Engineering: Theses and Dissertations

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  • ItemOpen Access
    The effect of thermomechanical processing parameters on the texture of Ti-6Al-4V forgings as a precursor to coarse grain growth.
    (2023) Wiley, Richard
    This thesis explores the relationship between forging parameters - total strain, strain rate, and forging temperature - and the emergence of abnormal grains during subsequent heat treatment of Ti-6Al-4V. Abnormal grain growth can compromise material properties, making its understanding crucial for optimizing manufacturing processes. Through systematic experiments, varying the forging temperature between 875 and 975°C and the strain rate between 0.1s⁻¹ and 10s⁻¹ , the study reveals how different forging conditions influence the as-forged microstructure through the alteration of the kinetics of flow softening and how this affects abnormal grain formation. Microstructural analysis through optical and scanning electron microscopy methods demonstrate correlations between these forging parameters and the occurrence of non-uniform grain distributions. The insights gained offer strategies to mitigate abnormal grain growth during heat treatment, advancing materials science and manufacturing practices. The results show that forging temperature and strain rates impact prior beta grain size differently. Higher forging temperatures at 975°C lead to larger grain sizes due to increased boundary mobility favouring grain growth. Lower forging temperatures at 875°C produce more consistent grain sizes due to uniform boundary energies resulting from a weaker texture. For samples forged at 925°C, varying strain rates cause significant differences in grain size due to the shift from dynamic recovery to dynamic recrystallisation as the primary strain relief mechanism. This shift in mechanisms is also reflected in stress-strain responses, with dynamically recrystallised samples showing higher peak stress and more transience. The dynamic recrystallisation process leads to the nucleation of strain-free grains with distinct orientations, contributing to a weaker textured material. The study validates that abnormal grain growth is influenced by strain rate and forging temperature, with increased strain-strengthening precursor texture. Lower forging temperatures lead to weaker texture and more normal grain growth. From the findings, it is recommended to forge above critical rates for recrystallization, at the required forging temperature. The research suggests forging above 5s⁻¹ up to 925°C or 0.95 Tβ, although this is adjustable to 0.1s⁻¹ at 875°C/0.9 Tβ. Billet size indirectly affects abnormal grain occurrence by affecting the strain rate, with smaller billets displaying uniform grain size after annealing. Thus, changes in the thickness of Ti-6Al-4V parts could cause abnormal grain growth in thicker sections during annealing and should be considered prior to forging.
  • ItemOpen Access
    The biofactory : implementing a life cycle sustainability assessment decision making tool for quantifying integral sustainability benefits of the wastewater circular economy in Chile.
    (2023) Furness, Madeline
    The “Biofactory” is a circular economy-based concept for wastewater treatment that improves water quality, promotes efficient use of materials and energy, recovering resources, generating stakeholder collaboration, and decreasing both emissions and costs. This proposes a solution for the global challenge of integrated water and sanitation management. Due to socio-economic bottlenecks, such as typical high costs and low public acceptance of novel resource recovery scenarios in wastewater treatment, realizing the Biofactory goals becomes a difficult task. Decision makers are currently unable to appreciate the environmental and social benefits of the Biofactory, as most decision-making tools focus on mainly technical and economic aspects. This research is the first to quantify integral sustainability benefits of co-product recovery of treated effluent, biosolids, biogas and nutrient in two full-scale “Biofactory” wastewater circular economies in Chile. Life Cycle Sustainability Assessment (LCSA) was implemented, combining Life Cycle Assessment (LCA), Social Life Cycle Assessment (SLCA) and Life Cycle Costing (LCC) with a Multi-criteria Decision Making (MCDM) model to quantify integral environmental, socio-cultural, and economic sustainability impacts of two Plants, A and B. Three scenarios for each plant were considered, discharge of wastewater without treatment, conventional wastewater treatment with no resource recovery, and biofactory wastewater circular economy configurations, to determine if each plant decrease impacts and determine which had better performance. LCA results showed Plant A decreased overall environmental impact by -37 % compared to baseline conventional scenarios, while Plant B -31 %. SLCA results showed Plant A decreased social impacts – 56 %, while Plant B – 18 %, therefore, Plant A had better overall environmental and social performance. However, Plant B decreased economic impacts by -48 % compared to an increase of 20 % in Plant A. Therefore, when combining scores using a MCDM model, Plant A decreased total sustainability impacts by -30 % and Plant B by -58 %, therefore, the resource recovery systems implemented in Plant B had better overall sustainability performance. These results were discussed across process contributions to environmental, social, and economic benefits. Model limitations were discussed, and recommendations were made for future applications of this research. The investigation demonstrated that the transition to WW-CEs improved integral sustainability according to the LCSAMCDM model implemented in both Plants. The urgent need to adopt sustainable decision-making models was highlighted and discussed, to not only improve sanitation coverage, but also improve sustainability performance of the sanitation industry across the globe.
  • ItemOpen Access
    Teaching dance with mixed reality mirrors : comparing virtual instructors to other forms of visual feedback.
