KN curves problem

Discussion in 'Stability' started by kaptcatb, Jan 27, 2013.

  1. TANSL
    Joined: Sep 2011
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    Location: Spain

    TANSL Senior Member

    I think you're not understanding the method that I describe (which is not mine). The method is completely accurate. Now if the method you use to calculate the volume is not accurate, the data you get will not be accurate. The "accuracy of my method" depends on the accuracy of the integration method you use.
    If you hold the AutoCAD, I can show you how to use it, without doing you any mathematical operation, calculate KN values​​.
    To answer your second question: The KN has nothing to do with the GZ. The dependent KN boat forms and GZ of the position of its center of gravity. That is, the values ​​of KN are "fixed" for certain forms of the boat, many times that the calculations always find the same values​​. In contrast, for the same boat, if you change the vertical position of its center of gravity will change GZ values​​. This is obvious but you do not seem to have it clear. And no, I do not know the Vlasov curves for integration.
    Trust me, using "my method", and forget about weird stuff that life is simpler than some we endeavor to make.
     
  2. kaptcatb
    Joined: Jan 2013
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    Location: Bulgaria , Varna

    kaptcatb Junior Member

    Hello again
    Yes i have autocad .
    The only thing in your method is how you set your new WL ? Arround which point you rotate you ship in autocad ? Cuz if you see different ordinates for the cross point ( w1l1 x w0l0 ) you get different submerged area , volumes , centers and etc . Will be interested to explain this part of the task .
    I'll be interested to explain this part of the task .
    In following link i set Q=30 for 2 different cross point ( different Yf , ah this Yf :D ) . Hope you understand my logic
    http://store.picbg.net/pubpic/7E/23/31732f6e6af97e23.jpg
     
  3. TANSL
    Joined: Sep 2011
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    Location: Spain

    TANSL Senior Member

    Could we, please, comunicate via e.mail?. Mine : 657677483@orange.es
    It would be much better to interchange information. Thanks
     
  4. maxxwell
    Joined: Jan 2013
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    Location: CA

    maxxwell New Member

    Why you dont use software?
    the ORCAD for RHINO and maxsurf calculate KN very fast
     
  5. TANSL
    Joined: Sep 2011
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    Location: Spain

    TANSL Senior Member

    Before using any software must know what is being done, how it is made and what it does. Unfortunately, it's going to a good user of software is believed ready to design boats and this is a mistake. Some people believe that a beautiful thing in Rhino, is a good boat just because it has be drawn in great detail. But how to find out, with Rhino, if the boat supports flood compartment, without sinking?. How to tell Maxsurf applying a stability criterion if you do not know what that is?. One must know how to do things "by hand", before using any software.
     
  6. kaptcatb
    Joined: Jan 2013
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    Location: Bulgaria , Varna

    kaptcatb Junior Member

    Hello all
    thanks to TANSL for helping .

    I finished my calculations for KN . Now my teacher want to generate ship model ( i dont know the reason .. i have already calculated in excel GM , KN , GZ for different wave crest and different ship direction in sea ) .
    I have little expirience with Maxsurf . From excel i generate ~ 600 markers , put in text filie and load it in Maxsurf . Then i select all markers -> group , sort markers by station . Then i need to fit curve to markes but dont have this option ( no Curve menu in main window ) . How to solve the problem ?
    I use this video from Formsys channel for "teacher" -
    http://www.youtube.com/watch?v=rsppUPaGuy8&list=PL49299184716EDEF2 ; see 01:06
     
  7. TANSL
    Joined: Sep 2011
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    TANSL Senior Member

    Unfortunately trying to define a surface in Maxsurf which adequately fit the markers is, in my opinion, impossible. You can make something that looks good but you will never have the assurance that passes through the points.
    For me the best is:
    - Draw transversal sections and longitudinal profile with AutoCAD.
    - Place it all in his true position in space, working in 3D.
    - Use the "_loft" command to generate surfaces forming the hull.
    - Creates a file .igs thereof.
    - Import this file in Maxsurf.
    You can also make a model in Rhino, and import the file .igs in Maxsurf.
    If you have problems, send me your body plan to see what can be done. But first, you try it.
    Good luck.
     
  8. Umair
    Joined: May 2020
    Posts: 9
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    Location: Pakistan

    Umair Junior Member

    Hello sir,
    Can you please help me with calculating KN curve?
    Can you share your work with me?
     
  9. TANSL
    Joined: Sep 2011
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    Location: Spain

    TANSL Senior Member

  10. Umair
    Joined: May 2020
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    Location: Pakistan

    Umair Junior Member

    Yes that's easy, but when inclined it thats make difficult to calculate anyhow I got the KN by finding the transverse buoyancy point BB'cos(phi) but it's little different like I got 2.34 and from software I am getting 2.30. is there any why I can get more precision.
     
  11. Umair
    Joined: May 2020
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    Location: Pakistan

    Umair Junior Member

    Is there any software or algorithm type thing from which I can direct find BB' (transverse center of buoyancy)…?
     
  12. kaptcatb
    Joined: Jan 2013
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    Location: Bulgaria , Varna

    kaptcatb Junior Member

    is it good idea to restore 6 years old thread? Method I have used is clearly described in post #12.

    As far as I remember -
    for method I used you need CAD program / Excel to integrate values . If youre good with MatLab it can also help.

    Draw all your frames, find volume of underwater part, CoB
    Draw inclined WL -> find volume of underwater part. If it dont match with volume in upright position move WL up or down until volume match.
    With massprop command you can find centroids of new underwater shape ( new CoB location ) , then I think its easy ..
    Repeat for all angle of heels - it may take alot of time so I suggest you to look for another method.

    Thanks Ignacio for great help

    Best regards
    Todor
     
    TANSL likes this.

  13. Umair
    Joined: May 2020
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    Location: Pakistan

    Umair Junior Member

    Thanks sir, this is what exactly I did in Solidworks. But it's way too time consuming. Any recommendations?
    Also recommend me some books to study KN curves, because no one explained it in details like some manual methods etc
     
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