China team takes on tech challenge of supercavitation

Aug 27, 2014 by Nancy Owano weblog
Credit: South China Morning Post

Shanghai passenger to captain: Excuse me sir, how long until we reach San Francisco? I don't know if I have enough time to watch a movie. Captain: You might just make it. A little under two hours.

Rub your eyes but a headline on Sunday in the South China Morning Post (SCMP) remains, "Shanghai to San Francisco in 100 minutes by Chinese supersonic submarine." That could be the case that results from ongoing research among scientists. Stephen Chen reported on Sunday that China has moved a step closer to creating a supersonic submarine that could make the trip from Shanghai to San Francisco in less than two hours..

This could indeed be part of the future of underwater travel. Scientists in China are exploring how supercavitation could get people where they want to go. During the cold war, said Chen, the Soviet military developed supercavitation technology, which involves enveloping a submerged vessel inside an air bubble to avoid problems caused by water drag. "A Soviet supercavitation torpedo called Shkval was able to reach a speed of 370km/h or more - much faster than any other conventional torpedoes," he said.

A paper from Caltech by Victoria Sturgeon in 2001 titled Racing Through Water: Supercavitation referred to the Shkval torpedo as an underwater missile that shatters speed records by using a phenomenon known as supercavitation. She said that it was first explored in the 1940s. The interest in supercavitation is due to how it exploits a loophole that allows underwater travel with minimal drag. "In supercavitation,"she explained, "the small gas bubbles produced by cavitation expand and combine to form one large, stable, and predictable bubble around the supercavitating object."

Then why has this concept of underwater travel in a bubble remained out of the limelight for so long? Sturgeon wrote that although supercavitation has been widely studied since the 1940s, many questions remain unanswered.

The SCMP highlighted two problems in supercavitation technology. First, the submerged vessel needed to be launched at high speeds, approaching 100km/h, to generate and maintain the air bubble. Secondly, it is difficult if not impossible to steer the vessel using conventional mechanisms, which are inside the bubble, without direct contact with water. As a result, its application has been limited to unmanned vessels, fired in a straight line.

Li Fengchen, professor of fluid machinery and engineering, told SCMP that the group's approach differs from any other approach such as vector propulsion or thrust created by an engine. "By combining liquid-membrane technology with supercavitation," he said, "we can significantly reduce the launch challenges and make cruising control easier." Nonetheless, Li said many problems still needed to be solved before supersonic submarine travel became feasible.

Cheng said the group, whose research is ongoing, is hardly alone in exploring the possibilities of such modes of travel. He said many scientists worldwide are working on similar projects, but "the latest progress remains unclear because they are regarded as military secrets."

Explore further: Enclosed tube maglev system tested in China

More information: www.scmp.com/news/china/articl… supersonic-submarine

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antialias_physorg
5 / 5 (8) Aug 27, 2014
"Shanghai to San Francisco in 100 minutes by Chinese supersonic submarine."

Hope you don't bump into any largish critter along the way. Tuna are rather more solid than birds... (OK, submarines are rather more solid than planes...but still: at that speed such an impact would not be pretty).
Anyone have an idea what one would use to look ahead to avoid collisions? Sonar probably won't work as the 100 minute mark is just (barely) above the speed of sound under water for the distance Shanghai-San Francisco (if my calcs are correct sound would need roughly 110 minutes to travel the distance). Maybe stationary sonar buoys along the way that use laserlight (or radio if it's not too deep) to communicate with the craft.
alfie_null
5 / 5 (7) Aug 27, 2014
What happens when the integrity of the protective air bubble is suddenly lost? What happens when the supercavitation driven ship encounters debris?
antialias_physorg
3.8 / 5 (4) Aug 27, 2014
What happens when the integrity of the protective air bubble is suddenly lost?

You get pancaked. (But we accept that engines must work in other modes of travel to avoid catastrophe - like airplanes - so I wouldn't call that a knock-out criterium)
Kedas
4 / 5 (2) Aug 27, 2014
Even if you can maintain this big bubble of high pressure air (I don't think it can be done), you still need all the energy to move even more water now than without the bubble.
Stratubas
3 / 5 (1) Aug 27, 2014
Even if you can maintain this big bubble of high pressure air (I don't think it can be done), you still need all the energy to move even more water now than without the bubble.

@Kedas but you don't care that the air is slowed down by water
akka69
4.3 / 5 (3) Aug 27, 2014
Since no water is in contact with the vehicle, you're not moving more water with it.
You're moving it away from your path, which takes less energy.

Anyway I can see no civilian use for this.
So I wonder why people should rejoice at the prospect of having a chinese war submarine less than 100 mn away from San Francisco..
antialias_physorg
4 / 5 (1) Aug 27, 2014
(I don't think it can be done),

The soviet Shkval torpedo would beg to differ.

you still need all the energy to move even more water now than without the bubble.

