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1 Stochastic Structural Dynamics Lecture-40 Dr C S Manohar Department of Civil Engineering Professor of Structural Engineering Indian Institute of Science Bangalore 560 012 India [email protected] Problem solving session-4
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Page 1: Stochastic Structural Dynamics Lecture-40 · 2017. 8. 4. · 1 Stochastic Structural Dynamics Lecture-40 Dr C S Manohar Department of Civil Engineering Professor of Structural Engineering

111

Stochastic Structural Dynamics

Lecture-40

Dr C S ManoharDepartment of Civil Engineering

Professor of Structural EngineeringIndian Institute of ScienceBangalore 560 012 India

[email protected]

Problem solving session-4

Page 2: Stochastic Structural Dynamics Lecture-40 · 2017. 8. 4. · 1 Stochastic Structural Dynamics Lecture-40 Dr C S Manohar Department of Civil Engineering Professor of Structural Engineering

2

20

Problem 40A sdof system driven by a filteredGaussian excitation is governed by the equations

2 ; 0 0; 0

Here is zero mean Gaussian white noise process

such that 2

x x x f t x x x

f f t

t

t t D

Set up the equations for time evolution of firsttwo order moments using Markov process approach.Consider the response in the steady state and evaluate

the response moments

Page 3: Stochastic Structural Dynamics Lecture-40 · 2017. 8. 4. · 1 Stochastic Structural Dynamics Lecture-40 Dr C S Manohar Department of Civil Engineering Professor of Structural Engineering

3

20

1 2 2 1

1

2

3

1 22

2 2 1 3

3 3

2 ; 0 0; 0

0; 2

2

x x x f t x x x

f f t

t t t D t t

x xx xx f

x x

x x x xx x t

Page 4: Stochastic Structural Dynamics Lecture-40 · 2017. 8. 4. · 1 Stochastic Structural Dynamics Lecture-40 Dr C S Manohar Department of Civil Engineering Professor of Structural Engineering

4

1 2

22 2 1 3

3 3

0

2

1 1 1

2

0 & 2

, , ; 0; 0

, ~ 1; ~ 1; ~

,

1,2

n n nt

j ijj i jj i j

dx x dt

dx x x x dt

dx x dB t

dB t dB t dB t D

dX t f X t t dt G X t t dB t t X X

X t f n dB t m G n md h X t tdt

h h hf X t GDGt X X X

Recall

Page 5: Stochastic Structural Dynamics Lecture-40 · 2017. 8. 4. · 1 Stochastic Structural Dynamics Lecture-40 Dr C S Manohar Department of Civil Engineering Professor of Structural Engineering

5

2

1 1 1

22 2 1 3

1 2

2

3 23 3

,

1,2

, 2

2

n n nt

j ijj i jj i j

d h X t tdt

h h hf X t GDGt X X X

d h hh X t t X X X Xdt X X

h D hXX X

Page 6: Stochastic Structural Dynamics Lecture-40 · 2017. 8. 4. · 1 Stochastic Structural Dynamics Lecture-40 Dr C S Manohar Department of Civil Engineering Professor of Structural Engineering

6

1 2

22 2 1 3

3 3

2

d X Xdtd X X X Xdtd X Xdt

Page 7: Stochastic Structural Dynamics Lecture-40 · 2017. 8. 4. · 1 Stochastic Structural Dynamics Lecture-40 Dr C S Manohar Department of Civil Engineering Professor of Structural Engineering

7

21 1 2

2 22 2 1 3 2

23 3 3

2 21 2 2 2 1 3 1

1 3 2 3 3 1

22 3 2 1 3 3 3 2

2

2 2

2

2

2

d X X Xdtd X X X X Xdtd X X X Ddtd X X X X X X Xdtd X X X X X Xdtd X X X X X X X Xdt

Page 8: Stochastic Structural Dynamics Lecture-40 · 2017. 8. 4. · 1 Stochastic Structural Dynamics Lecture-40 Dr C S Manohar Department of Civil Engineering Professor of Structural Engineering

8

0 0 0

1 0

2 0

3 0

2 2 21 2 3 1 2 1 3 2 3

Initial conditionsAssume that , & 0 = are all deterministic.

X 0

X 0

X 0

, , , , , 0@ 0

x x f f

x

x

f

X X X X X X X X X t

Page 9: Stochastic Structural Dynamics Lecture-40 · 2017. 8. 4. · 1 Stochastic Structural Dynamics Lecture-40 Dr C S Manohar Department of Civil Engineering Professor of Structural Engineering

9

2

22 2 1 3 3 2

1 2 3 3

1 2

22 2 1 3

3 3

1 2 3

Steady state response analysissteady state

, 0

2 02

0

2 0

0

0

d h X t tdt

h h h D hX X X X XX X X X

d X Xdtd X X X Xdtd X Xdt

X X X

Page 10: Stochastic Structural Dynamics Lecture-40 · 2017. 8. 4. · 1 Stochastic Structural Dynamics Lecture-40 Dr C S Manohar Department of Civil Engineering Professor of Structural Engineering

10

21 1 2

2 22 2 1 3 2

23 3 3

2 21 2 2 2 1 3 1

1 3 2 3 3 1

22 3 2 1 3 3 3 2

2 0

2 2 0

2 0

2 0

0

2 0

d X X Xdtd X X X X Xdtd X X X Ddtd X X X X X X Xdtd X X X X X Xdtd X X X X X X X Xdt

