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Re: [AWES] Overspeed? what's that?

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  • dave santos
    Rod, Overspeed is a confusing term, since it requires adverse electrical load interactions, just as you suggest. In principle, an unloaded (open circuit) wind
    Message 1 of 10 , Dec 13, 2012
      Rod,

      Overspeed is a confusing term, since it requires adverse electrical load interactions, just as you suggest. In principle, an unloaded (open circuit) wind generator does not burn out (although there would be some eddy current heating), but actually spins faster than its loaded thermal failure mode. With small rotors, high rpm is not a structural challenge, but it does become a critical load-limit factor at the largest scales. 

      A water-cooled "surface-gen" is a good idea; after all ships have long used seawater for engine cooling. A variable air-gap generator goes rather far into the "unobtainium" zone. We should probably master stock generators first.

      Furling or packing away (kite) sail area in storm conditions is the predicted AWES necessity, given the practical need to run sail materials at high working loads in low "most probable" windspeeds. On a racing sailboat, flying its wonderful light wind sails in a blow promptly ruins them. Traditional Dutch windmills furl sails. Many modern turbines feather. Kite sports switch to smaller kites on shorter lines. Airplanes are moved around storms. Flexible risk avoidance is a wise design strategy.

      Stowing kites below 20m deep in storms would avoid the brunt of most storms, but its a drastic design strategy. Offshore is really hostile, and its likely not the early AWES paradise so many folks have strangely implied it to be.

      Conclusion- Do not hope to ride out storms in a full-sail AWES mode, unless you trade away economically essential high-performance in normal conditions,

      daveS


    • roderickjosephread
      AWE is pretty radical in the first place. Our primary driver is a thin fluid moving relative to a surface. Racing yachts light sails are wonderful at catching
      Message 2 of 10 , Dec 14, 2012
        AWE is pretty radical in the first place.

        Our primary driver is a thin fluid moving relative to a surface.

        Racing yachts light sails are wonderful at catching power.
        Racing yacht hulls are poor at converting that power to speed
        The sails go wrong because the drag response of the yacht is disproportionately massive,
        this causes the sail to cut through the wind differently to it's designed flow.

        I believe for energy tapping
        Our ideal kite keeps a constant wind speed /sweeping speed ratio
        Is a single size & performance always flying sail, always keeping it's characteristic response to the wind.

        Keeping the COP, COE, L/D just driving harder within an engineered permissible SWL. We know this can be massive for UHMWPE & rip stop without much weight.

        As the wind picks up, Blades require to speed proportionately. Power output needs to go up (but not so dramatically as the drag of a ships hull dictates).
        We have the opportunity with response curves programmed into dc generators, clutches, water pumps, valves, blade angles...
        We have the opportunity to match the efficiency of our swept area , to match the required power output from a continuous ratio sweep through wind.

        With a generator mounted on a pole, you can't afford the weight of water cooling, wind braking, step down gearing, extra alternator shunting.

        We can and should be looking to keep a smooth stable device in the air, I don't think that has to be much heavier than the lightest sails. It may well take off slightly later.

        When we mine fuel for cars we don't change the size of the piston to match the needs of the driver.
        Furling multiple tarps along flexible lines is going to be tricky.
        Especially with the top ones furthest from the  winder.
        A kite surfer switches to a smaller kite because you physically can't hold a bigger one on a windy day, but a bigger kiter takes a bigger kite.

        Keeping flowing
        Keeping the balance
        Working with what you've got
        looking ahead
        Tactics and strategy
        That's how you win races

        Offshore too has some advantages.
        smoother flowing wind.
        Inherent easy wind tracking even with staked out legs.
        Less people.
        buoyancy control.
        cooling.
        power dumping....


