Coastal Hydrodynamic讲义s_复习 海岸动力学课件
海岸动力学英文PPT课件Coastal Hydrodynamics_5.1.
2/39
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.
海岸动力学英文PPT课件Coastal Hydrodynamics_复习
While the elevation of the water surface is
acoks x(t)
Substituting the velocity potential and the surface elevation into the K.F.S.B.C yields the dispersion relationship.
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§2.1 Description of Wave Motion 1. Classification of waves 2. Methods of describing fluid motion 3. Theories commonly used to describe
wave motion 4. Basic parameters of regular waves
H H0
1 c0 2n c
ks
3. Wave refraction
For straight coasts with parallel contours,
si n1si n2constsain n0 t
c1
c2
c0
HH0
1c0 2nc
b0 b
H0kskr
1
1
1
kr b b02cco o 0ss21 1 ssii2n 2n 04
2 gktankhh
gT2 2
L tanh h
2 L
c2gTtanh2Lh
A deep water wave is a wave whose wavelength is very small compared with the water depth.
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
Coastal Hydrodynamics_3.2 Ocean Wave Characteristics 海岸动力学课件
of the wave number vector must be balanced
by spatial changes of the wave angular
frequency.
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Chapter 3
If the wave field is constant in time, the wave
therefore concentrated.
Wave divergence （幅散） refers to a
phenomenon that waves refract and diverge
over the deep water so that the waves are
reduced in height.
wave motions but also provides the theoretical
basis for the experimental simulations
of water waves.
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Chapter 3
2. Wave transformation in shoaling water Assuming that the energy flux is conserved in the process of wave propagation, the wave height at a given water depth can be determined by:
In water with straight and parallel offshore contours, it is possible for us to determine the refraction coefficient（折射系数） kr directly.
海岸动力学课件 Coastal Hydrodynamics_6.1
“Bilingual Course”精品课程C t l H d d i Coastal HydrodynamicsHOHAI UNIVERSITYAifeng April 2013 / TAO AifengZHENGZHENG JinhaiJinhai/ TAOChapter 6 COASTAL PROCESSESCh t 6 COASTAL PROCESSESStating beach nomenclatureStating beach profileStating coastal change1/32In the treatment of coastal sediment transport, In the treatment of coastal sediment transport it is quite common to consider separately sediment movement perpendicular to the shoreline and that parallel to it. The sedimenth li d th t ll l t it Th di tp pmovement perpendicular to the shoreline is considered to be the more significant one for the short--term variation of coastal processes, th h t t i ti f t lthe shortpwhile that parallel to the shoreline is the more significant one for the longsignificant one for the long--term variation of the coast.2/3261General Beach Nomenclature §6.16.1 General Beach NomenclatureGeneral Beach Nomenclaturenearshore zoneoffshore zonei h f h backshorecoastline inshore foreshore backshorecliffbeachscarp3/32longshore bar longshore trough beach face berm crest bermsThe beach is an accumulation of unconsolidated The is an accumulation of unconsolidated sediment (sand, shingle, cobbles, and so forth) di h d f h l id extending shoreward from the mean low--tide extending shoreward from the mean lowline to some physiographic change such as ap y g p gsea cliff or dune field, or to the point where permanent vegetation is established. permanent vegetation is establishedWe require a more inclusive term, one that will encompass this underwater portion of the environment, since that is where the more environment,since that is where the more important processes occur which are responsible for the beach formation.i f f i4/32The term littoral is used to denote this entire Th t litt l i d t d t thi ti,environment, which extends across the beach and into the water to a depth at which the sediment is less actively transported by surface waves. This depth varies, of course, but is waves This depth varies of course but is generally considered to be some 10 to 20g ymeters. In the actual practice the term beach commonly is almost synonymous with the above definition of littoral zoneabove definition of littoral zone.5/32The littoral zone（沿岸带）is composed of four li l i f f portions: backshore, foreshore, inshore, and portions:backshore foreshore inshore and offshore.offshore.The nearshore zone extends seaward from the shoreline to just beyond the region in which the waves break, so that this term is particularly useful when discussing waves and currents within this environment.ithi thi i t6/32The comparatively flat Offshore（离岸区）: : The comparatively flat Off h Th ti l fl tp p gportion of the beach profile extending seaward from beyond the breaker zone to the edge of the continental shelf. This term is also used to refer to the water and waves seaward of the refer to the water and waves seaward of thegnearshore zone. The interesting feature in this region is the generation of sand ripples, which seem to have a strong influence on sediment movement.movement7/32Inshore（外滩）: : The zone of the beach profileThe zone of the beach profile:The zone of the beach profile extending seaward from the shoreline at mean low tide to just beyond the breaker zone.Th i h i i th l hThe inshore region is the place whereg pp distinguishable sediment movement appears, and