how to convert my DWG 3D model into stl file format?

[hypertent]

We are running another finite element software which need stl file format. I got this attached 3d dwg file. How can I convert this into watertight surface stl file? The dwg file only has 3D faces elements. 

I could convert my dwg file into igs or iges file format. But this file format doesn't work well inside that FEA software. There are more than 2000 3d faces in igs model which is impossible for me to do the FEA analysis on the model. I want to convert this 3d model into watertight surface so that I only need to work on a few surfaces. I knew new AutoCAD version can export dwg into stl file, I tried this on my side, it didn't work. Can someone please help me out?  Thank you very much. 

[arshadmirza786]

STLOUT

[pendean]

https://help.autodesk.com/view/ACD/2022/ENU/?guid=GUID-5E9946B5-D769-4881-BC0F-21F54840683D

[hypertent]

Thanks for your reply. I did try STLOUT command to convert dwg file into stl model. But it didn't work. see attached ConvertedtoSTL1.jpg.  The command didn't process at all. I also converted these 3D faces elements into faceted surface and converted them into stl model. It didn't work either. What I want is to simplify the whole triangles meshed elements into five big surface: four side surfaces and one downspout surface. see attached picture, Simplified Surface.jpg. 

As another CAE software need simplified surface model to carry on analysis. Current model has more than 3000 elements. 

[pendean]

@hypertent STLOUT requires specific content to convert, as I highlighted for you in the screenshot in my last reply.
If you don't have those objects types in place you cannot create an STL file. Sorry, there is no workaround.

Share your DWG file if you wish for others to examine the content.