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Visual AEM  Frequently Asked Questions

Modeling Issues/Errors
Visual AEM Capabilities

Q: Why are some of my menu entries greyed out?

A: There are two possible reasons, addressed below.

1. Engine incompatibility: Unlike some modeling user interfaces, Visual AEM supports multiple numerical engines: Bluebird/Cardinal, Split, and TimML. Some engines have certain elements/features but not others- for example, transport may only be performed using Bluebird/Cardinal. Usually, by switching engines, you can reveal new available elements (but unfortunately hide others). Before solving the model, Visual AEM should warn you of any potential inconsistencies in the model.

2. Element incompatibility: Some elements may not be used together, because they rely upon incompatible assumptions. For example, the interface has tools for modeling both transient and multilayer flow, but not both transient and multilayer.

Q: I am changing and re-solving the model, but my output is identical to what it was - what is going on!?

A: Re-solving the model must be followed by re-gridding (generating) the contour plots that correspond to the new solution.

Q: How do I know which elements are compatible?

A: There is a table in the manual (Appendix A)  that addresses which elements may be used with which engines and with each other.

I am hitting solve, but then nothing happens...why is the model not running?

A: This is a known issue for Visual AEM when installed on a machine with language settings other than English. In most cases, changing the Windows language settings to English (Canadian, British, or US) is sufficient to fix the problem. If language settings are not the issue, it is possible that you do not have sufficient priveleges to write to the model folder and files (a common issue if, for example, you are storing your model files in C:\Program Files (x86)\ on newer windows platforms without admin priveleges. If neither of these fixes are helping, please contact the author (Contact)

Q: When I try to run a multilayer model with TimML, the solver hangs after flashing the DOS prompt...what is happening?

A: This is usually due to an improper installation of TimML. Please follow the installation instructions from the TimML manual, and ensure that the windows environmental variable PYTHONPATH includes the Visual AEM directory (e.g., C:\Program Files\Visual AEM).

Q: How does Visual AEM compare to Modflow?

A: The numerical methods used in Visual AEM are fundamentally different from those used in Modflow. Modflow uses finite difference methods to solve the fully three-dimensional transient form of the groundwater flow equation, and requires grid discretization, where the resolution of the grid determines the accuracy of the solution.

The numerical models behind Visual AEM use the analytic element method (AEM), which is (for the most part) limited to 2D saturated steady-state groundwater flow, though limited support for transience and multiaquifer flow is available. The solutions are analytical, which means they solve the governing equations exactly without discretization artifacts. Boundary conditions are met with very high precision, and the accuracy of the model is dependent mostly upon the incusion of important features, correct parameterization, and the validity of the 2D steady-state assumption.

Q: How does Visual AEM compare to other AEM engines such as GFlow and TwoDAN?

A: Aside from the conveniences of the user interface, which are a matter of user preference, the assumptions and mathematics behind most analytic element models are very similar. Visual AEM does have a few things that the other AEM engines do not, such as contaminant transport and multilayer modeling with TimML. It also has a few extra elements, such as inhomogeneities in base and thickness, elliptical lakes/inhomogeneities, and a few special river boundary conditions. GFlow, on the other hand, has a more rigorous handling of groundwater-surface water interactions.

Q: Has Visual AEM gone through a formal evaluation/peer-review process?

A: Unfortunately, no, though the numerical engines have been extensively tested against analytical solutions and numerical models. Remember, most of the engines are research tools first, and therefore go through a good deal of peer review in the form of publications and endless programmer scrutiny :).

Q: Where are the linesinks, dipoles, and doublets? Isn't this an AEM program?

A: Behind the scenes. We purposely avoided using these terms so that hydrogeologists and students (rather than AEM experts) could use the software.

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