PPM 1.3.6: Bug during 3D meshing + inconsistency in Settings

1. Bug was introduced with changes in meshing parameters. Steps to reproduce:

  1. Open a new project read any 3D STEP file.
  2. RMB, Meshing Parameters, Create.
  3. Select “Yes” in “Quad-Dominated Mesh” category
  4. In the “Set Selection” window choose “Part” and select 3D body by mouse, OK.
  5. Try to create mesh. Meshing lasts forever, when cancelled, the following error message is shown: “Error during meshing. Please check the output window”. Output window does not contain any reason why meshing failed.

Of course, I know perfectly well that the “Quad-dominated mesh” option is available only for 2D meshes. However, not all my students are so wise:). Previously, this problem did not exist, because for a 3D body, “quad-dominated” option was automatically changed from “Yes” to “No” during meshing. A new version is not foolproof. Perhaps with “Quad-dominated mesh” option active program tries to create shell mesh using 3D body and fails.

2. In a new version, “Meshing” tab of the “Settings” windows is changed considerably. A user can select default mesh size definition method ( absolute or relative) and set min and max “element factor”. The last option is slightly misleading. First, it makes sense only when relative size definition method is used. Thus, if a user prefer more common absolute method these two options should be inactive. Second, at present, a user can input any number greater than 0 as a max/min relative element size. Unfortunately, numbers greater than 1 can also be used that leads to an error during mesh creation.

IMHO, understanding of the these two new parameters could be a bit improved if their names are changed into “Max/min relative element size” or “Max/min relative element size ratio”. In this case it is clear, that both parameters are for relative size definition method only.

The new settings were introduced to cope with assemblies. Sometimes you would like to make the mesh denser for a couple of parts only. If those parts are different in size there is no easy way to do that using one absolute setting. So relative settings were introduced that enable the creation of equally denser mesh on all parts.

This is definitely a bug, and I will look into it.

The settings menu is used to define the initial/default meshing parameters. The user can later decide if absolute or relative settings will be used for selected parts so the initial values for both, absolute and relative parameters must be set up in the settings window. So the default selection of absolute/relative inside the settings can be later changed for selected parts. And, when the parameters for selected parts are defined by the user, the absolute and relative parameters are not shown at the same time.

True. The relative element size is a size factor. It is a factor used to compute the absolute element size by using the length of the part’s bounding box diagonal (or something similar since I do not remember the exact equation).
The relative size must be converted to absolute size in order to perform the meshing inside netgen. The upper limit is hard to define since the absolute upper size limit does not exist. You can freely change the min and max element size inside netgen.

I think changing it to “Max/min relative element size” would be preferred for most users.

I am afraid you do not understand my message about bond check for the relative element size. The problem is that a user can input min relative element size greater than 1. Does it have sense?

Yes, I understand your point of view. But the user can also enter 1000 mm for a minimal absolute finite element size for a part whose size is only 10 mm. There is no limit check for that. And the meshing fails. For this reason, I did not include a check for a relative size larger than 1 since there is no check for an absolute size. But I agree that your point of view is valid.

Excuse me, just one more explanation. I am not speaking about the default “Settings” parameters, I am speaking about “Create meshing parameters” window. If in this window a user has explicitly selected “Relative” as a method for a mesh size definition it is clear that Max/min mesh size parameters should be definitely relative and should be less or equal to one. IMHO in such a case top limit check can be added.

This mini-bug is not important for an experienced user, but for students it could be useful.

I was thinking about it, and I cannot find any good reason to use a factor larger than 1. So I will probably limit it to 1. In the Settings and in the Create Meshing Parameters windows.

I have set the upper limits to 1.

I have also added two views of the meshing parameters since the number of settings parameters grew in the last release.

A default basic view:

and a more detailed Advanced view:


For the new version v1.4.0 I have fixed the problem with Quad dominated mesh setting on the solid parts. With this, I think this topic can be closed.

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