        --- In AirborneWindEnergy@yahoogroups.com, dave santos <santos137@...> wrote:
        >
        > Rod,
        >
        > Overspeed is a confusing term, since it requires adverse electrical load interactions, just as you suggest. In principle, an unloaded (open circuit) wind generator does not burn out (although there would be some eddy current heating), but actually spins faster than its loaded thermal failure mode. With small rotors, high rpm is not a structural challenge, but it does become a critical load-limit factor at the largest scales.�
        >
        > A water-cooled "surface-gen" is a good idea; after all ships have long used seawater for engine cooling. A variable air-gap generator goes rather far into the "unobtainium" zone. We should probably master stock generators first.
        >
        > Furling or packing away (kite) sail area in storm conditions is the predicted AWES necessity, given the practical need to run sail materials at high working loads in low "most probable" windspeeds. On a racing sailboat, flying its wonderful light wind sails in a blow promptly ruins them. Traditional Dutch windmills furl sails. Many modern turbines feather. Kite sports switch to smaller kites on shorter lines. Airplanes are moved around storms. Flexible risk avoidance is a wise design strategy.
        >
        > Stowing kites below 20m deep in storms would avoid the brunt of most storms, but its a drastic design strategy. Offshore is really hostile, and its likely not the early AWES paradise so many folks have strangely implied it to be.
        >
        > Conclusion- Do not hope to ride out storms in a full-sail AWES mode, unless you trade away economically essential high-performance in normal conditions,
        >
        > daveS
        >
        >
        > >
        >
      • harry valentine
        Thanks to all for providing insight into the over-speed problem as it relates to wind power (propulsion and power generation). Present and future research
        Message 3 of 10 , Dec 14, 2012
          Thanks to all for providing insight into the over-speed problem as it relates to wind power (propulsion and power generation). Present and future research definitely needs to develop alternative technical solutions that convert a wider range of wind velocities to usable power (or propulsion).

          At the present time, electrical generators deliver optimal efficiency at full power. Turbo-Hydraulic and turbo-pneumatic pumps deliver optimal efficiency over a narrow range of rotational speed .  . .  . positive-displacement technology is more versatile in this regard. 

          Positive-displacement hydraulic and pneumatic pumps involve much lower cost than electrical generating equipment. Some air-compressors allow the operator to load or unload individual cylinders .  .  . like some V-8 automotive engines that can operate on 2, 4, 6 or 8-cylinders. A kite driving an adjustable-flow-rate piston water pump or a piston air pump (or positive-displacement rotary technology) could keep operating at wind velocities that would overheat a liquid-cooled electrical generator.


          Harry



        • dave santos
          Its an interesting idea, to try and keep airspeed constant in  the hope to avoid variable wing states. Makani proposed stopping its normal looping to ride out
          Message 4 of 10 , Dec 14, 2012
            Its an interesting idea, to try and keep airspeed constant in  the hope to avoid variable wing states. Makani proposed stopping its normal looping to ride out high winds flying in place.

            There are a lot of problems still. Load-matching capability is reduced by this "one-speed" strategy. Looping or not is somewhat an all or nothing event, with a large gap in speed between the two states (figure eights can transition more smoothly). Even just looping tends to vary airspeed, unless you slave variable to airspeed. High winds mean turbulent gusty conditions, so actuator churn and hairier control processing are further costs to the constant airspeed requirement.

            Yachts and aircraft share a great need to operate at varied airspeeds. With aircraft, safe practical take-off and landing typically require slow-speed flight relative to normal cruise. Hence the elaborate variable wings seen on airliners. Even simple types usually have flaps. Slow flight of a hot wing is a dangerous flight mode. Trying to maintain sweeping flight in a fitful low wind is similarly high risk. Trading away early launch in light air is quite problematic: "Sucker wind" is a pattern of weak puffs that tempt the kite control to order constant launch and land cycles in a vain struggle. A one-speed-fits-all trade-off expands the sucker-wind envelope. Another way to look at the problem is to ask "Underspeed? Whats that?".

            Its hard to avoid the conclusion that only the most flexible set of wings operating over the widest range of windspeeds can really laugh at overspped and underspeed as critical limitations.

