Introduction to the Course Contents
Complexity in Aerospace SystemsAE-645
Department of Aerospace EngineeringIndian Institute of Technology Bombay
Mumbai
Complexity in Aerospace Systems
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,
These elements may include products (hardware, software, firmware), processes, people, . . .
Ref : Systems Engineering Handbook – A Guide for System Life Cycle Processes and Activities. INCOSE-TP-2003-002-03.2.1, 2011
System
System is a combination of interacting elements organized to achieve one or more stated purposes
Not a system
System
System is a combination of interacting elements organized to achieve one or more stated purposes
System
System
Not a system
System is a combination of interacting elements organized to achieve one or more stated purposes
System
Simple problems :
Monolith code (only main function)
Function (aero)
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end
Consider software:
Complex problems :
Monolith code. May prove too
difficult to evolve!
OR
Decompose, code, verify
and synthesize. Easy to evolve!
Function (aero
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end
Function (aero)
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end
Function (aero)
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end
Function (aero)
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end
System is a combination of interacting elements organized to achieve one or more stated purposes
What is Complex?
• Complex Vs Complicated
• Complicated can be simplified and improved
– eg. Mr XYZ is known to complicate things!
– ie. Whatever XYZ says is difficult to understand
– But can be said in a way that is easier to understand
• Complex if simplified goes wrong!
Measures of Complexity?
• Not really? When you face complexity, you know it!• However, some indices for complexity
– Degree of hierarchy: The nestedness, or levels within a system
– Network complexity. average number of connections per vertex.
– Statistical: The minimum information about a systems past behavior required to predict its near-future behaviour
– Algorithmic: The number of bits in the shortest computer program that completely describes the system.
– Logical depth: The number of steps a Turing machine would take to construct the series of 0s and 1s that completely describes a system.
– Transaction information: The number of bits of information required to identify the elements of a typical system
Largeness, Connectedness
Nonlinearity? Vague!
Uncertainty
Connectedness!
• 2003-04 : HAL Design leaders descend on us
• Brainstorm on what could be the reason for strange, catastrophic feel on control stick for lateral inputs (aileron for roll). IJT.
• After application of some input it abruptly loosens! �In-advertant application
• Flight mechanics? Hinge moments? No clue!
• Israeli experts � Teflon bush used in mechanical circuit!
• For want of a nail a kingdom can be lost!
δ
F
Do you have an example?Explanation of some observed behaviour of one element coming from another element
that is connected!
1. Yes
2. NoYe
s
No
56%
44%
Kindly post it on moodle
Uncertainty?
• Assume you are a CFD expert and have estimated the aerodynamics of an aircraft; CD0 = 0.0176
• Using this CD0 you estimate all performance parameters of the aircraft
– Max cruise velocity, Vmax = 311 m/s;
– Max range, Rmax = 5503 km @ V = 270 m/s
Vmax is given by
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0%11%
89%
How did you pick your answer to Vmax question?
1. Could recall the equation
2. Eliminated options that I
could argue are wrong
3. Guess ☺Could
reca
ll th
e equat
ion
Elimin
ated o
ptions
that .
..
4%14%
82%
How did you eliminate 2 wrong options?
1. They had parameters that had no business to be there
2. Dimension (units) check
3. Any other?They
had para
mete
rs th
..D
imensi
on (units
) check
Any o
ther?
7% 7%
86%
Uncertainty?
• Assume you are a CFD expert and have estimated the aerodynamics of an aircraft; CD0 = 0.0176
• Using this CD0 you estimate all performance parameters of the aircraft
– Max cruise velocity, Vmax = 311 m/s;
– Max range, Rmax = 5503 km @ V = 270 m/s
Uncertainty?
• Assume that you contact 14 CFD groups you know and have confidence in
• Together you have 14 codes and cannot arrive at a consensus on which grid (3 types) to use and which turbulence model.
• 35 different solutions are created!
Uncertainty?
• Largest value = 0.037• Smallest value = 0.012• Our estimate = 0.0176
What will you do?
What will you do?
1. Estimate for worst case (ie. Largest CD0 value)
2. Estimate performance for average of all CD0 estimates
3. Hold on to your estimate of CD0 and ignore that of others
4. Any other strategy?
Estim
ate fo
r wors
t ca
se (i
..
Estim
ate p
erform
ance
fo...
Hold
on to
your
estim
ate...
Any o
ther
stra
tegy
?
29% 29%
4%
39%
Non-linearity!• 1979 : Dr M Krishnamurthy, IITK spends one year at Lockheed investigating slender nose geometries. Interested in vortex shedding
• Finds that at high AoA, vortices are asymmetric, even when everything is symmetric
• Close inspection reveals tiny, tiny dent on one side
• Gets best (possible) finish model.
• Surprised and shocked to find that asymmetry prevails �
• Returns with tons of curiosity
• It was so much excitement to listen and wonder about this
Non-linearity!
• 1994. ADA developing LCA.
• Pressure recovery of intake drops suddenly on throttling down beyond a point!
• Opening throttle showed a hysteresis! Lets us hear this from the horses mouth! Jolly Video
Mass flow
Pressure Recovery
What is common betweenMillenium Bridge Vs metronome
• Bridge collapse induced by soldiers marching was known prior to 1850
• 1850 : Bridge collapses in France when soldiers cross
• Watch Millenium Bridge, Londonhttp://www.youtube.com/watch?v=eAXVa__XWZ8
• Watch what the metronomes do!1) 5 metronomes
http://www.collegehumor.com/video/3391870/metronome-sync
2) 32 metronomes
http://www.youtube.com/watch?v=kqFc4wriBvE
Top Level Motivation
• UG and PG programmes impart good understanding of elements of aerospace systems,
– Aerodynamics,
– Structures,
– Propulsion, etc.
• Today’s graduates are armed with good knowledge of
– Linear sub-systems
– Loosely connected to each other
– Operating under deterministic conditions.
Top Level Motivation
• Capstone design course offers opportunity to
synthesize the above knowledge in a limited sense.
• Today’s systems
– Have sub-systems designed to perform well
outside linear domain,
– Weather uncertainty.
– Tightly coupled to other subsystem(s)
• How to unravel the mystery of Complexity of
(Aerospace) Systems?
Why exposure to Complexity?
• Additional dimensions to think along, when faced with unexplainable behaviour
• Easier to comprehend what is happening
• Possible to suggest models that may capture observed behaviour
Is an R-L-C Circuit a System?
1. No
2. Yes
3. Not sureN
o
Yes
Not s
ure
18%
4%
79%