Hi list, I have a small test sim attached > flip liquid pouring into a simple tank

1) define a vel volume and use it to advect the flip particles in the tank while a liquid pours. Seems simple enough. If you use the old school method of defining the vel volume as a fluid source ( pump ) things work as expected the incoming vel is blended with the current vel and the pump volume on effects flip particles within the volume and of course in the example does not effect the flip liquid pouring in.

2) example two though same set up but uses a pop advect by volume > the volume is defined as above but the pop advect by volume effects all the flip particles in the simulation , even though the vel volume does not encompass all flip particles, so flip particles get effected even outside the volume.

Test scene attached Anyone know why this happens as a default ?

Hello Circus Monkey,

It was really interesting to figure out this problem.

So after a little help from my co-worker, we found that, in scenario (a) the pumpvel is defined such that the priminstrinsic value for the volumebordertype is “constant” which does not spread thoughout the bbox of the sim, whereas in scenario (b) the volumebordertype is “streak” so this according to my co-worker is the type of value that spreads all around, hence was disturbing the source as well, contrary to scenario (a) which seemed to be “self-contained”

This can be corrected by setting the primintrinsic volumebordertype attribute to “contant” by using the expr :

setattrib(geoself(), “primintrinsic”, “volumebordertype”, @primnum, -1, “constant”, “set”);

and adjusting the mask of the field as well

But I found that on the popadvectbyvolume node, in the group parm, if you just say !name_of_the_stream_group, everything else except for the source volume shall be affected by the vel field

I hope that help! :-D

Very helpful and a reply worthy of a book mark !