waves = energy in motion - west valley college
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Waves = Energy in Motion Waves - Energy in Motion
• Transmission of Energy, not mass• Interface between fluids of different density• http://www.surendranath.org/Applets.html• (What is a Wave)
• http://www.surendranath.org/Applets.html• (Transverse and Longitudinal waves)
Two Main Types
• Progressive Waves = energy movesforward
• Seiches - Standing Waves• http://www.surendranath.org/Applets.html(Standing Waves)
How do Waves Move?
• Energy is transmitted by moving particles acrosswater surface
• Moving particles do not travel• Moving particles accommodate the passing of
energy• “Orbital Motion - Orbital Waves• http://www.saddleback.edu/faculty/jrepka/notes/waves.h
tml (Orbital Waves)
Wind Waves
Wind waves are gravity waves formed by the transfer of wind energyinto water. Wind forces convert capillary waves to wind waves.
Wave Mechanics
• Crest and Trough• Still Water Level• Wave Height (H)• Wave Length (L)• Wave Amplitude (A)• Wave Steepness (H/L)
2
)( wavelength
)(height wave steepness Wave
L
H=
• Steepness is greater than 1/7 (1:7 ratio), thewave will break.
• If a wave has a 7 meter wave length (L), itcan not exceed 1 meter wave height (H).
Wave Period and Frequency
• Wave Period (T) -
• Frequency (f) -
1.74 cm200 Km20,016 Km
Half circumference of EarthPeriod of Waves
• Wind Waves• 8 to 10 seconds
• Tsunamis• 20 min.
Orbital Motion
The floating object moves incircles or orbits that have aradius equal to the waveheight at the surface
Figure 8-4
Wave Base - 1/2 the wave lengthWave Base = 1/2*(L)
Orbital sizedecreases withdepth to zero atwave base
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Deep Water and Shallow WaterWaves
• Deep Water Waves = (depth > L/2).
• Shallow Water Waves = (depth < L/20).
Figure 8-6a & b
Wave Speed
• Longer Wavelengths have greater velocityfor deep water waves.– These also have longer wave periods– First swell typically bigger surf waves
Wave Speed - Celerity (C)Deep water - C = L/T (m/sec)
Shallow Water - C = (gd)1/2, in m/sec.
Wind Generated WavesOcean Waves Begin at Sea
The “sea” and swell• Waves
originate in a“sea” area
• Swell describeswaves that:– Have traveled
out of their areaof origination
– Exhibit auniform andsymmetricalshape Figure 8-9
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Fully developed sea
• Factors that increase wave height:– Increasing wind speed– Increasing duration (time) of wind– Increasing fetch (distance)
• A fully developed sea is the maximumheight of waves produced by conditions of– Wind Speed– Duration– Fetch Figure 8-9
Wave Interference • http://www.kettering.edu/~drussell/Demos/superposition/superposition.html
Constructive– Increases
wave height• Destructive
– Decreaseswave height
• Mixed– Variable
pattern
Largest wind-generated wavesauthentically recorded
• In 1935, the vesselUSS Ramapo
• Wave height wasmeasured at 34meters (112 feet)
Figure 8-11
Pacific Ocean
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Waves undergo physical changesin the surf zone
Types of breakers• Spilling breakers
– Gentle beach slope allows waves to disperseenergy gradually
• Plunging breakers– Moderately steep beach slope gives waves a
curling shape that propels surfers• Surging breakers
– Abrupt beach slope makes waves build up andbreak rapidly at the shore
SpillingBreaker
PlungingBreaker
SurgingBreaker
Tsunami• Tsunami terminology
– Often called “tidal waves” but have nothing todo with the tides
– Japanese term meaning “harbor wave”– Also called “seismic sea waves”
• Created by movement of the ocean floor by:– Underwater fault movement– Underwater avalanches– Underwater volcanic eruptions
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Most tsunami originate fromunderwater fault movement
Figure 8-21a
Tsunami characteristics• Affect entire water column,• speeds over 700 kilometers (435 mi/hr)• Small wave height in the open ocean, so
pass beneath ships unnoticed (<1m)• Build up to extreme heights in shallow
coastal areas (30m)
Coastal effects of tsunami• If trough arrives first, appear as a strong
withdrawal of water (similar to an extremeand suddenly-occurring low tide)
• If crest arrives first, appear as a strongsurge of water that can raise sea level manymeters and flood inland areas
• Tsunami often occur as a series of surgesand withdrawals
Tsunami since 1900• Most tsunami
are created nearthe margins ofthe PacificOcean along thePacific “Ring ofFire”
• Internet video oftsunamimovementacross PacificOcean
Figure 8-23
Tsunami warning system• Seismic listening stations track underwater
earthquakes that could produce tsunami• Once a large earthquake occurs, the
tsunami must be verified at a nearby station• If verified, a tsunami warning is issued• Successful in preventing loss of life (if
people heed warnings)• Damage to property has been increasing