Page 11: Stochastic Structural Dynamics Lecture-40 · 2017. 8. 4. · 1 Stochastic Structural Dynamics Lecture-40 Dr C S Manohar Department of Civil Engineering Professor of Structural Engineering

11

21

222

23

2

1 2

1 32

2 3

21

22

23

1 2

1 3

2 3

0 0 0 1 0 0 00 4 0 2 0 2 00 0 4 0 0 0

1 0 2 1 0 00 0 0 0 1 00 0 1 0 2 0

0 0 0 1 0 00 4

X

XDX

X XX XX X

X

X

X

X XX XX X

1

2

2

2

00 2 0 2 0

0 0 4 0 0 01 0 2 1 0 0

0 0 0 0 1 00 0 1 0 2 0

D

Page 12: Stochastic Structural Dynamics Lecture-40 · 2017. 8. 4. · 1 Stochastic Structural Dynamics Lecture-40 Dr C S Manohar Department of Civil Engineering Professor of Structural Engineering

12

Problem 41In a study on reliability analysis of a cracked plate ithas become necessary to simulate a vector of six non-Gaussian random variables. The specification of theserandom variables is limited to the description of the 1storder pdf-s and the matrix of correlation coefficients.Develop a simulation procedure based on the Nataftransformation to simulate 5000 samples of the randomvariables. Estimate the 1st order PDF-s from the simulatedsample and perform the Kolmogorov-Smirnov test to verifyif the simulations have been performed satisfactorily.

Page 13: Stochastic Structural Dynamics Lecture-40 · 2017. 8. 4. · 1 Stochastic Structural Dynamics Lecture-40 Dr C S Manohar Department of Civil Engineering Professor of Structural Engineering

13

1 2 3

4 5 6 2

The distribution of the basic random variables are as follows:~ 60,10 ; ~ 1,0.2 ; ~ 2,0.1 ;

~ 1 ; , ~ 33.0,0.47,3.5,0.3, 0.9

1.0 0 0 0 0 00 1.0 0 0 0 00 0 1.0 0 0 00 0 0 1.0 0 00 0 0 0 1.0 0.8350 0 0 0 0.835 1.0

X N X LN X LN

X EX X X N

Page 14: Stochastic Structural Dynamics Lecture-40 · 2017. 8. 4. · 1 Stochastic Structural Dynamics Lecture-40 Dr C S Manohar Department of Civil Engineering Professor of Structural Engineering

1414

Partially specified non-Gaussian RVsNataf’s transformation

Let X1 and X2 be two random variables such that

•X1 and X2 are not completely specified•Knowledge on X1 and X2 is limited to first order pdfs and the covariance matrix.

Question: How to transform X to standard normal space?

Page 15: Stochastic Structural Dynamics Lecture-40 · 2017. 8. 4. · 1 Stochastic Structural Dynamics Lecture-40 Dr C S Manohar Department of Civil Engineering Professor of Structural Engineering

1515

1

2

1 1

2 2

*1 2 1 2 12

1 11 1 1

1 2

2 22 2 2

2 1

1

1 1 1 2

2 1 1 2 2

2 2

Let( ) ( )

( )

with ~ (0,1), ~ (0,1) &

( ) ( ); 0

( ) ( ); 0

( ) 0( ) ( ) ( )

( ) ( ) ( )0( )

X

X

P X U

P X U

U N U N U Udx dxp x udu du

dx dxp x udu duu

p x u uJu p x p x

p x

Page 16: Stochastic Structural Dynamics Lecture-40 · 2017. 8. 4. · 1 Stochastic Structural Dynamics Lecture-40 Dr C S Manohar Department of Civil Engineering Professor of Structural Engineering

1616

1 2

1 2

1 2

1 2

1 2

1 2

1 21 2 1 1 2 2

1 2

1 11 1 2 2

1 12 1 2 2

1 1 2 21 11 2

12 1 1 2 2 1 2 1 2

( , )( , ) ( ) ( )

( ) ( )

@ ( ) , ( )

( ) , ( )( ) ( )

( ) ( )

( )( ) ( , )

U UX X

X X

X X

X X

X X

p u up x x p x p x

u u

u P x u P x

P x u P xp x p x

P x P x

x x p x x dx dx

1 2

1 2

1 12 1 2 2

1 1 2 2 1 11 2

1 1 2 2 1 2

( ) , ( )( )( )

( ) ( )

( ) ( )

X X

X X

P x u P xx x

P x P x

p x p x dx dx

Page 17: Stochastic Structural Dynamics Lecture-40 · 2017. 8. 4. · 1 Stochastic Structural Dynamics Lecture-40 Dr C S Manohar Department of Civil Engineering Professor of Structural Engineering

1717

1 2

1 1

1 1

1 1 2 1

1 2 X 1 X 1 1 1 1 2

1 1 *12 1 1 1 2 2 1 2 12 1 2

&

( )( ) , ,

X X

X X

P x z P x z

dx dx p x p x z z dz dz

P z P z z z dz dz

Substitute

Page 18: Stochastic Structural Dynamics Lecture-40 · 2017. 8. 4. · 1 Stochastic Structural Dynamics Lecture-40 Dr C S Manohar Department of Civil Engineering Professor of Structural Engineering

18

1 2

*12

1 1 *12 1 1 2 2 2 1 2 12 1 2

*12

*12 1

( )( ) , ,

(1) Divide the range [-1,1] of into L divisions.

