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Volker Clausnitzer

Introduction to FEFLOW

DHI Groundwater Modelling Centre

www.dhi-wasy.de

FEFLOW – More than GroundwaterFEFLOW handles groundwater flow and related processes in one software environment, one user interface, and one simulation model:

• Variably saturated flow • Contaminant transport• Heat transport• Density-affected flow• Chemical reactions• And more ...

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FEFLOW – More than GroundwaterPrimary development goal: FEFLOW is intented to be

•Easy to use and intuitive – to quickly master everyday groundwater projects,

but at the same time

•Powerful and comprehensive –to model complex subsurface processes.

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Complex Processes - Geometry– Finite-element discretization– Triangular or quad elements (2D)– Prisms or cuboids (3D)– 3D or 2D horizontal/vertical/axisymmetric projection– 1D and 2D for fracture/pipe/borehole flow

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Complex Processes - PhysicsGroundwater and vadose-zone flow

• Saturated flow (Darcy law)• Unconfined conditions (different approaches)• Unsaturated / variably saturated flow (Richards equation)• Fracture flow• Density- and viscosity-dependent flow

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Complex Processes - PhysicsTransport

• Heat transport (advection-conduction equation)• Solute transport (advection-diffusion equation)• Combined solute/heat transport• Sorption, Decay• Multispecies simulation• Kinetic reaction systems

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Ease of use

• User interface for preprocessing, simulation, and postprocessing• GIS/CAD/ASCII file interfaces for import and export• 2D/3D map support• Advanced computational methods

– Powerful mesh generators– Automatic time-stepping scheme– Algebraic multigrid solver– Parallelization

• …

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Visualization

• 2D top / cross-section views• 3D views

• 2D / 3D map support• 3D clipping and carving• Live, interactive visualization

during simulation run

• Hardware acceleration via OpenGL

• 3D stereoscopic display/projector support currently in betatesting

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FEFLOW Viewer• Free (no license required)

• Works with existing FEFLOW models

• Visualization and analysis

• Export of figures and animations

• Model and results files

• Use by modeler

– No license necessary for postprocessing

– Share your model with colleagues even if licenses are limited

• Usage by consulting clients

– No need to purchase an additional license

– Deliver viewable model files to customers

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Extensibility• Open programming interface

– Documented API interface– User can develop plug-ins for

o Additional functionalityo Workflow automation

• Application Examples– Groundwater / surface water coupling– Integration of technical installations in geothermal modeling– Import of model properties– Export of model results

• Development Services– Plug-in development as a consulting service

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Fields of Application• Regional groundwater management

• Mine water management

• Construction and tunneling

• Groundwater – surface water interaction

• Agriculture (irrigation, drainage, salinization, nutrient management)

• Remediation / natural attenuation

• Capture-zone delineation

• Saltwater intrusion

• Geothermal energy

• Industrial porous materials

• …

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FEFLOW Community

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FEFLOW Community

www.feflow.info/forum

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User Support• We help by

– Giving advice on FEFLOW modeling

– Analyzing possible model improvements

– Explaining theoretical background and functionality

• In addition, we offer– Training courses– Solutions– Software customization– Consulting in modeling

projects– Model review

FEFLOW ServicesTeam

Support

Training

Plug-in Solutions

Dipl.-Ing. Alexander Renz

Dipl.-Ing. Julia Mayer

Dipl.-Ing.Bastian Rau

Dipl.-Ing. Peter Schätzl

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Why FEFLOW?• Highly scalable software package

– Different feature levels available• Optimal cost efficiency for every application• Upgrades possible at any time

– One software for current and future projects• No need for additional software and training• Saves time and money

• Commercial software– DHI guarantees consistent services– Close contact to support staff– Software performance benchmarked and documented– Quality assurance– Ongoing development

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Application Examples

1. Optimization of landscape water regime

2. Construction of an underground liquefied natural-gas storage system

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Agricultural Development PlanningGlietzener Polder, Germany

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ObjectivesConcept for landscape water regime that accommodates agricultural, environmental, and general landscape water balance goals:

•Improvement of agricultural conditions

•Sustainment of low-water discharge, securing of minimum discharge in low-water periods•Improvement of groundwater and surface water quality•Flood protection•Improvement of the ecological role of water bodies

