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An efficient and sustainable approach for cooling underground substations
No full textWith rapid rates of urbanisation and significant improvements in construction technologies, the number of subsurface infrastructure projects has drastically increased in recent years. In addition to their primary functions, these structures have shown great potential as energy geo-structures, exchanging heat with the ground to heat and cool spaces. Given their large contact area with the ground, energy tunnels are proving to be a sustainable source of thermal energy for effectively heating under- and above-ground spaces. However, their efficiency in cooling-dominated conditions has not yet been adequately studied. This paper tackles one of the key challenges regarding transport tunnels: sustainable cooling of underground substations, by introducing an efficient and cost-effective cooling method. The method takes advantage of airflow in the tunnels and relatively stable ground temperatures and involves heat exchangers in the form of water-filled high-density polyethylene (HDPE) pipes being integrated into the tunnel space. The efficiency of the proposed system is numerically assessed by analysing the spatio-temporal variations of temperature in the ground, substation, tunnel air, tunnel structure and heat exchangers caused by continuous heat rejection from the substations. A detailed 3D finite element heat and mass transport model is used, and alternative placements of heat exchangers are investigated. Results show that heat exchangers placed on the tunnel lining, and hence exposed to the tunnel airflow, could efficiently supply a substation's cooling demand, without significantly increasing the temperature of the tunnel air or the ground. The substantial economic benefits of this cooling system compared to a conventional cooling system is also demonstrated
Combined Zr and Y phosphate coatings reinforced with chemically anchored B<inf>2</inf>O<inf>3</inf> for the oxidation inhibition of carbon fiber
No full textThe use of carbon fiber-based composites in high-temperature environments has been hindered due to the inferior oxidation resistance of standard carbon fiber. Protective coatings comprised of refractory ceramics have served in enhancing the thermal endurance of carbon fiber significantly. Although zirconium and yttrium-based materials have been highly studied on their refractory characteristics, phosphate-based thermal barrier systems are scarce. Herein, we report the oxidation retardation capability of a B2O3-chemically anchored, Zr3(PO4)4/YPO4 coating system on carbon fiber. In-situ, sol-gel-developed coatings with varying thicknesses and constructs were investigated for morphology, crystallography, composition, mechanical properties and thermal integrity. A uniquely consolidated B2O3@Zr3(PO4)4/YPO4 molecular arrangement was indicated in coatings by infra-red and X-ray spectroscopy. Ultimately, superior oxidation protection with an enhancement of ~180 °C over uncoated fiber was exhibited by the integrated nanocoatings, indicating its potential suitability for thermal shielding of carbon-based composites at temperatures in the range of 900–1000 °C. The exhibited improvement in thermal performance was attributed to the fortification provided by the coordinated B2O3 network on the fundamental Zr3(PO4)4/YPO4 system
A taxonomy of barriers to the adoption of sustainable practices in the coffee farming process
No full textThis paper examines the barriers to adoption of Sustainable Agricultural Practices (SAPs) in smallholder coffee farming in Kenya. Previous studies identify several barriers, but there is limited research on where these barriers exist at different stages of the coffee farming operation processes i.e. nurseries for seed germination, planting, growing, and harvesting. This study seeks to examine whether barriers to SAPs adoption differ for different stages of coffee farming process, and if so, how. Drawing on semi-structured interviews with 32 small-scale coffee farmers in the Nyeri county in Kenya, a qualitative investigation was performed, from which several themes emerged depicting key barriers to adoption of SAPs. Based on our findings, we develop a classification system (taxonomy) illustrating the barrier types that hinder the adoption of different SAPs at different stages of the coffee farming process. Such distinctions can help policymakers, NGOs and researchers recommend interventions tailored to help increase adoption of sustainable practices in coffee farming
Transforming the construction sector: an institutional complexity perspective
No full textPurpose: Government initiatives to improve construction have increasingly become more focused on introducing a repertoire of technologies to transform the sector. In the literature on construction industry transformation through policy-backed initiatives, how firms will respond to the demands to adopt and use innovative technologies and approaches is taken for granted, and there is scarcely any attention given to the institutional implications of transformation agenda. The purpose of this paper is to discuss these gaps and offer directions for future research. Design/methodology/approach: Following a synthesis of literature on the UK’s industry transformation agenda, the authors use the concepts of institutional logics, arrangements, complexity and strategic responses to suggest seven research questions that are at the nexus of policy-backed transformation and institutional theory. Findings: In this paper, the authors argue that increasing demands for the adoption and use of digital technologies, platforms, manufacturing approaches and other “industry-4.0”-related technologies will reconfigure existing logics and arrangements in the construction industry, creating a problem of institutional complexity for general contracting firms in particular. Originality/value: The questions are relevant for our understanding of the nature of institutional complexities, change, strategic firm responses, field-level dynamics and implications for the construction industry in relation to the transformation agenda. This paper is positioned to spur future research towards exploring the consequences of industry transformation through the lens of institutional theory
Stability of trusses by graphic statics
No full textThis paper presents a graphical method for determining the linearized stiffness and stability of prestressed trusses consisting of rigid bars connected at pinned joints and which possess kinematic freedoms. Key to the construction are the rectangular areas which combine the reciprocal form and force diagrams in the unified Maxwell-Minkowski diagram. The area of each such rectangle is the product of the bar tension and the bar length, and this corresponds to the rotational stiffness of the bar that arises due to the axial force that it carries. The prestress stability of any kinematic freedom may then be assessed using a weighted sum of these areas. The method is generalized to describe the out-of-plane stability of two-dimensional trusses, and to describe three-dimensional trusses in general. The paper also gives a graphical representation of the 'product forces' that were introduced by Pellegrino and Calladine to describe the prestress stability of trusses
