creating one component as one part

Hyperworks is NOT CAD Software!

Did you tried export with displayed option.

Rahul, exporting with displayed option didn't work (same as exporting all) . Th question is how to convert an assembly (surface and solid) into one solid model

did you tried solid edit merge option to make one part.

I tried that option but it says selected solids do not share surface. However, when I look at by 3d Topo I see all green lines. I don't know how I can fix this issue

If your model have both solid and surfaces then delete all surfaces & try to use merge option.

I tried that option but it says none of selected solid share edges.

I have found another way to do it.

could you let us know same? 

boolean

Thanks for the update. I believe it worked fine.