Section after Section, How designers get a smooth continious 3d surface ?

Discussion in 'Hydrodynamics and Aerodynamics' started by mustafaumut, Aug 18, 2015.

  1. mustafaumut
    Joined: Jul 2005
    Posts: 29
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: Istanbul

    mustafaumut Junior Member

    When we look to the line drawings of an sail boat from bottom or from front , we see curves of sections. I am not sure , it is called as section but this is my comment.

    I could not understand which collection of formulas resulting to smooth continious curves around hull , there is no bumb or other thing.

    For example , we have a herreshoff design , someone removed a section from the plan , how can we redraw it ?

    Thank you very much,

    Mustafa Umut Sarac
    Istanbul
     
  2. NavalSArtichoke
    Joined: Oct 2013
    Posts: 431
    Likes: 8, Points: 0, Legacy Rep: 83
    Location: GulfCoast

    NavalSArtichoke Senior Member

    There are no formulas, or collection of formulas, making up a boat's lines.
    The lines were all drawn by hand and "faired", which means the shape of each curve was adjusted so that intersections in all three views, the body plan (station view), the profile, and the plan, agreed with each other.

    If you want to reproduce a given curve, overlay a gridwork on top of it and take offsets from a known reference along the length of the curve. One such gridwork usually is the stations, waterlines, and buttocks which you see drawn on a typical lines plan, like below:

    [​IMG]
     
  3. mustafaumut
    Joined: Jul 2005
    Posts: 29
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: Istanbul

    mustafaumut Junior Member

    I want to ask new question related to two posts above.

    I read few pages at google and understood that every calculation starts after the line drawing been put.

    Is there a method which hydrodynamic and stability and cfd results been put BEFORE the line drawings drawen ?

    Thank you,

    Mustafa Umut Sarac
    Istanbul
     
  4. NavalSArtichoke
    Joined: Oct 2013
    Posts: 431
    Likes: 8, Points: 0, Legacy Rep: 83
    Location: GulfCoast

    NavalSArtichoke Senior Member

    Not unless you want to obtain results which are meaningless.

    The stability of a vessel depends on its lines to a great extent, and, to a lesser extent, so does its hydrodynamic performance.

    As part of the design process for a vessel, you can estimate certain things about the final hull shape, like the block coefficient or the waterplane coefficient, which can be used before the lines are drawn, but the stability of the vessel must still be calculated after the lines are completed to confirm these initial estimates. So, too, for its hydrodynamic performance.
     
  5. philSweet
    Joined: May 2008
    Posts: 2,276
    Likes: 160, Points: 63, Legacy Rep: 1082
    Location: Beaufort, SC and H'ville, NC

    philSweet Senior Member

    It's a very good question, Mustafa. A serious issue with what you ask is where do you get these requirements from a priori? They are highly derived quantities that are the result of experience with real hulls' geometry. One should not assume that any hull shape that has equal values will perform equally.

    With that in mind, the technique is called reverse design. There is a free program called Godzilla written by a member here that will iterate until told to stop (it does not use CFD). It will try to find the lowest drag shape that complies with a large number of possible user defined restrictions. However, the real trick is knowing what those ought to be when it comes to stability and such. It is free to download and worth learning to use IMO.
     
  6. Heimfried
    Joined: Apr 2015
    Posts: 340
    Likes: 38, Points: 28, Legacy Rep: 37
    Location: Berlin, Germany

    Heimfried Senior Member

    That is correct, but Sir Isaak Newton gave us a formula, which creates from an input of a few points (in x,y-coordinates) a 2-dimensional polynomial curve.

    The results should be checked, but in most cases, any calculated point in the interval is on a fair line.

    I did an Excel-sheet (2002) which calculates it. It is downloadable as zipped file at
    https://www.boote-forum.de/showpost.php?p=3751040&postcount=11
    (Blue colored cells = input; blue colored cells to change only; don't touch other cells; reddish cells = output; "Diag" Tabs for checking the calculated polynome graphically; separated tabs for 5 given points (St├╝tzpunkte), 4 points, 3 points)

    It should be possible to find the offsets of a lost frame, if you input the offsets of the nearby frames.
     
