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ANSYS Mechanical APDL for Finite Element Analysis ANSYS Mechanical APDL for Finite Element Analysis Mary Kathryn Thompson, PhD John M. Thompson, PhD, PE Butterworth-Heinemann is an imprint of Elsevier The Boulevard, Langford Lane, Kidlington, Oxford OX5 1GB, United Kingdom 50 Hampshire Street, 5th Floor, Cambridge, MA 02139, United States Copyright © 2017 Elsevier Inc. All rights reserved. No part of this publication may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher. Details on how to seek permission, further information about the Publisher’s permissions policies and our arrangements with organizations such as the Copyright Clearance Center and the Copyright Licensing Agency, can be found at our website: www.elsevier.com/permissions. This book and the individual contributions contained in it are protected under copyright by the Publisher (other than as may be noted herein). Notice This book is solely intended for educational purposes. The examples and exercises contained within are purely hypothetical and based on simplified mechanical components and systems. In real world applications, the knowledge gained from this book must be combined with the facts of the particular situation, and the accumulated knowledge and experience of coworkers and supervisors. The authors, the publisher of this book, and the creators and licensor of the ANSYS Mechanical APDL software, therefore do not make any representation or warranty of any kind that this book and such software and documentation will prevent a problem which may arise when this book and such software and documentation are used in a particular real world situation. As engineers, you and your coworkers and supervisors are responsible for determining how to build a finite element model; what properties, values, and assumptions to include; whether or not the results of your model can be used to make or justify engineering decisions; and for the decisions that you and they ultimately make. The authors, the publisher, and ANSYS Inc. make no warranties, express or implied, and assume no liability for any work that you do based on, or after having read, this book. They also make no representation, expressed or implied, regarding the accuracy of the information in this book. When using knowledge gained from this book for an engineering project, the decisions which are made throughout the project, including decisions about the use of the ANSYS Mechanical APDL program and its documentation, should be reviewed and approved by an experienced licensed engineer or by the certification agency that has jurisdiction over the project. British Library Cataloguing-in-Publication Data A catalogue record for this book is available from the British Library Library of Congress Cataloging-in-Publication Data A catalog record for this book is available from the Library of Congress ISBN: 978-0-12-812981-4 For Information on all Butterworth-Heinemann publications visit our website at https://www.elsevier.com/books-and-journals Publisher: Joe Hayton Acquisition Editor: Brian Guerin Editorial Project Manager: Katie Chan Production Project Manager: Kiruthika Govindaraju Cover Designer: Mary Kathryn Thompson, John M. Thompson, Mark Rogers Typeset by MPS Limited, Chennai, India To Veronica Mother, Wife, Inspiration Preface Commercial finite element programs provide a powerful and extensive collection of tools for the design, analysis, and optimization of complex engineering systems. Unfortunately, learning to use finite element software can be a difficult and time-consuming process. This book was written to reduce the learning curve associated with ANSYS Mechanical APDL and to prepare you to use the program and its documentation as quickly and painlessly as possible. This book was written using the Academic Research version of ANSYS Mechanical APDL 17.2. Since ANSYS Mechanical APDL was designed to be backward compatible, you should be able to use the book with future versions of the program as well. We have marked information in the book that we believe is likely to become out of date quickly, such as specific product names and the number of reference manuals for a given product, with a superscript asterisk (�) for your reference. An appendix has also been included to help you to identify specific information in the program documentation, even if the documentation numbering changes. However, the authors of this book are not involved with changes that may be made in the future to the ANSYS Mechanical APDL software or the related documentation. Therefore the asterisks and appendix are for guidance only and may not identify all future changes in such software or documentation. Each chapter in the book includes suggested readings from the ANSYS Mechanical APDL user manuals. Most chapters are also accompanied by one or more hands-on exercises. This book does not duplicate or replace the information in the documentation. Instead, it is intended to help you to understand and use the documentation. Thus the reading assignments in the ANSYS user manuals are strongly recommended. To help you develop comfort and confidence as an independent analyst, each exercise introduces new skills and increases the complexity of the models while gradually decreasing the amount of guidance given. We recommend completing all of the exercises, even if they are not immediately relevant to your work. This book can be used for self-study or as part of a formal course in finite element applications. It is suitable for professional engineers and engineering students at all levels. When you have finished the book, you should be able to use the present ANSYS documentation to build, solve, and postprocess sophisticated