where longshore bars are generated by breaking waves. In this region, breaking wave b ki I thi i b kip yaction predominates to intensify the turbulent intensity of fluid motion, thus putting a large amount of sediment in suspension.8/32A longshore bar（沿岸沙坝）is a ridge of sand A l h b i id f d running roughly parallel to the shoreline. It running roughly parallel to the shoreline.It may become exposed at low tide. At times there may be a series of such ridges parallel to one another but at different water depths.A longshore trough（槽）is elongatedA l h t h i l t d depression extending parallel to the shoreline depression extending parallel to the shoreline and any longshore bars that are present.9/32The sloping portion of the前滩Foreshore（前滩）: : The sloping portion of the beach profile lying between a berm crest (or in beach profile lying between a berm crest(or in,ppthe absence of a berm crest, the upper limit of wave swash at high tide) and the lower--water wave swash at high tide) and the lowermark of the backrush of the wave swash at low tide. In this region, either suspended movement or bed load movement is dominant depending or bed load movement is dominant, dependinggon the breaking wave characteristics.10/32The term foreshore is often nearly synonymouswith the beach face but is commonly more with the beach face but is commonly more,ginclusive, containing also some of the flatportion of the beach profile below the beachface. A beach face（滩面）is the slopingsection of the beach profile below the bermwhich is normally exposed to the action of the which is normally exposed to the action of the wave swash.11/32The zone of the beach Backshore（后滩）: : The zone of the beachprofile extending landward from the sloping foreshore to the point of development offoreshore to the point of development ofvegetation or change in the physiography(sea cliff, dune field, and so on).(sea cliff dune field and so on)A beach berm（滩肩）is a nearly horizontalportion of the beach formed by the deposition ti f th b h f d b th d iti of sediment by the receding waves.A beach scarp（滩坎）is an almost verticalp p y escarpment notched into the beach profile by wave erosion.The seaward limit of a berm is named aThe seaward limit of a berm is named a bermcrest（滩肩缘）.12/32Beach Profile6.2 Beach Profile§6.262Beach Profile1.Equilibrium beach profile1Equilibrium beach profile2. 2. Beach profile changesBeach profile changes2.Beach profile changes13/321.1. Equilibrium beach profileEquilibrium beach profile During the progress of the experiment inq pg p g pwhich a constant wave input is maintained, the beach profile will reach a steady statecondition, that is, the beach profile in theflume will approach a particular one,which is named the equilibrium beach profile which is named the equilibrium beach profile.（海滩平衡剖面）.14/32On natural beaches the changing waves give rise to an ever--varying equilibrium whichrise to an everp pthe beach profile attempts to achieve butseldom does. One of the more importantaspects of a beach is its dynamic personality: aspects of a beach is its dynamic personality: the loose granular sediments continuouslyrespond to the ever changing waves andrespond to the ever--changing waves andrespond to the evercurrents imposed from the adjacent body of the water. However, the only way in whichbeach profiles can be understood is in terms of this equilibrium profile and how it isdetermined by wave conditions and thedetermined by wave conditions and thesediments which compose the beach.15/32It is still debated whether in reality there is It i till d b t d h th i lit th i an equilibrium beach profile in the fieldan equilibrium beach profile in the field where the tide and waves are continuously changing. Nevertheless, the concept of equilibrium beach profile is quite useful in understanding processes of coastal changed t di f t l hand in investigating the mechanisms ofand in investigating the mechanisms of erosion and deposition in the coastal region. 16/32Beach profile changes2. Beach profile changes2.¾Typical beach profiles¾Experimental study17/32There are two typical types of beach profile: Th t t i l t f b h fil one is the longshore bar type（沙坝剖面）, one is the longshore bar typewhile the other is the step type（滩肩剖面）.p ypThese different beaches are also found in the field. The former is also called a winter beach （冬季剖面）or stormy beach（风暴剖面）, and the latter a summer beach（夏季剖面）, ordinary beach or swell beachordinary beach or swell beach（常浪剖面）. 