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To view the .igs files, go to the pull down menu to the left of the File name text box and change it to Geometry File(...). Go to the location where you saved the monocoque.igs and click Open. Your workbench should look this:
Build the Geometry
This particular geometry have contains solids, surfaces and line bodies. In default setting, Ansys do not build the line bodies, but we can change that with following steps:
Double click Geomtry to bring up the Design Modeler
Select inch as the unit and hit OK
Under Detail View Penal, change Line Bodies to Yes as shown below:
Now CLick Generate to build the geometry.
This will make sure line bodies will be built along with the surface and solids.