    (2024) Treffer, Anna
    This research aimed to assess whether a virtual instructor and visual feedback combination displayed on a Mixed Reality (MR) mirror can be used to teach a beginner a simple dance routine, replacing the traditional instructor and mirror methods. A prototype was developed using a camera and projector that displayed a digital mirror image of the participant as they learned dances, with the system able to overlay computer graphics onto the image. The camera used to capture the image and motion of the participants was a Microsoft Azure Kinect camera. Three visual feedback types were developed and used as randomized conditions in the user study based on input from expert interviews and an online survey. These were Spheres, Rubber Bands, and Arrows. Three simple dance routines were developed, motion captured, and presented in random order in the user study. During the user study participants learned the dances by following a virtual instructor in the MR mirror (present for each condition), with the MR mirror providing a different form of visual feedback for each dance. After practicing a dance three times with the feedback, participants then performed the dance in front of the MR mirror following the virtual instructor without any feedback, and the system measured the accuracy of their performance by comparing the amount of time that the user’s joints, such as shoulders and elbows, were within desired bounds for each pose. Participants filled out an AttrakDiff Questionnaire describing their experience for each form of feedback, and gave comparative opinions of the different forms of visual feedback in a final interview. The results showed that participants performed best with the Arrows feedback variant which were a directional feedback showing their depth difference, however they ranked this variant the lowest based on their own preference. The most preferred form of feedback was Spheres, which were the simplest feedback, not providing any guidance into the correct pose, but participants performed poorest with them.
  • ItemOpen Access
    Toward a numerical implementation of cauchy-characteristic matching
    (2024) Zidich, Jack
    Our modern understanding of gravity was first introduced in the early 20th Century by the pioneering work of Albert Einstein, who formulated the General Theory of Relativity. This began in 1905 with him reworking classical notions of space and time: from his two postulates that (1) the laws of electrodynamics and optics hold in all inertial reference frames, and (2) the speed of light in a vacuum is always the same, he showed it followed that these measures which were previously held to be absolute are actually relative to a particular observer or coordinate system [26]. While this original theory was only valid in the absence of gravity, and so would later be termed the Special Theory of Relativity, it was soon generalized in 1915, with the publication of the Einstein Field Equations (EFEs) [27] [29], to take this additional layer of complexity into account, and so to be capable in principle of explaining all the phenomena covered by Newtonian mechanics, in addition to providing new testable predictions, such as regarding the perihelion precession of Mercury, on which it was found to be in greater agreement with observations than earlier theories were. In the General Theory, space-time is described by the 10 components of a symmetrical 4-dimensional tensor, known as the metric, which describes how distances between points are determined. Gravity is understood then not as a true force, as it is in Newtonian gravity, but instead using the tools provided by differential geometry, in which gravity can instead be interpreted a property of the geometry of space-time, which is curved by mass- energy, with particles merely following geodesic paths through this geometry. While the most straightforward gravitational phenomenon is that of the curving of space-time by the presence of a massive body, as early as 1916 [28] Einstein additionally proposed the existence of gravitational waves: the radiation of energy from a system due to the periodic change in space-time curvature caused by the motion of massive bodies relative to each other. In most cases, these gravitational waves are exceptionally small, and indeed entirely negligible, however, for some of the most extreme astrophysical events, such as in the collision of black holes, this ceases to be true, with multiple solar masses worth of energy being radiated away. Interferometers have been built around the world to attempt to detect the gravitational waves emitted from such events, including LIGO in the United States of America [41], KAGRA in Japan [54], and VIRGO in Italy [57]. LIGO first observed a confirmed signal from a black hole-black hole merger in 2015 [42], and in the following years dozens more detections have been made, including of a neutron star-neutron star merger that was also observed in the electromagnetic spectrum by the Fermi Gamma-ray Burst Monitor [43]. Such gravitational wave astronomy provides a wide range of possibilities, both as a new way of testing the limits of General Relativity, and also of observing distant astrophysical events and objects, which previously could only be investigated via electromagnetic radiation. While currently this is limited to certain classes of black hole and neutron star mergers, the next generation of gravitational wave detectors, such as the space-based interferometer LISA that is planned to be launched in the 2030s [44], will not only increase the rate at which mergers are detected by orders of magnitude, but will also be able to detect new gravitational wave sources, including extreme mass-ratio inspirals and the gravitational background that originated in the early universe. Yet, while this field shows a lot of promise, even just making predictions out of Einstein’s theory is exceptionally challenging. The first full analytical solution to the EFEs, the Schwarzschild solution describing the curvature around a single non-rotating and uncharged point mass, was published in 1916 [52], only a short time after Einstein’s original proposal of General Relativity, yet it would take until 1963 for this to be extended to the case of a rotating mass [40]. To avoid these analytical complexities, a range of numerical approaches have been developed, yet these too are far from trivial - the biggest additional difficulty of numerical relativity, when compared to classical mechanics, is that time is not an absolute universal variable over which a simulation can straightforwardly be evolved, but is instead itself part of the variable space-time geometry. In this thesis I will be focusing on two of these numerical approaches in