18/32storm profile swell profilep p常浪剖面bar trough sea cliffbermThe storm beach profile with barsversus the swell profile with a pronouncedberm that occurs under swell waves conditions 19/32The summer profile is characterized by a wideberm, the flat shoreward portion of the profile,and a smooth offshore profile without barsexcept perhaps in relatively deep water.The winter profile has almost no berm, thesand having shifted offshore to form a seriesof bars parallel to the shoreline. The overallprofile slope is smaller in the winter profilethan in the summer one. The volume of sandinvolved remains relatively constant. Thesediment shifts from the berm to bar and back20/32 again.Chapter 6Profile changes along Scripps Pier, California, showing the tendency to shift from a more evenly sloping swell (summer)profile to a storm (winter) profile and back again accordingto the season.21/32Chapter 6This accounts for the terminology---- summerand winter profiles. Such shifts in the profilewas first observed off the west coast of theUnite States, where storm waves are typical ofthe winter and long-period swell waves occurin the summer. Therefore, the shifts in theprofile corresponded with the winter andsummer. However, it is peculiar that thisterminology is sometimes used elsewhere inthe world where the seasonal connotations arenot 22/32 correct.Chapter 6winter profile under swell waves conditions in front of Nanri Sea dikeThe onshore-offshore shift of sand associated withprofile changes from storm to swell conditions isgenerally correlated with the wave steepness andthe grain size of the beach sediment.Johnson classified the stormy beach and theordinary beach by wave steepness parameter indeep water, H0/L0. He determined that with a wave steepness greater than 0.03 an offshore baralways forms, whereas if the steepness is less than0.025 an offshore bar is never formed.23/32Chapter 6Dean presented a model for the shift from a storm to a swell profile based on a consideration of the trajectory of a suspended sand particle during its fall to the bottom, acted upon at the same time by the horizontal water particle velocity of the wave.critical24/32Chapter 6In fact, our understanding of the critical wavesteepness which governs the shift from theswell profile to the storm profile is stillincomplete.This incompleteness is particularly true forfield studies. This is also due in part to thegreat irregularity of profile changes on realbeaches.25/32Chapter 6The development of a storm versus a swell profilecan be understood in terms of the directions ofsediment transport within the surf zone andbeyond the breaker zone. With storm waves thesand seaward of the breaker zone movesshoreward, while sand in the surf zone istransported in an offshore direction. Thisconvergence of the sand transport directions mustresult in an accumulation of sand at the breakerposition, forming a bar. With flatter swell waves,the sand is moved landward at all depths, withinthe surf zone as well as beyond the breaker zone,so that it accumulates on the berm.26/32Chapter 6The beach profile type is of importance to seacliff and coastal property erosion. With a swellprofile the sea cliffs are protected from thewave action by a wide berm and so experiencelittle or no erosion. During storm conditionsthe sand is shifted offshore and the berm lost,so that the more intense swash is able to reachand erode the sea cliffs. In other years thestorms are separated by quieter periods, andthe beach berm may not be entirely eliminated.27/32Chapter 6The beach changes from swell to storm profileinvolve principally onshore-offshore shifts ofsediment. Therefore, the profile changescannot be understood until we comprehendthe details of this transport normal to theshoreline. However, a complete comprehensionas is required is still very remote, so that onlythe broadest understanding is presentlypossible.28/32Chapter 6It is well known that storm waves transport beachmaterial offshore causing beach erosion and material offshore, causing beach erosion andforming a bar. Waves of gentle steepness betweensuccessive storms gradually move bar formingmaterial onshore,resulting in beach accretion material onshore, resulting in beach accretion and creation of a berm.According to their laboratory investigations, According to their laboratory investigations, Sunamura and Horikawa classified beach profiles from a different point of view.fil f diff i f iThey proposed the following semiy p p g p They proposed the following semi--empirical criterion on whether a beach will erode or accrete. This criterion is a function of three accrete This criterion is a function of three parameters, i.e., wave steepness, sediment grain size and bottom slope.The value for C is 4~8 to demarcate erosionTh l f i48t d t iand accretion of laboratory beaches.and accretion of laboratory beachesWhen C>8, beach erodes and the bar type,yp profile occurs.While C<4, beach accretes and the step typeprofile forms.When 4<C<8, the equilibrium profile is found. It was also found that=18for natural beaches It was also found that C=18 for natural beaches. 31/32“Coastal Hydrodynamics”——chapter 6ZHENG ZHENG Jinhai Jinhai / TAO / TAO Aifeng Aifeng Apr 2013THANK YOU。
海岸动力学英文PPT课件Coastal Hydrodynamics_2.2
on z=η
x ,z ,t x c,zt
3/21
Chapter 2
§2.3 Small Amplitude Wave Theory
1. Linearization of basic equations 2. Solution of the linearized equations 3. Dynamic & kinetic characteristics
Coastal Hydrodynamics 海岸动力学
Chapter 2 WAVE THEORY
Stating description of wave motion Stating basic equations of wave motion Stating the small amplitude wave theory Stating the finite amplitude wave theory Stating wave theory limits of applicability
G.D.E. B.B.C. D.F.S.B.C. K.F.S.B.C. L.B.C.
2 0
hz, x
0
z
on z= -h
on t1 2[ x2 z2]p 0g z0 z=η
0
t xx z
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Assumptions Water is treated as a uniform and incompressible fluid.
The fluid viscosity is normally ignored.
The surface tension and Coriolis force are ignored.
