What process is simulated by these moving dots ? a)- Diffusion b)- Dispersion c)- Advection d)- Free...
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Transcript of What process is simulated by these moving dots ? a)- Diffusion b)- Dispersion c)- Advection d)- Free...
What process is simulatedby these moving dots ?
a) - Diffusion b) - Dispersion c) - Advection d) - Free convectione) - Something elsef) - This is NO groundwater flow
Groundwater Flow/Transport Model
??
Groundwater Flow/Transport Model
The same model, now showing the
tracks followed by the moving dots
a) - Diffusion b) - Dispersion c) - Advection d) - Free convectione) - Something elsef) - This is NO groundwater flow
??
Groundwater Flow/Transport Model
Advection
2D projections of 3D streamlines
The model simulates 3D groundwater flow in a layered anisotropic aquifer
Complex Groundwater Whirl
Systems Kick Hemker & Mark Bakker
Groundwater flow in layered anisotropic aquifers
Introduction• Flow in layered aquifers • Anisotropy • Solution techniques
Some Numerical results• Parallel flow models• Well flow model
Analytical models • Solution for Well flow
• Parallel flow in heterogeneous
systems• Patterns of connected whirls• Complex whirl systems
Conclusions
Flow in confined layered aquifers
Parallel flow
Well flow well discharge
layer 1
layer n r
layer 1
layer n
0 x
y
z
high head
low head
Flow in anisotropic aquifers
Anisotropy of the hydraulic conductivity
K1
K2
K3
h Kv
z
y
x
v
v
v
v
z
h
y
hx
h
h
zzzyzx
yzyyyx
xzxyxx
KKK
KKK
KKK
K
K1
K2
y
h
v
Analytical and Numerical solutions
Numerical solution:• Finite element method• Finite difference method
MicroFEM software: ĥ = f (i,x,y)• horizontal flow -> triangular finite elements• vertical flow components -> finite differences
Analytical solutions: Fully 3-dimensional: h = f (x, y, z) Multilayer approximation: h = f (i, x,
y) Dupuit approximation: h = f (x, y)
layer i
layer 1
layer n
Finite element model + parallel
flowSimple two-layer model- a box-shaped confined aquifer- homogeneous isotropic- no-flow west and east sides- steady-state flow to the north
Simple two-layer model- a box-shaped confined aquifer- homogeneous isotropic- no-flow west and east sides- steady-state flow to the north
- long anisotropic block - two homogeneous layers - different horizontal anisotropies
Finite element model + parallel
flow
published
in
Ground
Wat
er
(mar
ch 2
004)
Finite-element gridof 2470 nodes and4800 elements
Model built with MicroFEM
Results:- five spiralling streamlines- rotating counter-clockwise
- one axis in the general flow direction,
at the layer interface
Groundwater Whirla bundle of spiral-shaped streamlines
rotating clockwise or counter-clockwise
- a confined aquifer with 20
sublayers
- no-flow west and east sides
- steady-state flow to the north
- isotropic layers K = 1 m/day - anisotropic block 10 by 10 m
Kmax = 1 m/day
Kmin = 0.1 m/day
30 m30 m
20 m
10
Finite element model + parallel
flow
Results:- 3 groundwater whirls- 3 axes in the general flow direction, at the layer interfaces- adjacent whirls rotate in opposite directions
• Layered aquifer
• Different anisotropiesWhirls
Well flow in a two-layer aquiferwith cross-wise anisotropy
Aquifer:- a single confined aquifer- two homogeneous hor.-anisotropic layers- cross-wise anisotropy
Well:- fully penetrating
Flow- steady state
Computation:- finite elements (MicroFEM)
T1 = 10 T2 = 1 m2/d
T1 = 10 T2 = 1 m2/d
Q
N
Schematic representation of four whirls induced by flow to a well
in a two-layer aquifer
Analytical solution using Dupuit
- a single (semi)confined aquifer- m homogeneous layers- anisotropic transmissivity in each layer
layer 1 layer
2
layer 3 laye
r 4
x
y
layer i
layer m
aquifer
z
Dupuit approximation: h = f (x, y)
- fully confined aquifer- two homogeneous layers top layer = isotropic
base layer = anisotropic
- fully penetrating well- steady-state flow
Example of two-layer well flowcomparison analytical
numerical
12 m
eter
12 m
eter
1
2
T1 =120 T2 =24 m2/d = -30
T1 =120 T2 =120 m2/d
Q
1
2
3
4
5
6
Streamlines to a well in a two-layer aquiferBakker & Hemker, Adv. Water Res. 25 (2002)
