Proceedings of Rogue Waves - Essay Example

Rogue Waves Source: Proceedings of Rogue Waves 2000 Conference, Brest, France - November 2000. Off the Internet at: http www.math.uio.no/%7Ekarstent/waves/BrestKBD.pdf Article Name: Modeling a "rogue wave" - speculations or a realistic possibility Author(s): Kristian B. Dysthe (Department of Mathematics at University of Bergen, Norway). Article Summary: This is an invited lecture dedicated to the physics behind rogue waves. Author concentrates upon the phenomenon of freak/rogue waves existing in the open ocean. How to deduce such enormous concentration of wave energy compared to the average Author analyses three main types of effects which are potential sources for the wave energy focusing. First factor is spatial focusing due to refraction by bottom topography or current gradients. This is significant for appearance of the coastal rogue waves, but it would seem that spatial focusing is negligible far offshore. Some numerical ray-tracing simulations show that the very weak refraction may produce "hotspots" of wave energy. However, author critiques this factor as "rather unrealistic". Second factor is temporal-spatial focusing which is the result of applying dispersion to a wave group with chirped spatial distribution of frequencies. Author notes that this mechanism can work for the "forced" wavetrains only which can not develop spontaneously. Finally, third factor is nonlinear focusing which produces solitons and so-called breathers as model representations of rogue waves. About real mechanisms of the rogue waves forming in the open ocean, author concludes that 'nobody knows the answer to these questions yet.' My Comments: This paper shows that there are some fields for researches with no direct and clear answers. Real mechanism of the rogue waves forming in the open ocean is yet unknown. Existing mathematical models for explanation of these phenomena are refined but not realistic. Indeed, considered mechanisms for the wave energy focusing are operable only for narrow sets of cases or for unnatural conditions. Details of mathematical notations (especially in Appendix) were not clear for me. Source: Beacon # 185, Skuld - June 2005. Off the Internet at: http://www.skuld.com/upload/News%20and%20Publications/Publications/Beacon/Beacon%202005%20185/Freak%20waves.pdf Article Name: Freak waves. Author(s): Chris Hall (Skuld Corp., Hong Kong). Article Summary: This is short but comprehensive introduction to the freak/rogue waves phenomenon. It contains well adjusted set of facts and ideas about rogue waves, namely: informal definition, brief history of observations with examples, discussion about causes of its origin, typical values of the break forces, sea conditions that may create (or accompany) freak waves, etc. There are no formulae at all. This article serves as global pattern for the rogue waves problem whereas numerous articles concentrate upon mathematical details and minor features of this phenomenon. My Comments: As for me, this is one of the best articles about rogue waves. Some facts are just amazing. For example, cases from the article show that freak waves greater than 25 meters in height are real and much more common than expected. Obviously, this phenomenon is far beyond so-called linear model. Than, actual causes and mechanisms of rogue waves are unknown (cf. previous article). Here, unpredictable freak waves are real miracles of the Nature, not mirages. It is important to distinguish freak waves and tsunamis. Then, article contains tremendous facts about the force of a breaking freak wave. It is about 100 MT/m2 for a 12-meter rogue wave which is much more than for wave in linear model. Article reading was easy and fascinating. Article is highly recommended for any scholar at the beginning stage of studying this phenomenon. Source: Proceedings of Rogue Waves 2004 Conference, Brest, France - October 2004. Off the Internet at: http://www.ifremer.fr/web-com/stw2004/rw/fullpapers/haver.pdf Article Name: Freak waves: a suggested definition and possible consequences for marine structures. Author(s): Sverre Haver (Marine Structures and Risers, Statoil, Norway). Article Summary: This article represents key ideas of statistical/probabilistic approach to studying the rogue waves phenomenon. Author considers two classes of so-called extreme waves, namely "classical" waves and freak waves. "Classical" extreme waves are rare members of a population of wave events defined by modeling the surface process as a piecewise stationary and homogeneous slightly non-Gaussian random field. On the contrary, author defines freak extreme waves as typical (sic!) members of population being defined by certain physical mechanisms. Author gives precise definitions for a freak wave event, both geometrical (via linear parameters of the wave) and statistical (as an outlier when seen in view of the population of events). Then, brief review for methodology of appropriate measurements is presented, e.g. processing freak wave indicators, freak wave amplification factor, etc. Finally, author gives several illustrations for statistics of a freak wave development. My Comments: Key idea of this work is to establish effective relations between abstract concepts of the rogue waves statistical modeling and practical needs, e.g. measurements, structural design, safety, etc. Mathematical notations are clear, but it is necessary "to feel" their meaning. This article is just one of formal points of view (namely, statistical) upon the rogue waves. I agree that statistic approach can be effective for practical purposes but studying physical mechanisms and "driving forces" of the rogue waves phenomenon seems to be much more interesting. Source: Aha Huliko'a Hawaiian Winter Workshop 2005 Proceedings. Off the Internet at: http://www.soest.hawaii.edu/PubServices/2005pdfs/Forristall.pdf Article Name: Understanding rogue waves: are new physics really necessary Author(s): G.Z. Forristall (Forristall Ocean Engineering, Inc., USA). Article Summary: In this article author makes attempt to "rehabilitate" the standard model of ocean waves (i.e. linear model) in the face of existing cases of rogue waves. Indeed, is it necessary to use high order nonlinear mathematical models to describe and analyze rogue waves Firstly, author examines the ability of measurements to accurately observe extreme waves. Then, the statistical evidence for rogue waves is investigated. Finally, author analyses the statistics of waves over an area. Results are somewhat unusual and located beyond the common trend of researches in this area. Precise measuring high waves is very difficult (and almost impossible in practice) procedure. In many cases, a very large wave is difficult to distinguish from noise. Author notes that many observations of high crests can be explained by such theories as perturbation theory, not high order nonlinear theories. Author agrees that strongly nonlinear focusing of waves may well exist in the ocean and then concludes that 'existing observations do not demand such a mechanism' for explanation of the rogue waves phenomenon. My Comments: This article is very disputable. Author's strategy of usage "as much as simple" theories for modeling rogue waves is plain, but corresponding argumentation seems to be inconclusive. It is really difficult to fix a rogue wave with precise measurements of its geometric and dynamical characteristics. However, this is not argument for rejection high order nonlinear models. Contrary instance: we know that neutrino exists and we use extremely complex theories to describe it whereas we do not know precise value of its rest mass. Similarly, we know that rogue waves exist and we really can (sic!) use complex theories to describe them whereas we do not know precise values of its parameters. Read More