Engineering: Conference Contributions

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  • ItemOpen Access
    NZ Perspective on Urban Forests
    (2024) morgenroth, justin
  • ItemOpen Access
    An Overview of the Unique DC Injection Campaign for Replicating GICs on High Voltage Transformers in New Zealand
    (2023) Lapthorn, Andrew; Hardie S; Subritzky S; Dalzell M; Clilverd M; Cobbett N; Beggan C; Huebert J; Eaton E; Brundell J; Rodger C
    Introduction: Between 21 and 29 January 2023, with the assistance of Transpower, we successfully utilised New Zealand's HVDC link to directly introduce current into the ground at Haywards substation. Our objective was to simulate the efffects of geomagnetically induced currents (GICs) and observe their impact on two 216 MVA, 220/110 kV autotransformers and one 80 MVA transformer, as well as to monitor the associated transmission lines.
  • ItemOpen Access
    Non-Fungible Programs: Private Full-Stack Applications for Web3
    (2024) Regalia, Blake; Adams, Benjamin; Vallarano N; Tessone CJ
    The greatest advantage that Web3 applications offer over Web 2.0 is the evolution of the data access layer. Opaque, centralized services that compelled trust from users are replaced by trustless, decentralized systems of smart contracts. However, the public nature of blockchain-based databases, on which smart contracts transact, has typically presented a challenge for applications that depend on data privacy or that rely on participants having incomplete information. This has changed with the introduction of confidential smart contract networks that encrypt the memory state of active contracts as well as their databases stored on-chain. With confidentiality, contracts can more readily implement novel interaction mechanisms that were previously infeasible. Meanwhile, in both Web 2.0 and Web3 applications the user interface continues to play a crucial role in translating user intent into actionable requests. In many cases, developers have shifted intelligence and autonomy into the client-side, leveraging Web technologies for compute, graphics, and networking. Web3’s reliance on such frontends has revealed a pain point though, namely that decentralized applications are not accessible to end users without a persistent host serving the application. Here we introduce the Non-Fungible Program (NFP) model for developing self-contained frontend applications that are distributed via blockchain, powered by Web technology, and backed by private databases persisted in encrypted smart contracts. Access to frontend code, as well as backend services, is controlled and guaranteed by smart contracts according to the NFT ownership model, eliminating the need for a separate host. By extension, NFP applications bring interactivity to token owners and enable new functionalities, such as authorization mechanisms for oracles, supplementary Web services, and overlay networks in a secure manner. In addition to releasing an open-source software development kit for building NFPs, we demonstrate the utility of NFPs with an interactive Bayesian game implemented on Secret Network.
  • ItemOpen Access
    Canopy Cover Dynamics in New Zealand’s Cities
    (2023) morgenroth, justin
  • ItemOpen Access
    Very Low Frequency Observations During an Active DC Injection Campaign that Simulated Geomagnetic Storm effects on High Voltage Transformers
    (2023) Clilverd M; Cobbett N; Brundell J; Dalzell M; Lapthorn, Andrew; Hardie S; Agger P; Subritzky S; Beggan C; Huebert J; Eaton E; Rodger C
    In January 2023, in collaboration with our industry partner Transpower Ltd (New Zealand’s national grid operator), a campaign was undertaken to inject large currents into operating high voltage transformers. New Zealand’s high voltage DC (HVDC) link was used to inject current directly into the ground at Haywards substation near Wellington, including into several 216MVA 220 kV / 110 kV autotransformers. Six injection test periods occurred, each lasting 1-2 hours. The peak current injected into the ground was about 621 A, spread across several transformers within the Haywards substation. The injection campaign was undertaken for New Zealand’s Endeavour programme “Solar Tsunamis: Space-Weather Prediction and Risk Mitigation for New Zealand’s Energy Infrastructure”. The technique of substation monitoring using nearby very low frequency (VLF) receivers has been previously reported by the lead author, based on observations of the Halfway Bush substation (HWB) in Dunedin, New Zealand. Evidence of harmonic distortion through enhanced odd and even 50 Hz harmonic amplitudes during geomagnetically induced current (GIC) events of up to 50 A, associated with large geomagnetic storms in 2017 and 2018, have already been observed and analysed in detail. Typically, enhancements in the amplitude of harmonics in the 100 Hz to 600 Hz range have been detected during GIC events. The VLF observations from HWB are consistent with the idea that the local transformers radiate even harmonics of the 50 Hz fundamental mains frequency due to half-cycle saturation driven by additive dc flux induced by GIC. During the Active Injection campaign at Haywards Station, two identical VLF receiving systems were deployed around the substation. Each VLF system comprised a set of orthogonal magnetic field loop aerials. Preliminary results from the VLF harmonic data suggest that observed variations in amplitude in the 100 – 600 Hz frequency range were correlated with temporal variations in the injected ground current, particularly after the current had been applied for more than 20 minutes. Prior to that, a slow increase in harmonic distortion occurred, beginning at the time of the injection onset. For injected substation earth currents ranging from 300 A – 600 A (about 20 A – 35 A for individual autotransformers) even small variations of the order of 10’s of amps appeared to be well correlated with the VLF amplitude variations of even order harmonics. In this study we present the VLF data during the injection events, describing the responses observed from a large, complex substation experiencing geomagnetic storm-like effects.
