1,721,022 research outputs found
Dataset for Modelling the dispersion of aircraft trajectories using Gaussian processes
No full textMatlab code and trajectory data supporting:
Eerland, Willem, Box, Simon and Sobester, Andras (2016) Modelling the dispersion of aircraft trajectories using Gaussian processes. Journal of Guidance Control and Dynamics.</span
Notes on the connections between shape definition and the objective function landscape
No full textThe key to effective shape optimization is the selection of the appropriate mathematical formulation for the parametric description of the geometry of the artifact being optimized. It is widely understood that a good parameterization scheme is concise, mathematically well-posed, robust and flexible. What is less clear, however, is the way in which the choice of parameterization approach influences the features of the resulting objective function landscape. In this article we examine the issue through a simple, four-variable design problem. Key words: optimal design, shape optimization, geometry design, brachistochrone, modality
Stratospheric Flight: Aeronautics at the Limit
No full textIn this book, Dr. Andras Sobester reviews the science behind high altitude flight. He takes the reader on a journey that begins with the complex physiological questions involved in taking humans into the "death zone." How does the body react to falling ambient pressure? Why is hypoxia (oxygen deficiency associated with low air pressure) so dangerous and why is it so difficult to 'design out' of aircraft, why does it still cause fatalities in the 21st century? What cabin pressures are air passengers and military pilots exposed to and why is the choice of an appropriate range of values such a difficult problem? How do high altitude life support systems work and what happens if they fail? What happens if cabin pressure is lost suddenly or, even worse, slowly and unnoticed? The second part of the book tackles the aeronautical problems of flying in the upper atmosphere. What loads does stratospheric flight place on pressurized cabins at high altitude and why are these difficult to predict? What determines the maximum altitude an aircraft can climb to? What is the 'coffin corner' and how can it be avoided? The history of aviation has seen a handful of airplanes reach altitudes in excess of 70,000 feet - what are the extreme engineering challenges of climbing into the upper stratosphere? Flying high makes very high speeds possible -- what are the practical limits? The key advantage of stratospheric flight is that the aircraft will be 'above the weather' - but is this always the case? Part three of the book investigates the extreme atmospheric conditions that may be encountered in the upper atmosphere. How high can a storm cell reach and what is it like to fly into one? How frequent is high altitude 'clear air' turbulence, what causes it and what are its effects on aircraft? The stratosphere can be extremely cold - how cold does it have to be before flight becomes unsafe? What happens when an aircraft encounters volcanic ash at high altitude? Very high winds can be encountered at the lower boundary of the stratosphere - what effect do they have on aviation? Finally, part four looks at the extreme limits of stratospheric flight. How high will a winged aircraft will ever be able to fly? What are the ultimate altitude limits of ballooning? What is the greatest altitude that you could still bail out from? And finally, what are the challenges of exploring the stratospheres of other planets and moons? The author discusses these and many other questions, the known knowns, the known unkonwns and the potential unknown unknowns of stratospheric flight through a series of notable moments of the recent history of mankind's forays into the upper atmospheres, each of these incidents, accidents or great triumphs illustrating a key aspect of what makes stratospheric flight aeronautics at the limit
Flight-test validation of a takeoff performance uncertainty model
No full textA Monte Carlo model designed for fixed-wing aircraft takeoff performance uncertainty quantification is benchmarked. The uses of an efficient takeoff simulator of this type range from rapid design variable and constraint sensitivity studies and large-scale conceptual level analyses to operational performance planning and real-time anomaly detection. The accuracy of the model is assessed against high-resolution flight-test data obtained through a campaign consisting of eight takeoffs flown with a specially instrumented commuter category transport aircraft: a BAe Jetstream Series 3100 twin turboprop. On all but one of the takeoffs, a close agreement is seen in terms of the takeoff distance, as predicted vs as observed, at the point of passing a 35 ft screen height; for the outlier, evidence of a sudden change in wind speed is presented as the probable cause of the discrepancy. Such studies are subject to many other sources of error and uncertainty, which are inherent in both flight-test data analysis and simulation, stemming from the highly dynamic and complex nature of this phase of the flight. The analysis presented also proposes to be a template for dealing with these issues, in a way that is applicable to other benchmarking studies
Self-designing parametric geometries
No full textThe thesis of this paper is that script-based geometry modelling offers the possibility of building `self-designing' intelligence into parametric airframe geometries. We show how sophisticated heuristics (such as optimizers and complex decision structures) can be readily integrated into the parametric geometry model itself using a script-driven modelling architecture. The result is an opportunity for optimization with the scope of conceptual design and the fidelity of preliminary design. Additionally, the proposed `self-design' philosophy of using an integrated design heuristic to construct much of the geometry is a good mechanism for de-constraining the design space, as we can take the design variables as a starting point from which we generate a feasible design, wherever possible. We illustrate these ideas through the parametric geometry model of a twin-engined light aircraft