particular that are used in the context of binary black-hole simulations, as is needed for interpreting interferometer data. The first of these is BSSN [5] [53], one example of a 3+1 approach in which the 4-dimensions of space-time are ’foliated’ into 3-dimensional sheets between which it is possible to evolve (albeit with added complications, when compared with a classical simulation, as to how one moves between these sheets), which has found substantial success in simulating black holes - being used, for example, for one of the first full simulations of a binary black-hole merger [20]. Yet BSSN comes with certain drawbacks, in that it is computationally expensive when simulating large regions of space-time, as for example is needed in order to investigate the transmission of a gravitational wave from a distant source to a detector on Earth. The second approach I will look at, meanwhile, has the opposite problem. This is the characteristic formulation, which can easily be written in ’compactified’ coordinates, which allow for one to simulate across even an infinite distance in a finite computation time, but which is not capable of accurately evolving a simulation close to a source. To take advantage of the strengths of both of these approaches, while avoiding their weaknesses, it was proposed by Bishop in the 90s to take a mixed approach, combining the usage of both into a single simulation. Two possible ways of accomplishing this, termed Cauchy-Characteristic Extraction (CCE) [12] and Cauchy-Characteristic Matching (CCM) [11], were suggested, of which CCE has seen successful implementation in determining wave- forms from black-hole mergers [48]. CCM, however, has yet to see such success, with it’s viability even having been questioned recently [33], and it is this, along with the component BSSN and characteristic parts, which I aim to investigate in this thesis. In chapter 2, I will provide a literature review, covering the key past developments regarding CCM. Then, in chapter 3, I will describe my own numerical implementation. Here I begin in section 3.1 by briefly discuss the numerical tools I used for my Python implementation, highlighting in particular my usage of the COFFEE package. This is followed in section 3.2 by an in-depth treatment of the Cauchy side of CCM, building up from ADM to Cartesian BSSN and then to BSSN in spherical polar coordinates, as well as a discussion of my choices in gauge and initial data for the BSSN system, and the SAT method that I implemented as an approach to provide boundary data. Then, in 3.3, I will move on to the characteristic formulation, here building up from the Bondi-Sachs metric and providing an overview of the usage of spherical harmonics, before again looking at a possible choice for the initial data. Finally, in 3.4, I will turn to CCM itself, describing one suggestion for a gauge choice as well as the requisite coordinate transformation for moving between the BSSN and characteristic systems. On to chapter 4, I will give the results of my implementation, explaining my success at implementing both the BSSN and characteristic systems, and highlighting in particular the new results derived from my use of the SAT method for the BSSN system, but ultimate failure to fully develop a working CCM implementation. I will then summarise what I have accomplished in chapter 5, and also discuss future work that could be done on CCM based on my results.
  • ItemOpen Access
    Entering the realm of the wetlands: design and evaluation of engagement for a mobile augmented reality game
    (2024) Yin, Wenliang
    This thesis explores the potential of Augmented Reality (AR) in enhancing environmental edu- cation, with a focus on the conservation of New Zealand’s wetlands. Through the development and evaluation of a mobile AR game titled “NZ Wetlands Invasion,” this research investigates how different perspectives in the game impact player engagement and learning outcomes. Em- ploying a mixed-methods approach, the study integrates quantitative data from pre-test and post-test quizzes with qualitative feedback from participants to assess the effectiveness of AR in fostering environmental awareness and knowledge. Findings from this study reveal that the first-person view (FPV) in the AR game significantly enhances player engagement by providing a more immersive experience compared to the bird’s eye view (BEV). However, contrary to initial hypotheses, there was no significant difference in learning outcomes between FPV and BEV perspectives. This suggests that while FPV may offer a more engaging and immersive experience, both perspectives are equally effective in facilitating learning about wetland conservation. The research results also highlight the influence of environmental factors and physical comfort on the AR learning experience, underscoring the need for careful consideration of the physical and environmental context in which AR games are deployed. Additionally, the study addresses the concept of response shift bias, illustrating the complexity of measuring learning outcomes. In conclusion, this thesis contributes valuable insights into the design and implementation of AR in environmental education, offering recommendations for future AR game development aimed at engaging and educating users about environmental conservation. The findings suggest broader applications of AR in enhancing learning experiences across various domains, encouraging for the integration of immersive technologies in Game-Based Learning Environments(GBLEs) to boost a deeper understanding and appreciation of environmental issues.
  • ItemOpen Access
    Damping models for inelastic structures
    (1980) Chrisp, D. J. (David John)
    A comparative study of different damping models has been made in an effort to gauge the effect of the damping model on the inelastic response of multi-storey reinforced concrete frames. It will be shown that the higher mode response in an inelastic analysis cannot be ignored as it can in an elastic analysis and, in fact, affects the response markedly. As a consequence, the amount of damping imposed on the higher modes becomes important. Using a dynamic analysis program to analyse six and twelve storey one way frames keeping all other parameters constant, the amounts of damping in the various modes of vibration were varied. Elastic and inelastic analyses were carried out to contrast their response due to varying the damping modes. Through an analysis of the results, some recommendations are made as to the amounts of damping to be associated with the different modes of vibration to help obtain a realistic structural response.
  • ItemOpen Access
    Trust and trustworthiness while exchanging virtual items in shared augmented reality.
