B Recreation of Famous Japanese Rogue Wave

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In 1995, the Draupner wave, a rogue wave measuring 84 feet, was recorded off Norway, challenging the belief that such waves were mythical. Researchers at the University of Oxford successfully recreated this wave in a lab setting, enhancing understanding of rogue wave formation mechanisms. The discussion highlights the dangers of rogue waves for mariners, emphasizing the unpredictable nature of these waves, which can occur even in calm conditions. Participants debated the physics behind rogue waves, including their asymmetrical shapes and the role of wave interference and dispersion. The conversation underscores the need for improved detection methods to warn vessels of potential rogue waves.
  • #31
sophiecentaur said:
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.

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.

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.
I agree the water wave is not purely transverse but just as a matter of interest, I do see some similarities with EM waves.
The wave on the wire of an antenna seems to resemble the single-wire mode to me, what I call TM01. The electrons on the surface of the wire are making longitudinal vibrations.
I agree with your explanation of the sloping beach, but it also resembles an impedance transformer, where the wave slows down and increases amplitude, then starts to deliver its energy to a load in the form of a longitudinal action as it breaks.
 
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  • #32
tech99 said:
The electrons on the surface of the wire are making longitudinal vibrations.
That's what we call a current induced in the surface and it's a boundary condition, imposed on a transverse wave. I don't make a big thing about terms normally but you are confusing the wave with the boundary, I think.
The issue of transverse vs longitudinal is not an issue - it's just the way the water moves; it cannot move just transversely so it is in no way a transverse wave. You only have to watch a buoy bouncing on a wave to realize that there is longitudinal motion for all water waves. If you are ever lucky enough to scuba dive a few metres under under some swell, you will see the rocks in front of you moving in circles and the kelp weed stays with you! (You accelerate too slowly to imagine you are moving so it's the rocks that 'move'). It is confusing at first but then, as a Physicist, everything will fall into place about what you learned about water waves.
 
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  • #33
johnbbahm said:
Energypeak= ∑ E1+ E2+E3...,
That makes a big assumption about the nature of the situation. If there is nonlinearity, the resulting height of the 'interference' peak could be anything - depending on the precise law. The vertical displacement depends on the forces at work and the peak is very narrow (much narrower than a sine wave) so the local density distribution of the PE around the maximum doesn't have to be what you would expect for a sine wave - or even for a low amplitude surface wave.
 
  • #34
sophiecentaur said:
That makes a big assumption about the nature of the situation. If there is nonlinearity, the resulting height of the 'interference' peak could be anything - depending on the precise law. The vertical displacement depends on the forces at work and the peak is very narrow (much narrower than a sine wave) so the local density distribution of the PE around the maximum doesn't have to be what you would expect for a sine wave - or even for a low amplitude surface wave.
I understand, I was simply trying to show that the possibility for rouge wave exists in the math as well.
You are correct that the randomness of waves of different directions, amplitudes, and frequencies would make the
actual peak interference very rare.
 
  • #35
johnbbahm said:
I understand, I was simply trying to show that the possibility for rouge wave exists in the math as well.
You are correct that the randomness of waves of different directions, amplitudes, and frequencies would make the
actual peak interference very rare.
I am saying more than that. I am saying that the waveforms involved can have the effect of exaggerating the straightforward effect that you get when adding sinusoidal waves. What counts is the peak value of GPE of a small mass of water (i.e. the height) at the top because it could be far higher than for the result of adding simple sinusoidal waves.
The statistics would apply for many different waveforms (for instance, the run of the mill regular ocean waves). We all agree that there is no surprise about the rarity of the occurrence of 'rogue' waves but the nature of these surface waves can lead to much worse localised effects at high amplitude.
Edit. I recommend having a play, next time you are in the bath and see what happens at the peaks of standing waves. They can be so extreme that they actually send up a vertical jet of water. don't get carried away by the experience or you could end up with a wet downstairs ceiling. :))
 
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  • #36
sophiecentaur said:
They can be so extreme that they actually send up a vertical jet of water. don't get carried away by the experience or you could end up with a wet downstairs ceiling. :))

Like this:



Cheers
 
  • #37
In the Kon Tiki expedition they described going over a train of three such waves, close up and intimate.
 
  • #38
The team successfully decoded the rogue wave's recipe: It simply needs two smaller wave groups that intersect at an angle of about 120 degrees, they found.
...
However, when waves cross at large angle (in this case, 120 degrees), wave-breaking behavior changes. As waves crisscross, the horizontal fluid velocity under the wave crest gets canceled out and so the resulting wave can grow taller and taller without crashing. "Thus plunging breaking no longer occurs and upward jet-like breaking, as illustrated in our video [see below], occurs. And, seemingly, this second type of breaking does not limit wave height in the same way," McAllister said.
https://www.livescience.com/64567-famous-great-freak-wave-recreated.html
 
  • #39
Thanks for sharing @Keith_McClary . But that article and video were too popularized. I would like to see the actual peer reviewed paper by the researchers.
 
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  • #42
The paper linked by @Keith_McClary does indeed provide a lot of light on this case. Thank you Kieth.

In a quick read, I see that almost all theories and explanations offered in this thread (harmonic, dissipative focusing, and wave breaking) are mentioned in the paper. I think all of us have been partially correct.

I would summarize it, but it would be better to read it yourself. The following is IMO a dramatic passage from the paper.

https://www.cambridge.org/core/journals/journal-of-fluid-mechanics/article/laboratory-recreation-of-the-draupner-wave-and-the-role-of-breaking-in-crossing-seas/65EA3294DAFD97A50C8046140B45F759/core-reader said:
Under crossing conditions, the breaking mechanism observed became fundamentally different. Figure 4 shows the onset of breaking when ΔΔ=120∘ . As the crossing waves combine, a jet forms that propels the water upwards. In this case, much of the horizontal motion is canceled out at the point of focus and this results in a partial standing wave. Typical plunging-type breaking is not observed. The formation of vertical jets on standing waves, which has parallels with wave impact on walls ..., has been examined by a number of authors ... Its occurrence is significant for two reasons. First, this form of wave breaking can be associated with extremely large fluid accelerations of the order of 10−100×g (... Second, this breaking mechanism does not directly limit the achievable wave height. In figure 5, the onset of breaking is shown for ΔΔ=60∘ . Here, as the waves combine, breaking occurs along the confluence of the two crests. A mixture of horizontal and vertical motion is observed in a combination of the effects observed in figures 3 ( ΔΔ=0∘ ) and 4 ( ΔΔ=120∘ ).

WOW, up to 100g vertical acceleration!

One thing the paper does not say (nor could it) is that the mechanism investigated is the one and only mechanism for rogue waves.