(2) For each value of solve the

X X

Lii

P z P z z z dz dz

Strategy for the determination of the unknown

12 1

12

*12 121

12

above equation

(numerically) and obtain the

corresponding values of . Note that

-1 1 1,2, , .

(3) Interpolate to obtain the value of

for which the target value of is r

Lii

i

Lii

i L

ealized.

Page 19: Stochastic Structural Dynamics Lecture-40 · 2017. 8. 4. · 1 Stochastic Structural Dynamics Lecture-40 Dr C S Manohar Department of Civil Engineering Professor of Structural Engineering

1919

12

*12

12specified

1 1

1

*12 determined

1

Page 20: Stochastic Structural Dynamics Lecture-40 · 2017. 8. 4. · 1 Stochastic Structural Dynamics Lecture-40 Dr C S Manohar Department of Civil Engineering Professor of Structural Engineering

2020

1 2

*12

1 1 *12 1 1 2 2 2 1 2 12 1 2

*

1 2

solve for by solving

( )( ) , ,

Simulate ~ 0, .

Simulate and us

X XP z P z z z dz dz

Z N

X X

Steps for simulation of 2 - dimensional Nataf random variables

Step 1

Step 2

Step 3

1

ing

; 1,2i X iX P U i

Page 21: Stochastic Structural Dynamics Lecture-40 · 2017. 8. 4. · 1 Stochastic Structural Dynamics Lecture-40 Dr C S Manohar Department of Civil Engineering Professor of Structural Engineering

2121

1.6 1.7 1.8 1.9 2 2.1 2.2 2.3 2.4 2.50

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

x

PD

F(x

)

simulation

target lognormal cdf

Page 22: Stochastic Structural Dynamics Lecture-40 · 2017. 8. 4. · 1 Stochastic Structural Dynamics Lecture-40 Dr C S Manohar Department of Civil Engineering Professor of Structural Engineering

2222

0 2 4 6 8 10 120

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

x

PD

F(x

)

simulation

target exponential cdf

Page 23: Stochastic Structural Dynamics Lecture-40 · 2017. 8. 4. · 1 Stochastic Structural Dynamics Lecture-40 Dr C S Manohar Department of Civil Engineering Professor of Structural Engineering

2323

Rho_equivalent_gaussianrho_t =1.0000 0 0 0 0 0

0 1.0000 0 0 0 00 0 1.0000 0 0 00 0 0 1.0000 0 00 0 0 0 1.0000 -0.88330 0 0 0 -0.8833 1.0000

Page 24: Stochastic Structural Dynamics Lecture-40 · 2017. 8. 4. · 1 Stochastic Structural Dynamics Lecture-40 Dr C S Manohar Department of Civil Engineering Professor of Structural Engineering

2424

Msim=59.8787 1.0019 1.9990 1.0044 5.1723e-015 3.4961

Stdsim= 9.9726 0.1986 0.0998 1.0104 2.5838e-015 0.2982

Rhosim=1.0000 -0.0154 0.0093 -0.0135 -0.0013 0.0126-0.0154 1.0000 0.0206 0.0025 0.0014 -0.00680.0093 0.0206 1.0000 -0.0016 0.0018 -0.0058-0.0135 0.0025 -0.0016 1.0000 -0.0180 0.0116-0.0013 0.0014 0.0018 -0.0180 1.0000 -0.83450.0126 -0.0068 -0.0058 0.0116 -0.8345 1.0000

Page 25: Stochastic Structural Dynamics Lecture-40 · 2017. 8. 4. · 1 Stochastic Structural Dynamics Lecture-40 Dr C S Manohar Department of Civil Engineering Professor of Structural Engineering

25

Problem 42A two dof system with cubic and hysteretic nonlinearstiffness characteristics is shown in the figure.

k1 k2 k3

c1 c2 c3

m1 m2

p1(t) p2(t)

u1(t) u2(t)

321

Left support

Right support

R1(t) R2(t)

1 2

3

Springs and have cubic force displacementcharacteristics and spring k is an inelasticspring modeled using Bouc's approach.

k k

Page 26: Stochastic Structural Dynamics Lecture-40 · 2017. 8. 4. · 1 Stochastic Structural Dynamics Lecture-40 Dr C S Manohar Department of Civil Engineering Professor of Structural Engineering

26

31 1 1 1 2 1 2 1 1 1 1 2 1 2

32 1 2 1 1

32 2 2 2 1 3 2 2 2 1 2 2 1

3 2 3 2 2

12 2 2

The system is taken to be governed by the equations

1

| | | | | |n n

m u c u c u u k u u k u u

u u p t w t

m u c u u c u k u u u u

k u k z p t w t

z u z z u z Au

3

1 1 1 4

2 2 2 5

w t

p p w t

p p w t

Page 27: Stochastic Structural Dynamics Lecture-40 · 2017. 8. 4. · 1 Stochastic Structural Dynamics Lecture-40 Dr C S Manohar Department of Civil Engineering Professor of Structural Engineering

27

5

1

2

1 2 1 2

3 1 2

1 2

are given to be a set of independent

white noise processes with .

