The Economist has an article on wave power technologies.

http://www.economist.com/science/tq/displaystory.cfm?story_id=11482565

Among the inventions is the Oyster:

"The Oyster, a wave-power device from Aquamarine Power, another
Scottish firm, works in an entirely different way. It is an
oscillating metal flap, 12 metres tall and 18 metres wide, installed
close to shore. As the waves roll over it, the flap flexes backwards
and forwards. This motion drives pistons that pump seawater at high
pressure through a pipe to a hydroelectric generator. The generator is
onshore, and can be connected to lots of Oyster devices, each of which
is expected to generate up to 600kW. The idea is to make the parts
that go in the sea simple and robust, and to keep the complicated and
delicate bits out of the water. Testing of a prototype off the Orkney
coast is due to start this summer."

This seems to generate up to 20KW/metre. Could these be used to
prevent coastal erosion by dampening waves?

Imagine a line of these devices stretching 200km along the East Coast
of England, generating up to 4GW of power.

If these devices could become almost cost competitive (say 10c/KWhr)
coastal defence subsidies might pay the rest.

escreveu na mensagem 
news:a9fe8d72-69c6-45c7-bb5d-c052754dc949@r66g2000hsg.googlegroups.com...
> The Economist has an article on wave power technologies.
>
> http://www.economist.com/science/tq/displaystory.cfm?story_id=11482565
>
> Among the inventions is the Oyster:
>
> "The Oyster, a wave-power device from Aquamarine Power, another
> Scottish firm, works in an entirely different way. It is an
> oscillating metal flap, 12 metres tall and 18 metres wide, installed
> close to shore. As the waves roll over it, the flap flexes backwards
> and forwards. This motion drives pistons that pump seawater at high
> pressure through a pipe to a hydroelectric generator. The generator is
> onshore, and can be connected to lots of Oyster devices, each of which
> is expected to generate up to 600kW. The idea is to make the parts
> that go in the sea simple and robust, and to keep the complicated and
> delicate bits out of the water. Testing of a prototype off the Orkney
> coast is due to start this summer."
>
> This seems to generate up to 20KW/metre. Could these be used to
> prevent coastal erosion by dampening waves?

The device generates 20kW/metre at a Sea of 100kW/metre.
Hence only 20% efficiency for a start.
Then it generates 20 kW/metre of sea water to be pumped some
distance.

Sea waves have potential energy and kinetic energy.
The potential energy is the water weight (the mass of water above
and below the sea level that changes over time).
The kinetic energy is very hard to visualise, since the water doesn't
move when the wave travels (in funny trains) miles distance without
losing energy (offshore). Well, the kinetic energy is equal to the
potential energy and therefore both are sinusoidal like (a sine wave).
The kinetic energy is translated by the longitudinal motion of waves
(around 15 m/s), zero at the top of the wave, maximum at the best
surfing point (sea level) and zero again on the bottom. Surfing up
trying to climb a wave is the negative part.

Well, the negative parts are a pain in the ass. Only a spring can fix
that pain. Where is the spring of the Oyster?

Well, the Oyster works solely on kinetic energy. The actual speed
for energy capture goes down exponential with deepth.

And power is force times displacement. Good displacements only
on top. So the 12 meters tall the Oyster has will capture power
accordingly (exponential down).

The spring required to capture energy during kinetic energy
reversal is a problem. Looking at the picture of a Oyster one
can see where the spring is. The spring is the coastal slop on
the back. The waving back and forth cause by the bottom of
the Ocean slop on shore. Therefore it's a coast line device that
already suffers from a loss on wave energy due to Ocean
bottom.

The main problem of Oyster is to be 20% of what exists and
those 20% are still water pressure
Nevertheless, the Oyters must be the cheapest device of all.
Doesn't look suitable for electricity generation.


> Imagine a line of these devices stretching 200km along the East Coast
> of England, generating up to 4GW of power.
>
> If these devices could become almost cost competitive (say 10c/KWhr)
> coastal defence subsidies might pay the rest.

There is 4 times more power on waves then in wind.
The problems are:
1 - Spring
2 - Resonance = displacement
3 - Looks impossible to combine motion so that to
capture potential and kinetic energy with on single
device. The only one known that can do that is known
by Salter's Duck, but lacks a fixed point so that can't
work.
4 - A good Power-take-off that could convert the primary
power (force of the waves times displacement of the capture
device) into electricity.

The power content on waves is huge but ...

