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rotation - 5.28

behave as if it is critically damped. (Note: Clearly this system is not second order, but in the absence of another characteristics we approximate it as second order.)

5.5SUMMARY

The basic equations of motion were discussed.

Mass and area moment of inertia are used for inertia and springs.

Rotational dampers and springs.

A design case was presented.

5.6PRACTICE PROBLEMS

1.Draw the FBDs and write the differential equations for the mechanism below. The right most shaft is fixed in a wall.

Τ

 

 

θ 1

 

 

θ 2

 

 

 

 

 

JM1

 

 

JM2

 

 

 

 

 

 

 

 

 

 

Ks1

 

 

Ks2

B

rotation - 5.29

2.For the system pictured below a) write the differential equations (assume small angular deflections) and b) put the equations in state variable form.

R1

 

R2

 

 

 

 

J1

F

Kd1

x2

Ks1

A lever arm has a force on one side, and a spring damper combination on the other side with a suspended mass.

M1

 

 

 

 

 

 

x1

 

 

 

 

 

 

 

3. Draw the FBDs and write the differential equations for the mechanism below.

θ 2

 

 

 

 

 

 

 

 

R1

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

JM1

 

θ 1

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

R2

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

JM2

Ks

 

 

 

 

 

 

 

 

 

 

 

 

K

 

d

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

x1

x2 M1

4.The system below consists of two masses hanging by a cable over mass ‘J’. There is a spring in the cable near M2. The cable doesn’t slip on ‘J’.

a)Derive the differential equations for the following system.

rotation - 5.30

b) Convert the differential equations to state variable equations

 

θ

JM

R

Ks1

 

 

Ks2

x1 M1

F

 

 

 

 

 

M2

 

 

x2

 

 

 

 

 

 

 

5.Write the state equations for the system to relate the applied force ’F’ to the displacement ’x’. Note that the rotating mass also experiences a rotational damping force indicated with Kd1

Kd1

 

 

 

 

 

F

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

r

 

 

 

 

 

x

 

 

JM

 

 

 

θ

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Ks2

M

 

Ks1

 

 

 

 

 

 

 

Ks3

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Kd2

6. For the system pictured below a) write the differential equations (assume small angular deflec-

rotation - 5.31

tions) and b) put the equations in state variable form.

 

 

 

 

 

 

 

 

 

 

 

 

 

A round drum with a slot. The slot

 

 

 

 

 

 

 

 

 

 

 

 

 

drives a lever arm with a sus-

R1

R2

 

 

R3

 

 

R4

 

pended mass. A force is applied

 

 

 

 

 

to a belt over the drum.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

J1

 

 

 

 

 

Kd1

 

 

 

 

 

 

 

 

 

 

Ks1

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

F1

 

θ 1

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

M1

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

x1

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

7.For the system pictured below a) write the differential equations (assume small angular deflections) and b) put the equations in state variable form.

 

 

 

 

 

R1

 

 

 

R2

 

 

 

 

 

 

 

 

 

 

 

 

Two gears with fixed

 

 

 

 

 

 

 

 

 

 

 

 

 

 

centers of rotation

 

 

 

 

 

 

JM1, N1

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

and lever arms.

x2

 

 

 

F1

JM2, N2

 

 

 

 

 

 

 

 

 

x3

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Ks1

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Kd1

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

M3

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

x1

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

8. For the system pictured below a) write the differential equations (assume small angular deflec-

rotation - 5.32

tions) and b) put the equations in state variable form.

Kd1

Ks1

M1

x1

Ks2

A mass slides on a plane with dry kinetic friction (0.3). It is connected to a round mass that rolls and does not slip.

 

 

JM2, R2

x2

θ 3

θ 2

M2

 

 

 

F2

 

 

 

9.For the system pictured below a) write the differential equations (assume small angular deflections) and b) put the equations in state variable form.

Apulley system has the bottom pulley anchored. A mass is hung in the middle of the arrangement with springs and dampers on either side. Assume that the cable is always tight.

 

 

 

 

 

 

 

 

 

 

Kd3

 

 

 

 

Ks3

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

M3

x3

 

 

Ks2

 

F1

 

 

R2,J2,M2

 

 

x2

 

 

 

 

θ 1

R1,J1

 

 

10. For the system pictured below a) write the differential equations (assume small angular

rotation - 5.33

deflections) and b) put the equations in state variable form.

M1

x1

Kd1

Ks1

R1

 

 

 

 

R2

 

 

 

 

 

 

 

 

 

 

A mass is suspended over a lever arm. Forces are applied to the lower side of the moment arm through a spring damper pair.

 

 

 

 

 

 

 

 

 

 

 

x2

 

 

 

 

 

 

 

 

 

 

 

Kd2

 

 

 

 

 

 

 

 

Ks2

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

F1 x3

11. For the system pictured below a) write the differential equations (assume small angular deflections) and b) put the equations in state variable form.

R2

 

 

R1

 

 

 

 

 

 

 

 

Two gears have a force on

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Kd1

 

 

 

one side, and a mass

 

 

 

 

 

 

 

 

 

 

 

 

N1

N2

 

 

 

on the other, both sus-

 

 

 

 

 

 

 

 

 

 

 

 

pended from moment

 

 

 

J1

J2

 

 

 

arms. There is a rota-

 

 

 

 

 

 

tional damping on one

F1

θ 1

 

 

 

Ks1

 

 

 

 

 

of the gears.

 

 

 

 

 

 

θ 2

 

 

 

 

 

 

 

 

 

 

 

 

 

M1

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

x1

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

12.Find the polar moments of inertia of area and mass for a round cross section with known radius and mass per unit area. How are they related?

13.The rotational spring is connected between a mass ‘J’, and the wall where it is rigidly held. The mass has an applied torque ‘T’, and also experiences damping ‘B’.

a)Derive the differential equation for the rotational system shown.

b)Put the equation in state variable form (using variables) and then plot the position (not velocity) as a function of time for the first 5 seconds with your calcula-

rotation - 5.34

tor using the parameters below. Assume the system starts at rest.

Ks

= 10

Nm

B = 1

Nms

--------

----------

 

 

rad

 

rad

JM = 1Kgm2

T = 10Nm

θ

T

J

Ks

B

c)A differential equation for the rotating mass with a spring and damper is given below. Solve the differential equation to get a function of time. Assume the system starts at rest.

θ'' + ( 1s–1 ' + ( 10s–2 = 10s–2

14.Find the response as a function of time (i.e. solve the differential equation to get a function of time.). Assume the system starts undeflected and at rest.

 

 

θ

τ = 10Nm

 

 

 

 

 

τ

 

Ks

JM

= 1Kgm2

 

 

 

 

K

 

Ns

 

JM

d

= 3------

 

 

m

 

 

 

Ks

N

 

 

 

= 9---

 

 

 

 

 

m

Kd

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