The various system paramters are as follows:1.0kg, 1.5kg, 0.1kN / m, 0.2kN/m,0.15kN/m, 0.05,

2,

i i

i i i

w t

w t w t

m m k kk

1 2 0

1 2 3 4

5

4, 0.05, 0.5, 0.5, 1, 3,10, 20, 15.6 , 2 , 0.00420.01N, 0.02N, 0.01N, 10.0N and 20.0N

Using 1.5 order strong Taylor's scheme, develop a procedure to simulate samples of the

A nT s t s s

sytem response.Hence estimate the response moments (up to second order)and the first order pdf-s.

Page 28: Stochastic Structural Dynamics Lecture-40 · 2017. 8. 4. · 1 Stochastic Structural Dynamics Lecture-40 Dr C S Manohar Department of Civil Engineering Professor of Structural Engineering

28

, 0 21

1

,

1

,0 ,0

, ,1

02 2

1 1

,

, 1 1

Recall

12

, ,2

2 1 2 ,

1 1 1 ,12 2

12

mn n n n j j nk k k k k

j

mj n j n j j j

k kj

j jj j j j

p

j i p j pi

p di

p k iki i k

d mi j lk k

i l j

x x a b W L a

L a Z b W Zt

W Z a a

i

L ati x

b b

2, ,

1

,d

j j i jki l i

ik k k

L bx x x

Page 29: Stochastic Structural Dynamics Lecture-40 · 2017. 8. 4. · 1 Stochastic Structural Dynamics Lecture-40 Dr C S Manohar Department of Civil Engineering Professor of Structural Engineering

29

1 1 2 2 1 2

1 1 1 0 1 2 1 1 1 2 1 2 3 1 31

4 1 4 5 1 5

2 2 2 1 0 2 2 1 2 1 2 2 211

13 2 3 4 2 4 5 2 5

3 3 3 0 3 2 11

12

12

12

t

k k k k k k k

k k

k k k k k k

k k k

k k k k

x t u t u t u t u t z t p t p t

x x a L a L a Z L a Z L a Z

L a Z L a Z

x x a W L a L a Z L a Zm

L a Z L a Z L a Z

x x a L a L a

3 1 2 3 2 3 3 3

4 3 4 5 3 5

k k k

k k

Z L a Z L a Z

L a Z L a Z

Page 30: Stochastic Structural Dynamics Lecture-40 · 2017. 8. 4. · 1 Stochastic Structural Dynamics Lecture-40 Dr C S Manohar Department of Civil Engineering Professor of Structural Engineering

30

4 4 4 2 0 4 2 1 4 1 2 4 221

23 4 3 4 4 4 5 4 5

5 5 5 3 0 5 2 1 5 1 2 5 21 3

3 5 3 4 5 4 5 5 5

6 6 6 4 0 6 2 1 6 1 2 6 21 4

12

12

12

k k k k k k

k k k

k k k k k k

k k k

k k k k k k

x x a W L a L a Z L a Zm

L a Z L a Z L a Z

x x a W L a L a Z L a Z

L a Z L a Z L a Z

x x a W L a L a Z L a Z

3 6 3 4 6 4 5 6 5

7 7 7 5 0 7 2 1 7 1 2 7 21 5

3 7 3 4 7 4 5 7 5

12

k k k

k k k k k k

k k k

L a Z L a Z L a Z

x x a W L a L a Z L a Z

L a Z L a Z L a Z

Page 31: Stochastic Structural Dynamics Lecture-40 · 2017. 8. 4. · 1 Stochastic Structural Dynamics Lecture-40 Dr C S Manohar Department of Civil Engineering Professor of Structural Engineering

31

0 1 2 1 1 2 1 3 1 4 1 5 11

1

1 2 20 2 1 1 31 2 1 2

1

2 3 4 521 31 2 2 2 2

1 1 1 1

1 2 2 2 3 21 21 2 22

1 2 1

, , 0, 0, 0, 0

3 3

3

, ,

k k k k k k k

kk k k k

k k k kk k

k k k

L a a L a L a L a L a L am

aL a k k x x xm

a a a ac c k x x cm m m m

L a c c L a c L am m m

4 2 5 24

1

0,

, 0k kL a L am

Page 32: Stochastic Structural Dynamics Lecture-40 · 2017. 8. 4. · 1 Stochastic Structural Dynamics Lecture-40 Dr C S Manohar Department of Civil Engineering Professor of Structural Engineering

32

0 3 4 1 3 2 3 3 3 4 3 5 32

2

1 220 4 3 12 2 2

2 2

3 4 523 12 3 2 2 3 3

2 1 2

1 4 2 41 22 2 32

2 1 2

3

, 0, , 0, 0, 0

3

3 1

, ,

k k k k k k k

k kk k k

k k kk k

k k

L a a L a L a L a L a L am

a aL a k x x cm m

a a ak k x x c c km m m

L a c L a c cm m m

L a

4 4 4 5 43 53

2 2

1 , 0,k k kk L a L am m

Page 33: Stochastic Structural Dynamics Lecture-40 · 2017. 8. 4. · 1 Stochastic Structural Dynamics Lecture-40 Dr C S Manohar Department of Civil Engineering Professor of Structural Engineering

