Engineering: Theses and Dissertations

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  • ItemOpen Access
    Feeling moved in VR concerts.
    (2023) Aguilar, David J.
    This research explores the user experience design elements necessary to evoke the emotion called kama muta, most commonly known as” being moved” or “being touched”, in a virtual reality concert. Previous research has been able to mediate this emotion using video, nevertheless, to the best of my knowledge, no work has been done related to evoking kama muta in Virtual Reality. Accordingly, a VR experience prototype was created to simulate the performance of a fictional pop singer called X-ABC, who would have been dealing with grief as a consequence of his brother being missing and decides to share his feelings with the audience. Twenty participants took part in a between subjects’ study, in which they reported their emotional state using the KAMMUS Two, and Bailenson’s social presence questionnaires. Ultimately, participants’ answers were analysed using quantitative and qualitative methods. Overall, the findings suggest that it is possible to elicit kama muta in a simulation by featuring a narrative that increases the intensity of communal sharing relationships, such as loss, reunion, or memories of loved ones. It was also found that the user-experience design elements that contributed the most to the emotional response were a set of floating screens with portraits of the siblings when they were children, a believable voice acting and a character with emotional facial animations which were also lip-synced with the acted voice.
  • ItemOpen Access
    Two generalisations of the wheels-and-whirls theorem.
    (2023) Toft, Gerry
    One of the most famous results in matroid theory is Tutte’s Wheels-and-Whirls Theorem. It states that every 3-connected matroid has an element which can either be deleted or con- tracted while retaining 3-connectivity, except for two families of matroids: the eponymous wheels and whirls. The Wheels-and-Whirls Theorem is a powerful tool for inductive argu- ments on 3-connected matroids. We consider two generalisations of the Wheels-and-Whirls Theorem. First, what are the k-connected matroids such that the deletion and contraction of every element is not k-connected? Motivated by this problem, we consider matroids in which every element is contained in a small circuit and a small cocircuit, and, in particular, when these circuits and cocircuits have a cyclic structure. The first part of this thesis is concerned with matroids in which have a cyclic ordering σ of their ground set such that every set of s − 1 consecutive elements of σ is contained in an s-element circuit and every set of t − 1 consecutive elements of σ is contained in a t-element circuit. We show that these matroids are highly structured by proving that they are “(s, t)-cyclic”, that is, their s-element circuits and t-element cocircuits are consecutive in σ in a prescribed way. Next, we provide a characterisation of these matroids by showing that every (s, t)-cyclic matroid is a weak-map image of a particular (s, t)-cyclic matroid. Secondly, what are the 3-connected matroids such that such that the deletion and con- traction of every 2-element subset is not 3-connected? In the second part of this thesis, we find all such matroids. Roughly speaking, these matroids can be constructed in one of four ways: by attaching fans to a spike, by attaching fans to a line, by attaching particular matroids to M (K3,m), or by attaching particular matroids to each end of a fan.
  • ItemOpen Access
    Redirected hands for reducing arm fatigue during mid-air interactions in virtual reality.
    (2023) Hobson, Alex
    Muscle fatigue is a major impediment to the long-term usage and acceptance of Virtual Reality (VR). Users must routinely manipulate objects, perform repeated teleportations, and interact with user interface elements using prolonged arm and hand gestures. One leading strategy for reducing arm fatigue is ray-casting, which gives the user a laser pointer metaphor, allowing them to select objects with a comfortable position of the arms, but limits the fidelity of interactions by deviating from how hands are used in the real world. In this thesis a lesser-explored strategy to address arm fatigue is explored: hand redirection. “Hand redirection” is a technique made possible with VR, where the user can be fooled into believing their hand is in a different location to where it is in the real world, since people are visually dominant and VR completely immerses a person’s vision. Existing hand redirection literature mainly relates to being able to redirect the hand to a sparse haptic proxy, allowing the user to feel objects in VR, however its impact on arm fatigue is lesser explored. In this thesis, hand redirection is explored as a practical mitigation strategy addressing arm fatigue in VR, which still supports natural hand interactions (unlike ray-casting). A system was built that provides hand tracking and a physical surface at different heights, such that the user can touch the lower or tilted surface, and still see themselves touching an upright surface at eye level in VR. A between-subjects study was then conducted with 48 participants across six conditions, using a 2×3 mixed-factorial design, with two levels of redirection (Tilted, Redirected) and a control (No Redirection), with (Present) and without (Not Present) a physical surface on which to tap. The findings show that hand redirection is a valid way to reduce arm fatigue in VR, since arm fatigue was dramatically reduced without a significant impact on task performance. This behaviour differs when looking at results when the surface was present versus when it was not, suggesting that the way in which users behave in the presence of hand redirection is different when there is a physical surface to touch. Finally, the Tilted condition (where the board was rotated but not moved vertically) did not reduce arm fatigue, suggesting that the main way to reduce arm fatigue is to introduce a vertical offset rather than changing the angle that the hand interacts with the virtual content.
  • ItemOpen Access
    Augmented reality for alternative measuring techniques in geospatial field work.
    (2023) Turton, David
    This thesis assesses the value of a LiDAR application created for the the collection of data in geospatial field work. Several interfaces were developed for this tool with the purpose of determining the best method of selection in 3D space using augmented reality for data collection. Background research evaluates multiple tools and the validity of mobile LiDAR for measuring and data collection. Selection in 3D space using augmented reality is complex and multiple tools were analyzed for how they could be adapted for this task. Two user studies were performed. The first user study was performed with non- professional users aiming to evaluate the effectiveness of the different interfaces developed based on time taken, efficiency, accuracy, and user experience. The second user study consisted of interviews and test runs with GIS developers who analyzed the interfaces, gave feedback on them, and discussed how they compare to existing workflows in GIS data collection. Feedback from these studies was used to determine the best possible interface for the application, how the interfaces can be improved, and if it can operate as a potential alternative measuring tool to existing workflow.
