Plate Mesh Failures in Large Assembly

[BEC_Kevin]

Hello! Looking for some help with plate elements in large assemblies. 

I have created a model constructed of 2D plates (mid-plane and shell surfaces) of a structure, and experiencing critical meshing errors. The model is imported into Simulation by .stp file conversion. The model is generated by an external modeling program, and is already composed of the 2D elements, I am not using the mid-plane mesh function in Simulation! The model is a large assembly, containing 95 parts. Mid-planes and shell surfaces are generated from 3D modeled structural tube, shapes, and plate. I am running a static linear structural analysis

The issues I am experiencing are surfaces disappearing after mesh function run. Mesh not matching to adjacent surfaces. Elements appearing in mesh that do not exist in CAD model.

The software we have is Autodesk Simulation Mechanical 2012, Build 2012.00.00.0163. 

I have attached an image of a portion of the structure, showing the poor quality of the mesh. I have experimented with VCAD function, refinments settings, and mesh size. All changes yield similar failures. 

Thank you in advance for your thoughts and support. 

[cooperjer]

Hello BEC_Kevin,

Here are a few suggestions to try:

1.  Double check the STP file for hidden nodes or planes that would cause the elements that stand out as being in the wrong place (i.e. the yellow and blue elements in the lower left of the image.)

2. Add some split surfaces to the STP file to help ensure the planes that intersect perpendicular to each other have a good mesh.

3.  Refine the mesh size at the edges of the poor meshing to be similar to an area that had good meshing.  Check the line element size of the good area and assign that to the bad area.

4.  If you feel comfortable removing the rounds and fillets from some of the tube and making them square corners please do so.

5.  In the Model Mesh Settings for planes the "tab" named Model, located below Surface, has a boxed section labeled Mesh matching.  Adjust the mesh matching to be smaller than your element size.  I would suggest it be 1/2 to 1/4 of your smallest mesh size.

6.  If that does not eliminate the bad meshing then manual modification of the few elements with a bad aspect ratio is also an option, assuming you do not have a lot of bad elements.

Good luck.