Pressure Underwater of Ship

Discussion in 'Hydrodynamics and Aerodynamics' started by waNsi, Apr 17, 2016.

  1. Ad Hoc
    Joined: Oct 2008
    Posts: 5,943
    Likes: 319, Points: 83, Legacy Rep: 2488
    Location: Japan

    Ad Hoc Naval Architect

    I'd go further. All research has many wonderful possible applications...military is just one of them. But sadly gets the lions share of the funding :(

    Exactly like the 'classic' temperature inversion one sees in valleys. Smoke rising from a fire in the depths of the valley..only going so far up..and the plateaus and is prevented from rising, by the 'oddly' located colder air above.

    If i recall correctly from my A-Level Physic, isn't that also Newton's Law of Cooling related to Black body radiation?
     
  2. Leo Lazauskas
    Joined: Jan 2002
    Posts: 2,696
    Likes: 145, Points: 63, Legacy Rep: 2229
    Location: Adelaide, South Australia

    Leo Lazauskas Senior Member

    It's too long ago for me to remember the details of how it enters calculations of energy
    and temperature but it's certainly not simple!
    There are many inter-acting pieces in the puuzzle.

    At one stage when my colleague and I were working on aerating and destratifying large
    bodies of water, my father-in-law was dying in hospital. I went to visit him on the night he
    died, and thanked him for all that he had done for me and for encouraging my scientific
    pursuits.
    I'm not sure he heard all I said, but his last words to me, delivered in a whispery wheeze,
    were: "Don't forget the latent heat of vaporization!".
    Some guys are just nerds to the very end!

    WAVE RESISTANCE OF MUDDY LAYERS
    I just remembered another very important reason why sea-bed pressures are important...
    Ship-induced sea-bed pressures can create waves in muddy layers. That increases the
    resistance experienced by the ship in a similar way to the "dead-water" phenomenon
    where fresh water lies above sea-water, e.g. near the fjords of Scandinavia after winter.
     
  3. rwatson
    Joined: Aug 2007
    Posts: 5,784
    Likes: 265, Points: 83, Legacy Rep: 1749
    Location: Tasmania,Australia

    rwatson Senior Member

    Bless him. A great ending.

    My favourite is ...

    ""When I meet God, I am going to ask him two questions: Why relativity ? And why turbulence ? I really believe he will have an answer for the first." — Werner Heisenberg (1901-1976), german physicist, on his deathbed.
     
  4. Leo Lazauskas
    Joined: Jan 2002
    Posts: 2,696
    Likes: 145, Points: 63, Legacy Rep: 2229
    Location: Adelaide, South Australia

    Leo Lazauskas Senior Member

    I think there is some uncertainty about the provenance of that quote " :p

    Horace Lamb was at Adelaide Uni for a few years, so I'm biased...

    "In 1932 Lamb, in an address to the British Association for the Advancement of Science,
    wittily expressed on the difficulty of explaining and studying turbulence in fluids. He
    reportedly said, "I am an old man now, and when I die and go to heaven there are two
    matters on which I hope for enlightenment. One is quantum electrodynamics, and the
    other is the turbulent motion of fluids. And about the former I am rather optimistic.""

    https://en.wikipedia.org/wiki/Horace_Lamb
     
  5. Mr Efficiency
    Joined: Oct 2010
    Posts: 7,391
    Likes: 233, Points: 63, Legacy Rep: 702
    Location: Australia

    Mr Efficiency Senior Member

    How ironic that the death-bed quip of Heisenberg is a matter of uncertainty, considering he is famous for the "Uncertainty Principle" !
     
  6. waNsi
    Joined: Apr 2016
    Posts: 12
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: Iran

    waNsi Junior Member

    Thank you very much for your PDF.

    It would be very helpful if you could mention some references related to your work which help me to proceed faster. Although we want to study the underwater pressure experimentally, numerical concepts would be some clues to our problem.

    I think science is pure and sinister is people who use them in bad manners. That is true that human did use atomic bomb to harm themselves but maybe one day human can use it for preventing their extinction. =))

    My project is a part of a commercial project for a harbor in the north of Iran. Our goal is to manage harbors so that they can define ships (automatically) for arranging them in the best way possible. In this project my part is using the pressure to distinguish ships, and other parts will tackle by others.
     
  7. waNsi
    Joined: Apr 2016
    Posts: 12
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: Iran

    waNsi Junior Member

    :) It seems you are suspicious. Leo made you afraid but don't be.

    My project is a part of a commercial project for a harbor in the north of Iran. Our goal is to manage harbors so that they can define ships (automatically) for arranging them in the best way possible. In this project my part is using the pressure to distinguish ships, and other parts will tackle by others.
     
  8. Leo Lazauskas
    Joined: Jan 2002
    Posts: 2,696
    Likes: 145, Points: 63, Legacy Rep: 2229
    Location: Adelaide, South Australia

    Leo Lazauskas Senior Member

    Here are a few references that you might find useful.
    There are many more in the bibliographies.