Well, the very best is potential energy.
The weight of a small 2 meters wave up, plus 2 meters down
is huge. The force per meter squared of the capture device
is 2 tons peak up and 2 tons peak down is a sinusoidal
fashion (with a spring).
The mass of water is resonance with a spring causes an
amplified displacement that could take it all (of the potential
only, which is 50% remember).

The problem with waves potential energy is velocity.
The velocity up and down of a 10 seconds period wave
of 2 meters up plus 2 meters down the sea level (4 meter
wave) is sinusoidal with a peak value of around 2*2pi/10
= 1.2 m/s.
The power will be those 2 tons of water at a speed of 1.2 m/s,
hence 20,000N*1.2m/s = 24kW per meter squared of a
device moving up and down.

A device the size of Oyster (whose area is 12*18 = around
200 meters squared) should capture 4,8MW of peak power and
4,8/1.4142 MW on average (if there is a spring).

... and the Power-take-off and no losses associated to motion.

Hence, Oyster is up to 600kW for waves of what content,
one may ask?

On 11 Jun, 03:33, "Dasse" <da...@mail.docaneco> wrote:
>  escreveu na mensagemnews:a9fe8d72-69c6-45c7-bb5d-c052754dc949@r66g2000hsg.googlegroups.com...
>
>
>
> > The Economist has an article on wave power technologies.
>
> >http://www.economist.com/science/tq/displaystory.cfm?story_id=11482565
>
> > Among the inventions is the Oyster:
>
> > "The Oyster, a wave-power device from Aquamarine Power, another
> > Scottish firm, works in an entirely different way. It is an
> > oscillating metal flap, 12 metres tall and 18 metres wide, installed
> > close to shore. As the waves roll over it, the flap flexes backwards
> > and forwards. This motion drives pistons that pump seawater at high
> > pressure through a pipe to a hydroelectric generator. The generator is
> > onshore, and can be connected to lots of Oyster devices, each of which
> > is expected to generate up to 600kW. The idea is to make the parts
> > that go in the sea simple and robust, and to keep the complicated and
> > delicate bits out of the water. Testing of a prototype off the Orkney
> > coast is due to start this summer."
>
> > This seems to generate up to 20KW/metre. Could these be used to
> > prevent coastal erosion by dampening waves?
>
> The device generates 20kW/metre at a Sea of 100kW/metre.
> Hence only 20% efficiency for a start.
> Then it generates 20 kW/metre of sea water to be pumped some
> distance.
>
> Sea waves have potential energy and kinetic energy.
> The potential energy is the water weight (the mass of water above
> and below the sea level that changes over time).
> The kinetic energy is very hard to visualise, since the water doesn't
> move when the wave travels (in funny trains) miles distance without
> losing energy (offshore). Well, the kinetic energy is equal to the
> potential energy and therefore both are sinusoidal like (a sine wave).
> The kinetic energy is translated by the longitudinal motion of waves
> (around 15 m/s), zero at the top of the wave, maximum at the best
> surfing point (sea level) and zero again on the bottom. Surfing up
> trying to climb a wave is the negative part.
>
> Well, the negative parts are a pain in the ass. Only a spring can fix
> that pain. Where is the spring of the Oyster?
>
> Well, the Oyster works solely on kinetic energy. The actual speed
> for energy capture goes down exponential with deepth.
>
> And power is force times displacement. Good displacements only
> on top. So the 12 meters tall the Oyster has will capture power
> accordingly (exponential down).
>
> The spring required to capture energy during kinetic energy
> reversal is a problem. Looking at the picture of a Oyster one
> can see where the spring is. The spring is the coastal slop on
> the back. The waving back and forth cause by the bottom of
> the Ocean slop on shore. Therefore it's a coast line device that
> already suffers from a loss on wave energy due to Ocean
> bottom.
>
> The main problem of Oyster is to be 20% of what exists and
> those 20% are still water pressure
> Nevertheless, the Oyters must be the cheapest device of all.
> Doesn't look suitable for electricity generation.
>
> > Imagine a line of these devices stretching 200km along the East Coast
> > of England, generating up to 4GW of power.
>
> > If these devices could become almost cost competitive (say 10c/KWhr)
> > coastal defence subsidies might pay the rest.
>
> There is 4 times more power on waves then in wind.
> The problems are:
> 1 - Spring
> 2 - Resonance = displacement
> 3 - Looks impossible to combine motion so that to
> capture potential and kinetic energy with on single
> device. The only one known that can do that is known
> by Salter's Duck, but lacks a fixed point so that can't
> work.
> 4 - A good Power-take-off that could convert the primary
> power (force of the waves times displacement of the capture
> device) into electricity.
>
> The power content on waves is huge but ...
>
> Well, the very best is potential energy.
> The weight of a small 2 meters wave up, plus 2 meters down
> is huge. The force per meter squared of the capture device
> is 2 tons peak up and 2 tons peak down is a sinusoidal
> fashion (with a spring).
> The mass of water is resonance with a spring causes an
> amplified displacement that could take it all (of the potential
> only, which is 50% remember).
>
> The problem with waves potential energy is velocity.
> The velocity up and down of a 10 seconds period wave
> of 2 meters up plus 2 meters down the sea level (4 meter
> wave) is sinusoidal with a peak value of around 2*2pi/10
> = 1.2 m/s.
> The power will be those 2 tons of water at a speed of 1.2 m/s,
> hence 20,000N*1.2m/s = 24kW per meter squared of a
> device moving up and down.
>
> A device the size of Oyster (whose area is 12*18 = around
> 200 meters squared) should capture 4,8MW of peak power and
> 4,8/1.4142 MW on average (if there is a spring).
>
> ... and the Power-take-off and no losses associated to motion.
>
> Hence, Oyster is up to 600kW for waves of what content,
> one may ask?

