DRP #4: Breakwaters
December 19, 2008 at 2:36 am #4518
If my family is part of a 200 person seastead it seems very hard for me to leave.
If my family is on a boat in a floating marina, we might only leave when the weather is nice, but that is most days.
If my family is in a single family seastead we go where we want anytime.
— VinceDecember 19, 2008 at 2:40 am #4520
> Here it depends whether each breakwater has a single central authority
The breakwater must have an owner. This owner will naturally become the central authority. Or the central authority will naturally become the owner :). A political system with several owners / authorities doesn’t look like a stable one. After some power fight, some one would win. The winner will become both the owner and the authority. So breakwater == state. To drop entry cost to the market of states we have to drop breakwater costs.
So it is really good news that the thing should be measured in wave heighs rather than in wave lenghts. If we need 100 meters rather than 2 miles, the cost will drop 32**2 times i.e. to 50K. Which is an affordable one-family breakwater for one-family seastead. Probably 50K is too optimistic. However, we should not commit ourselves to 50-million “communal” solutions until we are absolutely sure that a cheap one-family breakwater cannot be build.December 19, 2008 at 10:46 am #4521
What about combining the pneumatically-stabilised platform idea with the breakwater tubes with entrained water, with the tubes turned vertically, and then add turbine generators between the tubes so that air goes up and down in the tubes, running the turbines AND damping the waves at the same time ?
I’ll try to have a picture of that uploaded soon.December 19, 2008 at 1:15 pm #4522
Some seasteads may take the form of breakwaters themselves. Also, waves propagate mostly in one direction at any given time in the ocean, that of the wind that generated them, so a breakwater may not necessarily be a closed barrier if it can move into the path of the waves (half-circle ?). If these two verify, then we can have division of labor between seasteads, breakwaters, and no impeding of mobility.
Useful link: study of floating breakwater, which is close to the particular regime of any open ocean breakwater.
Quick review: because a floating breakwater relies on entirely dynamic properties, it damps waves only over a given range of wave frequencies, so it is ighly desireable that the breakwater be tuneable, through variable buoyancy, variable mass (entrained/tank water), variable draft or variable width.
In my opinion the ideal solution would be that the breakwater and the harbored seastead both constitute the whole dynamic system together, so that they can be easily tuned by varying the distance between the two.
Page 32 lists the wave conditions and acceleration limits for cargo and passenger transboarding: 1m surge, 0.6 m sway, 0.8 m heave, 1 degree yaw and pitch, 3 degrees roll, 0.275 G vertical and 0.12 G horizontal.
Page 41 shows the wave spectrum for North Sea and open ocean, and Page 47 gives the formulas for getting the surge, heave, sway, roll, etc. from the wave parameters. This thesis report is a gold mine.December 19, 2008 at 2:13 pm #4524
I’ve not contacted them, but the thesis report (link below) shows that a rectangular floating breakwater with 18 m width, 8 m draft and rigid screen of 18.5 m attenuates 95-100% of waves’ amplitudes when period is 9 seconds or less, and 65-70% for period over 13 seconds. It also shows a 30 m width and 10 m draft caisson gives similar results, with better attenuation rates on waves of period above 10 seconds (the rigid screen tends to amplify those). This should help estimate the cost.December 19, 2008 at 5:20 pm #4523
>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.
If the water inside the wall is pushed with the full force of the wave from the outside then the breakwater is not breaking the waves at all. If the circular shape of the breakwater is held firm so the whole breakwater moves as a solid structure then the force of the wave is spread out over the whole structure of the breakwater. Much of it will spread around the outside wall on the far side.
If I took the bracing ropes off my model the waves would go right through it. With the ropes it is like a bicycle wheel and rigid.
In a flexible wall design the mass of the wall could slow the waves. It would take a lot of mass though.
— VinceDecember 19, 2008 at 9:01 pm #4525
The wall indeed needs to resist the waves or it will not be of any use. I agree having a totally rigid breakwater will probably be optimal, if you can pull it off.
A flexible one could also work, but as you explain it clearly cannot be completely transparent to the waves. As much energy needs as possible needs to be deflected or absorbed.
Thanks for pointing out this error in my reasoning.
