investigate a class of matroids arising from sets of rooted triples that minimally encode trees, which we term triplet matroids. The matroid structure is useful for revealing which rooted triples in a set are essential and which are redundant. This ties in closely with the notion of closure, which concerns the lineage constraints logically implied by a set of rooted triples or phylogenetic trees. Our main result is that all triplet matroids are graphic. We provide a polynomial-time algorithm for constructing a graphic representation of a given triplet matroid, which serves as a helpful visualisation of the closure and dependencies of a set of rooted triples. In addition to this, we explore the unusual behaviour of the class of triplet matroids under deletion and contraction. We also demonstrate the effects of modifying a phylogenetic tree on its associated triplet matroid. Finally, we characterise the class of graphs that arise as graphic representations of triplet matroids. An additional chapter departs from triplet matroids, focusing instead on network greedoids. Greedoids and phylogenetic networks are generalisations of matroids and phylogetic trees respectively. We prove that a greedoid structure arises from exactly the networks that are tree-child, thus providing an additional characterisation of the class of tree-child networks. For future investigation, we introduce the greedoid polynomial and pose a question about its ability to distinguish network greedoids.
Open Access
Numerical simulation of two-phase flows with the conservative level set method.
(2024) Rate, Keetley
In this thesis, we will develop an implementation of Olsson and Kreiss’s conservative level set method. Do achieve this, we must cover key aspects of fluid dynamics, numerical methods for PDEs, including the finite element method. Prior to discussing aspects of two-phase flow, we first overview the foundational principles of fluid dynamics, as detailed in chapter 2. This chapter entails derivations of the governing equations of fluid flow which follow from conservation of mass and momentum, as well as some fundamental solutions to them. In chapter 3, we discuss how approximate solutions the Naiver-Stokes equation may be obtained via a splitting integration method and a projection step. To complete this, we discuss how the Finite Element Method is used to find the numerical solution a general boundary value problem, allowing us to solve the equations arising from projection methods for the Naiver-Stokes equations. This will give us the necessary tools for simulating two-phase flows in chapter 4, where we will see how the level set method can be used to solve the free-surface problem inherent in multiphase flows. This will leave us with a numerical method capable of tackling various problems with practical applications, some of which are detailed in chapter 5. In chapter 6, we examine one aspect of non-Newtonian fluid behavior within the context of viscoplastic or yield stress fluids. Here, we investigate the fundamentals of viscoplastic dynamics through the idealized Bingham fluids, which provide a simple model of viscoplasticity. We will also see how regularizing viscosity can be used to find the numerical solution to viscoplastic flows, allowing the modeling two-phase viscoplastic flows with a conservative level set method.
Open Access
A Kaupapa Māori approach to the Storage and Collection of Taonga Seeds
(2024) Shadbolt, Marcus-Rongowhitiao Te Puni
Due to the eﬀects of climate change and widespread ecological destruction, we are seeing global species loss on an unprecedented scale. In response to this, seed banking has become one method of storing at-risk species safely, while simultaneously supporting ecological restoration. Seed banking has therefore become a vital practice globally for ensuring the continual supply of seeds, in both agricultural and conservation projects. In Aotearoa, knowledge of how to store native seeds is limited, as the local science system has yet to truly utilise it as a method of conservation. This thesis therefore aims to look at both the technical aspects of how to store seeds native to Aotearoa, and what this may look like ethically, legally, and appropriately from an Indigenous Māori perspective. The technical part of this thesis focused on ﬁve species of the Coprosma genus and aimed to ﬁnd the optimal germination method for each one, as well as whether these species show signs of desiccation or freezing sensitivity. Of my study species, C. robusta was identiﬁed as orthodox, while C. propinqua, C. rugosa, C. rhamnoides, and C. autumnalis are all varying degrees of non-orthodox. Among them, C. propinqua is intermediate with decreasing viability as temperatures decreased, and C. autumnalis was completely recalcitrant with no germination after drying. Coprosma rugosa and C. rhamnoides are both intermediate but with a signiﬁcantly lower number of germinations than in C. propinqua. More research is needed on these species, speciﬁcally into how long in storage these species can last, in the case of those which can be stored safely. The cultural aspect of this thesis, however, focused on addressing the past injustices faced by Indigenous peoples, speciﬁcally Māori, in science and conservation, while discussing how to build an appropriate and ethical seed banking system from the outset in Aotearoa. This chapter aimed to bring together both international policy and legal precedents from Aotearoa related to seed ownership. Based on these, I propose a set of best-practice guidelines for working with Māori in relation to seed banking. These protocols bring together the current literature on appropriate engagement, and personal experiences of myself and colleagues as Māori people working in the environmental space. Ultimately, between these two seemingly separate aims, the overall goal of this thesis is to support the growth of the relatively new seed banking sector in Aotearoa, so that as the nation progresses, we do it from an ethical and appropriate position.
