Dear Fellow Scholars, this is Two Minute Papers with Dr. Károly Zsolnai-Fehér.
I am so happy to tell you that today, my dream came true. I can’t believe it. So,
what happened? I am going to show you my new paper that just came out. This is a short
Comment article published in Nature Physics, where I had the opportunity to be a bit of an
ambassador for the computer graphics research community. You see, this is a small field,
but it has so many absolutely amazing papers, I am really honored for the opportunity to show
them to the entire world. So, let’s marvel together today as you’ll see some amazing
papers throughout this video. For instance, what about this one? What are we seeing here? Yes,
what you see here is a physics simulation from a previous episode that is so detailed, it is almost
indistinguishable from reality. So, what you are seeing here should be absolutely impossible.
Why is that? Well, to find out, we are going to look at two different branches of fluid
simulations. Scientists who work in the area of computational fluid dynamics have been able
to write such simulations for more than 60 years now, and these are the really rigorous simulations
that can accurately tell how nature works in hypothetical situations. This is super useful,
for instance, for wind tunnel tests for cars, testing different aircraft and turbine designs,
and more. However, these simulations can easily take from days to weeks to compute.
Now, here is the other branch. Yes, that is computer graphics. What is the goal for
computer graphics simulation research? Well, the goal is exactly what you see here. Yes,
for us graphics people, a simulation does not need to be perfect. The goal is to create a simulation
that is good enough to fool the human eye. These are excellent for feature-length movies, virtual
worlds, quick visualizations, and more. And here is the best part, in return, most computer
graphics techniques don’t run from days to weeks, they run in a few minutes to a few hours at most.
So, computational fluid dynamics, slow but rigorous, computer graphics, fast but approximate.
These are two completely different branches. Now, of course, any self-respecting Scholar
would now ask, okay, but Károly, how do you optimize an algorithm that took weeks to run,
to now run in a matter of minutes? Well, here are two amazing ideas to perform that.
One is spatial adaptivity. What does that do? Well, it does this! Oh yes,
it allocates most of our computational resources to regions where the real
action happens. You see these more turbulent regions with dark blue. The orange or yellow
parts indicate calmer regions where we can get away with less computation. You see,
this is an approximate model, but a really good one which speeds up the computation
a great deal at a typically small cost. The hallmark of a good computer graphics paper.
Two, in my opinion, this is one of the most beautiful papers in all of computer graphics,
Surface-Only Liquids. Legendary work. Here, we lean on the observation that most of the
interesting detail in a fluid simulation is visible on the surface of the liquids,
so why not concentrate on that. Now, of course,
this is easier said than done, and this work really pulled it off.
But, we are not stopping here. We can also use this amazing paper to add realistic bubbles to
a simulation. And you will see in a moment that it greatly enhances the realism of these videos.
Look at that. I absolutely love it. If the video ends here,
it is because I cannot stop looking at and running these simulations.
Okay, it took a while, but I am back, I have recovered. So, the key to this work is that
it does not do the full surface-tension calculations that are typically required
for simulating bubbles, no-no. That would be prohibitively expensive. It just says that look,
bubbles typically appear in regions where air gets trapped by the fluid. And it also proposes
an algorithm to find these regions. And the algorithm is so simple, I could not believe
my eyes. I thought that this was some kind of a prank. It turns out, we only need to look at the
curvature of the fluid, and only nearby, which is really cheap, simple and fast. And it really
works! I can’t believe it. Once again, this is an approximate solution, not the real deal,
but it is extremely simple and fast, and it can even be added as a post-processing step to a
simulation that is already finished without the bubbles. How cool is that? Loving it!
Now wait, we just said that surface-tension computations are out of reach. That just costs
too much. Or, does it? Here is an incredible graphics paper from last year that does just
that. So what is all this surface-tension thing good for? Well, for instance, it can simulate
this paperclip floating on water. That is quite remarkable because the density of the paperclip
is 8 times as much as the water itself, and yet, it still sits on top of the water. We
can also drop a bunch of cherries into water and milk and get these beautiful simulations. Yes,
these are not real videos, these are all simulated on a computer. Can you tell the difference? I’d
love to know, let me know in the comments below! And get this, for simpler scenes, we only need to
wait for a few seconds for each frame. That is insanity. I told you that there are some
magical works within computer graphics. I am so happy for the opportunity to share them with you!
However, wait a second. Remember, we said that these graphics works are fast
and approximate. But is this really true? Can they really hold the candle to these
rigorous computational fluid dynamics simulations that are super accurate,
but take so long? That is impossible, right? A quick simulation on our home
computer cannot possibly tell us anything new about aircraft designs, can it? Well,
hold on to your papers, because it can! And it not only can, but you are already looking at it!
This is a devilishly difficult test, a real aerodynamic simulation in a wind tunnel. In
these cases, getting really accurate results is critical. For instance, here we would like to
see that if we were to add a spoiler to this car, how much of an aerodynamic advantage we would get
in return. Here are the results from the real wind tunnel test, and now, let’s see how the new method
compares. Wow. Goodness! It is not perfect by any means, but seems accurate enough that we can see
the wake flow of the car clearly enough so that we can make an informed decision on that spoiler.
Yes, this, and even more is possible with computer graphics algorithms. These approximate solutions
became so accurate and so fast, that we are seeing these two seemingly completely different branches,
computational fluid dynamics, and computer graphics getting closer and closer to each
other. Even just a couple years ago, I did not dare to think that this would ever be possible.
And yet, these fast and predictive simulations are within arm’s reach,
and just a couple more papers down the line, and we might be able to enter a world where
an engineer is able to test new ideas in aircraft design every few minutes. What a time to be alive!
So, all this came about because I am worried that as the field of computer graphics is so small,
there are some true gems out there, and if we don’t talk about these works, I am afraid that
almost no one will. And this is why Two Minute Papers, and this paper came into existence. And
I am so happy to have a Comment paper accepted to Nature Physics, and now, to be able to show
it to you. By the way, the paper is a quick read, and you can read it for free through
the link in the video description. I think we are getting so close to real life-like simulations,
everyone has to hear about it. So cool! If you wish to help me spread the word about
these incredible works, please consider sharing this with your friends and tweeting about it.
I would also like to send a big thank you for this amazing opportunity to write this paper,
and to Christopher Batty who sent super useful comments. So, what do you think?
What would you use these techniques for? Let me know in the comments below!
Thanks for watching and for your generous support, and I'll see you next time!