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Approx. Method for Analyzing Lightly Damped Nonlinear Systems with Broad Band Excitations, Slides of Stochastic Processes

Equations and discussions related to the analysis of lightly damped nonlinear systems under broad band excitations using an approximate method. Topics such as fpk equation, backward kolmogorov equation, first passage times, and safe regions.

Typology: Slides

2012/2013

Uploaded on 04/24/2013

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Markov Vector Approach-4
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Download Approx. Method for Analyzing Lightly Damped Nonlinear Systems with Broad Band Excitations and more Slides Stochastic Processes in PDF only on Docsity!

Markov Vector Approach-

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Moment equations form an infinite hierarchy of equations which at no stage provide sufficient

CL

number of equations

to solve for the moments:

This is the characteristic feature of

OSURE PROBLEM

Remarks  

moment equations

of non linear systems driven by random excitations

Closure approximations

Assume that the higher order moments, beyond a given order,are related to the lower order on

es as though they

obey an adhocly specified pdf (Ex: Gaussian closure)Neglect cumulants beyond a specified order 

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7

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m Question: Are the steady state mom

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ents realizable?

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perturb the solutions and see if

Strategy : perturbations die out.

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11

 

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0

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The moment equations can also be used to study stabilityof the system in terms of response moments.

small perturbation

exp

Y Perturbations do not g

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t

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st

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row in time if the real part of the

eigenvalues of

are all

A

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13

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14

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Consider the FPK equation

,

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16

 

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Let

be a scalar Markov process. For

we have

|^
|^
|^
|^
|^
|^
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 

 

Backward Kolmogorov equation and reliabilityfunction

2

1

2

1

1

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2

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2

2

1

2

1

(^22)

x

x

x

x

p

x

x

p

x

x

o

x

x

x

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17

(^2) 

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1

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p x

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t

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p

p x

t

x

t

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t

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p

x

x

p x

t

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x

p x

t

x

t

p x

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x

t

t

p

x

x

p x

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 

 

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 

2

1

2

1

1

2

2

2

2

1

2

2

1

2

2

1

1

2

(^22)

|^

;

1

;

|^

;

0

x

x

t

x

t

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o

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x

p

x

x

p x

t

x

t

dx

t

x

t

   

 

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19

 

 

 

 

0

2

0

0

0

0

1

1

1

0

0

0

0

0

0

0

0

0

0

1

,

,

;

0;

0

,

,

; |

;

ICS :

;

|

;

BCS :

1

n

n

n

t

j^

ij

j^

i^

j

j^

i^

j

n

i^

i

i

dX

t

f

t X

t

dt

G t X

t

dB t

t

X

X

p

p

p

f

t

x

GDG

t

x

t

x

x

x

p

p x t

x

t

p x t

x

t

x

x

j

 

 



Vector version of Backward Kolmogorov equation

0

0

, 2,

,

, lim

; |

;

0

j x

n

p x t

x

t



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20

If we are interested in pdf of

for a given initial condition

we use forward equation.

If we are interested in the pdf of time for first passage across a threshold, we use backward equation.

X

t

Remarks  

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