The Seasteading Institute

Here is another model of mine that does a good job of demonstrating the heave problem:

http://www.youtube.com/watch?v=mliXEhUMu-4

This bobbing is out of phase with the main wave period. When it is very low the waves are high and when it is high the waves are low. All the motion is driven by the waves (moslty bobbing/heave).

It foolish for a guy who joined 2 weeks ago to be calling me a “dunce” when I say that bobbing up and down can be an issue.

I didn’t call you a ‘dunce’ for saying the bobbing up and down can be an issue.

I called you a dunce for not knowing that ‘phase’ means.

Οὐκ ἐμεῦ ἀλλὰ τοῦ λόγου ἀκούσαντας ὁμολογέειν σοφόν ἐ&si

Tacoma Bridge was a resonance caused by wind. Not very accurate, when talking about heave, wave-forms etc. Not even remarkable, either.

As for bobbing out of phase, yes, it could be a big problem.

Take a close look at the FLIP ship(search this site, there’s enough info…). It’s designed to handle these problems. FLIP II would be even better at it. The one time they abandonned it, was because they don’t have any way to move it, other than tugs AND it was still anchored to the sea bed, so the waves were unavoidable. If it had had thrusters(I know, counter-productive to the research), it could have moved and avoided the problem all together… It has a small water-line… Nothing to do with it’s stability, other than reducing the energy imparted by the contacting waves… The thing is stable to 3 ft., in 30 ft waves. It’s just a giant, weighted bobber. To be that stable, though, it has to be long enough to submerge most of its’ length and relies on sea-water as ballast.

Later,

J.L..F.

If you can’t swim with the big fish, stick to the reef

Tacoma Bridge was a resonance caused by wind. Not very accurate, when talking about heave, wave-forms etc. Not even remarkable, either

In the case of the Tacoma Bridge the wind started a vibration in the structure, and the structure’s vibration caused an increase in aerodynamic load which increased the vibration, which increased the load, etc. So the twisting got worse and worse, kinda like a feedback loop, until it buckled.[/quote]

Resonance is a frequency, thus a vibration. You say I’m wrong, then use my arguement to prove yourself correct…

Now, as for your scenario, at some point you have to recognize gravity, buoyancy and weight distribution. A wave lifts, then the trough lowers, then the next wave lifts… To follow your logic, there would be no trough, therefore there can be no wave. There is not Lift-lift-lift, without the troughs between. Now you’re down to dealing with the harmonics of the structural design. Look at FLIP and FLIP II. FLIP is designed around the harmonics of wave motion, for stability. The video everyone uses as a ‘bad-example’ is of a particular situation that was preventable. All they had to do was cut the anchors and float away… Being tied to the bottom, the FLIP didn’t rise with the swells, so the waves won that battle, due to human stupidity.

All floating objects will have some point that they can be overbalanced, however it takes moving the center of gravity near or above the center of buoyacy to make it top-heavy enough to be easily toppled, even that is a broad generalization. The main idea proposed is to move away from in-coming storms, to prevent storm damage, in the first place. I don’t know about you, but I hated sitting in my house, 200 miles inland, as a hurricane blew through… At sea, where everything moves anyway, it would be worse, unless you just get out of the way of the ones that are going to do you damage.

Later,

J.L..F.

If you can’t swim with the big fish, stick to the reef

All they had to do was cut the anchors and float away… Being tied to the bottom, the FLIP didn’t rise with the swells, so the waves won that battle, due to human stupidity.

The reason FLIP did not rise with the swells is it has a small-waterline-area. It is a spar. This is the point of a spar. It is not tied to the bottom in such a way as to keep it from floating up and down.

If you want to go up and down in sync/phase with each wave you need something with a larger waterline area, like a boat.

Look at the simulation of the TSI design, which has a small-waterline-area. The structure is going up and down, but not with the waves. So it can be down when the waves are up.

http://www.youtube.com/watch?v=Gbv_9LCODfg

Most floating oil platforms are tied to the bottom so they don’t bob up and down and have the problem of going down when the wave is up. This is called a “tension leg platform”.

http://en.wikipedia.org/wiki/Tension-leg_platform

[/quote]

FLIP gets anchored with 3 deep-sea anchors, to stop the motion that would interfere with the measurements… Since then, the anchoring has been modified, using nylon ropes attached tobetween the anchor-chains and FLIP. I’ve done that research, so I know what I’m talking about, there. Yes, FLIP is anchored against a certain amount of buoyancy, to remain stable, the same as oil-rigs. It’s easy enough to find on their websites…

The harder choice is WHICH waves to move with or ignore. FLIP, unanchored, rises with swells and storm-surges, but ignores smaller stuff, by design. High-frequency waves are easy to design away from… Our ancestors used ballast to help with that, as we do today. Low frequency waves are less disturbing to most people. In 30′ waves, FLIP has a vertical motion of several feet, versus bouncing around with the little waves, like a boat. Even sea-going barges have trouble with the smaller waves, though they are loaded with many tons of garbage. It’s more a matter of displacement-versus-center of mass.

Part of the design of FLIP is it’s ability to put sensors far enough below the surface to avoid the noise caused by the motion at/near the water-line. It CAN float with excellent stability, without the anchors. Part of the design is the height above the waves, so equipment and personnel are out of the danger of the water, in various scenarios. If the downward motion is only 3′, in 30′ waves, you only need to be at 35′ to remain safe and relatively dry… That is the beauty of the spar design! FLIP is merely a proven example of the type. If it were only 21′ to the top and moved with the waves, the waves it commonly encounters are higher than it…

Later,

J.L..F.

If you can’t swim with the big fish, stick to the reef

You don’t necessarily need the cable tied to the bottom, if it reaches lower than about half the current wave’s maximal length, it’ll find still water that is not moving up and down. Attach a set of heave plates there, that would work almost as well as an anchor in damping vertical bobbing of the seastead, without compromising mobility (much).