Dear Fellow Scholars, this is Two Minute Papers with Dr. Károly Zsolnai-Fehér.
In a previous episode not so long ago, we burned down a virtual tree.
This was possible through an amazing simulation paper from 4 years ago, where each leaf has
its own individual mass and area, they burn individually, transfer heat to their surroundings,
and finally, branches bend, and, look can eventually even break in this process.
How quickly did this run?
Of course, in real time.
Well, that is quite a paper, so if this was so good, how does anyone improve that?
Burn down another virtual tree?
No, no, that would be too easy.
You know what, instead, let’s set on fire an entire virtual forest.
Oh yeah!
Here you see a simulation of a devastating fire from a lightning strike in Yosemite national
park.
The simulations this time around are typically sped up a great deal to be able to give us
a better view of how it spreads, so if you see some flickering, that is the reason for
that.
But wait, is that really that much harder?
Why not just put a bunch of trees next to each other and start the simulation?
Would that work?
The answer is a resounding no.
Let’s have a look why, and with that, hold on to your papers because here comes the best
part: it also simulates not only the fire, but cloud dynamics as well.
Here you see how the wildfire creates lots of hot, and dark smoke closer to the ground,
and, wait for it…yes!
There we go!
Higher up, the condensation of water creates this lighter, cloudy region.
Yes, this is key to the simulation, not just because of the aesthetic effects, but this
wildfire can indeed create a cloud type that goes by the name flammagenitus.
So, is that good or bad news?
Well, both!
Let’s start with the good news: it often produces rainfall, which helps putting out
the fire.
Well, that is wonderful news, so then, what is so bad about it?
Well, flammagenitus clouds may also trigger a thunderstorm, and thus, create another huge
fire.
That’s bad news number one.
And bad news number two: it also occludes the fire, thereby making it harder to locate
and extinguish it.
So, got it, add cloud dynamics to the tree fire simulator, and we are done, right?
No, not even close.
In a forest fire simulation, not just clouds, everything matters.
For instance, first we need to take into consideration the wind intensity and direction.
This can mean the difference between a manageable or a devastating forest fire.
Second, it takes into consideration the density and moisture intensity of different tree types
- for instance, you see that the darker trees here are burning down really slowly.
Why is that?
This is because these trees are denser birches and oak trees.
Third, the distribution of the trees also matter.
Of course, the more the area is covered by trees, the more degrees of freedom there are
for the fire to spread.
And, fourth.
Fire can not only spread horizontally from tree to tree, but vertically too.
Look!
When a small tree catches fire, this can happen.
So, as we established from the previous paper, one tree catching fire can be simulated in
real time.
What about an entire forest?
Let’s take the simulation with the most number of trees, my goodness, they simulated
120k trees there.
And the computation time for one simulation step was…95.
So, 95 what?
95 milliseconds.
Wow!
So this thing runs interactively, which means that all of these phenomena can be simulated
in close to real time.
With that, we can now model how a fire would spread in real forests around the world, test
different kinds of fire barriers and their advantages, and we can even simulate how to
effectively put out the fire.
And don’t forget, we went from simulating one burning tree to a hundred and twenty thousand
in just one more paper down the line.
What a time to
be alive!
Thanks for watching and for your generous support, and I'll see you next time!