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Model predictive control strategy with a decreasing horizon interval for a reusable launcher in a landing scenario
Get PDFThe descending and landing problem of an Reusable Launch Vehicle (RLV) concerns a wide variety of factors
to overcome, such as the instability generated due to the aerodynamic forces during the descent phases and the strict requirements for accurate pinpoint landing to be met with limited control authority. In addition, the Guidance algorithm needs to be continuously and rapidly updated, in order to cope with the dynamically changing conditions that the RLV can experience during the re-entry and landing phase. One of the key technologies being studied to solve this problem
is Model Predictive Control (MPC). MPC uses a linearized model of the problem to obtain a solution of the scenario, given a specific landing time in the future, called the prediction horizon (PH). In this paper, a new strategy to manage the PH of an MPC scheme is proposed for the landing scenario of an RLV. This strategy considers an offline predefined interval of PHs to obtain a valid solution instead of a single predefined PH. This strategy guarantees a wider set of feasible solutions to be searched with a Convex Optimization method, increasing the robustness of the algorithm at
the guidance stage. A simulation setup is introduced for the landing scenario of an RLV, including full simulation of translational and rotational dynamics, along with the control laws to actuate each of the actuators of the vehicle. The results of the presented algorithm are then shown for the landing scenario of the first stage of a rocket.75th International Astronautical Congress (IAC 2024
Performance test of a hydrogen-powered solid oxide fuel cell system and its simulation for vehicle propulsion application
Get PDFSolid oxide fuel cells (SOFC) have not received enough attention as a power source in the transportation sector. However, with the development of the technology, its advantages over other types of fuel cells, such as fuel flexibility and high energy efficiency, have made SOFC an interesting option. The present study aims at simulation and experimentally validation of the performance of a hydrogen-powered SOFC in an automotive application. A 6 kW SOFC stack is tested, and its model is integrated into a series hybrid electric vehicle model. A fuzzy controller is designed to regulate the charging current between the battery and the SOFC in the vehicle model. Experimental tests are also conducted in a few cases on the SOFC based on the simulation results. The performance of the real SOFC stack is then analysed under dynamic loads to see how the desired current is provided in practice. The results demonstrate a good performance of the SOFC stack under variable load conditions.The authors would like to thank the Republic of Turkey Ministry of National Education, Study Abroad Program, for sponsoring Ibrahim KASAR's study.Journal of Cleaner Productio
Navigating the intersection between postponement strategies and additive manufacturing: insights and research agenda
Get PDFPostponement is a popular principle used to improve supply chain responsiveness and increase customisation by delaying manufacturing and logistics operations until more accurate market demand information is available. In business environments where responsiveness and customisation are increasingly important, additive manufacturing (AM) has recently emerged as a high-potential manufacturing technology. Due to changes in customer behaviours that affect product life cycles and variety, AM could disrupt traditional manufacturing and greatly impact postponement decisions. However, the intersection between postponement and AM is largely underexplored. This study aims to investigate the intersection between postponement and AM to meet the escalating demand for customised products. We conceptualise opportunities and challenges related to when customisation is introduced, concerning the positioning of the customer order decoupling point and to where customisation takes place, as operations could shift across supply chain tiers or even jurisdictions. By shedding light on the intersection of postponement and AM and its implications for customisation, this study formulates a research agenda focusing on five main postponement improvement dimensions: uncertainty, volume, lead time, supply chain design, and environmental sustainability. Moreover, it formalises a set of managerial implications to pragmatically foster the strategic implementation of AM across different postponement scenarios.International Journal of Production Researc
Acoustic excitation as a flow control technique in a high-speed compressor cascade
