use the preview to see which offset you should use. the shell is a zero thickens FEA model and you are working on solids right?
If you are confused by the name shell just imagine it is a "sheet of metal"
Middle Surface The selected surface is the midplane reference of the "sheet metal." Top Surface The selected surface is the top surface of the "sheet metal." Bottom Surface The selected surface is the bottom surface of the "sheet metal." Specify Ratio The selected surface is a reference surface defined by an offset value that is a fraction of the total thickness. The offset value ranges between -0.5 and 0.5.
Hope this helps.
Thanks for your reply.
For example, in the pulley case in the simulation training manual its outside faces are selected, then which option of the offset should I use? Top?
Solidwork Help says that mesh is aligned to the mid plane by default.
just use the preview button...
on the example attached earlier I would have to use an offset that would make the shell preview go right.