Roll Cage Simulations Meshing and Setup

Preparing Roll Cage Geometry from SolidWorks to ANSYS

Create a series of sketches and planes to separate the roll cage geometry from the rest of the chassis
Utilize the “Split” feature to Cut out extraneous geometry

Create a series of planes around the roll cage to act as “cutters” for the extraneuous chassis geometry. You can use the faces of nearby tubes and the global planes as references to create these planes.

1a. I then created an additional plane that was offset from that plane by some arbitrary distance so that I did not cut off the joints of the roll cage.

Repeat steps 1-1a to create the rest of the planes (You should only really have 3 critical planes)

Using the split tool, select one of the planes you have created, and the tubes that the plane interesects with as the target bodies. Click “Cut Bodies”

Ensure that “consume cut bodies” is checked, and select every extraneuous chassis tube (every tube that is on the other side of the plane from the roll cage)

Repeat steps 2 and 3 for the two other planes

Create the coordinates for the loading patches - create a reference plane that is located somewhere above the roll cage

Create two points from a 3D sketch, ensuring the points are aligned in Z, vertically aligned with the center of each roll hoop (have sketches visible so you can see the relations), and on the plane you have just created

Create a new part file, ctrl+c and ctrl+v the 3d sketch feature in the feature tree into the new part file and save as → .IGS file. You’ll need this later for ANSYS Spaceclaim

File → Save As → Parasolid

Go to ANSYS

Preparing Roll Hoop Geometry In Spaceclaim

Loading Patches

Import the Roll Hoop loading patch coordinates into Spaceclaim and sketch the loading patch according the the reg-specified size (150 mm diameter).
We project this sketch so onto the roll hoop so that later when we simulate. We can scope the load onto this loading patch.

With Spaceclaim open, navigate to the assembly tab → file, filter .IGES, and select the .IGES you saved earlier

Create a plane, move the plane up to those points, and sketch the two 150 mm circles coincident with those points

Enter sketch mode, and ensure that “Layout Sketch” is checked. Create a circle of 150 mm, snapping to those points

In the design tab, select “Project” and click one of the circles, then select target faces, and select the hoop. Repeat for the rear

Right click the circles and plane → suppress for physics, then right click again → hide all suppressed

Simplifying Geometry to Help in Meshing

Use the Plane feature in Spaceclaim to create planes along tubes to split the body into a “Sweepable Body”.
- When a body is Sweepable, the mesher creates a 2D mesh of the cross-section and sweeps that mesh along the path of the tube.
- This method is very efficient to capture the full geometry of a prismatic tube and speCify the number of elements easier and allows us to save computing time
- However, we need another method to mesh the regions at the joints, which are not sweepable and may need careful refining of to accurately capture the complexity of the joint (i.e., where many tubes meet

Important Notes

IMPORTANT NOTE: The joints are where we expect stress values to be the highest, therefore, we want to segment those sections completely off and into their own bodies to be meshed respectively
ANOTHER IMPORTANT NOTE: Sometimes, ANSYS Spaceclaim is weird when converting .sldprt to parasolids, and therefore it won’t let you cut certain tubes. In this case, combine everything in Solidworks first then cut the tubes in Spaceclaim. You can combine the bodies that weren’t intended to be cut (because you can only cut along infinite planes which might interesect tubes you don’t want cut)

Cutting the Tubes into Sweepable Bodies

Create reference axes along the axis of the tube so that you can make the planes perpendicular to the axis (parallel to the cross section)

Select plane and click on the reference axis you just created

Click Move and double click the radial arrow such that the plane turns 90 degrees and is now perpendicular to the axis

Move the plane to be as close to the joint as possible while still maintaining the same cross-section

Select the plane, ctrl+c and ctrl+v, and then use move again to move the plane to the other side of the tube

Go to “Prepare” tab on the top, click “Split by Plane”.

Select Target - click the tube you want to split

Select Cutter - click the first plane you created, reselect cutter, then click the second plane

Repeat steps 1-6 for all continuous tubes

Tip: Mirror symmetric features

Create a reference plane across the midplane by going to “Plane” then selecting the x axis at the origin

Create your desired planes, then select “Mirror”->select the right plane, then select your desired planes to be mirrored about that right plane. Click esc to exit mirror command

Ensure that each joint has splits that will seperate them from the sweepable tubes

In the design tab, select Combine, and while holder ctrl, click each of the joint to combine into one joint

Preparing Roll Hoop Mesh in Mechanical

We’re going to use primarily two methods when meshing:
- Sweep - Creates a mesh of a tube cross-section and sweeps the mesh along the entire path of the tube.
  - Saves our computing time as we can uniformly mesh prismatic sections of tube.
  - Can specify number of elements (shoot for 3 elements through)
- Tetrahedral - Creates a mesh for a more complicated geometries such as regions where multiple tubes come at a junction
  - More seamless transition from courser mesh density to finer mesh

Open you mechanical model from you ANSYS Workbench workflow

In Mechanical, right click “Mesh” in the feature manager-->show-->sweepable bodies

Use this to verify that all the tubes you intend to sweep can be swept. The solver will not be able to sweep mesh if it does not identity the body as sweepable as shown here. Make adjustments in Spaceclaim as needed

Insert a Sweep method by right clicking “Mesh”-->Method. Using body selection feature (all green box in the top of ANSYS) ctrl+click all the sweepable tubes. Click apply in Geometry. Use these properties in the Details:

Insert a Tertrahedron methods using the same process but instead scoping to the remaining bodies. Ensure that you are using “Patch Independent” as the meshing algorithm. Use the details below

You can also insert a seperate sizing methods to specify the element size in certain specified regions, if you want a finer mesh in one face over another. Play around with this as you are meshing the frame but be weary that the smaller in element size you go, the more computationally expensive it will be.

Important Note: You should verify your mesh quality every time you mesh the roll cage, tweak the settings, make the mesh smaller, even try different methods. Keep in mind computation time/ANSYS crashing. It’s a trial-and-error process.

Setups

Ensure you have general joints scoped to the faces of each of the joint tube members. Ensure the Z axis is oriented along the length of the tube. The behavior of these joints should be deformable

In Analysis Settings for each Static Structural, ensure that weak springs are turned on and Large Deflection is turned on