ME4235 Fall 2015 1 Student Ed

7/24/2019 ME4235 Fall 2015 1 Student Ed

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ME4235

Introduction to Aeroelasticity (ME4235)

Lecture 1

John T. KimNational University of Singapore

Department of Mechanical Engineering

August 11, 2015


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ME4235 Agenda

1. About the instructor John

2. Prerequisites

3. Text books and references

4. Course outline

5. Teaching philosophy6. Grading and class rules

7. Aeroelastic triangle of forces

8. Historical background

9. Aeroelastic tasks in aeronautical industry

10. Simple mathematical description

11. Aeroelastic operators

12. Summary


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About the Instructor John

16.5 years of experience at Boeing Commercial Aircraft.

Specialty: fluid-structure-control interaction, a.k.a.,

Aeroservoelasticity, system identification & reduced-order

modeling, structural dynamics, control of structures, unsteady

aerodynamics, composite structures.

Have taught Computational Methods in Aeroelasticity at

Boeing, NASA Langley, AIAA Conf., NAL Bangalore, India.

Associate Fellow, AIAA (American Institute of Aeronautics and

Astronautics)

Research Associate at GaTech.

Ph.D. from M.I.T. Aero & Astro Dept.

Joined NUS in 2013.


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Prerequisites

ME2134 Fluid Mechanics I ME2114 Mechanics of Materials II

Familiarity with Structure (Vibration, Natural

Modes, Natural Frequencies), Aerodynamics,

(some) Control. Familiarity with Linear Algebra, ODE, PDE.

Some familiarity with airplanes.


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Familiarity with Subjects (Survey)

How many of you are NOT familiar with

Structural Mechanics, Strength of Materials?

Dynamics?

Fluid Mechanics, Aerodynamics?

Linear Algebra?

ODE, PDE? Classical Control Theory?

How many of you ARE familiar with

Structural Dynamics (Eigenvectors & values)?

Calculus of Variation, Energy Methods?

Mechanics of Composite Materials?

Random Processes?

Modern Control Theory?


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Text Books and References

1. Bisplinghoff, R.L., Ashley, H. and Halfman, H.,Aeroelasticity. Dover Science, 1996.

2. Hodges, D.H and Pierce, G.A., Introduction to

Structural Dynamics and Aeroelasticity, Cambridge

University Press, 2011.3. Y.C. Fung,An Introduction to the Theory of

Aeroelasticity, Dover, 1994.

4. Wright, J.R. and Cooper, J.E., Introduction to Aircraft

Aeroelasticity and Loads, John Wiley & Sons, 2008.

5. Dowell, E. H., A Modern Course on Aeroelasticity,Kluwer Academic Publishers, 1989.

6. Craig, R.R., Structural Dynamics: An Introduction to

Computer Methods, John Wiley & Sons, 1981.


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Course Outline

1. Introduction (0.5 wks)2. Structures & Structural Dynamics (3 wks)

3. Aerodynamics (2 wks)

4. Static Aeroelasticity (2 wks)

5. Flutter (3 wks)

6. Gust Response (1 wks)

7. Miscellaneous TopicsAeroservoelasticy, Nonlinear

effects, Experimental Methods, etc. (1.5 wks)


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Grading and Class Rules

HW (50%)+Mid and Final take home (50%).

Students are allowed to work together on HW but the

final work must be individuals effort.

Students are NOT allowed to work together on take

home quizzes.

Attendance is important.

Be diligent in taking notes!


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Teaching Philosophy

Questions are always welcome!

The only stupid question is question not asked.

Understanding the underlying physics is most important.

There will be plenty of mathematics but it is only used as

a tool, is not the end itself.

My class is not a series of seminars, so please do not

expect beautiful, sophisticated slides.

Will present equations on slides, but oftentimes derivethem on whiteboard.

Will try to strike a good balance between physics and

real applications.


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Lessons of Space Shuttle Columbiadisaster (Feb. 2003)

Only engineers and scientists with solid physical

backgrounds can prevent the disasters in the sky!


