海岸动力学英文PPT课件Coastal Hydrodynam(4)
海岸动力学英文PPT课件Coastal Hydrodynamics_复习
1. Statistical characteristics Zero-up crossing method Statistically representative waves
The significant wave (有效波高) corresponds to the average of the heights of the one-third highest waves.
Chapter 3 WAVE TRANSFORMATIONS
Stating ocean wave characteristics Stating transformations of waves entering shallow water
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§3.1 Ocean Wave Characteristics
§2.2 Basic Equations of Wave Motion 1. Assumptions 2. Governing equation 3. Boundary conditions 4. Discussion
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G.D.E.
2 0
h z, x
B.B.C.
Coastal Hydrodynamics
CONTENTS
Chapter1 Introduction Chapter2 Wave Theory Chapter3 Wave Transformations Chapter4 Nearshore Currents Chapter5 Coastal Sediment Chapter6 Coastal Processes
2 gktankhh
gT2 2
L tanh h
2 L
c2gTtanh2Lh
Coastal Hydrodynamics_3.1 WAVE TRANSFORMATIONS 海岸动力学课件
Statistically representative waves
➢ The maximum wave corresponds to the maximum height in a given wave group.
➢ The one-tenth highest wave corresponds to the average of the heights of the one-tenth highest waves.
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Chapter 3
Rayleigh distribution curve
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Chapter 3
From statistical theory H110 2.03H
we can obtain important H13 1.60H
relationships using the
distribution function Hrm s1.13H
a function of wave number. In fact, it has
been shown that the wave number and the
frequency are uniquely correlated.
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Chapter 3
If the amplitudes are plotted versus frequency,
There is a great amount of randomness in
the sea, and statistical techniques need to
be brought to bear.
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Chapter 3
Zero-up crossing method
海岸动力学课件 4.2
The pressure gradient of the sloping water
surface balances the change of the incoming
momentum. There is therefore a change in
mean water surface slope whenever there
3. Applications Radiation stress has been proved to be a very
powerful tool in the study of a variety of
oceanographic phenomena. In the context of
littoral processes, it has been used to predict
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Chapter 4
The radiation stress across the plane x=constant in the direction of wave advance is
The radiation stress of y-momentum across the plane y=constant
This was prompted by the agreement between
two seemingly independent estimates of the
change of wave momentum by breaking across
the shoreline.
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Chapter 4
The maximum value of wave set-up at the shoreline is
海岸动力学英文PPT课件Coastal Hydrodynamics_5.1.
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Chapter 5
1. Physical properties
Beach materials mainly consist of the sand and gravel transported by rivers, the sand composing dunes located in the
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§5.1 Characteristics of Coastal Sediment 1. Physical properties of coastal sediment 2. Modes of coastal sediment movement 3. Threshold of coastal sediment motion
influence of waves and nearshore currents in the
onshore or offshore directions, or parallel to the
shoreline. There are two modes of sediment
movement: suspended sediment movement and
and littoral drift, are distribution of grain size,
shape, roundness, mineral composition,
porosity, permeability, etc. Among them, grain
size distribution and mineral composition are
bed load movement.
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Chapter 5
Incoming waves reach a certain water depth (offshore region), then bed material sand particles there begin oscillatory motion due to wave action. In a slightly more shallow area, waves produce a net motion of sand particles in the onshore or offshore direction. The interesting feature in this region is the generation of sand ripples, which seem to have a strong influence on sediment movement.
海岸动力学课件 4.1
“Bilingual Course”精品课程Coastal Hydrodynamics C t l H d d iHOHAI UNIVERSITYAifeng March 2013 / TAO AifengZHENGZHENG JinhaiJinhai/ TAOChapter 3 WA VE TRANSFORMATIONS Stating ocean wave characteristicsStating transformations of wavesStating transformations of wavesentering shallow waterChapter 4 NEARSHORE CURRENTS Ch 4Stating types of currentsradiation stress(辐射应力) Stating concept of radiation stressStating concept ofwave set--up(波浪增水) Stating phenomena of wave setStating phenomena ofwave set--down (波浪减水)andand wave setlongshoreStating characteristics ofStating characteristics of longshorecurrents (沿岸流)currentsOutline of Currents4.1 Outline of Currents41O tli f C t §4.11.Ocean currents2. 2. Tidal currentsTidal currentsNearshore currents 3. 3. Nearshore currents3Nearshore currentsOcean currents1. Ocean currents1.In the ocean, there exit currents of almost constant direction and speed through the year. constant direction and speed through the year Ocean currents are mainly generated by windand gradientdrift currents andgradient and are classified as drift currentsand are classified as, or density currents and compensationcompensation currentsor density currents andcurrents, or density currents andcurrents according to generation mechanism. They are also classified aswarm or cold currents They are also classified as warm or cold currents depending on whether their temperatures ared di h th th i t thigher or lower than those of thegneighboring ocean region.Tidal currents2.2. Tidal currentsTidal currents are induced by the horizontalmovement of the sea water together with tidal movement of the sea water together with tidalmotion. The motion of tidal currents has periodswhich correspond to their tidal constituents.hi h d t th i tid l tit tTidal currents occasionally play an importanty p y prole in the nearshore region. They are easilyinfluenced by the sea bottom and coastal influenced by the sea bottom and coastaltopography, thus they have strongly localizedcharacteristics. Hence it is rather difficult toestablish a clear relationship between tides establish a clear relationship between tidesand tidal currents in general.Nearshore currents3. Nearshore