Troubleshooting Finite-Element Modeling with Abaqus - With Application in Structural Engineering Analysis

Foreword by Dr. Sonell Shroff

Foreword by Gautam Puri

Foreword by Prof. David Bassir

Preface

Acknowledgements

Contents

Abbreviations

Part I Methodology to Start Debugging Model Issues

1 Introduction

1.1 Global Mindset

1.2 The Four Absolutes of Quality in Analysis

1.3 Checklist for Performing Analysis

1.4 A Heuristic Analysis Confidence Ratio

References

2 Analysis Convergence Guidelines

2.1 Symptoms of Convergence Problems

2.2 Causes of Convergence Problems

2.3 Helping Abaqus Find a Converged Solution

2.4 General Tools

2.5 Tools for Contact Stabilization

2.6 Tools for Contact Related Convergence Problems

Reference

3 Method to Debug a Model

3.1 Debugging Flowchart

3.2 Job Diagnostic

3.2.1 Making a Test Model

3.2.2 Output Check

3.2.3 Syntax Check

3.2.4 Data Check

3.2.5 Loading and Boundary Conditions Check

3.2.6 Materials Check

3.2.7 Constraints Check

3.2.8 Elements Check

3.2.9 Interference Fits Check

3.2.10 Contact Check

3.2.11 Initial Rigid Body Motion and Over Constraints Check

3.2.12 Static Stabilization Check

3.2.13 Dynamics Check

3.3 Causality Energy Method

3.3.1 Basic Energy Approaches, Assumptions and Limitations

3.3.2 The Energy Method

3.3.3 Energy Method Example to Scale Analyses

3.3.4 Causality and Energy Derivatives

References

4 General Prerequisites

4.1 Vocabularies

4.1.1 Interpreting Error Messages

4.1.2 Interpreting Warning Messages

4.2 An Identified Unconnected Region in the Model

4.3 Correction of Errors During the Data Check Phase of an Abaqus/Standard Analysis

4.4 Tips and Tricks for Diagnostic Error Messages

4.5 Trying to Recover a Corrupted Database

4.5.1 Procedure 1

4.5.2 Procedure 2

4.6 Kinematic Distributing Couplings in Abaqus

4.6.1 Nature of the Constraint Enforcement

4.6.2 Defining Constraints in Abaqus/CAE

4.7 Abaqus Geometric Nonlinearity

4.8 Differences Between Implicit and Explicit Schemes

4.8.1 Equations for Dynamic Problems

4.8.2 Time Integration of the Equations of Motion

4.8.3 Automatic Time Incrementation with Abaqus Standard

4.8.4 Automatic Time Incrementation with Abaqus Explicit

4.8.5 Dynamic Contact

4.8.6 Material Damping

4.8.7 Half-Increment Residual Tolerance

4.8.8 Comparing Abaqus/Standard and Abaqus/Explicit

4.9 Unstable Collapse and Post-buckling Analysis

4.10 Low-Cycle Fatigue Analysis Using the Direct Cyclic Approach

4.11 Steady-State Transport Analysis

4.11.1 Convergence Issues in a Steady-State Transport Analysis

4.12 Heat Transfer Analysis

4.12.1 Transient Analysis

4.13 Fluid Dynamic Analysis

4.13.1 Convergence Criteria and Diagnostics

4.13.2 Time Increment Size Control

4.14 Introduction to the User Subroutines

4.14.1 Installation of a Fortran Compiler

4.14.2 Run a Model Which Uses a User Subroutine

4.14.3 Debugging Techniques and Proper Programming Habits

4.14.4 Examples of User Subroutine with Abaqus Standard

4.14.5 Examples of User Subroutine with Abaqus Explicit

4.14.6 Examples of User Subroutine with Abaqus CFD

References

Part II Stop Struggling with Specific Issues

5 Materials

5.1 Generalities

5.2 The Current Strain Increment Exceeds the Strain to First Yield

5.3 Convergence Behavior of Models Using Hyperelastic Materials

