China May Have A New Submarine Tracking Technology

Submarines have always been about stealth; that’s always been the whole point of putting them underwater. Tracking them can be difficult, even to this day, but China may have a new technique to help in this endeavour, as reported by the South China Morning Post.

Nuclear missile subs are nicknamed “boomers,” and can spend months underwater. Tracking them is of prime concern to many countries around the world. US Navy

The news comes from a study published in a Chinese journal, regarding detection of the most advanced American submarines. The stealthiest examples use all kinds of sophisticated systems to damp vibrations and reduce acoustic signatures to make detection as hard as possible. However, a new type of magnetic detector could change all that.

A research team used computer simulations to determine whether nuclear-powered submarines could be detected via the bubbles produced when cruising at high speed underwater. When these bubbles inevitably collapse, it can apparently produce a detectable signal that is orders of magnitude higher than the sensitivity of the best magnetic anomaly detectors. The signal is found on the order of 34.19 to 49.94 Hz, deep in the ELF range, according to researchers.

This could yet create another arms race, as submarine designers begin designing vessels to reduce bubble shedding at speed. Or, for all we know, this is already a well-known principle in the high-stakes world of submarine surveillance and combat. If you’re in the know, please don’t reveal any classified information in the comments section. It’s not worth your job or ours! If you recreate such a detector at home in a non-treasonous manner, though, don’t hesitate to let us know!

69 thoughts on “China May Have A New Submarine Tracking Technology

      1. It is well known that a boomer submarine has a job to go out to a specific box of the ocean and run deep and run silent. They are in no hurry to get anywhere just remaining under the radar.

  1. From experience, much of submarine travel is low speed. What speed creates these bubbles and as speed increases does the transmission distance increase?
    ELF can travel around the earth and oceans with lots of power and a very long antenna. Seems that these bubbles don’t have the necessary attributes for long distance undersea travel. Yes, I have no knowledge or insight into this secret world. Hope these ELF bubbles are just a novelty.

    1. Cavitation creates the bubbles.
      As an undergrad, 25 years ago, my physics professor said one of his projects from DOD prior to going academic was working in cavitation.

      In other words this has been a very very active branch of research for decades, probably since submarines became a thing.

      This is a non-story from China and basically propaganda. A boomer can sit on the bottom of the ocean for 4 months.

  2. When submarines turn their propellers above a certain rpm, particular to each propeller, they “cavitate” (“To form vapour bubbles in a flowing liquid in a region where the pressure of the liquid falls below its vapour pressure”) , that is, they produce air bubbles. This also produce a lot of noise. This has been known for a long time. What MIGHT be new is a way of detecting them at great distance.

    1. Nope, they don’t produce air bubbles. They produce bubbles of low pressure water vapour (including all other matter dissolved in the water, including tiny quantities of oxygen, nitrogen and carbon dioxide), which will collapse rather than rise up like normal air bubbles.

    2. The article is about cavitation bubbles from the hull, not the propeller

      Quote from the South China Morning Post:
      “The bubbles are an inevitable consequence of the submarine’s cruising speed, which causes the water flowing around the hull to move faster as its kinetic energy increases and its potential energy – expressed as pressure – decreases. This is because the total energy of a given system must remain constant. In the case of a fluid in motion, the sum of the kinetic energy – caused by the motion of the fluid – and the potential energy will not alter, but the balance of the two forces will shift. Southeast Asia nations boosting submarine orders amid US-China rivalry When the pressure decreases sufficiently, small bubbles form on the surface of the hull as some of the water vaporises. This cavitation process is most likely to occur on areas with a sharp curvature or rough surface, which can create regions of low pressure. As the water continues to flow around the hull, the bubbles grow bigger and move away from the surface, where the higher pressure – such as near the trailing edge of the hull – causes them to collapse violently. This process causes turbulence and and can produce an electromagnetic signature, in a phenomenon known as the magnetohydrodynamic (MHD) effect.”

      I’m not convinced that the signals will be all that easy to detect from a distance. Additionally, a 40Hz signal will have a wavelength of nearly 6000 kilometers. Good luck doing direction finding with that.

      The South China Morning Post article is for subscribers only, making it difficult for non-subcribers to read the whole thing (I mean, “view source” in the browser shows the whole thing but how many people will do that.)

      This article from Interesting Engineering isn’t obfuscated:

      1. I think the explanation about conservation of energy in the fluid is not correct and are about closed systems. The submarine produces very large forces on the water and if flow is turbulent, nobody knows what happens other than approximations.

      2. The US and USSR spent billions of dollars in research on propeller cavitation reduction specifically because it was easy to detect. I kinda suspect they also spent at least some time worrying about form drag cavitation.

    3. From what I learned at school 30+ years back, cavitation stops being a problem (with pumps / pipes) when pressures are above around 5 to 10 bar (0.5 to 1MPa for more modern people I believe). For cavitation bubbles to form, you have to get below the vapour pressure, and that does not happen anymore when the pressure in the pipes (submarine depth) is big enough.

      To me this just sounds like a silly story with absolutely nothing to back it up, and that “simulation” makes it a lot more dubious still.

      On top of that, assuming it is true, I very much doubt the chinese have discovered this first. Other countries just don’t go on with leaking it to the press.

      1. Sometimes you “leak” to the press to distract the enemy. You make your enemy spend resources on your “leak” and distract them from doing other things. Welcome to spy vs spy.

        1. Other times you leak to convince your population that you aren’t in a hopeless, backward ass state. e.g. So they won’t hang emperor poo bear from a lamp post.

