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Technical Support FAQs

FEMAP

How does one treat the high stresses that often result from using rigid-links to model bolted connections?

This is a very common issue and there are lots of different techniques to handle it. I'll run through a few of the more common ones.

Is this a plate model? You can release the rotational degrees of freedom.

For solid models, I will frequently constrain the inside of the bolt hole in planar directions and the washer surface in a normal direction. I guess this would work for plates as well, constraining the nodes along the edge of the hole in the planar direction and nodes under the washer in the normal direction. If you want to take this a step further, use cylindrical coordinate systems and constrain radial growth.

Sometimes I create "discontinuity" elements. Eliminate the row of elements that you apply the constraints to, from the contour. This validity of this technique is very dependent on the problem you are trying to solve. It is great for removing peak from the contour and getting a good look at general stress trends throughout the structure. However, it may not be conservative for local stresses near/at the bolt hole.

Long story short, there is no one single way to get around these stresses at the boundary conditions. It generally takes some creative playing around to find something that gives you a good balance of conservative and realistic.

Is there a way to create a group from entities (points, nodes, elements, etc) in the data table?

Yes. There's a few steps to the process, but it's pretty easy.

I've got the Data Table loaded up with my elements of interest. Hit the 3rd button from the right "Update Selection to Visible Rows". This will update the Selector with any entities you have in the Data Table.

Then from the "Selector Actions" button on the Selector toolbar, choose "Create Group".

What is the best way to connect two models together? I have two models that are connected together by bolts with a glued connection. I want to reduce the node count.

Using the glued connection is a bit like bringing a gun to a knife fight. I think the classic rigid link and beam element bolted connection can work great for some applications.

If you're unfamiliar, we have a brief introduction to connections:View Connections Document (PDF)Download the Accompanying Neutral Files (Zip)

A great "book" that can guide you through meshing and connection of models is in the Femap help file (choose HELP/Examples). It is an amazingly well written help file that I reference frequently.

The time spent on these tutorials and examples will be small in comparison to the time spent "spinning your wheels" without these crucial modeling skills.

I need advice on the transition between solid and plate elements. My model is pretty big and complicated. I have several transitions between plate and solid elements. Which transition method would you recommend in FEMAP?


This can be tricky since plates have 6 DOF and Solids have 3 DOF. There are several options:

The T-connection. Mesh the surface of adjacent solid elements (Mesh>Edge Members) with plates to transfer moments.

 

The embed. Mesh the surface of solid elements within the solid planar with the plate element.

 

It all depends and what you need the model to do… Results will vary between the two methods and you may need to build a full solid test model to 'tune' the thickness of your transition plate elements (as shown in green for my examples). One could use similar techniques with other element types (i.e. rigid). Regardless of the technique used, validation is key.

How do you record an .avi animation from within FEMAP (deflected shape motion)?

Turn the deformed style to Animate then File>Picture>Save.

Use the .gif format because it looks good and the file size is much smaller than the .avi. The number of images in the animation is controlled by frames in your animated style.

To create a .avi, just select the .AVI file format when it prompts you to save. If the deformed style isn't set to animate, you won't be able to select animated file formats.