    (2024) Ritter, Marko
    This thesis is split into nine chapters, which contain the following contents: Chapter 2. The Background chapter collects relevant insights from scientific literature as they concern this thesis. Chapter 3. Roleplay as an experimental method will be explored. Because Fantasy storytelling is an unconventional choice for a scientific work, so reasoning will be provided there as well. Chapter 4. A Pre-Trial was conducted to substantiate that the chosen narrative does in fact model the intended variables. Chapter 5. The Design and Development of the AR-prototype is described in detail. This follows the principles of an established design process called "Double Diamond". Chapter 6. The hypotheses, the design, the quantitative measurements, and procedures of the User Study is outlined. Chapter 7. Results presents the data collected during the user study and evaluate them by statistical means. Chapter 8. The Discussion chapter will interpret the findings and attempt to answer the research question. It will discuss the findings’ limitations and how they relate to the scientific literature. Chapter 9. The Conclusion chapter gives a broad summary of the findings.
  • ItemOpen Access
    Daddy long legs : a scale and speed up virtual reality locomotion technique for medium-scale scenarios.
    (2024) Zhao, Yue
    This study investigates the effectiveness of a novel natural walking-based locomotion technique, "Daddy Long Legs," for navigating medium-scale virtual scenarios. While real walking remains ideal for such scenarios, prolonged use can become physically demanding and inefficient. Conversely, artificial locomotion methods often induce disorientation or fatigue that comes from abrupt viewpoint changes or repeated gestures. Drawing inspiration from previous research on Seven-League Boots and Ground-Level Scaling, both with documented advantages and limitations, this study proposes a combined approach. We believed that their strengths and weaknesses could be effectively balanced through careful design, but there has been a lack of comprehensive study in this area. A user study involving 24 participants was conducted, in which they were required to perform a series of walking tasks within a medium-scale virtual garden. Furthermore, they did a Pre-Experiment Questionnaire and Post-Experiment Questionnaires, along with a brief one-on-one interview that specifically addressed their feelings and preferences regarding all the methods. Results indicate that Daddy Long Legs outperformed Seven-League Boots in all aspects. Notably, Ground-Level Scaling yielded the most natural walking behaviour, received the most positive feedback, and emerged as the preferred method.
  • ItemOpen Access
    Development and validation of processing algorithms to delineate individual foot reactions from a single-belt instrumented treadmill to generate synchronised acoustic emission and lower-limb biomechanics data
    (2023) Sinclair, James Thomas
    The human hip joint plays a vital role in daily activities such as walking, standing, and running, contributing significantly to health-related quality of life. The joint's natural structure involves a ball- and-socket connection between the femur and pelvis, allowing for complex movements. Unfortunately, various factors, including trauma, wear, arthritis, and pathological conditions, can compromise the integrity of the hip joint, leading to conditions like osteoarthritis, developmental dysplasia, Paget's disease, and more. Hip osteoarthritis, a prevalent cause of debilitating pain, often necessitates primary hip arthroplasty, a surgical procedure replacing the natural joint with an artificial implant. As the aging population undergoes increasing hip arthroplasties, monitoring the prosthetic's condition becomes crucial. Traditional inspection methods, such as x-ray and CT imaging, have limitations, including radiation exposure and can only capture a single frame. The research performed explores the use of acoustic emissions (AE) as a non-invasive and continuous monitoring method for prosthetic hips. AE consists of “listening in” to the sound waves generated by the prosthesis during movement. Unlike other conventional imaging methods, AE allows for dynamic inspection of the prosthesis without subjecting the patient to ionising radiation. This research builds on previous work performed at the University of Canterbury by Dr. FitzPatrick, transferring the AE monitoring procedure from an overground gait on a stationary forceplate, to an instrumented treadmill to collect continuous, prolonged recordings with a steady state walking gait. This study addresses key objectives, including successfully transitioning to an instrumented treadmill while still collecting the same quality of data to what was performed by Dr. FitzPatrick, reliably separating the combined ground reaction force during the double support stage of the walking gait into the left and right foot contributions, and the identification and mitigation of artefacts introduced by the instrumented treadmill. Additionally, modifications were made to the foot delineation methods that improved the accuracy of the delineation calculation, reducing the mean error. In conclusion, this research advances the application of AE monitoring as a method for inspection of prosthetic hips by facilitating a larger data set to be collected allowing for future researchers to make broader conclusions on the features and trends observed from AE monitoring. These findings contribute to the ongoing efforts to enhance the reliability and longevity of hip prosthetics in an ageing population.
  • ItemOpen Access
    Computing non-square elements of square norm in a number field.
    (2023) Kent, Joe
    In this thesis we explore the unit group of the ring of integers of number fields. In our exploration we look at Dirichlet’s unit theorem which shows that the unit group is a finitely generated abelian group. This will allow us to explore computing the generating set of the unit group. From this basis we then extend the computation of unit groups to describe and implement an algorithm in PARI for finding elements in the kernel of the norm mapping K×/K×2 Q×/Q×2. Elements in this mapping are of particular interest for finding Brauer Manin obstructions with current implementations using a set of fundamental units.
  • ItemOpen Access
    Assessing the effect of visual accessibility features on player performance in videogames through simulating visual impairments.
