B Recreation of Famous Japanese Rogue Wave

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https://arstechnica.com/gaming/2019/01/oxford-scientists-successfully-recreated-a-famous-rogue-wave-in-the-lab/

In 1995, a powerful rogue wave slammed into an offshore gas pipeline platform operated by Statoil in the southern tip of Norway. Dubbed the "Draupner wave," it generated intense interest among scientists, since the platform's various sensors and instruments provided precise details about the wave's dynamics. Rogue waves had long been considered a myth, so those readings—combined with damage to the platform consistent with a wave some 84 feet high—provided crucial evidence for the phenomenon

It wasn't long before scientists were attempting to recreate rogue waves in the laboratory, the better to understand the mechanisms behind how they form in the first place. Now a team at the University of Oxford in England has successfully recreated the "Draupner wave" in a circular water tank, according to a new paper in the Journal of Fluid Mechanics, shedding further light on the mechanisms that produced it. Bonus: the wave profile bears a striking resemblance to The Great Wave off Kanagawa, a famous 19th-century woodblock print by Japanese artist Katsushika Hokusai.
 

anorlunda

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Every one of my friends who has sailed across the Pacific reported being "knocked down" at night by an unseen unheard wave that came in moderate conditions. Some of them experienced that more than once. Of course there is no way to estimate the height of those waves.

It is a great argument for wearing a tethered safety harness at all times, and for people sleeping below decks to use lee-cloths to hold them in their bunk no matter what the boat does. After one painful experience, I put a pad eye in my bunk that I could clip my harness to. My wife had a safety belt she used when standing in front of the stove to prevent being thrown about.

It makes sense that "confused seas" (when waves come at you from multiple directions) is the condition when rogue waves are most expected.

Mariners are like everyone else, and they like swapping scary stories. One such story more scary than a rogue wave is a rogue trough. That would be a transient hole in the water into which the boat falls, then the sea overhead comes crashing in and the boat is instantly sunk. I do not believe that any such event has ever been confirmed. But thinking of physics, I see no reason why wave height (above sea level) should not be matched with trough depth (below sea level). I wonder if the researchers looked for both positive and negative maxima.
 

sophiecentaur

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But thinking of physics, I see no reason why wave height (above sea level) should not be matched with trough depth (below sea level).
You got me thinking here.
The shape of gravity waves is not symmetrical. Troughs are wide and flattish whilst peaks are - peaked - and can break. That would imply to me that an interference pattern between two ocean waves would tend to produce large peaks (twice the amplitude of a single wave) but the wide troughs on either side of the peak would not be such a big event . 'Cancellation' by interference would actually result in flat water and not a deep trough.
It would be interesting to know how many waves from different directions are involved in producing a seriously high rogue peak. I imagine there could be some focussing effect on one high, wide wavefront.
 

256bits

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Isn't that what happens when on splashes around in the bathtub.
Even though it isn't wind producing the waves, there does appear to be an "amplification" of wave height at times, from the reflections and forced oscillations, never on sync ( one can get high waves by being in sync but that is not what we are after ) and over the side of the tub the water goes - a mini rogue wave.
 

A.T.

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The BBC did a show on the Rogue waves that sunk a container ship and hit an oil drilling platform that were by estimation 2.2 x the size of swells at the time which is beyond that predicted by the linear model of wave formation.

For large waves, there is a deeper valley before the wave and that means a ship entering that valley will tilt down more allowing the large wave to crash overhead in other words it magnifies the apparent wave height dramatically as seen by the ship.

 

anorlunda

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That would imply to me that an interference pattern between two ocean waves would tend to produce large peaks (twice the amplitude of a single wave)
Yes, that's the interesting question. Why must those large peaks be directed up, and not down?

If I view is as just a exercise in Fourier superposition and interference, then I expect plus minus symmetry. But that doesn't seem to happen, so there must be additional physics that I'm missing.