Early detection of thermoacoustic instabilities in a cryogenic rocket thrust chamber using combustion noise features and machine learning
No full textWe present a data-driven method for the early detection of thermoacoustic instabilities. Recurrence quantification analysis is used to calculate characteristic combustion features from short-length time series of dynamic pressure sensor data. Features like recurrence rate are used to train support vector machines to detect the onset of instability a few hundred milliseconds in advance. The performance of the proposed method is investigated on experimental data from a representative LOX/H research thrust chamber. In most cases, the method is able to timely predict two types of thermoacoustic instabilities on test data not used for training. The results are compared with state-of-the-art early warning indicators
Heat-Flux-Based Condition Monitoring of Multichip Power Modules Using a Two-Stage Neural Network
No full textPower semiconductor chips are paralleled in modules to increase current rating. Under thermo-mechanical stresses in service, the die-attach solder layers will gradually develop into different levels of degradation. Early fault detection requires to monitor the occurrence of such an uneven degradation pattern. Internal temperature differences only slightly affect the current sharing between chips, and some temperature sensitive electric parameters are considerably weakened at module terminals. This article presents an external heat-flux-based condition monitoring method, implemented in a two-stage neural network. The first stage consists of a set of subnetworks to represent the mapping between the electrical operating point of the module and its external temperature distribution, for a range of solder degradation patterns and severities. The respective levels of matching are then extracted and applied to the second stage to diagnose the health condition of the power module. This condition monitoring method, validated by experiment, can sensitively detect individual solder degradation in multichip power modules or multimodule power electronic systems
Capacitive touchscreen sensing - A measure of electrolyte conductivity
No full textMobile technologies such as smartphones and tablets combine computational power with inbuilt sensors and networking capabilities, making them ideal measurement instruments. There is already a rich history of research and commercially manufactured accessories taking advantage of their sensing and data visualisation capabilities. However, to-date the touchscreen component has not yet been translated to the widely established fields of capacitance-based bio- and environmental sensing. Here, we demonstrate the concept of contactless conductivity sensing of fluid samples placed directly on top of a projected mutual capacitive touchscreen with the measurement of a variety of electrolytes, leveraging the touchscreen's multi-touch capabilities. Electrolyte ions are particularly susceptible to the electric fringe field induced by capacitive touchscreens, and we report here a near-linear response to the ionic concentration of metal cations interesting for drinking water quality and soil health monitoring across a range of 0–500 μM (up to 100 μS). Simulation results are compared with experimental findings to reveal both the working principles and the key parameters that will be important for future sensing applications. This sensor demonstration is a starting point for broader exploration of the use of projected touchscreen sensing in mobile technologies and the creation of tools that are accessible to everyone, allowing rapid measurements and communication of data
Retention not demolition: how heritage thinking can inform carbon reduction
No full textTwo key benefits of building retention and adaptation, over demolition and new build are identified in the academic literature as: the conservation of heritage, and reductions in embodied greenhouse gas emissions from construction materials. A four-year research project, including expert interviews, focus groups and three detailed case studies, developed extensive data on how these benefits are considered in decisions to demolish or retain buildings within larger urban development sites. The research found that heritage and embodied impacts are considered quite differently. Heritage is frequently a key driver towards retaining individual buildings, whilstembodied emissions are rarely key considerations. Where there are insufficient arguments based on heritage value, many buildings are therefore demolished and replaced rather than retained. To reduce the impact of construction on the environment it is crucial that we calculate the embodied as well as operational impacts of demolition decisions and retain and refurbish buildings where this is the lower carbon choice. Using heritage arguments as a basis, this paper proposes that the introduction of policy drivers for retention and against demolition, and the conversion of environmental value into economic uplift, are likely to be necessary conditions to encourage the retention of buildings for lower whole life carbon
Lévy State-Space Models for Tracking and Intent Prediction of Highly Maneuverable Objects
No full textIn this article, we present a Bayesian framework for maneuvering object tracking and intent prediction using novel \alpha-stable Lévy state-space models, expressed in continuous time as Lévy processes. In contrast to conventional (fully) Gaussian formulations, the proposed models are driven by heavy-tailed \alpha-stable noise and are, thus, much more able to capture extreme values/behaviors. This can better characterize sharp changes in the state, which may be induced by sudden and frequent maneuvers such as swift turns or abrupt accelerations. In particular, they are represented in a conditionally Gaussian series form, which ensures the tractability of the applied inference algorithms. A corresponding estimation strategy with the Rao-Blackwellized particle filter is then proposed, and an efficient intent inference procedure is introduced. Here, the underlying intent, driving the target's long-term behavior (e.g., reaching its final destination), is modeled as a latent variable. Real vessel data from maritime surveillance and human computer interactions (e.g., cursor data from motor-impaired interface users) are utilized to demonstrate the effectiveness of the proposed approach. It is shown to deliver noticeable improvements in the tracking and intent prediction performance (whenever relevant) compared with a more conventional Gaussian dynamic model