  • ItemOpen Access
    Playing with uncertainty : participatory modelling to facilitate social and technical investment negotiations for resilience planning.
    (2023) Avendano Uribe, Bryann Esteban
    BACKGROUND: Resilience has become a fundamental paradigm for communities to deal with disaster planning, particularly in the face of increasing climate change impacts. While formal methods are employed to prioritise and decide about investments for resilience planning, developing strategies to negotiate that go beyond formal modelling is essential. Participatory Modelling (PM) has emerged as an effective approach in facilitating data-driven decision-making, enabling stakeholders to create, adjust, and learn from interactive models and to use this experience to inform their decisions. THE PROBLEM: When making decisions related to disaster planning, experts, managers, and policymakers face challenges in recognising interdependence within and between social and technical systems. Therefore, a socio-technical systems approach is crucial to understand the challenge of integrating social and technical assets in resilience planning, their interactions, and interdependencies to make informed decisions. Thus, there is a need for an integrated set of investments that increase social resilience and, at the same time, improve critical infrastructure before natural hazard-caused or human-caused disasters. THE AIM: This PhD thesis aims to develop and trial a Participatory Modelling methodology that engages participants in the process of deciding where or whether to invest in technical and social resilience. The objective of this work is to simulate the decision-making process and understand the trade-offs when negotiating between technical/infrastructure and social resilience investments. The study focused on creating a collaborative process that ensures that the diverse interests and concerns of stakeholders are represented and integrated into the planning process. THE APPROACH: To achieve these objectives, the study developed a tailored methodology called Playing with Uncertainty, which includes role-playing simulations and game elements to enhance participant engagement. The methodology involved several steps, including a workshop to identify the interests and concerns of key stakeholder groups, a survey to capture participants' perceptions of the importance of different resilience factors, a simulation exercise to explore different flood management strategies and a debriefing session to discuss the results and lessons learned. The participation model considered the challenge of investment planning for a small coastal community at risk of sea level rise. A total of Five workshops were conducted between 2020 and 2022. Workshops were held at the Human-Interface Technology Lab HITLab NZ at the University of Canterbury. Each tailored session involved three categories of role-played stakeholders: community leaders or locals, policymakers, and resilience experts. Participants included students from the University of Canterbury, resilience experts, industry professionals and planners, and policymakers from the local government in New Zealand. This research was conducted under human ethics permission HEC-2020/88. Triangulation between three data collection methods was used: 1) Role-playing negotiations, 2) Investment decisions, and 3) Prospective Structural Analysis (PSA). In addition, observations from the facilitator and comments from participants during debriefing sessions in the workshops were used to refine the methodology. KEY FINDINGS: This exploratory research found why and how the Participatory Modelling methodology developed: Playing with Uncertainty engaged participants in the decision-making process for the problem tackled in this thesis. Three key findings can be summarised as follows: 1) The use of various methods adapted aimed at enhancing engagement and eliciting knowledge from participants indicates that Playing with Uncertainty could facilitate negotiations among participants on the inherent dilemma of Socio-Technical Systems (STS). The evidence presented on the implementation of game elements and the triangulation of methods: role- playing negotiations, PSA, and investment decisions; suggests why PM has the potential to enhance STS trade-off analysis. 2) It is crucial to determine the level of detail in the information provided to participants when facilitating trade-off negotiations in STS. Drawing on observations and participants’ comments during the trials of Playing with Uncertainty, striking a balance of information in PM could benefit stakeholders’ engagement, and the need to understand how much detailed and realistic information is provided could improve the practice of PM in the field. Hence, implementing better practices of PM could bridge the gap between scientific, local and policymakers expertise when conducting decision-making. 3) Implementation and use of game elements could be synergistically integrated into the methodology development base on its refinement process. Methodological considerations for developing and trialling Playing with Uncertainty suggest the need for refinement. Participatory modellers should prioritise refinement as an ongoing process to inform their creative "polishing approach" when engaging with multiple stakeholders. A framework is proposed for PM in STS. CONCLUDING THOUGHTS: This study contributes to the growing literature on Participatory Modelling as an attempt to approach community resilience planning. Before this research, little research had been conducted on STS in New Zealand, and an international research gap in this area inspired the endeavour to challenge the civil systems engineering community to produce participatory methods to desirable enhance community cohesion while also building resilience in a holistic manner. This work provides a framework for joint investment analysis in STS. The proposed framework and lessons presented in this thesis, along with the importance of refining the methodology, have broader applications and can guide scholars in implementing participatory approaches that foster interdisciplinary collaboration and encourage creative problem-solving. However, limitations on the use of PM in STS remain, and a debate over the need for a consensus on standards and guidelines in PM persists with no clear resolution in sight. FUTURE RESEARCH: It is recommended to conduct additional trials involving a broader range of participants to provide a more comprehensive perspective within the STS context. It is recommended to polish the use of methods to identify specific challenges and opportunities within PM methodologies. Moreover, it is crucial to refine the limitations when integrating game elements and explore immersive technologies in PM to help visualise aspects that enhance a holistic understanding of STS by creating engaging and interactive experiences. This approach could attract PM practitioners from diverse engineering fields and foster collaboration and innovation for community-driven engineering solutions in resilience planning.
  • ItemOpen Access
    Ionic liquid antifouling coating for marine environment.
