Input the surface flux boundary condition in terms of flow rate per unit area. The surface flux is a boundary condition used in Seepage/Consolidation analysis (Fully-Coupled).

Input the surface inflow/outflow rate of a specific point in terms of flow rate per unit area. It can be defined as either an [Edge Flux] or [Face Flux]. Generally, the [Edge Flux] is input for 2D models and [Face Flux] is input for 3D models.

The Face flux can be defined by entering the value on the edge or surface geometry, or directly entering it on the selected element edge.

Define the inflow input from rainfall etc. as a (+) value and define the outflow input from excavation or pumping etc. as a (-) value.  

Transient analysis (where the water level changes with time) can be defined as a [Function].

When using a function, the input value and function value are multiplied and reflected in the analysis.

The defined function is registered under Function > Seepage Boundary Function, and can be edited as a table using the right mouse click > Edit.

Rainfall Data can be inputted into GTS NX in the form of Surface Flux, this can be also be extended to certain nodes in case if a small portion is considered instead of total area. The application of rainfall data as surface flux is illustrated below:

Amount of Rainfall - 100 mm/hr ~ 0.028 mm/sec ~ 2.8e-5 m/sec

The flux data input is discharge per unit area can be interpreted as Q/m2 ( Discharge Q = m3/sec), when Q is divided per unit area, it gives the height of the rain column that is falling in that area as post application of dimensional analysis, the flux input becomes m/sec. Hence, you can enter the rainfall data as described before directly as 2.8e-5 m/sec. The distance inputs can also be changed into mm or cm and the time inputs into hours or days.  Using the seepage boundary  function, one can also enter the rainfall data distribution as available from the meteorological data.

If q > Ksat, then Total Head = Pressure Head

The flux-head boundary conversion condition for rainfall analysis.

For example, the Surface flux can be used to define the ground surface boundary conditions when the rainfall intensity on the ground surface is inputted.

This function applies a forced inflow rate, as large as the rainfall intensity, onto the ground surface. If the absorption capability of the soil stratum surface is larger than the rainfall intensity, the soil stratum absorbs all the rain water. However if the absorption capability is smaller, rain is absorbed into the ground surface by only the absorption capability amount, and the rest of the rain flows across the ground surface.

If the rainfall intensity is larger than the absorption capability, the ground surface is in a saturated state during rainfall, as if the groundwater level existed above the surface. Hence, the area of rainfall needs to be changed to a water level line.

Use the [If q > Ksat, then Total Head = Pressure Head] option to automatically change the ground surface boundary from the existing rainfall intensity inflow condition to a water level condition for analysis. This option is only available when the rainfall intensity acting on the surface is larger than the absorption capability of the ground surface.

Boundary Set

Register the set constraint conditions on the desired boundary set. The user can specify the name of the boundary set or create a new boundary set for the recently entered data values.