Get PDFA numerical investigation of the effectiveness of acoustic excitation is carried out to control flow separation in a NACA65-K48 linear compressor cascade (LCC) in the absence of cascade endwalls. The operating conditions for the LCC are Ma = 0.67 and Rec = 560 × 10^3, which are representative of an aeroengine. For the numerical investigations, Improved Delayed Detached Eddy Simulation (IDDES) is used due to its capability to capture flow separation and unsteady flow characteristics with reasonable computational requirements among the high fidelity approaches. The flow through the cascade passage does not experience any separation at the aerodynamic design point (ADP) of the cascade. Therefore, an incidence angle of i = 8° is used in this study where flow separation is observed over blade the suction surface at x/c ≈ 0.6. For acoustic excitation, both external and internal acoustic excitation techniques are investigated. In external acoustic excitation, the sound source is distributed at the inlet boundary of the computational domain whereas in internal excitation, sound waves are introduced into the computational domain from a thin slot located at the onset of flow separation on the blade suction surface. Sound waves are introduced in the flow field at the modal frequencies in the uncontrolled flow, which are Stc = 0.187, 0.409, and 0.618 in terms of Strouhal number based on the blade chord length at a constant excitation amplitude of SPL = 151dB. The results have indicated that external acoustic excitation has no major effect in controlling flow separation in the LCC. Internal acoustic excitation, on the other hand, has a strong effect in modulating the flow separation in the LCC passage such that a reduction of Δζmax ≈ 16% is observed in the total pressure loss coefficient on the measurement plane located 0.4Cax downstream of the cascade exit. Further investigations are also carried out for the effect of sound amplitude on the effectiveness of internal acoustic excitation. In overall, acoustic excitation can serve as a means of flow control in aeroengine compressor cascades.This work was supported by the UK Engineering and Physical Sciences Research Council (EPSRC) grant EP/S513842/1ASME Turbo Expo 2024: Turbomachinery Technical Conference and Expositio
Airline pilots’ perceived operational benefit of a startle and surprise management method: a qualitative study
Get PDFStartle and surprise can impair pilot performance and jeopardize flight safety. Self-management methods have been developed by the industry to address this acute source of stress, however, qualitative insights from pilots describing the quality of these methods are lacking. Ten semi-structured interviews with airline pilots, who had been taught a self-management method, were analyzed using thematic analysis). Pilots considered the method useful and reported positive effects (e.g., decrease in stress) when applying the method during operations. Pilots reported that the method was not often performed in full; specific steps were employed based on perceived benefit. Establishing fellow pilot status and situation awareness was considered most important, addressing own physical startle symptoms (e.g., muscle tension) were deemed less important. Pilots reported an urge to “act” rather than use the method, which is expected as the method aims to induce a pause and mitigate erroneous impulsi ve decisions. Barriers to applying the method included the difficult recognition of startle and surprise, and situational context. Suggested improvements for training dealt with recognition and sharing experiences from peers. The findings of the research provide directions for pilot training for startle and surprise. Future research will explore these pilot perceptions in a larger representative sample.International Conference on Cognitive Aircraft Systems (ICCAS
Spatial sensitivity of river flooding to changes in climate and land cover through explainable AI
Get PDFExplaining the spatially variable impacts of flood‐generating mechanisms is a longstanding challenge in hydrology, with increasing and decreasing temporal flood trends often found in close regional proximity. Here, we develop a machine learning‐informed approach to unravel the drivers of seasonal flood magnitude and explain the spatial variability of their effects in a temperate climate. We employ 11 observed meteorological and land cover (LC) time series variables alongside 8 static catchment attributes to model flood magnitude in 1,268 catchments across Great Britain over four decades. We then perform a sensitivity analysis to assess how a 10% increase in precipitation, a 1°C rise in air temperature, or a 10 percentage point increase in urban or forest LC may affect flood magnitude in catchments with varying characteristics. Our simulations show that increasing precipitation and urbanization both tend to amplify flood magnitude significantly more in catchments with high baseflow contribution and low runoff ratio, which tend to have lower values of specific discharge on average. In contrast, rising air temperature (in the absence of changing precipitation) decreases flood magnitudes, with the largest effects in dry catchments with low baseflow index. Afforestation also tends to decrease floods more in catchments with low groundwater contribution, and in dry catchments in the summer. Our approach may be used to further disentangle the joint effects of multiple flood drivers in individual catchments.Division of Earth Sciences, Directorate for Geosciences, UK Research and Innovation, Natural Environment Research CouncilEarth's Futur
Sustainable management of riverine N2O emission baselines