Streamlines to a well in a two-layer aquiferNumerical results using MicroFEM
- a confined aquifer with 20
sublayers
- no-flow west and east sides
- steady-state flow to the north
- isotropic layers K = 1 m/day - anisotropic block 10 by 10 m
Kmax = 1 m/day
Kmin = 0.1 m/day
30 m30 m
20 m
10
Analytic model + parallel flow
Streamlines starting at depths of -8 and -12 m
Streamlines starting at depths of -7, -8 and -9
m
Streamlines starting at depths of -8 and -12 m
Streamlines starting at depths of -7, -8 and -9
m
20 Streamlines and their projections
20 25 30 35 40 45 5020
10
0
x (m)
depth
(m
)
Projected streamlines
Stream function contours
Ψ = stream function
Ψ = 0 m2/d at model boundary and whirl
interfaces
max = 0.0015 m2/day at upper and lower whirl
axis
min = -0.0091 m2/day at central axis
Conclusions:- numerical and analytical results are very similar- analytical models are easier to build- whirls are best visualized as stream function contour plots
Patterns of connected whirls
50 100 150 200 250-18
-12
-6
0 o
o
50 100 150 200 250-18
-12
-6
0
Two whirls rotating counter-clockwise X saddle point
Two whirls rotating in opposite directions o----o whirl interface
Patterns of connected whirls
50 100 150 200 250-18
-12
-6
0
c
o o
50 100 150 200 250-18
-12
-6
0
Two whirls rotating in opposite directions o----o whirl interface
Two whirls rotating in opposite directions X saddle point
- a layered confined aquifer
- no-flow west and east sides
- steady-state flow to the north
- long anisotropic block - with many homogeneous cells in
the general flow direction- cells have varying anisotropies
100 m100 m
18 m
100 m
More complex analytic model
9065551358575105951251154590
9095457511513565125105855590
9012545105758511555951356590
9045955575105851156512513590
9011510512585455513565957590
9013510565459575115855512590
9055451358575951151056512590
9045105851159513575125556590
9045135659511510555758512590
A heterogeneous block of 9 layers 10 strips
90 cells with differenthorizontal anisotropies
Conductivities of all cells
K1 = 10 m/day
K2 = 5 m/day
Kz = 1 m/day
All principal directions randomly distributed between northeast (45°) and northwest (135°) within each layer
K2 K1
α
N
Kz
EW
50 100 150 200 250-3
-2
-1
0
1
2
3x 10
-3 Heads in all layers
layer 1layer 2layer 3layer 4layer 5layer 6layer 7layer 8layer 9
50 100 150 200 250-3
-2
-1
0
1
2
3x 10
-3 Vx (m/d) in all layers
layer 1layer 2layer 3layer 4layer 5layer 6layer 7layer 8layer 9
Cross-section with hydraulic heads in 9 layers
west east
west east
Cross-section with lateral flux in 9 layers
50 100 150 200 250-18
-16
-14
-12
-10
-8
-6
-4
-2
0
50 100 150 200 250-18
-16
-14
-12
-10
-8
-6
-4
-2
0
Stream function contours
Cross-section showing 9 * 20 streamlines
16 + 18 whirl axes ( and )28 saddle points (x) and 10 boundary points ( )
Clockwise and counter-clockwise whirl systems50 100 150 200 250
-18
-16
-14
-12
-10
-8
-6
-4
-2
0
50 100 150 200 250-18
-12
-6
0
Conclusions
1 - Simple finite element experiments
layered aquifer varying anisotropies
2 - Analytical models confirm numerical results complete view of whirl patterns easier tool for the study of whirls
3 - Heterogeneous analytical models spatially varying cell anisotropies → complex whirl patterns
whirls
Consequences of whirls
a - Increased lateral and vertical
exchange of groundwater
between layers (beds)
b - Increased contaminant spreading
within aquifers ( ‘dispersion’ )
? - Can transport models do without
layering and anisotropy ?
0 100 200 300 400 500 600 700 800 900 1000-100
-90
-80
-70
-60
-50
-40
-30
-20
-10
0Streamlines with times
Analytical model of 50 by 100 cells: stream function contours, 5000 streamlines
Groundwater flow in layered
anisotropic aquifers
Parallel Flow
Radial Flow
Numericalsolution
MicroFEM Hemker, v.d.Berg & Bakker:
2001-2004 Ground Water
Analyticalsolution
Dupuit approx.
Bakker & Hemker:
2002-2002 Adv.Water Res.
Multi-layer approx.
1 strip
Bakker & Hemker:
2004-2004
Adv.Water Res.
Meesters, Hemker &
v.d.Berg 2003-2004
J.Hydrology
n strips
Hemker, v.d.Berg & Bakker:
(in preparation)
For a complete list of publications on groundwater whirls see:
http://www.microfem.com/download/gwwhirl-papers/