
The U.S. Navy Tests Its Ships in This Indoor Ocean - smacktoward
http://www.smithsonianmag.com/innovation/navy-tests-ships-indoor-ocean-180952431/?no-ist
======
wallflower
All this serious oceanography research reminds me of something a little less
serious but in the same scientific arena:

1) "And this is why Lochtefeld may soon be hailed as some kind of prophet, for
he has created one technology, and champions another, that has the potential
to generate artificial waves even a surfer could love."

[http://archive.wired.com/wired/archive/7.08/kahuna.html](http://archive.wired.com/wired/archive/7.08/kahuna.html)

2)

"The archdruid of surf has undergrad degrees in math and geophysics. His
master's thesis - written in a house overlooking Sunset Beach on the North
Shore of Oahu - is a 240-page work titled "Wave Transformation Over Coral
Reefs." His PhD thesis is even thicker: a two-volume tome called "Sediment
Transport and Inland Tidal Inlet Hydraulics." ...

Black has cracked the code of the world's great breaks; they now lie
dissected, quantified, and digitized in his computer, ready to be
reconstituted anywhere - especially indoors. With the push of a button, his
patented pool floors will morph into an almost infinite variety of shapes to
produce steep 8-foot-high tubes that peel for 100 yards, or gentle 3-foot
rollers that peak after 40, or waves that break to the left or right every 12
seconds, all under a transparent dome and available for a few bucks a ride."

"Endless Summer (on Demand)"
[http://archive.wired.com/wired/archive/12.05/surfing.html](http://archive.wired.com/wired/archive/12.05/surfing.html)

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gamegoblin
This reminds me a bit of:

[http://en.wikipedia.org/wiki/Mississippi_River_Basin_Model](http://en.wikipedia.org/wiki/Mississippi_River_Basin_Model)

and:

[http://en.wikipedia.org/wiki/U.S._Army_Corps_of_Engineers_Ba...](http://en.wikipedia.org/wiki/U.S._Army_Corps_of_Engineers_Bay_Model)

\-------

I wonder to what extent the smaller scales affects water tension related
issues. I have no idea about the physics of it.

~~~
lutusp
Scale models of nautical craft have always been limited by some unrealistic
assumptions -- assumptions that are recognized but not well-adjusted for.

One important aspect of a scale-model ship/boat is that as you change the size
of a model but keep the relative dimensions constant, its surface area changes
as the square of its length, but its mass and volume change as the cube. If
you halve the size of a model, its surface area is 1/4 the original, but its
volume and mass will be 1/8 the original. Simply put, this means a scale model
won't behave very much like the full-size craft.

As models become more sophisticated, these unavoidable limitations of scale
modeling begin to argue for computer modeling, where you can model the full-
size vessel using a carefully designed numerical simulation, including many
factors that can't be realistically modeled in a laboratory tank experiment.

~~~
rtpg
couldn't you build a heavier model to compensate? I mean most boats are hollow
right?

I guess that changes some of the internal distribution of weight but if its
done in a uniform fashion things should work out ok right?

~~~
baddox
I don't think buoyancy would be much of an issue with scaling, because that's
just related to density and shape, neither of which change when scaling the
model (at least until you get small enough that surface tension becomes
noticeable, which I presume doesn't happen for ship modeling). I suspect the
bigger issue would be the structural integrity of the boat. A 10 foot steel
ship is going to be a heck of a lot stronger than the same ship scaled up to
100 feet.

~~~
lutusp
> I don't think buoyancy would be much of an issue with scaling, because
> that's just related to density and shape, neither of which change when
> scaling the model ...

But that's false. The hull wetted area of the model changes as the square,
while the volume and mass change as the cube, of the size change. If
corrective measures aren't taken, the model will displace more water
proportional to its wetted area as it becomes larger, as a result of which it
will gradually sit lower in the water as its size increases.

There are a number of ways to deal with these issues, but it's not true that
one can scale a model without considering them in detail, and carefully
ballasting the model to force it into an approximation of full-size reality.

~~~
baddox
Interesting. That doesn't match my initial intuition, but it sounds like
you're right. Can you point to a source, or perhaps explain this a little
more? I'm trying to imagine a pathological shape that would obviously float at
one size but not when scaled up.

~~~
lutusp
> I'm trying to imagine a pathological shape that would obviously float at one
> size but not when scaled up.

I wouldn't go that far. I know models sit at different heights for different
scales, all else being equal, but I don't think you will ever see a non-
pathological object sink at one scale but remain afloat at another. The reason
I think this is true is that, if I take two objects having the same overall
density and connect them together, this cannot change their position in the
water, their buoyancy. If I think of the two objects as a single model, the
same should be true.