海岸动力学英文PPT课件Coastal Hydrodynamics_6.1
11/32
Chapter 6
Backshore（后滩）: The zone of the beach
profile extending landward from the sloping
foreshore to the point of development of
vegetation or change in the physiography
which is named the equilibrium
Chapter 5
On natural beaches the changing waves give
rise to an ever-varying equilibrium which
respond to the ever-changing waves and
currents imposed from the adjacent body of
the water. However, the only way in which
beach profiles can be understood is in terms
breaking waves. In this region, breaking wave
action predominates to intensify the turbulent
intensity of fluid motion, thus putting a large
amount of sediment in suspension.
which a constant wave input is maintained,
the beach profile will reach a steady state
海岸动力学英文课件CoastalHydrodynam
The horizontal movement of water caused by tides, which can be either towards or away from the shore
Tidal streams
A narrow channel where strong Tidal currents meet, often resulting in turbulence and mixing
The study of coastal dynamics covers a wide range of topics, including wave dynamics, sedimentation transport, coastal erosion and retention, delta formation and evolution, island evolution, and the impact of human activities on coastal environments
The Physical Foundations of Coastal Dynamics
The vertical range of water level changes caused by the gravitational attraction of the moon and sun on the Earth's oceans
Description
01
A simplified model that considers only one spatial dimension, commonly representing the shoreline as a single point
海岸动力学英文PPT课件Coastal Hydrodynamics_2.2
on z=η
x ,z ,t x c,zt
3/21
Chapter 2
§2.3 Small Amplitude Wave Theory
1. Linearization of basic equations 2. Solution of the linearized equations 3. Dynamic & kinetic characteristics
the velocity potential be changed?
Chapter 2
Homework
A wave with the period of 5s travels in water of 5m, what is its celerity and what is its length?
A field of propagating waves consisting of many frequencies would separate due to the different celerities of the various frequency components.
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Chapter 2
G.D.E. B.B.C. D.F.S.B.C. K.F.S.B.C. L.B.C.
2 0
hz, x
0
z
on z= -h
on t1 2[ x2 z2]p 0g z0 z=η
0
t xx z
Coastal Hydrodynamics 海岸动力学
Chapter 2 WAVE THEORY
Stating description of wave motion Stating basic equations of wave motion Stating the small amplitude wave theory Stating the finite amplitude wave theory Stating wave theory limits of applicability
海岸动力学英文PPT课件Coastal Hydrodynamics_4.2
gradient directed offshore to counter 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
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.
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Chapter 4
At the breaking point, the maximum amount of wave set-down is
b
2 b
hb
16
The set-down is less than 5% of the breaking
depth because the breaking criterion equals
海岸动力学英文PPT课件Coastal Hydrodynamics_2.5 共40页
8 kT L sin4(hkh)
For finite height waves there is an additional term added onto the equation obtained in the linear wave theory.
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Chapter 2
The added term enhances the crest amplitude
and detracts from the trough amplitude, so
that the Stokes wave profile has steeper crests
separated by flatter troughs than does the
13/36
Chapter 2
Second-order solution Velocity components are
wHsinkh(zh)sink(xt)
T sinkhh)(
32H(H)sin2hk(zh)sin2(kxt)
4 T L sin4(hkh)
14/36
Chapter 2
15/36
Chapter 2
Comparison of bottom orbital velocity under Stokes wave with that of linear wave of the same height and length (H=4m, h=12m, T=12sec)
16/36
The relationship for the energy flux is
P T 10 Tdt 0 hp dudzE 1 2 c 1s2 ik2 n khh h Ecn
海岸动力学英文PPT课件Coastal Hydrodynamics_2.3
24/31
Chapter 2
The hydrostatic pressure exists without the presence of waves.
The dynamic pressure is a result of two contributions: the most obvious contributor is the surcharge of pressure due to the presence of the free surface displacement; the other is the vertical acceleration associated with the wave motion.
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Chapter 2
Water particle velocities in a progressive wave
23/31
Chapter 2
Pressure field
The pressure field associated with a progressive wave is determined from the unsteady Bernoulli equation.
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Chapter 2
Dispersion relationship
Substituting the velocity potential and the
surface elevation into the K.F.S.B.C yields
2 gktankhh
LgT2 tanh2h 2 L
cgTtanh2h 2 L
19/31
Chapter 2
In shallow water, the orbital semi-axes reduce
Coastal Hydrodynamics_4.1 NEARSHORE CURRENTS 海岸动力学课件
Since the end of the 1960’s, the application of
the radiation stress concept has been extended
to such as wave set-down, wave set-up, lonshore
currents, rip currents, and the nearshore
Chapter 4
It is seen that, under an oblique wave approach with both systems present, the current pattern becomes asymmetrical, with the zero velocity node just updrift from the rip current and a velocity increase extending from there to the next rip current.
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
Chapter 4
In 1941, Shepard 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 shoreward by wave action. The function of rip currents in carrying away fine suspended sediment particles from the surf zone to deeper water region seems to be important in the overall pattern of sediment movement in the nearshore area.