I am getting a substantially different result using tetrahedra mesh compared to a brick mesh as I try do do some standard benchmark tests between Algor and other tools. My model is very basic:
This should result in so decent tip displacement tip displacement.
Using the brick with 6 segments (produces 26 elements), Algor compares very favourably with other FEA analysis at a tip displacement of near 0.420. However, I switch Algor to tetrahedra and it produces 52 mesh elements and a displacement of 0.004 m!
Algor brick meshes of 82 and 4042 elements produce displacements of 0.429 and 0.431 m respectively. However, when using the same mesh parameters. But with tetrahedra, 164 and 8084 elements produce displacements of 0.038 and 0.352 m respectively (yes, there are order of magnitude differences here!).
The other FEA program used to do all the above with tetrahedra mesh, ranges from 0.426 m at a very coarse mesh (~50 elements) to 0.431 with over 27,000 elements (I know, this is way overkill but just testing).
Any thoughts on this?
Thanks
Solved! Go to Solution.
Solved by S.LI. Go to Solution.
Solved by S.LI. Go to Solution.
1.) For tet elements, please try it with mid-side nodes.
2.) Currently, Algor use de-generated brick to simulate tet for hybrid mesh model. It might cause some accuracy issue.
Hi,
The test you conducted seems having the issue of locking of brick element, i.e. when the incompatible mode is off it turns to be "very strong" for bending no matter how fine your mesh will be. When it uses 8-node bricks the incompatible mode is by default turning on so that you obtained reasonable results. But it has to be off for tet and other degenerated elements. As S.Li sugested, using midside in tet elements would likely resove such locking problem in genertal.
thanks.
-xli
Not sure if you get a chance to test Beta of Autodesk Simulation 2012.
Please give a try if not yet.
@S.LI wrote:1.) For tet elements, please try it with mid-side nodes.
2.) Currently, Algor use de-generated brick to simulate tet for hybrid mesh model. It might cause some accuracy issue.
Thank you for the insight here. I think "some accuracy issue" is a little understated in this model 🙂
I know now prefer brick over tet elements in Algor.
@S.LI wrote:Not sure if you get a chance to test Beta of Autodesk Simulation 2012.
Please give a try if not yet.
I saw it available on the website. I am a bit apprehensive to use it since Algor 2011 gives me enough trouble with crashing but I will start the process of downloading it to see. Thanks.
@S.LI wrote:1.) For tet elements, please try it with mid-side nodes.
I was sitting down to see how this would work and have two questions:
1) Are not mid-side nodes used when the model is thin compared to the mesh size?
2) Also, how is this set. I have been looking for how to set this in the mesh settings and I must be totally missing it.
Thanks.
s.li
Thank you much. There is not much info in the help on this so your notes were very helpful to get me where I needed to be. Tet element tests give the same order of mag. in displacement though still not very accurate.
Your further explanation on the use of tet v brick elements is also useful and will be a great further learning experience for me.
BTW, just finished downloading Simulation 2012 so will work on installing it.
Thanks again,
Allan
Hi
Are midside nodes turned on? 1st order tets (we default to 1st order) are stiffer than bricks and 2nd order (midside nodes) tets.
You should see much closer results with midside nodes turned on.
Sam
Sorry for taking so long to get back. Been very busy actually doing the models and installing and trying out a bunch of new Autodesk software. Changing to midside nodes did help in producing similar results to Inventor Simulation though still not as accurate as brick in my situation.
Again, thank you for your help here.
If I recall, there was about a 10% difference with same size mesh but was much lower using a finer mesh with the tets. Unfortunately, I do not have time to go study in more detail unless it is needed in an upcoming project.
try to make it clear
number of tet elements end deflection
I have to say this result looks not bad, even compared with other FEA packages.