Hydrus-2D Tutorial - PC

Computer Session 7a
Subsurface Line Source - Fumigant
The example in this computer session represents a modified Subsurface Line Source
example (tutorial 2 of HYDRUS (2D/3D)). It also considers a subsurface line source
(e.g., similar as for drip irrigation) in a vertical cross-section. The example considers
instead of water and nutrient pulse a short pulse of fumigant. The (x, z) transport domain
is again 75 x 100 cm2, with the source located 20 cm below the soil surface on the left
boundary of the transport domain. The short duration (0.01d) pulse of fumigant is applied
with infiltrating water (a radius of a dripper, r=1 cm; a circumference of a dripper;
O=2πr=2*3.1415*0.01 m=0.06283 m; infiltration flux, Q=Oq= 0.06283 m*0.60 m/d=
0.0377 m2/d). Unit (dimensionless) concentration is applied at the dripper. An
unstructured finite element mesh is generated using the Meshgen program. The example
is divided into four parts, evaluating effects of various surface boundary conditions
(resistances). This example will familiarize users with the basic concepts of transport
domain design in the graphical environment of HYDRUS, with boundaries and domain
discretization, and with the graphical display of results using contour and spectral maps.
Instructions are similar as for Tutorial 2. Different parts are emphasized in bold (and
highlighted). This example can be either carried out independently of Tutorial 2, or the
Tutorial 2 project can be modified as needed.
(0, 100)
(75, 100)
(0, 80)
(0, 0)
(75, 0)
Computer Session 7a
A. Injection of Fumigant From a Subsurface Source
(infinite resistance at the soil surface)
Project Manager (File->Project Manager)
Button "New"
New Project (or File->New Project)
Name: Fumig1
Description: Application of fumigant from a Subsurface Source (infinite
resistance at the soil surface)
Working Directory: Temporary – is deleted after closing the project
Button "Next"
Geometry Information (Edit->Domain Geometry->Geometry Information)
Type of Geometry: 2D Vertical Plane
Domain Definition: General
Units: cm
Initial Workspace: Xmin=-25 cm, Xmax=100 cm, Zmin=-25 cm, Zmax=125 cm
(to accommodate the transport domain)
Button "Next"
Main Processes (Edit->Flow and Transport Parameters->Main Processes)
Check Box: Water Flow
Check Box: Solute Transport
Button "Next"
Time Information (Edit->Flow and Transport Parameters->Time Information)
Time Units: days
Final Time: 7
Initial Time Step:
0.0001
Minimum Time Step: 0.000001
Maximum Time Step: 5
Time Variable BC:
Check
Number of Time-Variable BC: 2
Button "Next"
Output Information (Edit->Flow and Transport Parameters->Output Information)
Print Options:
Check T-Level Information
Check Screen Output
Check Press Enter at the End
Print Times: Count: 14
Print Times: 0.1, 0.25, 0.5, 0.75, 1, 1.5, 2, 3.5, 3.6, 3.75, 4, 4.5, 5.5, 7 d
Update
Button "Next"
Computer Session 7a
Water Flow - Iteration Criteria (Edit->Flow and Transport Parameters->Water Flow
Parameters->Output Information)
Leave default values as follows:
Maximum Number of Iterations: 10
Water Content Tolerance: 0.001
Pressure Head Tolerance: 1
Lower Optimal Iteration Range: 3
Upper Optimal Iteration Range: 7
Lower Time Step Multiplication Factor: 1.3
Upper Time Step Multiplication Factor: 0.7
Lower Limit of the Tension Interval: 0.0001
Upper Limit of the Tension Interval: 10000
Initial Condition: In the Pressure Head
Button "Next"
Water Flow - Soil Hydraulic Model (Edit->Flow and Transport Parameters->Water
Flow Parameters ->Soil Hydraulic Model)
Leave default values as follows:
Radio button - van Genuchten-Mualem
Radio button - No hysteresis
Button "Next"
Water Flow - Soil Hydraulic Parameters (Edit->Flow and Transport Parameters>Water Flow Parameters ->Soil Hydraulic Parameters)
Leave default values for loam
Button "Next"