33

3

0 5 4 5 5 1 4 5

5 4 5 1 4 5 5 2 5 4 5 1 5

24 5 5 12

22

4 5 2 5 4 5 5 3

2

| | sgn | |

| || | 1 | | | | sgn | | sgn

2 | |2

1 | || | sgn 1 2 | | | | sgn

2

n nk k k k k k

n n nk k k k k k k k k k

nk k k

n nk k k k k k k

L a a x x x x A

a x x n x x x x nx x x

x x xm

n x x x n n x x x x

25

4 5 2 5 4 5 5 2 5

24 5 2 5 4 5 1 5

1 | || | sgn 2 1 | | | |

1 | | sgn 2 | |

n nk k k k k k k

n nk k k k k k

n x x x n x x x x

n n x x x nx x x

Page 34: Stochastic Structural Dynamics Lecture-40 · 2017. 8. 4. · 1 Stochastic Structural Dynamics Lecture-40 Dr C S Manohar Department of Civil Engineering Professor of Structural Engineering

34

1 5 2 5 5 5 1 4 5222

3 5 4 5 1 4 5 5 2 5 4 5 2 53

4 5 5 5

0 6 6 1 6 2 6 3 6 4 6 51 4 1

0, | | sgn | | ,

| || | 1 | | | | sgn | | sgn ,

0, 0

, 0, 0, 0, ,

n nk k k k k k

n n nk k k k k k k k k

k k

k k k k k k

L a L a x x x x Am

L a x x n x x x x nx x x

L a L a

L a a L a L a L a L a L a

6

0 7 7 1 7 2 7 3 7 4 7 5 72 4 2

0

, 0, 0, 0, 0,

k

k k k k k k kL a a L a L a L a L a L a

Page 35: Stochastic Structural Dynamics Lecture-40 · 2017. 8. 4. · 1 Stochastic Structural Dynamics Lecture-40 Dr C S Manohar Department of Civil Engineering Professor of Structural Engineering

35

time s

1u t

Page 36: Stochastic Structural Dynamics Lecture-40 · 2017. 8. 4. · 1 Stochastic Structural Dynamics Lecture-40 Dr C S Manohar Department of Civil Engineering Professor of Structural Engineering

36

time s

1u t

Page 37: Stochastic Structural Dynamics Lecture-40 · 2017. 8. 4. · 1 Stochastic Structural Dynamics Lecture-40 Dr C S Manohar Department of Civil Engineering Professor of Structural Engineering

37

time s

2u t

Page 38: Stochastic Structural Dynamics Lecture-40 · 2017. 8. 4. · 1 Stochastic Structural Dynamics Lecture-40 Dr C S Manohar Department of Civil Engineering Professor of Structural Engineering

38

time s

2u t

Page 39: Stochastic Structural Dynamics Lecture-40 · 2017. 8. 4. · 1 Stochastic Structural Dynamics Lecture-40 Dr C S Manohar Department of Civil Engineering Professor of Structural Engineering

39

time s

z t

Page 40: Stochastic Structural Dynamics Lecture-40 · 2017. 8. 4. · 1 Stochastic Structural Dynamics Lecture-40 Dr C S Manohar Department of Civil Engineering Professor of Structural Engineering

40

time s

1p t

Page 41: Stochastic Structural Dynamics Lecture-40 · 2017. 8. 4. · 1 Stochastic Structural Dynamics Lecture-40 Dr C S Manohar Department of Civil Engineering Professor of Structural Engineering

41

Stochastic structural dynamics

Uncertainty modeling•Probability•Random variables•Random processes

Propagation of uncertainty•Analytical procedures forLTI systems (time/frequency)•Markov vector approach

Reliability analysis•First passage•Extremes•Fatigue

Monte Carlo simulations•Gaussian/non-GaussianRandom variables & random processes•Variance reduction

Applications•Earthquake•Fatigue•High frequency analysis

Page 42: Stochastic Structural Dynamics Lecture-40 · 2017. 8. 4. · 1 Stochastic Structural Dynamics Lecture-40 Dr C S Manohar Department of Civil Engineering Professor of Structural Engineering

42

What next?

•Structural system identification•Reliability model updating•Structural health monitoring

Further applications•Wind, waves, guideway uneveneness,…•Hazard and risk analysis

•Earthquake•Wind

•Performance based design•Design code development…..

Sensing + Computing

Page 43: Stochastic Structural Dynamics Lecture-40 · 2017. 8. 4. · 1 Stochastic Structural Dynamics Lecture-40 Dr C S Manohar Department of Civil Engineering Professor of Structural Engineering

43

Discussion on mean square estimation

Page 44: Stochastic Structural Dynamics Lecture-40 · 2017. 8. 4. · 1 Stochastic Structural Dynamics Lecture-40 Dr C S Manohar Department of Civil Engineering Professor of Structural Engineering

44

Introductory comments

Let X and Y be two random variables with a known jpdf. Assuming that in a particular experiment, the random variable Y can be measured and takes the value y. What can we say about the corresponding value, say x, of the unobservable variable X?

Suppose we make an estimate, say, x*, of the value of Xwhen Y=y, according to the rule x*=h(y). h(y)=unspecified function of y. The error of our estimate e=x-h(y).We can never hope to make e=0. Can we select h such that we minimize the expected value of some function of e?

