Wave power and the axial flux?

[capthook]

Wave power is an under-utilized, abundant power resource that is still in realitely early stages with recent work on buoy-type devices.

Might the air core/low drag design of the axial flux be incorporated into a wave-motion generator?

One problem is the non-unidirectional motion of a wave.  Up and down, from the east some days and the west on others etc.

One might utilize the bobbing motion is other ways than up and down, but rather side-to-side, or front-to-back.

Question:  How might the output of an axial flux alternator be affected by a bi-directional rotation? A cycle being 1/2 clockwise, and the other anti-clockwise?

Would the output look like one operating normaly EXCEPT for a 'flat spot' at the moment of directional change?

Would you see power output drop by 25%, 50%, x%?

Would you have to overcome additional BEMF because of the change of rotation?

(or does BEMF not an issue because it's AC? I don't know how it applies)

One solution to converting bi-directional rotation into uni-directional rotation is to use 3-shaft gearing.

http://www.ljsite.com/unigear.htm

However, it is complicated, expensive and lossy.

Would the axial flux underperform in this scenerio to the point that this might become a better option?

How will bi-directional - 1/2 cycle clockwise, 1/2 cycle anti-clockwise - operation of an axial flux alternator affect it's performance/output?

[Flux]

Way off my field of interest but as long as you want to end up with dc you can reverse any alternator but there will be flat spots when it stops.

If you want ac then it wouldn't make a lot of sense.

I instinctively suspect that some adaption of the linear motor would be better than reversing a rotary machine but at low frequencies the inertia issue may not be too bad for small set ups.

I really have no idea whether using an ironless stator would have any advantage, it all depends on size and the lowest wave energy you are trying to deal with.

Too far from the sea to worry about in my case.

Flux

[ghurd]

Could prototype it with 2 rear bicycle hubs.  One pulls on the way up, other pulls on the way down.

No need to involve reversing direction or inertia.

A NON iron cored machine will freewheel below cut-in RPM.

Sounds like a Huge project.  Delta tide, wave length, and wave height seems like a big nut to crack on a homebrew system.

G-

[Norm]

A straight linear machine isn't really necessary.

Who says a rotary alternator has to keep going

in one direction? sure there's inertia to

overcome....same as in a linear machine......

I just take a Stepper motor with the rubber rim

pulley on the edge of a table .....

battery doesn't care if the current stops and starts

  3 of these riding seperate waves....overlapping

pulses of dc current....

[tanner0441]

Hi

I spent some time looking at wave power machines purely out of interest.

The ones made in the UK and being used by Belgium in numbers use linear hydraulic pumps, as the wave action bends the device telescoping the rams, hydraulic fluid is forced through hydraulic motors which turn the flow into rotating moments driving the alternator.

By using accumulators and regulators (hydraulic) the frequency of the generated AC can be regulated, and with the use of two rams a more continuous action can be maintained.

There is a lot of information out there.

Brian

[capthook]

The problem with capturing close-to-shore wave energy, where the power might be tapped to it's greatest potential, is the NIMBY problem.  Like close-to-shore windmills, no one wants to look at them, hear them etc.

As such, the smaller off-shore waves need to be harvested in many/most cases.  This is part of the thinking of the air/core low drage/cogging of the axial flux.  Even small wave action might be captured as energy.

It's good to see input that a bi-directional generator is not considered a problem - eleminating the need for uni-directional gearing.

The current buoys use the up-down motion. Implementing an additional, small component - like a small axial flux - to capture the rocking (front to back and/or side-to-side) motion might offer an ouput boost at relatively low additional system cost.

As such - inertia isn't the issue - it's already rocking back and forth - the axial would just naturally do the same.

[capthook]

For example: you could use a balanced beama attached to axial flux shaft.  As the buoy rocks back and forth, the balance beams motion would do so as well, driving the axials shaft.

Not living near the shore - this isn't a protype I'm looking to build/test.

Rather it's more of a thought experiment. And maybe it will inspire someone of a different way of approaching/implementing the idea for a working solution. :-)

[frackers]

There was an item on Discovery Channel - maybe only the UK and its colonies called Planet Mechanics: Surf Power. Featuring Dick Strawbridge and Jem Stansfield.

It consisted of a large pipe bolted to the side of the quay with the bottom end below water but not touching the bottom. As the waves roll past the air inside blows in and out driving a turbine blade at the top of the pipe. I can't remember the name of the turbine design but it turned in the same direction on both suck and blow to driver a generator.

Assuming a pipe of large enough diameter to shift a large amount of air I'm sure an axial gen would be appropriate!!

[Simen]

I think i saw just the end of that program...

The large pipe got smaller in diameter at the top (to increase the windspeed), and the blades on the turbine was many short and aerofoil-shaped, and mounted straight along the wind-path (no twist). That way, the generator would always turn one way no matter the wind direction, due to the longer path along the one side of the blades.

[Ungrounded Lightning Rod]

Also one-way valves can "rectify" the hydraulic motion.

[Ungrounded Lightning Rod]

Were they "sharp" at both edges?

[Simen]

Yes. Well...

I don't remember for sure, but i think they were flat on one side and an even curve on the other side of the blade; sharp edges toward the wind. Not an ideal aerofoil, but enough to get a lift.

I wouldn't think the efficiency would be at its best, but it would turn one way no matter the wind direction... (in or out of the tube.)