          • roderickjosephread
            I m imagining the situation of a controllable scoop mothra lifting the hub of a ring of kites. In a low wind the back line of the mothra would be tightened to
            Message 5 of 10 , Dec 14, 2012
              I'm imagining the situation of a controllable scoop mothra lifting the
              hub of a ring of kites.
              In a low wind the back line of the mothra would be tightened to lift and
              drag more with more tarp presented to the wind.
              High winds, pay out the back lines and stretch the back foot back, front
              foot fore. presented face decreases but overall lift and drag remains.

              As for the generating component ... It's not a constant airspeed ...
              it's near constant relationships of ring rotational velocity to wind
              velocity that I see as essential for survival...
              This way the sail does load up force progressively as it reaches top
              storm speeds, but stays within it's acceptable parameters.
              Just like the jet engine turbine rings are doing, the blades on that
              ring are wings too.

              Kites can flex a gust away, flatten off a bit, but we want them staying
              tight and not being battered about by a big wind.

              As for sucker wind, with a sprung or counter balanced launch wand
              tempting a mothra leading edge upward, At least it's trying. What
              problems occur if it doesn't get up? on the day it doesn't get up ,
              there's no wind. When it's there it's there high up, we are going for
              good high air.




              --- In AirborneWindEnergy@yahoogroups.com, dave santos <santos137@...>
              wrote:
              >
              > Its an interesting idea, to try and keep airspeed constant in
              �the hope to avoid variable wing states. Makani proposed stopping
              its normal looping to ride out high winds flying in place.
              >
              > There are a lot of problems still. Load-matching capability is reduced
              by this "one-speed" strategy. Looping or not is somewhat an all or
              nothing event, with a large gap in speed between the two states (figure
              eights can transition more smoothly). Even just looping tends to vary
              airspeed, unless you slave variable to airspeed. High winds mean
              turbulent gusty conditions, so actuator churn and hairier control
              processing are further costs to the constant airspeed requirement.
              >
              > Yachts and aircraft share a great need to operate at varied airspeeds.
              With aircraft, safe practical take-off and landing typically require
              slow-speed flight relative to normal cruise. Hence the elaborate
              variable wings seen on airliners. Even simple types usually have flaps.
              Slow flight of a hot wing is a dangerous flight mode. Trying to maintain
              sweeping flight in a fitful low wind is similarly high
              risk.�Trading away early launch in light air is quite problematic:
              "Sucker wind" is a pattern of weak puffs that tempt the kite control to
              order constant launch and land cycles in a vain struggle. A
              one-speed-fits-all trade-off expands the sucker-wind
              envelope.�Another way to look at the problem is to ask "Underspeed?
              Whats that?".
              >
              > Its hard to avoid the conclusion that only the most flexible set of
              wings operating over the widest range of windspeeds can really laugh at
              overspped and underspeed as critical limitations.
              >
            • dave santos
              What sort of airborne hub is megascalable?  It seems well established that flying 3D rigid structure is a scaling dead-end. Even at your modest experimental
              Message 6 of 10 , Dec 14, 2012
                What sort of airborne "hub" is megascalable? 

                It seems well established that flying 3D rigid structure is a scaling dead-end. Even at your modest experimental scale, your experiments gave you a nice clear indication that larger torsion hubs can hardly fly up high into better wind. That's a great result, since it confirms a design path to avoid. Instead, you chose that architecture for a Kite Power Coop logo :) 

                Test every idea, even the obvious dogs. Unpromising results hide lessons that can steer us toward real solutions. The more failure-lessons one can bear, the greater the eventual success. Too many folks in AWE sink with their ships, rather than jump onto a better one. At best, only a large surface hub (that does not fly) is megascalable (carousels and ring tracks).

