Rogue Waves: Examining Why Linear Models Failed

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Discussion Overview

The discussion revolves around the phenomenon of rogue waves and the limitations of linear models in predicting their occurrence. Participants explore the implications of these models in the context of oceanography and wave dynamics, questioning the assumptions that have historically dismissed the existence of such waves.

Discussion Character

  • Exploratory
  • Debate/contested
  • Technical explanation

Main Points Raised

  • Some participants note that rogue waves, which can reach heights of thirty meters, were historically dismissed due to reliance on linear models that suggested such waves should occur very rarely.
  • Others argue that the ocean's surface is highly nonlinear, and thus predictions made by linear models are inherently limited and may not capture significant phenomena.
  • A participant mentions that a scientist applying a nonlinear wave equation observed large waves in simulations, which were subsequently rejected because they did not align with linear model predictions.
  • One post highlights an incident where an oil rig recorded a 30m wave, which matched predictions from a nonlinear model, suggesting that linear models may overlook critical behaviors in wave dynamics.
  • Another participant expresses skepticism about the dismissal of phenomena that cannot be explained by linear models, questioning the scientific rationale behind such rejections.
  • Concerns are raised about the general forgetfulness regarding the limitations of models, particularly when they are not of immediate practical concern.
  • Some participants emphasize that all natural phenomena are nonlinear, and linearization is only a useful approximation under specific conditions.
  • There is a claim that no singular "linear model" exists for wave height, length, frequency, or size distribution, challenging the notion of a failure of such a model.
  • A reference to linear shoaling theory is provided as an example of how linear models have been applied to ocean waves, although its applicability to rogue waves is questioned.

Areas of Agreement / Disagreement

Participants express a range of views, with no consensus on the validity of linear models in explaining rogue waves. Some argue for the necessity of nonlinear models, while others question the assumptions underlying the rejection of linear approaches.

Contextual Notes

Limitations of the discussion include the dependence on specific definitions of linear and nonlinear models, as well as the unresolved nature of the mathematical frameworks being discussed. The applicability of various models to rogue waves remains a point of contention.

Ivan Seeking
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Integral called my attention to a Sci Channel show about Rogue Waves called "Killer Waves". Rogue waves are now known to exist, but for about a century experts have argued that these thirty meter monsters can't exist because the linear model used by the shipping industry says that monster waves should only occur once every ten-thousand years. So it was assumed that centuries of mariners stories [eyewitness testimony] are all wrong.

I would bet that in the beginning we simply assumed that the linear model used applies to all ocean waves, maybe because it was the only model that was practical to use, and this was then used to argue what could and could not be possible.
 
Physics news on Phys.org
http://www.mxak.org/weather/waves.pdf#search='wind%20fetchwave%20height'
 
Makes you wonder just what all is going on yet unrecognized as being possible. I've been rather sad to find over the last few years that I have been investigating that so many thing I had thought were real have been thuroughly debunked. One of my exs would get angry with me when I would explain to her that so many of these "proofs" of the unexplained were in fact explained. I hope more things start to come out as real.
 
The show is on Discovery Science, I was nearly screaming at the TV. Alarm bells started chiming when early in the show they mentioned the "Linear Model" as the basis for rejecting the possibility of "killer" 30m waves. The problem, of course, is that the surface of the ocean is HIGHLY nonlinear. Therefore, anyone with a understanding of numerical modeling will know that the predictions made by a linear model will be limited. Specifically any interesting nonlinear behavior will not show up. It turns out that one scientist (possibly a physicist, but not I am not 100% on that detail) was applying the nonlinear wave equation and seeing huge waves in his results. But once again these predictions were rejected because they did not show up in the Linear model! This is an excellent example of misplaced faith in the abilities of math to model the real world.

Eyes were opened when an oil rig in the middle of the North Sea recorded a 30m wave. The wave shape was exactly that predicted by the nonlinear model.
 
a related story in the news.

A British research team has observed some of the biggest sea swells ever measured. A whole series of giant waves hammered into their ship that were so big, according to computer models used to set safety standards for ships and oil rigs, they shouldn't even exist [continued]
http://service.spiegel.de/cache/international/spiegel/0,1518,408953,00.html
 
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Picture the energy required to lift a wave to 30M above the suface. It obviously depends on depth. It also depends on the contour of the ocean bottom. A wave colliding with a deep sea ridge [transverse wave] will break high, and expend most of its energy on the surface. A wave traveling parallel to a deep sea ridge that slopes toward the shore is much more dangerous.
 
Every natural phenomenon is nonlinear. Only when we limit the amplitude of the phenomenon can we approximate a curve, a surface or a hypersurface by its tangent line, plane or hyperplane. This is called linearization and is useful to analyse most phenomenons.
If we talk about giant waves, it is very likely that a linear model could not apply. I wonder why any scientist would dismiss a phenomenon because it can't be explained by a linear model.
 
I think people simply forget about the limitations of models used when not of practical concern for the job they do.
 
SGT said:
Every natural phenomenon is nonlinear. Only when we limit the amplitude of the phenomenon can we approximate a curve, a surface or a hypersurface by its tangent line, plane or hyperplane. This is called linearization and is useful to analyse most phenomenons.
If we talk about giant waves, it is very likely that a linear model could not apply. I wonder why any scientist would dismiss a phenomenon because it can't be explained by a linear model.

That is exactly what had be screaming (well, nearly) at the TV the night I was watching that show. Supposedly these guys had PhDs How could they get the idea that the linear model (and that is what they called it!) predicted all possible wave phenomena. Using a variation on the Schrödinger wave equation, rogue waves are predicted, and are not all that rare.
 
  • #10
Integral said:
(snip)Supposedly these guys had PhDs How could they get the idea that the linear model (and that is what they called it!) predicted all possible wave phenomena.(snip)

TV science? What linear model? There is no "linear" model for wave height, length, frequency, velocity, or size distribution, therefore, no "failure of such linear model."
 
  • #11
Here is one example of linear modeling of ocean waves.

Based on linear shoaling theory, our surf zone model amplifies the wave heights of incoming waves as the bathymetry or depth of the ocean floor decreases. The wave amplification data is derived from the ocean engineering literature [1] which gives the relationship between a depth to wavelength ratio to a wave amplification factor.
http://www.d-a-s.com/ocean.html
 
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