    (2023) Fremaux, Andre
    This thesis evaluates the effectiveness of visual accessibility features in video games by measuring the player performance of participants who are experiencing simulated effects of Macular Degeneration with a Head Mounted Display. In this thesis, the following research questions are posed: • Q1: How does a non-visually impaired person’s performance playing videogames vary with and without simulated visual impairments? • Q2: How do accessibility features affect a person’s performance when playing games with simulated Macular Degeneration? A mixed methodology approach was used to evaluate the player performance across three types of videogames: First-Person Shooter, Racing, and 2D Platformer. For each videogame, the participant’s experienced three implemented accessibility features: Object Highlighting, Object Outlining, and Desaturation of the Environment. Participant interviews for each videogame were also conducted to gain insight into any changes in performance. Results indicate a difference in performance when participants played each videogame with simulated Macular Degeneration. However, even when accessibility features were introduced to mitigate or overcome the effects of simulated Macular Degeneration, performance was still negatively affected in the presence of simulated Macular Degeneration compared to playing unimpaired. Unfortunately, there is no quantitative or qualitative results that suggest any of the evaluated accessibility features significantly improved performance of users experiencing simulated Macular Degeneration.
  • ItemOpen Access
    Exploring the interface between engineering and the indigenous Maori dimension : a study concerning the seismic performance expectations of buildings for Ngati Toa and Ngai Tahu.
    (2023) Royal, Kākati Te Kākākura
    This thesis contains chapters which are associated with each research objective. Chapters generally build on each other and follow the general process of the research as it was carried out. Chapter 2 - A Cultural Statement: This chapter provides a comprehensive foundation for the thesis, connecting personal motivations, tribal priorities, and an institutional innovation process. Chapter 3 - Setting the research priority and context: This chapter highlights the crucial role of engineers in addressing New Zealand's challenges and opportunities, while simultaneously meeting the needs and values of Māori communities. It explores government policies, tertiary institution initiatives, industry efforts, and tribal organisations that aim to leverage Māori knowledge and assets. Chapter 4 – Current knowledge and practice to the engineering of buildings: This chapter discusses various methods for revising the design process and criteria to align with tribal performance objectives in the seismic design of light-framed timber buildings. Chapter 5 – Methodology: The chapter outlines a comprehensive methodology for incorporating indigenous Māori values and tribal seismic performance objectives into New Zealand's building regulatory system. This chapter introduces the Māori Performance Assessment Procedure (MPAP) as an adaptation of the (FEMA-P58-1, 2018) framework. Chapter 6 – Tribal Seismic Performance Objectives: This chapter provides essential clarifications of conducting tribal research within institutions and the challenges around representation. It then presents the results of interviews that were conducted to establish tribal performance objectives. Chapter 7: Design and Modelling of a Timber-Framed Building for Tribal Seismic Performance Assessment - This chapter outlines the design process and detailed model for light-frame wood buildings using state-of-the-art modelling software, Timber3D.
  • ItemOpen Access
    Forecasting the forest growing workforce demand within the Canterbury/West Coast region.
    (2023) Parkes, Heath
    The forestry industry has grown into becoming a major contributor to New Zealand’s economy and employment by becoming one of the country’s staple export earners. It is estimated that the industry currently employs over 40,000 individuals, this number has been rising steadily since 2015. Employment within the industry is heavily dependent on the export timber market in the short term and the area by age class distribution of the forestry resource in the long term and can at times create abrupt shortages in job-specific roles within the industry. A survey of the forest-growing workforce within the Canterbury/West Coast region was conducted in order to characterise the region's employment. A total of 42 businesses were identified during the study, of these businesses a response rate of 69% was achieved. Using data collected from the survey alongside publicly available information, a regional workforce forecasting model was developed in order to forecast regional demand between 2023 – 2053. Results were then analysed to determine the key trends in future workforce demand and more specifically demand which job roles experience the most fluctuation under the forecast conditions. Results showed that the majority of employment falls within forest harvesting and log transportation. It was found that these two sub-groups are affected the most by changes in wood availability, this is due to the fact that both harvesting and log transportation are completely reliant on future harvest volumes. It is expected that the Canterbury/West Coast forest workforce demand will contract significantly from 2023 – 2043 as regional wood availability reduces. Workforce demand is expected to recover from 2036 – 2044, however, still expected to be 23% lower than employment levels experienced during 2023. The Canterbury/West Coast forest industry needs to prepare for a reduction in forest harvest activity and employment. This research quantifies the impact of the decline in harvesting activity on those job roles associated with harvesting. The future trend in forest management and silviculture job roles also depends on the level of investment in new planting and replanting. Employment at the port depends on the volume of wood allocated to the export log market and to domestic processing. It is important to fully quantify how the workforce will be affected in order to make better decisions based on more robust data.
  • ItemOpen Access
    An assessment of ecosystem restoration at Styx Mill Conservation Reserve, Christchurch, New Zealand.
