Is there a way to delete a particular piece from a fractured object in a dynamic sim? I seem to be able to do it if I unpack the sim and select the fractured piece it in viewport and hit delete (creates a Blast node), however I need to delete it at a chosen frame in the sim, so unless there is a way to keyframe this it is not the way.

You could use a switch node at frame xy and a blast node with the name of the piece you need deleted.
I attached a quick scene file.

chf
You could use a switch node at frame xy and a blast node with the name of the piece you need deleted.
I attached a quick scene file.

Hello,

Thank you for taking the time to create the example file. This is simple to implement and good to know. I must learn some VEX.

If you need to delete pieces in the sim (rather than after), you can dive inside the RBD Bullet Solver and delete the RBDs there directly - here's an example, either using a geometry wrangle DOP or a SOP Solver to allow you to use regular SOPs to delete the RBD pieces you want to get rid of.

npetit
If you need to delete pieces in the sim (rather than after), you can dive inside the RBD Bullet Solver and delete the RBDs there directly - here's an example, either using a geometry wrangle DOP or a SOP Solver to allow you to use regular SOPs to delete the RBD pieces you want to get rid of.

Thanks, please take a look at this sim attached. I can't get the FBX to export (you will need to create your own Output Path for the ROP FBX Output node to where you want to save the fbx file.

I can export from an RBD Bullet Solver node setup OK, but I get an error if I try to export from a DOP Network node setup. It returns an error saying “Found invalid path attribute value…”) as it seems to lose track of the Path Attribute created by the Assemble node, i.e. op:/obj/sph

Thanks

The path attribute generated by the assemble node is nonsensical anyway and won't generate anything meaningful. You're also grabbing everything from the dopnet indiscriminately which is far from ideal - you have the ground geometry in there as well as an awful lot of attribute bloat (all of the bullet attribs that aren't of any use to you outside of DOPs).

Here's a fixed version, generating a new path using the pieces' name to ensure they each end up in their own hierarchy. Alternatively, you can simply disable the "Build Hierarchy from Path Attribute" option on the rop_fbx SOP.

npetit
The path attribute generated by the assemble node is nonsensical anyway and won't generate anything meaningful. You're also grabbing everything from the dopnet indiscriminately which is far from ideal - you have the ground geometry in there as well as an awful lot of attribute bloat (all of the bullet attribs that aren't of any use to you outside of DOPs).

Here's a fixed version, generating a new path using the pieces' name to ensure they each end up in their own hierarchy. Alternatively, you can simply disable the "Build Hierarchy from Path Attribute" option on the rop_fbx SOP.

Thanks, but if I disable the "Build Hierarchy from Path Attribute" option on the rop_fbx SOP it does not export the animation, only one static frame. On opening the file you created I get these errors (see below) in Houdini 18.5. The sim only works from the dopnet1 node if I activate its blue flag, for nodes below that it just shows a static sphere -- below are the error messages I get when I load your file:

Load warnings for /Users/greghughes/Downloads/fracsim_FIXED.hip

Warning:

/obj/sphere_object1/dopnet1/rigidbodysolver1:

Skipping unrecognized parameter "doage".


/obj/sphere_object1/scatter1:

Skipping unrecognized parameter "uvattrib".


/obj/sphere_object1/assemble1:

Skipping unrecognized parameter "createpath".
Skipping unrecognized parameter "path".
Skipping unrecognized parameter "createpackedfragments".


/obj/sphere_object1/dopnet1/rbdpackedobject1:

Skipping unrecognized parameter "allowinitialoverlap".


/obj/sphere_object1/rop_fbx1:

Skipping unrecognized parameter "embedmedia".
Skipping unrecognized parameter "computesmoothinggroups".
Bad node type found: dopimport::2.0 in /obj/sphere_object1.


/obj/sphere_object1/dopimport1:

Unknown channel(s) "integrateovertime" converted to spare parameter(s).


/obj/sphere_object1/dopimport1:

Skipping unrecognized parameter "doppath".
Skipping unrecognized parameter "objpattern".
Skipping unrecognized parameter "relpattern".
Skipping unrecognized parameter "donotsim".
Skipping unrecognized parameter "folder_geometry".
Skipping unrecognized parameter "importstyle".
Skipping unrecognized parameter "spacer".
Skipping unrecognized parameter "pointsquicksetup".
Skipping unrecognized parameter "geodatapath".
Skipping unrecognized parameter "pack".
Skipping unrecognized parameter "pivot".
Skipping unrecognized parameter "viewportlod".
Skipping unrecognized parameter "adddopobjectpath".
Skipping unrecognized parameter "adddopobjectname".
Skipping unrecognized parameter "dopobjectnameattrib".
Skipping unrecognized parameter "adddopdatapath".
Skipping unrecognized parameter "dopdatapathattrib".
Skipping unrecognized parameter "transferattributes".
Skipping unrecognized parameter "transfergroups".
Skipping unrecognized parameter "folder_xform".
Skipping unrecognized parameter "doposxform".
Skipping unrecognized parameter "dogeoxform".
Skipping unrecognized parameter "keepworldspacepos".
Skipping unrecognized parameter "pointvels".
Skipping unrecognized parameter "addtoexistingvel".

That hip file was saved in 19.5 and makes use of a newer dopimport::2.0 SOP.

Replace it with an old dopimport SOP, set the import style to "Create Points to Represent Objects", set the dop network to "../dopnet1" and the object mask to "rbdpackedobject1" - now the sphere pieces should move again.
You may need to attrib delete the path attribute created by the assemble SOP.