  • ItemOpen Access
    A displacement-based design method for low-damage dual systems with hysteretic and nonlinear viscous energy dissipation
    (2023) Gu, A.; Rodgers, Geoffrey; Henry, R. S.
    In 2019, a large shaking-table test was performed for a full-scale two-storey low-damage concrete wall building. The test building comprises unbonded post-tensioning (UPT) rocking walls and perimeter frames in both directions. The perimeter frames incorporated hysteretic energy dissipation devices at slotted-beam connections at the beam-column and beam-wall joints, so that both UPT walls and perimeter frames would resist seismic action in parallel as a low-damage dual system. High force-to-volume (HF2V) lead-extrusion dampers and nonlinear viscous dampers (NVDs) were adopted in the test building. This experimental test building was used as the basis for a parametric computational study in OpenSees, where a range of structural parameters were modified, including number of stories, wall- strength contribution ratios, effective period, and equivalent damping ratio. A displacement-based design method is proposed for the application of the low-damage dual system with energy dissipating device combination and compared against the computational results. Nonlinear time-history analyses (NLTHAs) were conducted to validate the methodology, and key response parameters from the time-histories are compared with the design values, to validate the proposed displacement-based design process. The global responses of the NLTHAs validated the proposed design process for both coupled and decoupled dual systems, with the average absolute relative error of the roof drift being 7.94%, considering NVDs’ EVD determined by the power approach. However, the proposed design process was shown to significantly underestimate the roof drift responses of the decoupled dual system when the wall strength portion was smaller than 0.7.
  • ItemOpen Access
    Learning Software Quality Assurance with Bricks
    (IEEE, 2021) Morales Trujillo ME
    Software Quality Assurance (SQA) and Software Process Improvement (SPI) are topics of crucial importance for software engineers; however, teaching them in a lecture room comes with several limitations due to lack of practical experience. With that in mind, we created KUALI-Brick, a LEGO-based activity that brings SQA and SPI concepts together applying them in order to successfully build a LEGO city. This hands-on activity has been carried out in a fourth-year Software Engineering course at the University of Canterbury, with current results showing high levels of fun, increased engagement and an improved learning experience. We present a step-by-step guide to replicate the activity as well as lessons learned after conducting the activity for three consecutive years.
  • ItemOpen Access
    What Can Go Wrong in a Software Project? Have Fun Solving It
    (IEEE, 2018) Morales M; García-Mireles GA; Maslova P
    Providing stimulating and real-life experiences is a key component in teaching software project management in Computer Science or Software Engineering programs. The diversity of topics that need to be addressed and restrictions that should be considered in university courses make a challenging task of it. This paper presents a serious game, called 'White Crow PM' whose objective is to make students aware of the risks they might face during software development projects. The paper describes the game design steps and provides results of its validation in Computer Science programs in two Mexican universities. The collected data showed that the participants had fun playing the game and its content is relevant for software project management courses. Although the game needs to be validated in other settings with more participants, we conclude that it fulfills the goal of motivating discussion and increasing awareness of project management concerns among students.
