Determining fluid speed is important to ensure proper blending between slices, when distributing up res fluids. To begin, you should look at the maximum velocity across the distribution boundary. If you only have vertical distribution cuts, gravity doesn’t matter.
One approach is to add the following nodes your low res DOP sim:
Gas Match Field to create two vector fields called
minspeedof the same size and sampling as
Gas Reduce of
maxspeedwith Maximum, and of
Next, run the simulation forward to where you see the most action across the future distribution boundaries, and extract those two fields. They will have constant value everywhere, so you can sample them using a
volumesample() to get what the max/min speed is. You can use the maximum speed for distribution.
You can likely get away with a lower speed, risking losing smoke at the boundary.
Another option is to scatter a bunch of representative points. Then use a VOP SOP to copy the velocity onto those points. You can then use an Attribute Promote to promote the point velocity to a detail velocity with the proper max/min, where you can read the results in the spreadsheet.