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Potential for conflict

AgricultureEnvironment

Landscape waterbalance

Conflicting Objectives

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Approach

1. Calculation of groundwater and surface water levels applying a coupled GW-SW model for different system states

2. Calculation of depth to groundwater using the groundwater levels and a DEM

3. Intersection of depth to groundwater with defined target levels, definition of areas of conflict

4. Simulation of scenarios lowering the potential for conflict, using the target levels as goal for future planning

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FEFLOW

Coupled Model FEFLOW-MIKE11

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Target Compliance, Initial State (March)

too drytoo wetacceptable

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Planned Measures• Modification of target water levels for pumping stations• Adaptation of structures, change of storage levels• Installation of weirs and low weirs (ground sills)• Desludging of ditches• Closure of Altreetz pumping station

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Paulshof I

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März (Plan - Ist)[m]

> 0.30.25 - 0.300.20 - 0.250.15 - 0.200.10 - 0.150.05 - 0.10-0.10 - -0.05-0.15 - -0.10-0.20 - -0.15-0.25 - -0.20< -0.25

Entschlammungs-strecken

Predicted Change in Water Level

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SW-Gebiet Paulshof I

0

5

10

15

20

25

30

35

40

45

50

Jan Feb März Apr Mai Jun Jul Aug Sept Okt Nov Dez

Monat

Fläc

hena

ntei

l [%

]Ist-Zustand Plan-Zustand

Target Compliance

PredictedInitialFr

actio

n of

Tot

al A

rea

[%]

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

Area Controlled by Pumping Station Paulshof I

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-3500

-3000

-2500

-2000

-1500

-1000

-500

0

500

1000

1500

2000

Zollb

rück

e

Paulsh

of I

Bienen

werde

r

Gabow

Zäck

erick

er Lo

ose

Paulsh

of II

Nasse

r Pold

er

Altreetz

SW-Gebiete

Diff

eren

z (b

erec

hnet

[Pla

n]-g

emes

sen

[Ist])

[m

³/d]

Reduction of pumped water quantity by 8%

~1.7 million m³/yr

Modification of Pumping Rates

Cha

nge

from

initi

alpu

mpi

ngra

te[m

3 /d]

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Cavern Construction for LNG Storage

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Ice RingIce Ring

InsulationInsulation

Stainless Stainless SteelSteel

CavernCavernLNG

-162° C

Principle

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Simulation Objectives

• Represent the dewatering process over a 4-year construction period with a complex construction schedule

• Inflow/drainage for all parts of the underground structure• Impact on groundwater level in the surrounding area• Seawater intrusion potential

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• Density-dependent variably saturated flow

• Advective-dispersive transport of dissolved constituents

Physical Processes

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Model Domain

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Model Domain

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Superelement mesh

•253 polygons

•463 lines

Spatial Discretization

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Finite-element mesh

•956,125 elements

•498,914 nodes

Spatial Discretization

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Finite-element mesh – Cavern structures

Spatial Discretization

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Finite-element mesh – Cavern structures

Spatial Discretization

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Saturated conductivity

Porosity

Granitic Gneiss 10-9…10-8 m/s 1%

Mica Schist 10-7 m/s 1%

Altered zone 1…2 x 10-6 m/s 5%

Insulation 10-11 m/s 1%

Material Properties

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Kr = Seffδ

Seff = (1 + |αψ|-n)-m

δ = 2

α = 0.1 m-1 n = 1.964 m = 0.509

Effective saturation vs. Pressure head

Relative conductivity vs. Effective saturation

Material Properties

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Groundwater recharge

Boundary Conditions

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Flow (Hydraulic head)

• Dirichlet condition along coastline

• No-flow (zero-value Neumann) condition elsewhere

Transport (Solute concentration)

• Dirichlet (fixed-concentration) condition for infiltrating seawater along coastline

• Zero-value Neumann condition for fluid leaving domain along coastline

• Impermeability condition elsewhere

Boundary Conditions

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Internal surfaces of the structure are treated asSeepage face

• Dirichlet condition of fixed atmospheric pressurefor outwarding-pointing head gradient

• No-flow (zero-value Neumann) condition otherwise

Boundary Condtions

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Simulation requires successive activation of seepage-face B.C.’s as construction progresses.

New B.C.’s must continuously be introduced during the simulation.

Solution:

Seepage-face activation via a separate module using the FEFLOW Open Programming Interface:

• arbitrary node groups and activation intervals

• arbitrary pressure

• import capability from ASCII files

• saves all information with the problem file

Transient Boundary Conditions

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Steady-state head and solute-concentration distributions obtained for undisturbed conditions

Initial Condition

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0 d0 d 360 d360 d

720 d720 d 1080 d1080 d

Pressure

Simulation Results

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Pressure

0 d

360 d

720 d

1080 d

Simulation Results

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Solute concentration

Simulation Results

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Groundwater table

Simulation Results