How to use FEA Structure/BCs?

[cean wang]

Hi,

I want to model with OpenVSP,  then export a FEA case file for Nastran-95/Mystran.  

I have tried to open a sample VSP3 model file. Then I opened Analysis/Structure/FEA Structure window.

Under Structure Tab, I added the Structure.

Under FEM tab, I ticked Nastran output type, Then click Intersect and Mesh, the Export FEM.

Just wondering how to use the BCs tab? How do I apply a pressure.

Cheers,

Cean

 

[Rob McDonald]

The BC's in the OpenVSP GUI are only constraints -- not loads.

To add them, you do as you've done, then go to the BC tab and click Add BC.

You then pick what kind of entity to constrain -- the entire structure, a single Part, or a single SubSurface.

In reality, Nodes are constrained -- you're working on building up a filter that selects which nodes to constrain.

After selecting the entity, you might jump down to the 'Region', where you can specify a coordinate box to identify the nodes.  For example:

Structure

Y < .01

Will select all nodes on the centerline of a half-model.

Note:  If you want to constrain a single point, you can add a 'FixedPoint' as a Part to the model -- you get to specify where it occurs.  Later, that fixed point will show up as a part that you can pick when applying BC's.

After you've identified the nodes to apply, you pick which DOF to constrain in the middle of the BC GUI.

Let me know if this doesn't make sense.

For now, you have to add all loads yourself outside of OpenVSP.

Rob

[cean wang]

Thanks Rob. 

This seems like to write out the SPC in Nastran's case.

BTW I noticed When starting, OpenVSP checks if ccx is in system's PATH. I am wondering which GUI button runs ccx? or it is not implemented yet, since FEM export seems can't export a full FEA case file.

If I use Nastran-95, would be nice to have a solver config window to choose like which SOL to output into the case file.

[Rob McDonald]

Yes, in 3.32.X the BC's get written out as SPC's for NASTRAN.  In 3.31 (and maybe a version or two earlier) they were written to the GRID points themselves.  Another user asked them to be moved to SPC's.

If you go into the 'Aero Structural...' gui, it is a vertical row of buttons....  It represents a process flow from top to bottom.

It is a really simple case of taking aero loads, meshing a FEA structure, mapping the loads onto the structure, and analyzing them -- all for the CalculiX set of tools.

The mapping of pressures to the FEM loads is done with the vsploads tool.  That tool does not yet have the ability to do this for NASTRAN.

I am not a NASTRAN user -- I don't even have access to a running copy of NASTRAN.  So, I rely on users like you to help make the OpenVSP structures capability the best it can be.

We have no intention of becoming a comprehensive pre-processing tool.  We're just trying to make it easier to go from an OpenVSP model to a structures model.

Rob

--
You received this message because you are subscribed to the Google Groups "OpenVSP" group.
To unsubscribe from this group and stop receiving emails from it, send an email to openvsp+u...@googlegroups.com.
To view this discussion on the web visit https://groups.google.com/d/msgid/openvsp/9a769daa-5f7c-4eb9-b810-9f70c9ff248fn%40googlegroups.com.

[cean wang]

I am playing with 3.32.1.

CalculiX just lack of real bar and shell.

Yeah,  pre-processing is too much. OpenVSP is quite good to have the filters to choose the nodes (and elements?). It is useful to apply loads, etc. Other softwares mostly apply loads before meshing.