Posted by
Hugh Trenchard on
Nov 26, 2009; 2:33am
URL: http://friam.383.s1.nabble.com/flocking-windmills-tp4062545p4069060.html
My understanding of drafting in the peloton is that
there is a low pressure area induced behind riders, meaning there is less air
resistance to the riders following, and hence less energy is expended by
riders following in low pressure areas (1,2). It's not lift, like it is in the bird vee formation (as Peter Lissaman
points out). There has been some suggestion that the lead rider also
benefits by a "nudge" from the rider behind who fills the low pressure
zone (3), but this is disputed (4). So energy savings in pelotons is not
strictly due to eddies either.
Efficiencies in bicycle
racing (ie. increasing speed for least possible power output) increase
as the peloton becomes denser, because greater energy
savings occur the closer a cyclist behind can get to the wheel in
front (1,2,4). This must be balanced against the increased risk for
collision cyclists undergo as peloton density
increases. The notion of a "shrink-wrapped" peloton well
describes the correlation between optimal peloton speed and density, and
seems to me a better description than the eddie model Roger C is
describing.
The staggering of cyclists in a peloton is due to
its dynamical nature and the necessity for cyclists to avoid collision, and not
because it is the theoretical absolute optimal energy savings
formation. That is to say that the maximum drafting benefit is directly
behind others (excluding cross-winds for the moment) (1,4), which does
not practically occur in a peloton (except in what I call a "stretched"
phase, which I won't get into here). Rather, a
dynamical arrowhead, rounded, or rotational effect to the peloton
occurs at a certain power output threshold (which is within a narrow
range for all riders) as riders rotate through positions at the front,
each seeking to save energy by drafting; optimal collective output occurs
during this phase (based on personal observation and analysis).
I don't profess a good understanding of the eddy
principles that Roger is describing in the windmill formation, but as I gather
them, the principles he describes do not seem to closely describe the
peloton formation, as you've pointed out. Also, unlike the static windmill
formation, the peloton is a dynamical system, and so its collective
output optimization also depends on the movements of the agents within
the system as they respond to each other and environmental
parameters. So, in that respect, the article may be a bit loose in
referring to the peloton as an analog.
However, it seems to me the main idea is that
there is overall energy saved by a particular collective formation.
Whether it's drafting or by creating eddies or by lift, the mechanism may
be different, but these principles of energy savings allow for generalized
flocking phenomena to occur in natural systems, which is, in general principle,
what the windmill engineers are exploiting.
Refs
1. Kyle C. 1979 "Reduction of wind resistance and
power output of racing cyclists and runners travelling in groups" Ergonomics
22: 387-397;
2. McCole et al 1990 "Energy expenditure during
bicycling" Journal of Applied Physiology 68: 748-753
4. Olds, T. 1998 "The mathematics of breaking
away and chasing in cycling" 77. Eur J App Phiol 492-497
----- Original Message -----
Sent: Wednesday, November 25, 2009 9:43
AM
Subject: Re: [FRIAM] flocking
windmills
Cyclists want lift??!! How do they
maintain contact with the road?
N
Nicholas S. Thompson
Emeritus Professor of Psychology and Ethology,
----- Original Message -----
Sent: 11/25/2009 10:26:08 AM
Subject: Re: [FRIAM] flocking
windmills
No, the pelaton uses the lead rider to break a
bow wave through the air, but the eddies from each rider's passage also curl
around to give some lift to the subsequent riders in the pelaton. If
you smoothed it out into one long cylinder, it wouldn't work as well.
The vertical wind turbines work as a flock because they induce
a sort of do-si-do of the wind through the flock, where each rank
of turbines is positioned to catch the eddy from the preceding rank and
throw it back to the next rank. Because the wind takes a longer than
straight path through the flock, it has to move faster than the unimpeded
wind. If you just set up a stonehenge in the same arrangement as the
flock of turbines, you'd get the same sort of velocity effect.
Having the flock adjust its geometry could be a big win. A fixed
installation would be tuned to the most likely wind speed and
direction.
