NLTR, connectors and concetrated masses...

[phill_scott]

Hi,

Having a few issues understanding the right way forward with a couple of things.  Have been working on a dashboard head impact model over the past few weeks and have been building up difficulty.  Preliminary runs were just shell surfaces bonded together with plain panel - all apertures removed.  I have this running.

I now have the final geometry which contains apertures for things like speakers and speedo.  There are also some joints that will be bolted.

I have used RBE2s to act as fasteners for the bolted joints.  I have also used RBE2 connectors to connect concentrated masses for things like speakers to the edge of apertures. 

This model will be used for non-linear transient response analysis with an impactor acting on the dashboard.  As a result I'm trying to get a good model of the connections and the frequency response.

Do I need to replace my RBE2s with BAR or CBUSH elements for all positions for the NLTR solver? and if so, what's the best way to do this?

For connectors I select the edge of the bolt hole on either side and place a point at the centre.

For the concentrated masses, I select the edge of the hole and have a point at the centre.  I then place the concentrated mass at the centre point.

I can't share the model, but here's a screenshot of the typical layout I have.

All help welcome.

[John_Holtz · Accepted solution]

Hi @phill_scott 

You wrote "Do I need to replace my RBE2s with BAR or CBUSH elements for all positions for the NLTR solver?"

I cannot think of any reason to replace them. The transient analysis will run with them. However, if the model is experiencing large displacements, then you may want to make a change. The default connectors (RBE2 in the Nastran file) follow small displacement theory. If the model tries to deform a large amount, the small displacement limitation will create some side effects.

Naturally, the rigid connector rigidly connects the nodes together. For the bolts, you could use a bolt connector.

You wrote "and if so, what's the best way to do this?"

Edit the Parameters (second to the last entry in the model tree), find the parameter RigidElemType, and change it from RBE to BARS or ELAS. 

Let us know if you have any other questions.