1-1 Waves in the Ocean

7/28/2019 1-1 Waves in the Ocean

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Waves in the Ocean



7.1 Properties of Ocean Waves

An ocean wave is an undulation of the sea surface.

• Wave parameters:

–Wave crest

–Wave trough–wave height (H)

–wave amplitude (1/2H)

–wave length (L)

–wave period (T).

• Progressive waves move across the sea surface.

–Surface waves

–Internal waves

–Tsunamis Surface waves

• Standing waves oscillate about a fixed point.

–Seiches



Defintions and symbols



Definition of terms- elementary, sinusoidal, progressive wav



7.1 Properties of Ocean Waves

Idealized Wave Spectrum





7.1 Properties of Ocean Waves Wind Generation of Waves

• The type of wave generated by wind isdetermined by:

–Wind velocity

–Wind duration

–Fetch (distance over which wind blows)• Simply put, wave size increases as the strength

and duration of the wind, and distance overwhich it blows increases.



Progressive waves are waves that “move”

forward across a surface.• As waves pass, wave form and wave energy

move forward, but not the water.

• Water molecules move in an orbital motion as

the wave passes.

• Diameter of orbit increases with increasingwave size and decreases with depth below thewater surface.

7-2 Wave Motions



Progressive Wave Types

• Sea - irregular waves in the area of generation

• Swell - more regular waves beyond area of generation

• Surf - waves that have reached the coast, grow in height,and break



Orbit Diameter and Stokes Drift



7-2 Wave Motions



Deep- and Shallow-Water Motion

• Wave base is the depth

to which a surface wavecan move water.

• If the water is deeperthan wave base:

– orbits are circular

– no interaction between thebottom and the wave.

• If the water is shallowerthan wave base

– orbits are elliptical – orbits become increasingly

flattened towards thebottom.





Flow of Energy,not Mass

7-3 Life History of Ocean Waves




seas insidefetch area.

Swells:wavefound

outsidethe fetc

Fetch is the area of contact between the wind and the water and is wherwind- enerated waves be in.



Progressive Wave Types

Sea

Swell

Surf

• Sea - irregular waves in the area of generation

• Swell - more regular waves beyond area of generation

• Surf - waves that have reached the coast, grow in height, and break

• Wave interference is the momentary interaction between



Wave interference is the momentary interaction betweenwaves as they pass through each other. Wave interferencecan be constructive or destructive.




7 3 Life History of Ocean Waves

•Dispersion: Gradual separation of wave types

based on their relative wavelengths and speeds

•Because celerity increases as wavelengthincreases:

-long waves travel faster than short waves.

-This causes dispersion outside of the fetch andregular ocean swell.

Transformation : Dispersion






7 3 Life History of Ocean Waves

Transformation : Shoaling




The shallower the water, the greater the

interaction between the wave and the bottomalters the wave properties, eventually causingthe wave to collapse.

• Wave speed decreases as depth decreases.

• Wavelength decreases as depth decreases.

• Wave height increases as depth decreases.

• Troughs become flattened and the wave profile becomesextremely asymmetrical.

• Period remains unchanged. Period is a fundamental

property of a wave.• Celerity equation of shallow water wave.

y

Transformation : Shoaling



Transformation : Breaking



Spilling, Plunging and Surging Breakers

•Spilling breaker: Top of wave crest ‘spills over’

wave. Energy releasedgradually across entiresurf zone.

•Plunging breaker: Crest ‘curls over’ front of wave. Energy dissipates

quickly. Common atshorelines with steepslopes

•Surging breaker: Neverbreaks as it never

attains critical wavesteepness. Commonalong upwardly slopingbeach faces or seawalls.Energy releasedseaward.





Wave steepness is a ratio of wave height

divided by wavelength (H/L).• In shallow water, wave height increases and

wave length decreases.

• When H/L is larger than or equals 1/7 (H/L 1/7), the wave becomes unstable and breaks.

• There are three types of breakers: spillingbreakers, plunging breakers, and surgingbreakers.







• Water is deeper at theshore area, allowing

waves to progressfarther inland.

• Storm surge isespecially severe

when superimposedupon a spring hightide.

Storm surge is the rise in sea level resulting from lo

atmospheric pressure and the accumulation of watedriven shoreward by storm winds.

Transformation : Storm Surge

7-4 Standing Waves



• Resonance amplifies the displacement at the nodes andoccurs when the period of the basin is similar to the period

the force producing the standing wave.

