What is method of other programs used to calculate hydrostatic properties?

Discussion in 'Software' started by xichyu, Apr 12, 2016.

  1. xichyu
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    xichyu Junior Member

    Some programs use lookup functions to match loading conditions with pre calculated tables of hydrostatic data. GHS uses the actual vessel geometry to calculate hydrostatic properties
    What is method of other programs used to calculate hydrostatic properties?
     
  2. TANSL
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    TANSL Senior Member

    No program can obtain hydrostatic values regardless of the geometry of the hull.
     
  3. DCockey
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    DCockey Senior Member

    Are you a student and this is a question from an assignment or test?
     
  4. xichyu
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    xichyu Junior Member

    I am learning ship theory now
    And I want to learn ship software further
     
  5. xichyu
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    xichyu Junior Member

    Thanks
    Have a nice day!
     
  6. xichyu
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    xichyu Junior Member

    So I want to know the methods of other program to calculate hydrostatic values
     
  7. Ad Hoc
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    Ad Hoc Naval Architect

    Is this the subject you are learning at university?..if so, may i suggest reading a book. All the answers to all the very simple questions you are currently asking (on various threads) are in any quality naval architecture text book.

    Thus a trip to the library is in order!...it is called learning!
     
  8. xichyu
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    xichyu Junior Member

    Recently, I search relevant material on ship book in the library. I knew
    “Some programs use lookup functions to match loading conditions with pre calculated tables of hydrostatic data. GHS uses the actual vessel geometry to calculate hydrostatic properties”
    So I think there are many softwares about ship, They can not use the only two methods to calculate hydrostatic properties.
    I want to know more methods about calculation. I want to compare them
    with each other.
    I am in library now. I also want to talk with others.
    That is my attitude for learning.
     
  9. gonzo
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    gonzo Senior Member

    What that says is that some programs will be analog, that is they use every point of a curve, while others are discrete and use pre-calculated points. Either one can give good results. Usually, it is not necessary to have every point on a curve, but just points at adequate intervals. Before cheap computers, points at intervals were always used.
     
  10. TANSL
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    TANSL Senior Member

    All that you say makes no sense and shows that you do not know the methods of integration, before to or after "cheap computers".
    All the old methods of integration used straight lines or curves passing through a number of points.
    Current programs that work with "wires" do exactly the same, working with second-degree polynomials. Software working with surfaces or solids use other methods, such as triangulation, flat or spherical triangles.
    Nobody now tries, nor has it ever done, get all the points of a curve. When you work for points, you work, always with a finite number of points. Try to work with the infinite points of a curve is stupid. What is done is to calculate equations of pieces of curves, third-order polynomials, that pass through a finite collection of points: polynomial interpolation in its many variants.
     
  11. mchl
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    mchl MCHL Stabilitycalculation

    xichyu : Softwares using sections calculate as follow :

    - The area below the current waterline of each cross section is calculated by integration.
    - When you plot a diagram of all sections area (x : position of the section, y : area of the section), you get what we call the "curve of areas" in m2.
    - When you calculate the area of the curve of areas, you get the immersed volume of the hull (in m3). You multiply it by the water density : you get the displacement of the vessel. The longitudinal position of the center of the curve of area give you the LCB (longitudinal center of buoyancy).
     
  12. gonzo
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    gonzo Senior Member

    mchl: A clarification please. Do you mean the centroid of the longitudinal area or the center of the curve length (arclenght)?
     
  13. mchl
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    mchl MCHL Stabilitycalculation

    GONZO : no. Centroid of the curve of areas as explained. Longitudinal origin is the same as the sections origin.
    Googlise : hull curve of areas
     
  14. DCockey
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    DCockey Senior Member

    My guess (and only a guess) is the lookup functions referred to in this quote are previously calculated curves of hydrostatic properties similar to Bonjean curves. The advantage of this approach is the integration of the of the hull does not need to be recalculated for every loading case. More information about Bonjean curves and their use are available in naval architecture textbooks about stability.
     

  15. xichyu
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    xichyu Junior Member

    Thanks! Do all softwares use this method?
     
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