Disclaimer
At the time of writing this I am a novice with Houdini there are mistakes in my workflow and methodology.
The method for this simulation is a tweaked version of the Cum Sim v41 to better fit small scale applications.
There was a small note in Cum Sim v4 about chaning the velocity transfer method from FLIP to APIC. I had forgotten to do this and was struggling to acheive good looking fluid, but after correcting this the simulations immediately looked a lot better.
Another technique used from Cum Sim v4 was changing a particles by viscosity by age. This would allow thinner strands to fly thorugh the air without currling in on themselves and larger sections to splash more on contact. Increasing the viscosity by age helps the fluid stick to the collisions mesh.
This method is an upadted version of this tutorial2 by 홍가네Cinema4D.
For meshing, I found that using manually surfacing the particles produced less flickering than using a particle fluid surface.
The particle fluid surface here is only converting the compressed fluid to particles. The particle data mush be transfered back over
meshed version if you want to use motion blur render (or keep any particle data).
This method is based of this tutorial3 by Alvaro Moreira for Entagma.
Post Mortem
Much more R&D needs to be done but the method is approching a useable production model.
FLIP solvers has a "stick on collision" option I was not able to properly implement, but this will be something I look into for the future to help the simulation look less flickery when meshed.
One major benefit of this method is art directablity. This sim takes less than an hour to bake meaning that directing where and how the liquid lands on the mesh can be tweaked and itterated upon. Future goals will improve this by making the fluid sourcing system more clear/robust.
I am still struggling with meshing the fluid. This VDB method does a better job than the particle fluid surface but leaves a lot to be desired, hopfuly a more static fluid as described above will help reduce this flickering.
This is my first project rendered in Houdini with Redshift and is very promising. Although, the cum shader needs more work and could look thicker on denser parts and thinner on less dense sections. I am not sure if it possible to ramp the ammount of subsurf in this fashion but will do more R&D. Excited to see how this method improves as I learn/get more comfortable with redshift.
Once the method is refined I would like to make a short tutorial series for using this method, but unitl then you're stuck with these janky website reports (I'm sorry). I included the houdini file if you are intrested in using what is here so far.
Thank you for reading, hope this can be useful for someone. Send me a dm on twitter if you have any questions : )
Sources
1. “Cum Sim v4”, Zaytha Temp Site, posted by Zaytha, http://zaytha.com/CumSimv4.
2. “Cream Simulation 크림 시뮬레이션 - viscosity [Houdini tutorial]”, Youtube, uploaded by 홍가네Cinema4D, 7 October 2020, https://youtu.be/LrUXgY3bZeo.
3. “Guest Tutorial: Meshing Small Scale Flip Sims”, Youtube, tutorial by Alvaro Moreira, uploaded by Entagma, 1 June 2020, https://youtu.be/LrUXgY3bZeo.