Open Access
Computational bioacoustics for the detection of rare acoustic events
(2024) McEwen, Ben
The field of computational bioacoustics is a rapidly developing area of research. Tradi- tional bioacoustic monitoring has a long history of use particularly for monitoring of avian species. Species that were previously infeasible to monitor due to resource and time constraints are now a possibility. In New Zealand, bioacoustic monitoring has never been applied to the detection and surveillance of invasive terrestrial mammals. This dissertation presents the first research of its kind investigating the use of computational tools for the detection of invasive species. We evaluate the use of computational methods for the detection of common brushtail possums (Trichosurus vulpecula) a species that is invasive to New Zealand we also investigate the potential of acoustic monitoring of other challenging target species such as mustelids and rats. Low population densities (such as post-eradication efforts) encounter extremely sparse detections where it becomes challenging to reliably differentiate between species absence and non-detection. This issue of non-detection is accentuated by the use of passive acoustic monitoring technology at a landscape-scale. Thousands of hours of raw acoustic data can be collected weekly. Most of this data is empty of events of interest. It is infeasible for a human to manually analyse this data. The post-processing of acoustic data is a common challenge for passive acoustic monitoring applications. Rare feature detection (especially for challenging applications such as incursion detection and probability of absence testing) is currently at the border of feasibility using state- of-the-art computational bioacoustics tools. We present an active few-shot learning methodology that combines semi-supervised prototypical learning methods for efficient analysis of acoustic data with limited existing samples. We evaluate this methodology on an invasive species detection dataset demonstrating high performance at a range of data availability contexts. This methodology achieves a test accuracy of 98.4% (with fine- tuning) as well as 81.2% test accuracy using 2-shot, 2-way prototypical learning without fine-tuning, demonstrating high performance at varying data availability contexts. The development of improved methodologies capable of detecting rare acoustic features has clear benefits for other bioacoustic monitoring applications. This technology can be applied to other challenging applications such as monitoring of rare and at- risk species. These methods can be applied to scale the efficiency of data analysis of existing bioacoustic monitoring applications to achieve landscape-scale monitoring. Invasive species detection using bioacoustics represents a challenging but valuable area of research. We present the development of publicly available methodologies, tools and the first invasive species dataset containing 3500 labelled samples and over 1300 samples of brushtail possum vocalisations. The results of this work indicate the potential of computational bioacoustic methods for the detection of invasive species as well as rare and at-risk species that encounter similar monitoring challenges. In addition to improved bioacoustic detection methods, we also investigate the use of bioacoustic noise reduction methods evaluating both signal processing-based methods and deep audio enhancement methods. We investigate the efficacy of noise reduction for the performance of downstream segmentation and classification tasks identifying the limitations of common perceptual metric-based approaches. We find that noise reduction results in no improvement in segmentation precision and recall with an average AUC performance decrease of 19.2%. We also demonstrate no benefit in classification accuracy when tested using state-of-the-art time-domain and time-frequency-domain audio classification models with a marginal decrease in average validation accuracy of 0.41%. We contrast these findings with common perceptual metrics which demonstrate consistent increases in perceptual quality when noise reduction is applied with SnNR increases ranging from 14.0% to 41.3%. We also present initial work that investigates the use of visual detection methods. We develop predictive tracking methods used to improve population estimates of low- resolution and low-frame rate thermal cameras. We discuss the use of these tools within the context of predator-free New Zealand and the current pest management paradigm.
Open Access
Robotic arm path planning for autonomous grape vine pruning.
(2024) de Wet, Andrew
The autonomous grape vine pruning robot being developed by the Computer Vision Research Group at the University of Canterbury will be capable of imaging vines to create a 3D model of them, navigating around orchards, and pruning vines with a high degree of freedom robotic arm. This thesis develops the system to plan and execute motions for the robotic arm. Path planning for robotic arms involves finding a sequence of joint positions in the robot’s configuration space that can be moved through to create a motion in Cartesian space that avoids any collisions and gets the end effector of the robot, in this case a pruning tool, to a goal position and orientation. Because of the infeasibility of representing the grape vine as an obstacle in the robot’s configuration space, sampling based path planning algorithms that only collision check specific randomly sampled joint positions offer the best approach. Robotics Operating System (ROS) is used as a framework that enables development with a simulated robot and operation of the real robot. The six degree of freedom UF850 by Ufactory is selected with its suitability to the application verified through simulating path planning on 30 synthetic vines, where for all vines a valid pruning strategy given the points the arm could reach can be determined. An implementation method where single paths are found between cut points and a safe plane offset from the vines is proposed to minimise the distance traversed by the planning algorithm and to configure the problem in a way that leads to high quality solutions. The performance of 10 different path planning algorithms with different features from the literature is tested. Following a successful extensive evaluation, Informed RRT* is the selected algorithm with an average length of individual paths of 1.88 seconds and 81.9% of possible cut points reachable. The proposed implementation to prune whole vines maximises the quality of the paths found by using all of the time spent executing one cut to plan the next. While operating the real UF850 it is able to successfully execute a realistic pruning strategy on all of the 20 vines tested. It does so with an average time per cut of 10.85 seconds and an average time per vine of 139.3 seconds. These results demonstrate that once integrated with the full rover the system developed provides an effective approach to autonomous grape vine pruning.
Open Access
Practical pavement distress detection via photogrammetry.
