MIT16_842F09_lec05a

MIT16_842F09_lec05a - October 9, 2009 16.842 Fundamentals...

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16.842 16.842 Fundamentals of Systems Engineering 1 Lecture 5 – Tradespace Exploration and Concept Selection Prof. Olivier de Weck October 9, 2009
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16.842 V-Model – Oct 9, 2009 Systems Engineering Overview Stakeholder Analysis Requirements Definition System Architecture Concept Generation Tradespace Exploration Concept Selection Design Definition Multidisciplinary Optimization System Integration Interface Management Verification and Validation Commissioning Operations Lifecycle Management Cost and Schedule Management Human Factors System Safety
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16.842 3 Outline ± Decision Analysis ± Issues in Concept Selection ± Simple Methods of Concept Selection ± Pugh Matrix ± Multi-Attribute Utility ± Non-Dominance ± Pareto Frontiers, Multiobjective Optimization ± Tradespace Exploration ± Contribution from SEARI
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16.842 4 Concept Synthesis Concept Screening Concept Selection System Design Conceptual Modeling & Optimization metric 1 metric 2 Decision Making Design Modeling & Optimization variable x 1 3 x 1 * Need Qualitative Quantitative “Optimal” Design System Architecture System Design System Architecture Æ Design SRR PDR CDR
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16.842 5 Decision Analysis ± Methods and Tools for ranking (and choosing) among competing alternatives (courses of action) ± Components of a decision ± alternatives ± criteria ± value judgments ± decision maker (individual or group) preferences A B C •cost • performance •r isk C(A)=1.1, + P(A)=0.8, - R(A)=1.5, 0 1.B 2.C 3.A B C A 0 ordinal scale cardinal scale
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16.842 6 Issues in Concept Selection ± multiple criteria – how to deal with them ? ± what if there are ties between alternatives? ± group decision making versus individual decision making? ± relates to stakeholder analysis ± uncertainty ± right criteria? ± right valuation? ± are the best alternatives represented?
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16.842 7 Simple Methods of Concept Selection ± Pugh Matrix ± Uses +, 0, - to score alternatives relative to a datum ± Named after Stuart Pugh ± Utility Analysis ± Maps criteria to dimensionless Utility (0 Æ 1) ± Rooted in Utility Theory (von Neumann-Morgenstern 1944)
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16.842 8 Pugh Matrix Steps 1. Choose or develop the criteria for comparison. Based on a set of system requirements and goals. 2. Select the Alternatives to be compared. The alternatives are the different ideas developed during concept generation. All concepts should be compared at the same level of generalization and in similar language. 3. Generate Scores. Use the “best” concept as datum , with all the other being compared to it for each criterion. If redesigning an existing product, then the existing product can be used as the datum. Evaluate each alternative as being better (+), the same (S, o), or worse (-) relative to the datum. If the matrix is developed with a spreadsheet like Excel, use +1, 0, and -1 for the ratings.
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MIT16_842F09_lec05a - October 9, 2009 16.842 Fundamentals...

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