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A Modular Finite-Element Model (MODFE) for Areal and Axisymmetric Ground-Water-Flow Problems, Part 1: Model Description and User's Manual

U.S. Geological Survey, Techniques of Water-Resources Investigations, Book 6, Chapter A3

by Lynn J. Torak


Table of Contents

Abstract

Introduction

Background

Purpose and Scope

Governing Equation

Procedure for Applying the Modular Finite-Element Model (MODFE) to Ground-Water-Flow Problems

Design Considerations for the Finite-Element Mesh

Concepts of the Finite-Element Method

Shape of the Anticipated Potentiometric Surface

Aquifer Geometry and Hydrologic Boundaries

Points of Known Hydraulic Head and Stress

General Construction Rules

Identifying Discretization Error

Node Numbering and Determining Bandwidth

Techniques to Enhance Computational Efficiency

Definitions

Solution Methods

Direct: Triangular Decomposition

Iterative: Modified Incomplete-Cholesky Conjugate Gradient

Aquifer-Simulation Capabilities

Nonhomogeneity and Anisotropy

Steady Vertical Leakage

Vertical Leakage of Water Stored Elastically in a Confining Bed

Areally Distributed Sources and Sinks

Point Sources and Sib&s

Initial Condition of Hydraulic Head

Boundary Conditions

Specified Head

Specified Flux

Head-Dependent (Cauchy-Type) Flux

Cross Sections

Axisymmetric Flow

Flow to a Well

Boundary Conditions Parallel to Z Axis

Boundary Conditions Parallel to R Axis

Water-table (Unconfined) Conditions

Conversion Between Confined and Unconfined Aquifer Conditions

Drying and Resaturation of Aquifer Material

Nonlinear Head-Dependent Flux

Cauchy Type

Point Sinks

Steady Vertical Leakage and Evapotranspiration

Steady-State Flow

Linear Conditions

Nonlinear Conditions

Selecting Stress Periods and Time-Step Sizes

Changing Stresses and Boundary Conditions with Time

Data Preparation

Combined-Element Incidences

Hydraulic-Property and Boundary-Condition Zones

Grouping Elements into Zones

Zones for Nonlinear Steady Vertical Leakage, Transient Leakage, and Specific Yield

Grouping Element Sides into Zones

Input Instructions

References

Appendices

Definition of Input and Output Files

Examples of Model Input

Examples of Model Output

 


 

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