HYDRUS Step by Step

The work with the HYDRUS GUI usually follows certain steps that are common to most applications. One needs to first create a HYDRUS project, define the geometry of the transport domain and generate finite element mesh. One needs to also specify various parameters describing soil properties, reaction and transport parameters, and how to organize the output. Finally, one needs to specify spatial distribution of domain properties, and initial and boundary conditions. Only then can one perform the actual calculations, and display and analyze results.

The GUI is organized in a way to indicate the sequential character of the process of defining the HYDRUS project. On the one hand, the Tabs at the bottom of the View Window are organized sequentially (i.e., Geometry, FE-Mesh, Domain Properties, Initial Conditions, Boundary Conditions, and Results), on the other hand the dialog windows, in which one specifies various parameters, have the Next and Previous buttons indicating, which information is to be provided next. Similarly, the list of objects on the Navigator Bar is sorted from objects that should be specified first (i.e., Project and Geometry), via those that needs to be specified next, to those that are obtained only after calculations are performed (i.e., Results).

The Table below summarizes basic steps, and their sequence, performed when working with a typical HYDRUS project.

Step 1	Project	The work on each project starts with the Project Manager or with commands from the File Menu (e.g., New, Open). Using the commands of the Project Manager, one can create a New HYDRUS Project, or copy, rename, delete, or open existing Projects. One can also specify the location of a Project and in which Project Group it should belong.
Step 2	Domain Type and Units	In the second step, users need to select whether they want to solve a two- or three-dimensional problem, what type of Geometry they want to consider, and what Length Units they want to use. The selection of the Domain Type (or Geometry Type) and units is done in the Domain Type and Units dialog window.
Step 3	Flow and Transport Properties	The Flow and Transport Properties are specified in a sequence of dialog windows, which starts with the Main Processes window. Here, one selects which processes are to be considered (e.g., water flow, solute transport, root uptake, etc). One can then proceed to further windows (e.g., Time Information, Output Information, Soil Hydraulic Properties) by simply clicking on the Next button (one can also go back using the Previous button). The sequence of these windows will depend on selected processes and will be unique for a particular application. Some windows will be skipped of not required for a particular application. Step 3 may be done after Steps 4 and 5, as neither Geometry nor Finite Element Mesh depend on selections made during this Step. It, however, has to precede Step 6, during which it needs to be known, which processes are to be considered.
Step 4	Geometry	In this step, the actual Geometry has to be defined. There are many different ways how this can be done, depending mainly on the Geometry Type. For Simple Domains, this can be done using dialog windows (e.g., Rectangular Domain Definition or Hexahedral Domain Definition). For General Domains, this is usually done graphically in the View Window by using basic geometrical objects, such as point, lines, splines, curves, or surfaces. It is also possible to import definition of Geometry from files of different formats (e.g., a text, DXF, or TIN file). For more details, see How to Edit Geometry.
Step 5	Finite Element Mesh	Once the Geometry is defined, it needs to be discretized (divided) into Finite Elements. How this can be done depends again mainly on the Geometry Type. For Simple Domains, which are discretized using structured FE-Mesh, this is done using dialog windows (e.g., Rectangular Domain Discretization or Hexahedral Domain Discretization). General Domains are discretized using unstructured FE-Mesh. Here, one needs to first select the global FE-Mesh Parameters (e.g., a Targeted FE Size, the Number of Mesh Layers, and Stretching Factors), refine the domain in certain parts (on a node, curve, or surface) as needed using the FE-Mesh Refinements, and finally Generate FE-Mesh. For more details, see How to Edit FE-Mesh.
Step 6	Domain Properties	Once the Geometry, and its FE-Mesh (this is not needed if the Domain Properties are defined on Geo Objects), are defined, one can specify the spatial distribution of Domain Properties. Domain Properties are variables or parameters (e.g., material distribution or observation nodes) that may vary in space and are therefore defined either on Geometrical Objects, from which they are then interpolated to the FE-Mesh, or directly on the Finite Element Mesh. For more details, see How to Edit Domain Properties.
Step 7	Initial Conditions	Initial conditions, i.e., conditions throughout the transport domain at the beginning of simulation, need to be specified for each considered process. If one simulates water flow, then one needs to specify initial water contents or initial pressure heads throughout the entire transport domain. Similarly, if one simulates solute or heat transport, one needs to specify initial concentrations or initial temperatures. Similarly as for Domain Properties, Initial Conditions can be defined either on Geo Objects or on the FE-Mesh. For more details, see How to Edit Initial Conditions.
Step 8	Boundary Conditions	Boundary conditions, i.e., what occurs at boundaries of the transport domain, need to be specified for each process that is simulated for the entire simulated time. For more details, see How to Edit Boundary Conditions.
Step 9	Calculations	Once all input parameters are specified, the actual calculations can be performed. Use the Calculations Menu commands for that. One can perform calculations for a single active project (Calculate Current Project) or calculate at the same time all open projects (Calculate All Open Projects). Various computational modules (e.g., direct, inverse, wetlands, Unsatchem) are used depending on the problem. Selected information is displayed in the DOS window at the desktop during HYDRUS execution.
Step 10	Results	Computational modules generate multiple output files, the content of which can be displayed either graphically or as text. See the Results Menu topic for a full description of available display options. A spatial distribution of various output variables (e.g., Pressure Heads, Water Contents, Velocities, Concentrations, and Temperatures) can be displayed graphically by means of Spectral maps or Isolines, Isosurfaces, or by means of Animation. Various other graphs, such as selected variables at observation nodes, boundary fluxes or run-time information, can also be displayed. The Navigator Bar (sections Results - Graphical Display and Results - Other Information) and the Results Menu provide a quick access to various types of displays of the output results. For more details, see How to Display Results.