(2024) Zhang, Meng
Overall, the proposed approach in this thesis offers a cost-effective, accessible, and accurate system for pavement distress detection, with the integration of fast perspective transformation and spatial data analysis playing a pivotal role in improving the assessment and management of road infrastructure. The structure of this thesis is organized as follows: • Introduction: This section sets the stage for the research by highlighting the importance of pavement distress detection, the challenges of traditional methods, and the contributions of the thesis. • Literature Review: This section provides a comprehensive overview of the existing literature, covering both background of general models in the field of computer vision and specific techniques in pavement distress detection, or anything directly related to the thesis: ‣ Background – Traditional Automated Techniques: Discussion on sensor-based solutions, stereo vision methods, and detection with structured light. – Deep Learning in Computer Vision: Examination of the evolution of deep learning models in computer vision, as well as important architectures such as the U-Net, the R-CNN, the YOLO model family, and latest transformer-based networks. – Depth Estimation Methods: Exploration of stereo vision and disparity maps, monocular depth estimation, and the integration of depth perception with an example. – Geographic Information Systems (GIS) Integration: Analysis of how GIS can be integrated into pavement distress detection. ‣ Related Work: Review of recent studies and research papers in the field of pavement distress detection, focusing on the methodologies, techniques, and findings. – Deep Learning based Distress Detection: include transfer learning and previous work on neural network based pavement distress detection models. • Data Collection, Cleansing, Labeling, and Transformation: This section describes the methodology and equipment selection, transportation selection, data collection strategy, data cleansing, data labeling, and data transformation processes. • Model Re-implementation and Tweaking: It focuses on model selection and re-implementation (Mask R-CNN), as well as model tweaking and hyperparameter optimization. • GIS Analysis for Pavement Distress Detection: This section discusses the integration of spatial data analysis using Geographic Information Systems (GIS) to provide geographic context to the pavement distress data. • Conclusion and Future Work: Providing the key findings of the thesis and outlines potential directions for future research.
Open Access
Modelling and adaptive control of quadrotor unmanned aerial vehicles
(2023) Morris, Daniel
Unmanned aerial vehicles (UAVs) have the potential for use in a number of high-precision applications, including industrial inspection and precision agriculture. Quadrotor UAVs are one of the most commonly used UAV platforms, as they are agile, lightweight and relatively inexpensive. A significant limitation of current quadrotor UAV flight control systems is their inability to adapt to changing flight conditions, as well as their inflexibility to changing airframe properties. Conventional methods utilise linearised or simplified models of flight dynamics which have limited capacity to respond to changing system parameters, and use control methods that are limited to low accuracy applications or to specific flight conditions. The development of a generalised, flexible flight control system for quadrotor UAVs would allow for a greater range of applications across a wide range of airframes, from specialist to civilian UAVs. This work investigates the development of such a flight control system. Firstly, a nonlinear dynamics model of a quadrotor UAV was developed. This dynamics model used a quaternion orientation representation; the majority of existing models use an Euler angle representation, which have known singularities, whereas using a quaternion representation allows for singularity-free orientation representation as well as more efficient computation. The dynamics model was developed in a minimal sense, with the core dynamics effects derived from first principles. The model was then parametrised into 13 parameters, using a lumped parameter approach as the initial model was structurally non-identifiable. Unmodelled non-ideal dynamics effects were included by augmenting each dynamic axis with a parameter representing the total dynamic impact of unmodelled effects on that axis. The dynamics model developed includes aerodynamic drag effects modelled using the Rayleigh drag equation. There is little consensus in the literature on how best to model aerodynamic drag for a multirotor UAV, so an experimental study of the drag behaviour of a quadrotor airframe was conducted. A quadrotor airframe was mounted at a range of pitch and yaw angles in a wind tunnel, and the drag forces on the airframe were measured across a range of wind speeds. The results of this study showed that a Rayleigh drag model accurately models the UAV’s aerodynamic drag behaviour. An experimental flight platform was then developed to allow for physical data collection. This platform consisted of a standard cross configuration quadrotor airfarme, with Hall effect sensors added to measure the angular velocities of the propellers. The Hall effect sensors and inertial measurement unit used were calibrated against known reference values, using test fixtures designed for each sensor, and their signal-to-noise ratios (SNRs) were derived, with all sensors having SNRs greater than 25 dB. Ground truth flight data was obtained using a motion capture system, and required the implementation of synchronisation between the onboard sensor clock and the external motion capture clock. A modified form of the IEEE 802.11 clock synchronisation protocol was implemented, with an infrared LED used to obtain a 20 Hz synchronisation pulse with the motion capture system. Next, identification of the model’s parameters was investigated. Parameter identification methods for UAV systems in the literature are typically applied prior to flight operations, whereas this thesis considers the use of such methods during flight operations to allow for online tuning and adaptation to changing flight conditions. Four common white-box parameter identification methods were implemented and were applied to both synthetic data and experimental flight data in an open-loop control configuration. Error metrics for the performance of each method were defined, including a definition of pose error that captured both the overall desired behaviour of the airframe, as well as including the quaternion orientation representation. Application of the parameter identification methods to the synthetic data showed that Levenberg-Marquardt gradient descent had the best performance, including when synthetic noise was added to the simulated data, with this method yielding pose errors 75% smaller than the other methods at SNRs down to 20 dB. Levenberg-Marquardt gradient descent was also the most performant method on the experimental flight data, with median quaternion distance errors below 0.3 rad, but maximum distance errors comparable to the experimental flight envelope. Finally, a nonlinear model predictive control system that incorporated both the nonlinear dynamics model and online parameter identification was developed. A novel cost function based upon the pose error metric was used to prioritise trajectory tracking, with comparison with a standard quadratic cost function showing that the pose error cost function gave better tracking performance and was better able to track target quaternion orientations. The controller was tested on synthetic flight trajectories, including airframe parameter changes and external wind disturbances, and was shown to maintain accurate trajectory tracking when subjected to these conditions, although the controller’s high computation cost prevented its use in an experimental setting.
Open Access
Development of a sustainable alternative to current MBBR carrier media.
