Michlyt Demo

Discussion in 'Software' started by Leo Lazauskas, Apr 21, 2013.

  1. quequen
    Joined: Jul 2009
    Posts: 370
    Likes: 15, Points: 28, Legacy Rep: 199
    Location: argentina

    quequen Senior Member

    Leo, could you please save the michlyt demo file to an older MS Office version (2003)?
    .xml could work
     
  2. Leo Lazauskas
    Joined: Jan 2002
    Posts: 2,696
    Likes: 155, Points: 63, Legacy Rep: 2229
    Location: Adelaide, South Australia

    Leo Lazauskas Senior Member

    I tried, but it didn't work.
    The 2003 version removed the charts and the button that calls the dll.
     
  3. DMacPherson
    Joined: Mar 2005
    Posts: 139
    Likes: 28, Points: 28, Legacy Rep: 209
    Location: Durham, NH USA

    DMacPherson Senior Member

    Leo:

    This is more a question about high-speed hydrodynamics than your code, but it does pertain to both Michlet and Flotilla. For background, we are working up a new re-evaluation of the Series 64, as we have found discrepancies between the popular publication (Yeh) and the original raw test data. I can fill you in more about this at some other time.

    At the very high FN range (>1), we find a curious upswing of drag in the Series 64, as well as SKLAD, NPL, and others. I'm trying to wrap my head around the physics of this, and am not reaching anything that really explains it. I see in your Flotilla PDFs (e.g., bignpl_230413.pdf) the same upswing of test data above the prediction at FN>1.

    I have tried dynamic wetted surface and added spray drag as possible explanations, but in both cases, other test data on models with and without spray rails have refuted my initial hypotheses. Insel and Molland ran "linearized wave resistance theory" on their NPL models and they did show this upswing in CW, yet every other code I see (yours, mine, Doctors, etc.) all do not pick up this characteristic. Robards does trend in the right direction, but I think this is from his treatment of form factor and not really a model of this test behavior.

    Comments? Is this simply an artifact of proper consideration of sinkage and trim? In some of the models, there is a corresponding increase in trim with drag, which from a "planing" perspective would be unexpected. So, I looked at spray (which I believe could influence the trim increase), but my predictions of added drag were generally not quite sufficient (although we are reviewing it again).

    A curious characteristic that I hope you can illuminate. Thanks.

    Don MacPherson
    HydroComp
     
  4. daiquiri
    Joined: May 2004
    Posts: 5,371
    Likes: 258, Points: 93, Legacy Rep: 3380
    Location: Italy (Garda Lake) and Croatia (Istria)

    daiquiri Engineering and Design

    Since I don't have an insight to the raw data in you hands, please consider this just a loud thinking. Also, please excuse me for jumping into a question directed to another person... :)

    A contemporary increase in trim and drag make me think that there could be some local phenomena related to the transom stern, which is not predicted by the mathematical model you use. Perhaps a local region of low pressure, some sort of "transom stern suction" in the speed range of transition between wet and dry transom condition, which might create said effects?

    Cheers
     
  5. Ad Hoc
    Joined: Oct 2008
    Posts: 7,774
    Likes: 1,679, Points: 113, Legacy Rep: 2488
    Location: Japan

    Ad Hoc Naval Architect

    I would be interested to see what discrepancies you have found and the raw data itself; if it's different from the published and what we have too.

    We have used series 64 hulls for pretty much all our cats, with slight mods. We donated one of our model to Prof Molland which he has used extensively since for his own research too.

    BTW..Leo is "deep in thought" on some research so wont be replying for several days or about 1 week.
     
  6. tomas
    Joined: Nov 2012
    Posts: 280
    Likes: 16, Points: 0, Legacy Rep: 147
    Location: California

    tomas Senior Member

    Hehe, he posted this in another thread recently:
     
  7. DMacPherson
    Joined: Mar 2005
    Posts: 139
    Likes: 28, Points: 28, Legacy Rep: 209
    Location: Durham, NH USA

    DMacPherson Senior Member

    We're working up a new series prediction method for the Series 64, with the intention of making it available once we're done (probably as a paper for a journal). I'll be able to provide more details later.

    If you pull out the Yeh paper and look at the three plots of CR curves (for the three CB values), you'll note that the 0.45 CB curves are very tight, while the 0.35 and 0.55 have much greater scatter. This seemed out of place to me, so we began cross plotting the figures.

    For example, plot the SLR=3 points against volumetric fineness coefficient (as opposed to block coefficient) and there is a lot of unfairness in the curve. We dug up the original test data, and it became clear that the manual fairing (and perhaps just bad test data) as presented in the Yeh paper was OK, but actually not a very tight representation of the real series. I believe that our current work is a more faithful representation of the "series" as a whole, not just a collection of plots of individual tests.

