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## HYDRUS 2.x - Introduction to Defining Properties on Geometric Objects

Inputting properties on **Geometric Objects** is one of the key innovations in version 2. Users can specify various domain properties, and initial and boundary conditions, on Geometric Objects, rather than only on FE-Mesh, as previously available in version 1.x. This can be very useful especially in cases when we need to modify the domain geometry and do not want to lose already defined input data. Despite this new option it is still possible to specify properties of the FE mesh or in a mixed mode (i.e., partly on Geometric Objects and partly on FE mesh). The main switch for the input mode can be found in the opening dialog **Domain Type and Units**.

A relatively simple example **Furrow** is used here to demonstrate how to enter (spatial) data on **Geometric Objects**. The starting point is an already defined geometry of the area, on which we then define, in a few short steps, the **Observation Nodes**, **Boundary Conditions**, and **Initial Conditions**. The tutorial shows how properties defined on geometric objects are transferred to nodes and elements of the FE mesh and what happens when properties defined on FE mesh are different from those defined on geometric objects. At the end, the tutorial demonstrates the main advantage of defining properties on the geometric objects, that is, when the geometry is changed and/or the FE mesh is deleted, properties defined on geometric objects are preserved and automatically transferred to the new FE mesh. Similarly, one can also define properties on geometric objects for more complex 3D problems. However, properties cannot be defined on geometric objects for the so-called Simple Domains (see Domain Types in HYDRUS), where there are no geometric objects defined (the area is defined parametrically).

### Step 1 - Defining Observation Nodes at Geometric Points

In order to shorten this tutorial we assume that we have already defined the geometry of this project (Furrow), as well as other flow and transport parameters (see also tutorial 3.03). As a first step, we demonstrate how to define Observation Nodes on geometric objects, which in version 1 of HYDRUS could have been defined only on FE mesh nodes. Now we can place observation nodes to the geometric points in any place of the domain. The coordinates of these geometric points can be defined exactly using the dialogue window for editing of points. If you need more points, you can also use several tools for their automatic generation. In the tutorial, uniformly distributed points are generated on the line segment, but one can also use other tools - such as Translate and Rotate with the specified number of copies.Note: When geometric points within the 2D domain (that is, not on the boundary), they are automatically integrated into the relevant Surface, and the FE mesh node is generated at each such point. In 3D domains (3D Professional version), it is possible to define geometric points anywhere inside the geometric domain, but their integration into the Solids and the FE mesh does not occur automatically. Internal objects must be specified explicitly in the dialog for editing the Solid. Video Tutorial (4.1 MB) - Play - Download |
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### Step 2 - Defining Initial Conditions

In this step we define the Initial Conditions. Each initial condition is represented by one object containing parameters of the initial condition and the list of Geometric Objects (in this case Surfaces), to which this initial condition is assigned. Where a particular initial condition is assigned can be easily checked visually with colors assigned to individual objects and conditions (the colors can be individually set). However, if we want to see the actual values of the initial condition (e.g., pressure heads), we need to first generate an FE mesh. Actual values are transferred on FE mesh automatically from specified Initial Conditions objects and the accuracy can then be checked on any node of the FE mesh. Video Tutorial (3.8 MB) - Play - Download |
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### Step 3 - Defining Boundary Conditions

Boundary Conditions are defined in a similar way as done in step 2 for initial conditions, with the difference being that the Boundary Conditions Objects are assigned to boundaries (in this case to boundary lines). It is worth mentioning that the condition with the higher serial number is assigned to a node between (shared by) two boundary lines. The conditions can be reordered using functions for the sorting and/or renumbering of the desired conditions. Video Tutorial (5.2 MB) - Play - Download |
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### Step 4 - Combination of Defining Conditions/Properties on Geometric Objects and FE Mesh

While we recommend defining conditions/properties of geometric objects, it is still possible to enter their values directly onto the FE mesh. Both methods can even be combined. It is, however, important to realize that the transfer of conditions/properties works only one way, i.e., always from geometric objects to the FE mesh. If you change values on the FE mesh, these changes will remain and be used in calculations. However, to avoid unwanted differences in the values on the FE mesh (and Geometric Objects), there is always a warning, if such differences are detected. This is demonstrated in the attached video tutorial. After the warning appears, the user can decide whether to keep the differences in values (and use FE mesh values in calculations), or whether to regenerate FE mesh values using conditions defined on geometric objects. Video Tutorial (2.9 MB) - Play - Download |
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### Step 5 - Maintaining the Input Data when Changing the Geometry of the Transport Domain

In this step, we will present one of the main advantages of defining conditions/properties on geometric objects. Suppose that we have already calculated results for the Furrow project (which is the initial state of this video tutorial) and we decide to modify the shape of the computational domain. This requires deleting the FE mesh and, in earlier versions of HYDRUS, represents a loss of all input data defined on the FE mesh (i.e., Domain Properties, Initial Conditions, and Boundary Conditions) and the need to reenter them. Now, this loss does not occur, and in the attached video you can see how easy it is to recalculate the results for the modified domain. Video Tutorial (6.5 MB) - Play - Download |
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