(2024) Stevens, Campbell
Cellulose and agar were tested extensively to assess their suitability as a replacement material for plastic for use in manufacturing Moving Bed Bioreactor (MBBR) biocarrier media. The influence of various additive materials and post-processing techniques applied to the biocarriers was also assessed. Additives included hemp, muscle shell and salt. Post processing included freeze-drying, rehydration, and chemical cross-linking. These materials met the criteria to reduce plastic waste and microplastic pollution of waterways. Cellulose and agar were chosen due to their renewability and general abundance. They were found to be better ecologically in terms of energy usage, harmful emissions and the end-of-life effects related to their manufacture, usage, and disposal in comparison to plastics. Of the two tested matrix materials, cellulose was found to be brittle in its behaviour and would fracture easily under small, applied loads. Alternatively, agar exhibited elastic behaviour which made them more suitable for resisting the small compressive loads typically applied to biocarrier media. Various agar compositions were tested, including samples with 5%, 6% and 7% total solid agar content alongside the noted additives. Agar 5% fared similarly to or better than all compositions under compression, cyclic, rheological and thermal testing. It was found that agar-based biocarriers were able to support the growth of nitrifying bacteria in a turbulent aqueous environment similar to what would be found in a MBBR plant. This bacterial growth showcased nitrate removal rates that were lower, but comparable, with traditional plastic biocarriers. While the per-biocarrier performance was not greater than industry standard biocarriers, agar showcased its higher removal rate potential when compared by protected specific surface area. In comparison to plastic biocarriers, the agar biocarriers were able to exhibit approximately twice the nitrate removal performance of plastic when normalised by specific protected surface area. Despite this apparent doubling in performance per square unit of protected surface area, agar biocarriers faced drawbacks to being suitable as long term biocarrier media. These related to the insufficient durability and structural integrity of the agar biocarriers when in use in a simulated MBBR environment. They are however highly suitable for locations that feature shorter-term peaks in wastewater production such as seasonal holiday destinations. Potential avenues of investigation into increasing agar biocarrier’s general mechanical properties, resilience, and protected specific surface area are noted. Following further development, agar biocarriers could be a highly performative and ecologically friendly alternative to industry standard biocarriers.
Open Access
Modelling and contol of interlinking converters for hybrid ac/dc networks.
(2024) Wasekar, Umang
An important way to integrate renewable energy sources into the current electrical system is the hybrid AC/DC grid. To increase power supply efficiency, reliability, and resilience, they integrate the benefits of AC and DC distribution systems. This system is a complex network of distributed energy resources such as solar photovoltaic (PV) systems, wind turbines, fuel cells, batteries, and other energy storage systems, which work together to provide reliable and sustainable power. The advantages of hybrid AC/DC grids over conventional AC grids include lower transmission losses and higher energy efficiency. Interlinking converters (ILC) manage the power flow between the AC/DC grids. The stability and performance of hybrid AC/DC grids are, therefore, highly dependent on the control of the interlinking converters. While hybrid grids and microgrids have numerous advantages, there are significant unresolved issues regarding how to control and stabilise the uninterrupted power flow between these grids. To tackle these problems, various control strategies have been implemented over time, of which droop-based schemes are predominant. In this research, we are going to focus on such strategies, specifically on the droop-based control strategies of interlinking control for the power flow. In this research project, various models of an AC/DC grid connected through Interlinking Converters are constructed using MATLAB and MATLAB/Simulink. Droop-based (dual droop and matching) control strategies are implemented in the model with various gains, and the results are compared. A key objective is to gain insight into the behaviour of AC/DC grids and assess how different control strategies for the ILC can affect their performance and stability under varying conditions. While it is impossible to accurately predict all scenarios, statistical analysis can be used to assess the robustness of network stability to parameter variation and changing conditions. In this thesis, therefore, a Monte-Carlo analysis is conducted on several hybrid AC/DC test systems in order to investigate four issues: the use of grid-forming vs grid-following interlinking converters, the modelling of grid-following phase-locked loops (PLLs), the effect of network topology and interconnectedness on stability and finally, the comparison between matching control vs dual droop. The conclusion presents the key findings of the work and discusses their application to power system design and converter control choices. Verification of the PLL model for a grid-following inverter is crucial for ensuring stability. The choice between a grid-following and a grid-forming ILC depends on grid strength. However, due to the coupling of DC voltage dynamics with AC frequency, GFM ILCs may require a higher stability threshold compared to battery-based GFM converters. Network topology also plays a significant role in stability, with additional interconnections potentially increasing the likelihood of interactions between converters. Matching control is found to be a better choice for grid-forming ILCs compared to dual droop, as the latter can cause destabilizing interactions with other converters and ILCs.
Open Access
Aeroelastic instability of reduced-scale high-altitude pseudo-satellite wings.
(2024) Durrant, Matthew
Literature indicated that existing wind tunnel wing models possessed aeroelastic properties unrepresentative of High-Altitude Pseudo-Satellites (HAPS). Therefore, this research aimed to develop HAPS representative aeroelastic wind tunnel wing models. Two wing varieties were constructed, wind tunnel destruction tested, and aeroelastically analysed with the geometrically nonlinear aeroelastic analysis code ASWING. The destabilising influence of increasing static unbalance was observed at alternate 25% and 75% of chord main spar locations. Ground vibration testing validated structural natural frequencies calculated from static stiffness test data. Model destruction occurred near the predicted flutter airspeeds at incidences from 0.17 to 4.17 deg, following subcritical limit-cycle oscillations, stall-limited bending-torsion flutter, and torsional divergence. Analysis of first bending and torsion mode phase and damping with airspeed revealed bending-torsion flutter instability of both wing designs. The 25% chord spar wings failed exclusively in flutter, whereas several 75% chord spar wings exhibited post-flutter divergence, qualitatively matching predictions. Linear stability analysis of the wing motion, composed of large static deflections with superimposed low amplitude oscillations, remained physically meaningful due to linearisation of the geometrically nonlinear deformed structure about the deformed equilibrium. The results show that the aeroelastic behaviour of highly flexible wing models is accurately predicted by ASWING.