5.4 Models Using Incompressible or Nearly Incompressible Materials

5.5 Equivalence of Uniaxial Tension and Compression Hyperelastic Test Data

5.5.1 Uniaxial Compression Test Data for a Rubber Material

5.5.2 Specifying Tension or Compression Test Data for the Marlow Hyperelasticity Model

5.5.3 Using Simple Shear Experimental Data for Hyperelastic Materials

5.6 Path Dependence of Nonlinear Results Using an Elastic Material

5.7 User Material Subroutine

5.7.1 Guideline to Write a UMAT or a VMAT

5.8 UMAT Subroutine Examples

5.8.1 UMAT Subroutine for Isotropic Isothermal Elasticity

5.8.2 UMAT Subroutine for Non-isothermal Elasticity

5.8.3 UMAT Subroutine for Neo-Hookean Hyperelasticity

5.8.4 UMAT Subroutine for Kinematic Hardening Plasticity

5.8.5 UMAT Subroutine for Isotropic Hardening Plasticity

5.8.6 UMAT Subroutine for Simple Linear Viscoelastic Material

5.9 VUMAT Subroutine Examples

5.9.1 VUMAT Subroutine for Kinematic Hardening Plasticity

5.9.2 VUMAT Subroutine for Isotropic Hardening Plasticity

References

6 Mesher and Meshing

6.1 Generalities

6.1.1 Mesh Control Options

6.1.2 Mesh Controls for a 2D Structure

6.1.3 Mesh Controls for a 3D Structure

6.1.4 Understanding a Mesher

6.1.5 Mesh as Grid Generation

6.2 The Abaqus Model Meshed Has Changed into a Nonphysical Shape with a Regular Pattern

6.3 Excessive Element Distortion Warnings

6.4 Compatibility Errors Printed to the Message File for a Model with Hybrid Elements

6.5 User Element Subroutine

6.5.1 Guideline to Write a UEL

6.6 UEL Subroutine Examples

6.6.1 UEL Subroutine for Planar Beam with Nonlinear Cross Section

6.6.2 Generalized Constitutive Behavior

6.6.3 UEL Subroutine for a Horizontal Truss and Heat Transfer Element

6.6.4 UELMAT Subroutine for 4 Nodes in Plane Strain

6.7 Using Nonlinear User Elements in Various Analysis Procedures

References

7 Contact

7.1 Generalities

7.1.1 Understandings

7.1.2 Define Contact Pairs

7.1.3 Define General Contact

7.1.4 Representation of Curved Surfaces

7.1.5 Contact Formulation Aspects

7.2 Friction

7.2.1 Static and Kinetic Friction

7.2.2 Change Friction Properties During an Analysis

7.2.3 Classic Friction Values

7.3 Hard or Soft Contact

7.3.1 Identification of the Mathematical Stiffness Function

7.3.2 Exponential Contact Stiffness

7.3.3 From Hard Contact to Exponential

7.4 Obtain a Converged Contact Solution

7.5 Convergence Difficulty in the First Increment

7.6 Causes and Resolutions of Contact Chattering

7.7 Understand Finite Sliding with Surface-to-Surface Contact

7.8 Using Penalty Contact

7.9 Using Augmented Lagrangian Contact

7.10 Using Stiffness-Based Contact Stabilization

7.11 Modeling Contact with Second-Order Tetrahedral Elements

References

Part III A Toolbox to Do the Job

8 Troubleshooting in Job Diagnostics

8.1 Guidelines with Abaqus Standard

8.2 Job with Abaqus Standard Completes, But the Results Look Suspicious

8.3 Model a Structure Undergoing a Global Instability

8.4 Correct Convergence Difficulties Caused by Local Instabilities

8.5 Correcting Errors During the Data-Check Phase of an Analysis

8.6 Analysis Ends Prematurely, Even Though All the Increments Have Converged

8.7 Debugging Divergence with Too Many Cutbacks in the Last Attempted Increment

