Individual density

[HeikoStark]

Is it possible to assign an individual density to each element (as with the fiber direction)?

Many materials have a very inhomogeneous structure (for example bones), where the description via an average value is too imprecise.

Best regards,
Heiko

[ateshian]

Hi Heiko,

Yes, if you use <febio_spec version="2.5"> you can do that in the <MeshData> section (following </Geometry>):

        <MeshData>
                <ElementData var="fem.material[0].density" elem_set="Part1">
                  <elem lid="1">1.2</elem>
                  <elem lid="2">1.3</elem>
                </ElementData>
        </MeshData>

Best,

Gerard

[HeikoStark]

Dear Gerard,

Thanks for the hint, I will try it out.

Best regards,
heiko

[maas]

Hi Heiko,

I want to point out that in FEBio3 there is another mechanism available. Since this alternative mechanism is going to be supported directly in FEBio Studio, you might want to consider this approach as well. In this case, you also define a map in the MeshData section, but you assign the map directly to the parameter. As follows:

<material id="1" name="mat1" type="neo-Hookean">
  <density [B]type="map"[/B]>density_map</density>
</material>

...

<MeshData>
  <ElementData [B]name="density_map"[/B] elem_set="Part1">
    <elem lid="1">1.2</elem>
    <elem lid="2">1.3</elem>
  </ElementData>

Notice that you need to use "name" instead of "var" in the map's definition. Let us know if you have any problems with either approach.

Cheers,

Steve

[HeikoStark]

Dear Steve,

Thanks for the hint!

At the moment I still have some problems to get FEBio3 working, because the file format / specification has changed. (For developers it would be helpful to see here when and in which version the respective identifier was implemented).

Nevertheless, the software is very helpful.

Best regards,
Heiko

[maas]

Hi Heiko,

Is the problem that you can't convert to the 3.0 format, or that the 2.5 format is not working for you in FEBio3? Most 2.5 files should work in FEBio3, with a few exceptions. The release notes contain some information about backward incompatibility issues. We also added support in FEBioStudio that reads files with the options that are no longer supported and convert them to the correct format when exporting. There is also a batch convert tool that allows you to convert a bunch of files at the same time.

If you are still have problems converting files or running older files, let me know and I'm happy to look into this further.

Cheers,

Steve

[HeikoStark]

Dear Steve,

I mainly have problems keeping my software up to date, so that it can generate FEBio files. In my software you can specify the output version, but I have to reduce the complexity.

But it is nice to hear that there is a converter. Where can I find it?

Currently, I have problems to implement the instruction "<Constraints><rigid_body..." correctly in 3.0.

I haven't got FEBioStudio running yet:

$ ./FEBioStudio
(process:81538): GLib-CRITICAL **: 15:11:53.822: g_hash_table_contains: assertion 'hash_table != NULL' failed
(process:81538): GLib-CRITICAL **: 15:11:53.823: g_hash_table_insert_internal: assertion 'hash_table != NULL' failed
Memory access error (memory dump written)

Best regards,
Heiko

[maas]

Hi Heiko,

The converter is part of FEBio Studio, so you would need to be able to run FEBio Studio. I'll reach out to you via email to see if we can help figure out why you are having problems running FEBio Studio.

Cheers,

Steve