Squid Jet Physics

Discussion in 'Physiology and Biology' started by OctoPussyAZ, Nov 22, 2005.

  1. OctoPussyAZ

    OctoPussyAZ Wonderpus Supporter

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  2. Fujisawas Sake

    Fujisawas Sake Larger Pacific Striped Octopus Supporter Registered

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    Actually, this is pretty cool.

    I think that its actually a biological application of Bernoulli's principle, with a few mods taking into account other forces. I could go into more detail if you like.
     
  3. Feelers

    Feelers Vampyroteuthis Registered

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    So can they only use one jet? And then have to stop and refill before using the jet again?

    I was thinking this just because the intake for the jet is also at the head end - so sucking in would create a pull forwards - equal to the push backwards?
    I dont know anything really about hyrdodynamics - Fujisawas Sake if you could go into a bit more detail I'm interested :)

    I had a look at http://home.earthlink.net/~mmc1919/venturi.html to see what Bernoulli's principle was, but I dont see how it can be used to jet away multiple times? My theory was that maybe the water is drawn in from above and below then squirted forwards?
     
  4. OctoPussyAZ

    OctoPussyAZ Wonderpus Supporter

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    More via Pharyngula

    This is from Squid Blog (never heard of it before today) -- thanks again to PZ at Pharyngula...

    http://www.squidblog.net/2005/11/22/jet-flow-in-steadily-swimming-adult-squid/

    Feelers: It seems to me that, although the intake also faces backwards, it is of enormous area relative to the jet nozzle... But what do I know?

    The writer on SquidBlog is talking about some arcane Vortex ring propulsion stuff, anf the conclusion is, after experiments, is that the squid does not use this method.
     
  5. OctoPussyAZ

    OctoPussyAZ Wonderpus Supporter

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  6. Feelers

    Feelers Vampyroteuthis Registered

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    OctoPussyAZ - I was just thinking of the idea of getting out what you put in - I'm trying to think about it in terms of floating through space.

    If you catch a ball (intake water) you gain its momentum(in this case get sucked towards where you are intaking water), then if you throw the ball(faster than you caught it) away in the direction you caught it from- you will have a net gain in momentum.

    At least thats how I can figure it - and like you say Bernoulli's Principle is used to increase the velocity of "throwing the ball".
     
  7. um...

    um... Architeuthis Supporter

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    Feelers, I would agree that there's probably a shot of 'negative' momentum on the intake, although it's probably tiny compared to the momentum gained from the jet. I took fluid mechanics a million years ago, and I can't seem to remember whether there would be any advantage to a high velocity flow over a slower flow of greater volume. Power? Is it easier for muscle to move a small amount of water very quickly in a rapid succession of contractions? I have a pdf of the article, which I downloaded a week or two ago, but I forgot all about it until yesterday when PZ brought it up (I'm moving in two days--causes some distraction).

    Must go pack. Too bad the textbooks have been sealed for a week. :sad:
     
  8. bigGdelta

    bigGdelta Vampyroteuthis Supporter

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    I was going to use an example much like feelers' (two kids playing catch) but got called away from the computer and he beat me to it.
     
  9. Feelers

    Feelers Vampyroteuthis Registered

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    Its interesting that the squid doesnt have the intake at the posterior end.
     
  10. dub_doctor

    dub_doctor Blue Ring Registered

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    Actually, I was just quoting this article: http://jeb.biologists.org/cgi/content/full/208/6/iii

    [Edit: Sorry OctoPussyAZ, I didn't see your next post]

    Myself, I can't make much of the original article.

    I'd still love someone to make an animation of squids in motion, to demonstrate the conclusions of this paper. The abstract-style pictures in the original article are so uninformative to the non-expert.
     
  11. dub_doctor

    dub_doctor Blue Ring Registered

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  12. OctoPussyAZ

    OctoPussyAZ Wonderpus Supporter

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    Squid Squirts

    Hello Dub_Doctor:

    Did not know you were a member! Yeah, that stuff is tough to follow for laymen.
     
  13. Fujisawas Sake

    Fujisawas Sake Larger Pacific Striped Octopus Supporter Registered

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    Okay, so here’s what I meant about Bernoulli’s Principle being attached to squid physics:

    Bernoulli’s principle deals with fluid dynamics, pressure, and overall conservation of energy. It also deals with Newton’s Third Law of motion – that for every force there is an equal and opposite force. While Bernoulli’s work deals mostly with constant flow rate, we can modify this a little bit.

    Think of a squid mantle roughly as a curved tube with a large opening and small exit. Water goes in one end and comes out the other at a greater velocity, since the amount of water going in has to equal the amount coming out (This isn’t exactly the case, but close enough for government work, as goes the old saying).