Sure. But it would be a mode of travel that would be independent of any weather phenomena. While the energy expenditure would be rather large, the size of the sub itself would be basically unlimited (as opposed to planes which are limited by structural specs and airport size). At a certain size this might be economical.

However, I think the ecological fallout of using this as mass transport might be severe (underwater pollution and noise).

What happens when the integrity of the protective air bubble is suddenly lost?

On second throught: I guess this system could be made much more multiply redundant than airplane engines.
As for debris: I'm not aware of the oceans being full of debris.(large fish, as noted, are another matter)
tonymsm
2.7 / 5 (3) Aug 27, 2014
Don't use air.
Instead, vibrate an envelope (including steering vanes) around the hull at a high enough frequency to replace the boundary layer with a thin layer of highly-agitated water molecules which cannot transmit viscous frictional forces. The sub should then slip through the water like a hot knife through butter, with the speed being any value you like.
But you would still have the collision avoidance problem.
marko
1.3 / 5 (6) Aug 27, 2014
The US Navy torpedoed the Kursk in Russian waters during Russian Navy exercises, in part, because the Russians wanted to export supercavitating torpedo technology to the Chinese, which the US objected to. It nearly caused world War Three.

As far as controlling a supercavitating submersible, a steerable nose and vectored rocket thrust at the rear seem like the way to go.

Watch out whales. I suppose theres no difference between being harpooned by the Japanese or Chinese, except it would be a faster death.
Jixo
4.3 / 5 (3) Aug 27, 2014
The collision with whale (or whatever else obstacle) at this speed would be interesting...
krundoloss
4.5 / 5 (6) Aug 27, 2014
I saw an article about supercavitating torpedoes back in 2002. Sounds pretty neat, but I just don't see it being useful for Travel, as it is so risky. Lets not forget the Concorde Jet, that was so fast, and expensive, and a failure. Travel needs to be as cheap as possible and as safe as possible, and I just don't see supercavitation under water as a safe method of travel, seems highly dangerous. Why would you want to travel through a liquid when you could zip through air which is 1000 times less dense than water, its a no brainer.
antialias_physorg
4 / 5 (5) Aug 27, 2014
Lets not forget the Concorde Jet, that was so fast, and expensive, and a failure.

But the concorde was very safe (only one crash in all its operational history of 14 craft over 27 years)...and the only crash did not occur due to any of its supersonic characteristics.

Travel needs to be as cheap as possible and as safe as possible

Travel needs to be as profitable as possible. Safety concerns only play a part in as far as prospective passengers might opt for another mode of travel if perceived safety is low (e.g. safety on planes is very high - but many people afraid of flying opt for less safe modes of travel like car or bus due to lower safety perception).

Why would you want to travel through a liquid when you could zip through air which is 1000 times less dense than water

Guaranteed travel time? No delays due to weather? Unlimited size?
krundoloss
4.3 / 5 (3) Aug 27, 2014
Oh, antialias. You love disagreeing with me don't you, LOL.

Yes it is feasible, but think about the energy expense to move an "unlimited size" craft, through water, at supersonic speeds, without collisions, safely, in the middle of the ocean.

Honestly it would probably take less energy to fly into space and re-enter at your destination.
antialias_physorg
4.5 / 5 (4) Aug 27, 2014
You love disagreeing with me don't you

I just love debate, because it's one of the few ways to actually learn something.

(Actually I agree with you that this will not be a viable mass transport system in the near future - so I play devil's advocate because I can see SOME arguments that speak for the system rather than against it.)

Only through debate can such not-so-clear-cut cases be explored (and possibly resolved one way or another). And in order to get to the exploring part someone has to take the 'pro' position.

(However, the technophile in me would love to see supersonic submarine transports/submarine fighter jets - at the same time the peacenik in me doesn't. It's a complex ol' world, and my guess is that some use will be made of this technology in the future for larger-than-torpedo craft)
axemaster
4 / 5 (2) Aug 27, 2014
Love the concept, but this sounds a bit too dangerous for my liking...
grondilu
4 / 5 (2) Aug 27, 2014
I wowed at "supersonic submarine". Mind blown.
Scottingham
4 / 5 (2) Aug 27, 2014
For a military sub it's a pretty bad idea. Think of how LOUD this sub would be as it moves. Considering how hard it would be to steer, leading a torpedo into its path would be trivial for today's sub tech.

Also, there are lots of uncharted underwater mountains that subs have hit before. I shudder to think what would happen if this happened to hit one. Or a whale.

Neat idea, but a pipe dream.
Sigh
4 / 5 (1) Aug 27, 2014
I think the ecological fallout of using this as mass transport might be severe (underwater pollution and noise).

Quite. Whales' long-range communication is already impaired by noise from conventional shipping, and military sonar has caused deaths. How loud will this be? Will there be shockwaves? If yes, how far will they travel?

