stresses at perpendicular shell elements. problem?
stresses at perpendicular shell elements. problem?
(OP)
hello,
I am modeling a structure with shell elements and I am having very high local stresses in the areas
where perpendicular shells are connected as you can see in the attached file. In the real strucutre
the webs are welded to the rest of the structure.
I've heard that perpendicular shell elements give pessimistic results. Is this issue relevant in my
model? Should I use a more detailed mesh?
To understand what I am talking about please look at the attached pdf.
My question is how relevant these modeling issues are, and which is the best way to model this
kinf of problems.
PD: The results shown in the attached file are from a random analysis.
thanks
I am modeling a structure with shell elements and I am having very high local stresses in the areas
where perpendicular shells are connected as you can see in the attached file. In the real strucutre
the webs are welded to the rest of the structure.
I've heard that perpendicular shell elements give pessimistic results. Is this issue relevant in my
model? Should I use a more detailed mesh?
To understand what I am talking about please look at the attached pdf.
My question is how relevant these modeling issues are, and which is the best way to model this
kinf of problems.
PD: The results shown in the attached file are from a random analysis.
thanks





RE: stresses at perpendicular shell elements. problem?
note the 3D solid web and the 2D shell body do not join as you might expect/desire. 3D elements have not moment freedoms at the nodes, so the 2D shell elements of the body have no where to react this load. so i think this is probably the least accurate model. the 3D solid web and body is probably the best representation of what you have, since the web and the body are compatable.
RE: stresses at perpendicular shell elements. problem?
When you use only shell elements did you just merge nodes or you have put a rigid element between the perpendicular parts?
did you try to use C-WELD elements to join the perpendicular shells?
sorry for my english level
RE: stresses at perpendicular shell elements. problem?
What kind of analysis are you doing? is it a strength/proof load of fatigue analysis? Looking at the solid model proportions it looks like shells should do the job if you use the correct averaging and ignore stresses in the virtual overlaps. A much finer solid would also work but may be more costly from time point of view. Either way you should be getting results that are much closer
RE: stresses at perpendicular shell elements. problem?
inline6: What is the origin of 4 elements of HEX8 thru the thickness? The minimum of 3 elements seems to me more intuitive (tension-neutral axis-compression). Have you ever compared 3 and 4 elm. solution? Are the differences significant?
RE: stresses at perpendicular shell elements. problem?
nodes are simply merged. I've never heard about cweld elements, don't they make the structure stiffener?
irq, yes, i am using Patran/Nastran. About averaging, I'am not very used to Patran, could you help me with this? how can i plot results wihtout averaging?
RE: stresses at perpendicular shell elements. problem?
RE: stresses at perpendicular shell elements. problem?
In patran do a fringe > Plot Options > Averaging Definition > Domain
RE: stresses at perpendicular shell elements. problem?
RE: stresses at perpendicular shell elements. problem?
RE: stresses at perpendicular shell elements. problem?
personally i'd strongly advise against merging nodes, 'cause i think you're creating a pinned joint at the interface.
RE: stresses at perpendicular shell elements. problem?
RE: stresses at perpendicular shell elements. problem?
BP846, Are u using Femap ??
RE: stresses at perpendicular shell elements. problem?
RE: stresses at perpendicular shell elements. problem?
i was talking about merging nodes directly (what i thought you'd done originally) between 3D and 2D elements. connecting the two elements with say CWELDs or RBEs isn't (in my imnd at least) "merging nodes".
RE: stresses at perpendicular shell elements. problem?
RE: stresses at perpendicular shell elements. problem?
Use shell-to-solid element connector (RSSCON Surf-Vol) from Elements/MPC to couple the different dof's between shell and solid and have the things done. It is much easier than RBE2 or RBE3 (you do not need to specify any dof's, the constraints are set automatically) and model exactly what you are looking for.
CWELD is general purpose connector in MSC.Nastran to enable a quick connection of the disimilar meshes without node alignment etc. MSC says that it is more accurate than RBE2/RBE3 but I have never checked it.