h a l f b a k e r yPoof of concept
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If a plane wave enters a parabolas openning, then the wave will bounce off the edge of the parabola once, then travel through the focal point of the parabola. This allows small amount of energy over a large area to be collected into a single point.
Knowing this, a very large parabola could be "sculpted"
into the side of an unimportant shore without (or with little) wildlife, such as a cliffside shoreline. This parabola would collect the incomming waves, directing them into the focal point. A large buoy would be placed at this focal point, connected cables. These cables would be attached to a flywheel on the ocean floor which would power a generator. Ideally, the focal point would be 1/4 of the common ocean waves wavelength to add efficiency.
A very large parabola would allow a great amount of power to be generated.
parabolic wave animations I made
http://broken.pc.cz.../parabolicreflector
Currently not complete. will make several animations to help see if this will work. [nomel, Oct 06 2004]
some wacky world wide wave ideas
http://www.ncbi.nlm...gov/pubmed/21719948
[pashute, Jun 17 2013]
Patent for concentrating sea waves
http://www.google.com/patents/US4255066
[pashute, Jun 17 2013]
[link]
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Aren't waves mostly water moving up and down and therefore the parabola should be horizontal like a dome over the ocean surface? |
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The waves are comming in from the ocean. The water moves up and down, but the waves move in a direction towards the shore. The energy is stored in the displacment of the water...but the wave is not travelling up or down.. It would be the same as holding a piece of string. You wigle the string, and the wiggle, as a wave (disturbance in a medium), moves to the other end of the string. The wiggle causes the string to move up and down, but that's where the energy is stored, in the displacment and velocity of the string...but the wave moves down the string. |
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[buddha_pest], that sounds like it would work! Although, a buoy might do better to absorb the energy. Ideally, you would want to absorb the entire wave. This would mean that if you sent a singel wave in, no wave would escape. I don't think that would be the case for this device. Although, I can't find many details on that page. They say they are pneumatic, which would mean air pressure. So, I'm assuming you would be using the weight of the water above to power bellows or something similar. I don't think this could absorb much energy, meaning lots of waves would be sent back out to sea...plus, less power would be made. I think a mechanical collector that physically "traps" the displaced water at the focal point would be best. |
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There is a lot of research going into snake type devices that lay acrosse the water perpendicular to the direction the wave is travelling so that when the waves pass, all the joints of the device pivot, absorbing the energy. I think this would be the best method. A starburst, or asterisk, type pattern could be used. A big benefit to this would be a nice transition for the wave...meaning not many reflections. |
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This idea is more about the wave collector than the actual power generation device. There has been too much research already done for wave power collectors to ignore them...this would just allow a large power collector rather than many small. This would most likely increase efficiency. |
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I have never seen an ocean wave bounce. Wont the incoming waves get in the way? |
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This idea could be tested using a smaller parabola about 10-20 feet, placed in a still swimming pool / pond. |
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I like it...and, in fact, you could reverse it, using the buoy to dampen the waves, creating a calm harbor. |
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[bungston], waves do bounce. You usually don't see them bounce because theyare absorbed by the shore. If you live by a peer or something similar, you can see the waves bouncing. Look in your bathtub next time you take abath. The wave will bounce off the sides...same as ocean, just much smaller scale. |
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The waves would pass through each other unimpeded. Watch waves from a boat...they just pass through each other. Plus, physics says they wont ;) |
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I went to the lake a couple days ago, but they wanted $5 USD to get in! So, I couldn't bring my supplies. Trying to make the parabola out of a hole dug in the sand didn't work at all :( Stupid sand. I'll try to go back when they don't charge (after 8pm). The problem with a pool is that any wave that bounces off the parabola would travel back out as a plane wave, hit the other side...and bounce back and forth. The boats at the lake make nice wave generators too. |
