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Waves

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Chapter 10 Waves Wave Formation Generating Force Restoring Force Surface tension Gravity Wave Formation Gravity waves Generating Force Wind Ripples Capillary waves ... – PowerPoint PPT presentation

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Title: Waves


1
Chapter 10
  • Waves

2
Wave Formation
  • Generating Force
  • Restoring Force
  • Surface tension
  • Gravity

3
Wave Formation
  • Gravity waves
  • Generating Force
  • Wind
  • Ripples
  • Capillary waves
  • Cats-paws

4
Anatomy of a Wave
  • Crest
  • Trough
  • Wavelength (L)
  • Wave height (H)
  • Amplitude 1/2H
  • Period (T)
  • Seconds/cycle
  • Frequency
  • Cycles/second

5
Wave Motion
  • As waves pass, wave form and wave energy move
    rapidly forward, not the water!
  • Two basic motions associated with waves
  • Forward motion
  • Orbital motion

6
Orbital Motion
  • As wave approaches, a water particle will trace a
    circular path
  • Diameter of orbit at surface wave height

7
Wave Base
  • Wave particle orbits are not detectable below
    1/2 wavelength

8
Wave Speed
  • Celerity (C)
  • C wavelength/period
  • C L/T
  • Period remains the same

9
Wave Measurement
  • The simplest technique is to examine the
    oscillation of waves against a pole fixed marked
    in meters
  • Oceanographers will employ pressure sensors
    anchored to the sea floor

10
Wave Measurement
  • Satellite Imagery

11
Deep-water Waves
  • Waves that propagate in water than is one-half
    their wavelength
  • Wave base is above the sea floor

12
Deep-water Waves
  • L (g/2p)T2
  • L (1.56 m/sec2)T2
  • L/T (1.56 m/sec2)T
  • C 1.56T
  • C2 1.56L

13
Storm Centers
  • Progressive wind waves (PWWs)
  • Wind
  • Gravity
  • Propagate in particular direction

14
Storm Centers
  • Progressive wind waves (PWWs)
  • Confused seas
  • Forced waves

15
Dispersion
  • Free waves
  • No longer wind-driven waves
  • Period does not change

16
Group Speed
  • Wave Train
  • Group Speed (V)
  • One-half the wave velocity for deep-water waves
  • V C/2

17
Constructive Wave Interference
  • Crests troughs coincide
  • Build up of crest deepening of trough

18
Destructive Wave Interference
  • Crest of one wave coincides with trough of
    another wave (and vice versa)
  • Dampening of wave

19
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20
Wave Height
  • The variety and size of wave generated depends on
    3 factors
  • Speed of the wind
  • How long the wind blows
  • Size of the fetch of the wind

21
Wave Height
  • 40-50o S
  • Ideal wave production
  • No landmasses to limit fetch
  • Westerlies
  • Typical maximum fetch
  • 920 km (500 miles)

22
Wave Height
  • Larger waves will be produced on the side of the
    storm where the winds are blowing in the same
    direction as the storm is moving
  • 10-15 m (33-49 ft)
  • 100-200 m (330-660 ft) long

23
Wave Height
  • Episodic waves
  • Produced as a result of constructive interference
  • Occur most often near edge of continental shelf
  • 20-30 m
  • 50 knots
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