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DRP #4: Breakwaters

Home Forums Archive Distributed Research Projects DRP #4: Breakwaters

This topic contains 76 replies, has 15 voices, and was last updated by Avatar of ellmer - http://yook3.com ellmer – http://yook3.com 4 years, 8 months ago.

Viewing 15 posts - 16 through 30 (of 77 total)
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  • #4501
    Avatar of
    Anonymous

    I don’t think you can repair tears during a storm. So you need to be sure the tears won’t spread much over a few days of heavy waves.

    #4504
    Avatar of Jesrad
    Jesrad
    Participant

    Reports on attempts to artificially grow kelp show it is a lot more difficult (and costly) to achieve than expected… Kelp needs a specific range of depth and floats to the surface, so it cannot be tuned to ocean waves, and a significant fraction of it gets ripped off coasts by storms already so they would probably make a poor breakwater – that’s why I would turn to growing a reef on artificial support instead.

    Seeding environant water and offering a convenient submerged support for coral and other biofouling organisms over time might be one cheap, if long, method for building a large marine submerged (and self-repairing to some extent)structure.

    #4505
    Avatar of Thorizan
    Thorizan
    Participant

    I like this idea… and it may be good to combine a seastead with an airstead… in case of emergency, you have a “port” to go back to, and a launching point for visitors and cargo.

    #4506
    Avatar of Patri
    Patri
    Keymaster

    Yes, that’s close to what I mean, except that the entire thing is submerged. The idea is that by the time the waves reach the inner ring, they have already piled up enough to be unstable, and broken.

    So there is no need to ever walk on it, and it never holds any water up off the ocean. It just nudges the waves from below to pile up and break.

    #4507
    Avatar of Patri
    Patri
    Keymaster

    Great for being able to be smaller.

    We could reinforce the plastic with a grid of compression members, if necessary, although of course that adds a lot to the cost.

    The problem with trying to do clever wave cancellation is that waves come as a spectrum. There is actually no such thing on the ocean as a single wavelength or height, instead there is a whole spectrum w/ different energies at different frequencies. We characterize the spectra by the highest energy frequency, but I think there is plenty of energy in other frequencies as well.

    A wall is the simplest solution, I just worry that it takes enormous quantities of concrete. Perhaps you could email that company and ask them how much they thought it would cost, per unit length, for a floating concrete breakwater to stop deep ocean waves?

    #4508
    Avatar of Patri
    Patri
    Keymaster

    This is a really important point, thanks for mentioning it! I’ve thought about it a bit, and I need to add a discussion on this to the book.

    The basic answer is that breakwaters do reduce the benefits of dynamic geography, but I believe they may reduce the costs of building on the ocean so dramatically that they are still worth it.

    Barrier to entry: Spar platforms that can resist the waves are really big and expensive. Based on my rough price estimates, a breakwater may not be any more expensive than a spar platform. Our spar platform to survive the waves off San Francisco is about $50M. My breakwater design (which may be completely bogus) is a similar cost. The size at which economies of scale render breakwaters to be a reasonable competitor to spar platforms may be within a factor of 1-5 of a single platform. So we aren’t hurting barrier to entry that much.

    Cost of switching: Here it depends whether each breakwater has a single central authority. The cost of switching between regional authorities within a breakwater is still very low. (Lower than a bunch of spar platforms, actually – mobility within a breakwater is very high). So the question becomes – how hard is it to move a calm-water structure from one breakwater to another? Here it’s going to depend on distance[1], on whether you can wait for a calm water period, on whether we can economically build large ships whose job is to move calm-water structures between breakwaters. I think it will be substantially more expensive, but again, if these calm-water structures cost 1/10th or 1/50th as much to build…seems worth it.

    It’s a bummer, and I wish that my reading of the situation was that purely modular structures could cost-compete with breakwaters. But I just don’t believe that. Ocean waves are huge and nasty and getting economies of scale on calming them is, I think, going to be essential for lowering the cost of “aqua firma”. One exception is the equatorial doldrums, where the water is fairly calm all year round.

    Anyway, I don’t think having breakwaters is a disaster. Yes, it will result in more centralization and less political wins. But we will still be dramatically lowering the barrier to entry and cost of switching compared to land. Still, this is an important point, and I’m glad you made it – nice to know that some people really “get” dynamic geography enough to make points like this!

    [1] One might imagine an upstart breakwater coming close to an existing city so as to poach its citizens away by making a short travel distance.

    #4509
    Avatar of Patri
    Patri
    Keymaster

    Love the 3d models – so much easier to discuss.

