Quebec Wind

Poisson d'Avril!!Swimming fish
Welcome Guest [Log In] [Register]
Add Reply
Les vagues!!!; définition
Topic Started: May 9 2007, 05:40 PM (667 Views)
le jeune
Default Avatar
Gorge addict
[ *  *  *  *  *  *  * ]
Voici ci-dessous de l'info super enrichissante sur la vague :o

LES VAGUES

Elle représentent des paramètres intimement liés au vent qui est la cause de leur formation. Elles sont un critère de choix essentiel pour tout véliplanchiste: il en veut ou en veut pas, il les craint ou les adore, les aime grosses ou petites, orientées par rapport à la côte ou au vent... Les vagues ne laissent personne indifférent, leur présence ou absence est indispensable pour naviguer. :victoire:

D'OÙ VIENNENT-ELLES?

En soufflant, le vent agite la surface de l'eau: il ne suffit de rien d'autre pour créer le phénomène de la houle :woo: dont l'ampleur dépendra de la force du vent. Lorsque cette houle rencontre des hauts fonds, elle se brise sous formes de vagues B) . Plus la houle a d'espace pour se créer et s'étaler, plus les vagues sont grosses et puissantes. La houle qui traverse le Pacifique après un ouragan apporte les plus beaux cadeaux de Noel aux surfers du North Shore hawaien. Sur une échelle moins grande et pour les même raisons, les houles d'Atlantique (Caraibes, Canaries) sont fort coquettes et tolèrent quelques erreurs car les vagues sont légèrement moins puissantes B) . La mer Méditerranée, plus petite et fermée, a du mal à créer de profonds trains de vagues, mais la violence des vent qui soufflent à proximité des côtes compense ce manque :copain: . Après tout, si l'orientation vent-vague n'est pas parfaite, la plage du Brusc à Sanary n'a pas été surnommée Brutal pour rien.



COMMENT SE BRISENT-ELLES?

Les fonds sous-marins peuvent remonter brusquement à l'abord des côtes, formant une barrière naturelle où la houle vient se briser: le rivage est alors protégé et on parle de "reef". C'est le cas de tous les rivages coraliens: Antilles, Hawai. Ce type de configuration est des plus agréables ; qui dit coraux dit chaleur, cadre idyllique, alizé régulier en intensité et direction, le grand jeu :sun: . La houle , elle aussi, va venir dérouler proprement son train de vague le long du reef et c'est comme ça qu'un beau jour les amoureux de la vague se sont mis à surfer sur des planches asymétriques (toujours Hawai). :surf: L'autre avantage des vagues cassant au large réside dans le terrain de jeu restant jusqu'à la plage. Celle-
ci reste d'un abord calme et il est ensuite possible d'aller se frotter progressivement aux "mousses"du reef. Yes2

La deuxième possibilité est une remontée progressive des fonds jusqu'au bord de la plage. Les vagues viennent s'y brisser sans logique. Lorsque les éléments sont un peu agités, l'euphorie quitte le rang des débutants qui éprouvent quelque peine à démarrer. Du côté des experts, les avis sont partagés car l'évolution devient rapidement très technique. :worship:

L'ORIENTATION PAR RAPPORT AU VENT

Les vagues ont, en général, le même axe que celui donné par la côte(les execptions sont surement nos lac à nous :lol: )

Lorsque le vent s'éloigne de la terre et s'en va vers le large, il est off-shore. L'absence de shore break est appréciable, mais attention, lors des débuts il est difficile, au bord de la plage, de se rendre compte de l'intensité du vent qui pousse au large. :grimace:

Si le vent vient du large et se dirige vers la terre, c'est le contraire, il est on-shore. Sécurité absolue pour le débutant, mais difficulté d'apprentissage en cas de shore break car le vent repouse systématiquement dedans.

L'idéal pour une session le fun, c'est le side-shore ou cross-shore, l'axe de navigation étant perpendiculaire à l'onde de houle. On peut aussi choisir le point d'attaque du saut ou attendre la vague pour la surfer au bon moment et dans tous les sens (back side et front side) :supercontent:

Cela dit, hormis quelques spots d'exception, la gauche de Silver Bands à la Barbade, la gauche de Diamond Head à Ohau, Hawai, la vague déferle toujours du même sens (vers la gauche) :blink:

Et hop...c'est le temps d'aller faire de la vague :wave:
Offline Profile Quote Post Goto Top
 
Yvente
Member Avatar
Propulsé par le vent
[ *  *  *  *  *  *  *  * ]
Tres interessant !!!

