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About this book

This book gives Abaqus users who make use of finite-element models in academic or practitioner-based research the in-depth program knowledge that allows them to debug a structural analysis model. The book provides many methods and guidelines for different analysis types and modes, that will help readers to solve problems that can arise with Abaqus if a structural model fails to converge to a solution. The use of Abaqus affords a general checklist approach to debugging analysis models, which can also be applied to structural analysis.

The author uses step-by-step methods and detailed explanations of special features in order to identify the solutions to a variety of problems with finite-element models. The book promotes:

• a diagnostic mode of thinking concerning error messages;

• better material definition and the writing of user material subroutines;

• work with the Abaqus mesher and best practice in doing so;

• the writing of user element subroutines and contact features with convergence issues; and

• consideration of hardware and software issues and a Windows HPC cluster solution.

The methods and information provided facilitate job diagnostics and help to obtain converged solutions for finite-element models regarding structural component assemblies in static or dynamic analysis. The troubleshooting advice ensures that these solutions are both high-quality and cost-effective according to practical experience.

The book offers an in-depth guide for students learning about Abaqus, as each problem and solution are complemented by examples and straightforward explanations. It is also useful for academics and structural engineers wishing to debug Abaqus models on the basis of error and warning messages that arise during finite-element modelling processing.

Table of Contents

Frontmatter

Methodology to Start Debugging Model Issues

Frontmatter

Chapter 1. Introduction

Abstract
Dealing with troubleshooting in FEA is a particularly common phase met by all analysts performing such tasks. Whatever the level of expertise of the analyst, students, young engineers, experts, and specialists in industries or in education schools, all have to struggle with troubleshooting at some point to solve a numerical problem using FEA software. Troubleshooting is therefore a consequence, but what is the cause? Prior to exploration of software features messages pointing out an error or warning issues, the definition of the formulation of a physics problem description into a machine language is the key milestone in minimizing the risk of troubleshooting. So what do analyst call, a consistent conditioning of the finite-element model to ensure its stability with the solver? The present chapter gives a methodology to make this translation between the space of physics to the numerical recipes as a guideline for analysts and good practices to perform FEA.
Raphael Jean Boulbes

Chapter 2. Analysis Convergence Guidelines

Abstract
The introduction chapter has provided a main focus on the methodology to minimize the risk of troubleshooting during analysis. A quality mindset and philosophy have been also given as a recommended way of working and as a good practice to follow in order to conduct an analysis properly. In order to minimize the convergence issue that will be described inside this chapter, there are two important phases to keep in mind to perform analysis as milestones of the modeling process: first, the phase (2) shown in Fig. 1.​1 and called the specification of work to define precisely what is the main analysis concern, and second, the phase (5) shown in Fig. 1.​1, which is related to the inspections of input data gathered to start computing the model. This chapter now will explain some potential causes of troubleshooting in general. Some convergence issues in the model and some tools will be given to avoid or to fix some common problems during the solution processing.
Raphael Jean Boulbes

Chapter 3. Method to Debug a Model

Abstract
The main aim of this chapter is to describe a methodology in order to perform a job diagnostic on a model which did not converge. Following the global mindset in chapter one along with the example of a global overview analysis flowchart methodology in Fig. 1.​1, this chapter will focus on a step-by-step procedure to establish convergence with the model showing different analysis techniques as a function of the modeling phases needed to create the model with Abaqus features. The procedure described here is therefore a deeper understanding of the single cell titled “-Job diagnostics” in Fig. 1.​1, showing users a logical approach toward corrective actions inside a puzzle of numerical difficulties.
Raphael Jean Boulbes

Chapter 4. General Prerequisites

Abstract
Within this chapter, users will find a general overview of Abaqus solver options, convergence issues, features definitions and usage plus a description of physics the solver can handle. It starts with the vocabulary and translation of error and warning messages in engineering terms; to fix troubleshooting errors, first users need to understand them. Classic preliminary control milestones with tips and tricks are also given to make debugging more efficient. Differences between both Abaqus solvers standard and explicit have been explained with the procedures and option settings, to stop struggling with time increment. Additional solver options and coupled field analyses including CFD are also clearly detailed to get stability and convergence in FEA model. After reading this chapter, users will have gained complementary knowledge regarding troubleshooting prevention.
Raphael Jean Boulbes

