Ocean Waves
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Transcript of Ocean Waves
Ocean WavesOcean Waves
CapillaryCapillary
GravityGravityWind Wind
generatedgenerated
TidesTides
TsunamisTsunamisSeichesSeiches
Capillary waves are driven by the surface tension produced by electrically polarized water moleculeproduced by electrically polarized water moleculeCapillary waves are driven by the surface tension produced by electrically polarized water molecule produced by electrically polarized water molecule
San Pedro LighthouseSan Pedro Lighthouse
WavesWaves are alternate rises and falls, are alternate rises and falls,
describable as simple/complex describable as simple/complex sinusoidalssinusoidals
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-0.75
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0.25
0.5
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0 45 90 135 180 225 270 315 360
Crest
Am
plitu
de
Amplitude
Height
Trough
Wave period or Wavelength
As a wave travels through the waver, the particles travel in clockwise circles. The radius of the circles decreases as the depth into the water increases. The following animation shows a water wave traveling from left to right in a region where the depth of the water is greater than the wavelength of the waves.
http://www.kettering.edu/~drussell/Demos/waves/wavemotion.html
WavesWaves are alternate rises and falls, are alternate rises and falls,
describable as simple/complex describable as simple/complex sinusoidalssinusoidals
only add-up, alwaysonly add-up, always
i.e., wave interference can be i.e., wave interference can be constructive and/or destructiveconstructive and/or destructive
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0.5
1
0 90 180 270 360
AABB
CC
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-0.75
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-0.25
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0 45 90 135 180 225 270 315 360
AABB
C = A+BC = A+B
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-0.5
0
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0 90 180 270 360
AABB
CC
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1
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0 100 200 300 400 500 600 700
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0 100 200 300 400 500 600 700
Waves interference is always additiveWaves interference is always additive
This is the algebraic sum of these
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Wave interference can be Wave interference can be constructive or destructiveconstructive or destructive
Constructive Constructive interferenceinterference
Constructive Constructive interferenceinterference
Constructive Constructive interferenceinterference
Destructive Destructive interferenceinterference
Destructive Destructive interferenceinterference-1
0
1
Second Harmonic
Standing Wave Pattern
First Harmonic Standing Wave Pattern
Third Harmonic Standing Wave Pattern
http://www.glenbrook.k12.il.us/gbssci/phys/mmedia/waves/swf.html
Waves and wave activity
• Standing waves
As waves can be thought of as single or complexsinusoids,we can lookat waves ascomprisingone or moreharmonics.
Waves and wave activity
• Traveling waves
Waves travel in groups,and thegroupvelocityis one-half the velocity of individual waves.
http://www.glenbrook.k12.il.us/gbssci/phys/mmedia/waves/swf.html
WavesWaves are alternate rises and falls, are alternate rises and falls,
describable as simple/complex describable as simple/complex sinusoidalssinusoidals
only add-up, alwaysonly add-up, always
i.e., wave interference can be i.e., wave interference can be constructive and/or destructiveconstructive and/or destructive
carry energy, not mattercarry energy, not matter
light is an exception, it travels light is an exception, it travels in waves and as particlesin waves and as particles
10-1 1 101 102 105104103 106 107
104
103
102
10
1
Wavelength (cm)
Wav
e sp
eed
or
velo
city
(cm
/s)
Cap
illar
y C
apill
ary
wav
esw
aves
Gravity wavesGravity wavesin deepwater,in deepwater,
V V 1.25 1.25 L L
Output from a shallow water equation model of water in a bathtub. The water experiences five splashes which generate surface gravity waves that propagate away from the splash locations and reflect off of the bathtub walls.
http://en.wikipedia.org/wiki/Ocean_surface_wave
Waves carry energy, not matterThe orbital motion of representative
water molecules: orbital size decreases with depth, with negligible water motion
at depth ½ wavelength
Circular path: waves of oscillation
Elliptical path: waves of translation
Waves break on reaching the shore. Why?
Waves break as the succeeding waves catch up with preceding waves
Spilling breakers form when the bottom slopes gradually
Spilling breakers form when the bottom slopes gradually
Plunging or surging breakers form when the bottom slope is steep
Plunging or surging breakers form when the bottom slope is steep
Three factors affect wind wave development:
(a) Wind speed, (b) Wind duration,
and (c) Fetch
How wind affects the wave height
WindWindspeedspeed
19 km/hr19 km/hr(10 knots)(10 knots)
37 km/hr37 km/hr(20 knots)(20 knots)
56 km/hr56 km/hr(30 knots)(30 knots)
74 km/hr74 km/hr(40 knots)(40 knots)
92 km/hr92 km/hr(50 knots)(50 knots)
FetchFetch
19 km19 km
139 km139 km
518 km518 km
1313 km1313 km
2627 km2627 km
WindWinddurationduration
2 hr2 hr
10 hr10 hr
23 hr23 hr
42 hr42 hr
69 hr69 hr
Wind ConditionsWind Conditions
AverageAverageheightheight
0.27 m0.27 m
1.5 m1.5 m
4.1 m4.1 m
8.5 m8.5 m
14.8 m14.8 m
AverageAverageLengthLength
8.5 m8.5 m
33.8 m33.8 m
76.5 m76.5 m
136 m136 m
212 m212 m
AverageAverageperiodperiod
3.0 sec3.0 sec
5.7 sec5.7 sec
8.6 sec8.6 sec
11.4 sec11.4 sec
14.3 sec14.3 sec
Wave SizeWave Size
Conditions conducive of a fully developed seaConditions conducive of a fully developed sea
20 50 100 200 500 1000
Rel
ativ
e w
ave
ener
gy
Wavelength (m)
75 km/hr
55 km/hr
37 km/hr
Wave energy versus wavelength for fully developed sea: Stronger winds generate waves that are both longer and more energetic, on average
http://www.oceanweather.com/data/global.html