  • ItemOpen Access
    Engineering activities differentiated by experience and gender
    (2023) Crossin, Enda; Gardner A; Naswall, Katharina; Pawsey F; Rowe G; Stewart E
    CONTEXT Research on ‘what engineers do’ is typically limited to the study of competencies required for practice (Mazzurco et al., 2021). Studies have identified variations in the importance of competencies (Passow & Passow, 2017; Pons, 2016), but there are limited studies on the frequency and importance of the common engineering activities that enable these competencies. Moreover, prior research has identified that engineering activities are likely gendered (Hatmaker, 2013). PURPOSE The goal of this research was to identify differences in the frequency and importance of engineering activities between graduate and experienced engineers. The secondary goal was to investigate if there is a difference in these activity measures by gender. The purpose of this research was to a) support engineering educators with an empirical understanding of practice, and b) to raise awareness of potential gendered engineering activities. APPROACH A cohort of 790 practicing engineers were surveyed on the frequency and importance of 85 common engineering activities. Participants were grouped by experience (0 to 4 years’, and 5 or more years’ experience) and by gender (woman/female and man/male). We normalised response data, then compared the distribution of ranks to test for differences in the frequency and importance of the activities by experience and gender groups. ACTUAL OUTCOMES Differentiated activities for graduate engineers related to seeking advice and interacting with materials and equipment. For experienced engineers, differentiated activities were associated with management. Differentiated activities for women/female engineers were associated with people-related activities, while physical activities were associated for males/men. CONCLUSIONS The observed differentiation by experience and gender confirms prior research. Further crosssectional and longitudinal analyses will provide further insights into the determinants and outcomes associated with this activity segregation.
  • ItemOpen Access
    Increasing resilience to natural hazards in the electric power transmission network
    (Electricity Engineers' Association, 2022) Avery, Hamish
    As a nation straddling two tectonic plates in the midst of open ocean, New Zealand is beset with natural hazards. Our electricity network consists of fragile conductors spanning faults and landslips or buried in liquefiable soils. This paper aims to highlight methods to improve our situational awareness of real-time risk by combining what we know about the electricity network’s exposure to natural hazards with currently available real-time data describing the hazards. This can improve our resilience by more precise deployment of repair crews and pre-emptive management of supply routing. It also looks at the potential for better real-time understanding of network condition by leveraging the technological advances made by the demand for Sensing Cities and the ‘internet of things’. These have driven the development of low-cost, low-power sensors, along with low-cost communications backbones that enable us to build affordable massive real-time datasets measuring a diversity of variables. These could potentially indicate risk at a resolution down to individual pylons or poles, pre-empting failure.
  • ItemOpen Access
    Direct shear response of gravel-glass-rubber mixtures
    (2023) Chiaro, Gabriele; Christian, Samuel; Goldingham, Logan; Murali , Arjun
    This paper reports on preliminary results of a feasibility study aimed at evaluating the potential use of recycled crushed green glass bottles and recycled granulated tire rubber mixed with gravel. Specifically, dry specimens of selected gravel-glass-rubber mixtures (GGRMs) are tested using a medium-size (100 mm × 100 mm × 53 mm - width × length × height) direct shear apparatus under three normal stress levels: 30, 60 and 100 kPa. The effect of glass and rubber content by volume on the peak shear strength, friction angle and energy absorption of the mixtures is investigated. It is shown that GGRMs having 40% rubber content by volume possess adequate strength (i.e., friction angle > 30o), reduced compressibility and excellent energy absorption properties, making such materials suitable structural fills for typical geotechnical applications.
  • ItemOpen Access
    The hydromechanical behaviour of unsaturated loess in slopes, New Zealand
    (EDP Sciences, 2023) Yates, Katherine; Russell, Adrian; Bardanis M
    Unsaturated loess and loess-derived soils in the Akaroa harbour area of New Zealand are vulnerable to shallow landsliding during rainfall events. Laboratory testing and long-term field instrumentation has been conducted to characterise the water retention and unsaturated shear strength of these materials, and better understand temporal changings in slope stability. Laboratory test results indicate that the same soil-water characteristic curve can be applied to both recompacted and intact loess when suction is normalised by the air entry value. Conversely the stress-strain behaviours of the recompacted and intact loess were different due to the unique microstructure of the intact loess that contributes to its shear strength. Long-term field instrumentation data showed that, for the duration of the monitoring period, the hydraulic state of the loess remained on a scanning curve. These data, combined with the laboratory testing, confirm that temporal variation in slope stability can be attributed to seasonal variability in suction and its contribution to unsaturated shear strength. These hydromechanical variabilities, resulting from wetting and drying, are affected by rainfall intensity and duration that occurs at the site.
