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Hair Dynamics Strange Behaviour
Confirmed, NormalPublicBUG


System Information
Operating system: Windows-10-10.0.18362-SP0 64 Bits
Graphics card: GeForce RTX 2080 SUPER/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 451.67

Broken: version: 2.90.0, branch: master, commit date: 2020-08-31 11:26, hash: rB0330d1af29c0

I have not seen hair behave this way before. For this example file, I have simply used the default hair dynamics settings. I have a bake in the file attached, and you can try bake yourself to replicate the issue. The hair will fly all over the place, it is not colliding with anything and I cannot figure out what is causing the issue. It was recommended by a developer that I post the issue here for others to have a look, many thanks.

Event Timeline

Interesting test, on the left is a singular strand of the problematic hair - gyrating around and doing it's own thing. In the middle is a brand new UV sphere with a new particle system completely at default settings, behaves normally - On the right is another new UV sphere, with the same particle system as the odd behaving hair - but it behaves fine

Sebastian Parborg (zeddb) changed the task status from Needs Triage to Confirmed.Mon, Sep 7, 6:11 PM
Sebastian Parborg (zeddb) changed the subtype of this task from "Report" to "Bug".

I can reproduce this.

It seems like the simulated hair will start freaking out if it is edited into a "C" shape:

I'm guessing that the cloth/hair springs gets bad initial values somehow perhaps. I haven't looked into it deeply yet though.