Four suggestions for better parametric geometries
No full textThe key challenge in building a parametric geometry for any stage stage of the aircraft design process is finding the right balance between the often competing objectives of conciseness, robustness and flexibility. This paper proposes four ways, in which the tensions between these objectives may be addressed. First, we describe a framework for parameterizing geometries at the concept selection level, using a hierarchical encoding. Second, we advocate the clear separation of shape and scale as part of the aerodynamic design process, leading to a non-dimensional shape design phase and a scaling based on performance constraint analysis. Third, we suggest improving flexibility without major robustness compromises by using functionals, instead of parametric functions, to describe the shapes of various components of a geometry. Finally, we discuss geometry-attached curvilinear coordinates as a means of simplifying the parameterization of complicated geometrie
Design space dimensionality reduction through physics-based geometry re-parameterization
No full textThe effective control of the extent of the design space is the sine qua non of successful geometry-based optimization. Generous bounds run the risk of including physically and/or geometrically nonsensical regions, where much search time may be wasted, while excessively strict bounds will often exclude potentially promising regions. A related ogre is the pernicious increase in the number of design variables, driven by a desire for geometry flexibility – this can, once again, make design search a prohibitively time-consuming exercise. Here we discuss an instance-based alternative, where the design space is defined in terms of a set of representative bases (design instances), which are then transformed, via a concise, parametric mapping into a new, generic geometry. We demonstrate this approach via the specific example of the design of supercritical wing sections. We construct the mapping on the generic template of the Kulfan class-shape function transformation and we show how patterns in the coefficients of this transformation can be exploited to capture, within the parametric mapping, some of the physics of the design proble
Ground structure approaches for the evolutionary optimization of aircraft wing structures
No full textAircraft wings have seen very few changes in the topological arrangement of the internal structures during the past decades. However, the traditional topology consisting of longitudinal spars and transverse ribs has not been conclusively shown to be the optimal. The purpose of this study is to develop a tool to explore the space of alternative internal structure topologies. We consider a pair of two-step optimization methods. First, a large set of potential structural members, i.e. a ground structure, is built inside the outer mold line of the wing. Second, an evolutionary optimization method is applied to search for the optimal subset of structural members. Two methods are used: a genetic algorithm (GA) and an evolutionary structural optimization (ESO) heuristic. The objective in both cases is to minimize the structural mass of the wing subject to stress and buckling constraints, which are evaluated by automated finite element analysis. The methods are applied to the structural design of the 3D printed wing of a small unmanned aerial vehicle (sUAV) and benchmarked against manually designed internal structures
Suborbital air-launch of very light payloads from a fixed wing platform
No full textThis paper presents the engineering analysis of CANOPUS, a proposed new concept of space launch operations designed to lift very light payloads over the Kármán line at a considerably lower cost than current systems, as well as offering the potential of near-immediate launch slot availability. The CANOPUS system comprises a self-launching, optionally piloted, high altitude sailplane, which acts as an upper tropospheric launch platform for a low cost, low weight rocket. The low ambient pressure (and density) at launch height means that suborbital space flights can be achieved by light payloads atop rockets of much reduced mass, complexity and cost compared to conventional ground-based systems. We show that a commercially available self-launching sailplane (the Phoenix Air U-15) and a solid fuelled rocket of a mass within the payload capabilities of the sailplane can be combined to lift a payload of the order of 1 kg to an apogee exceeding 100 km
Aircraft aerodynamic design: geometry and optimization
No full textOptimal aircraft design is impossible without a parametric representation of the geometry of the airframe. We need a mathematical model equipped with a set of controls, or design variables, which generates different candidate airframe shapes in response to changes in the values of these variables. This model's objectives are to be flexible and concise, and capable of yielding a wide range of shapes with a minimum number of design variables. Moreover, the process of converting these variables into aircraft geometries must be robust. Alas, flexibility, conciseness and robustness can seldom be achieved simultaneously.Aircraft Aerodynamic Design: Geometry and Optimization addresses this problem by navigating the subtle trade-offs between the competing objectives of geometry parameterization. It begins with the fundamentals of geometry-centred aircraft design, followed by a review of the building blocks of computational geometries, the curve and surface formulations at the heart of aircraft geometry. The authors then cover a range of legacy formulations in the build-up towards a discussion of the most flexible shape models used in aerodynamic design (with a focus on lift generating surfaces). The book takes a practical approach and includes MATLAB®, Python and Rhinoceros® code, as well as ‘real-life’ example case studies
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