    (2023) Kaniyadan Baiju, Sajith
    Biofouling, a phenomenon characterized by the accumulation of marine organisms on submerged surfaces, has spurred extensive research into innovative solutions. This study endeavours to assess the effectiveness of phosphonium ion gels, which consist of phosphonium monomers ([P444VB][AOT] and [P888VB][AOT]), as well as free ionic liquid ([P444n][AOT] and [P888n][AOT]) at varying concentrations (ranging from 10% to 50% by weight). Additionally, it explores the impact of altering the length of alkyl chains (with values of n= 8 and 14) and varying the concentration of copper(II) oxide biocide (ranging from 0% to 2% by weight). Another factor under investigation is the role of the docusate anion [AOT] in enhancing hydrophobicity. To evaluate the efficacy of these formulations, a seachest simulator was employed, positioned in New Zealand coastal waters and shielded from both light and tidal currents. The testing period encompassed the summer and autumn seasons. The performance of these anti-fouling formulations was subsequently correlated with the hydrophobic nature of the submerged surfaces, determined by the water contact angle, which ranged from 14° to 131°, and the concentration of the biocide. Notably, formulations exhibiting higher levels of hydrophobicity, achieved through a reduction in free ionic liquid content and the incorporation of longer alkyl chain substituents, demonstrated superior anti-fouling performance. Intriguingly, the presence of the copper (II) biocide had an adverse effect on anti-fouling performance by increasing the surface's hydrophilicity. Importantly, no significant correlation was identified between antimicrobial activity and anti-fouling performance in this context. In summary, this research underscores the potential of phosphonium ion gels as a promising avenue for combining anti-fouling and foul release properties, offering a multifaceted approach to addressing the persistent challenge of biofouling in marine environments.
  • ItemOpen Access
    Quantifying variation in paropsine defoliation within Eucalyptus.
    (2023) Mann, Leslie
    This thesis developed various methods to quantify and better understand paropsine (Coleoptera: Chrysomelidae) defoliation within Eucalyptus, with the overarching goal of reducing herbivore damage in plantation forests. To date, paropsine preferences and impacts on Eucalyptus in New Zealand remain poorly understood with only a few published studies (Lin et al., 2017a; Radics et al., 2018; T. Withers et al., 2017). Furthermore, defoliation was previously measured with visual ground-based assessment; as a consequence, quantifying defoliation is semi-subjective. Research needs to be undertaken to fill these knowledge gaps. This thesis expands on the work of Lin (2017) and includes E. bosistoana families and other Eucalyptus species identified as priority species by the New Zeland Dryland Forest Initiative (NZDFI). This thesis is composed of five chapters, which seek to improve our knowledge of Eucalyptus tolerance and resistance to paropsine defoliation. The first chapter is a review of previous literature, followed by four separate, but interconnected chapters detailing experimental results, which are summarised in a final concluding chapter. In chapter one, my literature review identifies knowledge gaps, especially with regard to Eucalyptus tolerance and resistance (Lin (2017a) already reviewed differences in Eucalyptus species resistance in the North Island) to paropsine beetles in the South Island, what drives paropsine beetle preferences, and the way that defoliation is currently assessed in the field. These gaps led me to develop four main research questions, each of which was explored by one of the four subsequent chapters. My research questions were: 1. Are there Eucalyptus species, Eucalyptus bosistoana families, clones or even provenances that are more resistant or tolerant to paropsine defoliation? 2. Are there Eucalyptus species more tolerant to controlled artificial defoliation at different water deficit? 3. Is there a relationship between Eucalyptus foliar chemistry and paropsine defoliation? 4. Can remote sensing be used to reliably quantify Eucalyptus paropsine defoliation? In chapter two, seven Eucalyptus species from two subgenera (Symphyomyrtus subg.: E. bosistoana, E. camaldulensis, E. tricarpa, E. quadrangulata, and E. cladocalyx; Eucalyptus subg.: E. globoidea and E. macrorhyncha), 74 Eucalyptus bosistoana families and 132 Eucalyptus bosistoana genotypes (clones) were measured in the Marlborough region between December 2019 and March 2021 to investigate variation in their resistance and tolerance to paropsine defoliation. Resistance was measured with the Crown Damage Index (CDI) and tolerance was measured with growth (height gain, DBH gain and new stem length) over time. Compared to the Symphyomyrtus subgenus, the Eucalyptus subgenus was generally more resistant to paropsine defoliation, with the exception of E. cladocalyx. Eucalyptus cladocalyx, E. macrorhyncha and E. globoidea were the most resistant to paropsine defoliation. Eucalyptus bosistoana’s most resistant family and genotype were family 805 and genotype 839a. Eucalyptus quadrangulata, E. bosistoana, E. tricarpa and E. camaldulensis were all potentially tolerant regarding the new stem growth, whereas E. cladocalyx, E. macrorhyncha and E. globoidea were the most tolerant regarding the height and DBH growth. The E. bosistoana family 835 and genotype 24a were potentially tolerant. In chapter three, two Eucalyptus species (E. bosistoana and E. globoidea) were placed in a greenhouse for 101 days to test defoliation and water tolerance in a more controlled environment. Three artificial defoliation severity levels, two water levels and two defoliation frequency levels were applied. Tree growth (height and diameter gain), dry biomass (total, leaf, stem, root) as well as leaf carbon and nitrogen content were measured. Both species were negatively affected by water stress, meaning that planting these species in drylands will likely exacerbate the negative impact of paropsines. Nevertheless, E. globoidea was more resistant to water deficit and defoliation than E. bosistoana. Low levels of defoliation stimulated E. bosistoana biomass (overcompensation), but high levels of defoliation negatively impacted this species. E. globoidea may generate taller trees as a mechanism to tolerate defoliation, whereas E. bosistoana may produce trees with denser overall biomass (stem in particular) and narrower trunk. Compared to trees that had only been defoliated once, trees that had been defoliated twice grew less. This demonstrated that both species exhibit some elements of tolerance to defoliation, but E. globoidea is more tolerant than E. bosistoana. In chapter four, leaves from seven Eucalyptus species from two subgenera (Symphyomyrtus subg.: E. bosistoana, E. camaldulensis, E. tricarpa, E. quadrangulata, and E. cladocalyx; Eucalyptus subg.: E. globoidea and E. macrorhyncha) were collected in a trial from the Marlborough region to study the potential relationship between foliar chemistry and paropsine defoliation. The leaves were then oven-dried, ground, extracted with ethanol and analysed with a High Performance Liquid Chromatography (HPLC). The Eucalyptus subgenus Symphyomyrtus and Eucalyptus foliar compound diversity were distinct. These preliminary experimental results suggest a relationship between foliar chemicals and paropsine defoliation. Defoliated species had higher foliar compound concentration and richness than non-defoliated species, except for E. camaldulensis, which displayed low foliar compound concentration and richness despite being significantly defoliated. Two compounds specific to E. cladocalyx may be paropsine repellent. In chapter five, six Eucalyptus species from two subgenera (Symphyomyrtus subg.: E. bosistoana, E. camaldulensis, E. tricarpa, E. quadrangulata, and E. cladocalyx; Eucalyptus subg.: E. globoidea) were measured in a trial from the Canterbury region with three LiDAR sensors to assess the potential of this technology to accurately detect defoliation. LiDAR data were compared to Crown Damage Index (CDI) field measurements to assess its prediction accuracy. The 5 % accuracy difference among the three LiDAR sensors under evaluation indicated that each could be useful for predicting paropsine defoliation and show good promise for further experiments. The most effective LiDAR metrics for predicting paropsine defoliation on Eucalyptus trees were itot, zimean, imax, imean, and isd, with zkurt, zpcum2 to zpcum9, p1th to p3th, pzabovemean, pzabove2, and ipcumzq10 to 70 being less useful. All of these metrics are related to either tree height or foliage density (canopy cover). My results contributed to a better understanding of tolerance and resistance to paropsine beetles within Eucalyptus. This contributes to limiting the effect of paropsines on the Eucalyptus forest industry. These findings are a valuable starting point to deeper exploration and guiding future Eucalyptus breeding in terms of paropsine herbivory.
