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The Global ETD Search service is a free service for researchers
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Showing 41 to 48 of 48 (0.014 seconds)| 41 |
Effects of engine placement and morphing on nonlinear aeroelastic behavior of flying wing aircraftMardanpour, Pezhman 13 January 2014 (has links)
Effects of engine placement on flutter characteristics of a very flexible high-aspect-ratio wing are investigated using the code NATASHA (Nonlinear Aeroelastic Trim And Stability of HALE Aircraft). The analysis was validated against published results for divergence and flutter of swept wings and found to be in excellent agreement with the experimental results of the classical wing of Goland. Moreover, modal frequencies and damping obtained for the Goland wing were found in excellent agreement with published results based on a new continuum-based unsteady aerodynamic formulation. Gravity for this class of wings plays an important role in flutter characteristics. In the absence of aerodynamic and gravitational forces and without an engine, the kinetic energy of the first two modes are calculated. Maximum and minimum flutter speed locations coincide with the area of minimum and maximum kinetic energy of the second bending and torsion modes. Time-dependent dynamic behavior of a turboshaft engine (JetCat SP5) is simulated with a transient engine model and the nonlinear aeroelastic response of the wing to the engine's time-dependent thrust and dynamic excitation is presented. Below the flutter speed, at the wing tip and behind the elastic axis, the impulse engine excitation leads to a stable limit cycle oscillation; and for the ramp kind of excitation, beyond the flutter speed, at 75% span, behind the elastic axis, it produces chaotic oscillation of the wing. Both the excitations above the flutter speed are stabilized, on the inboard portion of the wing.
Effects of engine placement and sweep on flutter characteristics of a backswept flying wing resembling the Horten IV are explored using NATASHA. This aircraft exhibits a non-oscillatory yawing instability, expected in aircraft with neither a vertical tail nor yaw control. More important, however, is the presence of a low frequency “body-freedom flutter” mode. The aircraft center of gravity was held fixed during the study, which allowed aircraft controls to trim similarly for each engine location, and minimized flutter speed variations along the inboard span. Maximum flutter speed occurred for engine placement just outboard of 60% span with engine center of gravity forward of the elastic axis. The body-freedom flutter mode was largely unaffected by the engine placement except for cases in which the engine is placed at the wing tip and near the elastic axis. In the absence of engines, aerodynamics, and gravity, a region of minimum kinetic energy density for the first symmetric free-free bending mode is also near the 60% span. A possible relationship between the favorable flutter characteristics obtained by placing the engines at that point and the region of minimum kinetic energy is briefly explored.
Effects of multiple engine placement on a similar type of aircraft are studied. The results showed that multiple engine placement increases flutter speed particularly when the engines are placed in the outboard portion of the wing (60% to 70% span), forward of the elastic axis, while the lift to drag ratio is affected negligibly. The behavior of the sub- and supercritical eigenvalues is studied for two cases of engine placement. NATASHA captures a hump body-freedom flutter with low frequency for the clean wing case, which disappears as the engines are placed on the wings. In neither case is there any apparent coalescence between the unstable modes. NATASHA captures other non-oscillatory unstable roots with very small amplitude, apparently originating with flight dynamics. For the clean-wing case, in the absence of aerodynamic and gravitational forces, the regions of minimum kinetic energy density for the first and third bending modes are located around 60% span. For the second mode, this kinetic energy density has local minima around the 20% and 80% span. The regions of minimum kinetic energy of these modes are in agreement with calculations that show a noticeable increase in flutter speed at these regions if engines are placed forward of the elastic axis.
High Altitude, Long Endurance (HALE) aircraft can achieve sustained, uninterrupted flight time if they use solar power. Wing morphing of solar powered HALE aircraft can significantly increase solar energy absorbency. An example of the kind of morphing considered in this thesis requires the wings to fold so as to orient a solar panel to be hit more directly by the sun's rays at specific times of the day. In this study solar powered HALE flying wing aircraft are modeled with three beams with lockable hinge connections. Such aircraft are shown to be capable of morphing passively, following the sun by means of aerodynamic forces and engine thrusts. The analysis underlying NATASHA was extended to include the ability to simulate morphing of the aircraft into a “Z” configuration. Because of the “long endurance” feature of HALE aircraft, such morphing needs to be done without relying on actuators and at as near zero energy cost as possible. The emphasis of this study is to substantially demonstrate the processes required to passively morph a flying wing into a Z-shaped configuration and back again.
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Multidisciplinary Design Optimization of an Extreme Aspect Ratio HALE UAVMorrisey, Bryan J 01 June 2009 (has links)
ABSTRACT
Multidisciplinary Design Optimization of an Extreme Aspect Ratio HALE UAV
Bryan J. Morrisey
Development of High Altitude Long Endurance (HALE) aircraft systems is part of a vision for a low cost communications/surveillance capability. Applications of a multi payload aircraft operating for extended periods at stratospheric altitudes span military and civil genres and support battlefield operations, communications, atmospheric or agricultural monitoring, surveillance, and other disciplines that may currently require satellite-based infrastructure. Presently, several development efforts are underway in this field, including a project sponsored by DARPA that aims at producing an aircraft that can sustain flight for multiple years and act as a pseudo-satellite. Design of this type of air vehicle represents a substantial challenge because of the vast number of engineering disciplines required for analysis, and its residence at the frontier of energy technology.
