Ttime-series and current expression boundary condition

Hello,

I would like to know it is possible to assign a boundary condition with current expression using time-series. the boundary conditions will be time-serie dependent but modified by the expression.

Example : I want to turn off a time-dependent boundary conditions when some criteria are satisfied (for instance saturation or head).

Thanks


Lucien

Dear Lucien,

What you need to use is a boundary condition constraint (BCC). These can swtich on/off the BC depending on certain criteria (e.g. min/max hydraulic head and min/max flow-rate). Constraints are applicable for flow, mass, heat and age problem classes in FEFLOW 6.2. You can also have time series of constraint.
You may take a look in the Help System or in the White Papers Vol. I.

Cheers,

Carlos

Dear Carlos,

Thank you for your answer.

Constraint conditions are limited to the "corresponding parameters". For instance, with the constraint, the hydraulic head BC could only be constraint with a flow rain constraint. Want i want to do is to turn off a boundary condition when the saturation or the pressure reach a certain value. Is it possible?

Thanks

I, also, would like to assign time-dependent b.c.'s to nodes using the Expression Editor, in a Vertical, planar model for simulation of coupled flow and mass transport. The thing is, the Expression Editor allows a user to write a time-dependent expression e.g. "Current = TS.1 @(Time )", but when I click on the Assign button of the Editor toolbar, it assigns a constant value at the selected nodes (the value is the evaluation of my expression at current time).

The problem is, this is not just about constraints. I need time-dep. expressions because the values I want to apply totally depend on time series. Specifically, I have a time series describing the sea level and I want to apply a typical seawater salt concentration if sea level is above ground, and a freshwater concentration otherwise. The expression would look like (c in mg/L):
Current = {
35000 if TS.1 @(Time ) > y_local
100 otherwise
}

Similarly, I need an expression for hydraulic-head BC's* **:
Current = {
TS.1 @(Time ) if TS.1 @(Time ) > y_local
y_local otherwise
}

*this expression is equivalent to min(TS.1@(Time), y_local), but I found no expr. function for min(...)
**moreover, I found no hydraulic-head constraint for the fluid flow h-head b.c., though it exists for mass transport mass-conc. b.c.

In the above expression, note that the condition is time-dependent AND spatially-dependent. That's why I want to use expressions instead of multiple time series: it would requires hundreds, thousands of TS!

So, how can I apply such time-dependent b.c.'s in FEFLOW?

My question is probably addressed to the FEFLOW team, but if as a user of the software you know a way to do this, your help would be precious!

Thanks in advance.

Marc.

Dear all,

Here I have couple of ideas/comments:

@ Lucien,
If the answer is not constraint, you would need to write a short plug-in to control the BCs depending on specific variables.

@ Marc,
- The Head BC should be always available during the model run. I think the answer is not an expression, you need an interpolation between two nodes with an assigned time-series. You can easily carry out this task by using the 1D Linear Interpolation interactive tool. You need to impose strategically time-series in important locations, and then interpolate in between.
- The Mass BC could be assigned already at the beginning of the simulation. The mass BC should be active if there is inflow from the sea to the aquifer. Otherwise, the mass concentration at the boundary nodes is not anymore imposed and it is the computed. You can control this behavior easily by means of a constraint (e.g. minimum hydraulic head).
- The most important point is not to forget the conversion from saltwater heads to equivalent freshwater heads. Such transformation is based on the density ratio in FEFLOW.

Good luck!

Carlos

Thanks for your ideas. But finally, I've decided to learn to write IFM plugins for this kind of density-dependent saltwater transport problem. And it worked well. It is still work in progress, but when the plugin reaches maturity, I may share it with the FEFLOW community. I found it pleasant, actually, to develop a plugin in the Microsoft Visual Studio Express environment, with the IFM-related documentation from FEFLOW help. This offers much more flexibility than the FEFLOW interface does.

A suggestion for the FEFLOW developers' team: If only expressions could be used to define boundary conditions (or even material properties) that depend on time or other variable, I think we would be able to run many complex models without having to develop problem-specific plugins. Expressions could be created the same way Time Series are; then, the user would associate an expression ID to a node or element. In other words, a parameter would be defined by either A) a constant value, B) a time-dependent value from a time series, C) an expression that is recomputed before or after each time step. Doesn't that sound good?

Thanks again for your replies. Bye.

Marc.