Chapter 9 waves and water dynamics
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Chapter 9: Waves and Water Dynamics. Fig. 9-10. Waves are moving energy. Forces cause waves to move along air/water or within water Wind (most surface ocean waves) Movement of fluids with different densities Internal waves often larger than surface waves Mass movement into ocean

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Waves are moving energy l.jpg
Waves are moving energy

  • Forces cause waves to move along air/water or within water

    • Wind (most surface ocean waves)

    • Movement of fluids with different densities

      • Internal waves often larger than surface waves

    • Mass movement into ocean

      • Splash waves


Slide3 l.jpg

  • Seafloor movement

    • Tsunami or seismic sea wave

  • Gravitational attraction Earth, Moon, Sun

    • Tides

  • Human activities

    • Wakes of ships

    • Explosions


Progressive waves l.jpg
Progressive waves

  • Longitudinal

    • “Push-pull”

  • Transverse

    • Side-to-side or up-and-down

  • Orbital

    • Circular orbit

    • Ocean surface waves


Types of waves l.jpg
Types of waves

Fig. 9-3a


Wave characteristics l.jpg
Wave characteristics

  • Crest, trough

    • Wave height is proportional to energy

  • Wave length

  • Wave height/wave length = wave steepness

    • Waves break when H/L is 1/7

  • Wave period, frequency


Wave characteristics7 l.jpg
Wave characteristics

  • Wave base is 1/2 wave length

    • Negligible water movement due to waves below this depth

Fig.9-6a


Deep water wave l.jpg
Deep-water wave

  • Depth of water is greater than 1/2 wavelength

  • Speed of wave form (celerity) is proportional to wavelength


Shallow water wave l.jpg
Shallow-water wave

  • 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


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Transitional waves

  • 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



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Wave equations

  • 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 l.jpg
Surface ocean waves

  • Most wind-driven

  • Small wind-driven waves

    • Capillary waves

  • Larger wind-driven waves

    • Gravity waves


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Sea

  • Storm at sea creates waves

  • Wave energy depends on

    • Wind speed

    • Fetch

    • Duration

  • Chaotic mixture of different wavelengths and wave heights


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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

  • Constructive

    • Wave heights increase

  • Destructive

    • Wave heights decrease

  • Mixed

    • Wave heights vary in wave train (surf beat)



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Rogue waves

Fig. 9-16

  • Unusually large waves

    • Constructive interference

    • Waves meet strong ocean current


Shoaling waves l.jpg
Shoaling waves

  • Waves reach surf zone

    • Wave speed decreases

    • Wave length decreases

    • Wave height increases

      • Wave steepness 1/7, wave breaks

      • Surface tension no longer able to hold wave together


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Breakers

  • Spilling

    • Gentle beach slope

  • Plunging

    • Moderately steep slope

  • Surging

    • Abrupt slope


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Wave refraction

  • Shoaling waves bend so wave fronts approach a shore nearly parallel

Fig. 9-19a


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Fig. 9-19b


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Wave diffraction

  • Wave energy transferred around or behind barriers

Fig. 9-20


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Wave reflection

  • Waves bounce back from steep slopes or seawalls

  • Reflected wave may constructively interfere with other waves


Standing waves l.jpg
Standing waves

  • Two waves with same wavelength moving in opposite directions

  • Node – no vertical movement

    • Greatest horizontal movement

  • Antinode – greatest vertical movement



Tsunami or seismic sea wave l.jpg
Tsunami or seismic sea wave

  • Caused by sudden changes in volume of ocean basin

    • Mainly submarine faults

    • Volcanic eruptions

    • Submarine landslides



Tsunami l.jpg
Tsunami

  • 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 l.jpg
Tsunami warning system

  • Monitor seismic activity

  • Monitor changes in unusual wave activity

  • Warning

    • People evacuate