dr. rer nat. wiwin windupranata · 2017. 8. 10. · hydrographic science and engineering working...

Hydrographic Science and Engineering Working Group

Faculty of Earth Science and Technology

Institute of Technology, Bandung

WAVESWAVESDr. rer nat. Wiwin Windupranata

coastal environmental survey windupranata@2010




WHY STUDY WAVES ?WHY STUDY WAVES ?





ShippingShipping





Coastal ConstructionsCoastal Constructions





Offshore ConstructionsOffshore Constructions





Beach Erosion and Sediment Beach Erosion and Sediment

TransportTransport





RecreationsRecreations





FUNDAMENTAL PRINCIPLESFUNDAMENTAL PRINCIPLES





Wave Parameters Wave Parameters

Wave Period = Time it Takes a Wave Crest to Travel one Wavelength (units of time)


Wave Frequency = Number of Crest per Unit Time Passing A Fixed Location (units of 1/time)

Wave Speed = Distance a Wave Crest Travels per Unit Time (units of distance/time)




Wave SpectrumWave Spectrum





Wave Classification Wave Classification





Most of the waves present on the ocean’s

surface are wind-generated waves.

Wave Classification Wave Classification

Size and type of wind-generated waves are controlled by Wind

velocity, Wind duration, Fetch, and Original state of sea surface

As wind velocity increases wave length, period and height increase,

but only if wind duration and fetch are sufficient

Significant wave height is the average wave height of the highest

1/3 of the waves present and is a good indicator of potential for


1/3 of the waves present and is a good indicator of potential for

wave damage




Addition of WavesAddition of Waves


Constructive

DestructiveMixed




Ideal Waves Ideal Waves

Propagate Energy not Propagate Energy not Propagate Energy not Propagate Energy not

Water MassWater Mass





Wave MovementWave Movement


Note that the water molecules in the crest of the wave move in

the same direction as the wave, but molecules in the trough

move in the opposite direction




Wave MovementWave Movement


Note the importance of the

relationship between

wavelength and depth in

determining wave type.




Wave RegionsWave Regions





Deep-Water Waves (Bottom Depth > L/2)– Speed is a Function of Wavelength Only

– Waves with Longer Wavelength move faster than Waves

Wave SpeedsWave Speeds

– Waves with Longer Wavelength move faster than Waves with Shorter Wavelength

Shallow-Water Waves (Bottom Depth < L/20)– Speed is a Function of Depth Only

– Waves (of any Wavelength) Travel Slower in Shallower Water


Intermediate region (L/20 < Depth < L/2) – Speed is a Function of Wavelength and Depth Only




Wave Speed as a Function of Wave Speed as a Function of

WavelengthWavelength





Wave Speed as a Function of Wave Speed as a Function of

Water DepthWater Depth





Wind speed - wind must be moving faster than the

Factors Affecting Wind Wave Factors Affecting Wind Wave

DevelopmentsDevelopments

Wind speed - wind must be moving faster than the

wave crests for energy transfer to continue

Wind duration - winds that blow for a short time will

not generate large waves

Fetch - the uninterrupted distance over which the wind


Fetch - the uninterrupted distance over which the wind

blows without changing direction




Factors Affecting Wind Wave Factors Affecting Wind Wave

DevelopmentsDevelopments





Wind Wave DevelopmentsWind Wave Developments


Wind waves are gravity waves formed by the transfer of wind energy

into water. Wind forces convert capillary waves to wind waves.




