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Hi all . . . Okay,
so I've dug through some more stuff, looked at Mothra1 videos, skybow
videos (most links from Yahoo group site to skybow material are dead by
the way), etc. Summarizing, arch kites have two potential applications in AWES. 1. Lift actual generators into the air 2. Generate power from oscillations of arches 1. Lift actual generators into the air This
seems a bit iffy to me because as a paraglider I watch videos of people
who know what they are doing with much simpler in air configurations
end up tangled, having collapses and being tossed around. The air is
chaotic. Putting multiple things close to one another in the air
on strings means that they will often end up wrapped around one another
in ways that degrade or eliminate flight, and take time to untangle as
well. Also, unless I'm missing something, arch
kites form shallow parabolas. All examples I was able to find had
much greater breadth than altitude. This implies one of two things,
both of which have limiting implications for power generation in higher
winds aloft, the point of the game. a/ I drew
a little diagram to help me understand. It's undoubtedly wrong in a few
ways, but it was helpful to me. Fundamentally, the area of concern is
the area under the arch at sufficient altitude to have strong and
stable winds. Individual small wind generators under the arch are going
to have much smaller swept areas than a HAWT. Even to get a bunch of
small generators, perhaps a dozen 75KW generators into the same wind
velocity space as a single 3MW HAWT would require an arch height of
roughly 180-200 meters, and an arch length likely four times that long,
700-800m. The scaling is rough and the assumption is HAWT
technology, but spacing is important and so without doing a lot of
math, it would seem that this have a total swept area substantially
smaller than the HAWT and generation of perhaps a third. Depending on
what you were intending to lift, you've got a downwind range of 200-300
meters as well for launch and landing. In
order to scale up, the arch has to get higher, but the span at the base
has to increase by a multiple factor of 3-4 it appears. This rapidly
becomes a limiting factor obviously. b/
Another option are these ring concepts where a ring structure requiring
high structural stability and substantial weight is lifted into the sky
by the arch with generators under the arch. Complexities and
liabilities increase exponentially. I also found and read this earlier post of Dave's on stacked arches (http://groups.yahoo.com/neo/groups/AirborneWindEnergy/conversations/topics/5943) .
This extends airspace upwards while covering more ground downwind of
course, and has the same problem of airborne complexity, low actual
swept area and heavyweight electrical components. Once again, if there
is anything more than the concept of lifting heavy objects and complex
inter-arch structures, please point me to it. Having looked at
pictures and videos of air structures, I see opportunity for very low
swept area generators filling in some empty space, but nothing to
compare to the equivalent swept area of a modern HAWT. I've
also looked at many of Rod Read's 3d models as well as videos of his
prototypes. 3D modelling, while a necessary and valuable step to reduce
overall development time, is even more problematic than
necessarily limited simulations (see below). I spent a couple of years
doing NURBS-based 3d models in Rhino of much simpler systems (e.g.
robotics, furniture, architecture) than complex, airborne kites in
dynamic suspension, and now how little connection 3d models have to
messy reality. All of these arch-based
lifting solutions require substantial amounts of electrically
conductive wiring, and will also require technology in the air to
aggregate the generated electricity for the conductive line to the
ground. None of this is light, and once again falls further and further
away from the concept of rags and string. Complexities in air are
increasing more than exponentially. So
I'm basically not buying lifting generators into the air using an arch.
It's not passing the sniff test. Using an unstable structure subject to
chaotic air conditions to lift large weights is not proven or reliable
as far as I can tell, and so lifting substantial generation capacity
into the air seems unlikely at best. Once
again, if there is a complete conceptual system with most parameters
laid out and calculations of generation capacity, please point me to
it. And if there are current examples of arches lifting complex
and heavy structures into the air and keeping them there in a
semi-stable way, please point me to them. Right now, I'm not seeing any
published technical papers or real world prototypes on this approach
outside of Mothra which is just keeping itself up. 2. Oscillation power generation The
Skybow example -- I found a video with RPM measurements -- is
informative. This is a case of very high RPM but very low torque, the
opposite situation of arches. In this situation, attempting to gain any
substantial amount so electricity from the rotations would kill them,
eliminating the value proposition. The skybow would rotate shut rapidly
and fall out of the air. This too fails to pass the sniff test
due to lack of sufficient torque. I'm happy to be proven wrong of
course. I'm very familiar with other
oscillation effects from my paragliding and kiting. However, while the
forces might be significant, introducing harvesting into the equation
will substantially alter them, and once again I would like to be
pointed to a technical paper or prototype that elaborates upon the
concept sufficiently that useful analysis can be done. I
found Jeroen Breukel's thesis and glanced through it, but it is
concerned with modelling individual kites and solid tethered wings, not
oscillations. At that, the modelling already requires supercomputer
resources. http://www.lr.tudelft.nl/fileadmin/Faculteit/LR/Organisatie/Afdelingen_en_Leerstoelen/Afdeling_AEWE/Applied_Sustainable_Science_Engineering_and_Technology/Publications/doc/Thesis_Jeroen_Breukels_Compressed.pdf Regarding
simulation, I'll put a cautionary note in. Complex fluid dynamic
calculations and simulations keep convincing people that ducted and
shrouded wind turbines of various types will work better than open air
HAWTs. Every built device vastly under performed simulations due to
factors not modelled and readily model able in simulations. Every
one. In other words, simulation is useful but nothing compares to
actually building a working prototype, especially if it expects to
fly. Net-net: I
think the idea of pumping a flywheel or similar mechanical device with
elastic oscillations interesting. Have any calculations been done on
this or is it purely conceptual at this point? I was unable to find any
published papers by Jeroen on that work. Please link if possible. |
