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I'm here at the Navy's
Indoor Ocean at Carderock.
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This is the biggest wave pool in the world
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and they can make all
kinds of different waves
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so they can test scale
ships and make them better
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before they actually go
out on the open ocean.
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I came in and I'd seen some pictures,
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but I just walked in here
and it's just, it's insane.
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'Cause they say indoor ocean,
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but it's exactly what it is.
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The water even looks ocean colored.
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(laughing)
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It doesn't look like a swimming pool,
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this looks like an ocean,
looks like a test facility.
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It is huge.
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- It is 360 feet long in this dimension,
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240 feet long in that dimension.
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It's 20 feet deep.
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Just about the size of a
football field out there.
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The dome above us was the
largest free standing dome
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for a while.
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- [Derek] Largest free
standing dome in the world?
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- Yep.
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- What?
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(Miguel laughs)
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In this pool they can make
waves of all shapes and sizes
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using huge paddles that
line two walls of the pool.
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- We have 216 individual wave makers.
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We can make waves from -45
degrees up to 135 degrees,
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which is kind of coming right back at it.
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- We are now behind the big
paddles that make the waves.
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These 216 paddles are programmed to move
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in incredibly well choreographed ways
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so that they can produce reproducible,
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perfect sized, perfect frequency waves
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that go across the entire pool.
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- You can see these air bellows
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that are what's making the angular motion.
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That vertical piece is
the force transducer.
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The other force transducer's
right up on the top.
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- [Derek] There are lots
of wave pools in the world,
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but what makes this one
different is control.
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You can create waves of a
specific amplitude and frequency
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and do so repeatedly.
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Can we try a one Hertz?
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- [Miguel] Yeah. Do me a
favor and dial up one Hertz.
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- [Operator] Amplitude
will be 0.078 at one Hertz.
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- Okay, go ahead and
send it from zero please.
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And so this is the largest
wave we can make, at one Hertz.
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That's based on the motion
and power requirement
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for the wave maker.
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- [Derek] There's something a bit surreal
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about watching this,
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'cause it almost looks like an ocean
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except you never see waves
this regular out there.
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- [Miguel] Yeah, correct.
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- One of the fundamental characteristics
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of a wave is its wavelength,
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the distance from one crest to the next.
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The first thing most people learn
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about waves is they transmit energy
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rather than material from
one place to another.
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In this case, as the wave
travels to the right,
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the water molecules themselves
basically move along
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circular paths.
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And the deeper the water,
the smaller this motion.
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All motion stops at a depth
equal to half the wavelength.
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This is known as the wave base.
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But even in an ideal water wave,
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the molecules do drift a bit
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in the direction of wave motion.
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And this is because the
molecules travel faster
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the higher up they are.
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So they move farther at
the top of their loop
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than they move backwards at the bottom,
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creating a spiral path.
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This place is perfect
for observing properties
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of different waves.
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I asked Miguel to show me some waves
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with different frequencies
but the same amplitude.
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- So what I'll have him do now is
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I'll have him stop this wave
and just change the frequency.
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'Cause we're at .6, we'll go to .5,
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so it'll be a two second wave.
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- Here I'm split screening
waves with frequencies
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of .67, .5, and .33 Hertz,
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all with the same amplitude.
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So two things to notice.
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Even though they all
have the same amplitude,
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the ones with higher frequency
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look like they have a greater amplitude
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because the slope of the waves is steeper.
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And second, the frequency
of a wave affects its speed.
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High frequency waves travel
slower than low frequency waves.
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In fact, as long as the water
is deeper than the wave base,
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wave speed is inversely
proportional to its frequency.
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They have a really cool demo
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that takes advantage
of the different speeds
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of different frequency waves.
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You can see it starting here.
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They send out high frequency waves first
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followed by lower and
lower frequency waves.
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And because the high
frequency waves travel slower,
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the lower frequency
waves gradually catch up.
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Whoa.
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And they've timed it so
that all the waves meet up
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at exactly the same time
and place in the pool,
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and this causes the wave to break.
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The ocean engineers can do this again
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and again,
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in exactly the same way,
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thanks to their precise
control over the waves.
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This demo also nicely illustrates
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the principle of superposition,
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that when waves meet they add together.
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The height of the water is
equal to the sum of the heights
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of the individual waves
meeting at that point.
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You can see how much
bigger the amplitude is.
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Those individual waves weren't that big,
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but when you add them all together,
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you can make this big breaking wave.
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They can also take advantage
of the superposition principle
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to create standing waves.
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- So what's coming up
next are two regular waves
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coming at each other.
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What we call the quilt wave.
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So we're gonna have a wave coming this way
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and a wave going this way,
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and it's gonna create standing waves.