Et voici ce que j'ai trouve:

Quote:
 
Highest Ocean Waves

According to Ned Mayo (see Ref), the highest reliably measured ocean waves were reported by officers of the Navy oiler USS Ramapo in the North Pacific on February 7, 1933. By triangulation on the ship's superstructure, they measured a wave height of 34 meters (112 feet) peak to trough. The period of the wave was 14.8 seconds and its wavelength was calculated to be 342 meters. Using the wave velocity expression for this wavelength in the deep water limit, the wave speed is calculated to be 23 m/s. Mayo calculates the power of one meter length of such a wavefront to be 17,000 kilowatts!

The crew of the Ramapo measured these waves and lived to tell about it because their relatively short ship(146 m =478 ft) rode these very long wavelength ocean mountains without severe stresses on the craft. Mayo expresses concern about the safety of some modern giant ships (>250 meter length) in such seas.


Posted Image Posted Image[/url] Posted Image Posted Image
Offline Profile Quote Post Goto Top
 
Clarencephil
Member Avatar
Ex Has-been
[ *  *  *  *  *  *  *  * ]
Extrait du New York Times

Quote:
 
Rogue Giants at Sea
               By WILLIAM J. BROAD
Published: July 11, 2006

Posted Image
Posted Image
STORM SURGE The chief engineer of the Stolt Surf took photographs as the tanker met a rogue wave in 1977. The deck, nearly 75 feet above sea level, was submerged.


The storm was nothing special. Its waves rocked the Norwegian Dawn just enough so that bartenders on the cruise ship turned to the usual palliative — free drinks.

Then, off the coast of Georgia, early on Saturday, April 16, 2005, a giant, seven-story wave appeared out of nowhere. It crashed into the bow, sent deck chairs flying, smashed windows, raced as high as the 10th deck, flooded 62 cabins, injured 4 passengers and sowed widespread fear and panic.

“The ship was like a cork in a bathtub,” recalled Celestine Mcelhatton, a passenger who, along with 2,000 others, eventually made it back to Pier 88 on the Hudson River in Manhattan. Some vowed never to sail again.

Enormous waves that sweep the ocean are traditionally called rogue waves, implying that they have a kind of freakish rarity. Over the decades, skeptical oceanographers have doubted their existence and tended to lump them together with sightings of mermaids and sea monsters.

But scientists are now finding that these giants of the sea are far more common and destructive than once imagined, prompting a rush of new studies and reRecherche projects. The goals are to better tally them, understand why they form, explore the possibility of forecasts, and learn how to better protect ships, oil platforms and people.

The stakes are high. In the past two decades, freak waves are suspected of sinking dozens of big ships and taking hundreds of lives. The upshot is that the scientists feel a sense of urgency about the work and growing awe at their subjects.

“I never met, and hope I never will meet, such a monster,” said Wolfgang Rosenthal, a German scientist who Aideed the European Space Agency pioneer the study of rogue waves by radar satellite. “They are more frequent than we expected.”

Drawing on recent tallies and making tentative extrapolations, Dr. Rosenthal estimated that at any given moment 10 of the giants are churning through the world’s oceans.

In size and reach these waves are quite different from earthquake-induced tsunamis, which form low, almost invisible mounds at sea before gaining height while crashing ashore. Rogue waves seldom, if ever, prowl close to land.

“We know these big waves cannot get into shallow water,” said David W. Wang of the Naval ReRecherche Laboratory, the science arm of the Navy and Marine Corps. “That’s a physical limitation.”

By one definition, the titans of the sea rise to heights of at least 25 meters, or 82 feet, about the size of an eight-story building. Scientists have calculated their theoretical maximum at 198 feet — higher than the Statue of Liberty or the Capitol rotunda in Washington. So far, however, they have documented nothing that big. Large rogues seem to average around 100 feet.

Most waves, big and small alike, form when the wind blows across open water. The wind’s force, duration and sweep determine the size of the swells, with big storms building their height. Waves of about 6 feet are common, though ones up to 30 or even 50 feet are considered unexceptional (though terrifying to people in even fairly large boats). As waves gain energy from the wind, they become steeper and the crests can break into whitecaps.