Open Access
Sensor and analogue electronics design for non-invasive food sensing and imaging system.
(2024) Perry, Stanley
This thesis presents the design of analogue electronics, including non-invasive magnetic field and surface potential sensors, for a new food sensing and imaging system. This system is targeted towards the dairy processing industry, to detect and characterise foreign objects flowing through food processing pipes. The food sensing and imaging system employs a new imaging technique known as electric and magnetic field detection electrical admittance tomography (EMFDEAT). This involves applying a sinusoidal excitation to a semi conductive medium and reconstructing the conductivity distribution from measurements of the surface potential and surrounding magnetic flux density. Two rings of electrodes, each containing 16 segments, are used to apply a 10 kHz sinusoidal excitation across a length of pipe. Changes in local conductivity inside the pipe due to a foreign object distort the applied current distribution, which is detected by an array of 128 magnetic flux and 128 surface potential sensors. The sensor array consists of 8 stacked rings of sensors, each containing 16 magnetic flux and 16 surface potential sensors. The sensor rings, which are located between the two electrode rings, are designed to fit around a 110mm (outer diameter) pipe. The magnetic field sensors consist of search coils, made by winding 1000 turns of 0.1mm diameter copper wire around an air-cored coil former, connected to an amplifier. The magnetic field sensors achieve a sensitivity of 2.45 V/μT with a 1.5 pT /√ Hz noise level at 10 kHz and dynamic range of ±2 μT. The surface potential sensors use transimpedance amplifiers to amplify a displacement current between the food surface and an electrode embedded in a circuit board through a 5mm PMMA (perspex) pipe wall. The surface potential sensors achieve a sensitivity of 10V/V with a 17.5 μV/√ Hz noise level at 10 kHz and dynamic range of ±500mV. Both sensors fit within a 20 × 20mm printed circuit board (PCB), with the surface potential sensor electrode located directly underneath the search coil, making the two sensors collocated in the circumferential and axial directions. Preliminary test results using a single ring of sensors indicate that raw data from the sensors can be used to detect the presence of a small plastic or metal object within a pipe filled with a saline solution that has a conductivity similar to milk (approximately 0.5 S/m). A Current transformer (CT) is used to produce a scaled-down replica of the excitation current at each electrode, which is measured using a transimpedance amplifier. An output filter is designed for a class-D amplifier chip, which can be used to generate the 10 kHz excitation at each electrode.
Open Access
Design of a prototype adaptive optics system for University of Canterbury’s 0.61 m Boller & Chivens telescope.
(2024) Johnson, Emma
Ground-based telescopes suffer from a loss of image quality away from the diffractionlimited resolution. Light from a science target travels through the atmosphere and encounters turbulence, which distorts the wavefront causing aberrations, commonly corrected by employing an Adaptive Optics (AO) system. This thesis outlines the method for building a prototype AO system for a 0.61 m diameter primary mirror telescope at Mount John. Previous work by Liu et al. demonstrated a 16.7% correction using a tip/tilt mirror system. In this thesis, a study of the environmental and design parameters is conducted using the end-to-end simulation tool Octopus, developed by scientists at the European Southern Observatory. The AO system is simulated for expected conditions and parameters based on the three-layer atmospheric model developed by Mohr, Johnston, and Cottrell for Mount John and the available wavefront sensors and deformable mirrors at the University of Canterbury. Simulation results suggest that the AO system can improve Strehl ratios above the seeing conditions at K and V bands under atmospheric conditions characterised by Fried parameters of 7 - 12 cm. The selected Shack-Hartmann wavefront sensor (SH WFS) should be operated to achieve the smallest latency, with the maximum achievable frame rate of 880 fps in high-speed mode, allowing Strehl improvements when there is a minimum guide star flux of 10 photons/subaperture/frame at K band and 50 photons/subaperture/frame at V band. Initial laboratory testing shows that the AO prototype provides significant correction of lower-order modes. The Full Width at Half Maximum (FWHM) of the Point Spread Function (PSF) shows improvement from the open loop FWHM when static aberration modes are applied. In particular, the defocus and astigmatism modes provide the best improvement in FWHM from the open loop FWHM for a given rms input aberration. Therefore, the prototype AO build is successful in the correction from the third to the tenth Zernike aberration mode. However, the analysis of an evolving generated atmospheric screen using Taylor’s Frozen Flow Hypothesis requires a Fried parameter of 30 - 40 cm to close the loop. Thus, the Thorlabs Deformable Mirror (DM) is unsuitable for on-sky operation at Mount John Observatory since it saturates for atmospheres characterised by a Fried parameter of 7 - 12 cm. Preliminary on-sky testing suggests that the wavefront sensor is insufficiently sensitive for on-sky use in the current optical configuration.
Open Access
Evaluating hydrogenotrophic and electroactive bio-electrochemical denitrifying systems for surface water bioremediation.