Not sure as to what waves, but note that Oyster is extracting energy
per linear m. I assume the device is several metres wide, so for
example can take your 24KW x 12m = 288 KW. Make the waves 3m rather
than 2 and you reach 600KW, but you still need a bit more given the
device efficiency.

So if you can becalm a patch of water 100m out to sea, will you stop a
large part of the wave energy hitting the coast?

"disgoftunwells"  escreveu na mensagem
news:5be7bfb5-cffe-4697-827e-67019c6e70eb@79g2000hsk.googlegroups.com...
> On 11 Jun, 03:33, "Dasse" <da...@mail.docaneco> wrote:
>>  escreveu na
>> mensagemnews:a9fe8d72-69c6-45c7-bb5d-c052754dc949@r66g2000hsg.googlegroups.com...
>>
>>
>>
>> > The Economist has an article on wave power technologies.
>>
>> >http://www.economist.com/science/tq/displaystory.cfm?story_id=11482565
>>
>> > Among the inventions is the Oyster:
>>
>> > "The Oyster, a wave-power device from Aquamarine Power, another
>> > Scottish firm, works in an entirely different way. It is an
>> > oscillating metal flap, 12 metres tall and 18 metres wide, installed
>> > close to shore. As the waves roll over it, the flap flexes backwards
>> > and forwards. This motion drives pistons that pump seawater at high
>> > pressure through a pipe to a hydroelectric generator. The generator is
>> > onshore, and can be connected to lots of Oyster devices, each of which
>> > is expected to generate up to 600kW. The idea is to make the parts
>> > that go in the sea simple and robust, and to keep the complicated and
>> > delicate bits out of the water. Testing of a prototype off the Orkney
>> > coast is due to start this summer."
>>
>> > This seems to generate up to 20KW/metre. Could these be used to
>> > prevent coastal erosion by dampening waves?
>>
>> The device generates 20kW/metre at a Sea of 100kW/metre.
>> Hence only 20% efficiency for a start.
>> Then it generates 20 kW/metre of sea water to be pumped some
>> distance.
>>
>> Sea waves have potential energy and kinetic energy.
>> The potential energy is the water weight (the mass of water above
>> and below the sea level that changes over time).
>> The kinetic energy is very hard to visualise, since the water doesn't
>> move when the wave travels (in funny trains) miles distance without
>> losing energy (offshore). Well, the kinetic energy is equal to the
>> potential energy and therefore both are sinusoidal like (a sine wave).
>> The kinetic energy is translated by the longitudinal motion of waves
>> (around 15 m/s), zero at the top of the wave, maximum at the best
>> surfing point (sea level) and zero again on the bottom. Surfing up
>> trying to climb a wave is the negative part.
>>
>> Well, the negative parts are a pain in the ass. Only a spring can fix
>> that pain. Where is the spring of the Oyster?
>>
>> Well, the Oyster works solely on kinetic energy. The actual speed
>> for energy capture goes down exponential with deepth.
>>
>> And power is force times displacement. Good displacements only
>> on top. So the 12 meters tall the Oyster has will capture power
>> accordingly (exponential down).
>>
>> The spring required to capture energy during kinetic energy
>> reversal is a problem. Looking at the picture of a Oyster one
>> can see where the spring is. The spring is the coastal slop on
>> the back. The waving back and forth cause by the bottom of
>> the Ocean slop on shore. Therefore it's a coast line device that
>> already suffers from a loss on wave energy due to Ocean
>> bottom.
>>
>> The main problem of Oyster is to be 20% of what exists and
>> those 20% are still water pressure
>> Nevertheless, the Oyters must be the cheapest device of all.
>> Doesn't look suitable for electricity generation.
>>
>> > Imagine a line of these devices stretching 200km along the East Coast
>> > of England, generating up to 4GW of power.
>>
>> > If these devices could become almost cost competitive (say 10c/KWhr)
>> > coastal defence subsidies might pay the rest.
>>
>> There is 4 times more power on waves then in wind.
>> The problems are:
>> 1 - Spring
>> 2 - Resonance = displacement
>> 3 - Looks impossible to combine motion so that to
>> capture potential and kinetic energy with on single
>> device. The only one known that can do that is known
>> by Salter's Duck, but lacks a fixed point so that can't
>> work.
>> 4 - A good Power-take-off that could convert the primary
>> power (force of the waves times displacement of the capture
>> device) into electricity.
>>
>> The power content on waves is huge but ...
>>
>> Well, the very best is potential energy.
>> The weight of a small 2 meters wave up, plus 2 meters down
>> is huge. The force per meter squared of the capture device
>> is 2 tons peak up and 2 tons peak down is a sinusoidal
>> fashion (with a spring).
>> The mass of water is resonance with a spring causes an
>> amplified displacement that could take it all (of the potential
>> only, which is 50% remember).
>>
>> The problem with waves potential energy is velocity.
>> The velocity up and down of a 10 seconds period wave
>> of 2 meters up plus 2 meters down the sea level (4 meter
>> wave) is sinusoidal with a peak value of around 2*2pi/10
>> = 1.2 m/s.
>> The power will be those 2 tons of water at a speed of 1.2 m/s,
>> hence 20,000N*1.2m/s = 24kW per meter squared of a
>> device moving up and down.
>>
>> A device the size of Oyster (whose area is 12*18 = around
>> 200 meters squared) should capture 4,8MW of peak power and
>> 4,8/1.4142 MW on average (if there is a spring).
>>
>> ... and the Power-take-off and no losses associated to motion.
>>
>> Hence, Oyster is up to 600kW for waves of what content,
>> one may ask?
>
> Not sure as to what waves, but note that Oyster is extracting energy
> per linear m. I assume the device is several metres wide, so for
> example can take your 24KW x 12m = 288 KW. Make the waves 3m rather
> than 2 and you reach 600KW, but you still need a bit more given the
> device efficiency.