My guess is that it is related to the sub-surface behavior. We have an asymmetry, sub-surface down is water, sub-surface up is air. It sounds like this earlier thread (where I was proven wrong by other PF members). But I don't see how to apply that to this case.

https://www.physicsforums.com/threads/is-the-water-pressure-below-ocean-waves-constant.915102/

Edit: I'm not sure the analogy is correct, but it makes me think of this picture. The column is generated by superposition of ripples after a drop hits the surface. But there is no such thing a a column of air like that directed downward.
Water_drop_impact_on_a_water-surface_-_%281%29.jpg
 

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sophiecentaur

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plus minus symmetry. But that doesn't seem to happen,
Isn't the assymetry just because the water at the peaks has nowhere to go and the water in the troughs can go / come from all directions.
It's certainly the result you get if you follow the circular motion that the water particles follow. Years ago I wrote a simple simulation prog, based on that and produced just the right looking peaky shape. Deep water waves are pretty well sinusoidal but, as the system isn't linear, the effects below the surface level wan be expected to be different from the effects above.
 

anorlunda

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Isn't the assymetry just because the water at the peaks has nowhere to go and the water in the troughs can go / come from all directions.
I think we are visualizing different cases. You speak of recurring peaks and troughs. The rogue wave case is one of a single anomalous peak, more akin to that water droplet picture I edited in to #7.
 

sophiecentaur

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I think we are visualizing different cases.
Probably. As I see it, there are two main ways in which the Energy can become localised. There is diffraction and there is dispersion. In one case a number of waves turn up in one location with appropriate phases for addition. In the other case, there are waves of different speeds which come in phase at one point. The simulated situation above seems to imply its a matter of dispersion, where a peak forms from waves of different speeds.
 

sophiecentaur

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Cool rogue wave simulation in a wave tank:
A good fun movie but it doesn't imply anything about how a rogue wave actually forms in the ocean. Hats off to the tank designers, though. That sort of facility must be very useful for designing more wave resistant hulls.
The whole field of water waves is so unlike the stuff we 'know' about the way waves behave in a linear medium. Not only is the medium non-linear but there can be significant Energy Input from the wind on the path of an ocean wave. This is so different from the familiar mechanisms of EM waves in space or on a transmission line.
 

anorlunda

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Cool rogue wave simulation in a wave tank:
Yes that was cool. But they staged it where the wave broke, simulating a boat anchored in the shallows at the beach. If they moved the sailboat forward to where the waves were not breaking, I think it might have survived just fine.

The danger of rogue waves is out in the open sea, not at beaches. And the danger to sailboats is when the wave approaches beam on rather than bow on. In confused seas, the waves approach from many directions, so you can't keep the beam into the waves.

If you watch that video on youtube, you'll see a vigorous debate in the comments. Half the commentors say that rogue waves always break, no matter the depth. The other half don't.

The debate is muddled because many viewers think that rogue waves happen only during severe storm conditions where the wind blows the top of the wave over. The preface to all such videos begin with film of breaking waves in a storm; pure hype. But the rogue wave problem can happen in calm wind local conditions with the waves arriving from far distant storms.
 

sophiecentaur

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But the rogue wave problem can happen in calm wind local conditions with the waves arriving from far distant storms.
. . . . . and augmenting in some way at some location - because I suspect they must disperse again or they would be observed more often.
So - interference or dispersion?
 
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Yes I believe you’re right. I suspect it’s because waves are more likely a nonlinear phenomena and are governed by different behaviors.
 

anorlunda

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because I suspect they must disperse again or they would be observed more often.
Yes, that's how I visualize it. The rogue wave happens only at the intersection point of two or more wave fronts. It is more or less a 1 dimensional column, and it lasts only a second or two.

I've always been interested in the rogue wave idea. I spent many hours on watch at sea looking toward the horizon (what else is there to do? :smile:). My theory was that an anomalous wave would look like a transient bump highlighted in silhouette against the horizon. Alas, after a thousand or so hours staring, zero hits. The horizon always appeared to be just a boring straight line.
 

LURCH

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I think that most of the eyewitness accounts describe a wave that breaks in deep water, with or without high winds, and the demonstration in the first post is an attempt to show how that happens. This would also be more in line with the hull damage sometimes attributed to rogue waves. It would be very difficult for a rolling wave to inflict the type of damage shown in the photos, or to produce the effect of “ringing the ship’s hull like a bell” described by many.
 

sophiecentaur

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Alas, after a thousand or so hours staring, zero hits. The horizon always appeared to be just a boring straight line.
Perhaps that's just as well or we might not be getting the benefit of your contributions here. :wink: Earth curvature would tend to cause tall, distant waves to appear no higher than lower, nearby waves so perhaps you did actually see the very peaks of some distant 50m giants.
My mind wandered in the direction of detection of rogue waves with satellites but this SA Article suggests that satellites actual miss them - along with several other anomalies.
Then there is the question of how localised they are. In a short searching exercise, I couldn't find any information about that. Strange because it would be very relevant to the statistics of being hit by one. (Shotgun vs rifle bullet idea) If you could be warned that one was in the neighbourhood and be able to avoid it then that could be worth the insurance companies spending money to pay for a system that could achieve this.

