Today I was testing SPH particles in Houdini. As in any other application using SPH particles, one easily runs into the problem of two ore more particles getting on top of each other. In most cases this results in an unwanted behaviour for those particles, as their strong interreacting forces shoot them out into space.

Well, most of my simulation's running fine and going as expected, but when particles are shooting away, I want them to be deleted, because I don't want them to be calculated anymorre and possibly making the simulation unstable.

In RealFlow (I have been using that for quite some time), there is a “killVolume” deamon. This is a box you can draw around your scene and any particle that's outside this box is deleted. Is there anything like that in Houdini or do I have to built it on my own?

You can do this in POPs or SOPs using the Group SOP and then delete the group of points outside.

Here's a technique to do something like that.
http://forums.odforce.net/index.php?/topic/10186-culling-sph-blobs-with-low-particle-density/ [forums.odforce.net]

The direct equivalent of killVolume is the particle fluid sink DOP, though by default its set up to delete particles inside the cube rather than outside it. You can use the sink particles shelf tool as one way of adding this to your DOP network.