1,721,092 research outputs found
High level requirements impact on configuration trade-off analyses in a multidisciplinary integrated conceptual design methodology
Full text linkThis paper aims at suggesting rational algorithms for the selection of general characteristics of trans-atmospheric vehicles, such as the staging and propulsive strategies, take-off and landing solutions and aero-thermodynamic configurations. The presented selection algorithms exploit different types of high level requirements coming from Stakeholders’ Analysis, Market Outlook, Regulatory Framework Analysis and Strategic Plan, to support drivers and criteria definition process for the selection of the optimal solution among the alternatives. The theoretical description of each single algorithm is supported by the results obtained from the application of the methodology to a suborbital vehicle aimed at parabolic flight and to a point-to-point hypersonic transportation system. Eventually, suggestions for on-going software implementation of the algorithms as well as their integration within a complex conceptual and preliminary design workflow are provided
Influence of high level requirements in aircraft design: From scratch to sketch
Full text linkThis paper suggests an innovative sketch procedure, especially envisaged for very complex and innovative transportation systems. In order to face with the increasing complexity and innovation levels, reducing development schedule and budget, a rational approach is developed and presented. At first, high level requirements, coming from different sources are elicited and then, through a detailed impact analysis, each design parameter used to sketch the vehicle layout is connected to one or more of these requirements. Then, different semi-empirical models, exploiting available statistical data, regulations and best practices, are developed and proper sizing algorithms are suggested to provide a quantitative base to the qualitative sketching procedure. In this approach, special attention is devoted to the evaluation of the impact of the integration of main subsystems (for example, propulsion, propellant, landing gear subsystems) into the final vehicle layout. Eventually, results of the application of the described procedure to an innovative hypersonic transportation system is reported, highlighting the benefit of the increased traceability of requirements into the final product
[Ebstein's anomaly: diagnosis and surgical treatment]
No full textEbstein's anomaly is a rare congenital heart disorder secondary to a malformation of the tricuspid valve and right ventricle. The heterogeneous spectrum of presentation of its structural anomalies and associated cardiomyopathy accounts for a widely varied clinical and hemodynamic manifestation of the pathology and its impact on timing of diagnosis and prognosis. Neonatal Ebstein's anomaly is characterized by reduced survival, while an average risk of mortality per year of 1% to 1.4% has been reported in infancy and adulthood. Medical management and a careful clinical and echocardiographic follow-up are advisable for all asymptomatic patients and those with minimal abnormalities. Surgical correction is recommended in presence of progressive dilation of the right atrium and right ventricle, development of right ventricular dysfunction, occurrence of supraventricular or ventricular arrhythmias or episodes of paradoxical embolization, reduced exercise capacity, or significant desaturation. Prosthetic valve replacement or repair of the tricuspid valve are both common strategies in the correction of tricuspid regurgitation. During the last three decades, important contributions in the development of repair techniques were driven from the experience of Danielson, Carpentier and da Silva, with satisfactory results in terms of safety and durability at long-term follow-up
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
Flight Control System Design and Sizing Methodology for hypersonic cruiser
Full text linkFlight Control System is considered a key enabler for future high-speed aircraft and therefore, the anticipation of its impact onto the aircraft layout and performance is crucial. On one side, a preliminary characterization of the control surfaces is essential for a precise estimate of the aerodynamic characteristics of the vehicle throughout the mission. On the other side, traditional design approaches widely used in subsonic aircraft design and based on on-design and standalone system sizing, may lead to wrong estimates of the peak power demand. Conversely, typical supersonic and hypersonic design solutions are investigated by means of numerical simulations which guarantee higher accuracy but may not be directly applicable during the early design stages. Therefore, this paper discloses an innovative methodology (i) to anticipate the Flight Control System design of future high-speed aircraft at conceptual design stage, (ii) to properly consider the interactions with other subsystems and (iii) to properly predict the behavior of the Flight Control System throughout the entire mission. The integrated subsystems design methodology disclosed in this paper starts with the suggestion of the most promising semi-empirical models for control surfaces geometrical definition. The newly defined surfaces can be analyzed to predict their single contribution to the vehicle lift and drag coefficients. At this stage, the interaction with the propellant system is fundamental to identify the minimum surfaces deflections required to guarantee the aircraft trim. Indeed, in order to minimize the exploitation of control surfaces and thus limiting