MIKE波浪泥沙模拟教程2

Current:

Profiles

extend

over

entire

depthcUNon

cohesive

sediment

traportw

ves

ancurrentsWaves:

Outer

orbital

motion

~

Potential

flowTurbulence

and

sediment

restricted

tothin

wave

boundary

layercUCombined

waves

and

currentIncreased

eddy

vicositIncreased

flow

resistay

near

the

bed

rnce.

Apparent

wetards

the

flow.ave

roughness:UIn

the

surf

zone:Wave

breaking

produces

turbulence,

suspended

sediment

over

theentire

water

depthWave

boundary

layerSurf

zone

turbulenceTurbulence

in

spilling

breaker

highenergy

dissipation

andproduction

of

turbulence:Production

at

RollerDownward

diffusionDissipationResult:

much

higher

turbulence

level

in

the

water

columnTurbulence

and

sedimentexchange

factor:Non-breaking

waves:high

near

the

bedBreaking

waves:High

nearthe

bed

and

awayfrom

the

bed:

’Bottle

neck’Sediment

concentration

profilesWaves

only:Very

close

to

the

bed

~

cmWaves

and

current:higher

into

the

water

columnWith

breaking

waves:over

entire

water

columnDrift:

Two

way

of

describing

drift,

same

phenomenon1.

Eulerian,

look

at

a

pointBelow

trough

level:Water

motion

back

and

forth-

Result:

no

mean

motionDrift:

Two

way

of

describing

drift,

same

phenomenon1.

Eulerian,

look

at

a

pointBetween

crest

and

trough:Forward:

waterBackward:

no

water-

Result

forward

velocityDrift:

Two

way

of

describing

drift,

same

phenomenon1.

Lagrangian,

look

at

a

water

particle,

elliptical

pathBelow

crest:Forward

motion,

follows

the

wave,

longerdurationBelow

trough:Backward

motion,

against

the

wave,shorter

durationUnder

crest:

particle

high,

larger

forwardvelocityUnder

trough:particle

low,

smallerbackward

velocity-

Result:

mean

forward

motionInside

a

waveDeep

waterShallow

waterEulerian

or

Lagrangian

drift,

same

discharge,But

flow

towards

the

coast

iszero:

offshore

directed

returncurrentDoes

drift

affect

suspended

sediment-??Yes,

the

concentration

profile

is

stretched

under

the

crest,and

the

sediment

travels

with/against

the

waveRequires

higher

order

representation

of

velocity

fieldl

m

me

t

mStreaming

–

m

m

m

tr

s

erVertical

flux

f

ho

izcf.

Reynolds

s

r

s:Pure

wave

motion

without

loss:So:

:

no

Shear

stressBut

the

wave

boundary

layer

is

causing

a

deficit

discharge,D,

which

varies

along

the

wave

and

induces

an

additionalverticalvelocity,

W0But

the

wave

boundary

layer

is

causing

a

deficit

discharge,D,

which

varies

along

the

wave

and

induces

an

additionalverticalvelocity,

W0W0

is

in

phase

with

u,

so

,

thiscauses

a

shear

stress,

and

drives

a

meanflow

in

the

direction

of

wave

propagationSeveral

other

mechanisms.

E.g.

nonlinearity:high

forward

velocity

for

a

shortdurationlower

backward

velocity

for

a

longer

timeResult:

mean

shear

stress

and

mean

flow

–

butonly

for

turbulent

boundary

layers!Shear

stress

and

flow

in

the

surf

zone

For

non

breaking

waves:

energydissipation

in

the

wave

boundary

layer,shearstresses

only

induced

near

the

bed

In

the

surf

zone

energy

is

dissipated

inparticular

near

the

surface,

shear

stressesare

induced

over

the

entire

water

columnSpilling

breaker/broken

wave:The

surface

rolle

is

a

body

ofwater

that

move

forward

withthe

wave

front,

velocity

cIn

many

ways

the

dynamicsare

similar

to

aSurfer:Force

balance

for

the

surfer,

the

weight

W

is

balancedby

the

normal

force

N

(pressure)

and

the

tangentialforce

S

(shear

stress).The

surfer

thusexertsthe

forces

N

and

S

on

the

water

in

thewave

below.The

velocity

difference

between

the

surferand

the

water

islarge,

equal

to

c.

Thetangential

force

S

is

associated

with

theshear

stress

in

the

boundary

layer

beneath

the

board.Energy

dissipation:

Force

x

Velocity

=

S

x

cSurface

shear

stress:

Tangential

force/area:Ef

=

Wave

energy

fluxD

=

energy

dissipationrate

per

bed

areaDEnergy

balance:

gradientinenergy

fluxcorresponds

to

dissipationSet-up

–

set

downuniform

coastSurface

shear

stress

determined

by

energy

dissipationshear

stress

distribution

linear,

modified

by

the

slope

ofthe

mean

surface.Condition:

cross-shore

discharge:zero.Undertow:Surface:

onshore

directedNear

bed:

offshore

directedSuspended

sedimentconcentrated

near

the

bed:Offshore

directed

transportOutside

the

surf

zone:Weak

transport

often