              • roderickjosephread
                That analysis might be a bit harsh. The lifting kite we used had a couple of thin flexible spars in it ... rigidity The steering for the lifter is a metal
                Message 7 of 10 , Dec 14, 2012
                  That analysis might be a bit harsh.
                  The lifting kite we used had a couple of thin flexible spars in it ...
                  rigidity
                  The steering for the lifter is a metal frame, radio, servo..rigidity
                  The top hub used was from a mountain bike and was too big for what was
                  needed... rigidity
                  All of the rigid matter up top lifted fine.

                  The problem with our last test was that the stem was too flexible to
                  hold the weight of the bottom hub (The hub bellow the ring set) and the
                  brake and the cuff and the tethering wheel...
                  It was all on a long flexible pipe.
                  This had the unfortunate side effect of drastically misaligning the
                  tethering ring and the kite ring.
                  In the rare seconds that they aligned, it looked good... really rare.

                  The first ring prototype never had that problem as there was no
                  alignment issue, all the tethering ran from 1 point.

                  If that extended ring set idea or even just one lifted ring idea is to
                  be lifted , then the bottom hub should be balanced in a gimbal to allow
                  the tension from the kite ring to align it...
                  Furthermore, the first (lowest ring or only ring) should be set as a box
                  ring kite (one ring sparred to a front tethering ring)

                  The lifted hub (yes it is weight up high) is not a heavy weight, It does
                  have to cope with the line tension, that will be a maximum when all the
                  rings stall and collapse... otherwise if the rings are flying the line
                  tension is reduced due to ring kites lift.

                  I am opposed to weight up high as well. But it is a simple elegant
                  method.

                  If we want to control kixels by line, we will need rigid smooth rings
                  mounted on our loadpaths to run control lines. OK they're tiny too but
                  still rigid.

                  This whole parametric algorithm design course I'm putting myself through
                  is mincing my head though...
                  I am definitely going to end up drawing meshes of organic loadpath
                  arches with triggered twitchy gill sails

                  Another good laddermill idea you'll not approve of Dave S.... may use 2
                  hubs lifted up to opposite sides inside an arch. a continuous rope with
                  the outermost edge of many kites runs through the hubs (wheel sets), the
                  inner edges of the kites are banded on a short band and the tethering
                  for the kite ring is collected to a central tether (spinning or
                  swivelled) Power is taken from the band at the arch feet as the band
                  runs through ground wheels.





                  --- In AirborneWindEnergy@yahoogroups.com, dave santos <santos137@...>
                  wrote:
                  >
                  > What sort of airborne "hub" is megascalable?�
                  >
                  > It seems well established that flying 3D rigid structure is a scaling
                  dead-end. Even at your modest experimental scale, your experiments gave
                  you a nice clear indication that larger torsion hubs can hardly fly up
                  high into better wind. That's a great result, since it confirms a design
                  path to avoid. Instead, you chose that architecture for a Kite Power
                  Coop logo :)�
                  >
                  > Test every idea, even the obvious dogs. Unpromising results hide
                  lessons that can steer us toward real solutions. The more
                  failure-lessons one can bear, the greater the eventual success. Too many
                  folks in AWE sink with their ships, rather than jump onto a better
                  one.�At best, only a large surface hub (that does not fly) is
                  megascalable (carousels and ring tracks).
                  >
                • roderickjosephread
                  you might have a good point about the logo Dave S needs to be a more cooperative design. a lifter and a crosswind driving device... Maybe an arch with big
                  Message 8 of 10 , Dec 14, 2012
                    you might have a good point about the logo Dave S
                    needs to be a more cooperative design.
                    a lifter and a crosswind driving device...
                    Maybe an arch with big "ears kites" pinned on to third way along the load path to stretch it out and lift a crosswind power device...


