Thanks a lot, Ruochun, Your help is really appreciated!
I have generated the mesh with a CAD exactly as you suggested, but something wrong may have happened in the conversion from .stl to .obj. I will create a new mesh for the objects. Have a nice weekend, Giovanni Il giorno sabato 22 luglio 2023 alle 06:06:38 UTC+2 Ruochun Zhang ha scritto: > Hi Giovanni, > > I took a closer look. While the simulation parameters can affect, I think > the main problem is actually *the mesh*. This is how Rhino thinks of > the coperchio mesh: > [image: rhino_report.png] > > As you can see, it purple part which is being complained about seems to be > connecting parts of this mesh. Rhino also reports this *mesh is open* > rather than closed. This mesh seems to be constructed out of 4 separate > pieces, then put together but not properly joined at all. This has left a > lot of hanging and degenerate facets, albeit not very visible if you render > it. But this is enough and will for sure kill numerical simulations with > this mesh. > > Another proof is that when I tried to reconstruct the mesh using quadratic > elements, Rhino gives cracks and holes in those regions, hinting the > original mesh is not properly made: > [image: rhino_reconstruct.png] > And these places happen to be where the particle phase-through happened in > this simulation. This says something. > > I do not know how you obtained the mesh, but if I were to resolve the > problem, I'd do this: This object can be made by a revolved solid (main > body) and 20 fins generated by a circular pattern. We can make them as CAD > objects and properly join them together (using boolean). After a valid > solid part is created, we convert it to mesh. This should give a closed and > properly conditioned mesh and I am very sure the problem will go away with > a correct mesh. I would certainly suggest exploring this path before > playing around more with the simulation part of things. > > Thank you, > Ruochun > > On Friday, July 21, 2023 at 1:34:12 AM UTC-5 Ruochun Zhang wrote: > >> I was able to get this script running fine by simply changing the step >> size to 2e-6 (it's running now. If things go wrong later on I can let you >> know). Of course, when you start using true material properties for your >> particles, this step size may need to be further adjusted. Keep in mind >> that large E, large CoR and small particle size make the simulation more >> challenging, and require smaller step sizes. I would guess if you use true >> material properties for everything in the simulation, then maybe 1e-6 is a >> good step size to start playing around. >> >> A few comments: >> 1. You generally just need the verbosity level to be at INFO. If it is at >> STEP_METRIC, it will try to check if contact pairs are mapped normally >> between 2 consecutive contact detections but this is usually not needed, >> and costs time. >> 2. I saw a warning in the output: a particle may have 0 mass or MOI. This >> is because your MOI is super small in the simulation (~1-13). It appears to >> be fine in this case, but you can also consider using a different >> underlying unit system so the numerics are not so small for masses and >> MOIs. This is perhaps a minor issue. >> 3. I suppose you originally got a "too many contacts per sphere" error, >> and simply changed the tolerance in your subsequent simulations. Usually >> you do not need to change that threshold: Each sphere having on average >> more than 100 contacts is indeed strange, don't you think? That is common >> if the physics went bad in the simulation, and the whole system diverged. >> Having an error indicating particles moving at a velocity higher than the >> threshold is also likely linked to it (but this can depend on your unit >> system: for example the default threshold is 1000, but if your particles >> are moving at 1000mm/s then perhaps it is not abnormal, and you may want to >> manually change the threshold). You usually change the physics to make the >> simulation run, not the thresholds. >> >> Ruochun >> >> On Thursday, July 20, 2023 at 11:24:44 AM UTC-5 Giovanni Bianchi wrote: >> >>> Thanks Ruochun, >>> >>> the mesh is composed of two objects, vasca is fixed, and coperchio is >>> moving. I share only the moving mesh otherwise I exceed the limit of MB. >>> >>> Thank you very much, >>> >>> Giovanni >>> >>> -- You received this message because you are subscribed to the Google Groups "ProjectChrono" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To view this discussion on the web visit https://groups.google.com/d/msgid/projectchrono/6c5c7879-5bd4-4473-908f-cede6e5fe3d4n%40googlegroups.com.