  • ItemOpen Access
    Reconstructing phylogenetic networks.
    (2023) Bai, Allan M.
    Phylogenetic networks are a generalization of phylogenetic trees that allow for reticulation. Reconstruction of phylogenetic trees from distances is well studied, but for networks, there are relatively few results. Recent results have focused on restricting the space of phylogenetic networks to speci c subclasses with desirable properties, in particular, normal, tree-child and orchard networks. In this thesis, we explore new methods of reconstructing phylogenetic networks, as well as extend existing reconstruction results beyond these classes. Orchard and temporal networks play a signi cant role in phylogenetic results, as they provide enough restrictions to exclude undesirable structures, whilst still having enough complexity to maintain mathematical interest. However, little is known about the structure of these networks. In particular, there are few structural characterisations for these networks. The rst part of the thesis outlines forbidden structures characterisations for orchard and temporal networks. The second part of the thesis explores reconstruction of phylogenetic networks using distance. We extend the results of Bordewich et al., and show that equidistant semibinary normal networks can be reconstructed using their minimum distances. We also show that equidistant orchard networks can be reconstructed using distances, up to an equivalence class known as sinks. Finally, the last part of the thesis considers reconstructing phylogenetic networks from the relative unexplored information type of ancestral pro les. We show that like distances, stack-free phylogenetic networks can be reconstructured using ancestral pro les, with the exception of some special structures.
  • ItemOpen Access
    Evaluating the feasibility of mediated microbial fuel cells driven by thermoacidophilic methane removing biotrickling filters.
    (2023) Gilbertson, Fletcher
    The following thesis investigates the feasibility of a microbial fuel cell (MFC) driven by thermoacidophilic methane removing biotrickling filters (BTFs) and chemical mediators. MFCs are primarily explored for wastewater treatment applications, generating electricity from an otherwise energy-consuming process. Methane is a potent greenhouse gas abundant in biogas from anaerobic digestion in wastewater treatment. Methane abatement in this industry primarily consists of flaring to less potent CO₂, due to corrosive contaminants (H₂S) commonly found in biogas. Alternatively, methane can be converted to CO2 while also generating electricity using methane-fed MFCs. The feasibility of methane-fed MFCs to treat biogas and other waste methane sources is hindered due to poor water solubility. One strategy to improve methane removal efficiencies is to utilize BTF reactors, which employ microbial biofilms in contact with gaseous compounds to improve mass transfer. By combining BTFs with MFCs, methane abatement, and thus, power density of the technology, could be improved. However, to capture electrons released from microbial methane degradation in the BTF, a method to bridge electron transport is required. One method is to utilize chemical mediators, which bridge electron flow from BTF biofilms to the electrode. For a mediated MFC and BTF to be feasible, a suitable methane-degrading organism with the ability to transfer electrons quickly to mediators is required. Methane-degrading organisms (methanotrophs) are ubiquitous in nature; however, thermoacidophilic methanotrophs are rarely investigated in biotechnical applications. Moreover, thermoacidophilic methanotrophs are naturally acclimatized to sulfur environments/compounds such as H₂S, which are commonly found in biogas and are inhibotry to mesophilic methanotrophs. Thus, thermoacidophilic methane removing microbial communities in BTFs were enriched, and used along with mediators for power generation in a MFC and BTF design for treating waste methane emissions. Thermoacidophilic methane removing microbial communities were enriched in BTFs independently of MFCs, using geothermally active soil from Rotokawa, New Zealand. Four BTF reactors were operated under both microaerobic (2% O₂) and aerobic (10% O₂) conditions for 2 years, with methane elimination capacities (ECs) between 7.6–30.7 g m⁻³ hr⁻¹ under non−limiting conditions. Microbial communities in all reactors were dominated by Verrucomicrobiota thermoacidophilic methanotrophs (Methylacidiphilum). Enriched BTF communities were screened for mediator reduction, using thionine acetate, methylene blue, and neutral red, showing reduction rates up to 0.023 mmol hr-1 g-biomass⁻¹. Limiting current and spectrophotometric methods were employed to monitor mediator reduction kinetics. Thionine acetate reduction rate was superior among all mediators examined and demonstrated first-order kinetics based on electrochemical monitoring. Mediator reduction was independent of methane oxidation, and dosing with the glycolytic inhibitor iodoacetamide partially ceased thionine reduction. Investigation of thionine in BTFs demonstrated that reactor biofilm could reduce thionine under low O₂ (< 0.1% v/v) conditions over multiple cycles. BTF microbial communities were acclimated to carbon felt anodes in a dual-chamber MFC with O₂ reduction at abiotic carbon felt cathodes. The combined thermoacidophilic BTF and MFC produced maximum power densities between 4.6−7.9 mW m⁻² and cell potentials of 0.37-0.45 V. Under micaerobic conditions BTF reactor EC was not inhibited by thionine presence; however, methane removal was undetectable during intermittent (1-5 day) O₂ starvation. The results of this thesis demonstrate a proof-of-concept of a combined BTF and mediated MFC for electricity generation and methane abatement using thermoacidophilic aerobic methanotroph communities. Moreover, electrochemical monitoring of bulk mediator reduction in suspended cultures, seeded from BTFs, revealed the dependence of mediator reduction on glycogen metabolism. These findings guide further development of methane-fed MFCs utilizing BTFs and reveal the microbial mechanisms driving mediator reduction in suspended communities.