The trough preceding a rogue wave can be quite deep, what nautical lore calls a “hole in the sea.” For anyone on a ship, it is a roller coaster plunge that can be disastrous.

Over the centuries, many accounts have told of monster waves that battered and sank ships. In 1933 in the North Pacific, the Navy oiler Ramapo encountered a huge wave. The crew, calm enough to triangulate from the ship’s superstructure, estimated its height at 112 feet.

In 1966, the Italian cruise ship Michelangelo was steaming toward New York when a giant wave tore a hole in its superstructure, smashed heavy glass 80 feet above the waterline, and killed a crewman and two passengers. In 1978, the München, a German barge carrier, sank in the Atlantic. Surviving bits of twisted wreckage suggested that it surrendered to a wave of great force.

Despite such accounts, many oceanographers were skeptical. The human imagination tended to embellish, they said.

Moreover, bobbing ships were terrible reference points for trying to determine the size of onrushing objects with any kind of accuracy. Their mathematical models predicted that giant waves were statistical improbabilities that should arise once every 10,000 years or so.



Posted Image
LASTING EFFECTS The Wilstar, a Norwegian tanker, suffered structural damage from a rogue wave in 1974. Scientists are focusing on how to make ships less vulnerable.

That began to change on New Year’s Day in 1995, when a rock-steady oil platform in the North Sea produced what was considered the first hard evidence of a rogue wave. The platform bore a laser designed to measure wave height.

During a furious storm, it Inscriptioned an 84-foot giant.

Then, in February 2000, a British oceanographic reRecherche vessel fighting its way through a gale west of Scotland measured titans of up to 95 feet, “the largest waves ever recorded by scientific instruments,” seven reRechercheers wrote in the journal Geophysical ReRecherche Letters.

Once-skeptical scientists were soon holding conferences to discuss the findings and to design reRecherche strategies. A large meeting in Brest, France, in November 2000 attracted reRechercheers from around the world.

It quickly became apparent that the big waves formed with some regularity in regions swept by powerful currents: the Agulhas off South Africa, the Kuroshio off Japan, and the Gulf Stream off the eastern United States, where the Norwegian Dawn got into trouble off Georgia. The Gulf Stream also flows through the Bermuda Triangle, famous for allegedly devouring large numbers of ships.

Dr. Bengt Fornberg, a mathematician at the University of Colorado who studies the giants, said the strong ocean currents appeared to focus waves “like a magnifying glass concentrates sunlight.”

“It’s the same idea,” he said. “There are a few places in the world where there is a regular current, like a steady magnifying glass. In other places, the eddies come and go, and that makes the waves less predictable.”

One way that rogue waves apparently form is when the strong currents meet winds and waves moving in the opposite direction, he said. The currents focus and concentrate sets of waves, shortening the distance between them and sending individual peaks higher. “That,” Dr. Fornberg said in an interview, “makes for hot spots in a fairly predictable area.”

A particularly threatening spot, he said, turned out to be where big oil tankers coming from the Middle East ride the Agulhas current around South Africa. There, the westward-flowing current meets prevailing easterly winds, at times disastrously.

“Three or four tankers a year there get badly damaged,” Dr. Fornberg said. “That’s one of the few places in the world where the phenomena is regular.”

“With a big storm, you get lots of big waves,” he added. “You have regular waves and then one or two giants. Then it’s back to regular again.”

The scientists who met at Brest in 2000, eager to track the phenomenon globally, laid plans to use radar satellites to conduct a census, calling it MaxWave.

They worked with the European Space Agency, which had lofted radar satellites in 1991 and 1995, as well as the German Aerospace Center and several other European reRecherche bodies. The radar beams were seen as potentially ideal for measuring the height of individual waves, based on the time it took the beams to bounce from orbit to the sea and back to space.

The MaxWave team, led by Dr. Rosenthal, examined three weeks of radar data and to its amazement discovered 10 giants, each at least 82 feet high. “We were quite successful,” he said.

The team even tracked monster waves in a region of the South Atlantic where two cruise ships, the Bremen and the Caledonian Star, had come under assault.

Further confirmation with a different set of instruments came in September 2004 when Hurricane Ivan swept through the Gulf of Mexico.

