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Where to find formulas for acceleration of compressed steel tubes

  1. May 25, 2007 #1

    mhl

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    Hi all

    Looking for simple formulas to describe maximum acceleration of steel tubes when tubes are compressed and suddenly released when submerged in water (dont know if the water does anything else than supply buoyancy).

    Please, also feel free to comment freely on the topic and formulas you might state....

    Hope you can help....


    thanks

    mhl
     
  2. jcsd
  3. Jun 13, 2007 #2

    xez

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    Compressed how? Axially, radially, filled with compressed air, etc. etc. Your description of the problem isn't sufficient
    to even begin to understand the question let alone answer it.

    As for simple equations, where are simple equations, and
    then there are usefully correct equations; the two aren't
    always overlapping when you're dealing with something
    like drag due to motion in water. There's a reason that
    engineers often build scale models of things and test them
    "for real" in water tanks rather than relying on the accuracy
    of estimates from fluid flow / drag calculations; it's
    often easier to build and test the thing rather than model
    it sufficiently accurately even with complex equations and
    computer models.

    If it's just a question of axial acceleration of a tube through
    water given a certain 'rocket' thrust from compressed air
    inside the tube released from an axial nozzle in the rear,
    then you could probably find a good simple formula for
    the drag of a cylinder of a given size in water, and the
    thrust will just be the simple rocket equation due to
    the momentum of the release of the gas given a certain
    escaping gas flow rate due to the pressure differential of
    the gas vs. the water and the size/performance of the
    nozzle the gas escapes through. That's about as simple
    as that gets, pretty simple to estimate with simple
    math and a notepad, but still not trivial.

    Unless you're talking about the mechanical relaxation /
    oscillation / 'springing' / ringing (like a bell) /
    expansion (like a bellows) of a structurally compressed tube
    under water in which case, well, good luck, that's likely
    a lot more complicated due to (in)elasticity, friction,
    drag, heat, possibly turbulent fluid flow, etc. etc.

    The simplest case would be like letting go of a coiled
    tube spring underwater in which case you're back to
    estimating the cylinder's drag and the the evolution of
    the 'spiringing away' based on the water's drag and the
    F=mx tension in the spring and how long the spring will
    be able to push against its dock......
     
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