Posted Fri, 11 Jun 2021 19:41:52 GMT by Assaf Wunsch
I am trying to program an equation for a constant-head boundary condition, so that the head will be a function of time.
In my simple test, the equation simply attempts to set the boundary head (m) to the simulation time value (d) when the simulation time is less than 20 days (so, linear increase of head), then keep the head constant at 20m after 20 days.

For some reason, the simple if.. then .. else formula that I am trying does not appear to work (attached). It seems that the head jumps to 20m very fast and completely ignores the time constraint.
I also tried the same approach with a piecewise defined function, and it didn't work either.

Posted Mon, 21 Jun 2021 07:23:16 GMT by Carlos Andres Rivera Villarreyes Global Product Specialist - FEFLOW
There are two types of equations in FEFLOW: those used for the assignment and those, which will dynamically be evaluated through the model run. In the case of boundary conditions, the expressions are only supported for assignments (before the model run). As soon as you click the buttom "Assign" the expression is evaluated and longer no more.
The second case of dynamic expression is supported for several material propeties. This is an option implemented in one of the latest release. The overview of parameters supported is below:

For your specific question, the easiest manner to control the boundary is via a simple Python function, which can be stored in the FEM file and call it through the run. The Support team ( could give you some hints about the usage.

Carlos Rivera
Posted Fri, 02 Jul 2021 15:35:53 GMT by Assaf Wunsch
Thanks Carlos,

so to reiterate, the equation editor only applies to material properties, not to boundary conditions.

So if I want to assign a boundary head that changes over time (say, a tidal or river boundary), I have two options:
1. Set it up outside of FEFLOW and bring in as POW file to the Time Series menu. Will lose the flexibility of the analytical ability to assign different heads to different nodes based on location (I mean, possible, but will result in as many POW files as nodes...)
2. Use python to code the equation.
Posted Tue, 23 Nov 2021 10:11:58 GMT by Michael van Til Ramboll
Following up from the query above, I'm looking to utilize the equation editor to apply a time-dependent function to a material property.

In my case, I'm wanting to multiple the value in a user-defined elemental distribution value (paved area coefficient) by recharge (In/outflow on top/bottom) for each timestep.

Is there a way to do this within the equation editor?

Thanks in advance,


You must be signed in to post in this forum.