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Chapter 10 Waves apillary Waves, ind Waves, sunamis, Internal waves big waves small waves huge waves rogue waves

Chapter 10 Waves Capillary Waves, Wind Waves, Tsunamis, Internal waves big waves small waves huge waves rogue waves

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Page 1: Chapter 10 Waves Capillary Waves, Wind Waves, Tsunamis, Internal waves big waves small waves huge waves rogue waves

Chapter 10

Waves

Capillary Waves, Wind Waves,

Tsunamis, Internal waves big waves

small waves

huge waves

rogue waves

Page 2: Chapter 10 Waves Capillary Waves, Wind Waves, Tsunamis, Internal waves big waves small waves huge waves rogue waves
Page 3: Chapter 10 Waves Capillary Waves, Wind Waves, Tsunamis, Internal waves big waves small waves huge waves rogue waves

Wave directionWave

wave energy – NOT the water particles – moves across the surface of the sea

wave form moves and with it, energy is transmitted

Page 4: Chapter 10 Waves Capillary Waves, Wind Waves, Tsunamis, Internal waves big waves small waves huge waves rogue waves

Fig. 10-2, p. 266

Direction of wave motion

A B

Wavelength

Height

Still water level Crest Trough

Frequency: Number of wave crests passing point A or point B each second

Orbital path of individual water molecule at water surface

Period: Time required for wave crest at point A to reach point B

Page 5: Chapter 10 Waves Capillary Waves, Wind Waves, Tsunamis, Internal waves big waves small waves huge waves rogue waves

more like a real wave

more like a sine wave

Anatomy of a Wave

Page 6: Chapter 10 Waves Capillary Waves, Wind Waves, Tsunamis, Internal waves big waves small waves huge waves rogue waves

Parts of a Wave

* Wavelength* height * Crest* trough * amplitude

* Frequency - # of waves passing a fixed point in

a given length of time

* Period - time for successive crests or troughs

(1 wavelength) to pass a fixed point

Page 7: Chapter 10 Waves Capillary Waves, Wind Waves, Tsunamis, Internal waves big waves small waves huge waves rogue waves

Direction of wave motion

Wave-length

Still water levelCrest Trough Crest

1/2 wave-length depth

Page 8: Chapter 10 Waves Capillary Waves, Wind Waves, Tsunamis, Internal waves big waves small waves huge waves rogue waves

Stokes drift (mass

transport)

No mass transport

Wave

Wave

Closed orbit after one period

Open orbit after one period

If we had this below, then there would be no net mass transport and no contribution of waves to the surface currents

BUT

in reality orbits are not exactly closed and waves DO contribute to mass transport

Page 9: Chapter 10 Waves Capillary Waves, Wind Waves, Tsunamis, Internal waves big waves small waves huge waves rogue waves

How do a waves form?• Wind blowing across calm water – if gentle breeze capillary

waves. Generating force = wind; restoring force = surface tension (cohesion); grow up to a wavelength of about 2 centimeters

• As wind speed increases - wave becomes larger. Generating force = wind; restoring force changes from surface tension to gravity

Types of waves - (1) progressive & (2) standing waves

(1) progressive = have a speed and move in a direction• surface waves: deep-water & shallow-water waves • big’ waves: large swells, tsunamis & episodic waves • internal waves at the pycnocline

(2) standing waves or seiches - do not progress, they are progressive waves reflected back on themselves and appear as alternating troughs and crests at a fixed position called antinodes, oscillating about a fixed point called node. They occur in ocean basins, enclosed baysand seas, harbors and in estuaries.

Page 10: Chapter 10 Waves Capillary Waves, Wind Waves, Tsunamis, Internal waves big waves small waves huge waves rogue waves
Page 11: Chapter 10 Waves Capillary Waves, Wind Waves, Tsunamis, Internal waves big waves small waves huge waves rogue waves

Seismic disruptionDisturbing forcelandslides

Gravity Wind

Restoring force GravitySurface tension

Type of wave Tide Tsunami Seiche Wind wave Capillary wave (ripple)

24 hr.