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So there's two regular waves coming out
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and if you look at the wave,
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it looks like a big
quilt pattern out there.
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- At some places in the pool,
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the waves always cancel
out to zero amplitude,
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and at other places the waves
add up for maximum amplitude.
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They can even send waves
from all directions,
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so they form circular wave fronts
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and then all the wave energy
is channeled into one spot
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they call the bullseye.
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- And so now we're gonna
run the bullseye wave
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which is essentially the same thing,
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but instead of having a line of waves,
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we're having it all coalesce
at one individual point.
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So you can start seeing the waves are
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coming from the long bank here,
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and you can see they're
making a spherical wave.
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And then you have another spherical wave
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coming from the short bank.
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And this is breaking due
to the coalescing waves,
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and the wave height being more than
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one seventh of the wavelength.
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- We tried throwing some toys
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into the wave to see what
would happen to them.
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Would they get pushed
into the breaking wave?
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Even though there's not much
net movement of the water,
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the ducky drifts with the waves,
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and pretty quickly is
pushed into the bullseye.
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How's the ducky doing?
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(Miguel laughs)
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- He's getting to the
danger zone right now.
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It's starting to funnel him
right into that breaking wave.
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Ooh, it's getting up, getting up.
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- [Miguel] Oh!
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(laughs) It swamped it.
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- [Derek] That's amazing.
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- That was right where we wanted it.
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- [Derek] Now the real
purpose of this facility
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is not to play with toys or
make perfect unnatural waves.
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It is to replicate on a small scale
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the types of waves Navy
ships will encounter
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in the oceans of the world.
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Research engineers place
ships modeled after
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billion dollar vessels in the water
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to see how different
designs actually behave
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in real world conditions.
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- [Miguel] Right now this
is coming from 45 degrees.
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It's gonna be about a five
inch significant wave height,
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which if we were to scale
it up for this model
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would be 20 foot waves.
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When we're doing a free
running model like this,
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we usually run a race track,
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like a big circle or a figure eight track,
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so we know the headings
that we're running in,
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so that we can correlate that
to the full scale vessel.
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- [Derek] For the model to provide
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an accurate representation
of the real world,
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a lot of things must
be taken into account.
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Is the water fresh?
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- Fresh water.
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- [Derek] Okay, not salty.
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- Nope. Fresh water.
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So when you're in salty water,
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you're gonna have a lot more buoyancy.
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So when we're balasting our models,
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we have to make sure that
they take into account
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that buoyancy difference.
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So when we go full scale
you're in the same conditions.
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- [Derek] For fluid mechanics,
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I always expect that you have
to keep the Reynolds number
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the same as in the real world phenomena.
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But actually to get the
right wave dynamics,
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you have to use a different scaling
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which is based on the Froude number.
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So the Froude number is a measure
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of the ratio of inertial
to gravitational forces.
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It's equal to the flow velocity divided
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by the square root of the
acceleration due to gravity
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times the characteristic length,
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like the length of the ship.
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In this case, the model ship's hull
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is 46 times smaller than the real thing,
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which means to get accurate data,
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it should be traveling at one
over the square root of 46
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times it's real world speed.
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And to make the footage from the model
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look the same as that
from the full size ship,
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you have to slow it down
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by a factor of the square root of 46.
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So roughly 6.8 times slower.
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I'm amazed at just how
well these shots match,
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but of course that's the idea.
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Scale the model and the the waves,
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so the physics are
identical to a real ship
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out on the open ocean.
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Naturally, I asked if I could
go swimming in the pool,
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but they said, very kindly, "No way."
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The closest I could get
would be on a little dingy.
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This is our boat.
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With a catch.
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It's pretty smooth sailing
out here right now.
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- (laughs) Yep. No waves
while we're out here.
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- [Derek] So I'm assuming
no one's ever been out here
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in waves?
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- Nope. That's one of the
no-nos they don't want us to do.
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I guess it's a risk thing, so...
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- This place seems like a... I don't know
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Like a massive playground kind of.
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(Miguel laughs)
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- It kind of is for engineers like us
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where we kind of dork out on the science
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and what we're doing here.
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It's a huge volume.
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Like I guess I never understood
how deep 20 feet was,
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until they emptied it to
put in the new wave makers.
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It's a large volume that's
taken up by this water.
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- [Derek] Yeah.
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- So as we come by, these
are our sensors right here.
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We have a big array here.
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These are ultrasonic sensors,
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and that's how we measure wave height
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and period and direction in the basin.
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So we wanna measure that to
make sure that what we test in
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is what we think we have.
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- [Derek] In this pool, they can create
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all sorts of different wave
conditions you might encounter
00:10:11
in different parts of the world.
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Most ocean waves are created by wind
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and the strongest winds
occur in and around storms.
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Five factors affect the size
and shape of waves created.