currents3.The nearshore current consists of the mass transport induced by wave action, the longshore current and rip currents.There are two wave current and rip currents.There are two wave--wave induced current systems in the nearshore zone. These are:ll i l ti t f i t d ¾ a cell circulation system of rip currents and associated longshore currents,associated longshore currents,¾longshore currents produced by an oblique wave approach to the shoreline.p,g gThe slow mass transport, the feeding longshore currents, and the rip currents taken together form a cell circulation system in the nearshore zone.zoneIt is well known that whenIt is well known that whenwaves approach a straightcoastline at an oblique angle, a longshore current is established l h t i t bli h dow g p e o e co s e flowing parallel to the coastlinein the nearshore zone.It is seen that under anIt is seen that, under an oblique wave approach withboth systems present, the current pattern becomest tt by, asymmetrical, with the zeroupdrift velocity node justvelocity node just updrift from the rip current and a f th i t dy g velocity increase extendingfrom there to the next rip current.The cell circulation is important in renewing thenearshore zone and removing water in thewater in the nearshorepollutions such as mud and sewage that may be dumped there.d d thThe current is particularly significant The longshorelongshore current is particularly significant Thein that it is responsible for the net transport of in that it is responsible for the net transport of sand or other beach material along the shore. sand or other beach material along the shore.Fishermen and others living near the coasthave been aware of these currents for severalyears through their experiences in nearshorewater.waterJohnson considered the longshore current andundertow as wave--induced currents in his undertow as waveclassic treatise. He attempted to treat coastal l i i H d l sediment movement and coastal processes by sediment movement and coastal processes by regarding these currents as the media of sediment transport.In 1941, Shepard et al. published a paper entitled In1941Shepard et al published a paper entitled “Rip Currents”, in which they defined rip currents as currents in the offshoreward direction which return the sea water transported di ti hi h t th t t t dyshoreward by wave action.The function of rip currents in carrying away fine suspended sediment particles from the surf zoned d di t ti l f th fp g pto deeper water region seems to be important in the overall pattern of sediment movement in the nearshore area.The rip current is the dark patch. There is intense wave breaking on both sides of the rip currents with little breaking within the deeper rip channel, where bubbles are advected seaward.In 1949 Putnam, Munk and Traylor proposedformulae to evaluate the mean velocity oflongshore currents. Their results encouraged l h t Th i lt dresearchers to undertake further studies to researchers to undertake further studies to clarify the longshore sediment transport clarify the longshore sediment transportec a s a d to est ate t e o gs o e mechanism and to estimate the longshore ptransport rate.In 1962, LonguetLonguet--Higgins and Stewart presented In 1962,In1962Longuet Higgins and Stewart presented the concept of radiation stress and applied it to analyze various water wave problems such as current and wave--wave interactions. wave--current and wavewaveSince the end of the 1960’s, the application ofSi th d f th1960’th li ti f the radiation stress concept has been extended the radiation stress concept has been extendeddown, wave set--up,lonshoreup, lonshore to such as wave set--down, wave setto such as wave setnearshore currents, rip currents, and thecurrents, rip currents, and the nearshore current system.Radiation Stress §4.24.2 Radiation Stress1.Definitionxpressions2. Expressions2. E3. Applicationspplications3. ApplicationsA3Applications1. DefinitionDefinition1.There is a stress field in water waves, which is similar to the Reynolds stress in turbulence. similar to the Reynolds stress in turbulence This force is usually called momentum flux, since it is resulted from the exchange of momentum among the water particles.among the water particlesRadiation stress is defined as the excess momentum flux induced by the existence f ti It l th diffof wave motion. It equals the difference between the total momentum fluxes and the hydrostatic pressure in the absence of waves.pThe radiation stress across the plane x=constant in the direction of wave advance isThe radiation stress of y-momentum across the l plane y=constantThe transverse radiation stress in the direction The transverse radiation stress in the direction of waves isradiation stresses on unit water columnExpressions2.2. ExpressionsIf the x-axis is placed in the direction of wave advance and the y-axis parallel to the wave advance and the axis parallel to the wave crests, then there are two nonzero components to the radiation stress: the x-and y-fluxes of x-momentum and y-momentum.momentum and momentumIn the more general case, when a linear wave is In the more general case when a linear wave is p p g g gpropagating at some angleθto the direction of wave propagation, we haveR di ti t h b d t b 3. 3. ApplicationsApplications Radiation stress has been proved to be a very powerful tool in the study of a variety of p y yoceanographic phenomena. In the context of littoral processes, it has been used to predict (set changes in the mean water level (set--up and changes in the mean water level (set up and set set--down) in the nearshore region and to analyze the generation of longshore currents.Other applications have been to the Other applications have been to thegeneration of surf beat, the interaction of waves with steady currents.“Coastal Hydrodynamics”——chapter 4ZHENG ZHENG Jinhai JinhaiMarch 2013THANK YOU。
海岸动力学英文PPT课件Coastal Hydrodynamics_6.2共42页文档
When Qin is equal to Qout, which indicates that there is neither erosion nor deposition within the compartment, therefore the coast is stable. The lack of either beach erosion or deposition indicates that a state of equilibrium exists between the sources and losses.