  • ItemOpen Access
    Control of grid-side converter for type-IV wind turbine connected to AC systems
    (2023) Wang, Hailong
    Voltage source converters (VSCs) are widely used in renewable energy conversion systems, such as wind generation and photovoltaic systems. Rich wind and solar resources are often located in remote areas and far from the load centres in many parts of the world. For integrating bulky renewable power into grids, hundreds of wind turbines (WTs) or solar generation units are grouped and tied to AC systems via long transmission lines, which results in a relatively low SCR (Short Circuit Ratio). The direct drive permanent magnet synchronous generator (PMSG) Type-IV WT is increasingly used due to its high efficiency and low maintenance. To output active power captured from the turbine and exchange reactive power with the AC system, the gridconnected converter of the WT must be synchronized with the grid. The synchronization can be achieved through two different types of schemes: Grid-Following (GFL) and Grid-Forming (GFM). However, the present GFL control schemes are inappropriate for weak grid conditions. The analysis shows that the GFL control scheme is a conditionally stable system and cannot drive the converter output current toward the synchronous state after the asynchronous state transition. Although the GFM converter technology achieves better stability in a weak grid than the GFL control, there are still more realistic problems and challenges when applied to Type-IV wind turbines. Unlike previous work, this thesis introduces a novel synchronized approach of the gridside converter with an AC system based on the newly defined concept of instantaneous magnitude and phase. This method only uses local measurement variables (DC terminal voltage, AC terminal three-phase voltage and current) and local reference commands (DC voltage, AC voltage magnitude and active-reactive power). The synchronization can be achieved by controlling the converter terminal active-reactive power and instantaneous voltage magnitude to their reference value. The system model is developed in the dq-frame with a fixed angular speed and is valid for synchronous and asynchronous states. Two nonlinear power control algorithms based on the instantaneous magnitude and phase of three-phase signals are presented to regulate the power outputs to track their references. One method achieves power regulation through an inner current control loop and another directly by a power control loop, namely direct current control (DCC) and direct power control (DPC) based on instantaneous magnitude and phase, respectively. The stability of these two control schemes in the whole system are proven via the Lyapunov theory. In the proposed DCC control scheme, the control of the GSC’s instantaneous active and reactive power is realized indirectly through the closed loop of the current. The output current of the GSC can be controlled quickly and accurately in a wide range of grid conditions. This control scheme has a simple control structure as it does not require complex mathematical models and calculations. Under unbalanced grid conditions, the novel current control scheme is proposed and includes two current controllers, a central controller, and an additional compensation controller. The central controller does not involve positive and negative sequence separation. The compensation controller is specially designed for controlling the negative-sequence current and is only activated when the voltage unbalances are detected. To obtain a fast and direct power transition trajectory control, DPC based on the instantaneous magnitude and phase control algorithm is proposed. Unlike the proposed DCC control method, DPC does not need to convert power variables into current variables but directly adopts instantaneous active and reactive power as dynamic control variables. Compared to the DCC scheme, the proposed DPC control method has the advantages of good robustness and fast power response. A limitation of the conventional DPC control approach, based on real and reactive variables, is that it does not provide inherent overcurrent limiting capability. A novel current limiting strategy for the proposed DPC control to overcome this drawback is presented. Simulation results using PSCAD/EMTDC demonstrate that the grid-side converter using the proposed control schemes are superior to the traditional vector current control and the state-of-the-art DPC control in the literature under various grid condition, i.e., a wide range of SCR (SCR≥1), temporary grid faults, large grid impedance varying and grid frequency drift. Additionally, the proposed control schemes can easily be retrofitted into the existing GFL VSCs without needing any extra hardware.
  • ItemOpen Access
    Nonlinear respiratory airway resistance and breathing effort estimation for respiratory disease monitoring and care.
