Transcript Chapter 9: Waves and Wave Dynamics

Chapter 9: Waves and Water
Dynamics
Fig. 9-10
Waves are moving energy
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Forces cause waves to move along air/water
or within water
 Wind (most surface ocean waves)
 Movement of fluids with different densities
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Internal waves often larger than surface
waves
Mass movement into ocean
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Splash waves
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Seafloor movement
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Gravitational attraction Earth, Moon,
Sun
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Tsunami or seismic sea wave
Tides
Human activities
Wakes of ships
 Explosions
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Progressive waves
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Longitudinal
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Transverse
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“Push-pull”
Side-to-side or up-and-down
Orbital
Circular orbit
 Ocean surface waves
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Types of waves
Fig. 9-3a
Wave characteristics
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Crest, trough
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Wave length
Wave height/wave length = wave
steepness
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Wave height is proportional to energy
Waves break when H/L is 1/7
Wave period, frequency
Wave characteristics
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Wave base is 1/2 wave length
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Negligible water movement due to waves
below this depth
Fig.9-6a
Deep-water wave
Depth of water is greater than
1/2 wavelength
 Speed of wave form (celerity) is
proportional to wavelength
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Shallow-water wave
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Water depth is less than 1/20 wavelength
Friction with seafloor retards speed
Wave speed (celerity) is proportional to depth
of water
Orbital motion is flattened
Transitional waves
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Water depth is 1/2 to 1/20 of
wavelength
Characteristics of deep and
shallow-water waves
Wave speed (celerity) is
proportional to both wavelength
and depth of water
Three types of waves
Wave equations
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Wave speed = wavelength/period
 S = L/T
Frequency = 1/period
 F = 1/T
Wave speed (m/s) = 1.56 x period
 S = 1.56 x T
Surface ocean waves
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Most wind-driven
Small wind-driven waves
 Capillary waves
Larger wind-driven waves
 Gravity waves
Sea
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Storm at sea creates waves
Wave energy depends on
Wind speed
 Fetch
 Duration
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Chaotic mixture of different
wavelengths and wave heights
Wave dispersion
Longer wavelength waves
outdistance shorter wavelength
waves
 Waves travel in groups or trains
with similar characteristics
 Swell made up of waves of
similar wavelength and period
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Wave interference
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Constructive
 Wave heights increase
Destructive
 Wave heights decrease
Mixed
 Wave heights vary in wave train
(surf beat)
Interference illustrated
Fig. 9-14
Rogue waves
Fig. 9-16
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Unusually large waves
Constructive interference
 Waves meet strong ocean current
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Shoaling waves
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Waves reach surf zone
Wave speed decreases
 Wave length decreases
 Wave height increases
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Wave steepness 1/7, wave breaks
 Surface tension no longer able to hold
wave together
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Breakers
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Spilling
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Plunging
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Gentle beach slope
Moderately steep slope
Surging
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Abrupt slope
Wave refraction
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Shoaling waves bend so wave fronts
approach a shore nearly parallel
Fig. 9-19a
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Wave energy
focused on
headland
Wave energy
dispersed over
bay
Fig. 9-19b
Wave diffraction
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Wave energy
transferred
around or
behind barriers
Fig. 9-20
Wave reflection
Waves bounce back from steep
slopes or seawalls
 Reflected wave may
constructively interfere with
other waves
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Standing waves
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Two waves with same wavelength
moving in opposite directions
Node – no vertical movement
 Greatest horizontal movement
Antinode – greatest vertical
movement
Fig. 9-22
Tsunami or seismic sea wave
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Caused by sudden changes in
volume of ocean basin
 Mainly submarine faults
 Volcanic eruptions
 Submarine landslides
Fig. 9-23a
Tsunami
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Very long wavelength
Travels fast
Raises sea level as crest shoals
 Trough causes sea level to fall
Disastrous for infrastructure at
coasts
Possibly much loss of life
Tsunami warning system
Monitor seismic activity
 Monitor changes in unusual
wave activity
 Warning
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People evacuate
End of Chapter 9: Waves and
Water Dynamics
Fig. 9D