Input the head of the model. Both the constant head value for steady state analysis and the changing head value for Transient analysis can be entered by applying the Seepage boundary condition function. The Nodal head is used as a boundary condition for Seepage/Consolidation analysis (Fully-Coupled).  

Directly input the head value of a specific point. The target can be selected from [Node], [Edge], [Face], [Free Face Node].

For [Node], the node is directly selected to define the head condition. Selecting [Edge] or [Face] defines the head condition at all nodes in the selected line/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.  Press  to open the Free face/line entity selection window to select the target.

There are two input methods:

1. [Total] : Input the head value calculated from the origin, regardless of the model position.

2. [Pressure] : Set the groundwater level condition by entering '0' for nodes that are on the groundwater surface.

Transient analysis, in which 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.

If Total Head < Pressure Head, then Q = 0

A head-flow rate conversion boundary condition for water level variation analysis.

As the water level changes with time, such as for rapid drawdown, suction can occur and the seepage flow can be reversed. If the water level falls suddenly for embankments or dams, the descending water level speed is generally faster than the seepage speed within the body. To simulate these real conditions, the head boundary conditions need to change automatically according to the water level. In other words, when the node boundary at the bottom of the water level is exposed to the top, the total nodal head is not the total head of the descended water level; it is the total head value before the descent, which is maintained for a certain period, after which it falls gradually with time.

This option can be applied where the water level changes periodically and can be applied simultaneously with a time variant function. However, if this option is checked when the input (total head) height of the water level is above the selected node position, the boundary condition is automatically eliminated and so, the option must be unchecked for this case.  

Boundary condition set

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

The nodal head is applied then the water level position is known in advance. It is used to simulate confined flow that does not form a phreatic surface. It is also used to simulate unconfined flow that creates a  seepage face.

The head boundary conditions can be selectively input between the Total Head and Pressure Head, depending on the analysis condition. As shown in the figure below, it is convenient to input the Total Head directly when the node position for boundary condition specification is easy to find from Z=0 on the GCS. However, if the exact height is hard to find or if the height changes, it is convenient to input the Pressure head as 0.

<Application of Nodal Head(ex.)>