    (2023) Lerios, Theodore
    This thesis presents a comprehensive study on the topic of nonlinear respiratory airway resistance and breathing effort estimation for respiratory disease monitoring and care. This section provides a concise overview of the main contributions of this study, insights gained, and discusses their potential impact on the field of respiratory disease monitoring and care using model-based, patient-specific methods. Presently, spirometry is widely regarded as the foremost standard for diagnosing COPD, with a focus on identifying a reduction in lung function by measuring the FEV₁/vital capacity (VC) ratio and employing methods based on linear airway resistance. However, incorporating nonlinear resistance modelling may offer valuable insights into an individual patient’s condition and the progression of the disease. Analysis of plethysmographic patient data with nonlinear modelling successfully identifies flow limited COPD patients with a nonlinear expiratory resistance in Chapter 5. Nonlinear modelling can provide novel insight into COPD patient-specific lung mechanics and potentially provide patient-specific, model-based metrics suitable for regular monitoring of COPD and lung status; and thus the ability to track disease state/progression. Chapter 6 introduces a novel approach to estimate work of breathing (WOB) and elastance (E) from plethysmographic data, aimed at developing a diagnostic and monitoring tool for COPD patients. The proposed method employs nonlinear modelling. There are novel further induced metrics using patient specific models which can be used to track disease and, using work of breathing, are directly related to patient specific feelings of disease management, as well as to critical or/and key clinical metrics such as WOB. While expiration is typically regarded as a passive process, some degree of expiratory flow is generated through patient effort, referred to as expiratory effort. Like expiratory resistance, expiratory effort is nonlinear in nature and requires modelling using nonlinear methods. In Chapter 7, a successful approach is presented for identifying nonlinear expiratory effort in flow-limited COPD patients, utilising nonlinear modelling techniques. These findings, combined with methods for estimating nonlinear resistance, may offer a valuable alternative for identifying COPD patients without the need for spirometry. Expiration is not a passive process in disease states like COPD and FL COPD, which means modelling must be able to account for this issue, which is typical of all lung mechanics model assumptions, and thus typical of models developed for healthy subjects which in turn are not optimal for dysfunction. Chapter 8 investigates the presence of nonlinear resistance in expiration for patients who have undergone mechanical ventilation (MV). A large subset of patients undergoing MV have underlying COPD. The aim of identifying this nonlinear expiratory resistance in MV patients is to improve optimisation of MV through model-based methods, reducing ventilator induced injury, and improving care. The expected result of translating methods from Chapter 5 to Chapter 8 was not realised without the quantification of inspiratory effort. There are potential areas where the key results translate to in hospital fully MV patients, but they require further modelling for some MV modes. However, the results can be generalised or have the potential to be generalised. This outcome contributes toward the aim of a single useful model in all or most all dysfunction scenarios. Chapter 9 presents three attempts at quantifying non-invasive, model-based estimation of patient effort in the MV patient data using esophageal pressure measurements. Each of the three methods had their respective trade-offs. While none of the methods demonstrated an ideal solution across all patients in the data, the second analysis provided the best overall approach. The models and methods presented can be translated to MV patients and initial invasive validation efforts showed good, though not perfect correlation where errors are attributable to model errors or assumptions made to ensure models remain identifiable and thus clinically useful. These final results show the trade-off of modelling efforts for accuracy with maintaining identifiability to ensure clinical utility.
  • ItemOpen Access
    Experimental and numerical study on an innovative multiple U-shaped flexural plate seismic bracing device.
    (2023) Chen, Yan
    The concept of seismic-resilient structure has perpetually held significant importance in maintaining the safety and durability of buildings. While most conventional seismic-resistant structures are capable of achieving one key aspect of seismic resilience, namely “robustness”, they often lack the attributes of “redundancy” and “rapidity of repair”. In recent decades, the incorporation of metallic dampers into conventional structures has significantly enhanced their seismic resilience. U-shaped flexural plate (UFP), recognized as one of the most effective metallic dampers, has been widely employed in conventional structures to effectively dissipate input seismic energy. Its innovative application, multiple UFP dissipater (MUD), in the form of a bracing member, not only offers superior strength, stiffness and energy dissipation capacity compared to conventional bracing members but also aligns with the seismic-resilience principle of “redundancy” and provide easier repairability. However, there is lack of comprehensive experimental and numerical research on both UFP and MUD. This research aims to address this gap by focusing on two parts: conducting experimental investigations on four full scale MUD specimens subjected to quasi-static cyclic load at various loading sequences and performing numerical studies on both single UFP and MUD member under monotonic load and cyclic load using ABAQUS. The experimental tests demonstrate that the MUD is capable of achieving its theoretical capacity and exhibits stable and repeatable hysteretic behaviour. It can dissipate significant amounts of energy, even after the individual UFPs have fractured. MUD has the potential to prevent sudden failure, as reductions in capacity and stiffness are gradual and the failure of an individual UFP does not result in the failure of the entire brace. In the numerical studies, reliable models of both UFP and MUD were developed and validated against the experimental results. The local deformation behaviour of UFP during rolling motion is discussed in details, including the transformation of the yield area, deformed shape and stress distribution. Furthermore, a parametric study was performed to investigate the effect of UFP geometry, specifically the slenderness ratio and section modulus of the UFP flange, on the amount of flange deflection. Additionally, the relationship between the overall stiffness of MUD and the stiffness of its individual components was analysed.
  • ItemOpen Access
    Modelling temporal networks with scientific machine learning.
    (2023) Smith, Connor
    Temporal networks appear in applications ranging from symptom prediction to social networks to epidemiology. This thesis proposes a flexible framework for modelling temporal network progression which utilises a combination of singular value decomposition, scientific machine learning, and symbolic regression. We demonstrate the usefulness of the framework for modelling the progression of a variety of small temporal networks. Additionally, we present a Julia programming package for streamlining work with temporal networks. This thesis demonstrates our framework as a proof of concept, and we are confident that with further research, this framework will be a useful tool for modelling temporal networks in many fields.
  • ItemOpen Access
    Determining the efficiencies of airborne droplet collectors in spray drift analysis using CFD.
    (2023) Williams, Reid Thomas
    Airborne sampling collectors are commonly used in spray drift analysis to measure the concentration of an airborne product, such as pollen or spray, by collecting the mass of the product during the sampler's operation. To help improve the accuracy of spray drift analysis, the collection efficiencies of airborne droplet sampling collectors were evaluated using computational fluid dynamics (CFD). The collection efficiency is defined as the ratio of the measured concentration to the actual concentration of the airborne product in the sampled air. This study aimed to evaluate the effectiveness of the string, flat plate, and Rotorod air sampling collectors for spray drift analysis. The collection efficiency of each sampler was modelled for a range of droplet sizes (25 − 1000 μ𝑚) and atmospheric boundary layer (ABL) conditions (𝑧0=0.02 − 3.08 𝑚), which resulted in a mean airspeed range observed at the height of the samplers of 0.340 – 5.120 m/s. The Stokes number was used as the metric for analysis, and measurements of the collection efficiency were obtained using Lagrangian particle tracking on precomputed flow fields. The results demonstrated that the string sampler exhibited more consistent collection efficiencies across the simulated Stokes range in comparison to the other samplers. Additionally, it demonstrated good agreement with prior correlations and expressions, whereas the flat plate and Rotorod deviated from their respective correlations. Collection efficiencies exceeding 100% were observed for all samplers, particularly at high Stokes numbers, which had not been previously explored. This was attributed to the samplers processing a larger area of upstream flow due to their influence on the surrounding flow field, as well as the trajectory of the spray cloud through the sampling region. When processing the results through an impaction splashing model to account for mass collection losses, the certainty of the sampler's measurements significantly reduced when the splashing criterion was reached. This effect was most pronounced with the Rotorod, which reached the splashing criterion at a low Stokes number due to its rotational motion. This study contributes to a better understanding of the performance of different air sampling collectors, which can aid in improving the measurements of spray drift and spray control measures.
