Gap between Cascade Connection

[Archaine]

I simulated this same scenario last week and there was not a gap between my cascades connection, I had some issues with my first run, so I have re-created the simulation, however gaps appeared between the two cascading sims, so I shifted their position a little and changed the overlap, but I still get a gap. The overall simulation is very large 750 feet in length, trying to see if it can simulate water buildup from a fire suppression system for one of our clients. Also the particles do not align in the second sim, they form a sort of grid and loose their randomness, I though the cascade took the particles exactly as they are from the first simulation?

[Archaine]

Better View - This is my first sim, there was not a gap, but a lot of other issues, so I recreated the simulations, but now I have the darn gap.

I did not realize the grid could be stretch differently in x,y,z. Maybe mention this in the documentation under grid creation. I re-created my grids ensuring square voxels. I think the stretchy problem occurred when I tired to do a grid over 20000cm with 1cm res, it truncated the voxels on that axis and they essentially stretched, and I used the scale tool to increase the size of my sims, this also appears to have stretched the grid, you can see the initial columns coming down are all squished in the z axis. Anyway when I re-created everything to fix these problems that's when the gap appeared.

[Archaine]

Hmm its saying I dont have permission to edit my own posts, was just going to add this image to the last one

[Svetlin.Nikolov]

Oh, you can scale your simulation grid only if you will only render it from this point on, but you should never do it if you intend to keep simulating with this grid afterwards.

In you latest setup, is any of your simulators stretched in some direction?

[Archaine]

No, I ensured no scaling or stretching for the re-worked simulation. I remade each simulator from scratch. So the gap is a mystery. Could it be a corruption or a bug, or did I do something wrong. How much of an overlap should a cascade have, the docs just say overlap, can that be 1cm or does it need to be 10cm, or just larger than the grid resolution?

Ok, I just measured it, I have a 20cm overlap between the two simulators. They both have 3cm grid resolution and 3 iterations per frame.

On a side note, the delete cache button is available even when no simulation is selected, I assume the button will delete ALL cache files for all sims in a max file, so If I have 3 good sims and 1 bad one in a cascade setup then I should manually delete the cache files for the bad sim that I plan to restart? Does info about the sim reside anywhere else, or does deleting the sims cache reset it completely?

FYI its tradition in 3dsmax to size a box with the scale tools, I saw the simulator bounds as just a box and initially scaled to get it to the size I wanted, you may want to clarify this in the documentation, I spent a lot of time re-running sims because of the stretch issue, now I know to just type the size if I need to adjust it.

[Svetlin.Nikolov]

Ahum, could it be that the steps per frame are causing the gap? What if both simulators use just one step per frame?

[Svetlin.Nikolov]

As for deleting the cache files - indeed the toolbar icon will ask you to delete the caches of all simulators if you have not selected any. You could also go to the Output rollout and delete the caches from the "..." menu of the cache path - the toolbar button is just a shorthand for this.

The cache files contain only the result of the simulation - they don't contain any settings, so you could safely delete them before starting a simulation, or if you don't - they will get overwritten one by one by the new simulation. No settings of the simulators will get changed by deleting the caches.

Check here for more info: https://www.chaos.com/blog/the-compl...ics-simulation

[Archaine]

So the steps per frame could cause the gap? I wanted a at least a few steps in there, assuming more steps means a more accurate simulation correct?
Thanks for the cache info. Been copying my cache to a backup folder in case I accidently mess them up.

Also, I need to add 400 frames to my 2000 frame simulation. It has cascades from sim1 to sim2 and from sim2 to both sim3 and sim4.
Do I just add 400 frames to the timeline, go to sim1 and restore/load & start from frame 2000, then do the same in turn for the other cascades?

[Svetlin.Nikolov]

Oh yes, more steps mean more precise movement of the fluid, but with cascade sims there is a catch - since the substeps do not get written to the cache files - the cache files are written only at the end of each timeline frame - when the second simulator receives the liquid, it can only see its state at the end of the timeline frame and can't see the substeps, so to the 2nd simulator it's the same as if the 1st simulator had 1 step per frame. This might cause some difference in behavior where the connection between the two simulators is, but it really depends on the scene and most of the time it's not noticeable.

For restoring, what you said is the exact correct way to do it!

Cheers!

[Archaine]

Ok, that makes sense, thanks for the explanation, and for the confirmation of my workflow to add frames.