feflow_user_manual_classic.pdf

A b c nqs ? rëéêû? jåìä j mêí ff nmk

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NQS ö rëÉêÛë j~åì~ä J m~êí ff NMK qìíçêá~ä NMKQKP píÉé O J ^ëëáÖåãÉåí ~åÇ ÅçåJ íêçä áå íÜÉ éêçÄäÉã ÉÇáíçê After having defined the basic stratigraphy and hav- ing added the buffers we need to reassign some prob- lem attributes and control the data flow. Return to the Problem editor menu. NMKQKPKN mêçÄäÉã Åä~ëë Switch the Problem class to Transient flow/ transient transport of an Unconfined aquifer for fully Saturated media. Click on the Edit free surface(s) button in the lower part of the menu. The Free surface(s) editor pops up. Here you can define the hydraulic properties of the slices. We will use the BASD technique for this simula- tion. For the theory of the Best-adaptation-to-strati- graphic-data method see the Reference Manual (Section 2.4). Using the BASD technique the finite ele- ment mesh is adapted in the z -direction in according to the movement of the upper water table as described by the hydraulic head at the top slice. All inner slices also change their vertical positions; FEFLOW computes their respective optimum position so as to maintain the stratigraphy-related information without smoothing (interpolating) the data from adjacent layers. In other words, it finds the best adaptation to the stratigraphic data. Only slices set to fixed or phreatic will not be moved. This technique is often useful in modeling multi-layer aquifer systems. The following slice types can be set: Free & movable : Only the top slice for free surface problems, BASD automatically activated. Phreatic : Defines the top of an unconfined aquifer; the slice cannot move and should be sepa- rated from a free & movable slice by a fixed slice. Fixed : Slice defines the top of a confined aqui- fer or aquitard. It cannot move. A free & movable slice cannot move below a fixed slice in case of an overlaying aquifer falling dry, instead natural con- straints are activated that force the water table to remain above the fixed slice (Reference Manual, Part I). Unspecified : For movable meshes FEFLOW adapts the slice automatically depending on the definition of the adjacent slices. Set the slices so that the upper layer is unconfined and movable while the lower aquifer is confined (free & movable, unspecified, unspecified, fixed, unspeci- fied, fixed). Now leave the Problem class menu. NMKQKPKO cäçï áåáíá~äë Make sure that the flow initials are set on every slice. Use the Copy tool (below the Assign tool, light blue button) if initials are missing on slices. Figure 10.24 Three-dimensional free surface definition.
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cbcilt SKM `ä~ëëáÅ ö NQT NMKQ qÜÉ Pa jçÇÉä NMKQKPKP cäçï ÄçìåÇ~êáÉë • 1st kind: applied only to the upper two slices. Use the Erase button for the remaining slices; • 2nd kind: on every slice belonging to an aquifer, not on slice 3 and 4; • 3rd kind: on the two upper slices.
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