    I am not convinced that circular will work better than rectangular bricks…seems like the inner half is not doing much. Entrained water is definitely good. And having something that can be made in a mold for mass production. You still have massive material costs for the concrete. Styrefoam does seem to be a standard way to make concrete floatable.

    I think connecting them is pretty doable – put bumpers between them and then put them all in tension. Say, tie each one to its neighbor.

    Anyway, I think this general idea of a series of segments in a circle is a good candidate, I just don’t think cylinders are the best segments. I like either “walls” (boxes that the waves smash into), or possibly short ramps, so that the waves quickly roll up and break. A short ramp would be something like a square cut diagonally, say 50m long and 50m high. Because the slope is so high, the waves are smashing into it quite a bit. But because it is a ramp, they are also rolling up it, and then breaking when they fall off the top.

    #4510
    Avatar of Patri
    Patri
    Keymaster

    Doesn’t look solid enough to break waves. I think they will wash right through it.

    #4511
    Avatar of Patri
    Patri
    Keymaster

    This is a frequent suggestion, and a good one. For the long-term, I think it is a great idea. For the short term, I worry about all the extra cost and engineering effort involved in having to solve 2 problems at once. I suspect that a wave power farm large enough to protect a substantial calm area would be hugely expensive – many times that of a plain breakwater. So I favor getting started with just a breakwater, and then trying to develop cost-effective power-generating breakwaters over time, perhaps experimenting by replacing a small segment.

    This should definitely be discussed in the book. Any more pointers to ideas? Our Isaac’s Wave Pump will act as a mild wave damper. Some others:

    #4512
    Avatar of Joep
    Joep
    Participant

    Coral reefs are a lot heavier, and not easy to wash through. But i guess much to slow to grow a nice breakwater in our lifetime.

    I’ll keep the thought of growing cheap stuff with a lot of drag at depths where the water is calm for the DRP “Keeping the spar upright with less ballast” :)

    #4514
    Avatar of Steffen
    Steffen
    Participant

    There is something about the estimated cost of a seastead which I seem to have completely misunderstood. I thought that in a couple of weeks you were going to come up with a design idea for a single family seastead and it would have an estimated production cost similar to that of a land based home in f.x. San Francisco. But I cannot believe that a normal family home in San Fransisco costs anywhere near 50,000,000 USD. Can you explain?

    #4515
    Avatar of Carl-Pålsson
    Carl-Pålsson
    Participant

    I knew I had seen the tubular snake-style wave generator somewhere… The good thing is that then we don´t need to invent them, we can just buy them from Pelamis. But of course we don´t know whether they are any good at damping waves. Theoretically of course they should be as they presumably are designed to absorb as much energy as possible from the waves. But perhaps not for really big waves.

    I think if you design a generation system cleverly the total cost might not be that much more than a passive wave break. Since it is by definition a very large structure the material cost is always going to be a substantial portion of it. And the tasks go together so well – we need to get rid of excess energy in the water – and we need to produce energy to use for general use – so it seems like a shame not to try.

    I agree a circular cross section breakwater might not be very efficient. Here is a different take on your inclined annulus idea:

    http://wiki.seasteading.org/index.php/Image:Collector_breakwater.jpg

    The waves go up the incline and gets collected in troughs, leading to turbines that produces energy from the potential energy of the water. I make no guarantees about the practicality of this…

    By the way does anyone understand the principles of the power generating breakwater by Buckminster Fuller two posts above this? I can´t tell how that thing is supposed to work.

    #4516
    Avatar of Carl-Pålsson
    Carl-Pålsson
    Participant

    The inner half gets pushed against the water inside the breakwater. Presumably with a force roughly equal to that of the wave. A rectangular brick is likely to need internal structure. A circle is strong in itself. Anyway that is how I reasoned with the tube. In the end I couldn´t say if it will be any good.

    An exponential ramp might be useful to decrease shock loads. Like a quarter pipe skateboard ramp.

    http://wiki.seasteading.org/index.php/Image:Quarter_pipe_breakwater.jpg

    #4517
    Avatar of Carl-Pålsson
    Carl-Pålsson
    Participant

    Ah, interesting…I sort of had the impression you were trying to lift half the ocean up in the air on a sheet of plastic.

    I can still imagine there being some pretty strong shearing and pulling forces on the PET sheet, but perhaps not too much given the large area everything is distributed across.

    Has something like this been tried in real life, experimentally or otherwise?

    #4519
    Avatar of Patri
    Patri
    Keymaster

    But it seems very amenable to computer and wave tank simulation, so it should be easy for our consultants to investigate

Viewing 15 posts - 16 through 30 (of 77 total)

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