-- rec --
On Wed, Nov 25, 2009 at 9:58 AM, Nicholas Thompson
<[hidden email]>
wrote:
Hugh,
Thanks for explaining this to me. I figured it was something
like that.
But the logic IS backwards with respect to the bike racer
model. The Bike racer pod is trying to protect the lead racer
from wind resistance, the wind mills are trying to pass that resistance
through to ever member of the pod.
We could shrink-wrap the bike-pod, and it would do its job even
better. Not so the windmill pod.
Right?
N
Nicholas S. Thompson
Emeritus Professor of Psychology and Ethology,
----- Original Message -----
Sent: 11/25/2009 7:15:27 AM
Subject: Re: [FRIAM] flocking
windmills
...that should read "rotate the position of
the fans 90 degrees" (it was late and I should have been in
bed).
----- Original Message -----
Sent: Wednesday, November 25,
2009 12:05 AM
Subject: Re: [FRIAM] flocking
windmills
It looks to me the article addresses
this. When windmills are in a conventional "face to the wind"
position, they do need to be well spread out in order to catch as much
wind as possible. But if you rotate the position 90 of the
fans degrees so that they are spinning "sideways", they spin with
greater efficiency when lined up behind each other in zones
of lower air resistance. The article appears to refer to this
fan position as a "vertical" rotation. The photo shows
"vertically" rotating tube like structures, which are much like long
fans turned on their sides. Aligning them in fish school
formation evidently is the most efficient in terms of space and
maximal wattage generation. That's how it all appears to me in
any event.
Hugh Trenchard
----- Original Message -----
Sent: Tuesday, November 24,
2009 9:45 PM
Subject: Re: [FRIAM] flocking
windmills
Sorry, everybody. What I meant to write was,
"Wait a blithering moment!!!", suggesting,
at least, that the metaphor between bunching up cyclists
and bunching up windturbines was backwards. Don't you WANT
your turbines to "feel" the "headwind"?
Of course I am wrong about this, but I sure would like to
understand why.
Nick
Nicholas S. Thompson
Emeritus Professor of Psychology and Ethology,
----- Original Message -----
Sent: 11/24/2009 10:13:22 PM
Subject: Re: [FRIAM] flocking
windmills
What they lack is mobility - lacking
some sort of mobile platform maybe they could get together and
decide where the next best placement would be and tell the
manufacturing and installation people. Some sort of
distributed instantiation - Group orders another member, turbine
shows up in the mail, speaks up, says, "I am a wind turbine, the
group has determined that it will be most efficient if you place
me over there." And the humans would go do that, since the turbine
family was usually right about such things.
So maybe the
turbines "want" some particular configuration, the friction is
just one criteria. If they were a phased array antenna
(in addition to being a group of wind turbines) then they would
have additional criteria.
C
Nicholas Thompson
wrote:
Now what a blithering moment. Cyclists flock to
reduce friction. Ditto fish, I suppose.
So, turbines want less friction with the wind?????
Something screwy here.
N
Nicholas S. Thompson
Emeritus Professor of Psychology and Ethology,
----- Original Message -----
Sent: 11/24/2009 7:36:30 PM
Subject: [FRIAM] flocking windmills
Same power production as existing wind farms in
100th the land area.
-- rec --
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at St. John's College
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FRIAM
Applied Complexity Group listserv
Meets Fridays 9a-11:30 at cafe at
St. John's College
lectures, archives, unsubscribe, maps at http://www.friam.org
============================================================
FRIAM
Applied Complexity Group listserv
Meets Fridays 9a-11:30 at cafe at St.
John's College
lectures, archives, unsubscribe, maps at http://www.friam.org
============================================================
FRIAM
Applied Complexity Group listserv
Meets Fridays 9a-11:30 at cafe at St.
John's College
lectures, archives, unsubscribe, maps at
http://www.friam.org
============================================================
FRIAM Applied Complexity Group listserv
Meets Fridays 9a-11:30 at cafe at St. John's College
lectures, archives, unsubscribe, maps at
http://www.friam.org