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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