Am

ou

nt

of

ener

gy

in o

cean

su

rfac

e

100,000 sec (1 1/4 days)

10,000 sec (3 hr)

1,000 sec (17 min)

100 sec 10 sec 1 sec 1/10 sec 1/100 sec

Period (time, in seconds for two successive wave crests to

pass a fixed point)

1 10 100

Frequency (waves per second)

12 hr.

Period (& wavelength) and Wave Energy

Page 12: Chapter 10 Waves Capillary Waves, Wind Waves, Tsunamis, Internal waves big waves small waves huge waves rogue waves

Progressive Waves

Deep- to Shallow-Water Waves

Page 13: Chapter 10 Waves Capillary Waves, Wind Waves, Tsunamis, Internal waves big waves small waves huge waves rogue waves

H

L

A

Keep in mind: wave energy, NOT the water particles move across the surface of the sea. Wave propagates with C, energy moves with V

Wave Speed is C - Group Speed is Vwave speed = wavelength / period or C = L / T

T is determined by generating force so it remain the same after the wave formed, but C changes. In general, the longer the wavelength the faster the wave energy will move through the water.

Wave Speed

Page 14: Chapter 10 Waves Capillary Waves, Wind Waves, Tsunamis, Internal waves big waves small waves huge waves rogue waves

Deep Water Waves

TgT

LgL

C 56.12

25.12

For example, for a 300 meters wave and 14 sec period, the speed is about 22 meters per second

• Period to about 20 seconds

• Wavelength to at most 600 meters (extreme)

• Speed to about 100 kilometers/hour (70 mi/hr) (extreme)

Page 15: Chapter 10 Waves Capillary Waves, Wind Waves, Tsunamis, Internal waves big waves small waves huge waves rogue waves

Deep Water Waves

* surface waves progressing in waters of D larger than 1/2 L

* as the wave moves through, water particles move in circular orbit

* diameter of orbits decrease with depth, orbits do not reach bottom,

particles do not move below a depth D = L/2

* The wave speed can be calculated from knowledge of either the wavelength or the wave period:

C = 1.56 m/s2 T or C2 = 1.56 m/s2 L

* Group Speed (which really transport the energy) is half of the wave speed for deep-water waves: V = C/2

Page 16: Chapter 10 Waves Capillary Waves, Wind Waves, Tsunamis, Internal waves big waves small waves huge waves rogue waves

Shallow-Water Waves

Seismic Sea Waves – Shallow-Water Waves

• Period to about 20 minutes

• Wavelength of about 200 kilometers

• Speed of about 750-800 km/hr (close to 500 mi/hr!!)

DgDC 1.3

Page 17: Chapter 10 Waves Capillary Waves, Wind Waves, Tsunamis, Internal waves big waves small waves huge waves rogue waves

Shallow-Water Waves• surface waves generated by wind and progressing in waters of D less than (1/20) L • wave motion: as the wave moves through, water particles move in elliptical orbits • diameter of orbits remains the same with depth, orbits do reach the bottom where they ‘flatten’ to just an oscillating motion back and forth along the bottom

* The wave speed and the wavelength are controlled by the depth D of the waters only:

* Group Speed (which transport the energy) is the same as the wave speed for shallow-water waves: V = C

DgDC 1.3

Page 18: Chapter 10 Waves Capillary Waves, Wind Waves, Tsunamis, Internal waves big waves small waves huge waves rogue waves

Wind Speed: velocity at which the wind is blowing

Fetch: distance over which the wind is blowing

Duration: length of time wind blows over a given area

Wind Blowing over the Ocean Generates Waves

Waves development and growth are affected by:

Larger Swell Move Faster waves separate into groups

wave separation is called dispersion

Page 19: Chapter 10 Waves Capillary Waves, Wind Waves, Tsunamis, Internal waves big waves small waves huge waves rogue waves

• Storm centers and dispersion• Winds flow around low pressure • Variety of periods and heights are generated

grouped into wave trains

Waves with longer period (T) and larger length move faster - these get ahead of the ‘pack’.

