RE: PLAXIS 3D MESH WARNING

Jozanga S. Fernandes — Fri, 22 Jul 2022 14:10:55 GMT

Hey,

Did you solve the issue?

RE: PLAXIS 3D MESH WARNING

Stefanos Papavasileiou — Mon, 18 Jul 2022 07:35:14 GMT

Dear Rohith,

In the cases that you cannot generate a mesh in PLAXIS 3D, the reasons why the procedure fails can be various.

To start with, in some cases, the PLAXIS mesher provides a bounding box with coordinates and warning messages that pinpoint the area that has caused problems in generation of the mesh. A first step would be to apply local refinements in that area to ensure that smaller elements are created in that region.

Note that local refinements are always needed for cases, for instance, where geometry details are modelled, large concentration of stresses and strains are to be expected, in areas where groundwater flow is occurring.

As I read this did not help overcome the problems, but it is always good to consider.

As a good practice, partitioning of the geometry can be performed. This can be done by using a volume to partition the created geometry or a closed box of surfaces. This will allow the mesher to isolate each partition and assist in the generation of the mesh.

Typically, this can be done using a top surface, then extrude that to the elevation covering your geometry (e.g. piles, tunnels).

In the special case of embedded beam elements, make sure that the bottom points lie on a surface or the bottom of the volume created.

There are other cases in which you might have geometry objects close to each other that the automatic mesh generator cannot fit (good-quality) elements around.
You can find such issues in the geometry by using this command in Structures and Mesh mode:

checkgeometry

This command checks if objects overlap or are adjacent and gives a list of items with their distance. So please check here the geometry that is marked as being close by.

In some cases, this command does not give any feedback. This command by default takes a distance tolerance related to the model's size. If the command does not give this info, then add a parameter to this command, e.g. 0.01 to check all geometry that is located within 0.01 m:

checkgeometry 0.01

You can also check the size of the of the intersected objects in Mesh mode to locate problems. To do so, make use of the tabulate command, see the examples below. You might want to adjust the numbers below to fit your model's size.

#To find small Surfaces:
tabulate Surfaces "Area" "Area<0.5"

#To find small Polycurves (e.g. used for Tunnels):
tabulate Polycurves "Length" "Length<0.1"

#To find small Volumes:
tabulate Volumes "Volume" "Volume<1"

#To find small SoilVolumes:
tabulate SoilVolumes "Volume" "Volume<1"

The list of Volumes might be different from SoilVolumes if you model volumes outside the borehole soil layers.

More details on the tabulate command, see here:
https://communities.bentley.com/products/geotechnical1/w/wiki/45942/obtaining-tabulated-data-from-plaxis-input

Apart from that, the snap and mergeequivalents commands can also help in making the geometry accurate in order to proceed in meshing procedure. For more information about these commands please check our Reference manual and Command reference (Help menu).

Please try to locate all potential problematic geometry in your model in Input and fix them. Note that not all reported objects are necessarily problems that need to be fixed.

If the meshing procedure succeeds, then note that the quality of the mesh in Output should also be checked. To see the quality of the mesh you can check the generated mesh in Output and select Mesh>Quality.

Be aware that the quality of the mesh is related to the generated element size. Badly shaped elements (slender or pie-shaped) might introduce problems in calculations.

Note that good elements are these with the same size for length, height and width of the element.
In general, it is recommended to maintain the lowest quality of no less than 0.01 (when possible). In some cases, this may also require applying local mesh refinements in the model to be reached.

I hope this helps.