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 cm 2 , 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 m 2 /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. (75, 100) (0, 100) (0, 80) (0, 0) (75, 0)
Transcript
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.
(75, 100) (0, 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 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)
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)
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.