  • ItemOpen Access
    Does Topology Provide Sufficient Structure for Non-Causal Explanations?
    (2023) Jha, Aditya
    There is a major debate as to whether there are non-causal mathematical explanations of physical facts that show how the facts under question arise from a degree of mathematical necessity considered stronger than that of contingent causal laws. Topology provides an ideal ground for such purported non-causal explanations since topological manifolds, on which the parameters of a dynamical system can be modelled, are typically associated with multiple invariants, which remain unaltered even if the manifold is bent, stretched or twisted, reflecting a change in the parameter modelled on the manifold. Understood in this sense, topological explanations seem to provide modal information about certain constraints on the system that may not be evident in detailed, and often, cumbersome causal explanations. This thesis examines some foundational issues in the applicability of topology to the natural world and their bearing on the debate on such purported non-causal (mathematical) explanations. More specifically, this thesis looks into various topological and geometrical formulations that essentially exploit the geometry of oscillating and complex systems, as an exercise in ‘geometric mechanics’, to provide a simple explanation of certain constraints imposed on their dynamics by the virtue of their geometry. The central question answered in this thesis is whether topology provide sufficient structure for such non-causal explanations. The answer, as the thesis demonstrates, is negative because topological explanations critically rely on idealisations, such as continuity and smoothness, which are realised only contingently in the natural world (or in mathematical approximations/models of the natural world); these idealisations impose some foundational limitations on the application of topology in modelling such systems ‘non-causally’. Consequently, purported topological explanations fail to fully circumvent the causal dependencies of such systems implying that these are not really ‘non-causal’ explanations. This thesis also extends the argument to mathematical explanations in general. It argues that purported mathematical explanations are essentially causal explanations in dis- guise and are no different from ordinary applications of mathematics to the natural world. This is because these explanations work not by appealing to what the world must be like as a matter of mathematical necessity, but by appealing to various contingent causal facts. These contingent facts, although assumed away in the why-question pertaining to a physical fact, still participate as causal facts in an explanation of why the fact obtains in the world. That is, the explained physical fact does not obtain because of a mathematical necessity but by appeal to the world’s network of causal relations.
  • ItemOpen Access
    Transverse velocities and shear stresses in river bends
    (2000) Plew, David Russell
    Expressions are presented for the transverse velocity profile and the transverse bed shear stress in a channel bend. These expressions are obtained from the momentum equations by assuming a logarithmic longitudinal velocity profile. The boundary conditions and expressions for eddy viscosity are consistent with the logarithmic longitudinal velocity profile. As a result, the transverse bed shear stress can be calculated without the need to use ratios of near-bed or slip velocities. The influence of non-zero depth-averaged velocities are included in the expressions. As a result, the expressions for the transverse velocity profile and transverse bed shear stress are not limited to situations of fully developed bend flow, as is the case with several previous profiles. The expression for the transverse velocity profile is verified by field experiments using acoustic doppler velocimeters to measure velocity profiles in two stream bends. A simple meandering stream bed topography model is developed illustrating how the expressions for transverse shear stress can be used. This topography model uses an analytical solution to the depth-averaged momentum and continuity equations to calculate depth_-averaged velocities. The shear stresses are calculated using the method presented in the thesis. Topography is calculated from sediment continuity. The use of a sine-generated curve to describe river meander geometry is briefly discussed. Regime equations are combined to give predictions of meander geometry from a known discharge and valley slope. Finally, results of experiments exploring behaviour of meandering channels in a sand tray are presented, illustrating various aspects of bed hydraulics and sediment movement.
  • ItemOpen Access
    Circular supply chains : enhancing consumer participation.
    (2023) Robertson, Juliet
    With increasing necessity for the world to respond to environmental crisis, environmental guardianship is essential and can be achieved through the circular economy (CE). The CE is defined by a rethinking of how resources are used, proposing a system of cascaded resource use and reuse, to fuel economic prosperity without depleting the earth’s resources. This is achieved through a circular consumption model that is in stark contrast to the traditional linear consumption model. To allow this change in society’s consumption, firms’ supply chains must also undergo change. The transformation of linear supply chains to circular closed-loop supply chains is on the horizon for many firms and is the topic of significant discussion within supply chain management research. An area that can be considered under-researched in this topic is that of consumers returning materials to the supply chain. As a result, this research addresses the question of how firms can invoke stronger consumer engagement in returning materials in closed-loop supply chains. To consider the consumer propensity to return materials, the extended theory of planned behaviour (ETPB) is employed as the theoretical lens. This study therefore focuses on the factors that influence consumers’ intentions to return materials. These include the traditional theory of planned behaviour factors as well as ‘habits’ and ‘moral norms’ that were expected to offer further explanation in this context. A survey, designed on Qualtrics, was created to collect data for quantitative analysis. The ‘intention to return’ dependent variable was investigated for three product categories that survey respondents used in their lives. Focus was given to product categories that are ‘low-involvement’, meaning little care is given to their purchase and their end-of-life. The three products were single-use coffee pods, printer cartridges and batteries. Data was collected from respondents who are users of these products from New Zealand and Australia, recruited through the Prolific platform. Research contributions are relevant to both supply chain practitioners moving towards a closed-loop system and for further research in the arena. The results showed a consistently significant influence from two variables across the three parallel studies: perceived behavioural control and moral norms. Given the minimal influence of other variables, this indicates a limitation to traditional consumer behaviour models on consumers engaging in low-involvement behaviours. Implications of these findings are in the theoretical, practical and policy realms. Potential applications of the findings are given throughout the discussion of results. A key contribution is the recommendation of robust policy to achieve the CE in New Zealand in regard to these unique goods.