Chapter 6
Subsequently, to prevent harbor shoaling, the breakwater was extended seaward and a suction dredge installed to pump sand past the harbor. It is seen that the work done in bypassing the harbor by dredging has replaced the natural transport system due to wave action.
Bay is an excellent example of the way in which
local beaches orient themselves parallel to the
refracted wave crests and develop the same
curvature.
Chapter 6
configuration in an attempt to reach a new
2019年-海岸动力学英文PPT课件Coastal Hydrodynamics_2.2-PPT文档资料-PPT精选文档
Chapter 2
Homework
A wave with the period of 5s travels in water of 5m, what is its celerity and what is its length?
2 gktankhh
LgT2 tanh2h 2 L
cgTtanh2h 2 L
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Chapter 2
Dispersion relationship
This relationship shows that the wave length continually decreases with decreasing depth for a constant wave period. That is to say, waves of constant period slow down as they enter shallow water.
The bottom is impermeable. Waves travel in the x-z plane.
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continuity equation
velocity potential
gravity only
zero velocity
Chapter 2
Boundary Value Problem of Wave Motion
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Chapter 2
2. Solution
Coordinates System
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Chapter 2
How to obtain the solution ? L.B.C G.D.E B.B.C
海岸动力学英文PPT课件Coastal Hydrodynamics_3.3
5. Wave diffraction 6. Wave breaking
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Chapter 3
1. Conervation of wave equation can be
high steepness values. In spilling breakers the
wave gradually peaks until the crest becomes
unstable and cascades down as “white water”
(bubbles and foam).
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Chapter 3
Limiting wave steepness
For any given water depth and wave period, there is an upper limit to the wave height at which the wave becomes unstable and breaks. The limiting steepness （极限波陡） is
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Chapter 3
Numerical Modeling of Surging Breaker
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Chapter 3
7. Case studies
Damage of Langtongmen Breakwater Caused by No.9119 Typhoon
Three-dimensional Experimental Study on Wave Characteristics in Front of Concave Breakwater
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SxxEnco2s1 22n1
SyyEnsi2n1 22n1
SxySyxEn2sin2
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Chapter 4
3. Applications
Radiation stress has been proved to be a very
powerful tool in the study of a variety of
there will be a shoreward flux of momentum.
This momentum flux entering the nearshore
zone with the incoming waves cannot simply
disappear but rather must be balanced by
oceanographic phenomena. In the context of
littoral processes, it has been used to predict
changes in the mean water level (set-up and
set-down) in the nearshore region and to
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Chapter 4
§4.3 Wave Set-down and Wave Set-up 1. Wave set-down 2. Wave set-up
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Chapter 4
If one considers waves arriving at the beach
with their crests parallel to the shoreline,
2 0
0 w2
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Chapter 4
Radiation stress is defined as the excess momentum flux induced by the existence of wave motion. It equals the difference between the total momentum fluxes and the hydrostatic pressure in the absence of waves.
opposing forces which will dissipate the
momentum.
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Chapter 4
Consider a train of waves encountering the coast with normal incidence. For a short distance dx, a force balance can be developed.
ddxSxxghddx
The pressure gradient of the sloping water
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Chapter 4
The radiation stress across the plane x=constant in the direction of wave advance is
Sxx hpzu2dz 0 hp 0dz
The radiation stress of y-momentum across the
analyze the generation of longshore currents.
Other applications have been to the
generation of surf beat, the interaction of
waves with steady currents.
Stating characteristics of longshore currents
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§4.2 Radiation Stress 1. Definition
2. Expressions
3. Applications
2/33
Chapter 4
1. Definition There is a stress field in water waves, which is similar to the Reynolds stress in turbulence. This force is usually called momentum flux, since it is resulted from the exchange of momentum among the water particles.
plane y=constant
Syy hp zv2dz 0 hp 0dz
The transverse radiation stress in the direction
of waves is
SxySyx
uvdz
h
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Chapter 4
2. Expressions If the x-axis is placed in the direction of wave advance and the y-axis parallel to the wave crests, then there are two nonzero components to the radiation stress: the x- and y- fluxes of x-momentum and y-momentum.
Sxx
E2n 1 2
Syy
En
1 2
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Chapter 4
In the more general case, when a linear wave is
propagating at some angle α to the x-axis, the
radiation stress can be expressed as
Coastal Hydrodynamics
Chapter 4 NEARSHORE CURRENTS
Stating types of currents Stating concept of radiation stress
Stating phenomena of wave set-up and wave set-down