Input the inflow/outflow per unit time on a particular position in terms of volumetric units. The target can be selected from [Node], [Edge], [Face], [Free Face Node].

For [Node], the node is directly selected to define the nodal flux. Selecting [Edge] or [Face] defines the flow rate conditions at all nodes in the selected edge/face.

For [Free Face Node], select a free face node and all points that make contact with the node-containing element at an angle smaller than the specified angle selected. Press the  button to select the reference node, target element and feature angle.

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 right mouse click > Edit.

Boundary Set

Register the set constraint conditions on the desired boundary set. The user can specify the name of the boundary set.

The nodal flux boundary condition is used to simulate the inflow and outflow that happens at a node. The (+) represents water flow into the node and (-) represents water flow out of the node. The time variant - flux boundary condition can be input by coupling with a seepage function.

<Application of Nodal Flux>

Surface Flux

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.

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.