Dear Fellow Scholars, this is Two Minute Papers with Dr. Károly Zsolnai-Fehér.
This new paper fixes many common problems when it comes to two-way coupling in fluid simulations.
And of course, the first question is, what is two-way coupling? It means that here,
the boxes are allowed to move the smoke, and the added two-way coupling part means that now,
the smoke is also allowed to blow away the boxes.
What’s more, the vortices here on the right are even able to suspend the red box in
the air for a few seconds. An excellent demonstration of a beautiful phenomenon.
However, simulating this effect properly for water simulations
and for gooey materials is a huge challenge, so let’s see how traditional methods deal with them!
Experiment number one! Water bunnies. Do you see what I am seeing here? Did you see the magic
trick? Let’s look again. Observe how much water we are starting with. A full bunny worth of water…and
then, by the end, we have maybe a quarter of a bunny left. Oh, yes. We have a substantial
amount of numerical dissipation in the simulator that leads to volume loss.
Can this be solved somehow? Well, let’s see how this new work deals with this. Starting
with one bunny…and ending it with one bunny. Nice! Just look at the difference of the volume
of water left with the new method compared to the previous one. Night and day difference.
And this was not even the worst volume loss I’ve seen…make sure to hold on to your papers,
and check out this one. Experiment number two, gooey dragons and bowls. When using a traditional
technique, whoa, this guy is GONE. And when we try a different method, it does… this. My goodness.
So let’s see if the new method can deal with this case. Oh, yes, yes it can!
And now, onwards to experiment number three. If you think that research is
about throwing things at the wall and seeing what sticks, in the case of this scene…you
are not wrong. So what should happen here, given these materials? Well,
the bunny should stick to the goo, and not fall too quickly…hm…none
of which happens here. The previous method does not simulate viscosity properly, and hence,
this artificial melting phenomenon emerges. I wonder if the new method can do this too?
And, yes! They stick together and the goo correctly slows down the fall of the bunny.
So how does this magic work? Normally, in these simulations, we have to compute
pressure, viscosity, and frictional contact separately, which are three different tasks.
The technique described in this paper is called Monolith because it has a monolithic
pressure-viscosity-contact solver. Yes, this means that it does all three of these tasks in one go,
which is a mathematically a tiny bit more involved, but it gives us a proper simulator
where water and goo can interact with solids. No volume loss, no artificial melting, no crazy
jumpy behavior. And here comes the punchline…I was thinking that alright, a more accurate simulator,
that is always welcome, but what is the price of this accuracy? How much longer do I have to
wait? If you have been holding on to your papers, now squeeze that paper, because this technique is
not slower, but up to 10 times faster than previous methods, and that’s where I fell
off the chair when reading this paper. And with this, I hope that we will be able to marvel at
even more delightful two way-coupled simulations in the near future! What a time to be alive!
Thanks for watching and for your generous support, and I'll see you next time!