principles of engineering system design
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Principles of Engineering System Design. Decision Making in System Design. Dr T Asokan [email protected]. Columbia Disaster. Columbia’s 28 th mission was originally scheduled for launch in January 2001. - PowerPoint PPT PresentationTRANSCRIPT
Principles of Principles of
Engineering System DesignEngineering System Design
Dr T Asokan
Decision Making in System Design
• Columbia’s 28th mission was originally scheduled for launch in January 2001.
• Technical problems led to number of postponements (about 18) and finally set for 16th Jan. 2003.
• Some of the insulation tiles had come loose in the previous launches and many engineers felt that the launch should be postponed till it was rectified.
• Top level management took the decision to go ahead.• During the launch few tiles ripped off and possibly damaged
the wings. • Management decided to go ahead and not to interrupt the
mission.• With wing temperatures over 1500 and speed exceeding
mach 24, Columbia disintegrated while entering the atmosphere.
Columbia Disaster
Decision making in Systems Design Many important decisions are made during the development
process
Most of the decisions are not made via a rational, explicit
process
Many uncertainties are to be tackled while making decisions
An important point in decision making is that decisions have
to be made with the best information available at the time,
realizing that the outcomes associated with the decision
remain uncertain when the decision is made.
Level of detail needed to make decisions in the engineering of
a system and the level of detail needed to ensure proper
implementation of the system’s components and CIs need to
be understood clearly.
• Creative generation of alternatives
• Identification and quantification of multiple conflicting criteria
• Assessment and analysis of uncertainty associated with the what is known and what is unknown about the decision situation.
Elements of decision problems
Two approaches
• Lateral Thinking
• Vertical Thinking
Decision Making by Search Process
Axioms of Decision Analysis
• Probability: A common approach in engineering
• Order rule: Our preferences are well defined that any possible list of outcomes associated with the alternatives can be ordered from least preferred to most preferred on each objective in the fundamental objectives hierarchy. The ordered list must be transitive.
• Substitution rule: Willing to substitute any combination of outcomes if we are indifferent between them.
Example: Lottery
Pick six numbers out of 49.
Assume Rs 10,000,000 as prize money
Influence Diagrams and Decision Tree
Decision Trees
Should we have the function in SAC or OAT?Dry
wet
Regret
SAC
OAT
Relieved
Perfect
Disaster
Dry
wet
Expected Utility (SAC)= 0.7x0.65 +0.3x .75= 0.68
0
0.9
0.75
0.65
0.7
0.3
0.3
0.7
Expected Utility (OAT)= 0.7x0.9 +0.3x 0= 0.63
Example: 2
• A company is trying to decide whether to build a conventional or automated plant to produce a new product with an expected life of 10 yrs. The decision must be based on the size of the market for the product.
• Demand is expected to be any of the following 3 cases. – High during the first two years and if found unsatisfactory by the
users, low thereafter– High over the next 10 yrs– Low over the 10 years
INFLUENCE DIAGRAMS
• A graph-theoretic representation of a decision.• Four Nodes: Decision, chance, value and
deterministic• Directed arcs between the nodes• A marginal or conditional probability distribution
defined at each chance node, value node and deterministic node.
• Decision nodes as square boxes, Chance nodes as Oval, value nodes as square with rounded corners
Requirements allocation decision for elevator system
Hitech control
Hi Tech Power
Low risk
Cost Requirements
Performance requirements
Availability Requirements
Cost
Performance
Availability
Fundamental objectives
Power technology
Controller Technology
Risk Management
• Strategies– Avoidance, Transference, Management, Analysis
Risk Avoidance: Selection of low risk alternative
Risk Transference: Options that transfer the risk to others
Risk Management: Use of fall back options in case a riskier option fails
Risk Analysis: Addresses risk explicitly when decisions are made in uncertain situations.
Risk= Exposure to the chance of loss
Risk: The combination of the probability of an event occurring and the significance of the consequences of the event occurring.
Dealing with Risk: Activity of managing the risks through various processes
Risk Analysis
• Utility or Risk Preference Function
Win
.5
Loose
.5
$1000
$-10
Win
.1
Loose
.9
$100,000
$-10000
Certain Equivalent: The value the decision maker is willing to accept
EV (1)=490; EV (2)= 1000
• Risk Premium xp of an event is the difference between the expected value and the certain equivalent.
• Risk-Averse decision: xp > 0
~
XXX p
• Decision making under uncertainty is commonly encountered in various stages of system design
• Identification and quantification of conflicting criteria is very important.
• Various tools are available to help the designer in arriving at a decision
THANK YOU THANK YOU