7 4 Standing Waves



Standing waves or seiches consist of a water

surface “seesawing” back and forth.

• Node : The line about which the surfaceoscillates.

– Located in centers of enclosed basins and toward theseaward side of open basins.

• Antinodes: Points where there are the maximumdisplacement of the surface as it oscillates.

– Antinodes usually located at the edge of the basin.

7-4 Standing Waves



• Geometry of the basin controls the period of the

standing wave. A basin can be closed or open.• Standing waves can be generated by storm

surges.

• Resonance amplifies the displacement at the

nodes and occurs when the period of the basin issimilar to the period of the force producing thestanding wave.

7-4 Standing Waves




A first order seiche. The undisturbed sea level is indicated the broken yellow line. Three water particles are shown as

an indication of water movement in the seiche.Note the node in the centre and that water under the nodemoves only horizontally, while water at both ends of thebasin moves vertically.

Standing wave




A first order seiche in a basin open to the deep ocean. Theundisturbed sea level is indicated by the broken yellow line.

Two water particles are shown as an indication of watermovement in the seiche.Note the node at the connection of the basin to the deep oceaand that water under the node moves only horizontally, whilewater at the end of the basin moves vertically

Seiche

7-5 Other Types of Progressive Waves



Internal waves form within the water columnon the pycnocline.

• Because of the small density difference betweethe water masses above and below thepycnocline, wave properties are differentcompared to surface waves.

• Internal waves display all the properties of surface progressive waves including reflection,refraction, interference, breaking, etc.

• Any disturbance to the pycnocline can generate

internal waves, including: Flow of water relatedto the tides., Flow of water masses past eachother, Storms, or Submarine landslides.

yp g



An internal wave propagating on the interface between twolayers. The undisturbed sea level is indicated by the yellowline. Water particles are shown as yellow and magenta dotsYellow dots sit in the middle of the water column and moveonly up and down. Magenta dots sit at the top and bottom othe water column and move only in the horizontal.

By watching a yellow dot you can see how a water particle the middle of the water column moves up and down, but donot move horizontally, as the wave passes through.

Internal Waves

Other Types of Progressive Waves



Internal waves form within the water column

along the pycnocline.

Other Types of Progressive Waves (Tsunami)



Tsunamis were previously called tidal waves,but are unrelated to tides.

• Tsunamis consist of a series of long-periodwaves characterized by very long wavelength(up to 100 km) and high speed (up to 760km/hr) in the deep ocean.

• Because of their large wavelength, tsunamis areshallow-water to intermediate-water waves asthey travel across the ocean basin.

• They only become a danger when reachingcoastal areas where wave height can reach 10

m.

• Tsunamis originate from earthquakes, volcanicexplosions, or submarine landslides.

Generation of a Tsunami




Tsunamies Generation



Tsunamies Generation











Wh t I R W ?



What Is a Rogue Wave?

A "rogue wave" is typically used to describe a wave that is significantly

larger than other waves during a given time, at a given location. Severalfactors can create rogue waves. Multiple waves can intersect to create a

much larger wave- up to the sum of the heights of the waves that combine.

Additionally, currents can contribute to the formation of rogue waves. And

rogue waves can result as a normal part of the wave spectrum. In other

words, waves are not created individually but rather, in large groups. And awave(s) within this group can be significantly larger than the rest.

Rogue waves have been witnessed all around the world. The North Sea,

Gulf of Alaska, S. African coasts are infamous for producing rogue waves-

some that have approached 100 feet in height.



Coastal

Rogue Wave



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هآCoast Beach or shoreاخن Nearshore zoneاخهدطقة

آز ور

Offsh

قطلخاآهآCoastal area

قعخاBackshore لخاForeshore

Surf Zone

Shoreface or Inshoreاخ ة

جسBottom

دگهقطةPlunge Pointفآ

Bermم

Crest of Berm طثآز

Coastرخادآ

ا آ د :آز ه ا آ آر طآ و د ن ا ث رد ا ارد و ف ل ج نآع و درا آت در آ آز و قط نخاا زآ ك ا

ا آت ج ارد و .

آخ اطقة اخل:آز ه ل ث ت آخن ا(اآز ا(آدر ث آخن )و ا آ)آدر ست قط اث و .اآدآ و

قخ ا گ د زل:آخا آ ر آ ع اث و و اخن درا در ث ا زآ ج ل دو ع تآ يآ قط6 رآد آدآ ارد ن ثآز ر در دآ ث ا .ج آز

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1-1 Waves in the Ocean