Page 45: Stochastic Structural Dynamics Lecture-40 · 2017. 8. 4. · 1 Stochastic Structural Dynamics Lecture-40 Dr C S Manohar Department of Civil Engineering Professor of Structural Engineering

45

Let x(t) and y(t) be two Gaussian random processes with a known joint pdf.Let it be assumed that we can observe y(t) and not x(t).Given the observation of a sample of y(t) for t in 0 to T, how to estimate the value of x(t) for some value of t?

Typical problem in dealing with random processes

Page 46: Stochastic Structural Dynamics Lecture-40 · 2017. 8. 4. · 1 Stochastic Structural Dynamics Lecture-40 Dr C S Manohar Department of Civil Engineering Professor of Structural Engineering

46

Problem 1

Let Y be a random variable and c be a constant. We wish to estimateY by a constant.Find c such that E[(Y-c)2] is minimized.

YEdyyypcce

dyypcycYEe

Y

Y

)(0

)(22

Page 47: Stochastic Structural Dynamics Lecture-40 · 2017. 8. 4. · 1 Stochastic Structural Dynamics Lecture-40 Dr C S Manohar Department of Civil Engineering Professor of Structural Engineering

47

Problem 2Let X and Y be two random variables. We wish to estimate Y by a function c(X).To find c(X) such that e=E{[Y-c(X)]2} is minimized.

2 2

2

2

0 0

2

( ) ( ) ( , )

( ) ( | ) ( )

( ) ( ) ( | )

would be a minimum if ( ) minimizes

( ) ( | ) for every fixed value of .

XY

Y X

X Y

Y

e E Y c X y c x p x y dxdy

y c x p y X x p x dxdy

p x y c x p y X x dy dx

e c x

y c x p y X x dy x

Page 48: Stochastic Structural Dynamics Lecture-40 · 2017. 8. 4. · 1 Stochastic Structural Dynamics Lecture-40 Dr C S Manohar Department of Civil Engineering Professor of Structural Engineering

48

From solution of Problem 1 we have

( ) ( | ) |Yc x yp y X x dy E Y X x

Remarks•If Y=g(X), c(x)=E[g(X)|X=x]=g(x) & e=0.•If X and Y are independent, c(x)=<Y>=constant

Page 49: Stochastic Structural Dynamics Lecture-40 · 2017. 8. 4. · 1 Stochastic Structural Dynamics Lecture-40 Dr C S Manohar Department of Civil Engineering Professor of Structural Engineering

49

2

22

2

2 2

min

Let ( )

0 0

0 0

Y X

Y X Y X

Y X X

XY XY X Y XY Y

X X X

Y X XY YXY Y

X

c X AX B

e E Y AX B

e E Y AX B B AB

e E Y AX A E Y A X

e E Y X A XA

r rA

re E Y r X

Linear MS estimation

2

22 21

X

YY XY X Y XY

X

E Y r X r

Page 50: Stochastic Structural Dynamics Lecture-40 · 2017. 8. 4. · 1 Stochastic Structural Dynamics Lecture-40 Dr C S Manohar Department of Civil Engineering Professor of Structural Engineering

50

22min 1 XYY

X

YXYXYXY

X

YXY

re

rABrA

Let X and Y be Gaussian

X

XYXY

X

YXY rxrxXYExc

|)(

For normal random variables, linearand nonlinear ms estimation lead to identical results.

Page 51: Stochastic Structural Dynamics Lecture-40 · 2017. 8. 4. · 1 Stochastic Structural Dynamics Lecture-40 Dr C S Manohar Department of Civil Engineering Professor of Structural Engineering

51

The orthogonality principle

2

0 0

Errordata

e E Y AX B

e E Y AX B XA

Y AX BX

Data is orthogonal to error

Page 52: Stochastic Structural Dynamics Lecture-40 · 2017. 8. 4. · 1 Stochastic Structural Dynamics Lecture-40 Dr C S Manohar Department of Civil Engineering Professor of Structural Engineering

52

1 1 2 2

2 21 1 2 2

1

Let be a random variable &ˆ

be an estimatior of .

ˆ

Select 0 1, 2, ,

tn n

n n

ni i

i

S

S a X a X a X a XS

P E S S E S a X a X a X

Pa i na

General case of linear ms estimation

Page 53: Stochastic Structural Dynamics Lecture-40 · 2017. 8. 4. · 1 Stochastic Structural Dynamics Lecture-40 Dr C S Manohar Department of Civil Engineering Professor of Structural Engineering

53

21 1 1 2 1 2 1 1

22 1 1 2 2 2 1 2

21 1 2 2 1

01 11 12 1 1

02 21 22 2 2

03

0 1 2

0

n n

n n

n n n n n

n

n

n n n nn n

SX a X a X X a X X

SX a X X a X a X X

SX a X X a X X a X

R R R R aR R R R aR

R R R R a

R RA A R

10R

Page 54: Stochastic Structural Dynamics Lecture-40 · 2017. 8. 4. · 1 Stochastic Structural Dynamics Lecture-40 Dr C S Manohar Department of Civil Engineering Professor of Structural Engineering

