13. Geometry : define flow area Au
0u
u u u
u upwind u
A uV
t x
A W h
h b
uW
How define bedlevel at u-point ?
ub
(Trick of Guus saves the day)
14. Bedlevel defined by cell center or by cell cornerub
max( , )u L Rb b b
ubupw
Xbeach, Sobek1D2D Delft3D, DFM
Tile Netnode
24. Cure : Higher order cell velocity reconstruction
Mart, Frank implicit reconstruction yet to implemented in DFM
Mohamed, explicit reconstruction already showed promising results,
both for improving horizontal eddy viscosity terms and advection
terms, but.. sometimes it fails
27. Cutcell: Approaching wall 1/3
Approaching wall not felt in cell 1 and 2
Sudden direction change in cell 3
Introduces advection losses
Approaching wall bij reduced flow area
Aligned cell center advection velocities
Smooth flow parallel to wall
1 2 3
28. Momentum conservation: Carnot losses
1 2 3
2 2
1 3 1 1 3 3 3 3
1 1 3 3
3 1 3 1 3
2 2 2
1 3
1 3
1 3
2
1 3
U U
U U
U U U
1
(U U )
2
U U
U U
2
1
(U )
2
Mom
Bern
Bern
Bern Mom
p A A p A A
A A
p p p
p
p
p p p U
Momentum 2-3 :
Bernoulli 2-3 :
Carnot loss 2-3 :
Reversed flow ; loss from 2 to 3 is equal to gain from 3 to 2
31. Flow from left to right, sudden contractions
Unphysical result, error in pressure assumption at position 2
better apply energy conservation in sudden contraction
36. 10 november 2015
DFM
Effect of the grid resolution for advection scheme D
(“momentum-conservative, 2nd order accurate”):
37. Mesoscale horizontal flow-field modelling at a channel-river-junction
Hydraulic Engineering · W2 · R. Patzwahl, F. Platzek, J.A. Jankowski · 6th november 2013Page
38. Mesoscale horizontal flow-field modelling at a channel-river-junction
Hydraulic Engineering · W2 · R. Patzwahl, F. Platzek, J.A. Jankowski · 6th november 2013
SCALE MODEL
4 km of river stretch = 67 m of model length
Length Scaling: 1:60
Height Scaling: 1:30
Stationary discharge conditions, non-movable gravel bed
Page
42. Subgrid: Analytic Conveyance approach
2
( )
( )
h(y)
C (y
R
)
U C Ri
Q AC R i K i
g
C
f
R
y
g
Uu
yU
u
j
iy
1iy
42
43. Spatial convergence of subgrid approach
,470
,475
,480
,485
,490
,495
,500
,505
,510
,515
0 10 20 30 40 50 60
standard
2D conv
Flooding
Discharge
Capacity
m3/s
Nr of cells in cross-sectional direction.
3, 6, 12, 24 or 48 cells
43
44. So far:
Tile depth approach in D3D morphology (Bedlevtype = 6)
Flat bed at u-point,
Level : max level of adjacent cells
Netnode depth approach in D3D Wave coupling (Bedlevtype = 3)
Sloping bed at u point
Level : max level of adjacent cells
Hydraulic radius R = A/P (Conveyance2D = 1)
No implementation of sloping bed at u-point in 3D yet
So: if 2D and 3D should match, use
(Bedlevtype = 3)
(Conveyance2D = -1)
in both models.
Warning: default advection is still not o.k. icw sloping bed on velocity point and
no bed friction.
46. Subgrid 2: non-linear volumes
1 1
1 1
1
0
p
p p p p
p p p p p
p p p p n
u u
out in
V
V V
V V A
V A V
A u A u
t
Thin water layer : Non – linear volume
Thick water layer : linear volume
46
59. Width of default scheme
Velocity points involved in limited higher order
( ) ( )
1
1 ( ) ( )
1
out
inL outL
u
in out
inR outR
u L R
in u Q u u
V
Q u u Q u u
V V V
Q u
59
68. Again geometry: Ks D3D style or Waqua style
12
18log
s
R
C
k
0
ln
g h
C
ez
‘gemiddeld tussen cirkel en breed kanaal’
Formule 13.15 in Vloeistofmechanica
WAQUA Style => Dykes can be lower
69. Spiral flow:
0
0,01
0,02
0,03
0,04
0,05
0,06
0,07
0,08
0,09
0,1
1 2 3 4 5 6 7 8 9 10 11 12
Spiral Intensity 1/s
Spiral…
Willem and Mohamed: Spiral Flow on unstructured net
Well under way: Influence on Morphology
Or: use 3D,
2, 3, 4, 5, 7,10,15,20 30 layers
0
5
10
15
20
25
0 5 10 15
cpu/cpu2D
cpu/cpu2D
Kmx = 2, cpu = 3*cpu2D
Kmx=30, cpu = 20*cpu2D
( Check weirs in 3D )
75. Grid convergence
Rooster Observatie DFM A DFM B DFM C DFM op
WAQUA rooster
Pannerdensekop 14.48 14.56 14.42 14.41 14.45
Nijmegen 12.30 12.47 12.33 12.33 12.34
Tiel 9.33 9.14 9.07 9.07 8.98
Zaltbommel 6.43 6.32 6.25 6.24 6.22
waterlevels
76. Computation times
DFM A DFM B DFM C DFM op
WAQUA
rooster
Aantal actieve
punten ()
22881 59331 187955 122328
Aantal
tijdstappen ()
8674 15161 35010 23826
Rekentijd (s) 228 959 8560 4243
Gemiddelde
tijdstap (s)
29.9 17.1 7.4 10.9
Tabel 3: Rekentijden voor 72 uur simulatie op Elitebook 8570w
77. Semi subgrid – tabellenboek, DFM A
Pannerdensekop +4 cm
Nijmegen +1 cm
Tiel +2 cm
Zaltbommel +2 cm
78. Discussion:
DFM makes it easier to refine some area and assess local modifications
DFM is still a lot slower than WAQUA , so how fine can the network be?
Can part of the network be 1D?
Does winterbed need same resolution as summerbed?
Spiral flow icw 2D or 3D instead? (Check subgrid weirs in 3D)
Trachytopen/Baptist/3D vegetation in winterbed ?
Bedform / roughness estimators in summerbed?
Hles? Settings for Regina’s problem? Higher order adv. in 3D problem!
Coupling to groundwater?
Non-linear volumes for dynamic high water simulation?
79. Is this true?
Summerbed friction is a certainty because of extensive land use
classification
== >
Winterbed is the only location where calibration is allowed.