(2024) Ahmad Zulkiflee Laidin, Ahmad Danish bin
This thesis investigates the potential utilisation of microbial electrolytic cells (MECs), driven by direct electron transfer (DET), mediated electron transfer (MET), or both, for the treatment of nitrate-polluted surface water. Nitrate pollution has been a widespread problem, both globally and locally, coinciding with the development of intensive agricultural and livestock production practices. Conventional nitrate abatement occurs via either ‘separation’ or ‘reduction-based’ processes. The former involves the use of reverse-osmosis (RO), electrodialysis, and ion exchange technologies, which are both energy intensive and produce highly concentrated nitrate effluents (i.e. brine). In contrast, reduction-based processes have classically leveraged heterotrophic microbial denitrification processes. While reduction-based processes are preferred, the need for carbon substrate supplementation (e.g. methanol, acetate) necessitates further downstream processing to prevent further environmental impacts. Autotrophic denitrification, which involves the use of inorganic carbon (such as CO2), could serve as an alternate solution to conventional reduction-based processes for nitrate abatement. Furthermore, the slower growth rates of autotrophic microorganisms have the potential of establishing a more biologically stable system compared to their heterotrophic counterparts. Autotrophic MECs have been previously investigated for surface and groundwater nitrate remediation because of their potential to minimise environmental impacts (e.g. brine formation, accumulation of denitrification intermediates and organic carbon substrates) and competitive energy consumption. Dual-chambered MECs have been previously used to establish autotrophic denitrification systems. In these systems, the cathode acts as an electron donor for both denitrification and the reductive assimilation of inorganic carbon (e.g. CO2). Dual-chambered MECs are thus able to overcome the absence of electron donors within environmentally sourced waters (thereby preventing further chemical dosing) while also offering a carbon capture solution for the remediation of CO2. Furthermore, autotrophic denitrifying systems are characterised as being ‘biologically stable’ due to the slower bacterial growth rates compared with their heterotrophic counterparts. However, the nitrate removal rates achieved by this strategy are slower than those achieved by other conventional nitrate abatement technologies. Extensive studies have been conducted on reactor configurations to improve nitrate removal rates, typically involving the use of larger electrode surface areas (such as granular activated carbon – GAC). The central tenant of this investigation is that by improving the denitrification performance of biofilm electrodes, more compact bio-electrochemical denitrifying (BED) systems could be developed to address issues of overpotentials and pH fluctuations, which are common in larger-scale BED technologies. In this thesis, electroactive, denitrifying microbial communities were enriched using different strategies in four parallel MECs from locally obtained sediments. Three BED reactors (BEDs 1, 3, and 4) were inoculated using microbial communities sourced from Okeover stream sediments, whereas one reactor (BED2) was inoculated using previously enriched Lowcliffe sediment samples. Three reactors (BEDs 1, 2, and 3) were operated with a cathodic poised potential of -1100 ± 2 mV (vs Ag/AgCl) while BED4 was operated using a cathodic poised potential of -700 ± 2 mV (vs Ag/AgCl). The cathodic poised potential of -1100 ± 2 mV has been demonstrated to generate hydrogen on the cathodic surface and was used for the enrichment of a hydrogenotrophic (or H2-MET) denitrifying biofilm. Conversely, -700 ± 2 mV has been widely used in prior studies for the enrichment of a DET-driven electroactive biofilm (EAB). During the nitrate loading experiments, BEDs 2 and 3 exhibited the fastest nitrate removal rates (e.g. 4.94 ± 0.04 and 8.62 ± 0.13 g NO3--N∙m-2∙d-1 respectively), revealing the potential of utilising both H2-MET and DET for nitrate remediation. Subsequent microbial community analysis conducted on the EABs of the four reactors revealed the enrichment of hydrogenotrophic denitrifiers (Hydrogenophaga spp., Simplicispira spp., and Dechloromonas spp.) in BEDs 1, 2, and 3, and the enrichment of Candidatus Nitrotoga spp. in BED4. Next, the cathodic poised potential was varied to investigate the effect of operating poised potentials on nitrate removal rates, which demonstrated increased nitrate removal rates at lower poised potentials (< -1100 ± 2 mV vs Ag/AgCl). Finally, the treatment of nitrate-supplemented surface water revealed several operational challenges regarding the application of this method, which were later addressed with suggestions for future studies. These findings usher in further development of BED systems utilising both MET and DET while uncovering the potential of utilising such systems to improve our understanding of electroactive denitrifying communities.
Open Access
Harnessing emotional design strategies to manage excessive use of short video platforms among young adults : a mobile application design demonstration.
(2024) Li, Hongyao
In recent years, the excessive use of social media among young people and its adverse effects on mental health have drawn widespread attention. Developing effective strategies to help them manage their excessive use of social media remains a significant challenge, especially in the context of short-form video (SFV) products, where this issue is particularly pronounced. SFV products, due to their high attractiveness and instant gratification, can easily lead users to become addicted. Therefore, this study explores and discusses design strategies based on emotional design principles to help young adults manage their excessive use of SFV products. The aim is to help them establish healthier engagement with digital products and better usage habits, thereby improving their mental health and overall quality of life. This research primarily focuses on three questions: 1) What factors influence young adults' excessive usage of SFV applications? 2) What emotional design-based design strategies can effectively regulate this usage? 3) How can a mobile application be designed to help users manage their excessive use of short-form video platforms? To answer these questions, the study initially employs the internet ethnographic method to understand the factors leading to the excessive use of SFV applications and the difficulties and challenges people face in trying to manage their SFV product usage. Through an online survey, the study then investigates the specific usage patterns of SFV applications among 144 young adults aged between 18 and 35 and their motivations and reasons for overconsumption of these products. Based on online ethnographic and survey results, the study integrates emotional design principles to explore what emotional design strategies can help young adults regulate unhealthy SFV application usage and how they can be implemented in the design of a mobile application for such purposes. Additionally, the study employs the co-design method to assist in the design of the application and evaluate the effectiveness and usability of the emotional strategies and the mobile application. This study proposes design strategies to help young adults manage their excessive use of SFV applications and presents a design demonstration of a mobile application to manage the overuse of SFV products. By emphasizing effective methods to promote healthier social media and digital product consumption habits, the study provides valuable insights for creating responsible digital products.