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wouldn't any wave that travels into a parabolic reflector bounce through the focus and travel out as a circular wave front? |
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I like it. Needs some more thought, but it could work. (+) |
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Oh, and please only delete posts that are offensive or inflammatory. Deleting posts that disagree with you is just rude, while deleting posts that do agree with a response that you're about to make is just confusing. What was it that [buddha_pest] said that sounds like it would work? |
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Interesting concept. I would expect the material would have to be reasonably solid. The sand on the beach tends to absorb the energy of the wave, thus you do not see much of the bouncing described above. That versus the wall of a bathtub, where the waves bounce quite happily. |
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If I deleted a post, I wasn't aware of it. Sorry if I accidintally did. And, even if someone did post something stupid, I'd leave it. Nice way to show people how that person is. |
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"wouldn't any wave that travels into a parabolic reflector bounce through the focus and travel out as a circular wave front?" |
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Almost. If there was nothing to absorb the waves energy, then yes...the wave would pass through the focal point, hit the walls, then travel back out to see as a plane wave front, not circular. If all the energy in the waves is absorbed by the bouy/upside down bowl/whatever, then, the waves wouldn't pass the bouy, but be absorbed by it. So, no waves should go back into the ocean. Obviously, all the energy can't be absorbed, so, yes...some small waves will probably make it back out to sea, just reducing the efficiency of the system. Also, if the waves come in at an angle, the focal point will not be where the waves collect...so those would go back out to sea. The general area would be about the same...so if the collector was big enough (it should be pretty big), then those would probably be absorbed a *little* too. |
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Another way to increase efficiency would be to have the parabola offset, such as a DishTV or primestar dish are. That way, the collector wouldn't block any waves. Doubt the benefits would be worth the extra room required though. |
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Again, sorry if I accidentally deleted your post...or anyone elses. |
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The only problem that I see is the axis of the parabolic wall would have to be perpendicular to the wave front. Anything that might be substantial enough to bounce your waves might be too substantial to, say, float slightly and aim. |
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I was under the impression that the incoming waves were planar. With a parabolic reflector, a planar wave becomes focused to a single point. If the energy is not completely absorbed at that point, the energy will continue back out to sea in a circular wave front, not planar. |
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Even if the waves do not come in directly aligned with the reflector, the focus will still be a single point. It will simply be located somewhere other than the geometric focal point. |
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Oh, and you didn't delete my post. I don't know for sure if you deleted any posts, but the comment "[buddha_pest], that sounds like it would work!" seemed to indicate that there had been a previous post by [buddha_pest], which was no longer there. I apologise if I was mistaken. |
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[Spare parts],
"The only problem that I see is the axis of the parabolic wall would have to be perpendicular to the wave front." |
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Yes, a vertical wall sticking out of the water...not hard to do. |
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"Anything that might be substantial enough to bounce your waves might be too substantial to, say, float slightly and aim." |
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[FreeFall], I didn't delete it, it's the second post, right under the idea! :p |
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"I was under the impression that the incoming waves were planar. With a parabolic reflector, a planar wave becomes focused to a single point. If the energy is not completely absorbed at that point, the energy will continue back out to sea in a circular wave front, not planar." |
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You're right, it would be circular. I forgot to consider the direction they'd be travelling...out not bounced back in. Actually, there's benefits to this. The wave would spread out over a large area, much nicer on small boats and whatnot. |
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Well, of course, if it's hollow. :p Even lead will float if it's hollow. |
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Water is 62.4lb/ft^2.