  • ItemOpen Access
    Uncertainty estimation of connected vehicle penetration rate
    (Institute for Operations Research and the Management Sciences (INFORMS), 2022) Jia , Shaocheng; Wong , S. C.; Wong , Wai
    Knowledge of the connected vehicle (CV) penetration rate is crucial for realizing numerous beneficial applications during the prolonged transition period to full CV deployment. A recent study described a novel single-source data penetration rate estimator (SSDPRE) for estimating the CV penetration rate solely from CV data. However, despite the unbiasedness of the SSDPRE, it is only a point estimator. Consequently, given the typically nonlinear nature of transportation systems, model estimations or system optimizations conducted with the SSDPRE without considering its variability can generate biased models or suboptimal solutions. Thus, this study proposes a probabilistic penetration rate model for estimating the variability of the results generated by the SSDPRE. An essential input for this model is the constrained queue length distribution, which is the distribution of the number of stopping vehicles in a signal cycle. An exact probabilistic dissipation time model and a simplified constant dissipation time model are developed for estimating this distribution. In addition, to improve the estimation accuracy in real-world situations, the braking and start-up motions of vehicles are considered by constructing a constant time loss model for use in calibrating the dissipation time models. VISSIM simulation demonstrates that the calibrated models accurately describe constrained queue length distributions and estimate the variability of the results generated by the SSDPRE. Furthermore, applications of the calibrated models to the next-generation simulation data set and a simple CV-based adaptive signal control scheme demonstrate the readiness of the models for use in real-world situations and the potential of the models to improve system optimizations. Funding: This work was supported by The University of Hong Kong [Francis S Y Bong Professorship in Engineering and Postgraduate Scholarship] and by the Council of the Hong Kong Special Administrative Region, China [Grants 17204919 and 17205822]. Supplemental Material: The online appendices are available at .
  • ItemOpen Access
    Investigation of mesh sensitivity in coupled thermal-hydrological-mechanical models: examples from Desert Peak, Nevada, USA and Ngatamariki, New Zealand
    (2013) Kelkar, S.; Dempsey, David; Zyvoloski, G; Pogacnik, J
    Dempsey et al. (this issue) have presented validation of a coupled thermal-hydrological-mechanical model through a comparative study of shear stimulation in geothermal fields at Desert Peak, Nevada, USA and Ngatamariki, New Zealand. Values of model parameters obtained from such validation studies are often used for extrapolating the model results beyond the domain of available experiments. Thus it is important to consider the sensitivity of these results to the specifics of the model setup as well as uncertainties in input parameters. In this presentation, we consider the sensitivity of history-matched parameter values to the numerical meshes on which computations are performed. During well stimulation, it has been noted that injectivity varies with time according to a power law, i.e., ࡵࡵ ∝ ࢔࢚, with ࢔ ranging between 0.3 and 0.7. Dempsey et al. propose that ࢔ depends on the geometry of the stimulated region. However, this result is dependent on permeability enhanced according to a Mohr-Coulomb failure criterion, which is informed by the stress solution. It is well known that that the finite element method, in linear elastostatics, displays optimal rates of convergence in the L2 norm of stress error with mesh refinement (Zienkiewicz and Taylor, 1994). However, the situation is significantly more complicated in fully-coupled THM modelling. Stress-induced permeability changes affect both the fluid mass balance and energy/enthalpy balance equations and the subsequent convergence of the entire coupled system of equations. Relying on solutions found on an un-converged discretization could result in significant errors. We evaluate this dependence for several grid geometries to establish the robustness of the model findings.
  • ItemOpen Access
    A Framework for Robust Analysis and Visualization of Geothermal Prospectivity
    (2016) Harp , Dylan R.; Lin, Youzuo; Glassley, William; Dempsey, David; Karra, Satish; Person, Mark; Middleton, Richard
    We describe a framework to synthesize geothermal data streams by joint inversion. Geothermal production robustness, a nonprobabilistic metric of geothermal prospectivity, is defined as the amount that uncertain model parameters can deviate from nominal, best-fit values and still produce simulations that meet geothermal production criteria. Larger parameter deviations indicate greater robustness in geothermal prospectivity. Results are automatically presented as 3D robustness maps using the open-source visualization software ParaView allowing interactive interpretation of the results.
  • ItemOpen Access
    Approaches to imaging feedzone diversity with case studied from Sumatra, Indonesia and the Taupō Volcanic Zone, New Zealand
    (2020) Wallis I; Rowland, J; Dempsey, David; Allan, G; Sidik, R; Martikno, R; McLean, K; Sihotang, M; Azis, H; Baroek, M
    There is a fast-growing inventory of studies on borehole image logs acquired in geothermal reservoirs as more operators elect to deploy this technology. Our contribution to this inventory is to illustrate how judicious use of these data may reveal the geologic controls on permeability. We also provide an open source Python library that enables others to replicate the methods described herein. Our study includes a discussion of geometric sample bias, as well as those data integrity and geological factors that influence fracture frequency. We also demonstrate slip tendency modelling as an approach to identifying fractures that may be relevant beyond the borehole wall, which is key for geothermal wells where thermal stresses have enhanced both the number and apparent aperture of fractures at the borehole wall. We illustrate these methods using seven well case studies from a wide range of lithologies, four reservoirs, and two tectonic settings—one dominated by a volcano-tectonic rift and the other a mega-shear zone. The reservoirs are Muara Laboh and Rantau Dedap in Indonesia and Ngatamariki and Wairakei in New Zealand.