    All types of fluid dynamics deal with a conservation of energy. Basically, energy going in has to be equal to energy going out. Amount of water entering in through large entrance is the same amount as water exiting through smaller tube end. It’s the same principle as using your thumb to jet water out of a garden hose. The water being forced through the small siphon exerts a force in the direction opposite the incurrent flow of water, causing the squid to jet “forward” (Newton’s Third Law).

    Also, if you take into account muscular mantle contraction and relaxation, those add more energy to the system, therefore you get a greater speed for jetting.

    I wonder if squid have mastered something akin to “circular breathing”? In humans, its something woodwind and brass players use to keep breathing while exhaling. In squid, it would mean that some water could enter the mantle while being expelled through the siphon.

    Bernoulli’s principles could also be used for determining the relationship between fin morphology and swimming energetics. For example, the four main forces in fluid dynamics are thrust, drag, lift, and weight. In an airplane, thrust comes from engines and tailwinds, drag comes from your coefficient of friction, lift comes from greater air pressure under the wing than above (another one of Bernoulli’s concepts), and weight is self-explanatory (The above example treats the atmosphere like a fluid – and that is exaclt what the atmosphere is). Well, do squid use their fins for powered swimming? Does the speed of the squid depend on the size of the fins? Is there an optimum morphological speed limit to each squid depending on what layer of ocean it inhabits?

    Food for thought.

    John
     
  14. um...

    um... Architeuthis Supporter

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    :feet:

    Actually, tailwinds don't produce thrust. If they're steady, then they simply add vectorially to the plane's speed over ground while remaining 'invisible' to the aircraft (i.e. not affecting airspeed). A sudden gust from astern would actually reduce the airspeed (bad!). This is one reason that planes take off going into the wind, if possible. Also, a significant portion of lift turns out to be due to Newton's third law: the wing produces a downwash which produces an upward-ish reaction force on the aircraft. Drag can be caused by factors other than friction (negative relative pressure at the rear of bodies, vortices, induced drag due to the aft-facing component of lift, etc.), although I think that skin friction is usually a dominant influence. And weight can be quite interesting if a plane is doing anything other than flying straight and level or sitting on the ground.

    :grad:

    :nofeet:

    An interesting application of Bernoulli to squid locomotion was brought up by Steven Vogel. A squid is streamlined, and when moving through the water experiences a lower static pressure around the outside of the mantle as suggested by Bernoulli (think of it as a cylindrical wing or an inside-out venturi tube). This reduced external pressure then aids in the reexpansion of the mantle. I'm curious about whether the effect actually saves the squid much energy.
     
  15. Fujisawas Sake

    Fujisawas Sake Larger Pacific Striped Octopus Supporter Registered

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    That's right! See? That's why I'm not majoring in physics! :lol: Yeah, I realized this error a few hours ago while I was making dinner and forgot to change it. Sorry. :tomato:

    You know, any bit of saved energy helps. I can see where that would be a great possibility.

    And it would be key in supporting a low-metabolism, high-speed lifestyle.

    Good question.
     
  16. Fujisawas Sake

    Fujisawas Sake Larger Pacific Striped Octopus Supporter Registered

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    Hey Um... - You into physics? What would you think the coefficient of friction for a squid skin?
     
  17. ArchyNorth

    ArchyNorth GPO Supporter

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    Wouldn't that have to depend on some environmental factors?

    Salinity is one I can think of off the top of my head.


    ** Edit. Humm, I think my college Physics is failing me here.

    The coefficient of friction is a constant right? So the environmental factors wouldn't influence it but act upon it... right?

    Man I need to pull those old text books out.
     
  18. Fujisawas Sake

    Fujisawas Sake Larger Pacific Striped Octopus Supporter Registered

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    You know, I'm really oversimplfying things - mostly because my own knowledge in Physics is so limited. I'm sure there's a lot more to friction (resistance) than I'm considering here.

    I think salinity would only affect density, but i'm not sure what other resistance factors would fall into play.
     
  19. monty

    monty Colossal Squid Staff Member Supporter

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    coefficient of friction may not be the appropriate metric here-- it usually refers to coulomb friction, which is linear in velocity, yet for drag stuff, usually the relevant factors are higher order in velocity. Fluid dynamics is frequently plagued with horrible nonlinearities.

    I'm not sure where conservation of energy comes in, either-- clearly, when jetting, the squid is expending energy in the mantle constriction, so it's not a constant-energy system. I'm pretty sure it's spending energy in sucking water in, too.

    My gut feeling is that energy alone is not the best way to look at this; I think understanding the momentum transfer of the intake and jet output of the water explains the gross behavior pretty well-- when the squid sucks in water, although it comes a bit more from the head than the mantle end, it's diffuse and comes in a wide aperture in a ring shape, so the change to the squid's momentum will be a little in the head direction (moving "backwards"). When jetting/exhaling, the mass of the water is ejected at higher velocity in a straight line directed by the funnel, pushing the squid forward. The mass of water is the same, but the velocity is both higher and much more directed.
     

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