Sunday, March 21, 2010

A long, strange trip...

So, yesterday we were talking about aircraft carriers and submarines. And this caused me to try to look up something about the 688 boats on Wikipedia.

Of course, I accidentally wound up on the page for the game 688 Attack Sub first, but luckily it had a hyperlink to the actual page for the Los Angeles-class subs.

I found the factoid I was looking for, and saw that there was a linkout to the Type 093-class attack subs of the People's Liberation Army Navy. That article mentioned that the new Chicom sub might be using an asymmetric propeller. Weird. There was no article for "asymmetric propeller". There was one for "asymmetric", but who doesn't know what asymmetric means? So I went to the article for "propeller" instead.

Huh. I knew cavitation was a big deal with boat propellers, but I didn't know that it caused little bubbles that imploded with such force that they eroded the metal. Or that dolphins actually had a speed limit more imposed by cavitation than by their shape or strength...

But that was nothing to the fact that there were critters that used the effects of cavitation like a Klingon sonic disruptor, to stun or kill their food. This was maybe the most awesome thing I've learned all week:



That's the pistol shrimp. He's the cute one in the family. His scarier-looking brother-from-another-planet, also armed with sonic disruptor technology, is the mantis shrimp:


Eccentric-looking thing, ain't he? Apparently they make great pets.

YouTube, by the way, is apparently absolutely littered with "My mantis shrimp versus _______" deathmatch videos, which are kinda creepy in a George R. R. Martin's Sandkings sorta way, and I say this as someone who fed live rats to a ball python.

18 comments:

Owen said...

oh yeah, mantis shrimp are awesome.

Will Brown said...

It's Ok, Tam, confession is good for the entertainment of others ... or something.

You're a snake fetishist; we understand.

It really isn't necessary to work your way quite so far around to getting to the point, but I'm sure we all appreciate the effort you put into not just bluntly blerting these things out like you do. We love you for your kinks as well as your curves, you know.

Or so it seems from this distance down range.

:)

Tam said...

Not really. I had a pet ball python for a few years, mostly to get over my fear of snakes.

Brad K. said...

The noise effects of cavitation by ship, and especially submarine, propellers is a significant war machine technology.

"Back in the mid-1980s, the Japanese company Toshiba sold propeller milling machinery to the Soviets through the Norwegian Kongsberg firm; this and other submarine intelligence furnished by the Walker spy ring resulted in significantly quieter Soviet subs by the later part of the decade. " (From http://americanhistory.si.edu/subs/anglesdangles/taming2.html)

Then, I found "(In fact, a new comment on Dan's original post suggests that such propellers are out of date, replaced by ducted pump jet propulsion on all the latest US, French and US models.)" at http://www.ogleearth.com/2007/08/microsofts_bird.html

Propeller noise is a trail that could be tracked. It is something navies want to deny their enemies.

Besides, any sound or cavitation is an amount of wasted energy, including thermal. I imagine tracing thermal contrails in the Arctic Ocean must be a favorite pastime for those on patrol there.

I kind of like the idea David Drake uses in "With the Lightnings" (SF novel), of using water jets to get a surface ship up to speed, then deploy electrostatic runners to ride atop the water on an electrostatic cushion (no water friction), and use current flow like a caterpillar tractor tread to move the vessel about.

Tam said...

Yes, I knew about cavitation making noise.

I did not know about it eroding metal.

Borepatch said...

George R.R. Martin had some mighty fine creepy in the opening chapter of "Tuff Voyaging", where he imagined new malevolent life forms created by a super genetic engineering spaceship.

I don't read much fiction, but he's on the list.

Will Brown said...

Not really. I had a pet ...

What, not enough smilies? A little low on snark today? It's snowing here.

I did not know about it eroding metal.

I believe the effect is more akin to that of spalling (from surface stress fractures) than it is to rust (the most common cause of metal erosion). Never mind that modern ship's screws (not propellers, please) aren't made of ferrous metals, they still wear away from ordinary wear-and-tear.