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AerodynamicForce

InertiaForce

ElasticForce

Flight DynamicsStability

StaticAeroelasticity

Mechanical

Vibration

Dynamic Aeroelasticity(Structural Dynamics)

Flutter Gust Loads Buffet

Aeroelastic Triangle of Forces

Aeroelasticity is a study of structure and aerodynamics, how they interact each

other, how the airplane responds under the fluid-structure interaction, how such

an interaction creates detrimental (or benign) effects on the design and

performance of the airplane, and can lead to a potential failure of the structure.


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Aeroservoelasticity

Aeroservoelasticity includes the effect of flight control

systems.

Auto-pilot, ride control, flutter suppression, gust andloads alleviation, etc.

NOTE: Most of airplanes nowadays have fly-by-wire

controls.

Flexible Airplane Dynamics

SensorInputs

Automatic Flight Control System

Control Surface Motion


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Topics in Aeroelasticity

Topics covered: Divergence, load distribution, controlsurface effectiveness, flutter, gust response, random

loads, aerodynamic forces on wings, wind effects on

buildings, aeroelastic tailoring, aeroservoelasticity,

nonlinear effects, experimental methods and flutter

testing. Static divergence and flutter are the most critical issues

and FAA specifically demands all airplanes be free of

them.


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ME4235 What is Flutter?

Flutter:A rapid self-feeding motion, potentially destructive,excited by aerodynamic forces, in aircraft structures,control surfaces and bridge engineering - Wikipedia


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ME4235 continued

http://www.youtube.com/watch?gl=SG&hl=en-GB&v=m686UO68AXI

Tacoma Narrow Bridge Collapse (Tacoma, WA USA, 1940):

http://www.youtube.com/watch?v=xox9BVSu7Ok


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ME4235 continued

Glider in flutter:

http://www.youtube.com/watch?v=kQI3AWpTWhM


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Historical Background

Samuel P. Langleys failed launch of Large Androme A on the

Potomac River (1903)torsional divergence in the wing.


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continued

The Wright brothers utilized warping of the wings to achieve

lateral control (1903).


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continued

Handley Page 0/400 bomber experienced an antisymmetric tail

flutter caused by lack of a torque tube connecting both sides of

elevators (WW I.)the first official record of flutter.


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continued

Fokker D-8 experienced both static wing divergence and wing

bending-torsion flutter.

Read B.A.H. Ch. 1


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theoretical development ( continued)

1. Hans Reissner (1926)theory of wing-load distribution andwing divergence.

2. Roxbee Cox & Pugsley (1932)theory of loss of lateral control

and aileron reversal.

3. Glauert, Frazer, Duncan, Kussner, and Theodorsen (1920-30)potential flow theory for flutter prediction

4. Finite element, computational fluid dynamics (CFD),


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Is Aeroelasticity Still Important?

Yes! As modern aircraft is designed to be lighter, bigger, and more

flexible, Aeroelasticity has become the most critical issue in

aeronautical engineering. Furthermore, addition of control

systems complicates the things, and requires understanding of

Aeroservoelasticity.

A380


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Aeroelastic Tasks in Aeronautical Industry

Static Loads

- static aeroelastic Flutter

- open-loop flutter

- closed-loop flutter

- LCO with nonlinear free-play

- LCO with nonlinear controller

Dynamic Flight Loads

- PSD (linear), TDG (linear & nonlinear)

- Monte Carlo (nonlinear)

Ground Loads

- gear & taxi loads

Engine and Vibration- engine vibration, wind milling, etc

Methods Development (R&D)

NOTE: LCOLimit Cycle Oscillation
http://www.google.com.sg/url?sa=i&source=images&cd=&cad=rja&docid=gL6Y8R4h1YfS6M&tbnid=s7tUwhDOB0Tx8M:&ved=0CAgQjRwwAA&url=http%3A%2F%2Fwww.aircraft-commerce.com%2Fconferences%2FMIA%2FSpeakers.asp&ei=PcAJUsKeKsf_lAW9qoDIDg&psig=AFQjCNF3ttbDKm1MPjuT7ZTnr8Ezaqa0dA&ust=1376457149755295http://www.google.com.sg/url?sa=i&source=images&cd=&cad=rja&docid=fn2AtZSuNw1caM&tbnid=En6DSP7soufMPM:&ved=0CAUQjRw&url=http%3A%2F%2Flogoshistory.blogspot.com%2F2010%2F12%2Fall-boeing-logos.html&ei=578JUq7jMcqfiQfv44CICw&psig=AFQjCNHcDzLY9C-7SPUyFN5kj4WfX7-b9Q&ust=1376457055484275


