Day 8 Webex ME208 Dynamic force analysis PDF

Preview

Summary

Download Day 8 Webex ME208 Dynamic force analysis PDF

Description

Day 8 (27.04.2020)

DYNAMIC FORCE ANALYSIS Dynamic equilibrium of systems with rigid body  Newton-Euler method (for planar mechanism) (1)

(2)

Here, inertia force

and inertia torque

If we treat inertia force and inertia torque in the same way as any other external force and torque, the dynamic equilibrium equations assume the same form as the static equilibrium equation:

1

General procedure for solving dynamic equilibrium problem in mechanism  Solve the position, velocity and acceleration kinematics of the mechanism to obtain the accelerations of all bodies with significant mass and angular accelerations of all bodies with inertia.  Compute inertia force and couple acting on each body  Apply inertia force and couple as external force to each link/body. The line of action of inertia force passes through the CG.  Draw free-body diagram of each member considering all external forces acting on that member and considering all reaction forces of the other members to which it is connected.  Write three force and moment equilibrium equations for each link/member  Solve the equations for unknown forces

Position, velocity and acceleration kinematics of mechanism Example

2

Steps 1. Draw the linkage to scale

Velocity analysis

3

4

Acceleration analysis 10.

5

6

Dynamic force analysis

Given

Find the driving torque that must be applied to the crank (member 2) to maintain a constant angular velocity in clockwise direction. Friction in each joint and mass moment of inertia of link 5 may be neglected.

7

Acceleration diagram

Since the geometry and velocity are identical with the earlier example, that solution can be used for part 1 and 2 of the solution procedure. However, it is necessary to find the acceleration of point G3 and G6.

8

Angular acceleration of link 3,

Angular acceleration of link 6 (obtained from earlier analysis),

Acceleration of slider (at point F), obtained from earlier analysis

aF = 13.9 in/s2

9...