It passed directly over six wave-tide gauges that the Naval ReRecherche Laboratory had deployed about 50 miles east of the Mississippi Delta. Dr. Wang and his colleagues analyzed the data and found to their surprise waves measuring more than 90 feet from trough to crest.

“We had no idea,” Dr. Wang recalled. “It was the right time and the right place.”

Already, the scientists said, naval architects and shipbuilders are discussing precautions. Some of the easiest are seen as increasing the strength of windows and hatch covers. But even the best physical protections may fail under assault by tons of roiling water, so the best precaution of all will be learning how to avoid the monsters in the first place.

Increasingly, scientists are focusing on better understanding how the big waves form and whether that knowledge can lead to accurate forecasts — a feat that, if achieved, may save hundreds of lives and many billions of dollars in lost commerce.

A suspected culprit, in addition to wind-current interactions, is the amplification that occurs when disparate trains of waves (perhaps emanating from different storms) come together. Such intersections are seen as sometimes canceling out waves, and other times making them higher and steeper.

Another birth ground is seen as choppy seas where several waves moving independently merge by chance. But scientists say a giant of that sort would live for no more than a few seconds or minutes, whereas some are suspected of lasting for hours and traveling long distances.

As for forecasts, oceanographers are focusing on the interplay of exceptionally strong winds and currents, especially in the Agulhas off South Africa.

Dr. Fornberg said that several years ago South African authorities began issuing predictions. “That’s the only place the theory has succeeded,” he said.

Dr. Rosenthal said that in the future the continued proliferation of radar satellites should create an opportunity to better understand not only the habitats of the giants but in theory also individual threats, bringing about a safer relationship between people and the sea.

“There will be warnings, maybe in 10 years,” he said. “It should be possible.”


Posted Image Posted ImagePosted Image
Offline Profile Quote Post Goto Top
 
Jp-ette
Member Avatar
Jp-ette-Média l'avait prédit!
[ *  *  *  *  *  *  *  * ]
Traduction Siyouplait!! :content:
Mise en garde: L'exposition prolongée au vent peut entrainer l'accumulation de bulles d'air dans le cerveau. Les séquelles sont permanentes.
Posted Image
Offline Profile Quote Post Goto Top
 
rich1
Default Avatar
Superstar
[ *  *  *  *  *  *  * ]
Je l'avais déjà lu dans le volume sur la mer du Time-Life, une vague de 500 mètres (500 MÈTRES!!!) avait frappé l'Alaska.

Je viens de vérifier sur Internet, voilà ce que j'ai trouvé: (adresse http://ask.yahoo.com/20010328.html). çà confirme ce que j'avais lu. Tout un surf... :blink:

Dear Yahoo!:
What was the biggest wave ever recorded?
Surf Seeker


Dear Surf:
A simple Yahoo! Recherche on "biggest wave" returned thousands of web pages. Fortunately, one of the first sites listed provided the answer.
The "Awesome Stats" section of Extreme Science claims the biggest wave on record occurred in Lituya Bay on the southern coast of Alaska in 1958.

An earthquake measuring 8.3 on the Richter scale hit the area and shook loose an estimated 40 million cubic yards of dirt and glacier from a mountainside at the head of the bay. When the debris hit the water, a massive 1,720-foot wave was created and washed over the headland.

How did the scientists know the wave was so incredibly enormous? Simple. To measure the height of the wave, scientists found the high-water mark -- the line where the water reached it's highest point on land.

Keep in mind that this probably isn't the biggest wave ever, just the biggest witnessed by a human. As a matter of fact, three fishing boats witnessed the Lituya Bay event. Unfortunately, two people on one of the boats were killed. Incredibly, the other two boats rode the waves and their
occupants survived.
Offline Profile Quote Post Goto Top
 
Stefrigaud
Member Avatar
En 2017, 40 ans de plancheEt ça ne paraît pas !!!
[ *  *  *  *  *  *  *  * ]
Le Jeune et Phil super interessants vos articles.

Rich1, c'est pas tout a fait exact cette grosse vaque Alaskaine ? Alaskienne ? Alaskoise ?

Ce n'était pas une vague au sens commun. C'était plutôt une masse d'eau en mouvement qui ne cassait pas comme une vague standard.

