Question:
I am trying to run a Static Analysis using shell elements, how do I set up my model and the analysis?
Answer:
This example demonstrates how to run a Static Analysis with Inertia Relief using shell elements applied to the aircraft components. The beginning of the workflow includes the construction of the aircraft; however, for the purpose of this article, we will not focus on the aircraft design. It also includes an Aircraft Flow Analysis, that will contribute to the Boundary Conditions for this analysis.
Note: Several blocks in the included example file are set to Manual Run Mode. Review the workflow description to run the necessary blocks.
Setting up Domains:
This workflow has several repetitive processes for creating the individual domains. The Meshing, Material, Domains section contains 3 aircraft components that follow the same process, and one that is very similar. The components we will be looking at are:
- Spar/Wingbox
- Ribs
- Fuselage Structs
- Aircraft OML
The section below will cover the steps for setting up the Spar Wingbox Domain.
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Meshes from Profiles - Using the Spar and Wingbox Profiles from the Structures section of the workflow, we generate the original mesh using the Meshes from Profiles block. It's important to note that this is a list of meshes, so we will need to combine these to prevent downstream issues.
Generating the meshed profiles of the Spar and Wingbox using the Meshes from Profiles block. -
Merge and Remesh - Use the Merge and Weld Meshes block to combine the Spar Wingbox Mesh list into a single mesh. We don't need to use the Distance Threshold input to collapse vertices since we are using the Remesh Surface block to create a more uniform element mesh. Both of the meshes generated in this step will have warnings present, this is expected considering they are not closed meshes.
Combining the mesh list using Merge and Weld Meshes. Uniform mesh elements are then created using the Remesh Surface block. -
Create the FE Mesh - For running a simulation, your meshes need to be converted to FE Meshes. Here we use the FE Surface Mesh block for this conversion.
Preparing the mesh for simulation by converting it to an FE Surface Mesh. -
Domain - The Solid Domain applies material properties to the FE Surface Mesh using a Solid Attribute. Considering we are looking to run our Static Analysis using shell elements, we apply a Shell Attribute. The material is Aluminum 7075, and is used across all of the Domains.
Creating the Solid Domain by applying a Shell Attribute to the Spar Wingbox FE Surface Mesh.
This same process is then repeated for the Ribs and Fuselage Structs. The only difference for the aircraft OML is that we don't have any profiles. We create a surface mesh of the aircraft OML using the Mesh from Implicit by AT block.
The only remaining Domain to establish is for the aircraft's payload. The payload is represented by a single point located at the aircraft's Bounding Box Centroid. FE Point blocks are represented as their own Solid Domains with a Point Attribute to apply the mass.
Connectors
Now that we have the Domains established, we can use Connectors to define the relative motion between the aircraft components. The gif below shows five Tie Constraint blocks that establish connections between the FE Meshes.
A Rigid Connector is applied to establish the connection between the Spar Wingbox FE Mesh and the FE Point that represents the aircraft's payload.
To learn more about the difference between Connector blocks, we recommend this article.
Boundary Conditions
Only two Boundary Conditions are being applied for our Static Analysis:
- Pressure: Applies the Pressure Field on the surface of the aircraft OML FE Mesh. This field was generated from the Aircraft Flow Analysis earlier in this workflow.
- Acceleration Load: Applies the Acceleration Vector to the body of the aircraft. This accounts for the aircraft's payload and gravity.
Static Analysis
The Model input of the Static Analysis with Inertia Relief block requires a Simulation Model. Use a Simulation Model block to combine the 4 aircraft component Domains, with the Connectors we established between these components.
Once you insert your Simulation Model and Boundary Conditions, you can run your Static Analysis with Inertia Relief block to view the simulation results.
Inertia relief balances the applied aerodynamic and thrust loads against the distributed inertia of the structure itself, allowing accurate stress and deformation analysis without artificial constraints.