Calculating kn values with maxsurf and AutoCAD

Discussion in 'Software' started by Siddarth Amaravathi, Apr 14, 2021.

  1. Siddarth Amaravathi
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    Siddarth Amaravathi Junior Member

    Gz = kn-kg*sin theta
    Where,
    Gz= gm sin theta
    Gm= km-kg
    Km= kb + bm.
    Kb is center of buoyancy
    Is this what you're asking sir?
     
  2. TANSL
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    TANSL Senior Member

    No, is not that.
    Those formulas are of little use to calculate the KN, if you don't know the position of the CoG and metacenter.
    The value of the KN depends exclusively on the shapes of the ship and has nothing to do with the CoG nor with metacenter.
    Could you make a drawing, and show it here, with the position of the CoB and what is the KN?
     
  3. Siddarth Amaravathi
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    Siddarth Amaravathi Junior Member

    sir since its a rectangular one, I've considered cob at the center of the area underwater and I heeled the vessel to 10 degrees about the cog which is center of the whole vessel. hope this satisfies the question you asked
    a.PNG b.PNG
     
  4. TANSL
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    TANSL Senior Member

    Before trying to calculate the KN you should find out what that is.
    Forget CoF and CoG and center yourself in CoB and what we know as KN.
     

    Attached Files:

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  5. Siddarth Amaravathi
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    Siddarth Amaravathi Junior Member

    woah. I'm perplexed right now. Could you explain me stuff please
     
  6. TANSL
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    TANSL Senior Member

    Frankly, I don't know what else you need me to explain. Should I clarify that instead of an inclination of 10º, in my picture of post # 19, I have considered an inclination of 30º to make it more evident, clearer, what each point is.
    Once the position of the center of buoyancy is known (and AutoCAD will give it with complete accuracy), trigonometry will allow you to obtain the value of the KN. If this is not enough, please look at the formula in the picture to the right of post #19.
     
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  7. Siddarth Amaravathi
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    Siddarth Amaravathi Junior Member

    I was actually wondering, about what point did you heel the ship to 30°. how are you titling it. Please explain stepwise what did you do in cad. I'm really sorry I'm asking you too many questions but then you're a gem teacher I could get.
     
  8. TANSL
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    TANSL Senior Member

    Do you know how to create a solid model of your barge in AutoCAD?
     
  9. Siddarth Amaravathi
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    Siddarth Amaravathi Junior Member

    Yes
     
  10. TANSL
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    TANSL Senior Member

    You must cut the solid through successive 10-degree inclined planes until you get a sectioned piece with a volume of 976 m3 (equivalent to 1000 tons). Get closer little by little until you get more or less that volume. Once achieved, the AutoCAD command "_massprop" will provide all the properties of the solid, including the position of the center of gravity of its volume, which is the center of buoyancy sought. With that data you can now use the previous formulas to calculate the value of the KN.
     
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  11. Siddarth Amaravathi
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    Siddarth Amaravathi Junior Member

    ok now I get it
     
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