Graphics Reference
In-Depth Information
proportional to the mean curvature:
[
p
]=
γκ.
The [
p
] notation means the jump in pressure, i.e., the difference in pressure
measured on the water side and measured on the air side,
γ
is the surface
tension coecient that you can look up (for water and air at room tem-
perature it is approximately
γ
0
.
073
N/
m), and
κ
is the mean curvature,
measured in 1
/
m. What this means for a free surface with surface tension
is that the pressure at the surface of the water is the air pressure (which
we assume to be zero) plus the pressure jump:
≈
p
=
γκ.
(1.4)
Free surfaces do have one major problem: air bubbles immediately col-
lapse (there's no pressure inside to stop them losing their volume). While
air is much lighter than water, and so usually might not be able to transfer
much momentum to water, it still has the incompressibility constraint: an
air bubble inside water largely keeps its volume. Modeling the air bubble
with a free surface will let the bubble collapse and vanish. To handle this
kind of situation, you need either hacks based on adding bubble particles
to a free surface flow, or more generally a simulation of both air and wa-
ter (called
two-phase
flow, because there are two phases or types of fluid
involved). Again, we won't get into that in this topic.
