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Unstable Vellum Weld constraints Feb. 11, 2019, 4:31 p.m.

What's happening is the welds are breaking, which re-enables collision between the points, but they're still close enough to each other to self-collide. This gives a fairly explosive tear as the points immediately collide in the next timestep. There are a few different ways to handle this, but an effective one for this case is to disable self-collisions on any unwelded points just for the timestep when they break.

You can do this in a GeometryWrangle into the third input of the Vellum Solver, with the group set to “broken”, and code of i@disableself = 2;. Setting that flag to 2 will disable self collisions for a point until it is no longer self-colliding, at which time it gets reset to zero. (You can set it to 1 to permanently disable self-collisions.) This gives a much smoother tear in this case, as does setting Breaking Frequency to Per Substep on the Advanced tab of the Vellum Solver.

See attached.

(Note this only works for DOPs-based Vellum setups, since the third input is not exposed in the Vellum Solver SOP, and the “broken” group is only set for that third input.)

no openCL device available Nov. 29, 2018, 3:10 p.m.

This issue should be fixed in today's Production Build of 17.0.416

no openCL device available Nov. 28, 2018, 12:13 p.m.

By the way, as a temporary workaround, you can go to the bin directory of your Houdini installation (usually something like C:\Program Files\Side Effects Software\Houdini 17.0.356\bin) and temporarily move or rename the OpenCL.dll file there. That will cause Houdini to use the system-wide OpenCL loader installed by NVIDIA, which should find your GPU driver. You'll lose the built-in CPU driver, however, but you might not care about that.