The central goal of this research was the development of a multidisciplinary tool for analysis, design, and optimization of HALE UAVs, facilitating the study of a novel configuration concept. Applying design ideas stemming from a unique WWII-era project, a “pinned wing” HALE aircraft would employ self-supporting wing segments assembled into one overall flying wing. The research effort began with the creation of a multidisciplinary analysis environment comprised of analysis modules, each providing information about a specific discipline. As the modules were created, attempts were made to validate and calibrate the processes against known data, culminating in a validation study of the fully integrated MDA environment. Using the NASA / AeroVironment Helios aircraft as a basis for comparison, the included MDA environment sized a vehicle to within 5% of the actual maximum gross weight for generalized Helios payload and mission data. When wrapped in an optimization routine, the same integrated design environment shows potential for a 17.3% reduction in weight when wing thickness to chord ratio, aspect ratio, wing loading, and power to weight ratio are included as optimizer-controlled design variables.
Investigation of applying the sustained day/night mission requirement and improved technology factors to the design shows that there are potential benefits associated with a segmented or pinned wing. As expected, wing structural weight is reduced, but benefits diminish as higher numbers of wing segments are considered. For an aircraft consisting of six wing segments, a maximum of 14.2% reduction in gross weight over an advanced technology optimal baseline is predicted.
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Application of Parent-Child UAV Tasking for Wildfire Detection and ResponseKubik, Stephen T 01 December 2008 (has links) (PDF)
In recent years, unmanned aerial vehicles (UAVs) have become a dominant force in the aerospace industry. Recent technological developments have moved these aircraft from remote operation roles to more active response missions. Of particular interest is the possibility of applying UAVs toward solving complex problems in long-endurance missions. Under that belief, the feasibility of utilizing UAVs for wildfire detection and response was investigated in a partnership that included NASA’s Aeronautics Research Mission Directorate and Science Mission Directorate, and the United States Forest Service. Under NASA’s Intelligent Mission Management (IMM) project, research was conducted to develop a mission architecture that would enable use of a high altitude UAV to search for reported wildfires with a separate low altitude UAV supporting ground assets.
This research proposes a “straw man” concept incorporating both a High Altitude Long Endurance (HALE) UAV and a Low Altitude Short Endurance (LASE) UAV in a loosely coupled, low cost solution tailored towards wildfire response. This report identifies the communications architecture, algorithms, and required system configuration that meets the outlined goals of the IMM project by mitigating wildfires and addressing the United States Forest Service immediate needs. The end product is a defined parent-child framework capable of meeting all wildfire mission goals. The concept has been implemented in simulation, the results of which are presented in this report.
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A muse of fire : British trench warfare munitions, their invention, manufacture and tactical employment on the Western Front, 1914-18Saunders, Anthony James January 2008 (has links)
The emergence of static warfare on the Western Front in late 1914, encouraged the reinvention of devices associated with siege warfare and the invention of hitherto unknown munitions. These munitions included hand and rifle grenades and trench mortars and their ammunition. At the outbreak of war, the British effectively possessed none of these devices and lacked an infrastructure by which they could be quickly designed, manufactured and supplied to the BEF. The British met this challenge with considerable success and the subsequent proliferation of trench warfare munitions had profound consequences for the evolution of British tactics on the Western Front. This thesis examines the processes by which these devices were invented, developed into manufacturable devices and supplied to the BEF. It considers their novelty in respect to similar devices from the American Civil War and the Russo-Japanese War. It looks at how their technical evolution affected tactical developments. The thesis discusses the relationship between the technical characteristics of these devices and the evolution of their tactical employment on the Western Front. It also considers how the characteristics of certain munitions, such as the Stokes mortar and the Mills grenade, directly effected tactics. It argues that the tactical employment of these munitions was dependent upon their functionality, utility and reliability. The present thesis provides a different model of trench warfare conducted by the British during the First World War and thereby demonstrates the significance of the novel munitions under discussion and the role they played in changing infantry warfare. This thesis also provides a different view of the Ministry of Munitions from that usually offered and argues that certain aspects of the Ministry’s role in providing the BEF with munitions has been overstated by virtue of its having underplayed the work of the War Office, while overlooking that conducted by the Royal Engineers in France.
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Logistika a řízení výroby ve vybraném podniku / Logistics and production management in the selected companyČIHÁKOVÁ, Pavlína January 2012 (has links)
The main topic of the thesis is the area of logistics and production with emphasis on saving time and place in the processing of order, the layout of machines, workplaces and warehouses in the production hall. The advantages and disadvantages were analyzed in the selected company, critical points were determined and solutions were designed, comparison and evaluation were carried out with the original condition. The work is based on the theoretical foundations of the subject, collected data from its own investigations and observations of the analyzed processes.