Solute Transport – General Info (Edit->Flow and Transport Parameters->Solute
Transport Parameters->General Information)
Leave default values
Button "Next"
Solute Transport - Solute Transport Parameters (Edit->Flow and Transport
Parameters->Solute Transport Parameters->Solute Transport Parameters)
Leave the default values
Bulk Density = 1.5 cm3/g
Disp.L = 0.5 cm
Disp.T = 0.1 cm
Frac = 1 (fraction of sorption sites at equilibrium with the solution)
ThImob = 0 (immobile water content)
Diffus.W. = 3 cm2/d (diffusion coefficient in the liquid phase)
Diffus.G. = 30,000 cm2/d (diffusion coefficient in the gas phase)
Button "Next"
Computer Session 7a
Solute Transport - Transport Parameters (Edit->Flow and Transport Parameters>Solute Transport Parameters->Solute Reaction Parameters)
Boundary Conditions:
d = 0.5 cm (thickness of the stagnant boundary layer at the soil surface)
Reaction Parameters:
Henry = 0.01 (Henry’s constant)
SinkL1 = 0.005 d-1 (degradation in the liquid phase)
Button "Next"
Variable Boundary Conditions (Edit->Flow and Transport Parameters->Variable
Boundary Conditions)
Time Transp
Var.Fl1 (variable flux)
cValue1
0.01 0
-60
1
7
0
0
0
Var. Fl1 = drip discharge distributed over the circumference of the drip
Button "Next"
FE-Mesh - FE-Mesh Generator (Edit->FE-Mesh->FE-Mesh Generator)
Radio button - Meshgen
Button "Next"
FE-Mesh - FE-Mesh Parameters (Edit->FE-Mesh->FE-Mesh Parameters)
Targeted FE – Size – Unselect Automatic and specify TS = 5 cm
Button "OK"
Definition of the Transport Geometry
Click on Grid and Work Plane Setting at the toolbar (or Tools->Grid and Work Plane)
Grid Point Spacing – Distance w = 1 cm, Distance h = 1 cm
Click on Snap to Grid at the toolbar (or Tools->Snap to Grid)
a) Outer Boundary
Select the Line-Polyline command from the Edit Bar (or Insert->Domain Geometry>Lines->Polylines->Graphically)
Nodes coordinates: (0,79), (0,0), (75,0), (75,100), (0,100),(0,81)
b) Drip
Zoom at the source.
Select the Arc via Three Points command from the Edit Bar (or Insert->Domain
Geometry->Lines->Arc->Graphically->Three Points) and specify coordinates of three
points: (0,81), (1,80), (0,79)
View All (View->View All).
Define the Base Surface
Domain Geometry->Surface->Graphically and click at the outer boundary
Alternatively select the Surface via Boundaries command from the Edit Bar and click at
the outer boundary
Computer Session 7a
Define FE-Mesh
Insert->FE-Mesh Refinement->Graphically: a dialog appears in which specify Finite
Element size S=0.5 cm
After clicking OK, select three nodes defining the drip at the left side.
Click on the Insert Mesh Refinement at the Edit Bar, click New, and specify Finite
Element Size = 2 cm. Assign this refinement to the node at the top left corner.
Click Generate FE-Mesh from the Edit Bar (or Edit->FE-Mesh->Generate FE-Mesh)
Specify Initial Condition:
On the Navigator Bar click on Initial Conditions – Pressure Head (or Insert->Initial
Conditions->Pressure Head)
Select the entire transport domain
Click on the Set Value command at the Edit Bar, and set equal to -400 cm (Pressure
Head Value).
Water Flow Boundary Conditions:
On the Navigator Bar click on Boundary Conditions – Water Flow (or Insert->Boundary
Conditions->Constant Head)
Zoom on source: (0,80)
a) Select Variable Flux 1 from the Edit Bar and assign it to the arc
Click on View All at the toolbar (or View->View All)
b) Select Free Drainage from the Edit Bar and assign to points at the bottom of the
soil profile
c) Select Atmospheric Boundary from the Edit Bar and assign to points at the
surface of the soil profile
Solute Transport Boundary Conditions:
On the Navigator Bar click on Boundary Conditions – Solute Transport
Do not change solute transport boundary conditions. The third type boundary condition at
the soil surface does not allow escape of the solute to the atmosphere.