Wave sorting of these free waves is dispersion

Page 20: Chapter 10 Waves Capillary Waves, Wind Waves, Tsunamis, Internal waves big waves small waves huge waves rogue waves

5 4 3 2 1

7 6 5 4 3

6 5 4 3 2

8 7 6 5

8 7 6 5

7 6 5 4 3

7 6 5 4

6 5 4 3 2 1

Wave Train (‘pack’, group)

• wave 1 transfers ½ of its energy to water (gets orbital motion going) and ½ to wave 2 (to keep that going)

• wave 1 disappear – mm later 2 and 3 and so on will disappear also as wave 6, 7, etc. form

• waves 1, 2, 3, etc. move at their deep-water wave speed C but the wave train moves at ½ of C = V, the group velocity, speed at which energy moves forward

Dispersion only affects deep-water waves, as depth decreases waves become shallow-water waves, they slow down until C=V

Page 21: Chapter 10 Waves Capillary Waves, Wind Waves, Tsunamis, Internal waves big waves small waves huge waves rogue waves

Wave size increases with increased wind speed, duration, and fetch. A strong wind must blow continuously in one direction for nearly three days for the largest waves to develop fully.

Fetch: uninterrupted distance over which the wind blows without significant change in direction.

Wind Speed, Fetch & Duration

Pacific Ocean: wind speed of 50 mi/hr, blowing steadily for about 42 hours over a region of size 800 miles will results in 8 meters waves – can get to 17 meter waves! (see Table 10.2)

Page 22: Chapter 10 Waves Capillary Waves, Wind Waves, Tsunamis, Internal waves big waves small waves huge waves rogue waves

7 across

1 high

120°

Wave Height, Wavelength & Wave Steepness

Typical ratio wave height to wavelength in open ocean = 1:7 = wave steepness – angle of the crest = 120°

Exceed these conditions and wave will break at sea whitecaps

Wave Height is controlled by (1) wind speed, (2) wind duration and (3) fetch (= the distance over water that the wind blows in the same direction and waves are generated) Significant Wave Height - average wave height of the highest one-third of the waves measured over a long time

Page 23: Chapter 10 Waves Capillary Waves, Wind Waves, Tsunamis, Internal waves big waves small waves huge waves rogue waves

Wave Interaction - Interference

Page 24: Chapter 10 Waves Capillary Waves, Wind Waves, Tsunamis, Internal waves big waves small waves huge waves rogue waves

1 2

a

b

Constructive interference

(addition)

Destructive interference (subtraction)

Constructive interference

(addition)

Page 25: Chapter 10 Waves Capillary Waves, Wind Waves, Tsunamis, Internal waves big waves small waves huge waves rogue waves

Wave interaction Constructive interference; (b) crests of waves coincide Destructive interference; (c) crest of one coincides with

trough of other

ask surfers about the ‘surf beat’, or impress them explaining that it is ‘just wave interference’!

Page 26: Chapter 10 Waves Capillary Waves, Wind Waves, Tsunamis, Internal waves big waves small waves huge waves rogue waves

1 2 4 53

Depth = 1/2 wavelength

Surf zone

Deep-water waves change to shallow-water waves as they approach the shore and they break

(1) The swell “feels” bottom when the water is shallower than half the wavelength. (2) The wave crests become peaked because the wave’s energy is packed into less water depth. (3) Water’s circular motion due to wave is constrained by interaction with the ocean floor and slows the wave, while waves behind it maintain their original rate. (4) The wave approaches the critical 1:7 ratio of a wave height to wavelength. (5) The wave breaks when the ratio of wave height to water depth is about 3:4. The movement of water particles is shown in red. Note the transition from a deep-water wave to a shallow-water wave.

