31,024 research outputs found

    Linear matching method for design limits in plasticity

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    In this paper a state-of-the-art numerical method is discussed for the evaluation of the shakedown and ratchet limits for an elastic-perfectly plastic body subjected to cyclic thermal and mechanical load history. The limit load or collapse load, i.e. the load carrying capacity, is also determined as a special case of shakedown analysis. These design limits in plasticity have been solved by characterizing the steady cyclic state using a general cyclic minimum theorem. For a prescribed class of kinematically admissible inelastic strain rate histories, the minimum of the functional for these design limits are found by a programming method, the Linear Matching Method (LMM), which converges to the least upper bound. By ensuring that both equilibrium and compatibility are satisfied at each stage, a direct algorithm has also been derived to determine the lower bound of shakedown and ratchet limit using the best residual stress calculated during the LMM procedure. Three practical examples of the LMM are provided to confirm the efficiency and effectiveness of the method: the behaviour of a complex 3D tubeplate in a typical AGR superheater header, the behaviour of a fiber reinforced metal matrix composite under loading and thermal cycling conditions, and effects of drilling holes on the ratchet limit and crack tip plastic strain range fora centre cracked plate subjected to constant tensile loading and cyclic bending moment

    A Game of Attribute Decomposition for Software Architecture Design

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    Attribute-driven software architecture design aims to provide decision support by taking into account the quality attributes of softwares. A central question in this process is: What architecture design best fulfills the desirable software requirements? To answer this question, a system designer needs to make tradeoffs among several potentially conflicting quality attributes. Such decisions are normally ad-hoc and rely heavily on experiences. We propose a mathematical approach to tackle this problem. Game theory naturally provides the basic language: Players represent requirements, and strategies involve setting up coalitions among the players. In this way we propose a novel model, called decomposition game, for attribute-driven design. We present its solution concept based on the notion of cohesion and expansion-freedom and prove that a solution always exists. We then investigate the computational complexity of obtaining a solution. The game model and the algorithms may serve as a general framework for providing useful guidance for software architecture design. We present our results through running examples and a case study on a real-life software project.Comment: 23 pages, 5 figures, a shorter version to appear at 12th International Colloquium on Theoretical Aspects of Computing (ICTAC 2015

    Flutter Prediction for Aircraft Conceptual Design

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    Flutter prediction is usually a knowledge-based analysis process that aims to reduce the cost of aeroelastic stability margin certification. However, early detection of flutter problems is beneficial in the development of unconventional aircraft. The recently developed automation tool ConceptFEA for structural sizing of aircraft concepts paves the way for rapid physics-based flutter prediction of aircraft concepts. A match-point iteration procedure using the p-k method is implemented for ConceptFEA with minimum user input requirements to generate flutter boundary points. A subsonic business jet concept and its high aspect-ratio wing variant are used to demonstrate how the newly developed flutter prediction capability can be used during aircraft conceptual design. Sized structures, flutter boundary curves, and flutter sensitivity analysis results are generated for these two concepts using ConceptFEA. The relevant equivalent plate theory is provided to show the quantitative relationships between a stiffened panel and its equivalent NASTRAN PSHELL panel. The rapid flutter prediction capability of ConceptFEA makes multidisciplinary collaborations between systems analysts and aeroelasticity experts feasible in practice

    Low-thrust trajectories design for the European Student Moon Orbiter mission

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    The following paper presents the mission analysis studies performed for the phase A of the solar electric propulsion option of the European Student Moon Orbiter (ESMO) mission. ESMO is scheduled to be launched in 2011, as an auxiliary payload on board of Ariane 5. Hence the launch date will be imposed by the primary payload. A method to efficiently assess wide launch windows for the Earth-Moon transfer is presented here. Sets of spirals starting from the GTO were propagated forward with a continuous tangential thrust until reaching an apogee of 280,000 km. Concurrently, sets of potential Moon spirals were propagated backwards from the lunar orbit injection. The method consists of ranking all the admissible lunar spiral-down orbits that arrive to the target orbit with a simple tangential thrust profile after a capture through the L1 Lagrange point. The 'best' lunar spiral is selected for each Earth spiral. Finally,comparing the value of the ranking function for each launch date, the favourable and unfavourable launch windows are identified

