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Josami

Problems with dandelion wire sim

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Hi! Hope everyone's doing great. I've been working on a dandelion scene, but I have some questions about the simulation itself. Hopefully, someone could help me figuring this out.

My setup feds some procedurally generated seeds into a wire simulation. The attributes klinear and kangular are already set in SOPs. Inside DOPs, several forces nodes try to replicate the behavior of the wind. To release the seeds, a Sop Solver compares how much force are receiving the constraints, with a threshold.

My questions are:

1.- While the seed is still attached, you can see every prob vibrating because of the “noise wind” node, but once it is released, the forces seem to act over it as a whole. It still moves around, but freezes in its last position. Do you know how I can get all my forces affecting the seed all the time?
2.- Well, the seeds are flying in the same position. Ok, they are moving fast and still rotating so it is not that noticeable. The problem is the last position is different depending on the amount of force received or the time when the seed is freed — I don’t know which, but I think is the first one. That’s kind of obvious, but let me explain. In “dopnet4”, seeds are released at the very beginning. I used two time shift nodes to show how the position of an arbitrary selected seed is affected by the forces, but jumps back to its original state after being released. However, in “dopnet5”, where the seeds are released at the end of the sim, that selected seed behaves as it should and both positions are the same. Do you know why is this happening?
3.- Can you animate forces inside of DOPs? Right now I’m using a vector field to prevent the wind nodes from reaching their goal position. That way the objects keep moving. Maybe there’s a better solution I’m not seeing at.
4.- My simulation starts at frame 0, before my scene begins. That’s because the start frame of all the wire sims I did was weirdly shaped. Maybe the solver needs an initial frame in order to properly load the object, but I was wondering if that’s the reason, or if there’s a proper way of solving it — assuming it is an issue. The “frame_0” nodes show what I’m talking about.


Here is the folder with the sim nodes and the baked geometry. It would be amazing if some of you know the anwers.

 

Thank you very much!


 

DANDELION_TEST.rar

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Ok, I think I found the answer to all the questions.

1.- The forces are being applied at all time, but the speed of the movement makes it difficult to notice. I slowed down the simulation using a Retime node and a Polywire, and the noise is there. A SOP alternative to intensify the vibration could be adding more noise over the rest position of the probes, but I think that won’t be needed.
2.- This one has to do with the force and the frame when the objects are released. In frame number 0 of the “dopnet4”, all the seeds have a pintoanimation value of 1. However, in the next frame, where the seeds are modified by the forces, that value has already become 0. I think the starting frame of the sim is used to feed the solver, so it makes sense to me that the next frame is some kind of stabilized version of frame zero, that is now being affected by the forces.
That being said, if you want to keep the modified shape of the seeds you also have to keep the “Solve on Creation Frame” box on the Wire object checked. Otherwise, they will jump back to their initial state, despite of the threshold being reached.
3.- You can animate forces if you change the Default Operation from Set Initial to Set Always. There’s more information in the next link: http://www.sidefx.com/docs/houdini/dyno/top10_medium.html#set-initial-vs-set-always
4.- As I said, I think the starting frame is used to load the object and forces. The noise in my example is due to “noise wind”. Once the sim really begins, everything behaves as it should.

 

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