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God's Newer Will: Four Examples of Victorian Angst Resolved by HumanitarianismSpeegle, Katherine Sloan 05 1900 (has links)
One aspect of the current revaluation of Victorian thought and literature is the examination of the crisis of religious faith, in which the proponents of doubt and denial took different directions: they became openly cynical and pessimistic; they turned from religion to an aesthetic substitute; or they concluded that since mankind could look only to itself for aid, the primary duties of the individual were to find a tenable creed for himself and to try to alleviate the lot of others. The movement from the agony of doubt to a serene, or at least calm, humanitarianism is the subject of this study. The discussion is limited to four novelists in whose work religious doubt and humanitarianism are overt and relatively consistent and in whose novels the intellectual thought of the day is translated into a form appealing to the middle-class reader. Their success is attested by contemporary criticism and by accounts of the sales of their books; although their work has had no permanent popularity, they were among the most discussed authors of their time.
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'Women's sphere' and religious activity in America, 1800-1860 : dynamic negotiation of reality and meaning in a time of cultural distortionNewby, Alison Michelle January 1992 (has links)
The thesis uses the case study of the experience of middle-class northern white women in America during the period 1800-1860 to explore several issues of wider significance. Firstly, the research focuses upon the dynamic relationships between the culturally-constructed categories of public/formal and private/informal power and participation at both the practical and symbolic levels, suggesting ways in which they intersected on the lives of women. Secondly, consideration is given to the validity of the stereotyped view that 'domestic' women were necessarily disadvantaged and dominated relative to those who aspired to public political and economic roles. Thirdly, the relationship of religious belief to these two areas is discussed, in order to discover its relevance to the way in which women both perceived themselves and were perceived by others. In seeking to explore these issues, the research has analysed the patterns of social and cultural change in the era under question, indicating how those changes influenced the perceptions and experiences of both women and men. Their reactions in terms of discourse and activity are located as strategies of negotiation in redefining both social role and participation for the sexes. The rhetoric of 'separate spheres', which was used by men and women to order their mental and physical surroundings, is reduced to its symbolic constituents in order to illustrate that the distinction between male and female arenas was more perceptual than actual. The motivating forces behind the activities and ideas of women themselves are investigated to determine the role of religion in the construction of both female self-images and wider negotiational strategies. The context of nineteenth-century social dynamics has been revealed by detailed analysis of extensive primary sources originated by both women and men for private as well as public consumption. Feminist tools of analysis which enable the conceptualisation of 'meaningful discourse' as including female contributions have further enhanced the specific focus on how women constructed their own world-views and approaches to reality. 'Traditional' approaches and tools are shown to have seriously skewed and misrepresented the reality and variety of both discourse and female experience in the era. Great efforts have been made to allow women to speak in their own words. This has produced an insight into a richness of female social participation and discourse which would otherwise be obscured. The research indicates that women were indeed actors and negotiators during the period. Those women who advocated as primary the duties of women in the domestic and social arenas were by no means setting narrow limitations on female participation in both society and discourse. The religious impulses and eschatological frameworks derived by women (varied as they were) served to order and renegotiate reality and meaning, whilst they produced female roles and influence of great significance. Women were not passive victims of male oppression. Religion can thus be perceived as a positive force which women were able to approach both for its own sake, and for their own particular ends.
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A Pragmatic Standard of Legal ValidityTyler, John 2012 May 1900 (has links)
American jurisprudence currently applies two incompatible validity standards to determine which laws are enforceable. The natural law tradition evaluates validity by an uncertain standard of divine law, and its methodology relies on contradictory views of human reason. Legal positivism, on the other hand, relies on a methodology that commits the analytic fallacy, separates law from its application, and produces an incomplete model of law.
These incompatible standards have created a schism in American jurisprudence that impairs the delivery of justice. This dissertation therefore formulates a new standard for legal validity. This new standard rejects the uncertainties and inconsistencies inherent in natural law theory. It also rejects the narrow linguistic methodology of legal positivism.
In their stead, this dissertation adopts a pragmatic methodology that develops a standard for legal validity based on actual legal experience. This approach focuses on the operations of law and its effects upon ongoing human activities, and it evaluates legal principles by applying the experimental method to the social consequences they produce. Because legal history provides a long record of past experimentation with legal principles, legal history is an essential feature of this method.
This new validity standard contains three principles. The principle of reason requires legal systems to respect every subject as a rational creature with a free will. The principle of reason also requires procedural due process to protect against the punishment of the innocent and the tyranny of the majority. Legal systems that respect their subjects' status as rational creatures with free wills permit their subjects to orient their own behavior. The principle of reason therefore requires substantive due process to ensure that laws provide dependable guideposts to individuals in orienting their behavior.
The principle of consent recognizes that the legitimacy of law derives from the consent of those subject to its power. Common law custom, the doctrine of stare decisis, and legislation sanctioned by the subjects' legitimate representatives all evidence consent.
The principle of autonomy establishes the authority of law. Laws must wield supremacy over political rulers, and political rulers must be subject to the same laws as other citizens. Political rulers may not arbitrarily alter the law to accord to their will.
Legal history demonstrates that, in the absence of a validity standard based on these principles, legal systems will not treat their subjects as ends in themselves. They will inevitably treat their subjects as mere means to other ends. Once laws do this, men have no rest from evil.
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