As for debris: I'm not aware of the oceans being full of debris.(large fish, as noted, are another matter)

Depends on depth. Plenty of lost shipping containers close to the surface, fishing nets as well. But debris is likely to be either at the surface or at the bottom, less likely to float at intermediate depths, where these things are likely to operate.
TheGhostofOtto1923
not rated yet Aug 27, 2014
So I wonder why people should rejoice at the prospect of having a chinese war submarine less than 100 mn away from San Francisco
This makes sense for torpedos but not for boomers and hunter/killers because it has got to be very noisy and easy to detect. Subs are already very fast and very quiet. And I assume the depth at which this could operate would be limited.

Oh I see scottingham already voiced this opinion.
TheGhostofOtto1923
not rated yet Aug 27, 2014
Anyone have an idea what one would use to look ahead to avoid collisions?
You would need a series of sonobuoys along travel routes which could monitor objects in realtime. These could relay info to an ELF facility which could communicate with the sub.

"The ELF system is the only system capable of providing continuous communications to submarines operating at designed depths and speeds. Without ELF, strategic submarines would be limited to operations at much slower speeds and at significantly shallower depths, severely restricting maneuverability and training. Similarly, attack submarines operating in support of battle group commanders would be restricted without the connectivity provided by ELF."

ELF antennas need to be very long.

"The antenna length in Republic, Michigan was approximately 52 kilometers (32 mi). The antenna is very inefficient. To drive it, a dedicated power plant seems to be required, although the power emitted as radiation is only a few watts."
TheGhostofOtto1923
not rated yet Aug 27, 2014
Such a sensor system has already been deployed by the US navy.

"SOSUS systems consisted of bottom mounted hydrophone arrays connected by underwater cables to facilities ashore. The individual arrays were installed primarily on continental slopes and seamounts at locations optimized for undistorted long range acoustic propagation. The combination of location within the ocean and the sensitivity of arrays allowed the system to detect acoustic power of less than a watt at ranges of several hundred kilometres (The system is so sensitive that it can even detect the presence of Soviet/Russian Tu-95 Bear 4-engine bombers flying overhead"
DonGateley
5 / 5 (1) Aug 27, 2014
If the cavity's integrity were lost you'd wouldn't have time enough to realize the change.
Skepticus
not rated yet Aug 28, 2014
Here is an idea: power the submarine with a nuclear reactor. Seawater will pass through the reactor heat exchanger system, turning into superheated steam. This steam will be piped to lots of opening all over the sub outer skin to create the gas bubble, as well as to thrusters for propulsion. This independently created gas bubble will eliminate the problem of ramp-up speed required for supercavitating condition, and enable the sub to run at below supercavitating speeds with very reduced drag.
antialias_physorg
not rated yet Aug 28, 2014
"For a military sub it's a pretty bad idea. Think of how LOUD this sub would be as it moves. "
Sometimes loud is OK if it's so fast that no one can catch it.
For comaprison: A modern (conventional) torpedo has a speed of about 100km/h. This sucker would have a speed of about 6000km/h. It's hard to roll something in front of such an object (especially on the short notice you'd be given)

So now we not only get ICBMs but also nuclear intercontinental submarine missiles.

As to the question: "How loud would this be".
Been pondering that a bit. The bubble mechanism would be loud. But the actual rocket motor probably wouldn't be as much as one might think - as the accoustic coupling between air and water is pretty bad.
antialias_physorg
not rated yet Aug 28, 2014
...and you wouldn't hear it coming at all, BTW...as it's faster than the speed of sound in water. (You'd only hear it once it passed you)
Urgelt
not rated yet Aug 28, 2014
Impractical for human travel; too much risk.

For weapons, it's another matter, and it's military applications which motivate this research. The Chinese aren't the only ones diving into it (no pun intended).
Nik_2213
5 / 5 (1) Aug 30, 2014
"The US Navy torpedoed the Kursk in Russian waters"

Do we have an unimpeachable source for this ?? Such outrageous claims demand robust verification...
antonima
not rated yet Aug 30, 2014

Been pondering that a bit. The bubble mechanism would be loud. But the actual rocket motor probably wouldn't be as much as one might think - as the accoustic coupling between air and water is pretty bad.


Perhaps, but the acoustic energy still has to go somewhere. Would it just get re-absorbed by the hull of the sub then? That could be a problem if there were any passengers aboard.
ECOnservative
not rated yet Aug 31, 2014
Wouldn't the energy required to displace the water with the bubble be affected by depth? This would seem to limit operation to relatively shallow depths for practical and economic reasons. As to detection, I don't see how this could function without leaving a huge trail of bubbles in its wake.
Jayded
not rated yet Sep 01, 2014
Surely most debris would get moved around the air bubble?
scotteggenberger
not rated yet Sep 10, 2014
My concern is always about quality when it comes to 'Made in China.' I trust Russian quality like on their caterpillar drive submarines, but one of my clients does hardness testing for thread plug gages at http://www.westpo...es.html. He mentioned the focus on quality parts and the ore minerals used for steel may not be as reliable from China. What testing do they do? Great article by the way. Thanks!