Breakout Modeling (Submodeling)in Femap: Example Walkthroughs

Example #1: Small Design Change

Example #2: Local Stress Riser

Example #1: Small Design Change

In this example, avionics has asked you to add a small pass-through to one of the ribs in the wing model.

Here is the wing model:

1. First find the rib of interest

Use the “Draw Erase Selective Mesh – Property” command (Femap 11.3 and up).

Select the properties you want to hide.

2. Create a new group for the breakout rib

Right click on the Full Model Group, select New, name the group “Breakout Rib” and press OK.

3. Add rib to new group

Add the rib to the new group by selecting the elements.

Go to Group > Element > ID

In the “Entity Selection – Select Element(s) for Group” dialog, press the Method ^ button and select

“Property”.

NOTE: If you are unable to select the rib, you may have an Active Group on. If this is the case, right click

on your breakout model group and select “Show Full Model”. Then repeat the previous steps to select

the property of interest.

Select the rib you want in the breakout model and use the highlight button to make sure you have

selected the correct property.

Right click the 3…Full Model group and select Active to isolate the Rib.

Next, Right click the Breakout Rib group and select Add Related Entities

This command will add associated nodes, properties, and materials to your group.

4. Create New .modfem

Go to File > New to create a new Model and then use the File > Merge command to open the Model

Merge Manager.

1. From the “From Model” dropdown, select the Wing Model.modfem.

2. Press All Off since you don’t want the entire model.

3. From the “From Group” dropdown, select 14…Breakout Rib (our breakout group).

4. Click Add Related and Associated Entities

5. Click Update All to update the values.

6. Click OK

As you can see, it brings in the coordinate systems, nodes, elements, materials, and properties from the

group.

The model should now look like this:

5. Remesh the model

This is a breakout so you could keep the mesh and adapt it but, in this case, create a higher fidelity mesh

since you’re looking for local stress risers.

Go to Mesh > Editing > Refine

Refining the mesh instead of remeshing is recommended.

Refine maps the load by locating the node as close to the original node as possible. If it can’t find it, it

interpolates or executes another method (which will be covered later).

Refining the mesh keeps the nodes in their original locations and adds more elements and nodes.

The Mesh Editing Element Refine dialog provides options for turning one element into four or nine

elements. In this example, use four.

Use the Area Drag to select the entire Rib.

Which results in a refined mesh:

6. Add a pass-through to the Rib

To create the pass-through, use the Create Surface from Mesh command.

Go to Geometry > Surface > From Mesh…

Select a square..

And select OK.

In the Surface From Mesh dialog that pops up, press OK.

Whenever working with 2D Geometry, you must define a workplane.

Right-click on the window background and select Workplane…

Right click on the model and select Smart Snap and then select Select Plane… in the Workplane

Management Dialog Box.

Select any three points on the Rib

Now that you have defined the workplane, go to Geometry > Curve – Circle > Center

In the “Locate – Enter Location at Center of Circle” Dialog, press the Methods button and select

“Between” and select the following nodes to create a circle approximately in the center.

Set a radius of 0.75.

Project the circle by going to Geometry > Curve – From Surface > Project…

Select the circle and press OK.

You have successfully created the circle for the pass-through.

7. Mesh the pass-through

The Meshing Toolbox will be used to make a high-quality mesh around the hole.

Click the Meshing tab and under Geometry Editing, select the Point to Edge tool and press the select

button (Icon with a green arrow).

Start at each corner and then select the closest edge on the circle. This will create guide curves around

the circle.

Then join the broken edges by using the Add By Point command under Combined / Composite Curves to

select the curves.

Next go to the Mesh Surface window.

Set the property and under Meshing Method choose Mapped Mesh.

Click on the four regions outside the circle to apply a mapped mesh to each region.

Since you are just editing the mesh, you do not need to apply a non-manifold add. It will remain

separate.

Next, use the Mesh Sizing tool can be used to match up the nodes:

Go to the Mesh Sizing tool in the Meshing Toolbox. You can use the Increase, Decrease, or Set To

commands to interactively adjust the size of the mesh.

In this case, the Set To command was used to update the top and bottom sections to 11 elements and

the side sections to 6 elements.

8. Coincident Node and Free Edge Check

There are now free edges, so perform a coincident node check.

Go to Tools > Check > Coincident Nodes…

Box select a section that includes the pass-through.