But the difference between connecting two models, and a proportional scaled-up
model, is that the ratio of surface area to volume is different for the
scaled-up model compared to the two independent models. So the comparison
isn't perfect.

(pause for thought ...)

For a solid object sitting on a table, making the object larger and noting the
previously described square-versus-cube rule, the table loading should
increase for each square unit of table area as the model's size increases, by
a unit rule, meaning if you double one of the three dimensions, the table
loading (per unit of area) doubles also. But because a boat model sinks into
the water as its mass increases, and because that sinking is across curved
surfaces, it's more like a three-dimensional area increase than a two-
dimensional one, so it can't be compared to an object with a flat bottom
sitting on a table.

The tl;dr: the more I think about this, the more I think I was wrong to say it
the way I did -- and I say this because the shape of the boat hull means the
wetted area can increase as fast as the boat's mass, i.e. as the cube of a
dimensional change.

Expressed another way, even though a larger boat model sits lower in the
water, with some care the waterline position on the hull can be made to stay
the same.

My mistake -- sorry.

~~~
baddox
If the water line can be made to change when scaling the boat up, it should be
trivial to make a pathological object that will sink when scaled. Just make
the shape of a box without a lid, weighted so that the water line is just at
the top of the walls. If scaling the shape raises the waterline, then water
will flow into the box and it will sink. I still can't intuitively convince
myself that the waterline would shift when the model scales.

~~~
lutusp
I should have made clear what I meant by "sits lower in the water", and I'm
responsible for the confusion.

Because the boat is a three-dimensional object, and because the subsurface
part contacts the water in three dimensions, if it is scaled up with all else
the same, it should still have the same waterline, but (obviously) its keel is
deeper in the water.

> I still can't intuitively convince myself that the waterline would shift
> when the model scales.

Your instincts are serving you well, and the answer is simple -- I wasn't
sufficiently careful in how I described it, and I let an error creep into
yesterday's conversation. In fact, a model whose dimensions are held constant
but is scaled up, should show the same waterline at all scales.

Again, I apologize for sounding so sure of myself when I wasn't.

~~~
baddox
Okay, so you were talking about the keel of the larger model being deeper
underwater in absolute terms. I suppose that would effect buoyancy, because
pressure increases as depth increases. This might be significant enough to
warrant adjustments, at least when scaling very large ships down to very small
models.

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dustinupdyke
> "There are no freak waves in the world,” says naval architect Jon Etxegoien.
> “They are all predictable."

This book argues that there are waves that do not follow a logical pattern:
[http://www.amazon.com/Wave-Pursuit-Rogues-Freaks-
Giants/dp/0...](http://www.amazon.com/Wave-Pursuit-Rogues-Freaks-
Giants/dp/0767928857/ref=sr_1_1?s=books&ie=UTF8&qid=1409575088&sr=1-1&keywords=ocean+waves)

~~~
Tloewald
That statement bugged me too. After all, we can't predict earthquakes. But
then hubris in ship designers is hardly new.

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kaishiro
So, incredibly off topic - but do facilities like this scare anyone else? I've
always had this incredibly irrational fear of really large things like this
when they're connected to water. And anyone ever see pictures of water
sinkholes? Seriously gives me the creeps.

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rdl
I'm curious to what extent model testing is better than CFD calculations,
still

~~~
nusq
CFD is improving at great speed, along with the increase of computer power,
but isn't yet in the level required to replace all scale model tests and they
can still be very computer intensive. I guess that nowadays the state of the
art are these new Smoothed-particle hydrodynamics models. I've worked with
basins like that to test harbour and breakwaters designs and I can tell that
it is common and good practice to test breakwater designs in scale models
before being built, there are too many variables and hydrodynamic process
(like turbulence, porous media flow, wave breaking, over-topping etc..) that
cannot yet be reliably modelled using CFD, specially when they cannot be
simplified to a 2D domain. Nonetheless there are types of scale models that
are increasingly rare these days because they were replaced by CFD modelling,
like sediment transport, although they were/are pretty cool to watch. Also
scale models are very useful to calibrate CFD models.

~~~
walshemj
And you do need to back prove your mathematical models against reality.

------
anuraj
Isn't this quite common in Naval Architecture? I thought this is the way all
ship models are tested.

~~~
krschultz
The article doesn't do a great job explaining it, but this is the premiere
testing facility. Carderock Naval Base is home to several facilities,
including the David Taylor Model Basin. I toured the space for an interview
once and it was very impressive.