finite element models on your own. The world is full of interesting and important problems. This book gives you some of the tools that you need to help solve them. Good luck! Mary Kathryn Thompson and John M. Thompson Pittsburgh, PA, USA xv Acknowledgments This book was originally developed as the course text for a graduate level IAP course at the Massachusetts Institute of Technology (MIT). The goal of that course was to prepare students to perform research quality finite element analyses with ANSYS in 5 days or less. We began writing in 2002 and began teaching with the book in 2004. In 2008 the book and the course moved to Korea. In 2012 the book moved to Denmark. And in 2016 it moved home again to the United States. Over the years, we have received a tremendous amount of support from wonderful people all over the world. We would like to acknowledge some of them here. The software licenses for the MIT IAP course and for the development of this book were provided through an ANSYS Academic Partnership. We are grateful for the generous support that we have received from ANSYS, Inc. over the years. We would especially like to acknowledge the late Mr. Jerry Bittner, former Director of ANSYS Global Technical Services, who started this journey with us, and Dr. Paul Lethbridge, Senior Manager for Academic and Start Up Programs at ANSYS, who saw it through to the end. We would also like to thank Sheryl Ackerman, Cordell Blackshere, Vishal Ganore, Helen Renshaw, and the rest of the incredible team, past and present, at ANSYS Worldwide Headquarters in Canonsburg, PA, USA. We would like to thank Prof. Alexander H. Slocum, Prof. Rohan Abeyaratne, Prof. David M. Parks, Prof. Lallit Anand, Prof. Thomas Peacock, and the MIT Department of Mechanical Engineering; Prof. Heekyung Park, Prof. Chung-Bang Yun, and the KAIST Department of Civil and Environmental Engineering; and Prof. Hans Nørgaard Hansen, Prof. Leonardo De Chiffre, and the DTU Department of Mechanical Engineering for their encouragement and support of this project as it has traveled around the world. We would like to acknowledge Dr. Veronica V. Thompson for her tremendous assistance in editing this book. She has helped us to become the writers we are. We would like to thank Anne M. Thompson and Will C. Lauer for all of their logistical and moral support over the years. We could not have done it without them. We would like to thank Courtney S. Bermack, Jeffrey Chambers, Chad Foster, Marissa Jacovich, Christina Laskowski, Michael Mischkot, A. Zachary Trimble, and Antonio Vicente for their help in testing and improving various versions of this book. Their help and feedback is greatly appreciated. We would like to thank our wonderful publication team at Elsevier, especially Brian Guerin, Katie K. Chan, and Kiruthika Govindaraju who made this process a pleasure. Finally, we would like to thank Prof. Nam P. Suh, Prof. Donald A. Norman, Prof. Sami Kara, and Prof. Guan Heng Yeoh. They have all provided crucial advice and opportunities at critical times. We are glad to have traveled with them on this journey. xvii Chapter 1 Introduction to ANSYS and Finite Element Modeling Suggested Reading Assignments: None CHAPTER OUTLINE 1.1 What Is the Finite Element Method? 1.2 Why Use the Finite Element Method? 1.3 Basic Procedure for Finite Element Analysis 1.4 Engineering Software—Not an Engineer 1.5 A Brief History of ANSYS and Finite Element Analysis 1.6 ANSYS Today* 1.7 ANSYS Licensing 1.8 Functionality and Features of the ANSYS Mechanical APDL Family 1.9 ANSYS: Backward Compatibility and Legacy Code This chapter provides an introduction to finite element analysis and the ANSYS Mechanical APDL family of software. It begins with an overview of the finite element method, its benefits, and its limitations. It summarizes the current ANSYS Mechanical APDL products and program capabilities. Finally, it describes the program’s evolution and how that influences the use of ANSYS, Inc. products. 1.1. What Is the Finite Element Method? The finite element method (FEM) is a mathematical technique for setting up and solving systems of partial differential (or integral) equations. In engineering, the finite element method is used to divide a system whose behavior cannot be predicted using closed form equations into small pieces, or elements, whose solution is known or can be approximated. The finite element method requires the system geometry to be defined by a number of points in space called nodes. Each node has a set of degrees of freedom (temperature, displacements, etc.) that can vary based on the inputs to the system. These nodes are connected by elements that define the mathematical interactions of the degrees of freedom (DOFs). For some elements, such as beams, the closed form solution is known. For other elements, such as continuum elements, the interaction among 1 ANSYS Mechanical APDL for Finite Element Analysis. DOI: http://dx.doi.org/10.1016/B978-0-12-812981-4.00001-0 Copyright © 2017 Elsevier Inc. All rights reserved. the degrees of freedom is estimated by a numerical integration over the element. All individual elements in the model are combined to create a set of equations that represent the system to be analyzed. Finally, these equations are solved to reveal useful information about the behavior of the system. Just as a regular polygon approaches a perfect circle as the number of sides approaches infinity, a finite element model approaches a perfect representation of the system as the number of elements becomes infinite. Since it is impossible to divide the system into an infinite number of elements, the finite element method produces the exact solution to an approximation of the problem that you want to solve. When