                    --- In AirborneWindEnergy@yahoogroups.com, "roderickjosephread" <rod.read@...> wrote:
                    >
                    > That analysis might be a bit harsh.
                    > The lifting kite we used had a couple of thin flexible spars in it ...
                    > rigidity
                    > The steering for the lifter is a metal frame, radio, servo..rigidity
                    > The top hub used was from a mountain bike and was too big for what was
                    > needed... rigidity
                    > All of the rigid matter up top lifted fine.
                    >
                    > The problem with our last test was that the stem was too flexible to
                    > hold the weight of the bottom hub (The hub bellow the ring set) and the
                    > brake and the cuff and the tethering wheel...
                    > It was all on a long flexible pipe.
                    > This had the unfortunate side effect of drastically misaligning the
                    > tethering ring and the kite ring.
                    > In the rare seconds that they aligned, it looked good... really rare.
                    >
                    > The first ring prototype never had that problem as there was no
                    > alignment issue, all the tethering ran from 1 point.
                    >
                    > If that extended ring set idea or even just one lifted ring idea is to
                    > be lifted , then the bottom hub should be balanced in a gimbal to allow
                    > the tension from the kite ring to align it...
                    > Furthermore, the first (lowest ring or only ring) should be set as a box
                    > ring kite (one ring sparred to a front tethering ring)
                    >
                    > The lifted hub (yes it is weight up high) is not a heavy weight, It does
                    > have to cope with the line tension, that will be a maximum when all the
                    > rings stall and collapse... otherwise if the rings are flying the line
                    > tension is reduced due to ring kites lift.
                    >
                    > I am opposed to weight up high as well. But it is a simple elegant
                    > method.
                    >
                    > If we want to control kixels by line, we will need rigid smooth rings
                    > mounted on our loadpaths to run control lines. OK they're tiny too but
                    > still rigid.
                    >
                    > This whole parametric algorithm design course I'm putting myself through
                    > is mincing my head though...
                    > I am definitely going to end up drawing meshes of organic loadpath
                    > arches with triggered twitchy gill sails
                    >
                    > Another good laddermill idea you'll not approve of Dave S.... may use 2
                    > hubs lifted up to opposite sides inside an arch. a continuous rope with
                    > the outermost edge of many kites runs through the hubs (wheel sets), the
                    > inner edges of the kites are banded on a short band and the tethering
                    > for the kite ring is collected to a central tether (spinning or
                    > swivelled) Power is taken from the band at the arch feet as the band
                    > runs through ground wheels.
                    >
                    >
                    >
                    >
                    >
                    > --- In AirborneWindEnergy@yahoogroups.com, dave santos <santos137@>
                    > wrote:
                    > >
                    > > What sort of airborne "hub" is megascalable?�
                    > >
                    > > It seems well established that flying 3D rigid structure is a scaling
                    > dead-end. Even at your modest experimental scale, your experiments gave
                    > you a nice clear indication that larger torsion hubs can hardly fly up
                    > high into better wind. That's a great result, since it confirms a design
                    > path to avoid. Instead, you chose that architecture for a Kite Power
                    > Coop logo :)�
                    > >
                    > > Test every idea, even the obvious dogs. Unpromising results hide
                    > lessons that can steer us toward real solutions. The more
                    > failure-lessons one can bear, the greater the eventual success. Too many
                    > folks in AWE sink with their ships, rather than jump onto a better
                    > one.�At best, only a large surface hub (that does not fly) is
                    > megascalable (carousels and ring tracks).
                    > >
                    >
                  • dave santos
                    Sorry to seem harsh. The point is not how well your hub worked at its small scale, which looked OK (if a bit elaborate). KiteLab testing has consistently found
                    Message 9 of 10 , Dec 14, 2012
                      Sorry to seem harsh. The point is not how well your hub worked at its small scale, which looked OK (if a bit elaborate). KiteLab testing has consistently found that small hubbed rotors at low altitudes work well.

                      The intended lesson is that even at your current scale you are getting definite indications of just how severe the cubic-mass scaling penalties will be, once you know to look carefully for the harsh scaling law's predicted effects.

                      Our harshest critic is reality, which often whispers.
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