    (2023) Walters, Emma
    With human arrival in New Zealand, many indigenous flora and fauna have become extinct or endangered. The 90% loss of lowland wetlands, due to conversion and fragmentation, is of significant concern. Large-scale restoration efforts must occur across the country to preserve the remaining ecosystems and re-establish degraded areas. Styx Mill Conservation Reserve (SMCR), Christchurch, New Zealand is a remnant freshwater wetland where restoration activities are occurring. The progress of ecosystem restoration at SMCR will be assessed by understanding how species composition varies across the reserve, determining whether the restoration efforts are creating an ‘ecologically authentic’ representation of the historic ecosystem, and identifying whether, and where, natural seedling regeneration is occurring. A hierarchical cluster analysis used vascular species composition to identify four vegetation communities at SMCR (low forest, high grassland, riparian/marshland, and low shrubland). An nMDS ordination showed that the low forest community was most distinct from the other communities. The low forest community was abundant in indigenous Griselinia littoralis and Cordyline australis. The other three communities were abundant in exotic Lotus pedunculatus; suggesting that its abundance reduces as forest canopy closes. Indigenous species that are present in the four О̄tautahi Christchurch Ecosystems Map plant lists (Wet plains – Kahikatea, Dry plains – Tussock, Dry plains – Ti Kouka, and Dry plains – Houhere) were most dominant (mean importance value= 0.22) across the reserve (exotic species= 0.12, indigenous species not present on lists= 0.07). The low forest plots were the only community where the indigenous – present species were significantly greater (p-value= 2.21x10-6) than the indigenous – not present and exotic species. The species regenerating the most were Coprosma robusta (0.45 seedlings/m2) and Griselinia littoralis (0.42 seedlings/m2). All seedlings were found in the low forest plots, aside from one Coprosma robusta seedling in a riparian/marshland plot. Restoration at SMCR can be thought of as incomplete, due to the high abundance of exotic species and lack of seedling regeneration in all areas of the reserve apart from the low forest community. The incomplete areas of restoration will require the most attention by management and efforts should be focused on assisting these areas to move to a composition similar to that of the low forest community.
  • ItemOpen Access
    Comparing performance of Douglas fir growth and yield models in the South Island of New Zealand.
    (2023) Walker, Liam
    Douglas fir (Pseudotsuga menziesii) is New Zealand's second most important plantation tree species. Of the total plantation area (100,105 ha), approximately 75% is planted in the South Island regions of Canterbury, Otago, and Southland. There are three common growth and yield models for Douglas fir in the South Island: the 500 Index model (500 Index), South Island Douglas fir model (SIDFIR) and the Douglas fir National model (DFNAT). Although frequently used, it is unknown how the models perform on datasets outside those used for initial validation. Predictions of mean top height (MTH), basal area/ha and stocking by the three models were compared to 315 growth measurements across 8,376 ha of Douglas fir forests throughout Canterbury, Otago, and Southland. The ability of each model to match actual historical growth measurements in an independent dataset formed the basis for comparison. The effects of region and several site characteristics were also tested for their impact on residual errors of model predictions. Site characteristics shown to affect residual errors significantly were used to adjust model predictions to increase precision and reduce bias. Substantial imprecision, systematic bias, and regional variations were found in predictions of MTH, basal area/ha and stocking by the 500 Index, SIDFIR and DFNAT growth and yield models. Regional variations and significant effects of site characteristics were also shown to exist. The SIDFIR model performed the best with the most precision and least bias of the three models; however, predictions still displayed considerable imprecision and bias. Thus, developing a new growth and yield model for Douglas fir in the South Island is recommended. This model should utilise a hybrid modelling approach to account for climatic variations between sites and provide increased precision and reduced regional variation. A new model would allow forest managers to make effective decisions to ensure the productivity, profitability, and sustainability of Douglas fir forests in the South Island of New Zealand.
  • ItemOpen Access
    Assessment of wood stiffness by species and aging: a Nelder experiment.
    (2023) Wright, Nathan
    Pinus radiata timber is inherently hindered by low stiffness due to high microfibril angle in the corewood zone. Determining how foresters can manipulate microfibril angle in plantation forests to increase stiffness is of high economic and silvicultural importance. A Nelder systematic spacing design in Canterbury was used to assess the stiffness and tree dimensions of 16-year-old P. radiata (n = 344) and 15-year-old Eucalyptus nitens (n = 211) at stocking levels ranging from 271 stems per hectare to 40,466 stems per ha. Using regression modelling independent variables species, aging and stocking were used to predict response variables outerwood stiffness, diameter at breast height (DBH) and tree height. Stocking, species and physiological aging had a significant effect on modulus of elasticity (MOE). Outerwood MOE significantly increased with increasing stocking for P. radiata up to 17,564 stems per hectare and up to 1,023 stems per hectare for E. nitens (P < 0.001). There was little stiffness gain in planting E. nitens at a greater stocking than 1,023 stems per hectare. By planting P. radiata at 2,505 rather than 823 stems per hectare, stiffness can increase by 14%. Stiffness was 41% greater for E. nitens however, P. radiata stiffness can be significantly (P < 0.001) increased by up to 1.2 GPa by planting physiologically aged clones. Stocking had significant effects on tree dimensions (P < 0.001) for both species: DBH decreased in an exponential trend, whereas tree height decreased more linearly. Physiological aging significantly affected DBH (P < 0.0067) but not tree height (P = 0.31). Wind direction was a significant predictor of MOE and as such standing tree stiffness should be measured on the windward and leeward sides of the tree to account for compression wood. At present, the potential of E. nitens as an alternative structural timber species is limited by its poor sawing and machinability due to growth stresses. However, the increasing trend of MOE seen with increasing stocking demonstrates that foresters have a lot of control over the stiffness of a tree crop through the choice and manipulation of stocking, seed stock and species.