Stop Struggling with Specific Issues

Frontmatter

Chapter 5. Materials

Abstract
One of the main troubleshooting issues to deal with involves the material properties and definition of nonlinearity after the elastic behavior. In this chapter, details of large strain connected with the material law of behavior, especially, those used for hyperelasticity and rubber materials are given. The user will also find useful informations when the material definition is coupled with the User Material (UMAT) file to establish the correct settings or debugging protocol. The classic basis of a viscoelastic–plastic material behavior is still explained with a simple uniaxial stress versus strain curve, in order to prevent the reader from becoming overloaded by too many theory details, for instance, those available inside theoretical Abaqus documentation.
Raphael Jean Boulbes

Chapter 6. Mesher and Meshing

Abstract
Meshing part is one of the most challenging parts in FEA modeling and there is no way to link some theoretical criteria applicable for a categorization or standardization of the model. Because each model is almost unique despite similar designs, small changes always lead to a new thinking to mesh the structure. The mesh pattern is geometry dependent but independent of boundary and loading conditions, which explains the need to understand mesher features first. This can be seen more like an artistic mesh as opposed to an accurately physics-related one. However, all types of art obey rules and principles and these are described inside this chapter with a deep understanding of what an Abaqus mesher is and what it can do. That the best way to minimize troubleshooting with mesh element distortions.
Raphael Jean Boulbes

Chapter 7. Contact

Abstract
This chapter will investigate the contact interaction physics and contact properties implemented with both Abaqus standard and explicit solvers. Contact definition is a source of high nonlinearity in FEA model and therefore, a good understanding regarding how to make a correct representation of physics in the model with the proper parameters will help to avoid numerical difficulties or an unconverged solution. Contact interactions are less complex to understand but more difficult to use because of the multiple combinations of settings to make a proper contact definition. This is why the sections in this chapter will take a closer look at contact generalities, contact and friction, hard and soft contact, and then different procedures used to fix certain troubleshooting issues related to contact. A series of examples will also be given to have a better overview of some option setting consequences.
Raphael Jean Boulbes

A Toolbox to Do the Job

Frontmatter

Chapter 8. Troubleshooting in Job Diagnostics

Abstract
The content of this chapter will provide solutions and procedures to fix some common and uncommon troubleshooting issues, mainly with Abaqus standard. Clear explanations and guidances regarding error and warning messages related to the troubleshooting obtained from the Abaqus model are given here with a step by step guideline in order to understand all the different potential causes of numerical difficulties or the unconverged solutions from the user model. All the different packages used to carry out troubleshooting are the core of the job diagnostics used as a toolkit by analysts to make the FEA model run properly. The troubleshooting descriptions are a nonexhaustive list of problems which an analyst can address with an Abaqus model.
Raphael Jean Boulbes

Chapter 9. Numerical Acceptance Criteria

Abstract
Numerous control parameters are associated with the convergence and integration accuracy algorithms in Abaqus standard. These parameters are assigned default values that are chosen to optimize the accuracy and efficiency of the solution for a wide spectrum of nonlinear problems. The user can change the solution control parameters, as described in the following chapter, to help the convergence solution or optimize the accuracy versus computational time. As these parameters are only defined for solver purposes, the user needs to get some knowledge about what can be mainly set with these parameters to obtain a proper converged solution. Parameters which also need to be modified properly in accordance with the physics of the FEA model in order to ensure a realistic results. A summary of essential considerations regarding these criteria come from the definitions and recommendations written in Abaqus documents.
Raphael Jean Boulbes

Chapter 10. Need Some Help?

Abstract
In addition to carrying out diagnostics regarding error or warning messages, it can be useful to have a global overview of how Abaqus documentation can help users looking for some close examples in different expertise field and in some analysis skills. The analysts will be able also to find some additional procedures to use on FEA model types is given to allow sub-modeling, restart and Shell models, for instance, to be performed correctly. The content of this chapter complements the troubleshooting by providing users with more information about modeling techniques and good practice to perform analyses.
Raphael Jean Boulbes

Chapter 11. Hardware or Software Issues

Abstract
Some troubleshooting are not related to simulation, but need to be fixed prior to compute a solution. In this chapter the user will find the most critical error code due to non-simulation issues, these issues and errors are quite different from ones like numerical singularity warnings or convergence errors. As such, they are not problems in the finite-element model, but are issues with software bugs, operating system, hardware, and so on. In addition, the user will find a complete cluster solution implementation to multi-process the computed solution provided by Microsoft with Windows HPC Compute Clusters.
Raphael Jean Boulbes

Backmatter

Additional information

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