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Gyroscopes for Orienting Submarines

  1. May 12, 2010 #1
    I am considering the use of gyroscopes to provide 3 dof attitude control of underwater craft, similar to how control moment gyroscopes have been used in the attitude control systems of satellites. It is hoped that this could replace the standard rudder configuration to minimize effects to the external flow field, leading to benefits in engine efficiency and more agile maneuvers.

    Does anyone know of previous work done related to this or any resources that may aid in my understanding of utilizing gyroscopes to orient submerged vehicles?

    Thanks,
    -Mark
     
  2. jcsd
  3. May 13, 2010 #2

    FlexGunship

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    I had a design that would do this in aircraft to protect against pitching during turbulence. The reason it works so well in satellites is their extremely low mass. You will find that in order to develop a stabilizing gyroscope big enough for a sub, the mass would make it almost useless in any practical setting. The additional fuel just to move the gyros makes it prohibitively expensive.

    Remember, satellites don't need to keep from sinking and they don't need to expend fuel to lift their gyros.

    Sorry to disappoint.
     
  4. May 13, 2010 #3
    Thanks for the help! I agree with you and I am definitely concerned about the size of the gyroscope and large amounts of power needed as the size of the vessel increases up to a military submarine, so most of the research may end up being focused on smaller, remote-controlled craft. However, maybe a nuclear submarine could provide the extra power needed?
     
  5. May 13, 2010 #4

    FlexGunship

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    Well, there are two ways to increase stabilization: increasing gyroscope speed and increase gyroscope mass. You can use the excess power on a nuclear submarine possibly to increase the rotational velocity, but you'd have to decrease it for the purpose of making intended moves that fight the gyro's inertia.

    I would start solving it on a piece of paper. I think you'll find the energies involved to create a rotational inertia capable of stabilizing something as massive as a submarine are simply not practical.
     
  6. May 13, 2010 #5

    mgb_phys

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    More the tiny external motions that the gyros are reacting to and the very slow rates of movement required.
    Hubble has a slew rate about the speed of the minute hand on a watch (360deg takes 1 hour) and the external forces of solar wind, atmospheric drag etc are tiny.
    A gyro in a vessel that is fighting a current and needs to turn more quickly would be vast.
     
  7. May 13, 2010 #6

    FlexGunship

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    Well, I would argue that (just a little... you are correct, of course), since even a tiny motion only a high-inertia system would require a large gyro. Go to the extreme example, a brick of lead in space with a gyro the same size as a satellite to stabilize it. Suddenly, tiny movements are impossible to correct for because the gyro's inertia is not on the same order of magnitude as the brick of lead's.

    However, even large impulses could be resisted if the inertia of the gyro were matched to the satellite. Granted, the resulting motion would still not be prevented.

    Gyros add inertia only. They can't do anything else. So, if a water current is enough to deflect a sub, then you need to increase the inertia beyond the ability of the current effect. In the case of a high-mass sub, the gyro would have to have a similar inertia (or significantly more). So... either very high speed, or very high mass.
     
  8. May 13, 2010 #7

    mgb_phys

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    Yes you obviously need a gyro with more intertia than the thing you are pushing it with - but that's not enough.

    Hubble weighs 13t, but a Hubble size gyro wouldn't orientate a 12t submarine to a fraction of an milli-arcsec in a storm.
     
  9. May 13, 2010 #8

    FlexGunship

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    Agreed x 10^7th. (Although, I think most subs are a little more massive given that a buoyant Seawolf-class displaces over 8,000 tons of water.)

    I suppose we have each picked one of the two fundamental flaws in this idea. As I said, I worked on a design for stabilizing an aircraft experiencing turbulence. Aircraft are much less massive than submarines and the numbers still don't work. The cost in fuel is unacceptable.
     
  10. May 13, 2010 #9

    mgb_phys

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    You could always put the gyro in a gimbal in the center and run it at constant speed than simply uncage the bearing to maneuver. Then you never need to spin down the gyro.

    all I can remember of the equations relating how much power you take out a gyro to react against it - is that i was very glad I would never have to use them!
     
  11. May 13, 2010 #10

    FlexGunship

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    And make three axially-independent gyros. Each would have an arbitrary angle relative to the sub, but they would all be aligned 90 degrees perpendicular to each other?

    Actually, if you used a clutching mechanism that is capable of partial engagement, you could change the bandwidth of frequency response in the sub. If it were partially engaged, low frequency movements (i.e. turning) would be allowed, but high frequency movements (a sudden impact of a water current) would be largely stabilized.

    Neat idea... not sure if its any more practical though.
     
  12. May 13, 2010 #11

    mgb_phys

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    I just come up with the brilliant ideas - it's upto the production guys to make them work ;-)
     
  13. May 13, 2010 #12

    FlexGunship

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    Yeah, us engineers need a presence in the think-tank too. Gosh... I hate some of the nonsense that comes out of our research department.
     
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