629 research outputs found
Launch Vehicles Multidisciplinary Optimization, a Step from Conceptual to Early Preliminary Design
No full textA recent collaboration between Politecnico di Milano and Universität Bremen within ESA’s PRESTIGE PhD program has stemmed a significant research effort in the field of Multidisciplinary Design Optimization (MDO) for launch vehicles. This work is aimed at the development and integration of optimization algorithms and engineering methods in a software environment capable of assisting in the conceptual and early preliminary design of space launchers, potentially leading to relevant reductions in development effort and life cycle cost. The implemented MDO approach allows in fact efficient exploration of the design space throughout successive global and local, single and multi-objective optimization processes, guided by the engineering experience of the designer. The main obstacle to the successful application of MDO lays in the difficult task of finding a good compromise between models simplicity and accuracy. To tackle this issue, the engineering models were developed in two successive levels of detail, from conceptual to early-preliminary design. The paper is focused on this modelling effort, showing how a critical analysis of the first level’s results was exploited to improve fidelity and functionality. An overview of the conceptual design models is first presented, together with a quantitative assessment of their accuracy and of the impact of the disciplinary errors on global performance indexes. The models selection converged towards well-known disciplinary tools (NASA’s CEA and USAF’s Missile DATCOM), complemented by a set of ad hoc models in the following disciplines: propulsion, geometry, aerodynamics, weights, trajectory, guidance and control, costs and reliability assessment. The validation campaign showed how system-level errors in performance below 20% can be expected, and allowed identifying the most critical modelling aspects to be improved. In a second part, the paper focuses on the model enhancements stemming from the analysis of the conceptual design results, in particular: solid grain geometry and internal ballistics analysis, pressurization systems and engine cycles modelling, simplified structural sizing for all load bearing components, effect of wind and steering losses on the trajectories, and safety-related analyses (boosters/stages impact ellipse determination, upper stage end-of-life strategy). Validation results are presented with a comparison of the conceptual and early preliminary frameworks, highlighting the advantages in terms of accuracy (down to 12% of worst case system error on performance) with a limited increase in computational effort. The foreseen future research lines are finally discussed, especially those aimed at further increasing the design fidelity and at targeting less traditional launch systems, such as manned and reusable vehicles
A First Step Towards SVAGO: the Space Vehicles Analysis and Global Optimization MDO Tool
No full textBranch and Bound Technique to Efficiently Solve Control and System Design Problems with Mixed-Integer Variables Domains
No full text
eTrust : forming relationships in the online world
No full textThere is one thing that moves online consumers to click "add to cart,"that allows sellers to accept certain forms of online payment, and that makes online product reviews meaningful: trust. Without trust, online interactions can't advance. But how is trust among strangers established on the Internet? What role does reputation play in the formation of online trust? In eTrust, editors Karen Cook, Chris Snijders, Vincent Buskens, and Coye Cheshire explore the unmapped territory where trust, reputation, and online relationships intersect, with major implications for online commerce and social networking. eTrust uses experimental studies and field research to examine how trust in anonymous online exchanges can create or diminish cooperation between people. The first part of the volume looks at how feedback affects online auctions using trust experiments. Gary Bolton and Axel Ockenfels find that the availability of feedback leads to more trust among one-time buyers, while Davide Barrera and Vincent Buskens demonstrate that, in investment transactions, the buyer's own experience guides decision making about future transactions with sellers. The field studies in Part II of the book examine the degree to which reputation facilitates trust in online exchanges. Andreas Diekmann, Ben Jann, and David Wyder identify a "reputation premium"in mobile phone auctions, which not only drives future transactions between buyers and sellers but also payment modes and starting bids. Chris Snijders and Jeroen Weesie shift focus to the market for online programmers, where tough competition among programmers allows buyers to shop around. The book's third section reveals how the quality and quantity of available information influences actual marketplace participants. Sonja Utz finds that even when unforeseen accidents hinder transactions-lost packages, computer crashes-the seller is still less likely to overcome repercussions from the negative feedback of dissatisfied buyers. So much of our lives are becoming enmeshed with the Internet, where ordinary social cues and reputational networks that support trust in the real world simply don't apply. eTrust breaks new ground by articulating the conditions under which trust can evolve and grow online, providing both theoretical and practical insights for anyone interested in how online relationships influence our decisions.</p
eTrust : forming relationships in the online world
No full textThere is one thing that moves online consumers to click "add to cart,"that allows sellers to accept certain forms of online payment, and that makes online product reviews meaningful: trust. Without trust, online interactions can't advance. But how is trust among strangers established on the Internet? What role does reputation play in the formation of online trust? In eTrust, editors Karen Cook, Chris Snijders, Vincent Buskens, and Coye Cheshire explore the unmapped territory where trust, reputation, and online relationships intersect, with major implications for online commerce and social networking. eTrust uses experimental studies and field research to examine how trust in anonymous online exchanges can create or diminish cooperation between people. The first part of the volume looks at how feedback affects online auctions using trust experiments. Gary Bolton and Axel Ockenfels find that the availability of feedback leads to more trust among one-time buyers, while Davide Barrera and Vincent Buskens demonstrate that, in investment transactions, the buyer's own experience guides decision making about future transactions with sellers. The field studies in Part II of the book examine the degree to which reputation facilitates trust in online exchanges. Andreas Diekmann, Ben Jann, and David Wyder identify a "reputation premium"in mobile phone auctions, which not only drives future transactions between buyers and sellers but also payment modes and starting bids. Chris Snijders and Jeroen Weesie shift focus to the market for online programmers, where tough competition among programmers allows buyers to shop around. The book's third section reveals how the quality and quantity of available information influences actual marketplace participants. Sonja Utz finds that even when unforeseen accidents hinder transactions-lost packages, computer crashes-the seller is still less likely to overcome repercussions from the negative feedback of dissatisfied buyers. So much of our lives are becoming enmeshed with the Internet, where ordinary social cues and reputational networks that support trust in the real world simply don't apply. eTrust breaks new ground by articulating the conditions under which trust can evolve and grow online, providing both theoretical and practical insights for anyone interested in how online relationships influence our decisions.</p
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