Mostafa kh

Did you checked your collision guide? maybe your collision object is too low res that it has some holes. make a sdf inside sop and introduce to you static object as proxy volume and set the mode to volume sample.

a simple setup

I don't know that what do you want the velocity do for generating particles. I guess assume you want more particles from point with higher velocity. So this is what I would do:

pointvop (bind v length to speed attr) + pointreplicate (generate from attr on and speed attr in it)
and also a volume from velocity to use as particle advect by volume source.