Training Module #9: FEA Iteration - HyperFEA (Click-Along)

Ensure the FEM is correctly imported:

In this exercise, we have already organized the wing into Structures. We can focus on those Structures by hiding the CAD Entities using the CAD Tree.

The wing features composite skins and an orthogrid internal substructure. Let's review the corresponding Design Properties to better understand the setup.

The upper and lower skins both use an Effective Laminate Design Property which can be found in the Property Tree.

The internal structures are metallic orthogrid.

The active Analysis Properties include strength, local buckling, and crippling Failure Modes. Additionally, on the "... - HFEA Buckling" Properties, panel buckling criteria are used with a required margin of -0.25. This allows us to achieve panel designs that are a good starting point for FEA buckling without being overly conservative. We'll expand on that a bit more later in the tutorial.

All Structures are assigned a Filtered Load Property with the Peak Load option enabled.

This FEM has Buckling Modes from FEA prior to any updates in HyperX. At this stage, the FEM has a boilerplate design (uniform thickness) as a starting point.

We can review the FEA Buckling Modes using the Legend:

In the next part of this exercise, HyperFEA will adjust the stiffness constraints on the Zones to push the minimum FEA buckling eigenvalue above a target value of 1.5

Now that we've reviewed the setup, the next step is to define a FEA Buckling Constraint. To begin:

Next, we will create a Buckling Automated Constraint:

When you close the "Edit Constraint" form you can see that the Constraint we defined is automatically enabled. Click "Apply" to save the changes and close the form.

Instead of setting a fixed number of iterations, we will use Convergence Criteria to determine when to stop HyperFEA. First, click the "Convergence" button to enable Convergence Criteria. Next, click the dropdown arrow beneath it and select "Edit Convergence Criteria" to open the Convergence Criteria form.

On the Convergence Criteria form, you can define criteria of various types and combine them into a logical expression that will automatically stop HyperFEA iterations once met. Convergence Criteria Templates can be saved and loaded into other Projects, which is what we will do in this exercise:

This default set of criteria will cause HyperFEA to exit once the weight of the structure changes by less than 3% from one iteration to the next, and the FEA Buckling Constraint is met.

The Convergence Criteria can be run in two stages to allow refined control over the iteration process. Activate the advanced settings at the bottom of the Convergence Criteria form. This will put HyperFEA in “2-stage” mode when it runs, where it will iterate until converged twice, with different behavior in each stage.

The first option deactivates the FEA Constraints (buckling in this example) in the first stage allowing HyperFEA to converge the load path prior to enforcing constraints. The second option allows the user to deactivate specific failure criteria in either the first or second stage. In this example, the analytical buckling criteria will be deactivated in the second stage. They will be active in the first stage to establish a good starting point for the FEA buckling.

Click "Apply" and close each form as needed to return to the main HyperFEA form. Then, click the "Start" button and select "Start with Sizing (default)". Note that this operation will take quite a bit of time to fully process.

HyperFEA will automatically stop once the Convergence Criteria are satisfied. The yellow plot represents the Buckling Constraint that activated in the second stage beginning at iteration 4.

Like we did at the end of Part 1, let's use the Legend to review the FEA Buckling Modes. Open the Legend, plot "FEA Displacements" > "Buckling Subcase" and check the "Mode" values for both "20001" and "20002". You will notice that all eigenvalues are above our target of 1.5.

Next, we can cycle through the ABD panel stiffness terms to see where HyperFEA added stiffness to meet the FEA Buckling Constraint.

Finally, we can cycle through various Sizing results on the skin and orthogrid Structures to see what changes were made to satisfy the FEA Constraints.

You can also view Design Results for particular Zones of interest.