          Still other times you leak to convince your population that your rival isn’t in a hopeless, backward ass state. e.g. So they’ll let you buy _another_ ivory back scratcher, from your nephew, for a completely fair price.

    4. Thank you. Yes, tracking vehicles by the super-cavitation of their propellers isn’t new. Making propellers that are less subject to super-cavitation isn’t even new. This might be an improvement in detection range, and it would be something that the US military would classify. The news here is that China is telling people.

  3. I think I key term here is magnetohydrodynamics (or hydro­magnetics).

    When bubbles from prop cavitation collapse they create a magnetic field. Hence they are hoping to use sensitive magnetic anomaly detectors to look for submarines.

  4. A solution might be to coat the entire outside of a submarine with Shark Skin Technology for maximum aquaplaning (lowest water resistance).

    I suspect that not many people have rubbed a naked hand along the body of a shark, as have had a hand or finger licked by a cat. So the easiest way to describe texture of SST, is that it is in a lot of ways similar to that of a cats tongue but with the direction reversed 180 degrees.

    1. A great deal of research was done trying to duplicate the skin of the bottle-nose porpoise. And I recall there was some success 40 or 50 years ago by the US Navy . I wonder where that stands today.

  5. “A research team used computer simulations to determine whether nuclear-powered submarines could be detected via the bubbles produced when cruising at high speed underwater. ”

    Um, . . .

    1. That’s called ‘cavitation’. We already know how to detect that from *listening to it*.

    2. Subs don’t travel ‘at high speed’ – because then they would cavitate and you would hear them. The only time that happens is in an emergency, like, you know, another sub has already detected them and fired a torpedo and you need to get the heck outta Dodge real quick.

    1. That confused me too, until I saw the word “magnetohydrodynamic” in another comment (read the article? aw hell no). MHD effects come from the interaction between conductive fluids and magnetic fields, where movement of the fluid will drag magnetic field lines around with it. It’s a very weak effect in water, because even seawater isn’t a very good conductor and the velocities involved aren’t terribly high, but it’s not nothing.

      Turbulent flow would twist the existing geomagnetic field into complicated forms and thereby store energy in the field, which gets released as the field lines relax. Most of the energy would be burned off through electrical resistance, slightly warming up the water. A tiny fraction of it would be radiated and could be detected remotely. I find it rather dubious that it would be easier to detect cavitation that way than the traditional acoustic approach.

      1. Collapsing cavitation bubbles create plasma by adiabatic heating.

        The central claim in cold fusion was that there was energy coming from somewhere unknown when this was caused to happen under certain conditions. They proposed it was from fusion, but no neutrons (IIRC) have been found.

        I’m sure the research has progressed, last I saw the source of the extra energy was still unknown.

  6. I think pretty much every modern film I’ve watched that features sub hunting mentions ‘cavitation’ from the propellor and it’s a bad thing if you’re trying to be quiet because it’s *loud* but I’m not sure what speeds a sub would have to travel at for the hull to create cavitation or even if that’s the cause here?

    Cavitation is weird though, there’s some really strange effects when the bubble collapses including light being emitted, high intensity shock waves, sound and, it seems, magnetic pulses.

    So given the weirdness, I guess it’s not a surprise it’s detectable with what sounds like relative ease to track subs (in comparison to other publically known methods, who knows, it could be the Chinese are decades behind the curve here and, just maybe, the two US navy officers who were arrested earlier this year on espionage charges…)

  7. The CCP is notorious for controlling the flow of information to the public. So unless China’s already found a way to mitigate this effect in its own subs (and the US would surely already know by now), then the message here seems to be “If we all keep our nuclear subs where we can all see them, everything wil be fine”.

    So maybe the South China Sea dispute just got dialled back a bit.

  8. That is why the NSA hacking of the Chinese seismic detectors using an existing backdoor, was so important. It determined if the Chinese where already using these frequencies to detect US subs. For more information come over to Top secret: on Facebook.

  9. I think it’s all just internal propaganda, just as the Russians are winning the war, every North Korean missile destroys a Western country, China tries to sell superiority to its citizens.
    Perhaps you are wondering why? Simple, China has been facing a big financial crisis that was delayed by the C19 but that now has been very strong, look for the Chinese real estate market, or the population decline, predatory fishing, etc.
    They need an external enemy and they need to show superiority, the rest is politics.

  10. I think this may work on a similar concept to the Pistol Shrimp. They move water so fast that the collapsing bubble causes a micro-fusion reaction. Now although the bubbles on a submarine aren’t going that fast, their collapse could still make a very micro amount of detectable magnetic radiation in a similar way which with a big enough antenna, might be detectable.

    Maybe this is what this discovery is about?

    1. Shrimps do not cause fusion reactions with their little claws. They did inspire a fusion power startup, but no there isn’t a crustacean that can fuse atoms and make little tiny H-bombs.

  11. This ranks with the stupidest articles I’ve ever seen. Go *read* “The Hunt for Red October”. This is as “ground breaking” as a submarine. Clancy got it right.

    Please take a few minutes to learn something about the subject before posting junk. As a consequence of a comment to a coworker at Amoco in NOLA on the street car, 6 people left to join the ASW group in New London in the early ’80s.

  12. Do you know what power and antenna you need to make a 40Hz radiated EM signal. Even in water with a dielectric constant of 80, so you can make the antenna sqrt(80) smaller, you need a serious setup. And they want the energy of a cavitation buble to reflect against the ionosphere and detect AND direction find it. I like theoretical exercises but I call this BS.

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