Extract internal volume out of a complex geometry

Hi all,
Thanks for reading this.
I am very new to Rhino and grasshopper.
Would like to see if someone can give some pointers on how to extract the internal volume of a complex geometry?
This particular case is a triply periodic minimal surface which I built using the millipede and weaverbird plugins.
Regardless, having a CAD background, there was a tool that would build this for you provided that you patch the boundaries.
Alternatively this could be done using boolean subtract but for some reason my computer crash whenever I tried this. No matter how simply my gyroid is.
Can you help? please :slight_smile:
Many thanks,

Any photos/code for reference?

what do you need it for?

Sorry Leepaklong, I was not thorough with the explanation of my case. I’ll try to do better this time.
Baris, I want this for CFD analysis. Currently working on setting a job on ladybug/butterfly.
The picture attached is the surface I mentioned in my original post.

As I mentioned before this was created using an isosurface tool from millipede and then meshed with another plugin called weaverbird. But I think this is kind of irrelevant.
Also, I mentioned I had problems doing boolean operations with this.
The picture below shows the boolean difference I was trying to achieve.

After some digging I think the problem was the solid created using meshtobrep.
I found that doing this through pufferfish meshtopolysurface gave me better results
The coding more or less looks like this:

What follows, still not sure if is the best or even a good way of doing this but seems to work. I take my two solids and use booleandifference directly in Rhino
I ended up with somewhat I am looking for:

It is not there yet but I think is getting close. A few adjustments on the corners would make it look better or closer to what I need. And I think it will get me there. I am sure there are plenty of better ways of doing this. This is just a convoluted way of doing it :slight_smile:
If you have a better way of doing this please let me know.
Thanks for reading,

Hi all,
Me again.
Forgot to add to my last post that before trying to do this through solid boolean operations I tried doing it through meshboolean instead but I was not able to do this.
For my application, this would be the preferred solution as the end product would be a suitable input for a CFD case.
Furthermore, if anyone here has some pointers on mesh refinements on surface e.g. boundary layer. That would be much appreciated.
Many thanks,