I have a particle simulation and after caching I copy a sphere to the points and then I use a VDBfrompolygons node and then convertvdb node. I did that to merge the spheres when they interact with each other. However; I don't have velocity anymore, as a result, the motion blur doesn't work at rendering. Any suggestions for this problem?

You can recover your velocity using an attribute transfer from your original source to the meshed particles. Another option is to include the velocity in the VDBFromPolygons. That node discards most attributes, but you can add them in to travel downstream as a companion VDB. ConvertVDB can recover them, but you have to set it up manually.

if it's literally just spheres you are copying onto your points and if your points have f@pscale attribute you can use

Particle Fluid Surface SOP
- set Method to Spheres
- set Particle Separation to 1 and Voxel Scale to equivalent of your VDB From Polygons
- include any attributes you want to transfer in Transfer Attributes parameter
- play with Filtering tab if you want the spheres to blend together a bit

Enivob
You can recover your velocity using an attribute transfer from your original source to the meshed particles. Another option is to include the velocity in the VDBFromPolygons. That node discards most attributes, but you can add them in to travel downstream as a companion VDB. ConvertVDB can recover them, but you have to set it up manually.

Thank you so much. It worked with an attribute transfer node.

tamte
if it's literally just spheres you are copying onto your points and if your points have f@pscale attribute you can use

Particle Fluid Surface SOP
- set Method to Spheres
- set Particle Separation to 1 and Voxel Scale to equivalent of your VDB From Polygons
- include any attributes you want to transfer in Transfer Attributes parameter
- play with Filtering tab if you want the spheres to blend together a bit

Thank you so much for your help.