Data panel by default. They
can be added to the tree by using the context menu of the corresponding
boundary condition.In FEFLOW, all boundary conditions can be physically constrained. Constraints are thus limitations for all types of boundary conditions or single point conditions (well-type conditions) that define a range of validity of the parent boundary condition. For example, a fixed hydraulic-head condition at a certain node can be limited by a maximum or minimum flow. They can be expressed in the following form:
| < Maximum Bound else replace BC by Maximum Bound | |
| BC is valid if | and |
| > Minimum Bound else replace BC by Minimum Bound |
Technically, these constraints are realized by temporarily changing the respective boundary condition. If the flow at a fixed head boundary condition would exceed the maximum flow set as a constraint, the corresponding boundary condition is internally transformed into a well boundary condition with the value of the maximum flow, and the time step is repeated. Because this test is performed for all affected nodes at every time step, considerable computational effort can be associated with the use of constraints.
Constraints are typically complementary to the respective boundary condition, i.e., head-type boundary conditions are constrained by minimum/maximum flow, while flux-type conditions are constrained by minimum/maximum head. Exceptions from this rule include additional constraints for transfer boundary conditions (to limit the infiltration at disconnected rivers) and for all transport boundary conditions (to limit their application to a certain range of hydraulic head).
Constraints are not shown in the
Data panel by default. They
can be added to the tree by using the context menu of the corresponding
boundary condition.
Algebraic signs for constraints and budget.
|
When using BCC, it is recommended to use a transient model approach! The reason for doing so is the fact that the check whether the boundary condition or the constraint should be active is done at every time step for a transient run. In a steady-state model, this check is only done for the first iteration and then kept for the subsequent iterations. |
In the case that Well BC is constrained by a Minimum Hydraulic-Head, and the constraint is activated, FEFLOW coverts the Well BC to a Hydraulic-Head BC (equal to the minimum head). Under some specific configuration, e.g., location of constraint is nearby another Hydraulic-Head BC node, an unwanted infiltration can happen at the location of the well. To avoid this situation, since the FEFLOW version 10.0, a second verification of the Boundary Condition Constraint is applied. If the Well BC has outflow conditions (i.e., a positive quantity was assigned to the boundary node), any potential inflow artificially created by the constrained is now automatically cancelled.