the number of elements becomes sufficiently large, the approximation becomes good enough to use for engineering analysis. However, this may increase the number of equations to be solved beyond the point where it is practical or desirable to solve them by hand. For this reason, the finite element method is associated with computer programs that set up, solve, and visualize the solutions of these large sets of equations for you. 1.2. Why Use the Finite Element Method? The cost, in terms of the manpower and computer resources, required to set up and solve a finite element model for a simple problem like a cantilever beam is very high compared to the benefit. Simple problems can—and should—be solved with simple methods (or obtained from engineering handbooks). But not all problems are simple. For example, if a bridge is built using a simple truss supported by two piers, the deflections and stresses in the bridge can be found using information taught in an introductory statics and strength of materials class. But as the complexity of the truss increases, solving this problem using the engineering fundamentals becomes more difficult, leaving the analyst with long hours of error-prone calculations. As system complexity continues to increase, closed-form analysis rapidly becomes impossible. The real benefit of finite element analysis lies in the ability to solve arbitrarily complex problems for which analytical solutions are not available or which would be prohibitively time consuming and expensive to solve by hand. 1.3. Basic Procedure for Finite Element Analysis There are 10 basic steps in any finite element analysis. First, the solid model geometry is created, the element type(s) and material properties are defined, and the solid model geometry is meshed to create the finite element model. In ANSYS, these steps are performed in the Preprocessor (PREP7). Next, loads and constraints are applied, solution options are defined, and the problem is solved. These steps are performed in the Solution processor (SOL). After the solution is ready, the results are plotted, viewed, and exported in one of the postprocessors (POST1 or POST26). Finally, the results are compared to first-order estimates, closed-form solutions, mathematical models, or experimental results to ensure that the output of the program is reasonable and as expected. (Processors will be addressed in more detail in chapter 2.) 2 ANSYS Mechanical APDL for Finite Element Analysis /PREP7 1. Define the Solid Model Geometry 2. Select the Element Types 3. Define the Material Properties 4. Mesh /SOLUTION 5. Define the Boundary Conditions 6. Define the Loads 7. Set the Solution Options 8. Solve /POST1 or /POST26 9. Plot, View, and Export the Results 10. Compare and Verify the Results It is sometimes possible to omit one or more steps. For example, the default solution options are often sufficient for a simple analysis. It is possible to perform some steps out of order. For example, the element types and material properties can be defined in either order. Similarly, the loads and boundary conditions can be defined in either order. It is occasionally necessary to perform these steps out of order. For example, solid model geometry is not required for a finite element analysis. When the nodes and elements are generated directly, the element type(s) must be specified before the geometry can be created. Finally, complicated analyses may involve multiple trips through one or more processors. For simplicity, this 10-step procedure will be used in this book whenever possible. 1.4. Engineering Software—Not an Engineer As with all computer programs, the quality of your results will depend on the quality of your model. This includes the accuracy of the material properties, the appropriateness of the material models, how closely the simulated geometry and loads match the actual geometry and loads, and the validity of the simplifications and assumptions made. Simply put, Garbage In 5 Garbage Out. Finite element software programs can be thought of as very sophisticated cal- culators that help you to analyze engineering systems that could not otherwise be evaluated. They integrate the section properties of the system with the material properties to generate the equations to be solved. They convert the applied loads to the appropriate forms and apply them to the specified DOFs. They solve the generated system of equations. And, they help you to visualize and understand the results. But a finite element program will not comment on the validity of any assumptions made in setting up the model as long as the laws of physics are not violated. It also will not ensure that you are using the correct laws of physics for a given problem. Any errors that the program reports will be associated with the use of the program, and not with the physical or analytical system. In addition, it will not provide any commentary on the quality or implications of the results. Finite element software is only a tool. In the end, you, and you alone, are responsible for determining whether or not the results of your finite element model can be used to make or justify engineering decisions. 