Contact pairs bugs

General Questions
1

Hi there, it’s a while that I am using PrePoMax for my projects with great satisfaction. In this while, I think I came across a couple of bugs, unless I am mistaken.

  1. When looking for contact pairs in tie contact, one is master and the other is slave. In the contact menu there is an Appearance subsection where I presume you can specify the colour of these but, to my understanding, to no effect. Master seems red and slave violet regardless. And in fact I’m not even sure this is the colour association, how am I supposed to know ?
  2. In complex assemblies, which I deal with a lot, where different parts are to be joined, I use the tie constraint and the search for contact pairs tool, which is fab. However, if the geometry is complicated, I have to hide much of it to narrow down the number of possible pairs, otherwise I get unresolved contacts. As a result, I sometimes inadvertently create the same constraint pair twice, but maybe in the opposite order (master/slave). It would be great to be able to catch such double occurrence at the run stage or even before. Anyway, if the tie is repeated but in the opposite order, I may wish to swap master/slave for one constraint (without realising that it already exists in the long list of constraints) and at that point PPM goes crazy: after having issued a warning that a double constraint exists which prompts you to delete either, it then keeps prompting “an item with the same key has already been added the given key was not present in the dictionary”. I believe it’s a bug. I cannot recover form that.
    Finally, let me suggest a small and easy improvement which could be useful.
    In the BCs and loads tags, I suggest to add a note field, so that one can specify some extra info, such as this load comes from this times this and so on. This would greatly benefit future readability of the model.
    Thanks,
    Andrea
2 Likes
2

  1. The color options are not for preselection but for the display of surfaces after creating the contact pair. By default, both surfaces are yellow but it can be changed this way.

  2. Keep in mind that it’s often easier to use compound parts instead of tie constraints. In more complex models it’s hard to keep track of all the possible pairs even with the Search Contact Pairs tool. Often manual or semi-manual definition is better. The same applies to Abaqus (except that there you can use general contact which is not supported in CalculiX).

An option to account for existing pairs in the Search Contact Pairs tool (at least show them on the list) would be useful.

What you mention later indeed looks like a bug:

bug
bug783×610 73.2 KB

bug 2
bug 2736×253 18.4 KB

  1. Yes, that would be nice. Abaqus has this for some features (not for loads and BCs but for steps, for instance).
1 Like
3

Hallo, thanks for the reply. Just one point: when you speak of creating “compound parts” I guess you mean to create a compound out of many geometry parts and then mesh it as a whole. In fact, there is no way that I know of to merge existing meshes, right ? In which case your suggestion cannot be followed because I often have to deal with complex parts which I mesh individually in gmsh with great care and effort and then import in PPM. At that point my only option is tie constraints, I’m afraid.
Also, my parts may not be in contact because welding is supposed to take place and there’s some clearance between them.
Regards,
Andrea