Drag Forces on a Flat Face Barge

Discussion in 'Hydrodynamics and Aerodynamics' started by mitch10284, Mar 5, 2013.

  1. mitch10284
    Joined: Mar 2013
    Posts: 2
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    Location: St Louis

    mitch10284 New Member

    Hello. I'm working on constructing an anchoring system for Barges on the MississippI River in St Louis and need to determine the force the river will impose on an anchored barge. I'm using the Drag Force Equation

    F = 1/2 x velocity^2 x density x Area x Cd

    Assumptions

    Drag Coefficients
    Cd = 1.98 for the bow
    Cd = .005 for bottom and sides

    Density = 62.4 lb/ft^3 for water

    Barge is 35'x195' and sits 11' in the water

    I've been told by a few Barge Captains the river can reach 26 ft/s during a strong flood. I'm designing for worst case so I've used this number.

    The problem I'm having is that the drag force numbers I'm getting seem to be way high.

    Bow - 16,576,329 lb
    Sides - 466,433 lb
    Bottom - 742,053 lb

    Hoping someone can confirm these numbers are incorrect and can help me out.

    Thank You
     
  2. Submarine Tom

    Submarine Tom Previous Member

    Isn't water density 1.0?

    Don't discount windage.
     
  3. mitch10284
    Joined: Mar 2013
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    Location: St Louis

    mitch10284 New Member

    Using US Customary Units and the Mississippi is fresh water in St Louis.

    Regards
     
  4. TANSL
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    Location: Spain

    TANSL Senior Member

  5. DCockey
    Joined: Oct 2009
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    Location: Midcoast Maine

    DCockey Senior Member

    Yes. Nothing special about a Cd value of 1. The table in my old fluid mechanics textbook shows a drag coefficient of 2.00 for an infinitely wide flat plate normal to the flow, 1.20 for a rectangular flat plate with an aspect ratio of 5 normal to the flow, and 1.10 for a square plate normal to the flow. Those are drag coefficients for an object completely immersed in an "infinite" flow.
     

  6. DCockey
    Joined: Oct 2009
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    Location: Midcoast Maine

    DCockey Senior Member

    You need to divide by the "density" of water of 64.4 lb/ft^3 by 32.2 ft/sec^2 to obtain the mass density of 2.0 slugs/ft^3. That will reduce the drag force numbers by a factor of 32.2.
     
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