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Vol. 9  No. 1

STEADY STATE vs. TRANSIENT MODELING

&
FEFLOW

January 2008 Discount: $65.00 off FEFLOW 2D Flow Download Package (Use Coupon# 1199580384)

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Steady State vs. Transient Modeling

Groundwater flow models describe their capabilities as either steady state and/or transient.  It is important when deciding upon groundwater modeling software to know which options are necessary for your needs.  This month's newsletter will describe the key differences between steady state and transient modeling.

Steady state flow occurs when the magnitude and direction of flow is constant with time throughout the entire domain.  Conversely, transient flow occurs when the magnitude and direction of the flow changes with time.  In other words, the hydraulic head doesn't change with time in a steady state flow system, but does change during transient flow. This does not mean that in a steady state system there is no movement of groundwater, it simply means that the amount of water within the domain remains the same, and that the amount of water that flows into the system, is the same amount as flows out.

The steady state flow conditions simplify the groundwater flow equation significantly. When steady state flow occurs, time is no longer an independent variable and thus the storage term in the groundwater flow equation disappears; since there is no change in the amount of water within the domain (no change in hydraulic head) there is obviously no change in the amount of water stored in the domain.  Below are simplified equations that describe transient and groundwater flow.  

There are a variety of software available which do both transient and steady state flow and transport modelling.  One of these products is FEFLOW.

References

 

Fetter, C.Q. (1994). Applied Hydrogeology. Published by Maxwell Macmillan International, New York.

Freeze, R.A, and Cherry, J.A. (1979). Groundwater. Published by Prentice Hall, Inc., New Jersey.

 

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FEFLOW

FEFLOW is an advanced 3D Finite-Element modeling solution offering sophisticated analysis tools and robust numerical algorithms.  FEFLOW is designed with an easy-to-use graphical interface that gives you all of the tools necessary to simulate:

• Steady-State or Transient Flow 

• Variably-Saturated Systems 

• Density-Dependent Flow 

• Heat and Mass Transport

• Fracture Flow

• Multiple Water Tables

FEFLOW is a popular groundwater model, and while many people use the product, they do not how some of the newest changes to the software can help with a variety of products.

Why upgrade to version 5.3?

New Mesh Generator: For the generation of the finite element mesh, the mesh generator Gridbuilder, developed by Rob McLaren at the University of Waterloo, Canada, is available. Gridbuilder has its main advantages in very flexible refinement along add-ins and polygon borders and in the handling of complex superelement meshes.

Optional Type 1 Boundary Condition input: Instead of using values of hydraulic head, the input of 1st kind (Dirichlet) boundary conditions can be done by using pressure values, setting a seepage face condition, automatically converting a saltwater head into a freshwater head or setting saturation or moisture content under unsaturated conditions.

Species-dependent Density Relationships: In the previous FEFLOW release concentrations of multiple species lead to a cumulative effect on fluid density, only considering one single density ratio. Now for each species a seperate ratio can be specified, considering different concentration-density relationships for the simulated species.

Scatter Plots for Comparison of Results and Observation Data:   Scatter point plots are now available for comparing both steady-state results with observation values and measured and calculated time curves. The locations of the compared points are indicated on the model domain, values are shown by tool tips.

Greek Characters as/in Variable Names: Greek characters can now be used in formulae as variable names or parts of variable names.

For more info click here:  FEFLOW
To purchase click here: Order Online

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