Menu

Discussion Forum

New Discussion
Filter

Note: This discussion is about an older version of the COMSOL Multiphysics® software. The information provided may be out of date.

Discussion Closed This discussion was created more than 6 months ago and has been closed. To start a new discussion with a link back to this one, click here.

Continuity in a Beam Model

Posted Jun 24, 2011, 1:10 p.m. EDT Geometry, Modeling Tools & Definitions, Parameters, Variables, & Functions, Structural Mechanics Version 4.0a, Version 4.1, Version 4.2 4 Replies

Rameen Aryanpur
Send Private Message Flag post as spam

Please login with a confirmed email address before reporting spam

Hey everyone,

I'm having a little trouble figuring out what seems like should be a very simple task in 4.0a. I've essentially drawn two lines and would like to connect them at the ends. I don't want them to be welded, so I've selected "Form Assembly" instead of "Form Union." In a mathematical sense, I'm trying to achieve boundary conditions such that the displacements are continuous at the connected ends but each line can rotate independently of the other.

I've attempted to do this by defining the connection point as a pin, but this doesn't achieve what I'd like because the connection shouldn't be constrained to zero displacement. I also tried to define an identity pair and then add a continuous boundary condition to the pair, but Comsol isn't allowing me to pick points for the identity pair, only domains. I'd like to simply pick the two end points on each line and couple them with an identity pair. The continuity condition should then constrain them to having the same displacement. Has anybody done something similar to this? Is it possible to define a point identity pair for one-dimensional geometries such as lines? Again, it seems like a very simple task, but I'm having trouble figuring out how to implement it.

Attachments:

4 Replies Last Post Jun 27, 2011, 11:08 a.m. EDT
Nagi Elabbasi Facebook Reality Labs
Send Private Message Flag post as spam

Please login with a confirmed email address before reporting spam

Posted: 1 decade ago Jun 24, 2011, 2:44 p.m. EDT
One way to do that is to define an identity mapping at one of the two points that you want to join (you can define identity maps on points). Call it say id1, then add a prescribed displacement at the other point and set u=id1(u) and v=id1(v) and keep the rotation free.

Nagi Elabbasi
Veryst Engineering
One way to do that is to define an identity mapping at one of the two points that you want to join (you can define identity maps on points). Call it say id1, then add a prescribed displacement at the other point and set u=id1(u) and v=id1(v) and keep the rotation free. Nagi Elabbasi Veryst Engineering
Rameen Aryanpur
Send Private Message Flag post as spam

Please login with a confirmed email address before reporting spam

Posted: 1 decade ago Jun 24, 2011, 3:43 p.m. EDT
I was thinking about doing it this way, but I'm not sure how to specify the displacement of the identity map in the prescribed displacement node. I followed your steps to create an identity map, then tried setting u=id1(u) and v=id1(v) at the second connection point, but get the error "unknown function id1." Am I specifying the variable name wrong? How do I access the "u" and "v" of id1? Is it id1.u and id1.v?

Thank you
I was thinking about doing it this way, but I'm not sure how to specify the displacement of the identity map in the prescribed displacement node. I followed your steps to create an identity map, then tried setting u=id1(u) and v=id1(v) at the second connection point, but get the error "unknown function id1." Am I specifying the variable name wrong? How do I access the "u" and "v" of id1? Is it id1.u and id1.v? Thank you
Nagi Elabbasi Facebook Reality Labs
Send Private Message Flag post as spam

Please login with a confirmed email address before reporting spam

Posted: 1 decade ago Jun 24, 2011, 4:06 p.m. EDT
The variable names are right. Make sure you name the identity mapping id1 and you select the proper point in the selection window.
The variable names are right. Make sure you name the identity mapping id1 and you select the proper point in the selection window.
Rameen Aryanpur
Send Private Message Flag post as spam

Please login with a confirmed email address before reporting spam

Posted: 1 decade ago Jun 27, 2011, 11:08 a.m. EDT
Ah yes, it worked! My id mapping was named idmap1 instead of id1. Thank you.
Ah yes, it worked! My id mapping was named idmap1 instead of id1. Thank you.

Note that while COMSOL employees may participate in the discussion forum, COMSOL® software users who are on-subscription should submit their questions via the Support Center for a more comprehensive response from the Technical Support team.

Suggested Content