the detrimental effects onto the aerodynamic efficiency, propellant tanks can be properly shaped and integrated on board, and ad-hoc depletion sequencies can be adopted to match the desired center of gravity shift throughout the mission. Maximum required control surfaces deflections are used as inputs for the estimation of hinge moments to be counteract by the actuation system. A novel approach is here suggested to extend the formulation available in literature beyond the transonic regime. Eventually, the Flight Control System design is completed with the selection of actuators and finalization of the System architecture including power distribution lines and connections with the avionic system. The integrated design methodology has been developed in the context of the H2020 STRATOFLY Project and it has been exploited for the design and sizing of the Flight Control System of the STRATOFLY MR3 vehicle, a Mach 8 waverider concept for civil antipodal flights
Performance assessment of low-by-pass turbofan engines for low-boom civil supersonic aircraft
No full textThis paper presents an approach to evaluate the performance of low-bypass turbofan
engines without afterburner for a low-boom supersonic aircraft operating at Mach 1.5. The
proposed method focuses on optimizing the propulsive performance by minimizing fuel
consumption while meeting mission profile requirements. The study contributes to the
MORE&LESS project, providing methods for rapidly designing novel supersonic propulsion
concepts with improved environmental performance. The research conducts a thermodynamic
analysis for on-design engine conditions based on the Modified Specific Heat (MSH) gas model.
Specific non-installed thrust and fuel consumption are estimated for cruise phase. Then, the engine
cycle analysis is also performed to study off-design performance, including simplified models to
account for engine drag and calculate installed thrust and fuel consumption. MATLAB simulations
are employed to determine thrust and consumption based on the specific mission profile of the
Mach 1.5 case-study, allowing for comparison of different engine types. Ongoing work involves
the optimization of engine parameters such as compression ratio, bypass ratio, and turbine inlet
temperature, targeting further fuel consumption reduction and pollutant emission estimations
Propellant subsystem design for hypersonic cruiser exploiting liquid hydrogen
Full text linkThe possibility of establishing a new paradigm for commercial aviation towards high-speed flight in the next decades shall be inevitably preceded by the increase of Technology Readiness Level for those relevant enabling technologies associated to propulsion, thermal management and on-board subsystems, with particular attention also to environmental sustainability and economic viability of the proposed concepts. New design methodologies for both aircraft and on-board subsystems design shall then be based on holistic approaches able to catch the strong interactions between vehicle configuration, mission and subsystems architecture, which characterize high-speed aircraft layouts. This paper proposes a methodology for the preliminary sizing of propellant subsystems for liquid hydrogen powered hypersonic cruisers. Making benefit of traditional approaches, the process aims at introducing new design aspects directly connected to the peculiar multifunctional architecture of on-board subsystems for high-speed vehicles, so to be able to include additional analyses in early design stages, especially in case of high level of on-board integration. Notably, impact of requirements for Center of Gravity control, thermal, and, in general, energy management are considered as integral part of the method, with crucial implications on architecture selection. After the introduction of design algorithms for subsystem sizing, the STRATOFLY MR3 hypersonic cruiser is taken as reference case study in order to provide a practical example of application of the proposed approach on a highly integrated platform
Towards a methodology for new technologies assessment in aircraft operating cost
Full text linkThe need for a greener and competitive aircraft is leading to the use of new technologies. A thorough assessment of these technologies is mandatory from the initial phases of aircraft design to understand their feasibility and to select the most promising one both in terms of performances and in terms of costs. This paper proposes a methodology to assess the operating cost of innovative technologies for regional aircraft. In particular, two NASA studies have been adopted to determine the impact onto costs of MEA and AEA technologies and advanced ECS solutions for two innovative regional aircraft concepts developed during the European Clean Sky 2 research. The proposed methodology is able to assess the effect of on-board systems electrification level in terms of fuel and maintenance costs savings. The methodology, which allows to evaluate the effect of specific technological improvements onto costs, is applied exploiting the results provided by a reliable cost model and gives the opportunity to quantify operating cost savings for different regional aircraft. Applying the modified cost model to the reference aircraft under study, savings ranging from 1.6 to 3.1% of direct operating cost are estimated for MEA and AEA technologies. Greater savings are estimated for the individual cost items involved. More specifically, a reduction of fuel cost ranging from 6 to 14.5% is envisaged as a consequence of the lower SFC associated to innovative ECS technologies
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