[FRIAM] Swirlies redux

Fri Aug 4 23:09:39 EDT 2023

Thanks, Eric.  '
I think it's startling to we ordinary mortals when we can toggle a physical
system from one obvious state to another with so little effort.  I realize
that that is what I am doing whenever I press a key on this computer, but
the computer has been arranged for my convenience.   Yes, the bottle and
the sink have also, but it does make me a little giddy to think that with
so little effort on my part I can alter the course of history in the sink.
It reminds me a little of Peirce's notion that the world appears orderly
only because order, however rare, has been seized upon by our evolutionary
ancestors.  To use Gibson's terminology, disorder affords nothing.  Well,
perhaps it does in the flight of butterflies or mosquitoes.

Anyway, sorry to press my luck.   It's great to hear from you, and I hope
you are well.

Nick

Nick

On Fri, Aug 4, 2023 at 10:44 PM David Eric Smith <desmith at santafe.edu>
wrote:

> Goddamnit.  “The fact that you can stir water ….”  (Not “store water”)
>
> Goddamned spell-changer does not work with a 12-inch screen and eyes that
> no longer work.
>
> On Aug 5, 2023, at 11:38 AM, David Eric Smith <desmith at santafe.edu> wrote:
>
> I think you have several variables in play at the same time here, Nick,
> and that will make it challenging to get clear what-all is involved, and
> what is controlling in what combinations.
>
> 0. Let me say something general, which won’t be comprehensible within this
> bullet, but which I will unpack a little in a later one.  I _expect_ that
> for some fairly symmetric shapes like soda bottles or sinks and drain pipes
> or whatever, under constant atmospheric conditions etc., water of
> properties that doesn’t change while it flows (not clear this applies to
> dishwashing remnant water with soap foams and scums), and so forth, there
> would be some unique steady state that was the true dynamical state the
> system would settle into over a sufficiently long time.  The simplest set
> of questions you could try to ask about would be the properties of that
> steady state: what it does as a transport process; what boundary conditions
> it depends on, etc.  What that means is, no bifurcations into several
> possible, but distinct, indefinitely long-persisting steady flow
> conditions. Give me that expectation for now, so I can make another point.
> Proving when it applies will be some nightmare of going into details, which
> I probably couldn’t do, certainly don’t have time and patience to try, and
> probably couldn’t put into English even if I could do it.  From that one
> question, everything else gets harder because more dimensions come into
> play.  In particular, there could a whole continuous parameter range of
> long-lived transients, which decay toward the long-term steady state only
> very slowly.  Your problem as a dishwasher or bottle tilter is: you may not
> have as long to wait as it takes those transients to decay.  It’s Keynses
> “in the long run, we are all dead” (Strictly: that was the point he was
> making.)
>
> 1. So at the least, the fact that you can store the water before pulling
> the plug, and affect the drain time, means you can put different amounts of
> angular momentum into the water that cannot get transferred out fully, fast
> enough to not leave an imprint on the draining.  Since the only way to get
> down the drain is to first get _to_ the drain, if you put enough angular
> momentum into the water, it makes it harder for any of it to get to the
> center.  Why (among other factors) hurricane eyes don’t close.  So indeed,
> you can stir in a way that gives the water slower access to the drain, and
> causes it to take longer to all get through it.
>
> 2. There is a different issue of closed versus open.  The reason the soda
> bottles mouth-to-mouth are so useful is that the only way water can go down
> is if air goes up.  But the bottles are small enough that for air to bubble
> up through the water requires getting through enough surface tension that
> it significantly affects the draining.  Having “enough” vortex to obviate
> that need then speeds your drainage.  But with the soda bottles too, if you
> spun them continuously, to keep introducing angular momentum to the water
> faster than it could transfer away toward the steady state by dissipation,
> I think it is sure you can affect the drainage.  I suspect the shape of the
> soda bottles is such that angular momentum equalizes toward the steady
> state more quickly.  A sink with a flat bottom should be very hard, because
> you can put in tons of angular momentum that doesn’t get quickly reflected
> back.  (Also, square or round perimeter and bowl shape of the sink, how
> full is it relative to width, and other such things.  It can get as
> complicated as billiards (not really, but figuratively), if you consider
> all the momentum reflecting around.).
>
> 3. The hard thing to do in emails or posts, and which really will require
> some computer program in the general case, is to figure out how gravity —
> in the infinitely long term — interacts with pressure and wall friction to
> resupply angular momentum to maintain a steady-state vortex, for a given
> vessel shape, mouth width, etc.
>
> The question of when you can make a universalizing claim, such as
> “symmetry breaking (like adding a rotation) will certainly increase or
> decrease a downward flow”, remains an important one, and many of us have
> daily instances of that problem in one or another area (ecological
> dynamics, physiology versus natural selection in populations, and on and
> on).  So, good to have ongoing interest.  The amount one has to say to have
> spoken carefully, to figure out what categories are coherent for which to
> try to generate answers, remains striking (at least to me).
>
> Eric
>
>
>
> On Aug 5, 2023, at 11:05 AM, Nicholas Thompson <thompnickson2 at gmail.com>
> wrote:
>
> Ok, folks. I apologize to those of you who are fed up with my kitchen
> physics, but there has been a bit of a development in that saga that I want
> to share with those few of you who aren’t.   Years ago, I came home for
> the summer with my ears ringing with the notion that structures are formed
> to dissipate gradients.  Please set aside any teleological implications
> of this statement and ask the question in its most neutral form:  Do the
> structures that sometimes form as a gradient is dissipated dissipate it
> more quickly once the structure has been formed.   Or, as I came to
> interpret it, does facilitating the formation of such a structure speed the
> dissipation of the gradient.
>
> I was the family dishwasher at the time.  I deplore washing dishes, but I
> love messing around with warm soapy water, and so I started to experiment
> with starting the vortex that forms *after* you pull the plug out of the
> sink *before* I pulled the plug.  Quickly, it became apparent that
> facilitating the vortex formation in that way GREATLY SLOWED the emptying
> of the sink.  Triumphally, I wrote Steve on Friam only to be greeted by a
> torrent of scatological raillery, so intense and so persistent from the
> fluid dynamicists on the list that I never heard from Steve. The burden of
> this raillery I have distilled into Roberts Rule of Order:  DEFROCKED
> ENGLISH MAJORS SHOULD NOT BE ALLOWED TO TALK about fluid dynamics.
>
> More than a decade later, I am back in Massachusetts, washing dishes at
> the same sink, and the question occurred to me again. I raised it finally
> with Steve, and he generously sent me the little two-bottle toy, where you
> flip it over and the water drains from one bottle to the other.  As it
> drains, it forms a vortex in the draining bottle, and the occurrence of the
> vortex greatly *increases* the speed of the draining.  Finally, if one
> facilitates the formation of the vortex by rotating the bottle a bit, the
> bottle drains even more quickly.  Thus, the result is entirely different,
> especially if one substitutes two large pop bottles for the ones included
> in the kit.
>
> At the risk of bringing another round of raillery down on my head, I opine
> that the difference has something to do with the fact that two bottle
> situation is more of a closed system than the sink situation.  The test
> would be to saw the bottom off both bottles and demonstrate that
> vortex-formation now slows drainage.
>
> It will be a while, though, before I can get two extra bottles to destroy.
>
>
> Does anybody care to make a prediction and offer an explanation why the
> results should be different in the two cases?
>
> Nick
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