VSPAERO Input Files and Aerostructural Analysis

[Abdullah Mejbil]

Hi Everyone,

First, thank you for delivering the 2025 workshop, it was very helpful!

I'm trying to get a static aerostructural analysis working. I have a few questions regarding VSPAERO input files and aerostructural analysis:

1. Does VSPAERO accept modified or built-from-scratch input files (.vspgeom)? For example, can I modify a .vspgeom file based on a deformed mesh from a .F06 NASTRAN file, if I can transfer the mesh to .vspgeom?

2. Does the "Apply Loads" have an API alternative. I found the following command: vsploads.exe -interp [vspaero .adb file]  [calculix .inp file] -dynp [dynamic pressure value]. I'd like to understand vsploads.exe a bit more.

3. Are the generated loads only 2D? assuming I run the VLM solver which degenerates the model into 2D panels? Does this assume equal pressure on the top and bottom of the surface?

4. How do VLM loads apply to the FEA mesh? I found the following file on Github: OpenVSP/src/vsp_aero/Adb2Load/interp.C. Is this where I should look to understand how it works?

I would appreciate any suggestions or resources for any of the questions.

Thank you.

[Rob McDonald]

On Wed, Sep 17, 2025 at 7:46 AM Abdullah Mejbil <amej...@gmail.com> wrote:

Hi Everyone,

First, thank you for delivering the 2025 workshop, it was very helpful!

I'm trying to get a static aerostructural analysis working. I have a few questions regarding VSPAERO input files and aerostructural analysis:

1. Does VSPAERO accept modified or built-from-scratch input files (.vspgeom)? For example, can I modify a .vspgeom file based on a deformed mesh from a .F06 NASTRAN file, if I can transfer the mesh to .vspgeom?

For structural (or optimization) type deformations, you should be able to write a program that will move the points in the *.vspgeom file.

You need to leave the number and topology of the points the same -- i.e. the general arrangement of the points and how they are connected.  The point coordinates are at the top of the file, the connectivity information comes later.

The format of the *.vspgeom file is documented here.  Although the file supports multiple resolutions, only a single resolution is currently used, so nmesh==1 is true for now.

When multiple resolution files are supported, they all use a strict subset of the nodes.  I.e. if the finest mesh uses N points, then there are N points in the file.  The first coarsened mesh uses about N/2 of the points.  The next coarsened mesh uses about N/4 of the points, etc.  The points are sorted such that the subset of points used by the coarsest mesh come first, then the next finer mesh, etc.

If you are deforming a mesh, you'll just want to deform all the points.

The points don't 'know' what surface they are on.  If you need to identify whether a point is on a fuselage or a wing (for example), you'll need to look at the panel list, see what Part it is from, reference the *.vkey file, and check which points are associated.  The Part will also identify the surface U,V for each point.

Of course, points along a wing/fuselage junction will be used by both Parts.  The xyz of the points are the same, but there are different UV values associated with each Part.

 

2. Does the "Apply Loads" have an API alternative. I found the following command: vsploads.exe -interp [vspaero .adb file]  [calculix .inp file] -dynp [dynamic pressure value]. I'd like to understand vsploads.exe a bit more.

No, the Apply Loads is not exposed through the Analysis Manager to the API.  It is just a simple wrapper around the command you've identified above.

 

3. Are the generated loads only 2D? assuming I run the VLM solver which degenerates the model into 2D panels? Does this assume equal pressure on the top and bottom of the surface?

Yes, it splits the pressure from a VLM surface onto the top / bottom surface of a wing.

 

4. How do VLM loads apply to the FEA mesh? I found the following file on Github: OpenVSP/src/vsp_aero/Adb2Load/interp.C. Is this where I should look to understand how it works?

Yes, that is where to look.  I'm actually not very familiar with the details of how it is done.

Rob

[Abdullah Mejbil]

Thank you for the explanation Rob!

If anyone knows how the loads are transferred from the VLM pressure solution into the CalculiX (.inp) file when the 'Apply Loads' button is clicked, I’d really appreciate any insights you can share.