  • ItemOpen Access
    Non-destructive wood evaluation : operationalising a resistograph in the South Island of New Zealand.
    (2023) Doyle, Ryan
    In New Zealand, some sawmills are requesting logs above a stiffness grade, prompting forest managers to integrate stiffness-related data into their resource inventories. The IML PD400 resistograph provides a rapid and non-destructive means of sampling trees for density with studies demonstrating a high correlation between site-average estimates of basic density and site-average stiffness of board outturn at a sawmill. OneFortyOne New Zealand has purchased a resistograph with the intention of using the estimates of basic density that it provides to segregate their stands for stiffness. This study investigated the sampling intensity necessary to achieve a probable limit of error (PLE) of 10-15 % for stand-level basic density estimates to help OneFortyOne operationalise the tool. High-intensity sampling was carried out across 15 stands that covered a range of environmental conditions. Simulations of the PLE equation were run in R with the sampling intensity systematically reduced to assess the influence on PLE. Results suggested that sampling programs for stand-level estimates of basic density can be carried out at a very low sampling intensity. With only 10 total measurements across two sample plots, a PLE of less than 12.5% was achieved across the range of stands assessed. Increasing the sampling intensity to 30 total measurements across 15 plots returned a PLE of 2.5-5%. However, beyond this point, further increases to sampling intensity yielded diminishing returns. Decisions relating to sampling intensity should be an operational call that takes into account the findings of this study alongside manager experience and knowledge of wood variability across a forest estate. Further research should be conducted to confirm the relationship between site-average estimates of basic density and site-average stiffness of board outturn. The IML PD400 and the processing software is a rapidly evolving space that will likely continue to be adopted as wood product customers demand higher quality logs.
  • ItemOpen Access
    Immersive virtual reality for children in formal education.
    (2023) Belter, Meike
    This PhD thesis explored the integration of virtual reality (VR) technology into formal education, specifically targeting school-aged children. While VR has gained traction primarily for entertainment, this study sought to harness its immersive potential for educational purposes within, for example, schools. Games have long been recognized as valuable tools for enhancing learning experiences. In recent years, schools have increasingly adopted them, particularly in subjects such as math. Not all learning methods and tools are inclusive to all learners. Common challenges for children in a school context are inattention and hyperactivity. VR, with its ability to create immersive and customizable environments, presents an intriguing avenue for addressing these challenges. To address this, a VR math game was developed for this research, drawing from established educational frameworks and insights garnered from subject matter experts. Through qualitative interviews and thorough requirement analysis, the game’s design was refined. Subsequently, two user studies were conducted within real-world school environments. The initial study focused on assessing usability and refining the prototype based on user feedback. Encouraging outcomes paved the way for a more extensive second study. This followup delved into the influence of a reward system and virtual agent on the user experience, and comparing the VR game against a non-VR counterpart. The findings demonstrated that the VR game not only cultivated positive user experiences but also heightened motivation and engagement. Despite these promising results, further exploration is necessary to determine the role of ‘peerpresence’ in VR learning, and the game’s suitability for children with clinically diagnosed attention and hyperactivity issues. This research adds valuable insights into the process of creating inclusive and effective VR learning experiences. Through a comprehensive research approach, including design, usability testing, and user studies, the thesis underscored the potential of VR to enhance user engagement and experiences within educational contexts.
  • ItemOpen Access
    Percolating networks of nanoparticles for neuromorphic computing.
    (2024) Heywood, Zachary
    Inspired by biology, neuromorphic (brain-like) computing aims to capture the incredible capabilities of the human brain with physical devices. The brain completes numerous complex tasks such as pattern recognition using a fraction of the time and energy of conventional computers. In order to build systems with similar computational abilities, it makes sense to investigate systems that have intrinsic brain-like qualities. Percolating networks of nanoparticles (PNNs) have many features that make them suitable for neuromorphic computing. The neuromorphic properties of PNNs have previously been demonstrated for simple two-electrode devices. Multiple electrodes are required, however, for the implementation of PNNs as the reservoir in a conventional reservoir computing (RC) scheme, where multiple inputs and outputs are used. This thesis focuses on simulations of PNNs and it is demonstrated that the neuromorphic properties are conserved in devices with multiple electrodes. RC utilises temporal correlations in a dynamical system in order to perform computation. A model for operating in the low-voltage tunnelling regime is described, which allows PNNs to be used as the physical reservoir. A range of benchmark tasks are successfully performed and the effect of network size on RC performance is investigated. The RC scheme is extended to the emulation of swarming behaviour, like that seen in flocks of birds. A number of approaches are investigated and a novel method is developed that produces ‘swarm-like’ behaviour with PNNs for the first time. The results presented in this thesis demonstrate that PNNs have capability for neuromorphic computing and show that there is promise for solving even complex problems.
