Generally we have problem with the meshing module in PLAXIS 3D. The only time that we get a successful meshing of the program is where the project is made of horizontal/vertical lines/surfaces. Otherwise, majority of inclined/curved/irregular surfaces/volumes ending up in a frustrating loop of failed mashing process due to surface/volume size.
Considering that some of the complex geometries cannot be simplified much and identification and fixing the issues are very time consuming, that would be great if I can have your advice on whether this is general problem within the PLAXIS 3D users and if yes, how to make this process quicker and more user-friendly.
Ramtin, I share your frustration with meshing. I always seem to be under a lot of time constraints to bring my models in on budget and schedule and it is usually meshing that is a prime concern and my biggest unknow. I've found that Plaxis has made great improvements on the reliability (and quality) of 3D meshing and I no long have the issues and frustrations that I had several years ago. That said, I have a lot of tricks and suggestions, some of which I have seen the Plaxis staff offer up on this forum. Time spent meshing is as important as time spend analyzing. Here's what I do.
1. I generate surfaces and volumes from points and lines that I know the coordinates.
2. I limit the number of decimal places on the coordinates that I enter to 2 places (i'm using ft, so maybe 3 for m.).
3. I mesh often, after I add a few geometrical objects. I don't try build the entire model and then mesh. Be methodical, build geometry mesh, save , build some more mesh again, save.
4. Recognize that small details in a large model difficult to mesh. Small details should only be included if they are necessary.
5. It is hard to mesh from a large dimension to a small dimension. To minimize this it's always best to include a box around a small detail, so that the small detail is meshed inside the box, and then the rest of the model is meshed to the box.
6. Recognize that very small angles are difficult to mesh and produce bad meshes. It's best to eliminate small angles.
7. Spend a lot of time on making the geometry clean, and simple as possible. I have very little luck importing geometry from clients that create surface in AutoCAD 3D because the surface are not perfect, and Plaxis (or any FEA) demands that the mesh is 100% non overlapping, no holes etc.. it needs to be a perfectly formed geometry.
8. Look out at all time for the possibility of incorrectly snapped geometries, I almost always create the geometries from known lines and points, and I give all the lines and points names that I know. if I start to get a Line_1 or Point_1 showing up I know my model is starting to get out of control.
9. Sometimes you just need to know when the model is out of control, and I start all over again. I only save meshed model.
But I must add that the Plaxis team has really improved meshing. I might also add that I recall meshing BY HAND, which is a nighmare I like to forget.
Hope this helps.
Martin
Dear Martin,
Great thanks for the detailed reply. Very helpful and structured information.
Also I want to mention two articles on Virtuosity site about meshing and calculations:
→ How To Efficiently Speed Up Mesh Generation→ How to Speed Up Calculation Time with PLAXIS
There is also a link to recording a webinar on these topics.
Thanks Martin for the detailed response. Much appreciated.
In general, during my model development, I am following the suggestions made in your message. However, I had few terrible experiences with the meshing module that I couldn't fix them, even with taking into consideration the reasonable rules:
- Converting volumes into surfaces leaves some unresolved faces that create problem with intersections.
- Merging equivalent object does not work properly.
- Intersection and re-clustering leave unresolved objects.
- From time to time, the structure module does not snap points and changes manual round inputs into very small deviations.
After such a long journey with PLAXIS, I am getting to a point that I expect Bentley to take responsibility for the shortcoming of its meshing algorithm and find an effective solution to this issue. In our industry, basic operations such as meshing shall not be a barrier and we must not spend significant time on fixing meshing issues that may be fixed by further software development.
Dear Ramtin,
Sorry to hear that you experience issues when meshing your PLAXIS 3D model. We have made a huge effort to improve our mesher in our latest versions as we have seen some impressively complex 3D projects that, with the reasonable effort considered, produced good results.
The suggestions by Martin are spot-on. I agree in general that a step-by-step process when building the model, intersecting, meshing is needed to ensure one has a workable model and easy to identify the reason for any issue encountered.
All points mentioned in your last post should be clarified in the specific project you have. I would be happy to assist you with each one if you can please submit a service request: https://apps.bentley.com/srmanager/ProductSupport