Autoclaved concrete may be as light as 25-40lb/ft^2 |
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ok...we all get that airated (hollow) stuff floats. |
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Obviously, the appropriate materials should be used for the situation...hollow and airated concrete not being an appropriate material. Although, with rebar, and since it will be fastened to a cliffside, it might be usable. |
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Since there seems to be so much interest, I have to ask...What would be the benefit in using hollow concrete? |
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"the material would have to be reasonably solid. The sand on the beach tends to absorb the energy of the wave, thus you do not see much of the bouncing described above. That versus the wall of a bathtub, where the waves bounce quite happily." |
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I think that the biggest loss of wave energy is from breaking on the shore. As the waves run into the upward sloping ground (which actually begins to occur far out from shore, as waves can reach pretty deep), they begin to "pile up" and become distorted. This eventually leads to them becoming so unstable that they fall over and break on the shore. |
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It is like if you take a bouncy ball and throw it down at an angle so that it bounces forward. While it is bouncing forward, if it were to encounter a wall, it would basically reverse direction, but keep a similar bouncing motion. But if it encountered a gentle upward slope while it was bouncing, it would continue to bounce up the slope until it ran out of energy, then roll back down. This is what the waves do. They travel up the shore, break and are then swept back out in the undertow. |
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Anyhow, now that I have gone on for a while... I was just trying to say that shape will have a lot more to do with bouncing the waves than hardness will. You will need a deep vertical wall (like the sides of a tub) to accomplish it. |
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I think it would be simpler and easier to build giant parabolic reflectors in isolated desert hills. Sites could be chosen for natural contours to minimize digging. |
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If you were in a city trying to break a naval blockade, you could install an enormous parabolic reflector along the shore in parts, all submerged. At night you would raise it all up at once, with the focal point aimed at an enemy ship. The ship would suddenly be hit by a huge wave, founder and sink. By altering the components you could go on to target other ships, even those quite far out to sea. |
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For lakeside testing, the same principle should work for those rented paddleboats. |
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[leucke],
"It is like if you take a bouncy ball and throw it down at an angle so that it bounces forward. While it is bouncing forward, if it were to encounter a wall, it would basically reverse direction, but keep a similar bouncing motion. But if it encountered a gentle upward slope while it was bouncing, it would continue to bounce up the slope until it ran out of energy, then roll back down. This is what the waves do. They travel up the shore, break and are then swept back out in the undertow." |
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yes...then the ball continues back the other direction with the exact amount of energy because none was lost since it was purely a gravitational force. The waves would do close to the same if the sand wasn't their to absorb the energy. |
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Obviously you would want a wall that went deep under water...that's what I meant in cliffside shoreline. |
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[bobad], It would probably be hard with all the sand. Look at the leaning tower of Pisa :) Plus, the sand would be hard to keep out of the porabola, making the ocean floor less deep. Plus, you'd have much less to support the parabola's material against. Rock would solve all of these. Don't get me wrong, a desert would work....it'd probably just make things a lot harder. Plus, you'd have to run the powerlines to the power grid. |
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[bungston], muhahaha! Good thinking! >:) |
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Interesting idea and great first post. I've always been a little fascinated by the multiplication that occurs at the focal point when I tip a half-full soda bottle. It's quite percussive if you have the right shape to quickly displace the air in the way. |
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You should make it so that it could automatically adjust with the tides. |
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Ideally, the parabolic wall would be deep enough where the change in water depth from the tides wouldn't change anything. If the sea floor wasn't smoothed, then, low tide might add some losses due to waves comming closer the jaggies on the sea floor...but that is something that needs to be researched. |
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If you are going to mark the idea with a (-), can you please give a short reason why? |
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Okay, I didn't give it a vote yet, but it seems to me that all of this wave energy converging to a single point will be too powerful to harness. |
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Then you de-focus it or have more, smaller parabolic regions. Not difficult to do. |
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I'm all for brainstorming, but this idea should go to bed now. ocean waves aren't focusable really. focusing, as in a satellite dish, depends on a clean coherent signal coming from a consistent source direction, a perfect reflector, etc. Only in incredibly perfect conditions could this work, and only with a perfect non-turbulent wave. if the wave came in a few degrees off angle, an irregularity in the ocean floor or winds or seasonal changes distort the wavefront, and it won't work. although classical energy waves are well-behaved, surface waves are not if they become at all turbulent. when they are turbulent, they will not "pass through each other" or bounce or focus.. they smash into each other because they've been converted to chaotic kinetic energy at that point. so your reflector would have to be unbelievably rigid so that it reflects (instead of absorb) the energy, and also it must be perfectly shaped in the z-axis so the wave doesn't get turbulent. you'd be constantly having to dredge the sand the ocean puts there, because it would compromise your "reflector". |
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"ocean waves aren't focusable really. focusing, as in a satellite dish, depends on a clean coherent signal coming from a consistent source direction, a perfect reflector, etc." |