    Advances in architectural concepts to support distributed systems design

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    This paper presents and discusses some architectural concepts for distributed systems design. These concepts are derived from an analysis of limitations of some currently available standard design languages. We conclude that language design should be based upon the careful consideration of architectural concepts. This paper aims at supporting designers by presenting a methodological design framework in which they can reason about the design and implementation of distributed systems. The paper is also meant for language developers and formalists by presenting a collection of architectural concepts which deserve consideration for formal support

    Design leaps: Divergent thinking techniques across media for architectural design

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    This thesis examines the moments of divergence that occur across media in the early stages of the architectural design process. The term ‘divergent thinking’, coined by Joy Paul Guilford (1967) as a key component of creativity, describes the flexibility and elaboration entailed in an individual’s ability to come up with new ideas. Research across architectural design and cognitive science has previously identified the importance of the balance between divergent and convergent thinking, for creativity within the architectural design process (Lawson, 2006). However, preceding studies have consistently sought to model, and thus converge the very nature of divergence as a form of behaviour. This thesis, instead, shifts focus on the media and techniques that enable the architectural designer to think divergently. In this context, the research is particularly concerned with the creative exchanges between digital and analogue media and the opportunities for design that these create.The research responds to concerns that recent trends within the development of architectural software have shifted the design process away from conceptual thinking, towards processes of simulation. The thesis stipulates that, traditionally, divergence is enabled in the process of architectural design through an iterative process of production, which is articulated in the transition across media, such as drawing and modelling, in their various degrees of resolution. As this iterative switching between media and environments is increasingly short-cut or bypassed within environments of simulation, this thesis examines the possible exchanges between analogue architectural media and the digital context, in order to reveal how architectural divergence can emerge within an expanded field of media.In the context of this thesis, the exploration of divergent thinking has been carried by combining a design research methodology with visual ethnography. A series of key projects explore and develop methods for the introduction of divergent prompts into the architectural design process, drawing techniques from architecture, as well as literature and the visual arts. The implementation of the prompts across design-based projects, draws from the pedagogical context of the design studio to address a wider field of architectural creative practice. Applications examined include student projects, workshops, architectural competitions and engagements with artist and community groups, as sites for the critical analysis and further development of divergent techniques and their respective media contexts. Film, drawing, photography, and their exchanges play a critical part in observing and understanding these divergent moments. The clash between the connotative qualities of abstraction found in architectural drawing and the denotative nature of the digital image, becomes central to this examination of architectural media through the creative practice of divergent strategies.The use, iteration and study of explicit divergent techniques, contributes to the definition of the ‘design leap’ as a response to, and expansion of, the cognitive science term of the ‘leap’ (Wallas, 1926), to describe the moments that actively diverge the designer’s perspective of the process through the media. Defining distinct kinds of ‘design leaps’, the thesis proposes a renewed understanding of subtle divergent processes that already exist within architectural design tradition, as well as a more explicit understanding of the architectural habitus. Further, it reveals the diachronic quality of architecture to adapt to, as well as infuse with divergence, new tools and techniques, through the spatial-representational lens of its pre-existing tools

    A dynamic conductance model of fluorescent lamp for electronic ballast design simulation

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    A Spice-compatible dynamic conductance model of a fluorescent lamp for use in electronic ballast simulation is presented. The time-dependent conductance of the fluorescent lamp is derived from a plasma ionization balance equation that uses simplified descriptions of the physical processes within the lamp as its basis. The model has been designed to enable user-defined lamp radius, length, buffer gas pressure and cold-spot temperature as input parameters thus representing a valuable tool for ballast simulations. Simulation results are compared to experimental measurements and satisfactory agreement is achieved
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