8.8 Using Follower Loads in Nonlinear Analyses

8.9 Understanding Negative Eigenvalue Messages

8.10 Divergence with Numerical Singularity Warnings

8.11 Zero Pivot Warnings in the Message File

8.12 Convergence Difficulty in the First Increment of a Contact Analysis

8.13 Explicit Stable Time Increments When Using the Marlow Model with Noisy Test Data

8.14 Cause of an Analysis Ending in a Core Dump

8.15 Debugging User Subroutines and Post Processing Programs

8.16 No Free Memory Available on Linux at the End of an Analysis

Reference

9 Numerical Acceptance Criteria

9.1 Generalities

9.1.1 Commonly Used Control Parameters

9.1.2 Controlling the Time Incrementation Scheme

9.1.3 Activate the Line Search Algorithm

9.1.4 Controlling the Solution Accuracy in Direct Cyclic Analysis

9.1.5 Controlling the Solution Accuracy and Mesh Quality in a Deforming Mesh Analysis with Abaqus CFD

9.1.6 Convergence Criteria for Nonlinear Problems

9.1.7 Time Integration Accuracy in Transient Problems

9.1.8 Avoid Small Changes to the Time Increment Size During Implicit Integration Procedures

9.2 How Much Hourglass Energy Is Acceptable

9.2.1 Enhanced Hourglass Control and Elastic Bending Moment

9.2.2 Enhanced Hourglass Control and Plastic Bending Moment

9.2.3 Kelvin Viscoelastic Hourglass Control

9.3 Errors Printed to the Message File for a Model with Hybrid Elements

Reference

10 Need Some Help?

10.1 Retrieving Files Referred to Examples in the Abaqus Documentation

10.2 Using the Abaqus Verification, Benchmarks, and Example Problems Guides

10.3 Excessive Memory Usage with Cavity Radiation Problems

10.4 Perform a Sub-model Analysis

10.4.1 Implementation

10.4.2 Loading Conditions

10.4.3 Sub-model Boundary Conditions

10.4.4 Interpolation

10.4.5 Step-by-Step Procedure for a Sub-model

10.4.6 Setting Options

10.4.7 Shell to Solid

10.4.8 Changing Procedures

10.4.9 Frequency Domain

10.4.10 Thermal and Stress Analysis

10.4.11 Dynamic Analysis

10.4.12 Limitations of Sub-modeling

10.5 Perform a Restart Analysis

10.5.1 Step-by-Step Procedure for a Restart

10.6 Generate a Shell Part from a Solid Part

10.6.1 Benefits for Using Shell Structures

10.6.2 Applications to Model Shell Structures

10.6.3 Step-by-Step Procedure to Convert Solid Model to Shell Model

10.7 Compile and Link a Post-processing Program Using the Standalone Abaqus ODB API

10.8 Create Executables Using the C++ ODB API Libraries Outside of Abaqus/Make

11 Hardware or Software Issues

11.1 Solving File System Error 1073741819

11.2 Interpreting Error Codes

11.3 Obtaining a Traceback from a UNIX/Linux Core Dump

11.4 Windows HPC Compute Clusters

11.4.1 Classics Troubleshooting with HPC Cluster

Reference

Appendix Guidelines and Good Practices Examples

A.1 Using *COUPLING to Simulate Pure Bending of Thin Walled Pipes

A.2 Available Degrees of Freedom with Kinematic Relation at Coupled Nodes

A.3 Stability and Accuracy of the Trapezoidal Rule

A.4 Accuracy Control in Highly Nonlinear Problems with a Half-Increment Residual Tolerance

A.5 The Art of Meshing

A.5.1 Free Meshing Technique

A.5.2 Model Partitioning with a Strategy Based on Design Symmetry

A.5.3 Model Partitioning with a Strategy Based on the Dominant Geometry

A.5.4 Small Edges and Consequences for the Mesher

A.5.5 Incompatible Mesh

Index