Kyle had a great question about sheetmetal FEA, mid-surface, etc... Thanks for it!
I didn't want to propound it with my (hun) english words.
Rather I asked Dr. Louis Komzsik (Chief Numerical Analyst (NX Nastran) at Siemens PLM)
about this in nutshell:
Here is his answer, I hope this will help:
"The shell element technology in NASTRAN is very close to the physical behavior of thin shells. Quadrilateral element (QUAD4, QUAD8) based surface meshes are very regular and provide good results. The mid-surface generation makes this modeling approach much easier. Historically, this technology was troubled by the need to “stitch” the shell components together with the difficult RBE* type elements. The glue connection technology (specifically the edge to surface connection) enables the user to connect shell models without the connection difficulties in the past.
Solid element modeling of thin shells with elements through the thickness is not as accurate. The automatically meshed tetrahedral elements are not as regular and on occasion, very poor element shapes are obtained. The system (stiffness and mass) matrices (in the case of multiple layers of elements through the thickness) are larger in size and the computational costs are more.
Consider the geometric model shown below and its tetrahedral and mid-surface shell mesh.
The normal modes analysis of the two provided almost identical results:
with a much faster execution time in the shell model."
All information is coming from Dr. Louis Komzsik!
Ps.: Who is Dr. Louis Komzsik? In my mind, his role at NX Nastran is very similar to Dan at Solid Edge! Thanks to them and respect for all!
Thank you so much for digging into my question and getting a very detailed answer from Dr. Komzsic. Very interesting.