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U of M CE 5214 - Engineering Systems - Notes from the MIT ESD

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1Reminders• handouts• Returns• Homework 3 due next week• Draft term paper due next weekEngineering Systems:Notes from the MIT ESDSymposium, March 2004David LevinsonEngineering Systems• We are interested in systems with the followingcharacteristics:– Technologically Enabled– Large Scale (large number of interconnections andcomponents)– Complex– Dynamic, involving multiple time scales and uncertainty– Social and natural interactions with technology– May have Emergent PropertiesES Requires• An Interdisciplinary Perspective—technology,management science and social science• The incorporation of system properties, such assustainability, safety and flexibility in the designprocess. (These are lifecycle properties rather thanfirst use properties.)• An Enterprise Perspective• The incorporation of different stakeholderperspectivesES Examples• Military Aircraft Production & MaintenanceSystems• Commercial & Military Satellite Constellations• Megacity Surface Transportation Systems• The Worldwide Air Transportation & Air TrafficControl System• The World Wide Web & the Underlying Internet• Automobile Production & Recycling Systems• Consumer Supply Logistics Networks• Electricity Generation & Transmission SystemsHierarchy ofKnowledge• 1. Observation• 2. Classification• 3. Abstraction• 4. Quantification and Measurement• 5. Symbolic Representation• 6. Symbolic Manipulation• 7. Prediction2Disciplines with ES• Systems Engineering• Operations Research• Engineering Management• Technology PolicySystems Architecture• an abstract description of the entities of a systemand the relationships between those entities.• System engineering theory works most smoothlywhen the product can be broken into modules thatare relatively independent - Modular.• When products cannot be decomposed simply, orwhen their behaviors interact, they are calledintegral. Examples of Desirable andUndesirable Anticipated andEmergent System PropertiesInfluenced by Architecture4 Types ofArchitectures• The functional architecture (a partially ordered list ofactivities or functions that are needed to accomplish thesystem’s requirements)• The physical architecture (at minimum a node-arcrepresentation of physical resources and theirinterconnections)• The technical architecture (an elaboration of the physicalarchitecture that comprises a minimal set of rules governingthe arrangement, interconnections, and interdependence ofthe elements, such that the system will achieve therequirements)• The dynamic operational architecture (a description of howthe elements operate and interact over time while achievingthe goals)Why is SystemArchitecture Important?• Architecture Is A Way To Understand ComplexSystems• Architecture Is A Way To Design ComplexSystems• Architecture Is A Way To Design Standards AndProtocols To Guide The Evolution Of Long-livedSystems• Architecture Is A Way To Manage ComplexSystemsDecomposition ofArchitecture3Further DecompositionProperties• Delivery of Basic Function: Performance & Cost• Illities: Flexibility Robustness Scalability SafetyDurability Sustainability Reliability RecyclabilityMaintainability Quality• Characteristics: Complexity, Emergence, SystemsArchitecture, UncertaintyRobustness• Robustness is defined as “the demonstratedor promised ability of a system to performunder a variety of circumstances, includingthe ability to deliver desired functions inspite of changes in the environment, uses, orinternal variations that are either built-in oremergent” (ESD 2002).Adaptability• Adaptability is defined as “the ability of asystem to change internally to fit changes inits environment,” usually by self-modification to the system itself (ESD 2002).Flexibility• Flexibility is defined as “the property of a systemthat is capable of undergoing classes of changeswith relative ease. Such changes can occur inseveral ways: a system of roads is flexible if itpermits a driver to go from one point to anotherusing several paths. Flexibility may indicate theease of ‘programming’ the system to achieve avariety of functions. Flexibility may indicate theease of changing the syscomplexity and rework”(ESD 2002).Safety• Safety is defined as “the property of being freefrom accidents or unacceptable losses.” Associatedwith this definition are several others: An accidentis “an undesired and unplanned (but notnecessarily unanticipated) event that results in aspecified level of loss” (human, economic, etc). Ahazard is “a state or sets of conditions that, togetherwith worst-case external conditions, can lead to anaccident.” Risk is “the level of hazard combinedwith the likelihood of the hazard leading to anaccident, and the duration of exposure to thehazard” (Leveson 1995).4Scalability• Scalability is defined as “the ability of asystem to maintain its performance andfunction, and retain all its desired propertieswhen its scale is increased greatly, withoutcausing a corresponding increase in thesystem’s complexity” (ESD 2002).Complexity is Complex• 1. Behavioral complexity—A system is deemed behaviorally complex if itsexternal behavior is difficult to predict. Unfortunately, it does not take much toachieve this state of affairs. Chaotic and thus unpredictable behavior can beachieved with a relatively simple mechanical arm.• 2. Interface complexity—A system has a complex interface if it has numerouscomponents, such as knobs and dials, in its interface to humans or to othertechnical systems. Systems with complex interfaces are usually difficult forhumans to operate or successfully integrate with other systems. George Millerwrote a famous paper in psychology called The Magical Number 7±2 (1956).An interpretation of the paper is that humans are limited in their processingability to dealing with no more than 7±2 different things at any one time.• 3. Structural complexity—A system is structurally complex if it has numerouscomponents whose interconnection, interaction or interdependence is difficultto describe or understand. Our discussion below will emphasize structuralcomplexity. It is hoped that systems whose structural complexity is reasonablylimited will meet the traditional, and some non-traditional, properties and goalswithout too much difficulty.SustainableTransportationTwin Cities Transit &Land Use• Attached Case• Questions:• Consider


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