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These are the wind
speed, the wind duration,
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the distance over which
the wind is acting,
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which is known as the fetch,
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the width of the fetch,
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and the depth of the water.
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As waves travel out from a storm,
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the higher frequency waves
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dissipate their energy more quickly.
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So the waves that travel a long way
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are the fast moving low frequency waves,
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which are called swell.
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- When those waves end up
becoming hundreds of miles away,
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like if you have it in the Pacific,
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eventually you'll get long
period swell from them.
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So you're no longer near the storm,
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but it created enough
energy to make long waves,
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and that's where you get
your open ocean swell.
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- Tell me if this is a good analogy.
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I feel like with sound, a
lot of the high frequencies
00:11:07
will die off quickly away from a source.
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- Yep.
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- [Derek] But the low frequencies
will travel much further.
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- Correct.
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- So is it the same thing with the waves?
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It's like you're walking
away from a concert,
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and you can still hear the bass,
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but you can't see any
of the high frequencies.
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- That's a great analogy. Yep.
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- What's the deal with rogue waves?
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- People like to think it's a rogue wave
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where it just came outta
nowhere and just came up.
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No, it's usually multiple
waves that are meeting up
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and creating an amplitude
that's much larger
00:11:33
than what the self-standing wave would be.
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So when it meets it's gonna break,
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because you have this large wave
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creating this huge amplitude
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that it just can't hold it and it breaks.
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- [Derek] On a calm day,
when you see waves crashing
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at the beach around 10 seconds apart,
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that is swell.
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But because of its long wavelength,
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swell isn't really a concern for ships
00:11:55
out in the open ocean.
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- You know, if you're
in a long period swell,
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your ship's probably just
gonna heave a little bit.
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You're more worried about the steep waves
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and the windy waves
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that are really moving you around.
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- [Derek] Wind waves are
formed in three steps.
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First, as wind blows across the surface
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of perfectly still water,
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the turbulent motion of
the air creates regions
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of slightly higher and
slightly lower pressure.
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And this makes tiny ripples
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with wavelengths of around a centimeter.
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But now the wind can act on these ripples
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creating larger pressure differences
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between the front and the
top of the wave crest,
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pulling them up into bigger waves.
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And the interaction of
the wind with these waves
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then creates even larger
pressure differences
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and even larger waves.
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The waves are mostly
uniform at this point,
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but as they interact with each other,
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they create a range of
different wavelength waves.
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And as the wind keeps blowing,
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these waves begin breaking
transferring their kinetic energy
00:12:53
into swirling eddies that
dissipate their energy as heat.
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Once the energy dissipation matches
00:12:59
the energy input from the wind,
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the waves have reached their maximum size
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and this is known as
a fully developed sea.
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- [Miguel] So this is
gonna be an irregular wave.
00:13:11
- [Derek] This is irregular?
00:13:12
- Irregular wave,
00:13:13
so what you saw earlier
with the regular waves
00:13:15
were one frequency, one amplitude.
00:13:18
This is what we call a spectra,
00:13:20
or multiple frequencies
and multiple amplitudes.
00:13:24
You can see there's higher
frequency with the waves
00:13:26
that kind of go travel slower
than the low frequency waves.
00:13:29
Those low frequency waves will
travel fast and overcome 'em
00:13:32
and that's what's making 'em look peaky
00:13:33
or kind of dulling it out.
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- [Derek] What surprised me
00:13:38
is that the different oceans of the world
00:13:40
have different mixtures
of wave frequencies
00:13:43
or different spectra,
00:13:44
depending on their geography
and the types of storms
00:13:47
that occur there.
00:13:49
For example, the North Sea and
other small bodies of water
00:13:52
have a peakier spectrum,
and this is due to
00:13:55
the limited fetch of
storms that occur there.
00:13:58
In the mid-Atlantic, a broader
spectrum best describes
00:14:01
the developing or
decaying open ocean waves
00:14:04
that you'd find there.
00:14:06
And in the North Atlantic,
00:14:07
the steady wind across an open ocean
00:14:10
produces the broadest
spectrum of wind waves.
00:14:13
So when testing, engineers
first have to figure out
00:14:16
where the ship will be deployed,
00:14:17
and which spectra best
match these locations
00:14:20
before creating them in the pool.
00:14:23
For most people I think,
an ocean is an ocean.
00:14:26
But you're saying that there's sort of
00:14:28
different conditions
depending on where you are?
00:14:30
- The destroyer when I was in command,
00:14:32
we did an operation off
the coast of South Korea
00:14:34
in the spring.
00:14:36
Very rough sea keeping conditions.
00:14:39
But then, when you're
crossing the Pacific,
00:14:41
a lot of that is a lot calmer.