Open Access
Stress reduction therapy in immersive environments : does rotation mode have an effect on mental stress?
(2024) Feng, Yuming
Mental stress, exacerbated by various contemporary factors including the COVID-19 pandemic, rapid technological advancements, and global crises, poses significant challenges. Immersive technologies like virtual reality (VR) offer promising avenues for stress relief. This paper explores the efficacy of VR immersion, particularly the impact of rotational motion, in mitigating mental stress. Through heart rate monitoring, it investigates the intricate interplay between immersive VR environments and stress reduction. Integrating insights from VR therapy, meditation practices, and heart rate analysis, the study contributes to the burgeoning field of mental health technology. It proposes VR as a novel tool for stress management, providing multisensory meditation experiences. The study also explores the use of innovative hardware like the NOVA Ball to induce immersive meditative states. The experimental design seeks to understand VR’s therapeutic potential for stress reduction, bridging the gap between technological innovation and practical mental health solutions. Research Background and Purpose: This study systematically evaluates user experiences in a VR environment integrating physiological data, focusing on the influence of physical rotation elements. It uncovers correlations between heart rate variations, physical rotation, and user experiences, informing future VR design. By delving into the relationship between heart rate fluctuations and participants’ emotional and cognitive states under physical rotation conditions, the study deepens understanding of rotation actions’ mental health effects in VR. Additionally, it assesses VR’s potential as a mental health intervention, particularly in stress reduction, by merging subjective experience questionnaires with objective physiological heart rate data. This holistic approach enriches VR’s role in mental health and guides future developments in user experience design and VR therapy applications.
Open Access
Deformation mechanism map and microstructural behaviour of austenitic stainless steel incoloy 800H tube during uniaxial creep
(2018) Beardsley, Aaron Luke
Incoloy 800H is an austenitic stainless steel alloy with nominal composition Fe-32Ni-21Cr developed by the Special Metals Corporation in the 1950s. The alloy was developed for the purpose of creating a corrosion- and creep-resistant metal which was cheaper than its nickel-based superalloy counterparts. It has a solid substitution strengthened single-phase Fe-Ni-Cr matrix, with additional strengthening from Ti(C,N) and M23C6 precipitates. As a result of this, it has since been used in various applications. In particular, it has been used in the petrochemical industry for methane reformer exit tubes. These tubes are created from 800H billets by a pilgering process, which involves several multiaxial, pseudo-periodic deformation steps in order to reduce the wall thickness to the desired level. Following the pilgering process, the tubes are solution annealed to recrystallize the material and increase the average grain size to the American Society for Testing and Materials (ASTM) grain size number 5 or coarser. In the field, the pigtail tubes can operate at temperatures in excess of 900 °C and stresses up to 10 MPa. They have a target service life of 20 years. To quantify the creep performance of a material, researchers devised creep deformation mechanism maps (CDMMs). These maps plot isominimum strain-rate lines as a function of normalised stress and homologous temperature. During creep deformation, there are several competing creep mechanisms, such as the diffusion-controlled climb of edge dislocations, or the diffusion of vacancies through grain boundaries. CDMMs present regions on the map where each mechanism is the dominant mechanism, which is defined as the mechanism which contributes the largest amount to the total minimum strain-rate. Despite being used extensively in creep-based applications, there is a significant lack of knowledge about the creep performance capabilities of 800H. To date, a CDMM for 800H has not been created. This means that the industry uses the alloy without any knowledge of the true failure mechanism during service, or the limits to which they can maximise the temperature and stress during service. There is also significant lack of knowledge about how the microstructure, in particular the average grain size, affects the creep performance. Filling these voids of knowledge will be the primary objective of this research. For this research, 800H was received in an as-pilgered condition. This was useful as it meant that there was more control over the microstructure, as each batch of material could be heat-treated for different average grain sizes by solution annealing at different temperatures. In this research, separate batches of creep test samples with mean grain diameters of 109 μm, 180 μm and 248 μm were achieved by solution annealing for 2 hours at 1100 °C, 1150 °C and 1200 °C respectively. With sixteen samples from each heat-treatment, and an addition ten samples of unknown heat-treatment, a total of fifty-eight samples were creep tested. These tests were performed at temperatures ranging from 750 - 1020 °C and stresses ranging from 15 - 105 MPa. Of the fifty-eight tests, twenty-four were tested until rupture, and the remainder were terminated after the minimum strain-rate had been passed in order to save time. Test times ranged between 10 - 2000 hours. By fitting data to a hyperbolic-sine power-law model, minimum strain-rates were reliably extracted from the raw creep test data. Minimum strain-rates varied from approximately 1.6 x 10-6 - 2.0 x 10-10 s-1. These testing conditions covered a comprehensive region of the CDMM. The primary creep mechanisms of interest are power-law creep, which can be divided into high-temperature and low-temperature submechanisms, Coble creep, and Nabarro-Herring creep. By summing the constitutive equations for these models, the total minimum strain-rate as a function of temperature, stress and average grain size can be modelled. Using a computational optimisation algorithm called the genetic algorithm (GA), the material constants for the model were numerically fitted to the experimental data, a novelty for this application. The solutions were then assessed using a training and testing technique. Once the material constants were optimised, the CDMM was created for 800H. This map was then expanded to three-dimensions by showing a series of maps with different average grain sizes. Several novel CDMM concepts were explored, such as adding colour to visually represent the contribution of each mechanism to the total minimum strain-rate, converting the axes to absolute units, and truncating the axes of the figure to show more detail in the more important region of the map. Other creep models, such as a hyperbolic-sine model, and a model based on the Larson-Miller and Monkman-Grant equations were also