# Objective:

Learn how to select boundaries of an FE Mesh using the FE Boundary by Body method.

# Applies to:

• Simulation
• Topology Optimization

# Procedure:

The FE Boundary by Body block selects entities of an FE Mesh (faces, edges, nodes) within the desired tolerance of an Implicit Body. Depending on the Tolerance, the Implicit Body can be intersected with the mesh or not touching. The Reverse box can be toggled on or off to select the opposite of what was selected.

#### How to decide which Entity type to choose:

Choosing your entity depends on the boundary condition you are using. Does it make a difference if you apply the boundary condition on a face/edge/node? For example, all the restraints (Point, Displacement, Temperature, Initial Temperature, Applied Temperature) evaluate their value at the nodes. However, the Force block acts differently. If you select nodes, it divides the applied force evenly among them. If you choose edges, it divides the force evenly among the total length of the edges, and if you select faces, it divides the force over the entire area of your selection.

For example, if you use nodes in the FE Boundary, regions with more nodes will generally see more force since, with this option, we are taking the force divided by the total number of nodes and applying that value to each node. Instead, if you use the Faces option, the force is divided by the total area, and this applies as a force per unit area to each element face which results in a more evenly spread force across the entire FE Boundary.

Some boundary conditions have preferred boundary element types, like Heat Flux and Pressure only allow face entities.

1. Choose and Prepare the Body for Selection: In this example, we want a Force Boundary Condition to act on the brake pedal's head. To choose that area on the mesh, we need to extract the CAD face (select CAD Face and right-click), convert it to an Implicit Body, and Thicken the body. Thickening the body turns the thin implicit face into an object that can be rendered and used to select entities on the mesh.

2. Select Boundary: Once the selection body is prepared, it needs to be intersected with the FE Mesh to choose the boundary. Follow the steps below to do this:

• Add an FE Boundary by Body block.
• Double click on the Mesh input to add the existing FE Mesh
• Choose 'Nodes' for the Entity
• Insert the Thickened Body from the last step into the Body input
• Tip: The Body input takes in Implicit parts that don't have to be a thickened surface. There are a variety of other methods available to select the part you want. An example of useful blocks, but not limited to:
• Implicit Body from Curve
• Implicit Body from Thick Lattice
• Implicit Body from Mesh

And that’s it! You’ve successfully selected a boundary using the FE Boundary by Body block

Are you still having issues? Contact the support team, and we’ll be happy to help!

Move on to the next article in this series and learn how to use FE Boundary by Flood Fill.

# Keywords:

Mesh FE select analysis simulation faces boundary body design condition loaded region by FEA set up edges boundaries nodes BC