Carlos Andres Rivera Villarreyes Global Product Specialist - FEFLOW

Dear Usman,

The Null Space Monte Carlo approach has several variants (conceptually), which may be complicated to explain full details here. For example you could make the analysis with an uncalibrated model (i.e. pre-calibration approach) or after the calibration is done (post-calibration approach). If you are interested in more background, you can get some insight on the philosophy from the now available PEST Book (http://www.pesthomepage.org/PEST-The_Book.php).
You can take PEST out of its box with some help of FePEST. In the next release FEFLOW 7.0, the methods are fully incorporated and straightforward.
For Instance, you could calibrate your model constrained by a Tikhonov regularization and quite-probably using any other device (e.g. such as SVD-Assist). On the basis of the calibrated model, generate parameters as explained below (or other post) using RANDPAR & PNULPAR and finally evaluate the predictive uncertainty from the results of all the realizations.

Regards,
Carlos

Dear Anne,
If you would like to apply an expression for the outflow flux, you can only do it by means of a material property named "Sink/Source" (or Inflow/Outflow on top/bottom for 3D models). If the model is transient for flow, you can simply make a right-click on the parameter name and activate the expression editor. In such a manner, the fluid-flux BC is free for other purposes such as recharge.
Regards,
Carlos

Dear Rapheul,

All the process variable charts (hydraulic-head, concentration and temperature) and budget charts (rate and period) contains always all the time steps used for the model run. If you want to extract information from specific time steps, you can use the standard export based on nodal selections for specific time and/or all times in the DAC file.

Regards,
Carlos

Dear Ali,

There are two possible explanations:
1) The value of PD1 is not so large compared to PD0. Therefore, PEST cannot maximize/minimize the observation. You need to extend your definition of a "calibrated" model in the parameter space.
2) The hydraulic heads are not so sensitive to the calibrated parameters (i.e. the parameters are indeed changing, but the observations do not).

You may try to go further in your analysis and carry out a Monte Carlo analysis with FePEST. You need a couple of manipulations in the command line to get started in FePEST (see the post [color=blue][i][b]"Null space Monte Carlo with FePest?"[/b][/i][/color])

Regards,
Carlos

Dear Ali,

A run under the PEST predictive mode, it means that PEST would start modifying the parameters in other to minimize/maximize certain observation, but keeping the model "calibrated" at the same time.

PD0 is the target objective function. This is the value what you would expect for a calibration model. Normally, you can take this value from a previous PEST run (i.e. standard estimation mode).
PD1 is the acceptable objective function. Since you want to keep the model "calibrated", then you would need to say what "calibrated" status means. This is simply few percentages above PD0 (e.g. 1-2%).
PD2 tells PEST when to change to the next iteration after having try several Marquardt Lambdas.

You can find all the details in the PEST Manual (section 6-14, page 192).

Regards,
Carlos

Hi Thomas,

It is not correct that you set a head BC equal to the topographic level, this would reflect the behavior of a seepage boundary. For an artesian well, the head BC should get a value, which depends on the high pressure located down in the aquifer. I would recommend you the following options:
Head BC -> Pressurized value
Minimum flow-rate constraint = Maximum flow expected through the artesian well in m3/d
Maximum flow-rate constraint = 0 m3/d (avoid possible water inflow).

Depending on the local settings, you may use a discrete feature element (DFE), which can enhance the vertical flow. Thus, the outflow would be mainly dominated by the deeper aquifer and not the shallow locations. Phreatic and piezometric surfaces may be complicated, so the most-correct evaluation can be only reached by using the Richards' approach in FEFLOW.

Regards,
Carlos

Dear Lucien,

Maybe the recharge parameter is not sensitive to the observation data provided. You can easily demonstrate this hypothesis by means of the Sensitivity tool provided in FePEST.

Regards,
Carlos

Hi,

You can run a steady-state simulation. When the model run completes, save the FEM file and subsequently advance it to a transient simulation. No need of importing initial hydraulic heads.
Moreover, the import of any parameter, which requires data regionalization is carried out via the Link to Parameter option. You may take a look in the "How To" section in the FEFLOW Help.

Regards,
Carlos

Dear Spencer,

You can store the boundary nodes in the Spatial Units panel as a nodal selection. Here you can activate the Budget Charting Mode option, which provides the advantage to track the budget flux or imbalance in this exact location of the model domain. Such option will create a separate line in the Rate/Period Budget charts, which can be easily exported as a time-series.

Regards,
Carlos

Dear Usman,

You may take a look in a previous post ([color=blue][i]Coupling Feflow and FePest for not assigned Parameters (Manual Coupling of PEST)[/i][/color]) in the FePEST forum child board. Although this is not exactly the parameter estimation of a BC, the workflow is very similar. You can find all the definitions of the IFM API functions to get/set BC values in the FEFLOW Help System.
If you are new in IFM programming, I would recommend you to take a look in our documentation in the FEFLOW website. Alternatively, this forum has a very interesting child board related to plug-ins, you may find some information here as well.

Best regards,
Carlos