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Using mobility to reduce maximum wave design parameter
Sun, 06/15/2008 - 10:27 — vincecate
The maximum wave we could face determines what we have to design for. If we could be sure we never had to face over 30 foot waves we would not need to design for 100 foot waves. This would make things much easier. I think if we have the right migratory pattern we could do this.
Imagine we are using kites to move in a big circle around the Sargasso Sea each year. I am thinking Anguilla, Bermuda, Azores, back to Anguilla. We could time it so that we were in the North-Eastern half of this loop to avoid the hurricane season in the South-West and then in the South-Western half of the loop to avoid the cold stormy season in the North-Atlantic. With computers controlling the kites and sea anchors I think we can move at the right speed to make this happen. I think if we checked historical information that doing this you would never have had to face even a 30 foot wave in the last 100+ years.
A related idea is that even slow movement can probably get out of the way of a hurricane, even if you start in the path of one. These days you can get more than 4 days warning for a hurricane. If you can move 2+ MPH then in 4 days you can move over 200 miles. This should be enough to reduce the maximum wave to less than 30 feet.
My favorite design should be mobile enough to do this.
http://wiki.seasteading.org/index.php/User:Vincecate/Tension_circle_hous...
If this is 112 feet wide then a 30 foot wave would not really bother it.
My pilot charts show this is rather safe route
I made a guess at where we would want to be when:
http://wiki.seasteading.org/index.php/Image:MigratoryPath.jpg
Then checked against my "Pilot Charts" for the North Atlantic. My route seems safe from hurricanes.
My charts also have contour lines for the chances of waves over 12 feet. The lowest probablility contour is either 5% or 10% and the places/times on my route are always less than the lowest contour line.
My charts also have chances of a gale. Where I have June is right between 0% and 1% chance of a gale during the month (should have made it just a bit lower). The rest of the time the chance of a gale is around 0% (they note that 0% means closer to 0 than 1% but maybe not really 0). By "gale" my charts mean at least force 8 on the Beaufort scale which might be just 18 foot seas:
http://en.wikipedia.org/wiki/Beaufort_scale
So it looks like we could make a route with a 1% chance (or maybe less) of an 18 foot sea once during during the year.
It is at force 9 that waves start breaking in the open ocean, which can be particularly hard on structures:
http://books.nap.edu/openbook.php?record_id=11635&page=62
So I still think the odds are you could go 100 years on a route like this and never see waves over 30 feet or breaking waves. But would be nice to get more information. I doubt I have the most optimal route already but it gets the idea across.
Won´t the energy of the
Won´t the energy of the waves slamming in to the breakwater transfer via the wires to the house, vibrating it rather uncomfortably? Or is the idea that waves that don´t break are gentle enough not to matter in this regard?
Where the wave energy goes
The structure is supposed to be stiff like a bicycle wheel. We are only moving between 0 and 2 MPH probably. So mostly the waves will just be going around or lifting the structure but not slamming. You can see the model in the video. Most of the force that does not go around really pushes on the wall sections next to it and so on to the back side where it pushes on water again. So the house movement should be gentle enough.
Cycloidal Drive - Voith Schneider Propellor and sails
A ring of cycloidal sails around the top of the ring and cycloidal propellor blades underneath could provide wind propulsion from any direction. The rings spins from the sails changing angles to catch the wind while the prop blades change angle to provide thrust in the desired direction.
http://en.wikipedia.org/wiki/Voith_Schneider_Propeller
cycloidal drive: interesting
For Vince's circle tension house, the foamed concrete island, or some other lighter-than water structures that are extremely shallow in draft, (hexagonl lash barges, "Spiral Island"-like structures) I can imagine that instead of a few hydrofoils on a shaft, a setup where a chain- or track-driven set of hydrofoils that encircles the entire structure would be possible.
larger propulsion surface = lower power, higher efficiency
Yes, the idea is to have the sails and blades along the perimeter. A larger propulsion surface reduces the velocity required and corresponding drag for a given amount of thrust. This is similar in principle to a larger diameter fan requiring less power to move the same amount of air, or a larger diameter rotor requiring less power to produce the same amount of lift in a helicopter. If the breakwater ring spins then there is no need for the tracked drive train. The tracked drive train would make sense for a large solid structure like a barge.
Capturing waves breaking on a sloped surface and channeling the water to produce thrust and run high volume, low head vane avial turbines to produce power may also be an option.
Another good thing about
Another good thing about this is, for a powered solution, the engine can be anywhere. The problem of vectoring thrust pretty much goes away. For redundancy, two engines could be located on opposite side of the structure and either balance the load or one can be a smaller engine kept in reserve for emergencies (this is a cost savings). Locating close to the edge makes it easier to service and fuel these engines.
Couple wiki pages
I made two wiki pages on the migration and kite stuff:
http://wiki.seasteading.org/index.php/User:Vincecate/Migration
http://wiki.seasteading.org/index.php/User:Vincecate/KiteAndSeaAnchor
Two Comments
First, I really like the idea of using mobility to manage wave height/length. It also allows you to manage average temperature. Great idea!
Second, when it comes to comfort in large waves, both the wave height and wave length matter. The larger waves tend to have fairly long wave lengths. The tension circle house is really going to thrash its occupants sitting up there when it encounters wave lengths that are 1/2 the circle diameter. One edge will be down in the trough and the other up on the crest.
big waves are long waves
>First, I really like the idea of using mobility to manage wave height/length. It also allows you to manage average temperature. Great idea!
Thanks. Trying to get an idea of the potential for wind to move something big in the water I took a 3 foot diameter sea-anchor out with me and my boys on the kayak yesterday. With about 20 MPH wind blowing on the 3 of us we moved past an anchored 35 foot boat in 1 minute. This is about 0.4 MPH. With a kite instead of just our bodies we could have gone faster. Scaling for model size this is plenty fast enough.
When I get my waterproof camera and a few models built I will try to measure speed vs force on these.
<blockquote>Second, when it comes to comfort in large waves, both the wave height and wave length matter. The larger waves tend to have fairly long wave lengths. The tension circle house is really going to thrash its occupants sitting up there when it encounters wave lengths that are 1/2 the circle diameter. One edge will be down in the trough and the other up on the crest. <blockquote>
As you say, larger waves tend to be longer waves. A typical 5 foot high wave has a period of like 8 seconds. There is a formula saying deep ocean wave speed in m/s is 1.56 times the period.
http://www.oceanographers.net/forums/showthread.php?p=1579
From this we can calculate a speed of 12.4 m/s. And in 8 seconds such a wave goes about 100 meters. So a typical small wave has a wavelength of nearly 3 times my width. Big waves have longer wavelengths. I think any wave with a wave length that is half my 112 foot diameter is a small wave, or at least not too much of a problem.
If you compare my 112 foot width to a 28 foot wide boat, I am talking 4 times the width. This makes for a gentler motion and people are ok on 28 foot wide boats in huge waves.
Some of my model tests had big waves where the wavelength was not far off and there was no thrashing.
If a 30 foot wave with a 12 second period goes under a 112 foot wide tension circle, just how much thrashing are you thinking of? Does tilting 10 degrees and then back in 12 seconds count as thrashing?
Updated the migration page
I changed the migration path a bit (moved East side further East). I also found some more information about tropical storm and hurricane probabilities by the month. Idea still looks reasonable.
http://wiki.seasteading.org/index.php/User:Vincecate/Migration
You have to take life as it happens, but you should try to make ithappen the way you want to take it. - German Proverb