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They are waves...they are focasable. Coherent...yes...phase needs to be the same...mentioned later. Source is important...mentioned later. A perfect reflector...no way. You think the dish network parabolic reflectors are perfect? Don't think so. An imperfect reflector will just cause the focal point to broaden. |
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"if the wave came in a few degrees off angle" |
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This is true. I've found that even 4 degrees is enough to severely mess with the focal point. I used to live by the ocean. On the straight beaches, I always remembered the waves crashing all at once along the beach all year round. Someone will have to see how much the angle changes. Due to some randomness...I doubt it's enough to matter that much. It would only be a problem IF the waves WERE completely on angle and coherent. |
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"an irregularity in the ocean floor" |
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obviously, a place with a consistent and flattish seafloor would be choosen...like mentioned. |
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"winds or seasonal changes distort the wavefront" |
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We are only conserned with the angle, not frequency or shape. As long as its phase is consistant along the whole wavefront, everything is fine. The position of the sun relative to the earth shouldn't change this...but and the winds will be mostly constant anywhere on the waters surface (due to randomness). |
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The crosswinds winds might change the angle...observations would have to be made. |
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"surface waves are not if they become at all turbulent" |
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All that is needed is a straight wave made a swell of water. bumpiness of this swell and whatnot are of little concern. |
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"when they are turbulent, they will not "pass through each other" or bounce or focus" |
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A wave is a wave is a wave. A wave is a disturbance created in a medium. You have to realise the water depth will be deep, so, the waves will remain as swells, not large wave crests like you see on the beach. And, a turbulant wave would mean two waves superimposed upon each other, one with lower frequency and much greater amplitude (the wave of interest) and the other being useless noise. We don't care about the noise since it will be random and pretty much cancel. If you don't think turbulant waves will bounce...then obviously you've never been on a crouwded lake in the evening after everyone has been water skiing all day and gone home. Haven't you ever played in a bathtub or in a pool and made standing waves??? |
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"so your reflector would have to be unbelievably rigid so that it reflects (instead of absorb) the energy" |
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I've mentioned this several times...CONCRETE. it will be PLENTY rigid (come on)...and heavy. Obviously there will be SOME losses since we can't have infinite rigidity...but we don't need it. The correct materials will obviously be choosen to get the job done. No use in using Jello or foam. |
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"and also it must be perfectly shaped in the z-axis so the wave doesn't get turbulent" |
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If by the z-axis you mean upwards (like in physics and math, not video games) then yes...a flat parabolic wall will do nicely. And, wouldn't have to be perfectly flat...just flat. |
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"you'd be constantly having to dredge the sand the ocean puts there, because it would compromise your "reflector".
" |
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again, obviously, the correct environment would be choosen. If the ocean floor was deep and fairly flat, the energy would cause very little turbulance at the ocean floor from the waves (watch videos taken under the ocean...do you see sand and whatnot flying everywhere? no...it's very still.) And, like mentioned in the idea...a rock shoreline could be used...meaning no sand and stable surface...meaning no constant dredging. |
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Please don't ever say an idea won't work like that. It might not work very well. Obviously from the arguments you provided, it's your OPINION not fact...there were no experiments done and you did not try to build one (that I know of)...meaning, you could only have said "it might not work" or "I don't think it will work" or something similar. |
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I have done some simulations and am getting the animations ready. One of them is a non perfect reflector, and wave comming in at an angle, and visualisation of standing waves in a shallow and deep parabolic reflector. |
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I have some of them up now. Some can be seen at
http:\\broken.pc.cz\gallery\parabolicreflector
The site uses java for the animations cause I didn't have a GIF animator on the computer I was using. |
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To sum everything up, I do agree that a change in angle could be a problem. I personally don't think it will change enough just from unthoughtfull observations...but what I or you or anyone thinks doesn't matter in this case...only what actually happens. |
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Please respond with anything you disagree with. |
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<yabba do yabba dabba>, hahaha...thanks for the compliment ;) |
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Can someone summarize the last 6000 words of anno for me? |
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//Can someone summarize the last 6000 words of anno for me?// |
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no. but i would recommend the animations (link). |
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<Spinster>,
Read the last paragraph silly. I knew people wouldn't want to read it all, that's why I put that :) |
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This idea is more about the collection of the energy to a small area rather than the power generator that's used. But you're right...it would be a lot of work, especially for large power output...but we need large power output for the dense populations and power usage we have these days. |
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I started doing the calculations of the maximum theoretical energy you could extract from a massive wave at the lake a couple days ago, but I couldn't remember how to derive one of the equations and I didn't have my math book with me. |
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I'll try to figure it out soon. |
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