Page 27: Chapter 10 Waves Capillary Waves, Wind Waves, Tsunamis, Internal waves big waves small waves huge waves rogue waves

The Surf Zone - Breakers

plunger

spiller

Wave Breaking: wave becomes unstable as water particles at the crest travel much faster/farther than water particles in the trough

Breaker type is determined by slope, composition and contours of the bottom

Page 28: Chapter 10 Waves Capillary Waves, Wind Waves, Tsunamis, Internal waves big waves small waves huge waves rogue waves

Breaker Types

Page 29: Chapter 10 Waves Capillary Waves, Wind Waves, Tsunamis, Internal waves big waves small waves huge waves rogue waves

Wave Refraction – slowing and bending of waves as they approach shore at an angle

depth contours

crests

oblique angle between direction of motion of waves and depth contours

part of wave in shallow water slows down

part of same wave still in deep water hence faster

Page 30: Chapter 10 Waves Capillary Waves, Wind Waves, Tsunamis, Internal waves big waves small waves huge waves rogue waves

Wave refraction- propagation of waves around obstacles, for example over a shallow ridge – energy is focused (waves get ‘interrupted’, waves generate other waves)

Page 31: Chapter 10 Waves Capillary Waves, Wind Waves, Tsunamis, Internal waves big waves small waves huge waves rogue waves

Wave refraction in a shallow bay – energy is spread

Page 32: Chapter 10 Waves Capillary Waves, Wind Waves, Tsunamis, Internal waves big waves small waves huge waves rogue waves

Wave Reflection

Page 33: Chapter 10 Waves Capillary Waves, Wind Waves, Tsunamis, Internal waves big waves small waves huge waves rogue waves

Wave Diffraction

narrow opening

diffraction and wave interaction

Page 34: Chapter 10 Waves Capillary Waves, Wind Waves, Tsunamis, Internal waves big waves small waves huge waves rogue waves

Wave diffraction behind the breakwater

Page 35: Chapter 10 Waves Capillary Waves, Wind Waves, Tsunamis, Internal waves big waves small waves huge waves rogue waves

Review:

Refraction: waves approaching shore are refracted (bent) as they move from deep to shallow water - change in wavelength and wave speed

Diffraction: spread of wave energy sideways to the direction of wave travel.

Reflection: Waves that encounter a solid vertical surface (such as a seawall) will abruptly change direction without much loss of energy. Though not as simple as a ball bouncing off a wall, the reflection of a wave obeys the same principles, where the angle of incidence is equal to the angle of reflection. When the angle is zero (as measured from a line perpendicular to the reflecting surface), reflection may generate standing waves.

Page 36: Chapter 10 Waves Capillary Waves, Wind Waves, Tsunamis, Internal waves big waves small waves huge waves rogue waves

Tsunamis• Vertical sea floor displacement• Shallow water waves

Long wavelength Low period

• Wave height changes (quite dramatically!) At point of origin Close to shore where depth decreases

when????

Page 37: Chapter 10 Waves Capillary Waves, Wind Waves, Tsunamis, Internal waves big waves small waves huge waves rogue waves
Page 38: Chapter 10 Waves Capillary Waves, Wind Waves, Tsunamis, Internal waves big waves small waves huge waves rogue waves

Satellite images of a coastal village in

Banda Aceh, Indonesia, before

and after the December 26, 2004

tsunami.

http://www.seed.slb.com/en/scictr/watch/living_planet/tsunami.htm

Page 39: Chapter 10 Waves Capillary Waves, Wind Waves, Tsunamis, Internal waves big waves small waves huge waves rogue waves
Page 40: Chapter 10 Waves Capillary Waves, Wind Waves, Tsunamis, Internal waves big waves small waves huge waves rogue waves
Page 41: Chapter 10 Waves Capillary Waves, Wind Waves, Tsunamis, Internal waves big waves small waves huge waves rogue waves
Page 42: Chapter 10 Waves Capillary Waves, Wind Waves, Tsunamis, Internal waves big waves small waves huge waves rogue waves

Tsunamis become dangerous only near shore

Page 43: Chapter 10 Waves Capillary Waves, Wind Waves, Tsunamis, Internal waves big waves small waves huge waves rogue waves