As to cavitation, any solid object passing through a liquid medium leaves a detectable disturbance in that medium. Surface ships are tracked from orbit by spotting their wakes, then the camera(s) zoom in for a closer look. Submarines cause a similar effect, as do whales and tuna. Since the screw is the only part of the ship that must travel through the water sufficiently quickly to create such an effect, it gets a lot of attention of course. In reality, the nature of the ship's hull coating has a far greater influence on the ship's vulnerability to sonic detection though. It was this technology differential that was a key advantage for US submariner's vs the Soviet Navy. I'm not competent to make a reliable judgement from the little I read of Chinese efforts along these lines, but given the cutting edge nature of the materials science (where they are admittedly no slouches) along with the technical challenge of applying such materials during the construction process (their demonstrated willingness to dance around quality control proceedures seems pertinent here) makes me question their capability, at least in this regard.

reflectoscope said...

Ultrasonic parts cleaners work on the same principle. They work wonderfully too, just so long as you need not sit beside they while they work.

Jim

fast richard said...

Sonic Disrupter.

Tam, this is one of the reasons I read your blog every day. In addition to the first class snark and commentary, you go wandering about the internet and find things like this for our eddification and entertainment.

Tam said...

Will,

"What, not enough smilies? A little low on snark today?"

Just a little disorientated in the AM. :)

William said...

I had forgotten about the "Sandkings." I remember reading that story when it was first published in Omni magazine. That must have been 30 years ago. Oh the corrosion due to cavitation is due to the heat produced radicals formed when the bubbles collapse. I am sure that some of the corrosion is probably due to the high temps produced when the tiny bubbles collapse as well. This cavitation occurs due to ultrasonic acoustics.

Anonymous said...

No rational member of the aquatic public would be opposed to reasonable laws to control the Pistol Shrimps pistols, eh?

Rabbit said...

Wow.. Sandkings. I bought that issue of Omni when I was in college lo those many years ago.

Pistol shrimp were always popular with the littoral marine ecology students when I'd teach that down at the coast.

Regards,
Rabbit.

Anonymous said...

Wasn't there some talk recently about cavitation bubbles collapsing so violently that they caused hydrogen fusion to occur?

B.S. philosopher said...

Mantis Shrimp make great pets... In a tank by themselves. If however, they hitchhike into your reef tank in a piece of live rock, they grow to huge size and stalk the tank like an aquatic "Predator"

It's damn near impossible to get a mantis shrimp out of a fully set up reef tank short of completely breaking the tank down.

og said...

Some time back, a company which competes with mine sold some technology to the former soviets. This tech allowed them to make prop blades that would not cavitate as readily as the ones they had previously used, and it allowed the russkies to have very quiet subs, how quiet is supposedly classified.

I know there was a large brouhaha about this, and we all had to take classes about what kind of tech was allowed to be exported and what was not, and I have to be escorted into and out of certain facilities so that I may not see certain things, or so I'm told. All pretty cool, to a geek, though painfully boring, in practice.

We did a job for a company where we polished prop blades with a very large robot. The robot was able to control the contours very accurately, and the contours were generated by some pretty cool modeling software which supposedly could predict surfaces where cavitation could start and subtly altering the shape so that it could not. The resulting shapes were... not as smooth and as continuous as you might imagine. Think of the feathered edges on some of the little muffin fan blades that make them quiet. Anyway, cool post, and great to see you all again. Sorry I couldn't get more S&W stuff, they pretty much clammed up after the "sting"

William said...

In regard to the heat and pressures generated in cavitation bubbles being used for fusion. Yes that is the theory and several groups are working on that now. One is on my campus, but they have not gotten to the point where they will be using Deuterium or needing a Neutron detector yet. When they get ready to start generating energy, I expect to be retired or dead.

perpster said...

You need to add a global warming / climate change tag to this post. Apparently these shrimp are responsible for man-made heating of the earth. If they can create bubbles that implode at the heat of the sun then clearly man had some nefarious role in making it or letting it happen.

MUST . . . EAT . . . MORE . . . SHRIMP. Doh!