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CONCEPTS OF DESIGNSlide Number 2TradeoffsSlide Number 4Other Views of Design …The Objectives TreeA Decision Matrix: Flettner RotorshipKnowledge vs. ConfidenceCombine Knowledge and Confidence: BeliefFunction AnalysisUnderstanding ComplexityWhy does it take so long!?Gantt Charts: a Graphical ScheduleA Few References…Massachusetts Institute of Technology, Subject 2.017CONCEPTS OF DESIGNMassachusetts Institute of Technology, Subject 2.017Yours truly, as a high-school senior!Massachusetts Institute of Technology, Subject 2.017Tradeoffs• Everything interesting that you do in LIFE and in DESIGN is a tradeoff – getting what you want at the expense of something else.Industrialmachinesbreakdowns/yearpurchase coststrengthweightBuildingmaterialsBrand ABCcarbonfibersteelAlMotorservopositioning errorpower consumptionA smartercontroller!Old vs. used?Maintenance?Cost? Fatigue?Heterogeneous?Finish? Corrosion?Complexity? Robustness? Cost?Massachusetts Institute of Technology, Subject 2.017• Design is a process of – Understanding the problem– Creating solutions– Evaluating solutions• Crucial role of modeling and testing– Refining and revising– Detailing the designNeed/GoalProblem StatementCandidatesBest CandidateProductClarify functions and objectivesCreateEvaluateDetailDOCUMENTATION THROUGHOUT !Massachusetts Institute of Technology, Subject 2.017Other Views of Design …Math, Science, Engineering FundamentalsPracticalKnowledgeQuantitativeDesign Analysis,OptimizationPragmaticDesign AnalysisProduct“formal”“modeling”“hands-on”“what works”“organization”“classwork”“planning”timedesign freedomknowledgegeometrypayloadsea-keepingpropulsionpowercontrolsensorsmaintenanceDesign SpiralMassachusetts Institute of Technology, Subject 2.017The Objectives TreeBroad objectives…… Specific objectivesHOW ? WHY ? Have a positive experiencein 2.017Get a good gradeLearn a lotHave funParticipate, innovate, initiateDo assigned workTake advantage of resourcesRequest lecturesUse the shopApply prior knowledgeGet alongPlan aheadEstablish responsibilitiesUse a few design methods !The FSH Objectives TreeMassachusetts Institute of Technology, Subject 2.017A Decision Matrix: Flettner RotorshipWhat is the impact of these ENGINEERING ATTRIBUTES, relative to REQUIREMENTS?A: High rotary speed B: Large rotor diameter C: Stiff inner structureD: Number of rotors E: Height of rotorREQUIREMENTS Weighting A B C D EPropels the boat 40 2 2022Robust to damage 10 -1 0 2 -1 -1Easy to fabricate 30 -1 0 -1 -1 -1High boat stability 20 0 -1 -1 0 -2Weighted sums: 40 60 -30 40 -40• Attribute B (a large rotor diameter) is most important to meeting the requirements.• Attributes C and E (stiff inner structure, tall rotors) have negative impact on meeting the requirements. • The calculation helps identify and document priorities and the direction of the design.• It suggests areas where further clarification of requirements or attributes is needed.• Related to “House of Quality” and “Quality Function Deployment”Massachusetts Institute of Technology, Subject 2.017Knowledge vs. Confidence• Knowledge about an idea and confidence in it are not the same thing! • Target: a specification, criterion, requirement• Idea: one possible solution• A measure of knowledge: what is the probability of you getting a true/false question right about the idea? Clueless: K = 0.5 Expert: K = 1.0• A measure of confidence: what is your certainty that the idea will meet the target? Impossible  Doubtful  Likely  PerfectC = 0.0 C = 0.3 C = 0.7 C = 1.0Confidence is subjective!Knowledgeable but probably not confident at the moment – his vehicle just went into the ocean for the first time!Photo removed due to copyright restrictions.Massachusetts Institute of Technology, Subject 2.017Combine Knowledge and Confidence: Belief• A measure of belief: confidence that an idea meets the target, based on current knowledge.• Using the above numerical values and Bayesian analysis, Ullman (2001) computes Belief = 2KC - K - C + 1, leading to a “belief map” knowledgehighlowconfidencehighlow0.50.80.20.60.4Belief Contours:Decisions should be based on a high level of belief – you have to have knowledge of the idea AND confidence that it meets the targetEOEPMassachusetts Institute of Technology, Subject 2.017Function AnalysisFlow-Chart: Algorithm design, ProcessesLayered Functions: A complex system having multiple functionsDrive robot toward targetRange rate?Go in a straight line for one minuteTurn aroundCaptured!_0+Allows a person to write and edit words or images on paperMakes mark on paperFits in hand comfortablyErases own marksAutonomous underwater vehicle homing to an acoustic beaconSimilarity to objectives treeRobot and docking mechanismMassachusetts Institute of Technology, Subject 2.017Understanding Complexity• Complexity is often what causes the hardest problems – and solutions that are time-consuming and expensive.• High costs of errors once a product is out the door.• Piecemeal vs. Holistic design.• Fundamental rules of design – e.g. grounding & isolation, stainless steel, well-known vendors, etc.• Basic rule: Layered Sub-functions  Complexity.Main functionSubfunction 1Subfunction 2Subfunction 3Subfunction 1.1Subfunction 1.2Subfunction 3.1Level 123How many functions does a car door serve?Fluid mechanics rig at the MIT Testing TankMassachusetts Institute of Technology, Subject 2.017Why does it take so long!?Person-hours design effort can be estimated asH = A * B * C whereA = a constant depending on communication and size of engineering group: values typically in the range 30-150 in commercial world – it may be lower or higher for students!B = sum of products of level number and number of subfunctions at that level (1+6+9 = 16 in figure above).C = difficulty (1 is easy – known technologies, 3 is hard – many unknown technologies) Even a seemingly simple project easily runs into thousands of hours @#$%^&* Role of complexity should be kept in mind when milestones are defined and setAutonomous kayak in Singapore Harbor – lots of functions but not too many subfunctionsMassachusetts Institute of Technology, Subject 2.017Gantt Charts: a Graphical ScheduleClarify problemModeling BrainstormingFirst design iterationExperiments &


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MIT 2 017J - CONCEPTS OF DESIGN

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