    So, in trying to put a more contemporary treatment on CR prediction, we looked to a variety of hydrodynamic "frameworks", and none did a good job treating or explaining the sharp upswing of the drag curve above FN=1. Leo notes in a couple of his validation papers that he considers this splash or spray. It very well could be, except that Insel shows this characteristics in his linear code without any consideration of splash or spray. I'm still looking int the spray drag possibility, but I am not optimistic that this tells the whole story.

    Don
     
  8. Leo Lazauskas
    Joined: Jan 2002
    Posts: 2,696
    Likes: 155, Points: 63, Legacy Rep: 2229
    Location: Adelaide, South Australia

    Leo Lazauskas Senior Member

    Don,
    Apologies, but I don't have time to go into much detail at the moment.

    I am very wary of experimental data for depth-based Froude numbers
    Fn_h > 0.8 because it is not always possible to achieve a steady
    state. The DTMB basin is very long and quite wide, so that should
    help. I know many NA's who use the Series 64 data, but I really wish
    somebody would re-run the tests, preferably in another tank for
    comparisons. I don't like relying on one set of experiments and it
    wouldn't surprise me if there were differences of 10% or more for some
    Froude numbers.

    It would also seem imprudent to use that Series 64 data to extrapolate
    from finite depth, finite width results to full scale in deep water of
    infinite extent.

    The Series 64 experiments were conducted in water of depth h=6.71 m.
    That means that Fn_h = 0.8 at a speed U = 6.49 m/sec, which corresponds
    to a length based Froude number of Fn_L of about 1.2. That's roughly
    where there the "upswings" begin. Squat behaves peculiarly at those
    Fn_h too, which complicates matters.
    And to make matters even worse, in narrow tanks there is a jump
    (downwards) in the wave resistance at the critical Fn_h. Again, that
    shouldn't be much of an issue in the DTMB basin, but it is in narrower
    tanks.

    The NPL results (NPL 3b to NPL 6c) are also very dodgy for Fn_L > 0.8.
    For these hulls (which were measured in water of depth 1.85 m) I am
    suspicious of the experiments for Fnh > 0.8, or Fn_L > 0.87.

    Splash and spray will play some role in the discrepancy but, like you,
    I'm not convinced it's the whole story.

    Robards' results should be treated with caution because of the form
    factors he applies to the wave resistance and skin-friction. It's a
    perfectly acceptable engineering technique but, as one of your more
    poetic professors once said to me: "Give me two free parameters and I
    can fit a curve to my grandmother's fat ***".
     
    Last edited: May 3, 2013
  9. DMacPherson
    Joined: Mar 2005
    Posts: 139
    Likes: 28, Points: 28, Legacy Rep: 209
    Location: Durham, NH USA

    DMacPherson Senior Member

    No worries, Leo. We can let this simmer for a while.

    However, I am pretty confident that shallow water effects are not the cause of this behavior. While I am in complete agreement that things begin to happen at FNH=0.8 and that this is about FNL=1.2 for the Series 64, the other metrics against water depth are far too low for shallow water drag to be meaningful (e.g., AX^0.5/H=0.014, L/H=0.45, T/H=0.019).

    So, I'm going to revisit the possibility of spray as the culprit, and gather some additional test data to try and develop a simple estimate for the influence of spray. We will see what we see...

    Don
     
  10. fedevrzz
    Joined: May 2013
    Posts: 1
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: Varazze

    fedevrzz New Member

    Leo,

    i'm working on a power prediction for a catamaran of 20 meters and i would like to use the program Michlet.
    But i'm not sure that i can study this hull with this software.
    Below you can find a hull transversal view.
    [​IMG]
    As you can see the catamaran has 2 hulls mirror each other instead of 2 identical hulls transversally spaced from each other by a determined distance "y".
    I think this hull has been created by divising a classic mono-hull.
    Let me know if Michlet can also function in this case.
    Starting from 3D Rhino surfaces, i would like to import half catamaran to Delftship (Delftship reflects the other half automatically) and then export it all in Michlet considering the catamaran as a mono-hull.

    Can i use Michlet in this way?

    Need to use another method?

    thank you
     

  11. Leo Lazauskas
    Joined: Jan 2002
    Posts: 2,696
    Likes: 155, Points: 63, Legacy Rep: 2229
    Location: Adelaide, South Australia

    Leo Lazauskas Senior Member

    Michlet will not help you much with this vessel.

    I use my own program "Flotilla" to study similar hulls when they are used as
    the side walls of Surface Effect Ships, but I have not yet released that
    program into the public domain.
    (If you are prepared to pay, I can calculate the resistance, squat and wave-wakes for you.)

    Good luck!
     
Loading...
Similar Threads
  1. bingli
    Replies:
    2
    Views:
    3,512
  2. yipster
    Replies:
    0
    Views:
    2,321
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.