  • ItemOpen Access
    Noodle : design of a modular and re-configurable serpentine robot, with series elastic actuators and modular ventral panels.
    (2023) Lay, Gordon
    In the field of mobile robotics, there is a substantial challenge surrounding reliable navigation of unstructured environments with irregularities. A robot capable of versatile and robust locomotion is required, in order to handle randomly cluttered environments, which may also vary in substrate. This problem has two interdependent components; the physical form of the robot, and its mode of locomotion, or gait. By observing nature, researchers can find inspiration in organisms that have spent decades of evolution becoming expertly adept in particular tasks, and manifest this through behaviours and physical features. As a species, snakes are fascinatingly versatile at locomoting; depending on the substrate and irregularities of the environment, various gaits are used. The physical features of biological snakes are also diverse; microscopic ventral scale structures vary with habitat and primary gait. These scale structures impact the frictional properties of the ventral scales, resulting in varying degrees of anisotropy. The physical form of biological snakes is also attractive from a design perspective; a slender form, instrinsic stability and hyper-redundancy make a snake-inspired robot (snake robot) ideal for navigating cluttered environments. A snake robot able to harness the diverse set of available snake gaits presents an appealing solution to versatile locomotion. The aforementioned relationships between substrate, gait and ventral scale structure are conflicting, however; for a snake robot to perform all snake gaits, it must also possess ventral scales that can vary in structure. This thesis presents Noodle; a cost-effective snake robot with modular ventral panels on the sides of its body. This enables configuration of the ventral contact surfaces prior to deployment onto a given substrate, and the ability to ‘select’ its ventral side simply by rolling. By modularising the contact surfaces into these panels, access to varying degrees of frictional anisotropy is granted simply by swapping them. The cross-section of Noodle ressembles a chamferred square; thus, there are up to 4 unique sets of panels able to equipped at a time. Two panel designs are 3D printed from PLA, to assess the effectiveness of altering geometry to achieve frictionally isotropic and anisotropic designs. The anisotropic design is able to achieve 3 times more friction in the lateral direction than longitudinal when interacting with carpet, which served as a textured, slightly yielding surface. The body of Noodle is modularised into identical single degree of freedom (DOF) segments, which may be appended to one another with the rotational axes in parallel, or alternating in pitch and yaw; these achieve the planar and 3D configurations, respectively. Through the inclusion of series elastic actuators (SEA), compliance and torque sensing are achieved. The SEA is realised by attaching a compliant element in between the servo motor and driven segment. A conventional hobby servo was used. Two designs of compliant element, or series elastic element (SEE), are presented: coil spring and elastomer, where the latter is used in the final design. The material properties of elastomers depend on temperature, while the elastomer itself exhibits dampening and hysteretic deformation; the coil spring SEE offers higher temperature invariance and no hysteresis, but meeting the stiffness requirements of the SEE were challenging. Furthermore, the elastomer SEE is much simpler to manufacture, and its shortcomings have been shown to be relatively minor in the use case of a snake robot SEE. The elastomer SEE is experimentally characterised to have a torsional stiffness constant of 3.54 [N·m/rad]; with a 12-bit rotary encoder resolution, a 0.005 [N·m] torque-measurement resolution is achieved. Each segment of Noodle consists of a custom embedded system, SEA, and 3D printed body. Special attachments to ressemble the head and tail are also included in the proposed design. These attachments, the segment bodies, and parts of the SEA, are 3D printed from PLA; a cost-effective manufacturing decision that also allows for rapid prototyping. To validate the design and assess gait-execution capabilities, Noodle is configured in the planar configuration, with a total of 8 joints. The average cost per segment module is 158 NZD. In the planar configuration, with the joints acting in the pitching direction, the rectilinear gait can be implemented; the robot propels itself by executing successive poses that ressemble a dorsally-propagating wave. The impacts of the wave parameters on average movement speed are investigated; keeping temporal frequency constant (which will self-evidently affect movement speed) and using a range of values for amplitude and phase shift, speeds between 2.5±0.1 and 5.2±0.1 [cm/s] are achieved. A control architecture and system are proposed, based on the embedded architecture and torquemeasuring SEAs. Local stiffness control (LSC) is implemented, which allows closed-loop control of the joint stiffnesses, which in turn achieves adaptive behaviour in response to environmental stimuli. The effectiveness of the LSC is evaluated across several experiments wherein Noodle successfully overcomes an obstacle approximately 70% of its own height, using the impedance variation of the LSC. The results show decreased time taken to conquer the obstacle with increasing torque control gain, to an extent; beyond a certain gain value, the decrements in the times taken become marginal. The implications of the control and embedded architectures on the control system responsiveness are also evaluated. Noodle, with its modular ventral panels, poses an appealing solution to the problem of conflicting snake gaits, ventral surface properties, and traversed substrate. Preliminary planar control with joint torque feedback is demonstrated, paving the way for the implementation of sophisticated 3D gaits. Ultimately, these elements make Noodle an excellent intermediate platform in the pursuit of mobile robots capable of navigating unstructured environments with irregularities.