54

1 1 2 2

2

1 1 2 2

1 01 2 02 0

ˆWe have 0 1,

ˆ 0

ˆ ˆ ˆ ˆ0

ˆ ˆ ˆ ˆ ˆ

ˆ ˆ

ˆ

i

n n

n n

n nt

E S S X i n

E S S a X a X a X

E S S S S S S

P E S S S S E S S S E S S S

P E S S S E S E SS

E SS E S a X a X a X

a R a R a R

A R

0

20

tP E S A R

Page 55: Stochastic Structural Dynamics Lecture-40 · 2017. 8. 4. · 1 Stochastic Structural Dynamics Lecture-40 Dr C S Manohar Department of Civil Engineering Professor of Structural Engineering

55

21 2

21 2

21 2

21 2

0 0

( , , , )

( , , , ) ( , )

( , , , ) ( | ) ( )

( ) ( , , , ) ( | )

n

n SX

n S X

n SX

P E S g X X X

s g x x x p s x dsdx

s g x x x p s X x p x dsdx

p x s g x x x p s X x ds dx

Nonlinear estimation

1 2

is minimum when the second integrand is minimum for any

( , , , ) |n

Px

g x x x E S X x

Page 56: Stochastic Structural Dynamics Lecture-40 · 2017. 8. 4. · 1 Stochastic Structural Dynamics Lecture-40 Dr C S Manohar Department of Civil Engineering Professor of Structural Engineering

56

1 1 2 2

1 1 2 2

We have

( ) 0 1,

ˆi.e., 0 1,

ˆ 0 for any 1,

n n i

i

n n i

E S a X a X a X X i n

E S S X i n

E S S c X c X c X c i n

General orthogonality principle

Page 57: Stochastic Structural Dynamics Lecture-40 · 2017. 8. 4. · 1 Stochastic Structural Dynamics Lecture-40 Dr C S Manohar Department of Civil Engineering Professor of Structural Engineering

57

If ( ) is the nonlinear ms estimator of , the estimation error ( ) is orthogonal to any function ,linear or nonlinear function of data.

:

( ) ( ) ( ) ( ) ( , )

(

SX

g X SS g X w X

E S g X w X s g x w x p s x dsdx

s g x

Proof

) ( ) ( | ) ( )

( ) ( ) ( | ) ( )

( ) ( ) | ( )

( ) | ( ) ( )

( ) ( ) ( ) ( ) 0

S X

S X

X

X

X

w x p s x p x dsdx

w x s g x p s x ds p x dx

w x E S g X X x p x dx

w x E S X x g x p x dx

w x g x g x p x dx QED

Page 58: Stochastic Structural Dynamics Lecture-40 · 2017. 8. 4. · 1 Stochastic Structural Dynamics Lecture-40 Dr C S Manohar Department of Civil Engineering Professor of Structural Engineering

58

If S and X are jointly normal it can be shown that linear and nonlinearestimations of S are equal.

Page 59: Stochastic Structural Dynamics Lecture-40 · 2017. 8. 4. · 1 Stochastic Structural Dynamics Lecture-40 Dr C S Manohar Department of Civil Engineering Professor of Structural Engineering

59

Estimation of a random process

Let S(t) & X(ξ) be two random processes with .ba

Consider the problem of estimating S(t) for a fixed t in terms of X(ξ)specified for every ξ in an interval of finite or infinite length. X(ξ) = data available.

ba

Page 60: Stochastic Structural Dynamics Lecture-40 · 2017. 8. 4. · 1 Stochastic Structural Dynamics Lecture-40 Dr C S Manohar Department of Civil Engineering Professor of Structural Engineering

60

2

1

1

1

ˆ( ) ( ) ( )

( ) ( ) ( )

Select ( ) such that is minimized.

ˆ( ) ( )

error ( ) ( )

Orthogonality principle

( ) ( ) ( )

b

a

b

a

n

k kk

m

k kk

m

k k jk

S t X h d

P E S t X h d

h P

S t h X

S t h X

E S t h X X

1

0 1,

( , ) ( ) ( , ) 1,m

SX j k XX k jk

j m

R t h R j m

Page 61: Stochastic Structural Dynamics Lecture-40 · 2017. 8. 4. · 1 Stochastic Structural Dynamics Lecture-40 Dr C S Manohar Department of Civil Engineering Professor of Structural Engineering

61

0lim ( , ) ( ) ( , )

Smoothing: Prediction: ; , Forward prediction: Backward prediction: Filtering:

b

SX XXa

R t h R d

a t bX t S t t a b

t bt a

X t S t

Page 62: Stochastic Structural Dynamics Lecture-40 · 2017. 8. 4. · 1 Stochastic Structural Dynamics Lecture-40 Dr C S Manohar Department of Civil Engineering Professor of Structural Engineering

62

2

2

Problem: Let ( ) be a stationary random process. Estimate ( ) in terms of .ˆ( ) ( )

( ) ( )

0 ( ) ( ) ( ) 0

( , ) ( )( , )

SS SS

SS S

S tS t S t

S t aS t

P E S t aS t

P E S t aS t S ta

R t t RaR t t

Page 63: Stochastic Structural Dynamics Lecture-40 · 2017. 8. 4. · 1 Stochastic Structural Dynamics Lecture-40 Dr C S Manohar Department of Civil Engineering Professor of Structural Engineering

63

2

( ) ( ) ( ) ( )

( ) ( ) ( )

(0) ( )

( )(0)(0)

