Export mesh from Fluent in Nastran format
 

I am trying to link CFD results from Fluent to a BEM analysis using LMS Sysnoise. In the help files of Sysnoise I read one can import the mesh from Fluent, but it is necessary in Nastran format.

In Fluents user guide (chapter 4.13 and 4.14) I read it's possible to export elements and nodes in Nastran format using File -> Export -> Solution Data. But when I try this, there is no Nastran in the dropdown menu for file type.

Another possibility was the command line. I've tried file/export/nastran but then I don't know which parameters I should give.

Somebody knows what to do?

UDF solution
 

We did it in the past for FSI modelling (http://www.torvergata-karting.it/art...eview/72/1/16/), this option is still active in our FSI module:
- during initialization we write the boundary mesh in Nastran format and we build the connectivity between FEM and CFD id
- stiffness and mass matrices are then generated and imported
- during the transient simulation CFD forces are used to dirve the structural simulation (the solver is embedded in the UDF)

We are now experimenting a different strategy based on RBF (http://www.rbf-morph.com/) with promising results: in this case we can exchange information using non conformal meshes.

I guess that you can solve your problem using standard features; if you need a custom solution do not hesitate to contact me.

Regards.

Marco

Hi Marco,

your solution looks promising, but I think it's too complex for the purpose I want. My project is about a rear view mirror in a flow of air and I don't need deformations of geometry...

In the Fluent user guide I've found following sentence: "ANSYS FLUENT supports exporting polyhedral data only for ASCII, EnSight Case Gold, and Fieldview Unstructured file formats."
Since I am working with a polyhedral (hexa) mesh, that's why I can't export my mesh to Nastran format.
Do you think RBF can help?

Rbf
 

Radial Basis Functions (RBF) can help if you have non conformal meshes.
Basically using RBF you are able to transform any scalar function defined at discrete locations (nodes, cell centroids) in a continuous one (i.e. you have a closed form access to the function).
This is very useful to transfer data between different models.
RBF Morph is a software that allows to modify the mesh and it's intended for shape optimisation: in this case RBF are used to represent the prescribed deforming field. However we are currently exploring its application for FSI using non conformal meshes: RBF are used to interpolate the data exchanged between CFD and FEM models.

RBF are one of the most powerful mathematical tool that I ever have used.

For your specific problem try first with ANSYS support: maybe they are able to find a workaround for your problem. Investing in a specific UDF for a one shot problem could be not wise. However if you need the set-up of this methodology we can discuss it.

Regards.

Marco

Hi Macro,

I am trying to make simply problem that it will get external force matrix on MSC.NASTRAN. It is great tool when I see your contribution related to FSI (FLUENT and NASTRAN) as well as morphing mesh approach. Could your give me some ideas how to get forces from NASTRAN.

Thank you so much,
Tran

Have a look to the FSI mapping tool of Fluent. It allows to map flow forces onto an existing FEM model; Nastran format is supported and I have a positive experience in its use.

Hi Marco

Thank you for your response. Your information is very useful for me. I still confuse that how can you map flow forces onto an existing FEM model that constructed by solid element. There is map tool for surface from CFD to existing FEM model in NASTRAN.
Best regards

Usually a skin of shell element is added to solid model (FEM side). This allows to clearly identify wet surfaces.

Hi Marco,

That sounds great! You have more positive experience in its use. Please give me some advise how can I access a skin of shell element in NASTRAN. It is a great for me.

Best regards.

Meshing software allows to put skins on a solid mesh; they can be used as a stress recovery tool. Use a very small thickness otherwise you will change the stiffness!