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Functions of the Flutter Engineering Group

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Flutter Design &

Certification

Testing

Wind Tunnel Flutter ModelsGround Vibration Testing

Flight Flutter Testing

Components Testing

Flutter AnalysisDesign and Certification

Analysis of Flutter Models

Analysis of Flight Test Airplanes

Others

Others

Fleet Support (service bulletins)Research: Methods and Process

Program planning


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ME4235

The coupled fluid-structure can be thought of as aplant(structure) with feedback loop (fluid) and thedynamic pressure as the gain factor.

Aerodynamics

Structure

qdynamic pressure

wing motion

(output)

aerodynamic

force (input)

Simple Mathematical Description

(plant)


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ME4235

Coupled!

Coupled Fluid-Structure is hom ogeneous , self-exci tedsystem.

2

21

pressuredynamic

V

q

coupled equation ( continued)


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ME4235 dynamic instability ( continued )

et

0

XX

00)( XXA q

i


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ME4235 mode tracking of 2D airfoil (continued)

Root locus plot:

V-g plot:

o

ox

x

V VVf

g(damping)

(freq.)

oPlunging (h) @ V=0Pitching (a) @ V=0x

x

x

o

oRe

Im

V increasing

a

h

Unstable

Unstable

Stable

Stable

V


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Creativity is Intelligence Having Fun.


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Concept of Aeroelastic Operators

Can see unifying features of aeroelasticity by introducing

aeroelastic operators:

3 types

Operators operate on deflectionto produceforces.

a) Structural Operators

Linear Spring:

can writewhere

Inertial

cAerodynami

Structural

kx

koperator,structural

xdeflectionq

FforceQ

)S(

,

,

(q)Q S


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continued

operatormatrixsquarek

matrixcolumnqq

matrixcolumnQQ

ij [)S(

:]

:}{

:}{

Elastic body in finite d.o.f.:

Continuous beam:

}]{[}{ qkQ ij

)('''' beamBernoullipIw

operatoraldifferentidx

dEI

wq

pQ

)S( :4

4

d


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continued

There are also Inverse Structural Operators

Spring:

Elastic body:

Continuous beam:

Inverse operators operate on force to obtain deflections

(Q)q -1S

/

kF

1

/

1

)(

][][)(

}{][}{

11

1

ijij

ij

ck

Qkq

S

peratorintegral odxc

functionnelcdpxcw

l

l

)(S

(

:),()(

)ker)(),(

0

1

0

i d


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continued

b) Aerodynamic operators

2D section in steady flow:

=1

22

( . )

can write

where

,

,

=1

2

2

(q)Q A

i d


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continued

can write

where

,

,

1 1

1/2

NOTE: Inverse operators often convenient in Aerodynamics.

(Q)q-1

A

i d


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continued

More general wing:

where

Also,

V

caupwash

V

wq

V

cadiffpress

q

p

Q

a

a

.@

2/1

[email protected]

0

)V

w(

q

p aa A

0

)qp(

Vw aa

0

1-A

ti d


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continued

c) Inertia operators

For concentrated mass:

can write

where

2

2

)(

,

,

dtdmeratorinertia op

xdeflectionq

FforceQ

)I(

(q)Q I

2

2

dt

xdm

ti d


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continued

Application to Aeroelastic Problems

Force acting on structure:

May then write (DAlmebertsPrinciple):

esdisturbancexternalgivenQ

inertiaQ

caerodynamiQ

D

I

A

ADTOT QQQQq )(

DQqqq

or

)()()( IAS

ti d


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continued

S


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ME4235 Summary

Aeroelasticity deals with interaction betweenaerodynamics and structures and hence covers a broad

spectrum of topics that are critical in design, analysis,

and testing of airplanes, lifting surfaces, bridges,

buildings, etc.

It would not exist if structures were perfectly rigid. It requires a comprehensive understanding of fluids and

structures, how they interact. It also requires system

engineering perspective because it is truly an

interdisciplinaryfield. In aeroelasticity, structure is the plant subjected to forces

created by aerodynamics and external loads.

ME4235 Fall 2015 1 Student Ed

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