  • ItemOpen Access
    Heat Extraction Analysis of Multi-Stage Hydraulic Fracturing Doublet Horizontal EGS Wells
    (2021) Yu, P; Dempsey, David; Archer R
    Enhanced Geothermal System (EGS) are developed using various stimulation technologies to improve the production of heat energy from hot dry rock (HDR) that has ultra-low permeability. In this study, a horizontal EGS well design with partially bridging multistage hydraulic fractures is presented. Based on the proposed design, a semi-analytical model for temperature is derived assuming bi-linear heat transfer in the fractures and stimulated reservoir volume (SRV). The model considers heat conduction and advection in the SRV, and, depending on the number and spacing of fractures, can be used to optimize EGS design. A 3D numerical model is also developed to validate the semi-analytical model and test geometry effects. The numerical model is constructed in the COMSOL finite element solver and compared to a fully bridging hydraulic fracture design. The results show that the partially bridging design can obtain a longer period of high temperature production, delaying thermal breakthrough by forcing water to traverse the SRV.
  • ItemOpen Access
    A Users Guide to Leak-off Test Procedures and Interpretation for Geothermal Wells
    (2021) Wallis I; Pye, DS; Dempsey, David; Rowland, J
    Leak-off Tests (LOT) and Extended Leak-off Tests (XLOT) are conducted during drilling to verify the competence of the cement around a casing shoe and determine the maximum allowable mud weight for the next hole section. (X)LOT interpretation yields the fracture gradient, which is a key parameter in well control procedures, mud program design and cement operations. These data are also one of the minimum requirements for any geomechanical study that seeks to understand the role fractures play in reservoir permeability. Despite its utility for successful well completion and studies investigating reservoir permeability, (X)LOT procedures are often poorly implemented and the interpretation methods used are not always appropriate for geothermal conditions. Using a case study, we describe the test procedures and interpretation process for typical geothermal conditions. We address key issues that set geothermal apart from oil and gas, such as the impact of high temperatures on test results, the high frequency of naturally occurring fractures, and the variable physical properties of hydrothermally altered volcanic rocks. We illustrate the impact of quality checking an existing (X)LOT dataset and review methods for estimating the fracture gradient prior to drilling in extensional environments. While our paper addresses a number of detailed technical issues related to interpretation, it aims to be a pragmatic and geothermally-relevant guide for those who aspire to improve the quality of these tests.
  • ItemOpen Access
    Reservoir Microearthquake Modeling Analysis: a Proof-of-concept Study and Its Application to Injection Fluid-Induced Seismicity
    (2021) Rivera, J; Dempsey, David
    Microearthquakes (MEQs) occur when fluid is reinjected into the reservoir, raising the pressure in the vicinity of the injection well. The pressure build-up in the reservoir due to fluid injection decreases the rock yield strength, which causes shear failure, thus triggering a seismic event. This mechanism presents a further opportunity to use microseismicity as a means to calibrate reservoir parameters, particularly the active faults which tend to be the most conductive fluid flow pathways. The study aims to integrate MEQ modelling to the reservoir development workflow and to the calibration workflow to estimate the permeability of the formations and the faults. The proof-of-concept study considers a synthetic induced seismicity model which represents an area where the fluid is being injected. Reservoir simulation is conducted to evaluate pressure migration through the reservoir for a given reservoir and fault parameters. The earthquake model uses the pressure change from the simulation to compute the average seismicity rate of the fault as well as the spatiotemporal evolution of the seismic events. Synthetic MEQ data is then generated from the earthquake simulation using the Poisson model, which serves as the data for calibration and inverse modelling. Synthetic inversion is then performed to estimate the permeability of both the reservoir and the fault using Markov Chain Monte Carlo (MCMC) sampling method. The study also includes the effects of variation in MEQ data and other uncertainties in the model in parameter estimation. The method developed in this study is then applied to an injection fluid-induced seismicity from a wastewater injection site.