hydrostatics calculation

Discussion in 'Software' started by sujeethmonu, Aug 1, 2013.

  1. sujeethmonu
    Joined: Jan 2013
    Posts: 29
    Likes: 0, Points: 1, Legacy Rep: 3
    Location: india

    sujeethmonu Asst Professor(mech dept)

    In freeship, I tried to find the hydrostatics by entering the
    start draft=0m
    end draft=1.7m
    step draft=0.010m
    trim=0.377m (which is the default value when i opened "hydrostatics" under calculation tab.
    I got the result in .txt format which shows the calculation only till draft of 0.280m. I tried varying draft step and tried other combinations as well but unable to calculate hydrostatics till the actual draft of 0.377.

    1) What is the reason for this?
    2) When i click on "hydrostatics", i get a window where the trim is default at 0.377m WHY?
    3) In "design hydrostatics" midship draft =0.377m. Is trim = midshift draft. I think Trim=draft forward-draft aft.
    I hope i'm not completely mistaken. Please help!
     
  2. daiquiri
    Joined: May 2004
    Posts: 5,373
    Likes: 247, Points: 73, Legacy Rep: 3380
    Location: Italy (Garda Lake) and Croatia (Istria)

    daiquiri Engineering and Design

    My guess is that the calculation stops at 0.28 m because on the next step the program finds a leak point, a hull opening, an open transom or similar. In simple words, you have a point in your hull through which water can enter. In mathematical wording, at some draft the underwater surface which describes your hull is no more simply connected, which appears to be a necessity for Freeship in order to work properly.

    How about posting your .fbm model here, so that we can check it out and try to find the leak point?

    Cheers
     
  3. sujeethmonu
    Joined: Jan 2013
    Posts: 29
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    Location: india

    sujeethmonu Asst Professor(mech dept)

    hydrostatics

    thanks for the help
     

    Attached Files:

  4. daiquiri
    Joined: May 2004
    Posts: 5,373
    Likes: 247, Points: 73, Legacy Rep: 3380
    Location: Italy (Garda Lake) and Croatia (Istria)

    daiquiri Engineering and Design

    I have performed the calculation with no problems. However, I have set the trim to 0.

    A trim of 0.377 is equal to boat's design draft, which means that the ship is so inclined that very soon the transom would get submerged during the calculations. That is probably the reason for the premature end of calcs.

    Cheers
     
  5. daiquiri
    Joined: May 2004
    Posts: 5,373
    Likes: 247, Points: 73, Legacy Rep: 3380
    Location: Italy (Garda Lake) and Croatia (Istria)

    daiquiri Engineering and Design

    A note about your model: it has awfully lots of control points! :eek:

    It must have been a real mess to create a fair surface with such a huge number of control points. They also slow down and eat the memory of the computer, because with so many points the hull surface becomes mathematically too complex.

    My advice is to keep the number of control points to a minimum required to give the hull a shape which you need. In this case a net of 15x10 control points should have been enough.

    Cheers
     

  6. sujeethmonu
    Joined: Jan 2013
    Posts: 29
    Likes: 0, Points: 1, Legacy Rep: 3
    Location: india

    sujeethmonu Asst Professor(mech dept)

    thanks a lot for the help, after changing trim to zero, i got hydrostatics till draft of 0.450
    evn if end draft is 1.7m. and the reason is leak point at/after 0.450m of draft
    i increased control points thinking it may give accurate values as meshing increases.
    but actually, trim is not equal to zero. because by running design hydrostatics (in "design hydrostatics.txt"), angle of trim=2.001dgr

    Part of the text file is as follows
    Parameters of ship sinkage:
    Difference of midship draft : 0.000 m
    Midship draft : 0.377 m
    Initial transverse metacentric height ho : 2.653 m
    Initial longitudinal metacentric height Ho : 21.125 m
    Angle of heel Psi : 0.000 degr
    Angle of trim : 2.001 degr
     
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