Get PDFThe riverine N2O fluxes are assumed to linearly increase with nitrate loading. However, this linear relationship with a uniform EF5r is poorly constrained, which impedes the N2O estimation and mitigation. Our meta-analysis discovered a universal N2O emission baseline (EF5r = k/[NO3−], k = 0.02) for natural rivers. Anthropogenic impacts caused an overall increase in baselines and the emergence of hotspots, which constitute two typical patterns of anthropogenic sources. The k values of agricultural and urban rivers increased to 0.09 and 0.05, respectively, with 11% and 14% of points becoming N2O hotspots. Priority control of organic and NH4+ pollution could eliminate hotspots and reduce emissions by 51.6% and 63.7%, respectively. Further restoration of baseline emissions on nitrate removal is a long-term challenge considering population growth and declining unit benefits (ΔN-N2O/N-NO3−). The discovery of EF lines emphasized the importance of targeting hotspots and managing baseline emissions sustainably to balance social and environmental benefits.National Natural Science Foundation of ChinaThis work was supported by the Key Projects of the Joint Fund of the National Natural Science Foundation of China (U22A20557), the Autonomous Region Collaborative Innovation Center for Integrated Management of Water Resources and Water Environment in the Inner Mongolia Reaches of the Yellow River, and the National Natural Science Foundation of China (52379084).National Science Revie
On leakage flows in a liquid hydrogen multistage pump for aircraft engine applications
No full textA comprehensive operational characterization of a representative, liquid hydrogen (LH2) aircraft engine pump, a key enabler for future hydrogen aviation, is presented in this work. The implications of leakage flows are investigated in a two-stage, high-pressure pump for a wide range of flow rates and rotational speeds, through three-dimensional (3D) (unsteady) Reynolds-averaged Navier–Stokes simulations. The study compares two configurations: a baseline model comprising the primary flow path components—inducers, impellers, and volutes, and a realizable pump hardware that includes hub, shroud, and power unit cavities. Performance metrics, including head changes and efficiencies, are extracted both at a component and system level. Leakage flow rates of 27.6% and up to 92.9% of the overall pump flow rate are recorded at design and lowest flow points, respectively. The head loss in the mid to low flow rates does not exceed 4.5%, but the efficiency diminishes by up to 13.5% at off-design operation. The component analysis indicates significant penalties in impeller efficiency. At high flow rates, the presence of leakage flows improves the overall pump performance by 43% and 27% in head rise and efficiency, due to reduced losses in volutes and connecting ducts. The detailed characterization of pump behavior described in this work is of importance in development of safe, reliable, and predictable design of aircraft LH2 pumps. These aircraft pumps are different from LH2 pumps utilized in rocketry and for cooling in nuclear industry due to the requirement to operate with wider turn-down ratios and often, at low specific speeds. Therefore, this study addresses design considerations in this enabling technology that ensures the delivery of preconditioned fuel according to the aircraft operating conditions.International University of Korea: 10039770The authors would like to thank ATI/iUK for funding this work through UKRI, project LH2GT, with Reference No. 10039770 and Rolls-Royce plc. for their support and allowing its publication.Journal of Engineering for Gas Turbines and Powe
Critical materials: demand-side resource efficiency measures for sustainability and resilience
Get PDF© Royal Academy of EngineeringThis report provides an overview of the underutilised policy options for achieving reductions in our demands for critical materials and therefore our dependency on imports of scarce materials. This includes both existing uses of critical materials, and future ones associated with low-carbon technologies.
The UK is economically and physically dependent on many materials that are mined elsewhere, and specific technological components that are not made here. Recent supply chain crises have driven increasing concern about the growing need for ‘critical’ materials, as the projected demands for these are likely to outstrip available supplies. This poses a risk to the resilience of the UK; if material demand significantly exceeds supply, it would interfere with not only economic prosperity but also the capacity of the UK to achieve the infrastructure transformation required to reach net zero. Expansion of demand for critical materials also comes with environmental and social harm that would work against global goals of mitigating climate change and of a just transition to net zero. These impacts
are often not visible to the public or decisionmakers.Royal Academy of Engineerin
Development of a virtual environment for rapid generation of synthetic training images for artificial intelligence object recognition
Get PDFIn the field of machine learning and computer vision, the lack of annotated datasets is a major challenge for model development and accuracy improvement. Synthetic data generation addresses this issue by providing large, diverse, and accurately annotated datasets, thereby enhancing model training and validation. This study presents a Unity-based virtual environment that utilises the Unity Perception package to generate high-quality datasets. First, high-precision 3D (Three-Dimensional) models are created using a 3D structured light scanner, with textures processed to remove specular reflections. These models are then imported into Unity to generate diverse and accurately annotated synthetic datasets. The experimental results indicate that object recognition models trained with synthetic data achieve a high rate of performance on real images, validating the effectiveness of synthetic data in improving model generalisation and application performance. Monocular distance measurement verification shows that the synthetic data closely matches real-world physical scales, confirming its visual realism and physical accuracy.Electronic