Supersonic Chinese Submarine

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tfbncc
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Re: Supersonic Chinese Submarine

Post by tfbncc »

Yeah, I don't think it's going to happen anytime soon. My kids and I discussed this. I had to point out a few flaws in the logic of this so called submarine. First off, supersonic in what medium? According to the article, the sub surrounds itself with a gas bubble to achieve unheard of before speeds. Speed of sound in air is 1100 feet per second (or approx. 720 mph). Speed of sound in water is 4800 feet per second at sea level so in order to be supersonic in water, he would have to be doing approx. 3000 mph give or take a 100. So let's assume they are using the 1100 fps number for reference. The shock wave that a mass the size of a small to medium sub would create at that speed would dwarf any tsunami in recorded history. Think 100 plus foot tall waves and such. Cavitation technology may work for small torpedoes, but when you increase the size of the mass, the displaced water and wake would grow exponentially. Stealthy it ain't.
Aesop
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Re: Supersonic Chinese Submarine

Post by Aesop »

Pure bullshit. :lol:

I'm guessing that on the Chinese Calendar, today is April Fool's Day.
"There are four types of homicide: felonious, accidental, justifiable, and praiseworthy." -Ambrose Bierce, "The Devil's Dictionary"
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Yogimus
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Re: Supersonic Chinese Submarine

Post by Yogimus »

Would make for a hell of a carrier group killer.
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Vonz90
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Re: Supersonic Chinese Submarine

Post by Vonz90 »

I have a BS in Naval Architecture. I don't work in the field but I know the theory and I did some coursework in advanced marine vehicles back in the day. The word for this is bullshit.

Super cavitation works, but it doesn't work that way. You alway have some percentage of the craft in contact with the water, so you don't completely eliminate the frictional resistance (proportional to Reynolds number if you are keeping score at home). However, it gets worse. More than half of the resistance in water (in most cases) comes from the pressure wave formed by the body moving through the water (proportional to Froude number). So you can't just reduce the wetted surface through cavitation magically reduce the total resistance if doing it increases the pressure resistance. This is not really true for aero applications so sometimes non naval architects miss this.

This is is the problem people run into when the are looking for magic bullets for marine vehicles. Of course you can make anything go fast if you put enough energy behind, but that would be an incredible amount of energy and where would it come from?
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kapikui
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Re: Supersonic Chinese Submarine

Post by kapikui »

I'm reminded of a Robin Williams joke from back in the day. "The way to build a stealth aircraft is to go into the forest, spread some wreckage and say 'one of them crashed.'"
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Jericho941
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Re: Supersonic Chinese Submarine

Post by Jericho941 »

I'm a fan of the Oatmeal too, I just like Zefrank's whole "that is how a _____ do" schtick. Especially how a cuttlefish do.
Aesop
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Re: Supersonic Chinese Submarine

Post by Aesop »

No engineering degree here, but I passed fourth grade math:
skb12172 wrote:Bullshit or Bulltrue?
Researchers at the Harbin Institute of Technology in China have told the South China Morning Post that they’re working on technology that could allow a submarine to travel the 9,816 km from “Shanghai to San Francisco in 100 minutes”.
9816km is 5889.6 statue miles.
Covered in 100 minutes is 3533.76 MPH.

In water. :roll:

To date, we've only made one aircraft that could do 2/3rds of that, and it had to first get to >80,000 ft ASL to accomplish the feat.

So yeah, the Chinese will be able to do it with a vessel 200-300 ft. long, displacing 9000 tons or so, through water sitting in the water column at the 20-30 atmosphere density level.

As if.

Of course, the technology has been well-documented since the mid-1980s, but so far it only works on the Sci Fi Channel. :lol: :lol: :lol:

Anyone who seriously believes the OP should not be entrusted with taking the family cow to the market on Saturday, lest they return with a handful of magic beans in trade.

The only thing the story was missing was a byline from John Bigboote in the Shanghai Yangcong. 8-)
"There are four types of homicide: felonious, accidental, justifiable, and praiseworthy." -Ambrose Bierce, "The Devil's Dictionary"
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Vonz90
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Re: Supersonic Chinese Submarine

Post by Vonz90 »

Aerospace engineering myself... but the physics and equations are the same... I'm just used to working with lower density compressible fluids and corresponding reynolds numbers ;-); though I've actually done some boat design work just for fun (messing about with small racing boats), and done design reviews on larger vessel designs. Many boat designers (particularly in sail racing) are trained as aerospace engineers
The equations are the same if you try to solve it as a potential flow problem (also need to model for surface tension resistance - proportional to Webber number). The problem is that you will never get an answer if you model it with enough accuracy to be more than a first order approximation. So, that isn't how it is done in practice.
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Weetabix
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Re: Supersonic Chinese Submarine

Post by Weetabix »

CByrneIV wrote:What is not mentioned is just exactly how much energy it takes to do so, the answer being a HELL OF A FUCKING LOT; and that said energy increases logarithmically with mass, volume, surface area, frontal area, (though for many calculations we can simplify the volume, surface area, and frontal area as something called the EFPA - equivalent flat plate area); and in non linear and non proportional complex discontinuous curves as velocity increases.

Shockwaves, harmonics, hypersonic cavitation collapse...

This shit gets really complicated ...and incredibly destructive by the by... very quickly.
Only a lowly civil here but with fluid mechanics background, and this was my thought.

It would take enormous energy. It would be enormously loud. Something has to be in contact with the water to steer, and that something would get the shit eaten out of the trailing edge with the cavitation collapse going on there, I'd think.

If you want those speeds, why not just do a missile.

And if your physics-ninja-fu is strong you can defeat water, do a submarine that goes that fast through the earth and really impress us.
Note to self: start reading sig lines. They're actually quite amusing. :D
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