HYDRUS Editions
The HYDRUS program is available in several editions, sometimes also called HYDRUS Levels, which differ in the dimensions (i.e., 1D, 2D, and 3D) and complexity (i.e., simple, layered, general) of the transport domain. This gives users the ability to choose the right edition for their needs and not pay for features they don't need. The following table provides an overview of the features available in each edition.
HYDRUS Editions and Their Features
Feature No.

Feature Description

1D Standard

2D Lite

2D Standard

3D Lite

3D Standard

3D Professional

1

1D Simple Domain

Yes

Optional (*)

Optional (*)

Optional (*)

Optional (*)

Optional (*)

2

2D Simple Domain, Structured FEMesh

No

Yes

Yes

Yes

Yes

Yes

3

2D General Domain, Unstructured FEMesh

No

No

Yes

No

Yes

Yes

4

3D Simple Domain, Structured FEMesh

No

No

No

Yes

Yes

Yes

5

3D Layered Domain and FEMesh

No

No

No

No

Yes

Yes

6

3D General Domain, Unstructured FEMesh

No

No

No

No

No

Yes

(*) 1D projects are enabled with the H1D addon module.
The following examples show the differences between different types of transport domains and FEmeshes.
Simple Domain 1D/2D/3D
The transport domain is defined using the onedimensional profile or relatively simple twodimensional rectangular or threedimensional hexahedral objects. Dimensions and other parameters of the transport domain are specified numerically in the Domain Definition dialog window. In all these cases the transport domain is discretized into a structured finite element mesh.
In the Rectangular or Hexahedral Domain Definition dialog windows, users need to specify the vertical and horizontal dimensions of the transport domain, as well as a possible slope of the base of the domain in different directions. Nodes along the upper boundary may have variable zcoordinates. However, the lower boundary must always be horizontal (or have a specified slope), while the left and right boundary lines (sides) must be vertical.

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2D General Domain
General TwoDimensional Domains can be formed using one or more Surfaces that can touch each other, but cannot overlap. Each of the Surfaces is defined by a set of Boundary Curves that enclose the transport domain. All surfaces must lie in the same plane. Surfaces can contain openings, internal points, or internal curves. It is also possible to create an opening in a surface and then enter another surface into it.
An unstructured Finite Element Mesh is used to discretized 2DGeneral Domains. The very flexible unstructured finite element generator (MeshGen2D) can be used for virtually any type of complicated domain. The generator attempts to generate finite elements with the size defined using the parameter Targeted FE Size. This FE size can be further modified in different parts of the domain using various tools, such as Stretching in different directions to make the mesh anisotropic, specifying the Maximum and Minimum Numbers of Nodes on a Boundary Curve, or using Finite Element Mesh Refinement, that can be defined around Points, and for Lines and Surfaces.

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3D Layered Domain
3DLayered Domains are defined using a Base Surface (a General TwoDimensional Domain, see the text above) and one or more Thickness Vectors. Thickness vectors do not have to be perpendicular to the Base Surface. The Domain can be divided into one or more Layers, which subdivide the domain into multiple, usually horizontal, Subdomains. These Layers can be used, for example, to keep constant thicknesses of selected horizons or constant discretization close to the soil surface. Relatively general threedimensional domains, fulfilling the needs of most HYDRUS users, can be defined using the 3DLayered Domains.
However, 3DLayered Domains still have certain limitations. For example, Layers have to be continuous and some shapes cannot be directly considered (e.g., spheres). All these limitations are overcome in the most general option (Level) of HYDRUS, i.e., in 3DGeneral Domains (3DProfessional).

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FEMesh in 3D Layered Domains
The Base Surface of the 3DLayered Domains is discretized first using, as above for 2DGeneral Domains, the unstructured finite element mesh generator MeshGen2D. The same options as for 2DGeneral Domains, i.e., Targeted FE Size, Stretching, FEMesh Refinement (see the text with Figure 3 above), can be used when discretizing the Base Surface as well.
Discretization in the vertical (perpendicular to the Base Surface) direction follows Layers defined at Thickness Vectors. Users can specify the number of horizontal FELayers to discretize the Domain in the vertical direction. Users have high flexibility in defining the vertical spacing of FELayers, by specifying, for example, the relative sizes of elements at the top and the bottom, with element sizes then proportionally distributed.

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3D General Domain
In the 3DProfessional version, the 3D General Domains (general threedimensional domains) can be formed from threedimensional objects (Solids) of general shapes. Threedimensional objects (Solids) are formed using Boundary Surfaces, which can be either Planar Surfaces or Curved Surfaces (Quadrangle, Rotary, Pipe, BSpline). Boundary Surfaces of a Solid must enclose a closed space and cannot intersect each other.
In more complicated cases it is also possible to use Intersections of Surfaces and Solids to create, in this way, openings in solids or to carry out with Solids various logical operations. Internal Solids, Cavities, and Integrated Objects can be defined as well.

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FEMesh in 3DGeneral Domains
The mesh generator Genex/T3D is used to generate threedimensional FE meshes for the 3DGeneral Domains. The generated unstructured FEMesh is composed from either only tetrahedrals or from elements of different shapes (e.g., tetrahedrals, triangular prisms, and others). Similar options as in MeshGen2D, i.e., FEMesh Refinements at Points, on Curves, Surfaces, and Solids, and FEMesh Stretching, are available in Genex/T3D as well.

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Edition 3DProfessional  Example 1
This figure shows a complex threedimensional domain (3DGeneral) with Discontinuous 3D Layers. This is an example of a problem that could not be developed using 3DLayered Domains (available in the 3DStandard Level).

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Edition 3DProfessional  Example 2
This figure shows a complex threedimensional domain (3DGeneral) with a complex drainage system.
Unlike the version 3DStandard, the version 3DProfessional allows you to create comfortably inside of the transport domain a complex system of internal holes or objects. Examples could be, for example, Tutorial 5.12 or Tutorial 5.15.

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Edition 3DProfessional  Example 3
This is another example, for which we recommend using the 3DProfessional version. The reason being the markedly variable thickness of the transport domain that requires variable spatial discretization (FE Mesh) in the vertical direction at different locations (XY) of the domain. The disadvantage of the 3DLayered domain is the fact that the number of finite elements must be the same in the vertical direction for the whole region (or for the whole Base Surface).

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Edition 3DProfessional  Example 4
This figure shows a model of a more complex landscape with a Tunnel through curved geological layers, created using an Intersection of multiple Curved Surfaces. The Hillside is defined using three major geological layers: the bottom layer (dark blue), the intermediate layer (light blue), and the surface layer (green), each defined using curved surfaces.

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Edition 3DProfessional  Example 5
The picture shows an example of the test of defining internal objects. Internal objects can be points, curves, surfaces, internal solids, and/or holes/cavities. The displayed domain contains several Internal objects of spherical shape filled with various materials.

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