00:14:44
So again, you know from there
to the coast of South Korea
00:14:49
to the Arabian Gulf, all those
very different conditions.
00:14:53
- Were there any conditions that were
00:14:55
particularly rough for you?
00:14:56
- So my bed was actually
in the middle of a room
00:15:01
and the seas were so bad,
00:15:02
and this was either
South or East China Sea.
00:15:05
The seas were so bad that one night,
00:15:08
I woke up in the middle of the night
00:15:10
and my whole mattress with me on it
00:15:12
was sliding off of my bed frame,
00:15:15
and that's a pretty
significantly sized mattress.
00:15:18
So you can imagine the
seas we were in that night.
00:15:23
Much bigger than this would terrify me.
00:15:25
I know it probably looks benign, but...
00:15:27
(laughs)
00:15:28
Much bigger than this,
00:15:29
I think that model will
take a lot of water.
00:15:33
- Why do you care about how
much water goes on the deck?
00:15:36
- So on the back of this DDG
is a helicopter landing pad.
00:15:39
They don't want any water on the deck
00:15:40
when a helicopter's about to land.
00:15:42
That's a big problem.
00:15:43
You know, that's one of
the tests that we do here
00:15:45
is we'll put cameras to look at the deck
00:15:47
and understand how much water washes on.
00:15:50
- [Derek] Since I knew
they wouldn't wanna risk
00:15:52
their fancy model in rough conditions,
00:15:54
we brought along a little
remote controlled boat to test.
00:15:59
- Yeah, I wouldn't be happy on that boat.
00:16:03
A lot of people would be getting seasick.
00:16:08
- Whoa!
00:16:09
(Miguel laughs)
00:16:10
- Oh no.
00:16:12
- [Miguel] Is it gone?
00:16:12
- [Derek] It's gone.
00:16:14
- [Miguel] No, it's
right there. It came up.
00:16:14
It's upside down.
00:16:15
(laughs)
00:16:16
- It was totally gone.
00:16:18
It was in the air, then it went under.
00:16:22
Now, not all the models tested here
00:16:24
can be remote controlled.
00:16:27
- So on the carriage is where
00:16:28
we're gonna do captain model tests
00:16:29
where you can tether, put
power and instrumentation
00:16:31
onto a model that can't hold it itself.
00:16:34
So usually the model go in
this moon bay right here.
00:16:37
- [Derek] The models are hooked up here
00:16:38
and then the whole lab
speeds over the waves
00:16:42
towing the model underneath.
00:16:45
(pensive music)
00:16:46
(waves crashing)
00:16:49
People have been making
ships for thousands of years.
00:16:52
- Mm-hm.
00:16:53
- Is there actually any innovation today?
00:16:55
- Most definitely.
00:16:57
So sometimes, you know,
00:16:58
people say that's the
way we've always done it.
00:17:00
And then when you look into it,
00:17:01
there's some validity to some hair-brained ideas,
00:17:04
And when we test them,
00:17:05
that's why you cut your
cost of doing a model test
00:17:08
versus building the full thing and saying,
00:17:09
"Oh that didn't work."
00:17:11
Every ship that's in the Navy's
fleet has gone through here,
00:17:14
has gone through either our purview,
00:17:16
or has been tested peripherally with us.
00:17:19
But all of the Navy-owned ships
00:17:20
have been tested in this facility,
00:17:22
and there is a ship out there
with a tumble home design
00:17:24
where if you look at this ship
behind you, it flares out.
00:17:27
So this flare is usually
what helps protect you from,
00:17:29
when you start rolling, it
gives you a reaction force
00:17:32
or helps push you back.
00:17:34
A tumble home is shaped, you
know, the opposite direction.
00:17:37
And if you have a ship
shaped in that direction,
00:17:40
it doesn't have as much of a
restoring force when you roll.
00:17:43
- But what is the idea with
making a ship like that?
00:17:45
- There's a lot of different reasons
00:17:46
why you want to change a hull design.
00:17:48
Some of it is the above water signatures.
00:17:50
It's all about the
shape and radar sections
00:17:53
and there's a lot that goes into that.
00:17:55
You always wanna be stealthier,
00:17:56
you always want to be faster,
00:17:57
you always wanna have more power.
00:17:59
And that's always what
the innovations come.
00:18:04
- [Derek] So most of
the sailors aren't aware
00:18:06
of the work that's going
on in the background
00:18:08
to support what they do.
00:18:11
- When I was in the fleet,
00:18:12
and I've been in the Navy 27 years,
00:18:15
I never had any idea,
00:18:16
certainly not the
magnitude of what they do.
00:18:19
I'm not exaggerating when I say
00:18:21
it's impacted every ship
and submarine in the fleet.
00:18:25
(waves crashing)
00:18:27
(electronic zoom)
00:18:31
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