    Zilman, G., Miloh, T. and Doctors, L.J.,
    "THE INFLUENCE OF A BOTTOM MUD LAYER ON THE RESISTANCE OF MARINE VEHICLES",
    Ship Technology Res, v 43 n 2, May 1996, p. 51.

    Shemdin, O., Hasselmann, K., Hsiao, S,V, and Herterich, K.,
    "Nonlinear and Linear Bottom Interaction Effects in Shallow Water",
    in Turbulent fluxes through the sea-surface, wave dynamics and prediction.
    pp. 347-372.

    Hans van Haren,
    "Ship-induced effects on bottom-mounted acoustic current meters in shallow seas",
    Continental Shelf Research,
    Volume 29, Issue 15, 20 August 2009, pp. 1809–1814.
     
  9. waNsi
    Joined: Apr 2016
    Posts: 12
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: Iran

    waNsi Junior Member

    Thanks you very much Leo.
     
  10. cmckesson
    Joined: Jun 2008
    Posts: 161
    Likes: 7, Points: 18, Legacy Rep: 55
    Location: Vancouver BC

    cmckesson Naval Architect

    So, the original question was "Can we do this experimentally? Will it scale properly? Which towing tank should we use?"

    I think it's a clever idea, to use the pressure signature to characterize the arriving ships and make this data available for harbor management. On our coast, since we have mandatory pilotage and VTS, we would rely on VTS and AIS data for this. But we do have underwater hydrophone arrays monitoring ship acoustic emissions...

    Returning to the original questions: If Ernie Tuck found that a Michell's Integral based predictive approach worked, then this confirms to me that this problem YES will scale properly using Froude scaling from experiment.

    Next, the question is "What characteristics of towing tank are needed?" I think the key here will be to have proportions that avoid blockage in the tank. I haven't looked at the references on that, but my guess is that this means a tank width at least 5x the depth, thus 100m (scaled.) Finding a tank the wide and shallow will be hard - most are approximately square in cross-section proportion.

    So now I wonder, can we install a false bottom in the tank in order to get the wide/shallow proportions we need? (Note that we _do_ need a bottom, or the pressure effects will not represent the full scale case.)

    So now, we are looking for a tank that can accept a false bottom, and that has a library of appropriate ship models so that we can collect signatures without the expense of a lot of model construction.

    I don't know what tanks are "local" to Tehran. My own research has mostly been conducted in Trondheim Norway at Marintek. But I wonder if some of the academic tanks could be used? Michigan has a good facility. The University of New Orleans has a good facility at very moderate prices. Those, of course, are in the USA which may not be practical.

    Are there any tanks in Turkey? Does NTUA in Athens have a tank?

    All the best,

    Chris McKesson
     
  11. Leo Lazauskas
    Joined: Jan 2002
    Posts: 2,696
    Likes: 145, Points: 63, Legacy Rep: 2229
    Location: Adelaide, South Australia

    Leo Lazauskas Senior Member

    Minor point: Tuck used slender body theory which is even simpler than Michell theory.
    The required equations end up as special functions that can be approximated very
    quickly and accurately by series.
     

  12. daiquiri
    Joined: May 2004
    Posts: 5,372
    Likes: 239, Points: 73, Legacy Rep: 3380
    Location: Italy (Garda Lake) and Croatia (Istria)

    daiquiri Engineering and Design

    Sounds like a very interesting projects, but I wonder how practical it is to use pressure sensors for this purpose?
    I do not have a specific knowledge in underwater pressure sensor technology, but I do know how quickly the marine fouling can spoil man-made things.

    Given that these sensors will be permanently positioned in an array (or a net) on the sea bed, I wonder how long will it take before the nature deteriorates their sensing characteristics?

    Edit:
    Found this interesting article which discusses the issue and impact of biofouling on underwater sensors: http://www.ocean-sci.net/6/503/2010/os-6-503-2010.pdf
    It also gives an answer to the question "how long will it take..." - it can be a matter of just a week, if the environmental conditions are right.
     
Loading...
Similar Threads
  1. Zha
    Replies:
    8
    Views:
    477
  2. Thiago da Silva Lopes
    Replies:
    0
    Views:
    428
  3. Hildershavn
    Replies:
    28
    Views:
    2,134
  4. wavebridge
    Replies:
    5
    Views:
    976
  5. Binze
    Replies:
    16
    Views:
    4,704
  6. kalvens
    Replies:
    9
    Views:
    3,363
  7. MechaNik
    Replies:
    58
    Views:
    12,181
  8. endorium
    Replies:
    38
    Views:
    4,931
  9. jerseysportfish
    Replies:
    1
    Views:
    1,839
  10. fredschmidt
    Replies:
    173
    Views:
    39,603
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.