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numerical methods - 17.35

b)

 

 

 

 

 

s2 + 4

 

 

 

 

 

A

 

B

C

D

s------------------------------------------------------------------

4

+ 10s

3

+ 35s

2

 

 

 

=

s-----------+ 1

+ s-----------+ 2

+ s-----------+ 3

+ s-----------+ 4

 

 

 

+ 50s + 24

 

 

 

 

 

 

 

 

A =

 

lim

 

 

 

 

s2 + 4

 

 

=

5

 

 

 

 

 

-------------------------------------------------

 

 

 

 

 

--

 

 

 

 

 

 

 

s –1 ( s + 2) ( s + 3) ( s + 4)

 

6

 

 

 

 

B =

 

lim

 

 

s2

+ 4

 

 

=

8

 

 

 

 

 

 

 

 

 

 

 

-----

 

 

 

 

 

 

 

s –2 ( s + 1) ( s + 3) ( s + 4)

 

–2

 

 

 

 

C =

 

lim

 

 

 

s2

+ 4

 

 

=

13

 

 

 

 

 

 

 

 

 

 

 

-----

 

 

 

 

 

 

 

s –3 ( s + 1) ( s + 2) ( s + 4)

 

2

 

 

 

 

D =

 

lim

 

 

 

s2

+ 4

 

 

=

20

 

 

 

 

 

 

 

 

 

 

 

-----

 

 

 

 

 

 

 

s –4 ( s + 1) ( s + 2) ( s + 3)

 

–6

 

 

 

 

5

t

 

 

 

–2t

 

13

–3t

 

10

–4t

 

 

 

 

 

 

6--e

 

– 4e

 

+ ----- -----

2 e

 

3 e

 

 

 

 

 

 

10.

θ( t) = – 66 10–6e–39.50t – 3.216e0.1383t + 1.216e–0.3368t + 2.00

17.12ASSIGNMENT PROBLEMS

1. Prove the following relationships.

 

 

 

 

t

 

 

=

aF( as)

a)

L

f

 

--

 

 

 

 

 

 

a

 

 

 

 

b)

L[ f( at) ] =

1

s

--F --

 

 

 

 

 

 

 

 

a

a

c)

L[ eatf( t) ] = F( s + a)

d)

lim f( t)

=

lim sF( s)

 

t → ∞

 

s 0

e)

lim f( t)

=

lim sF( s)

 

t → ∞

 

s 0

 

 

 

d

f)

 

 

----

L[ tf( t) ] = –dtF( s)

numerical methods - 17.36

2.The applied force ‘F’ is the input to the system, and the output is the displacement ‘x’.

a)find the transfer function.

 

 

 

 

 

 

K1 = 500 N/m

 

 

 

 

 

 

K2 = 1000 N/m

 

 

 

 

 

 

x

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

M = 10kg

 

 

 

 

 

 

 

 

 

 

F

 

 

 

 

 

 

b)What is the steady state response for an applied force F(t) = 10cos(t + 1) N ?

c)Give the transfer function if ‘x’ is the input.

d)Find x(t), given F(t) = 10N for t >= 0 seconds using Laplace methods.

3. The following differential equation is supplied, with initial conditions.

·· ·

y( 0) = 1

·

y + y + 7y = F

y( 0) = 0

 

F( t) = 10

t > 0

a)Solve the differential equation using calculus techniques.

b)Write the equation in state variable form and solve it numerically.

c)Find the frequency response (gain and phase) for the transfer function using the phasor transform. Roughly sketch the bode plots.

d)Convert the differential equation to the Laplace domain, including initial conditions. Solve to find the time response.

4.Given the transfer functions and input functions, F, use Laplace transforms to find the output of the system as a function of time. Indicate the transient and steady state parts of the solution.

x

=

D2

F = 5 sin ( 62.82t)

--

------------------------------

F

 

( D + 200π ) 2

 

x

=

D( D + 2π )

F = 5 sin ( 62.82t)

--

------------------------------

F

 

( D + 200π ) 2

 

numerical methods - 17.37

x

=

D2( D + 2

π )

F = 5 sin ( 62.82t)

--

------------------------------

F

 

( D + 200π

) 2

 

17.13 REFERENCES

Irwin, J.D., and Graf, E.R., Industrial Noise and Vibration Control, Prentice Hall Publishers, 1979.

Close, C.M. and Frederick, D.K., “Modeling and Analysis of Dynamic Systems, second edition, John Wiley and Sons, Inc., 1995.