In the Check/Merge Coincident Dialogue, check the Merge Across Output CSys checkbox, change the

tolerance to 0.1, and click Preview.

All the coincident nodes appear to be selected.

To double check, check the free edges by pressing F6 to bring up the View Select dialog. Under Model

Style, select Free Edge and press OK.

Looks as expected.

9. Apply Loads

Go to Model > Load > Map Output From Model…

This dialog allows you to grab loads from other models.

1. Select the Wing Model.modfem in the From Model dropdown menu.

2. Select the Breakout Rib group from the Results on Group dropdown menu.

3. Select the Output Set (in this case we only have one to choose).

4. In the Output Vector dropdown menu there are many options. In general, anything that Nastran

can output, you can apply. For this example, we used 1…Total Translation.

5. In the Values for Locations with No Map dropdown menu, there are options for what Femap

should do if it can’t find a node. We have found best results with 3…Interpolate. Test the

options to see what works best for your model.

6. In the To Model Loads tab, set Nodal as 3…Displacement. Make sure that the option that you

choose here matches the value you set for Output Vector.

7. Press OK.

Select the target nodes on the perimeter. Press OK.

10. Apply Constraints

In the Model Info Tree, right click on Constraints and click New.

Set a name for your Constraint and press OK.

Right click on Constraint Definitions and select Nodal.

In the Entity Selection – Enter Node(s) to Select dialog, press Previous. This will grab the nodes we

selected in the last command. Press OK.

In the Create Nodal Constraints/DOF dialog, click the Pinned button under DOF. Press OK.

11. Run the Analysis

Right click on Analyses in the Model Info Tree. Select Manage.

Press the New… button. Set a name for the analysis and press OK.

Press the Analyze button.

Click the button to view the contour

Here is the pass-through model compared with the control rib:

You can see that there are local stress risers around the hole.

You have successfully created a breakout!

Example #2: Local Stress Riser

In this example, you will create a zipped-in breakout of an orthogrid pressure plate to find local stress

risers around the boss.

Start with the the geometry for the full plate model.

1. Split the geometry

Start by defining the workplane.

Right-click on the window background and select Workplane…

Right click on the model and select Smart Snap and then select Select Plane… in the Workplane

Management Dialog Box.

Go to Geometry > Curve – Line > Rectangle…

Make sure that under Methods^, that you are using Locate.

Select the first point as the top left corner of the rectangle. Then select the bottom right corner of the

rectangle.

When creating the rectangle, try and get as close to the original nodes as possible. The results will be

more accurate the closer you get to those nodes.

Split the solid using Geometry > Solid > Slice…

Grab the solid and select each of the four curves to slice the model.

1. Remove overlapping portions of the model

To clean up the model, we can delete the rest of the solid model.

Go to Delete > Geometry > Solid…

Select the outer solid and press OK.

We can also delete the portion of the plate mesh that is going to be replaced by the solid mesh.

Go to Delete > Model > Mesh…

Select the top corner element that overlaps the solid model and the opposite corner.

Make sure to not delete the inner faces. It will be easier to keep them.

2. Mesh the Solid

Go to Mesh > Geometry > Solids…

Keep the default settings and press OK.

3. Connect the solid breakout to the shell model

Mesh > Connect > Rigid

Hide the solid elements to easily see the nodes.

Select the source nodes. The source nodes is the least number of nodes. There is one node here that

needs to go to multiple solids. These are going to be my source and the target is going to be the solid.

Do not click the interface.

Press OK.

Set “Rigid Element Type” as RBE2.

NOTE: In this example, we used RBE2 but RBE3 could have been used. The RBE to use can depend on its

application in your breakout

For Target Node Selection, you can use Automatic, but it will start reaching into the solid model. In this

case, you want it to grab the outer so use User Defined.

Turn the solid elements back on and select the nodes (use the by face selection command).

Highlight to make sure you selected everything:

Turn off the checkbox for Preview Target Nodes and press OK.

Bring back the plates and update the RBE that manages the bolt.

Modify > Edit > Element

Select the RBE and press OK.

In the Define RIGID Element – Enter Nodes or Select with Cursor dialog, press the Nodes… button.

Press Reset and then use the On Surface Method to select the inner surfaces.

In a short amount of time, you were able to model an accurate representation of the local stiffeners on

this orthogrid plate!