Introduction to the Course Contents

Complexity in Aerospace SystemsAE-645

Department of Aerospace EngineeringIndian Institute of Technology Bombay

Mumbai

Complexity in Aerospace Systems

? ?

,

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%