DHIJWASv Software FEFLOW 6.1

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• General Anisotropy with Computed Angles:
The principle directions for the main conductivities
K_1m, K_2m, K_3m coincide with the layer
inclination. The inclination is determined separately
for each element.
• General Anisotropy with User-Defined Angles:
The principle directions for the three main conductivities
and the three Euler angles needed for
the rotation of the coordinate axes are defined as
material properties for each element.
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FEFLOW offers iterative solvers and a direct equation
solver. As the computational demand of the direct
solver increases with the third power of the number of
mesh nodes, the applicability of this solver has a practical
limit of about 100,000 nodes.
Iterative solvers are therefore used by default. Separate
iterative solver types can be selected for the (symmetric)
flow and (nonsymmetric) transport equation
systems. The default options are a preconditioned conjugate-gradient
(PCG) solver for flow and a BICG-
STABP-type solver for transport. Alternatively, for
either type of equation systems an algebraic multigrid
solver can be chosen (SAMG). The main advantages of
SAMG are its parallelization on multicore or multiprocessor
systems, and its more efficient solution algorithm,
in particular for steady-state simulations and
simulations with large ranges of element sizes in the
mesh. As the algebraic multigrid technique is not
always the most efficient one, the SAMG solver automatically
selects between a CG-type or AMG-type
solution strategy according to the current conditions.
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In this exercise we load a number of models with
different problem types to get familiar with the available
problem settings.
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We start with a very basic 2D flow model. Start
FEFLOW and click Open to load the file quadmesh.fem.
To check the basic settings of the model,
open the Problem Settings dialog via the Edit
menu.
On the Problem Class page we can see that the standard
(saturated) groundwater-flow equation is used for
the flow simulation and that confined conditions are
assumed. Switch from a Horizontal projection to
Vertical, planar and click Apply. The option
Unconfined conditions is now disabled as Vertical,
planar models are always assumed to be confined.
Additionally, the Gravity Direction page is displayed
under Problem Class.
Switch back to a Horizontal projection and
choose Unconfined conditions. Once we confirm
the changes with Apply, the Free Surface page is
added in Problem Class. In the Data panel, the
material-properties list automatically adapts to the
changed settings. Transmissivity is replaced by the
parameter Conductivity [max], and Top and Bottom
elevation now need to be defined.
Additionally, for unconfined (phreatic) models head
limits for unconfined conditions can be set to define
the model behavior when the water table touches the
top surface, or the model falls dry at the bottom.
Leave the Problem Settings dialog with
Cancel and close the model without saving the