  7. TANSL
    Joined: Sep 2011
    Posts: 6,004
    Likes: 255, Points: 93, Legacy Rep: 300
    Location: Spain

    TANSL Senior Member

    The frames can be deduced through the water lines. If you have those lines do not need to know the nearby frames. If you have no water lines, you can not get any additional frame. You can interpolate, as seems to suggest Heimfried, but the result can be very inaccurate. I think the right way is by graphic procedures.
    If we talk of a 3D model the situation is totally different.
    Nor do I speak of hulls with chine or knuckles, for whom the problem is still more complicated
     
  8. Rurudyne
    Joined: Mar 2014
    Posts: 1,145
    Likes: 33, Points: 48, Legacy Rep: 155
    Location: North Texas

    Rurudyne Senior Member

    Just an aside: Hercules had a gorgeous sheer line, well, lines in general I suppose. Yes, underwater she'd not be modern, but a yacht with all the modern improvements where they can't be seen could be a stunner with those lines where they can be seen.

    Of course I write that as one with a way too anemic bank account to even hope to try....
     
  9. SukiSolo
    Joined: Dec 2012
    Posts: 1,270
    Likes: 25, Points: 0, Legacy Rep: 271
    Location: Hampshire UK

    SukiSolo Senior Member

    As pointed out above, all three views have to 'agree' dimensionally. If they do not, then some part is unfair. If something is missing in one view, it can be recreated by using the one or two views. Basic drafting techniques should let you do this whether on paper or CAD.

    As for checking the 'smoothness' of lines and fairing, that is largely a function of the diagonals used. These are often shown as draft curves on lines plans, commonly in the plan/waterline top view.
     
  10. Heimfried
    Joined: Apr 2015
    Posts: 340
    Likes: 38, Points: 28, Legacy Rep: 37
    Location: Berlin, Germany

    Heimfried Senior Member

    Just to give an example of the application of Newton's formula:

    The first picture shows an offset table of a boat.
    In the first line are the stations (x-coordinate, longitudinal) given in mm (point means not decimal separator, but serarates thousands).
    In the second line shows the hights of the sheer (z-coordinate, vertical) at the stations.

    The second pic shows six marked stations and the separately marked number "1.288" is assumed to be lost.

    The third pic shows the calculation sheet with the nearby values of the offset table inserted (x1, y1, x2, y2, ... Excel-cells B6 to C10). In cell B28 the station with the lost value is inserted (x = 3.200) and C28 shows the calculated y-coordinate (z = y in this case).

    The result of 1.286,6 instead of 1.288 is within the allowance, I think.

    The last pic shows a diagram of the Newton polynom to check, if it is fair. The diagramm is normalised (non scale), as it has only the purpose, to prevent false results, caused e.g. by faulty insertion of coordinates.
     

    Attached Files:

  11. Squidly-Diddly
    Joined: Sep 2007
    Posts: 1,559
    Likes: 76, Points: 48, Legacy Rep: 304
    Location: SF bay

    Squidly-Diddly Senior Member

    I'd take the frames you have, enter them into one of those computer hull performance programs, and let the computer fill in the blanks.
     
  12. Alexanov
    Joined: Feb 2003
    Posts: 162
    Likes: 13, Points: 28, Legacy Rep: 10
    Location: Norway Sola

    Alexanov Senior Member

    Nice lines!
     
  13. Alexanov
    Joined: Feb 2003
    Posts: 162
    Likes: 13, Points: 28, Legacy Rep: 10
    Location: Norway Sola

    Alexanov Senior Member

    Ship design process based on iterations. With every new run you try to make surface better and better. Start point of this process depends only from designer experience.
     
  14. Oleboynow

    Oleboynow Previous Member


  15. jehardiman
    Joined: Aug 2004
    Posts: 2,613
    Likes: 261, Points: 83, Legacy Rep: 2040
    Location: Port Orchard, Washington, USA

    jehardiman Senior Member

    Actually, you start the design with the requirements. See the linked post.

    http://www.boatdesign.net/forums/boat-design/lines-plan-29882.html#post310553
     
Loading...
Similar Threads
  1. PieroF
    Replies:
    1
    Views:
    125
  2. Slingshot
    Replies:
    16
    Views:
    1,855
  3. Luk
    Replies:
    5
    Views:
    836
  4. massandspace
    Replies:
    3
    Views:
    1,687
  5. sigurd
    Replies:
    10
    Views:
    1,918
  6. lucdekeyser
    Replies:
    5
    Views:
    1,191
  7. MichaelRoberts
    Replies:
    40
    Views:
    9,443
  8. motorbike
    Replies:
    37
    Views:
    7,268
  9. Remmlinger
    Replies:
    12
    Views:
    1,694
  10. Sherkin
    Replies:
    10
    Views:
    5,219
Forum posts represent the experience, opinion, and view of individual users. Boat Design Net does not necessarily endorse nor share the view of each individual post.
When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Your circumstances or experience may be different.