Lateral Spreading of Wave Energy Lateral Spreading of Wave Energy

from a Storm Sourcefrom a Storm Source


(95% of Energy Contained Within ±45o of Storm Direction)




The Importance of FetchThe Importance of Fetch





Fetch Fetch is the area of contact between the wind and the water is the area of contact between the wind and the water

and is where windand is where wind--generated waves begingenerated waves begin

Seas Seas is the term applied when the fetch has a chaotic jumble is the term applied when the fetch has a chaotic jumble

Life History of Ocean WavesLife History of Ocean Waves

Seas Seas is the term applied when the fetch has a chaotic jumble is the term applied when the fetch has a chaotic jumble

of new wavesof new waves

Waves Waves continue to grow until the sea is fully developed or continue to grow until the sea is fully developed or

becomes limited by becomes limited by fetch restriction fetch restriction or or wind durationwind duration

Wave interference Wave interference is the momentary interaction between is the momentary interaction between

waves as they pass through each other. Wave interference can waves as they pass through each other. Wave interference can

be constructive or destructivebe constructive or destructive


be constructive or destructivebe constructive or destructive

Because celerity increases as wave length increases, longer Because celerity increases as wave length increases, longer

waves travel faster than short waveswaves travel faster than short waves




Wave Wave

InterferenceInterference





Wave TransformationsWave Transformations





Wave Wave

TransformationsTransformations

Wave separation, or dispersion, is a

function of wavelength. Waves with

the longest wavelength move the


the longest wavelength move the

fastest and leave the area of wave

formation sooner. The smooth

undulation of ocean water caused

by wave dispersion is called swell.

The process known as a wave train.




The shallower the water, the greater the interaction The shallower the water, the greater the interaction

between the wave and the bottom alters the wave between the wave and the bottom alters the wave


between the wave and the bottom alters the wave between the wave and the bottom alters the wave

properties, eventually causing the wave to collapseproperties, eventually causing the wave to collapse

Celerity decreases as depth decreases

Wave length decreases as depth decreases

Wave height increases as depth decreases

Troughs become flattened and wave profile becomes extremely

asymmetrical


asymmetrical

Period remains unchanged. Period is a fundamental property of

a wave

Refraction is the bending of a wave into an area where it

travels more slowly




Wave steepness (stability) is a ratio of wave height Wave steepness (stability) is a ratio of wave height

divided by wave length divided by wave length


divided by wave length divided by wave length

wave stability = H/Lwave stability = H/L

In shallow water, wave height increases and wave length

decreases

When H/L is larger than or equals to 1/7 (H/L ≥ 1/7), the


When H/L is larger than or equals to 1/7 (H/L ≥ 1/7), the

wave becomes unstable

There are three types of breakers:, Spilling breakers,

Plunging breakers, and Surging breakers




Spilling waves occur on gradually sloping ocean bottoms.

The crest of a spilling wave slides down the face of the wave as it

Waves Approaching ShoreWaves Approaching Shore

The crest of a spilling wave slides down the face of the wave as it

breaks on shore

Plunging waves break violently against the shore, leaving an air-filled

tube, or channel, between the crest and foot of the wave.

Plunging waves are formed when waves approach a shore over a

steeply sloped bottom


Surging waves occur on a very steep sloped bottom where the beach

slope exceeds wave steepness.

The wave does not really curl and break but runs up against the shore

while producing foam and large surges of water




Wave refraction - the slowing and bending of waves

in shallow water


in shallow water

Wave diffraction - propagation of a wave around an

obstacle

Wave reflection - occurs when waves “bounce back”

from an obstacle they encounter. Reflected waves


from an obstacle they encounter. Reflected waves

can cause interference with oncoming waves,

creating standing waves




Waves RefractionWaves Refraction

Bending of shallowBending of shallow--water wave water wave

fronts due to change in bottom fronts due to change in bottom

depthdepth

The leading edge of a wave front The leading edge of a wave front

enters shallower water and slows enters shallower water and slows

while the remaining front while the remaining front


while the remaining front while the remaining front

continues at higher speedcontinues at higher speed

The net result is a rotation of The net result is a rotation of

wave fronts toward being parallel wave fronts toward being parallel

with bottom depth contours. with bottom depth contours.




