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
3. Cycling Performance Tips. Excercise Physiology - Energy Requirements of
Bicycling http://www.cptips.com/energy.htm
4. Olds, T. 1998 "The mathematics of breaking away and chasing in cycling" 77.
Eur J App Phiol 492-497
----- Original Message -----
From: Nicholas Thompson
To: Roger Critchlow
Cc: friam@redfish.com
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,
Clark University (nthomp...@clarku.edu)
http://home.earthlink.net/~nickthompson/naturaldesigns/
http://www.cusf.org [City University of Santa Fe]
----- Original Message -----
From: Roger Critchlow
To: nickthomp...@earthlink.net;The Friday Morning Applied Complexity Coffee
Group
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
<nickthomp...@earthlink.net> 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,
Clark University (nthomp...@clarku.edu)
http://home.earthlink.net/~nickthompson/naturaldesigns/
http://www.cusf.org [City University of Santa Fe]
----- Original Message -----
From: Hugh Trenchard
To: The Friday Morning Applied Complexity Coffee
Group;nickthomp...@earthlink.net;Carl Tollander
Cc: Friam@redfish.com
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 -----
From: Hugh Trenchard
To: nickthomp...@earthlink.net ; The Friday Morning Applied
Complexity Coffee Group ; Carl Tollander
Cc: Friam@redfish.com
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 -----
From: Nicholas Thompson
To: Carl Tollander
Cc: Friam@redfish.com
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,
Clark University (nthomp...@clarku.edu)
http://home.earthlink.net/~nickthompson/naturaldesigns/
http://www.cusf.org [City University of Santa Fe]
----- Original Message -----
From: Carl Tollander
To: nickthomp...@earthlink.net;The Friday Morning Applied
Complexity Coffee Group
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,
Clark University (nthomp...@clarku.edu)
http://home.earthlink.net/~nickthompson/naturaldesigns/
http://www.cusf.org [City University of Santa Fe]
----- Original Message -----
From: Roger Critchlow
To: The Friday Morning Applied Complexity Coffee Group
Sent: 11/24/2009 7:36:30 PM
Subject: [FRIAM] flocking windmills
Same power production as existing wind farms in 100th the
land area.
http://sciencenow.sciencemag.org/cgi/content/full/2009/1124/1
-- rec --
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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
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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