  • ItemOpen Access
    Acting aids in virtual production.
    (2023) Moisset, Sylvain
    Previous research has shown how using virtual production could solve some of the inherent problems that suffers the traditional film making workflow mainly by bringing more flexibility to the overall process, allowing more iterative work and more communication between all the departments involved. That being said, studies have also shown that for actors, working on a film that involves visual effects can put a lot of strain on their concentration and attention and lead to a frustrating experience for them and potentially less optimal results for the film. This project’s aim is to study if a virtual production setup can be used to provide actors, in a visual effects film making environment, with acting aids in the form of visual cues on a display. It also aims at studying which cues are more helpful for actors. A simple setup was designed to mimic the experience of acting in a professional virtual production volume. The system includes the possibility of displaying different cues within the virtual production environment. A user study was run on a sample of actors to identify if cuing using a virtual production setup leads to better results. Experts opinions were collected during the design phase of the project to assess the relevance of the project and get directions for the design of the prototype and the use study.
  • ItemOpen Access
    Visual-inertial odometry for windblown vegetated environments.
    (2023) Schofield, Sam
    Aerial manipulation (performing interaction tasks with unmanned aerial vehicles) can revolutionise the forestry and arboriculture industries by automating tree pruning and similar tasks. A major challenge currently preventing aerial manipulation from being used in these industries is the inability to accurately estimate the UAV's pose (position and orientation) in the target environments, specifi cally those with abundant wind- blown vegetation. Standard methods of UAV pose estimation, such as GPS, do not provide enough precision to allow aerial manipulation, while more precise methods, like visual odometry (VO), do not work reliably in environments dominated by such scene motion. This work takes several steps towards remedying the latter problem. First, a novel approach was proposed for aligning a motion-capture rigid body with the optical centre of a camera. The proposed method was more accurate than the existing approach and removed the need for a specially prepared calibration target. This work enabled more accurate ground truth trajectories to be captured and was also used when lab-testing a tree-pruning UAV that used a combination of camera and motion capture data for navigation. Next, a novel analysis of the state-estimation requirements of UAVs was performed to determine how existing VO algorithms would need to be improved to enable aerial manipulation in windblown vegetated environments. Preliminary experiments, completed in simulation and then verif ied using a real UAV, showed that VO accuracy was not a bottleneck to UAV position-hold performance in normal operating conditions. This result directed later research to focus on improving the robustness of VO in dynamic vegetated environments (such as forests) instead of trying to improve VO precision further. Several state-of-the-art visual-inertial odometry (VIO) algorithms were evaluated in scenes containing moving vegetation to determine whether existing algorithms met the desired robustness requirements. A preliminary analysis was performed using real data, followed by a more in-depth evaluation using a semi-synthetic dataset (consisting of real IMU data and synthetic images). These experiments con firmed the assumption that existing VIO algorithms were not suitable for use onboard a UAV performing manipulation tasks in a windblown forest. While generating the aforementioned semi-synthetic dataset, a major aw in existing methods for producing semi-synthetic data was discovered and addressed. A detailed comparison showed that VIO algorithms that were evaluated using data generated with the proposed approach performed signi ficantly (79%) better than when evaluated using data generated with existing methods. Finally, a novel outlier detection method was proposed that utilised the difference in nature between camera and scene-motion-induced optical ow. Experiments showed that, when used as a pre-processing step to RANSAC, the proposed method signi ficantly improved visual odometry accuracy (up to 20%) with minimal computational overhead in windblown forest environments.
  • ItemOpen Access
    Non destructive evaluation of Nothofagus fusca (red beech) wood properties within the North West Coast of the South Island, New Zealan
    (2005) Silcock, Paul
    This study is comprised of two major research objectives: 1) to quantify the incidence and proportion of defect in beech forests and explore the efficacy of applying defect detecting technology to natural forest management; and 2) to identify and assess those physical and mechanical wood properties of red beech that influence wood quality and forest operations from two sites (Howard valley and Wooly river) managed by Forever Beech Ltd. Overall there is a significant incidence of defect (56 %) in standing red beech and a low stem-to-timber conversion rate (40 %). An acoustic tomographic tool, Fakopp 2D, can be used to detect the presence of internal defect in standing trees, although the software used in this study was not able to consistently predict the location or volume of defect, it was a cumbersome instrument to use in the forest and data collection was a slow process. No case could be made for incorporating this technology in beech forest management practice. Four wood quality properties were used to assess beech forest in the NW Coast of New Zealand. Basic density and hardness are measures of wood quality and quantity on which many end-use and customer specifications are based. Green density is a measure of wood quantity which is used in forest operations to determine log bucking patterns for heli-lifting. The green dynamic modulus of elasticity (MOE) is another useful measure of wood quality, assessed using the TOF instrument - TreeTap. Measuring stress wave velocity (SWV) in standing red beech using time of flight (TOF) instruments provides a means to evaluate wood quality prior to harvesting. Forests of the North West (NW) Coast of the South Island were found to have low average basic density in comparison to average national values. Basic density and associated wood properties exhibited greater variation between trees than between sites. Trees sampled in the Wooly river site had higher basic density, green density, MOE and hardness values than those growing in the Howard valley. The trees of Wooly river also exhibited higher growth rates and a lower incidence of defect. All assessed wood properties of red beech decreased with altitude. MOE increased with increasing growth rate. These data provided for customer specifications and the operations and management of Forever Beech Ltd. The advantages of using MOE as a measure of timber quality are discussed.