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Vermelding onderdeel organisatie
November 4, 2014
Wave-driven flow in topographically complex environments
Johan Reyns, Dano Roelvink (UNESCO-IHE)
Sander van der Pijl, Herman Kernkamp (Deltares)
1
Why?
3
Walsh et al., 2012
erosion/overwash/inundation
/ Swell Waves
TRADITIONAL SANDY BEACH
Why?
4
REEF-FRONTED BEACH
Wind Waves / Swell Waves Long waves
Reef flat Lagoon
Beach
erosion/overwash/inundation
Salinization
Why?
5
Image by Robert A. Rohde Knutsen et al, 2010 This is why
Why?
7
Long-period swell waves in equatorial zone (no cyclones)
- Generated by storms at mid to high latitudes in the band
of easterly trade winds
- Enter tropical regions with a
- dominant SE direction in the N hemisphere
- dominant NE direction in the S hemisphere
Why?
8
In a reef system, long wave energy is equally/more dominant than
wind/swell (=short) wave energy beyond the short wave breakpoint
Pomeroy et al., 2012
XBeach modeling concepts
Wave groups Bound and free long waves
Wave breaking and
surface rollers
Sediment transport and
bed level changes
cg
gh
Wave-flow motions time
scale:
25 s <T< 250 s
2D-wave action balance
yxc Ac A c AA D
t x y
( , , )( , , )
( , )
wS x yA x y
x y
A(
) A(
)
A(
)
Propagation is resolved for wave
action in each directional bin similar
to HISWA (Holthuijsen et al., 1989)
however retaining the non-
stationarity of the wave field to allow
for wave groups.
Wave breaking dissipation D
according to Roelvink 1993
X
Y
Flow modeling
sx bx xFu u uu v g
t x y h h x h
sy by yFv v vu v g
t x y h h y h
0hu hv
t x y
E Su u u
E Sv v v
GLM description (Walstra et
al., 2000)
xyxxx
xy yy
y
SSF
x y
S SF
x y
Wave forcing
( )
( )
2
2
11 cos
2
sin cos
11 sin
2
g
xx w
g
xy yx w
g
yy w
cS S d
c
cS S S d
c
cS S d
c
Radiation stresses
Bottom shear stress Pressure gradients Wave forcing
In practice…
- Set up a D-Flow FM* model, add a waveenergybnd
- All flow-related parameters go into the .mdu file
- Add a params.txt XBeach parameter file to the model folder
- Add the wave related parameters into params.txt
- Add additional wave bc files if necessary (eg spectrum file)
- Set wavemodelnr to 4, and run the model!
* D-Flow FM = hydrodynamic simulation engine of Delft3D Flexible Mesh
In practice…
In *.mdu file: … [waves] Wavemodelnr = 4 … [numerics] cstbnd = 1 … In *.ext file: … QUANTITY=waveenergybnd
In practice
nx = 317
ny = 3
xori = 0.
yori = 0.
alfa = 0.
depfile = boers.dep
vardx = 0
dx = 0.1
dy = 0.1
posdwn = 1
thetamin = -180.
thetamax = 180.
dtheta = 360.
CFL = 0.7
eps = 0.005
back = 0
left = 1
right = 1
tstart = 0
tintg = 1
tintm = 133
tintp = 1
tstop = 1800.
taper = 0
nt = 12000
rho = 1025
g = 9.81
tideloc = 0
zs0 = 0.
instat = 4 …………… and much much more!
thetamin = -180.
thetamax = 180.
dtheta = 360.
thetanaut = 0
instat = 4
bcfile = jonswap1.txt
rt = 1800.
dtbc = 0.5
fcutoff = 0.03
sprdthr = 0.01
hmin=0.005
break = 1
roller = 1
beta = 0.1
gamma = 0.43
gammax = 5.
alpha = 1.
delta = 0.0
n = 10.
nspr = 1
D-Flow FM XBeach
Directional grid
Wave parameters
To do…
- Validate the implementation more thoroughly by setting up a test bank (help needed!)
- Add wave-current interaction
- Standardize wave outputs for morphology module