Hell all,

I am having some trouble figuring out what is going wrong with my flip sim and hope someone can shed some light on the issue. I have attached a .hip file, in it there is a ‘pop object’ emitting some spheres. I am using this to collide with a flip object, the particles birthing below the fluid object and moving through the fluid. However… at frames 62 and 94 the velocity (I have enabled the show velocity in the surface/collisions of the collision object in the AutoDopNetwork) seemingly inverts and sends the sim crazy for no apparent reason. The emitted spheres/pop net are pulled into the AutoDop as deforming object.

Thanks in advance

During that frame range you may have noticed that there are two particles that are in collision with with each other as they enter the FLIP sim. They are grinding away at each other increasing velocity data as they do thus causing the explosion.

What I did was go into your Emitter network and disable the Trail sop. For the collisionSource set velocity approximation to None. This caused the velocity information to not be transfered to the FLIP sim but still allow the collision to work. I am not sure how important the Trail is to your final but at least you know that the additional velocites are what are causing the FLIP to freak out. Perhaps you could simply remove the attribute at the end..? Or change the particle system random seed to avoid particle inter-collision..?

Thanks for the reply Enviob,

I hadnt realised that the ‘Collision Source’ had a built in trail sop, which is good to know. But I manged to decipher that the reason for the erroneous velocity was due to the particles dying within the volume. As soon as they are given a much longer lifetime, the problem is fixed. So the trick is to scale them down to a very small number when inside the volume as opposed to allowing them to die.