Thin Surfaces or 3D solid model?
 

Hi everybody,

I am a college student learning Ansys and CFD. I am running a two-ways FSI simulation of a wing with Transient Structural and CFX (the wing is hollow inside with a skin thickness of 0.5 inches). I used one side of the wing as the fixed support. The goal is to find the equivalent stress and the deformation of the wing.

First, I modeled the geometry using the thin surface option. I used 3 different surfaces: the wing skin, the support (where it attaches to the fuselage), and the wingtip surface. I set the surfaces thickness offset type to "middle" (This causes the mesh of the skin to merge with the mesh of the support and wingtip. Is this a problem?)
When I look at the FSI results, I get a deformation of about 2 cm, and an equivalent stress of 37 MPa.
Then, to check my results, I ran the same FSI simulation with a 3D hollow body of the same wing imported from Creo. The equivalent stress is very similar (35 MPa) but the deformation is much larger (23 cm!!!).

I believe this is due to the different geometries in the Modeler, because everything else is exactly the same. Could someone please explain me why I get such a big difference in the deformation, while the stress is almost the same?
Also, when is it appropriate to use thin surfaces, and when is it better to use 3D solid bodies?

The first two pics show the thin surface wing, while the last two pics show the 3D solid body wing.



I am stuck and would really appreciate some help. Thank you very much! :)