I was interested to find the frequent use of the term "non-gaussian statistics' and I detected a bit of resentment about that as if Nature is being 'sneaky' in some way. But Statistics is, by definition, an attempt to condense information and that will always involve chucking some away.
 
Are these rogue waves similar to solitons?

Cheers
 

anorlunda

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Are these rogue waves similar to solitons?
No, in many ways they are the opposite. Solitons are long-lasting, rogue waves supposedly last only seconds.

https://en.wikipedia.org/wiki/Soliton said:
I was observing the motion of a boat which was rapidly drawn along a narrow channel by a pair of horses, when the boat suddenly stopped – not so the mass of water in the channel which it had put in motion; it accumulated round the prow of the vessel in a state of violent agitation, then suddenly leaving it behind, rolled forward with great velocity, assuming the form of a large solitary elevation, a rounded, smooth and well-defined heap of water, which continued its course along the channel apparently without change of form or diminution of speed. I followed it on horseback, and overtook it still rolling on at a rate of some eight or nine miles an hour, preserving its original figure some thirty feet long and a foot to a foot and a half in height. Its height gradually diminished, and after a chase of one or two miles I lost it in the windings of the channel.
 

tech99

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This is so different from the familiar mechanisms of EM waves in space or on a transmission line.
But I have noticed that a transverse water wave, when it breaks, delivers longitudinal energy. In a similar way, a transverse EM wave, on encountering an antenna, produces a longitudinal wave on the wire. Ships try not to couple energy out of the wave - a milk bottle survives a gale but a rock is smashed. A sloping beach seems like a tapered horn antenna, enhancing breaking action.
 

sophiecentaur

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a transverse water wave,
Surface waves on water are not just transverse. There has to be a longitudinal displacement as well as a transverse displacement. The water that piles up at the peaks has come from the area of water just in front of the wave and it goes backwards to the trough behind it.
a longitudinal wave on the wire.
The wave that's carried by a coax cable is TEM (Transverse Electric Magnetic fields). Any resistance in the conductors will cause a small wave tilt but the main feature is transverse fields.
A sloping beach seems like a tapered horn antenna
The wave speed gets slower as the water gets shallower and also there is dispersion - making the waves more and more peaky. Friction with the ground beneath produces the forward wave tilt which causes the wave to break in a forward direction.
 

LURCH

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The wave speed gets slower as the water gets shallower and also there is dispersion - making the waves more and more peaky. Friction with the ground beneath produces the forward wave tilt which causes the wave to break in a forward direction.
This, I think, is very similar to what happens with a rogue wave, or the wave demonstrated in the first post in this thread, and would explain why rogue waves break in deep water. If two waves are traveling in the same direction and at slightly different speeds, there can be some “piling up” of one wave on the other, but if two waves are traveling in different directions, at an angle to one another, then each wave will encounter the other as a significant impediment, much like a shallow spot, and both get bunched up, and stacked on top of one another.

I must confess, though, that I don’t understand the mechanics of how “Rogue waves can measure eight times higher than the surrounding seas…” ( from the MIT link in Post #10). Double or triple would be easy to understand, but eight times? I need to research that further.
 

sophiecentaur

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traveling in the same direction and at slightly different speeds
The speed of surface waves is a function of their wavelength so, if two short wave trains have been generated in different places, they may have different wavelengths (depending on water depth and wind speed etc.. So dispersion will cause one wave to catch the other up which can bring the region of the peak amplitude together. That goes against our familiar wave interference experience and it difficult to accept as normal for ocean waves.
eight times higher
Yes, that does go against our intuition. However, our intuition is based on waves in a linear medium where two waves can form a peak of only twice amplitude which is four times the local energy density. With a surface wave, the peak / trough displacement ratio gets progressively greater as the amplitude increases. It is not so unreasonable that the resultant energy density (the GPE = mgh of the water at the crest) could be more than four times???

, rogue waves supposedly last only seconds.
I was looking for some information on that. Do you have a source?
 

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