explored and compared to the traditional model. After finalising the CDMM for 800H, it was determined that these maps alone are not sufficient for practical applications. The maps show the mean minimum strain-rate based on the fit of the model to the experimental data. Although error for the fitting process was minimised by using a GA, the error still exists and is not represented on any maps that exist today. Therefore, it was decided to create a map which showed the level of certainty for the minimum strain-rate as a function of the position on the CDMM. Using several statistical analyses of the data to quantify aspects such as the variability of data tested at the same temperature and stress, and the extrapolability of the data, an error contour map was created. This novel concept is a first approximation and will require further development before it can be implemented. The final section of work focused on microstructural aspects during creep deformation of 800H. Using several different microscopy techniques, in particular, energy-dispersive X-ray spectroscopy (EDS) and electron backscatter diffraction (EBSD), the microstructure of creep deformed 800H was explored. This work focused on the accumulation of damage as a function of creep strain, and the determination of the creep mechanism involved during the deformation. Key microstructural aspects that were assessed include the formation of subgrain boundaries, precipitation and void formation. The gathered information was compared to a 20-year service 800H pigtail tube, which was used to determine the level of strain in the observed microstructure. Overall, this work provides a significant contribution towards the understanding of the creep performance characteristics of 800H. This includes novel contributions to the fields of creep model optimisation, statistical analysis of creep data, and microstructural characterisation, all of which can be potentially extrapolated to related materials. Specifically, this work acts as a foundation for the understanding of creep deformation of 800H, which others can build upon. With this work, industries should be able to more reliably predict the creep deformation performance of 800H.
Open Access
Cognitive Biases and Perceptual Distortions in Human-Computer Interaction
(2024) Suwanaposee, Pang
People interact with user interfaces daily to perform tasks such as web browsing, sending emails, watching videos and playing games. Many of their interactions will involve making judgements and decisions, such as judging the duration of software updates, the quality of video recommendations and deciding whether to examine word suggestions above a mobile keyboard. However, prior work from psychology and behavioural economics literature exhibits that people are susceptible to cognitive biases and perceptual distortions, implying that they can influence judgements and decisions in interaction. Examples of these effects relevant to this thesis include perceiving time as longer or shorter than it is, the Barnum effect (people’s tendency to assign higher quality ratings to personality descriptions presented as personalised for them than identical descriptions presented as generally true of people), and prob- ability weighting (the tendency to overweight small probabilities and underweight large probabilities). If cognitive biases and perceptual distortions apply in interaction, user interface designers must be aware of them, and helping designers understand them can lead to opportunities for improving user experiences. Therefore, the primary goal of this thesis is to provide novel knowledge and insights for improving research and practice in HCI by investigating the influence of cognitive biases and perceptual distortions in interaction. In addressing this goal, this thesis presents three empirical studies. Study 1 explored the influence of audio effects and attention on users’ perceived duration of interaction. This study was motivated by computer delays leading to user frustration, prior psychology literature of factors such as audio and attention influencing time perception, and the opportunity to extend from a previous HCI study demonstrating distortions in users’ duration judgements using audio effects. Study 1 had two stages: estimation of a wait duration (indicated with a progress bar) and pairwise comparisons between the duration of two interactive experiences with different effects. The first stage results revealed that perceived duration varied across different audio conditions, and the second stage results confirmed previous findings that increasing-tempo beeps could shorten the perceived duration but also extended these findings to interactions involving visual feedback (progress bar) and direct interaction (playing a game). These findings suggest that designers can use audio to alter users’ time perception during wait periods and reduce the adverse effects of computer delays. Study 2 examined the effect of purported personalisation on users’ perceived quality of system recommendations. This study was motivated by the prevalence of recommender systems in contemporary user interfaces and the widely observed Barnum effect. The experiment showed participants a set of identical movie recommendations that were purportedly personalised or non-personalised. Opposite to the Barnum effect, the results showed that personalised recommendations had lower mean quality scores but no significant difference. This result suggests that Barnum-like effects of personalisation have minimal influence on perceived quality and that designers should be cautious about depending on this effect to improve user experience. Study 3 investigated the probability weighting function influencing users’ decisions to examine or ignore text entry suggestions. The probability weighting function implies that users will exhibit a bias in which they overuse suggestions at low accuracy and underuse them at high accuracy, which can harm their text entry time. This study tested this prediction by having participants interact with five text entry suggestion systems, each with a unique probability of showing the participant their required word each time the suggestions were updated and examining users’ decisions to examine or ignore the suggestions. Experimental results confirmed the prediction, suggesting that designers should be wary of users exhibiting this bias and harming their performance. Moreover, as part of analysing users’ bias, this study contributes a method for analysing and modelling text entry to examine the costs and benefits of text entry suggestions. In summary, this thesis makes four primary contributions: (1) a review of prior work on a set of cognitive biases and perceptual distortions and their potential influence in interactive contexts; (2) an investigation of audio effects and attention influencing users’ perceived duration; (3) an investigation of the Barnum effect influencing users’ perceived quality of recommendations; and (4) an investigation of the probability weighting function in text entry suggestion interaction.