Just something I'm working on.
it seems that your model is a half under the ground
Yes, agree with mirko :-\
Other than the point made correctly by mirko, I'd suggest to increase Tessellation Quality.
Tessellation?
Tesselation : the number of polygons if your polygons are triangles.
Renders are often better with quadrangles. But it's my opinion...
How do I increase the number of polygons? I am using KeyShot that came with my CAD package (Alibre).
Depending on what package you use ...
There have been 2 situations so far I think. Either you can set tessellation detail on the import dialog in KS. If not, you need to find such a setting in your CAD program.
The tessellation can be seen in your render on the edges of the round parts. There where you got corners instead of a smooth circle ..