Ce tsunami s'est engouffré de front dans un fjord très large à l'embouchure mais qui rétrécissait rapidement et continuellement sur des parois rocheuses relativement droites et lisses. L'eau n'a eu aucune difficulté à gravir les parois graduellement pour qu'une fois rendu au fond elle ait presque rempli le fjord.

Il est fjord le Stef, hein ? :P
Bon Vent !

PROPRIÉTÉS À VENDRE ici (Bords de l'eau)
Offline Profile Quote Post Goto Top
 
Stefrigaud
Member Avatar
En 2017, 40 ans de plancheEt ça ne paraît pas !!!
[ *  *  *  *  *  *  *  * ]
Question: Nommez moi une célèbre cantatrice d'opéra Norvégienne ?

Réponse: La Castafjord !

:P
Bon Vent !

PROPRIÉTÉS À VENDRE ici (Bords de l'eau)
Offline Profile Quote Post Goto Top
 
rich1
Default Avatar
Superstar
[ *  *  *  *  *  *  * ]
Stefrigaud,May 11 2007
11:29 AM
Question: Nommez moi une célèbre cantatrice d'opéra Norvégienne ?

Réponse: La Castafjord !

:P


Joli nom, Stef :lol:

Peut-être aussi pour un nouveau modèle de camion, CastaFord :blink:
Offline Profile Quote Post Goto Top
 
Yvente
Member Avatar
Propulsé par le vent
[ *  *  *  *  *  *  *  * ]
Posted Image

Un bon lavage de pont :lol:
Posted Image

Belle vague pour partir en back-loop :frantic:
Posted Image
Posted Image Posted Image[/url] Posted Image Posted Image
Offline Profile Quote Post Goto Top
 
Yvente
Member Avatar
Propulsé par le vent
[ *  *  *  *  *  *  *  * ]
Interessant B)
Posted Image

Waves entering shallow water
As waves enter shallow water, they slow down, grow taller and change shape. At a depth of half its wave length, the rounded waves start to rise and their crests become shorter while their troughs lengthen. Although their period (frequency) stays the same, the waves slow down and their overall wave length shortens. The 'bumps' gradually steepen and finally break in the surf when depth becomes less than 1.3 times their height. Note that waves change shape in depths depending on their wave length, but break in shallows relating to their height!

How high a wave will rise, depends on its wave length (period) and the beach slope. It has been observed that a swell of 6-7m height in open sea, with a period of 21 seconds, rose to 16m height off Manihiki Atoll, Cooks Islands, on 2 June, 1967. Such swell could have arisen from a 60 knot storm.

Posted Image




Posted Image Posted Image[/url] Posted Image Posted Image
Offline Profile Quote Post Goto Top
 
Clarencephil
Member Avatar
Ex Has-been
[ *  *  *  *  *  *  *  * ]
Tiens parlant de vagues, en voici de belles à Maui
Bon juste des surfers et un kiteux, mais imaginez vous là dessus

[dohtml]<object type="application/x-shockwave-flash" width="425" height="350"wmode="transparent" data="http://www.youkiteboard.com/flvplayer.swf?file=http://www.youkiteboard.com/flvideo/488.flv&autostart=true&showfsbutton=true">
<param name="movie" value="http://www.youkiteboard.com/flvplayer.swf?file=http://www.youkiteboard.com/flvideo/488.flv&autostart=true&showfsbutton=true" />
<param name="wmode" value="transparent" />
<param name="allowScriptAccess" value="sameDomain" />
<embed src="http://www.youkiteboard.com/flvplayer.swf?file=http://www.youkiteboard.com/flvideo/488.flv&autostart=true&showfsbutton=true" loop="false" width="425" height="350" allowScriptAccess="sameDomain" type="application/x-shockwave-flash" pluginspage="http://www.macromedia.com/go/getflashplayer" />
</object>[/dohtml]

Si ça ne marche pas, essayez ce lien .
Posted Image Posted ImagePosted Image
Offline Profile Quote Post Goto Top
 
1 user reading this topic (1 Guest and 0 Anonymous)
ZetaBoards - Free Forum Hosting
ZetaBoards gives you all the tools to create a successful discussion community.
Learn More · Register Now
« Previous Topic · Parlons Planche · Next Topic »
Add Reply



Image marquee annonceurs

Board Designed by BigAir