Set waves

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Set waves

Postby mellowmarshy » Sun Nov 06, 2005 7:13 pm

Hey, do any of you guys know actually WHY we get set waves? Obviously its great they exist! 8) Just wondering why.
Cheers if anyones in the know.
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Postby jd83 » Sun Nov 06, 2005 7:43 pm

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Postby surfguru » Mon Nov 07, 2005 1:11 am

Groundswell ,They are very nice and have traveled along way its to do with the churning of the seas due to large storms 1000s of miles away from your break, try throwing a large stone into flat no wind water or into a large puddle to see the effect the small rippes go to all the sides of the water and get smaller after the impact , large winds in the storms whip up the seas in all directions rather like a huge bashing onto the sea this churning is the cause of groundswells.
There are several great books on this subject but thats how i see those swells your on about been created in simple terms anyway.
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Postby ow3n » Tue Nov 08, 2005 3:00 pm

It is a documented phenominon that a group of waves travelling through a medium will re arrange their energy distribution (amplitude/size) to have smaller waves at the front and back of the group, with the biggest waves in the middle.

So a group of waves, just for this case let's say five, all started at the same point with regular frequency and amplitude, will gradually change from a group of five identical waves, into a group that goes smallest,middle, biggest, middle, smaller.

There is actually no scientific theory explaining why this happens, but it does. One theory to do with it being the most effecient way to move a group of waves along sort of explains how, but that doesn't explain why.

The above phenominon combined with interference(from the same source, and secondary sources) ,diffraction and refraction (an effect from waves entering water with a different depth) will probably combine to give you sets. probably.
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Postby Monkey_Alan » Tue Nov 08, 2005 3:12 pm

Nah, it's the mermaids playing just under the surface
When the shit goes down, you better be ready....
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Postby Banana_man » Tue Nov 08, 2005 3:50 pm

Carrying on from Owens explanation, Ive always imagined the first wave (out of the 5 in this example) must travel slowest as it sets the path and takes all the crap (smaller chop etc..), kinda like cycling where they all sit in each other slip-stream! Then the 2nd wave must catch up and so on.....

Does that make sense to anyone or am I confusing things further? :?
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Postby Monkey_Alan » Tue Nov 08, 2005 4:03 pm

Dont forget that the water molecules themselves don't actually move in the swell direction. In reality the waves are a transference of energy, not a physical movement of water

The water actually circulates within the wave while transfering energy in the swell direction









Or it could just be the mermaids :oops:
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Postby Grizzly » Tue Nov 08, 2005 4:15 pm

Because water is a dispersive medium (different wavelengths travel at different velocities), the energy of a wave is propagated at a different velocity from the wave itself so you in effect get a 'ghost' wave train superimposed upon the real waves, at a slightly different wavelength. Next, because there are two wavetrains superimposed, each having a different frequency/wavelength, you get what are called 'beats' - the resultant wave has an amplitude that oscillates slowly over time. When we get a bit where the amplitude is at a maximum, that's your set :lol:
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Postby mellowmarshy » Wed Nov 09, 2005 5:48 pm

Thanks for the replies everyone. Im pretty sure I get what your all saying, so nobody has confused me......not after the 3rd time reading anyway! Thanks very much all.
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Postby village-idiot » Wed Nov 09, 2005 10:39 pm

I'm confused :lol:

Any train of waves that hits your break is basically made up of a combination of a large number of regular (constant amplitude & wavelength) waves

if you can imagine two regular wave trains of different wavelengths coinciding its easy enough to see that where peaks coincide the resulting wave will be at a maximum amplitude, where peak and trough they'll cancel out

If you can imagine a combination of a 100 such regular waves of different amlitude and wavelengths you can see how we end up with what is a seemingly random wavetrain

A 'set' wave is basically a larger peak than the majority of the other peaks in its vicinity.

That's about as simply as I can explain it :?
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Postby Chris F » Fri Feb 03, 2006 12:50 pm

I always assumed it was to do with interference. Swell is usually not generated from a single point, so swells from different "sources" sometimes combine, to make a bigger swell, and sometimes don't. I know there is a scientific term for the effect, but I'm buggered if I can remember.
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Postby glasgow_kaz » Sat Feb 04, 2006 2:14 am

i did this is physics but i can't be bothered typing out a good explanation. maybe tomorrow
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Postby Chris F » Fri Feb 17, 2006 3:17 pm

You said that two weeks ago? And we wait.....
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Postby KFPC » Sat Jul 08, 2006 9:39 pm

Please see the posting 'Sets' and my response (I'm KFPC.)
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Postby bigfeller » Sun Jul 09, 2006 2:55 am

I think I preferred the mermaids
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