Observation Nodes
On the Navigator Bar click on Domain Properties – Observation Nodes (or Insert>Domain Properties->Observation Nodes)
Click on the Insert command on the Edit Bar and specify 5 points arbitrarily in the
transport domain between source and drain
Menu: File->Save (or from Toolbar)
Menu: Calculation->Run HYDRUS (or from Toolbar)
(Execution time on 3 GHz PC – 5 s)
OUTPUT:
Computer Session 7a
Results – Other Information: Observation Points (from the Navigator Bar, or Results>Observation Points from menu)
Pressure Heads
Water Contents
Concentrations
Results – Other Information: Boundary Fluxes (from the Navigator Bar, or Results>Boundary Information->Boundary Fluxes from menu)
Variable Boundary Flux
Free Drainage Boundary Flux
Results – Other Information: Cumulative Fluxes (from the Navigator Bar, or Results>Boundary Information->Cumulative Fluxes from menu)
Variable Boundary Flux
Results – Other Information: Solute Fluxes (from the Navigator Bar, or Results>Boundary Information->Solute Fluxes from menu)
Cumulative First-Order Reaction (degradation)
Cumulative Variable Boundary Flux 1 (injection)
Cumulative Free Drainage Boundary Flux (leaching)
Results – Other Information: Mass Balance Information (from the Navigator Bar, or
Results->Mass Balance Information from menu)
Results – Graphical Display: Pressure Heads (from the Navigator Bar, or Results>Display Quantity->Pressure Heads from menu)
Use Listbox Time Layer or Slidebar on the Edit Bar to view results for different
print times
Check Flow Animation
Select Boundary Line Chart from the Edit Bar and draw pressure heads for one
vertical column
Select Cross Section Chart and draw pressure heads through the middle of the
column
Select different display modes using Options->Graph Type
Results – Graphical Display: Water Contents (from the Navigator Bar, or Results>Display Quantity->Water Contents from menu)
Results – Graphical Display: Velocity Vectors (from the Navigator Bar, or Results>Display Quantity->Velocity Vectors from menu)
Results – Graphical Display: Concentrations (from the Navigator Bar, or Results>Display Quantity->Concentrations from menu)
Computer Session 7a
B. Injection of Fumigant From a Subsurface Source
(no resistance at the soil surface)
Close the Fumg1 Project (click Save Project at the Toolbar or File->Save)
Project Manager (File->Project Manager)
Select the Fumig1 project
Button "Copy"
Name: Fumig2
Description: Application of fumigant from a Subsurface Source (no resistance at
the soil surface)
Button "OK"
Solute Transport Boundary Conditions:
On the Navigator Bar click on Boundary Conditions – Solute Transport
Select Volatile Type from the Edit Bar and assign to points at the surface of the soil
profile
Menu: Calculation->Run HYDRUS (or from Toolbar)
(Execution time on 3 GHz PC – 4 s)
OUTPUT:
Results – Other Information: Solute Fluxes (from the Navigator Bar, or Results>Boundary Information->Solute Fluxes from menu)
Cumulative First-Order Reaction (degradation)
Cumulative Variable Boundary Flux 1 (injection)
Cumulative Atmospheric Solute Flux (volatilization)
Cumulative Free Drainage Boundary Flux (leaching)
Results – Graphical Display: Concentrations (from the Navigator Bar, or Results>Display Quantity->Concentrations from menu)
Click with the right mouse button on the color scale and from the pop-up menu click on
Min/Max Global in Time. See how the display changed.
Computer Session 7a
Fumig1
Fumig2
Computer Session 7a
C. Injection of Fumigant From a Subsurface Source
(finite resistance at the soil surface)
Close the Fumg1 Project (click Save Project at the Toolbar or File->Save)
Project Manager (File->Project Manager)
Select the Fumig2 project
Button "Copy"
Name: Fumig3
Description: Application of fumigant from a Subsurface Source (finite resistance
at the soil surface)
Button "OK"
Solute Transport - Transport Parameters (Edit->Flow and Transport Parameters>Solute Transport Parameters->Solute Reaction Parameters)
Boundary Conditions:
d = 500 cm (thickness of the stagnant boundary layer at the soil surface)
Menu: Calculation->Run HYDRUS (or from Toolbar)
(Execution time on 3 GHz PC – 4 s)
OUTPUT: as in B.
Computer Session 7a
D. Injection of Fumigant From a Subsurface Source
(no resistance at the soil surface; surface irrigation)
Close the Fumg1 Project (click Save Project at the Toolbar or File->Save)
Project Manager (File->Project Manager)
Select the Fumig2 project
Button "Copy"
Name: Fumig4
Description: Application of fumigant from a Subsurface Source (no resistance at
the soil surface, surface irrigation)
Button "OK"
Variable Boundary Conditions (Edit->Flow and Transport Parameters->Variable
Boundary Conditions)
Time Prec Transp Var.Fl1 (variable flux) cValue1
cValue2
0.01 0
0
-60
0
1
0.5
0
0
0
0
0
1.5
1
0
0
0
0
7
0
0
0
0
0
Var. Fl1 = drip discharge distributed over the circumference of the drip
Button "Next"
There is an infiltration of 1cm/d between time 0.5 and 1.5 d.
Solute Transport Boundary Conditions:
On the Navigator Bar click on Boundary Conditions – Solute Transport
Zoom on source: (0,80)
Select Third-Type from the Edit Bar and assign it to the arc
Click on View All at the toolbar (or View->View All)
Menu: Calculation->Run HYDRUS (or from Toolbar)
(Execution time on 3 GHz PC – 4 s)
OUTPUT: as in B.
Computer Session 7a
1.4
Infinite Resistance
Solute Flux [M/cm]
1.2
No Resistance
Finite Resistance
1
No Resistance + Irrigation
0.8
0.6
0.4
0.2
0
0
1
2
3
4
Time [d]
5
6
7