1,721,124 research outputs found
Value driven design of additive manufactured unmanned aircraft
No full textThis thesis introduces a novel value driven design methodology for mission-specific rapid-manufactured Unmanned Aerial Vehicles (UAVs). It is based on a holistic design environment that integrates a multi-disciplinary aircraft design tool, an agent-based operational simulation, and a life-cycle cost-benefit model. The definitions of the stakeholders’ value drivers, the concept of operations, and the operating environment are used to create a detailed simulation capable of evaluating the mission effectiveness of the system and its life-cycle cost as well as, remarkably, the impact of the system performance on the operation of the other agents participating in the mission. This enhances the understanding of the design space and allows the designer to elicit the system characteristics that lead to the best value for the stakeholders.This methodology is applied to the design of an unmanned aircraft to support search and rescue in cooperation with lifeboats. This case study demonstrates that counterintuitive effects can arise from the operation of the UAV in a complex environment. The holistic design environment canunveil these emergent behaviours and provide quantitative relationships between the technical characteristics of the system and the overall mission value, therefore improving design decision making. This study also highlights the importance of providing the decision maker with a comprehensive set of simulation outputs in order to facilitate the understanding of the factors and dynamics that contribute to the value generation.This thesis also discusses the impact of additive manufacturing on the design of UAVs with a focus on selective laser sintering of plastic. The merits and limitation of this technology are discussed through the analysis of a number of case studies, including the design and test of the first entirely 3D printed UAV. Additive manufacturing decreases the product development time, increases its adaptability, and facilitates the continuous system development. The absence of penalties associated with the production of complex geometries generates opportunities for mass and cost savings through multi-functionality and structural integration. Additionally, this research offers a principle to guide the architectural design of partly 3D printed UAVs. The principle is based on a measure of the manufacturing complexity, engineering judgment and network analysis of the product architecture and can identify the parts that would benefit the most from the adoption of additive manufacturing as well as highlight the opportunity for components integration and modularisation of the assembly
On spatial beam self-cleaning from the perspective of optical wave thermalization in multimode graded-index fibers
Full text linkThe input power-induced transformation of the transverse intensity profile at the output of graded-index multimode optical fibers from speckles into a bell-shaped beam sitting on a low intensity background is known as spatial beam self-cleaning. Its remarkable properties are the output beam brightness improvement and robustness to fiber bending and squeezing. These properties permit to overcome the limitations of multimode fibers in terms of low output beam quality, which is very promising for a host of technological applications. In this review, we outline recent progress in the understanding of spatial beam self-cleaning, which can be seen as a state of thermal equilibrium in the complex process of modal four-wave mixing. In other words, the associated nonlinear redistribution of the mode powers which ultimately favors the fundamental mode of the fiber can be described in the framework of statistical mechanics applied to the gas of photons populating the fiber modes. This description has been corroborated by a series of experiments by different groups. However, some open issues still remain, and we offer a perspective for future studies in this emerging and controversial field of research
Aerodynamic performance of aircraft wings with stationary vertical lift propellers
No full textImprovements in battery and motor technology are facilitating innovative aircraft configurations capable of vertical take-off and landing. Of these configurations, lift+cruise is popular for its inherent redundancy and the option to tailor separate propulsion systems for each flight regime. During cruise, the vertical flight propellers of a lift+cruise design are inactive and often exposed. Increasing the projected area of a body is understood to increase the drag, but the aerodynamic performance of an edgewise, stationary propeller and its influence on neighboring bodies is less clear. This study aimed to quantify the impact of two, tandem, edgewise and stationary propellers on the aerodynamic performance of a wing using wind tunnel measurements. The stationary position of the front and rear propellers were varied in 30
∘ increments between 0-150
∘, at angles of attack between -4
∘ and 10
∘. Results at Re = 4.3×10
5 showed the propellers and supporting systems had negligible influence on the lift. However, a drag increase of up to 30% was recorded when propeller positions were aligned perpendicular to the wing chord instead of parallel. Variations in the stationary position of the propeller altered the lift to drag ratio by up to 36% in a typical cruise configuration.
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Femtosecond extreme nonlinear optics with multimode fibers
No full textWe overview the nonlinear spatiotemporal propagation dynamics of femtosecond laser pulses in multimode optical fibers. Whenever the pulse peak power approaches the fiber breakdown threshold, several exotic nonlinear effects are observed
Design and flight test of a civil unmanned aerial vehicle for maritime patrol: the use of 3D-printed structural components
No full textThis paper describes the design of the “Spotter” unmanned aerial vehicle, developed by the University of Southampton as part of the 2SEAS-3i European Interreg project. Spotter is a twin engine, 4m wing span, fixed-wing aircraft which has been designed to perform long-endurance, all-weather patrol missions in coastal and maritime environments. Reliability and safety have been among the strongest design drivers of this project; Spotter is able to survive the failure of one engine and of any single control surface. A modular approach has been adopted for the payload unit in order to allow the users to rapidly interchange the sensors required to perform different missions.One of the most innovative aspects of Spotter is the extensive use of the Selective Laser Sintering (SLS) technology (also known as 3D printing) for many of the components of its airframe. By eliminating tooling and manual labour, the 3D printing technology allows the designer to produce complex and high-performance structures at a relatively low cost and within hours of the completion of the design. Spotter and a sub-20kg version, codenamed 2SEAS-20, have undergone an extensive flight test campaign, totalling hundreds of autonomous flights (including autonomous take-off and landings) and many flight hours. This has provided the opportunity to test the reliability and robustness of the system and to gain a deeper insight into the opportunities and problems presented by the use of 3D printed structures for large airframe components
Spatiotemporal ground risk mapping for uncrewed aerial systems operations
No full textIn this paper we propose the use of spatiotemporal population density data in the analysis of ground risk posed by UAS (Uncrewed Aerial System) operations. The spatiotemporal population density maps are generated through the combination of authoritative data sources, open source geospatial databases, and past works to dynamically classify proportions of a population to their expected daily activities based upon a given time. This adds a further dimension to analysis allowing evaluation and optimisation of ground risk, both spatially and temporally. This approach is used to analyse the ground risk posed under ballistic and gliding descents of a parameterized UAS along a case study path. An open source tool is implemented as part of this work to aid the decision making of operators and promote safer UAS operations
Spatiotemporal ground risk mapping for uncrewed aircraft systems operations
No full textIn this paper we propose the use of spatiotemporal population density data in the analysis of ground risk posed by uncrewed aircraft system (UAS) operations. The spatiotemporal population density maps are generated through the combination of authoritative data sources, open source geospatial databases, and past works to dynamically classify proportions of a population to their expected daily activities based upon a given time. This adds a further dimension to analysis allowing evaluation and optimization of ground risk, both spatially and temporally. This approach is used to analyze the ground risk posed under ballistic and gliding descents of a parameterized UAS along a case study path. An open source tool is implemented as part of this work to aid the decision making of operators and promote safer UAS operations
Characterization of the modal distribution from linear and nonlinear mode coupling in multimode fibers
No full textWe introduce a new modal decomposition method which permits to analyse, with unprecedented accuracy, the mode power distribution from long spans of multimode optical fibers. We show that a Bose-Einstein distribution permits to describe the steady-state distribution both in the linear and in the nonlinear regime, up to soliton generation. The distribution results from the interplay of strong linear disorder caused by fiber imperfections, and nonlinear four-wave mixing
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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