Let ( ) exp | |

exp | |exp | |

SS SS

SSSS

SS

SS

P E S t aS t S t aS t

E S t aS t S t

R aR

aRRR

R A

Aa

A

Page 64: Stochastic Structural Dynamics Lecture-40 · 2017. 8. 4. · 1 Stochastic Structural Dynamics Lecture-40 Dr C S Manohar Department of Civil Engineering Professor of Structural Engineering

64

1 2

1 2

2

1 2

11

1 2

2

ˆExample : Let ( ) ( ) ( )

Note: ( ) ( ) ( ) ( ), ( )

( ) ( ) 0

( ) ( ) ( )

0 ( , ) ( , ) 0

( , ) ( )( , )

0 (

SS SS

SS SS

SS S

SS

S t a S t a S t

S t a S t a S t S t S t

E S t S t

P E S t a S t a S t

P R t t a R t ta

R t t RaR t t

P Ra

2 2

( , ), ) ( , ) 0

( , )SS

SSSS

R t tt t a R t t a

R t t

Page 65: Stochastic Structural Dynamics Lecture-40 · 2017. 8. 4. · 1 Stochastic Structural Dynamics Lecture-40 Dr C S Manohar Department of Civil Engineering Professor of Structural Engineering

65

1 2 1 2

1 2

1 2

( ) ( ) ( ) ( ) ( ) ( )

( ) ( ) ( ) ( )

(0) ( ) ( , )SS SS SS

P E S t a S t a S t S t a S t a S t

E S t a S t a S t S t

R a R a R t t

Page 66: Stochastic Structural Dynamics Lecture-40 · 2017. 8. 4. · 1 Stochastic Structural Dynamics Lecture-40 Dr C S Manohar Department of Civil Engineering Professor of Structural Engineering

66

2

2

Filteringˆ( ) ( )

( ) ( )

(0)0(0)

( ) ( ) ( )

(0)(0)(0)

SX

XX

SXSS

XX

S t aX t

P E S t aX t

RP aa R

P E S t aX t S t

RRR

Page 67: Stochastic Structural Dynamics Lecture-40 · 2017. 8. 4. · 1 Stochastic Structural Dynamics Lecture-40 Dr C S Manohar Department of Civil Engineering Professor of Structural Engineering

67

Interpolation

t-NT t+NTλt t+T

To estimate s(t+ λ) in the interval t to t+T in terms of samples of S(t), S(t+kT), k=-N,-(N-1),…,0,1,2,…,N

S(t)

Page 68: Stochastic Structural Dynamics Lecture-40 · 2017. 8. 4. · 1 Stochastic Structural Dynamics Lecture-40 Dr C S Manohar Department of Civil Engineering Professor of Structural Engineering

68

2

ˆ( ) ( ); 0

( ) ( )

0 ( ) ( ) ( ) ,

Set of 2 1 equations for

N

kk N

N

kk N

N

kk Nj

Nk k N

S t a S t kT T

P E S t a S t kT

P E S t a S t kT S t jT j N Na

N a

Page 69: Stochastic Structural Dynamics Lecture-40 · 2017. 8. 4. · 1 Stochastic Structural Dynamics Lecture-40 Dr C S Manohar Department of Civil Engineering Professor of Structural Engineering

69

0

0 1

2

0 10

00

1

Quadrature

( )

ˆ (0) ( ) ( );

( ) (0) ( ) ( )

0 ( ) ( ) (0) ( )

( ) ( ) ( ) ( ) 0 0,1 equations in 1

b

N

b

N

b

k

n

Z S t dt

bZ a S a S T a S NT TN

P E S t dt a S a S T a S NT

P E S t S kT dt a E S S kTa

a E S T S kT a E S nT S kT j NN N

unknowns

Page 70: Stochastic Structural Dynamics Lecture-40 · 2017. 8. 4. · 1 Stochastic Structural Dynamics Lecture-40 Dr C S Manohar Department of Civil Engineering Professor of Structural Engineering

70

Estimate present value of ( ) in terms of values of( ) for

( ) ( ) ( )

ˆ( ) ( ) ( )

ˆ( ) ( ) ( ) ,

( ) ( ) ( ) ( ) 0

( ) ( ) (SX XX

S tX

X t S t t

S t h X t d

S t S t X

E S t h X t d X t

R h R

Smoothing

)d

Page 71: Stochastic Structural Dynamics Lecture-40 · 2017. 8. 4. · 1 Stochastic Structural Dynamics Lecture-40 Dr C S Manohar Department of Civil Engineering Professor of Structural Engineering

71

1

Probelm of dynamic state estimationProcess equation

Measurement equation

: 1 state evector: 1 process noise; iid sequence N(0,1): state transistion matrix: 1 measurem

k k k k

k k k k

k

k

k

k

x x w

z H xx nw n

n nz m

ent vector: relates states to measurements

: 1 measurement noise; iid N(0,1)k

k

H m nm

Page 72: Stochastic Structural Dynamics Lecture-40 · 2017. 8. 4. · 1 Stochastic Structural Dynamics Lecture-40 Dr C S Manohar Department of Civil Engineering Professor of Structural Engineering

72

0: 1:

1:

| 1:

| | | 1:

Probelm of dynamic state estimationDetermine

|

|

|

|

k k

k k

k k k k

k k k k k k k k k

p x z

p x z

a x z

x a x a z

Kalman filter provides the exact solution to this problem


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