Out of curiosity, do you have any idea what kind of tensile loads the spokes of your tension circle will be subjected to?December 19, 2008 at 9:45 pm #4526
Spending time designing large breakwaters => better large breakwaters => less mobility because the advantages are only gained if you stay (trapped) inside a large breakwater => “High Cost of Switching” and “High Barrier to Entry” => less freedom.
The same arguments can be made for large seasteads. They too have lock-in and high cost of switching for the individual. And need high capital investment.
You have a point in that it makes sense to start with smaller structures (one-family seasteads etc). But that probably shouldn´t mean that we should not research bigger future projects as well.December 20, 2008 at 9:27 am #4527December 20, 2008 at 5:02 pm #4528
The area within a breakwater is inflexible. Seasteads ought to expand easily when more people want to join.
How hard is it to design breakwaters so that another breakwater could be attached alongside? Is this easier if they are hexagonal rather than circular?December 21, 2008 at 9:05 pm #4530
The scissor mechanism looks somewhat fragile and complicated. If you want to be able to enlarge your protected area, is not a simple modular system where you just add more segments more fool-proof (as well as more expandable)?
Also this seems like it would make it difficult to get the tubes close to one another making the breakwater quite transparent to waves.
I like the idea of vertical tubes more, but perhaps in a simpler layout. Something like a palisade perhaps. http://en.wikipedia.org/wiki/File:St_Fagans_Celtic_village_palisade.jpg
Generating power with fans between different tubes also seems worth looking into. I guess you would have to tune the system to the wave frequency to make compressing tubes (wave up) connect to an expanding one (wave down) as often as possible.
The rigid circular shape is probably also good. I am beginning to have second thoughts about the damping ability of systems with segments that move and flex individually.December 21, 2008 at 9:17 pm #4531
I’ll have to admit an interest in airsteading as well. I’ve considered permanently aloft aircraft circling the world which use smaller, faster to transfer people and cargo from the ground. I also like Buckminster Fuller’s idea of large tensegrity structures which can stay aloft using warm air for bouyancy.December 21, 2008 at 9:22 pm #4532
If you have a system made up of modular segments you can enlarge your breakwater by just adding more segments.
Then when it gets too big, perhaps it could divide like a cell. I don´t know how feasible this is. It would be pretty cool though. http://www.youtube.com/watch?v=QrMoyOfim2s
To attach several breakwaters next to each other my instinct tells me that it would be better if they were rigid structures rather than flexible chains. In any case they would probably have to be much stronger than one that does not need to attach, because of the added external loads.
Hexagonal is probably a bit easier to attach, but I think a circle is a better shape for strength and efficiency. Perhaps some kind of inbetween would be good, like a circle with extended hardpoints for attachment.December 21, 2008 at 9:31 pm #4533
It probably could. But the question is how deep, wide and dense it would have to be to be of any practical use.
Also the growing time is a problem, like you say. I guess one could grow them big and fat in like a big kelp forest factory in a calm area before selling them to customers though. Or just manufacture a synthethic equivalent.
Perhaps hanging many sheets of plastic or whatever straight down next to each other would have the same effect.December 22, 2008 at 10:17 am #4534
Well, the picture is just that: an illustration. If actually built I would think the tubes would be instead tied together with cables, directly, just like the palissade, leaving hardly any space between the tubes for water to pass. The mechanism here is meant for the breakwater to adapt in realtime or fast enough – I’m not sure you can haul modules out, open your breakwater, add the new modules then close it back while there’s a storm hitting the structure, then do it again to remove modules after the storm. Stacking the tubes together and in a circle would also ensure they are only working in compression and not shear-pulled through their joints, with the intent of making the entire thing distribute the loads across the whole structure like a geodesic dome. I’ll modify the 3D model and post updated pictures soon.
Since larger waves contain much more energy, it would be beneficial to connect all the tubes together through a large ring so the vaster up and down movements spanning the entire breakwater can be harnessed. By actively timing valves this thing could be made dynamically self-pressurizing and add an active part to the otherwise passive damping. Or maybe each individual tube could be made into an Isaacs’ pump ? I’ve always favored purely mechanical and/or passive systems over active and electronically-controlled systems.
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