Rogue wave detection & mitigation
October 20, 2008 at 11:23 am #3989
The brute force appraoch is usually obvious, but not necessariloy trivial.
I still submit that the phenomenon has not been studied and documented well enough to say that it is undetectable until the worst has already happened. The idea of tracking incoming artillery and shooting it out of the sky was science fiction not so long ago.October 21, 2008 at 11:03 am #3993
Rogue waves may be chaotic and largely unpredictable; they “appear out of nowhere”. OTOH non-linear dynamics may be able to model them. But they’re much less predictable than an artillery shell or mortar round which follow newtonian physics pretty closely, show up on radar relatively long (many seconds) before they arrive, etc.
The obvious answer is to design for very tall waves.October 22, 2008 at 1:34 pm #4005
OK so what is the problem with very tall waves?
It’s probably somewhere between “Everything on my deck got drenched” to “Holy Shizzit the boat capsized and sank!”
On a spar the problem would seem to be the wave over-topping the spar and damaging its deck, possibly dumping water into the interior. It doesn’t seem likely to actually capsize the spar, from the smaller moment of leverage above water vs the long lever below water. Even dumping water into the interior momentarily seems unlikely to sink it, though possibly causing damage, injury or loss of life. Maybe it could exert enough lateral force to crack or snap the spar? This last would not be solved by height, but by strength.
On a cantilevered spar/platform combo, we see essentially the same as above, with the additional possibility of damage to the platform, or the join of the platform and spar, but seemingly lesser possibility of the interior of the spar flooding simply due to being overtopped by a wave, because the platform would act like a lid that is mostly closed.
I don’t think the possibility of a rogue wave justifies all the disadvantages of creating a spar platform that is beyond the reach of a rogue wave. Not just the economic cost and engineering difficulty of construction, but the disadvantages of being so far above the water in daily life.
For other types of platforms, floating islands, rube goldberg hamster habitats, whatever, I think you’re better off spreading your stability out laterally and designing for some combination of strength, shape, and flexibility that allows for occasional waves overtopping the deck. Then you keep an operations crew or some type of automated monitoring going round the clock.October 22, 2008 at 3:04 pm #4011
One of the very sophisticated oil exploration platforms was sunk by water from a rogue wave breaking a small window and flooding the active bouyancy control system. All the people on it were lost. Does your platform have any windows? How many tons of water (really energy from moving water) can each window withstand?
Water is very dense. A large amount of moving water contains a very, very large amount of energy.October 22, 2008 at 4:05 pm #4017
Lesson: Do not rely on active buoyancy control systems. And make any windows and doors as tough as the wall they sit in. Expect all of them to get hit by massive waves.October 22, 2008 at 6:13 pm #4020
A properly designed spar platform is unlikely to be sunk by a rogue wave. There can be a bunch of pretty expensive stuff up on top that be damaged by a rogue wave — solar panels, wind generators, etc. One possible solution is to damage problem is to purchase a rogue wave insurance policy.
My latest designs expect the lower deck to encounter waves in bad weather. The solar cells and expensive stuff are placed higher on a very light weight platform.
It is all a trade-off.October 25, 2008 at 1:48 pm #4050
Of course there are necessary trade-offs, but it’s still good to acknowledge occasionally to keep it firmly in mind.
Designing to be able to occasionally overtopped by a wave and survive seems much more sensible than trying to design something that cannot be touched by waves. It’s more likely to provide an economical and usable design, and more likely to incorporate a philosophy of graceful failure- not good to put all the eggs in one basket, i.e. “I will build this thing so tall a wave can’t touch it” until of course, a wave comes along that is taller than your wildest dreams…June 19, 2010 at 8:03 pm #10496
Another article on rogue waves… nothing new except that it seems they can stabilize after forming and travel for miles… maybe that’s old news but it’s new to me, thought others might be interested.
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