My previous approach (to give the 24kW/m) doesn't go proportional
to the square of the wave height, therefore it's not the usual approach.
I mean that a 4 meter significant wave height, compared to a 6 meter
significant wave height, will be only 6/4=3/2 =1.5 times larger in power,
not 6^2/4^2 = 9/4 = 2.25 times larger in power.
The known power expression is given here:
http://en.wikipedia.org/wiki/Wave_power
Nevertheless, in the above article it's said that it is the energy flux,
and not the actual power generated by a wave power device.
In major storms, the largest waves offshore are about 15 meters high
and have a period of about 15 seconds. According to the articel
deep-water  formula, such waves carry about 3.2 MW/m of power
across each meter of wavefront. At moderate conditions, for a wave
height of about 3 m and a wave period of 8 seconds, a wave power
location will have an average flux much less than this: about 70 kW/m.

The above values must be cut by two, since no device can get
potential and kinetic energy at the same time.
And kinetic and potential are 90 degrees out-of-phase.

Well, the truth is that I'm talking about power per area and the
article talks about energy flux per meter of wavefront. I knew that
something didn't smell good.
And still doesn't smell, but that's a long story. I'm talking about
peak power and assuming the device is a point (or a point absorber).

The above comment on 3.2MW/m power reminds me the
most important subject of all - survivability in case of heavy
storms. There only one type that can survive - submerged
and stopped.


> So if you can becalm a patch of water 100m out to sea, will you stop a
> large part of the wave energy hitting the coast?

Yes, no matter where a wave energy capture device is placed.
Even an offshore device (the best and the actual research trend)
will have potential to cut by two the wave power relative to the
device exposed width. I mean cut by two since no working known
device can capture both, kinetic and potential.