FAQ  •  Login

Dynamics+Relative Constraints

Moderator: RaduS

<<

F13thibault.12

Newbie
Newbie

Posts: 27

Joined: Thu Aug 29, 2013 3:46 pm

Unread post Fri Dec 06, 2013 3:40 pm

Dynamics+Relative Constraints

Hello Dr. Serban,

Is it possible to do dynamics on mechanisms having absolute/relative distance constraints. relative x and relative y constraints, etc.?

Basically, in kinematics, we could model different aspects of a mechanism and leave certain bodies out of the model and replace them with relative constraints or absolute distance constraints. I'm wondering if one can study dynamics this way, or do we have to have all the bodies present in dynamics analysis? I assume all bodies will be present in a dynamics analysis, since each has mass and inertia contributing to the dynamics, however, for the final exam, you want us to have absolute distance as one of our constraints. So I am confused as to what constraints we can do dynamics on.

Thanks,

Matthew T
<<

RaduS

Jr. Member
Jr. Member

Posts: 97

Joined: Wed Aug 14, 2013 3:08 pm

Unread post Mon Dec 09, 2013 9:43 pm

Re: Dynamics+Relative Constraints

Matthew,

Any of the constraint types we discussed can be used in a dynamics simulation. In the context of dynamics, the bodies that are replaced by using composite joints are called "massless links". Their only role is to model the kinematics that would otherwise be imposed by bodies of negligible inertia properties.

-Radu
<<

F13thibault.12

Newbie
Newbie

Posts: 27

Joined: Thu Aug 29, 2013 3:46 pm

Unread post Mon Dec 09, 2013 10:14 pm

Re: Dynamics+Relative Constraints

Thank you, Dr. Serban.

Followup question: Can you still find reaction forces between at a joint between a body and one of these"massless" links? Or would you have to have the second body present in the simulation to study that reaction force?

Thanks,

Matthew
<<

RaduS

Jr. Member
Jr. Member

Posts: 97

Joined: Wed Aug 14, 2013 3:08 pm

Unread post Tue Dec 10, 2013 7:59 am

Re: Dynamics+Relative Constraints

Calculation of reaction forces is the same as for any other joint constraints. Of course, you cannot directly find reaction forces on the massless link itself (as it's not part of the analysis). What you can compute however, are reaction forces on the bodies in the system that are connected through the composite joint.
-Radu

Return to ME451 Fall 2013: Kinematics and Dynamics of Machine Systems

Who is online

Users browsing this forum: No registered users and 1 guest

cron
Powered by phpBB © 2000, 2002, 2005, 2007 phpBB Group.
Designed by ST Software.