Waves RefractionWaves Refraction

Consequence of wave refraction:

Focusing of wave energy on


energy on headlands

Defocusing of wave energy on bays




Waves DiffractionWaves Diffraction


Propagation of wave around an obstaclePropagation of wave around an obstacle




Waves ReflectionWaves Reflection

Wave reflection - occurs when waves “bounce back” from an

obstacle they encounter. obstacle they encounter.

When approaching a steep solid object, waves are bounced

back, creating a confused sea or interfering waves

Sometimes part of the energy is absorbed and the remaining

energy is reflected

Reflected waves can cause interference with oncoming waves,


Reflected waves can cause interference with oncoming waves,

creating standing waves




Waves ReflectionWaves Reflection





Storm surge is the rise in sea level resulting from low Storm surge is the rise in sea level resulting from low

atmospheric pressure associated with storms and the atmospheric pressure associated with storms and the

Storm SurgeStorm Surge

atmospheric pressure associated with storms and the atmospheric pressure associated with storms and the

accumulation of water driven shoreward by the windsaccumulation of water driven shoreward by the winds

Water is deeper at the shore area, allowing waves to

progress farther inland

Storm surge is especially severe when superimposed

upon a high tide


upon a high tide




Standing WavesStanding Waves

Standing waves or seiches consist of a water surface Standing waves or seiches consist of a water surface

“seesawing” back and forth“seesawing” back and forth

A node is an imaginary line across the surface which experiences

no change in elevation as the standing wave oscillates. It is the

line about which the surface oscillates

Antinodes are where there is the maximum displacement of the

surface as it oscillates and are usually located at the edge of the

basin

Geometry of the basin controls the period of the standing wave


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 Resonance amplifies the displacement at the nodes and occurs when

the period of the basin is similar to the period of the force the period of the basin is similar to the period of the force

producing the standing waveproducing the standing wave




Internal WavesInternal Waves


Waves that occur at the boundaries of water layers

with different densities are called internal waves.




Internal waves form within the water column on the Internal waves form within the water column on the

pycnoclinepycnocline


pycnoclinepycnocline

Because of the small density difference between the water masses Because of the small density difference between the water masses

above and below the above and below the pycnoclinepycnocline, wave properties are different , wave properties are different

compared to surface wavescompared to surface waves

Internal waves display all the properties of surface progressive Internal waves display all the properties of surface progressive

waves including reflection, refraction, interference, breaking, etcwaves including reflection, refraction, interference, breaking, etc

Any disturbance to the Any disturbance to the pycnoclinepycnocline can generate internal waves, can generate internal waves,


Any disturbance to the Any disturbance to the pycnoclinepycnocline can generate internal waves, can generate internal waves,

including: flow of water related to the tides, flow of water masses including: flow of water related to the tides, flow of water masses

past each other, storms, or submarine landslidespast each other, storms, or submarine landslides






Thin Layers of Phytoplankton Oscillating with an Internal Wave Formed along the Continental Shelf




Tsunamis were previously called tidal waves, but are Tsunamis were previously called tidal waves, but are

unrelated to tidesunrelated to tides

TsunamiTsunami

unrelated to tidesunrelated to tides

Tsunamis consist of a series of long-period waves characterized by

very long wave length (up to 100 km) and high speed (up to 760

km/hr) in the deep ocean

Because of their large wave length, tsunamis are shallow-water to

intermediate-water waves as they travel across the ocean basin

They become a danger when reaching coastal areas where wave


They become a danger when reaching coastal areas where wave

height can reach 10 m

Tsunamis originate from earthquakes, volcanic explosions, or

submarine landslides




TsunamiTsunami





Longshore Current and Longshore Current and

Sediment TransportSediment Transport





Longshore Current and Longshore Current and

Sediment TransportSediment Transport


Along-Shore Sediment Transport Obstructed by Groins

dr. rer nat. wiwin windupranata · 2017. 8. 10. · hydrographic science and engineering working...

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