1.5. A Brief History of ANSYS and Finite Element Analysis The finite element method was first proposed in the early 1940s as a numerical technique for solving partial differential equations. At that time, a mesh of elements could be defined and the interaction of the elements could be used to create the system of equations to be solved. However, the system of equations still had to be solved by hand. This limitation rendered the finite element method an academic curiosity until the early 1960s when computers that could 3 Chapter 1 - Introduction to ANSYS and Finite Element Modeling solve large systems of simultaneous equations started to become available. This made it possible to apply the finite element method to general problems. As a result, interest in using the finite element method in engineering practice began to grow. Early finite element programs were specialty codes that were developed to solve a specific type of problem. They generally contained a single element type (e.g., beams, axisymmetric shells, or plane stress solids) and included a single type of physics (structural, thermal, etc.). This limited the type of problem that each program could solve. It also meant that there were no standard analysis tools. It was common for different groups in the same organization to use different computer programs. In many cases, each group of engineers developed and used its own finite element code. This led to concerns about the compatibility of results from different programs, the overall quality of those results, and whether the engineers’ time was being used efficiently. 1.5.1. The Development of NASTRAN In 1965, the United States National Aeronautics and Space Administration (NASA) issued a request for proposals to create a computer program that could be used by all of its engineering organizations to solve a variety of structural problems related to the development of lunar exploration technology. The resulting program was known as NASTRAN. In 1969, NASA began to develop coupled thermal-structural capabilities in order to predict the optical performance of a large space telescope system that was exposed to changing orbital thermal conditions. By 1971, NASTRANs was available for commercial use. It is still the default finite element program in the aerospace industry today. 1.5.2. The Development of ANSYS While NASA was focused on lunar exploration, Westinghouse Electric Corporation was developing nuclear reactors for space propulsion and nonconventional energy production. Like their aerospace counterparts, the Westinghouse mechanical and nuclear engineers needed to predict transient stresses and displacements in reactor systems due to thermal and pressure loads. Dr. John Swanson, then an employee at the Westinghouse Astronuclear Labs in Pittsburgh, believed that an integrated, general-purpose finite element program would save both time and money when doing these types of calculations. He began developing such a program, called STASYS, for Westinghouse in 1969. In 1970, John Swanson left Westinghouse and founded Swanson Analysis Systems, Inc. (SASI) where he continued to develop a commercial general-purpose finite element program that he called ANSYSs. The original version of ANSYS contained 40 elements of various types (springs, dampers, beams, bricks, etc.) including several elements with thermal degrees of freedom. Westinghouse became ANSYS’s first customer by the end of the year. The program was rapidly adopted by other companies and became the default finite element program for much of the power industry. Today, ANSYS products are used in all major engineering fields including the aerospace, automotive, chemical processing, construction, consumer goods, electronics, energy, health care, offshore, marine, and materials industries. 1.5.3. The Evolution of ANSYS With every new release since 1970, new features and functionality have been added to ANSYS. Many additions were specifically developed for the program. For example, the first elements with thermoelectric (1975) and electromagnetic (1983) DOFs were developed by ANSYS engineers. Some capabilities have been added by interfacing ANSYS with other programs. For example, computational fluid dynamics (CFD) capabilities were first added in 1989 by building an interface between SASI’s ANSYS and Compuflo’s FLOTRAN. Similarly, explicit dynamics capabilities were added in 1996 by developing an interface between ANSYS and Livermore Software Technology Corporation’s LS-DYNAt. Finally, some capabilities have been added by 4 ANSYS Mechanical APDL for Finite Element Analysis incorporating other programs into ANSYS. For example, SASI purchased Compuflo in 1992 and FLOTRAN was fully integrated into the program by 1994 (revision 5.1). In 1994, SASI was sold to TA Associates and the company was renamed ANSYS, Inc. This introduced a need to distinguish the company from its flagship product. It also marked a major shift in the strategic development of the company’s software. In the late 1990s, ANSYS, Inc. began to move from a single product to a portfolio of simulation products by acquiring other businesses. For example, they acquired ICEM CFD in 2000, CFX in 2003, and Fluent in 2006 to strengthen their computational fluid dynamics offerings. Similarly, ANSYS, Inc. purchased Century Dynamics in 2005 to add AUTODYNs to its suite of explicit dynamics capabilities. The company has also continued to invest in the development of new products and technologies. For example, in 2009 (revision 12.0), ANSYS, Inc. introduced a new explicit dynamics product named ANSYS Explicit STRt. In the 1990s, development also began on a new user-friendly platform that would become the ANSYS Workbench environment. Workbench was intended to combine the strengths of existing ANSYS, Inc. technology with new capabilities including improved solid modeling and more robust CAD importation. From this point on, new technology that was purchased from other companies was no longer integrated into the original ANSYS environment. Instead, new products and new capabilities were to be integrated into the Workbench environment and all ANSYS, Inc. products would interface with each other using Workbench. 1.6. ANSYS Today* Today, ANSYS, Inc. offers a wide variety of computer-aided engineering products. Some are for general use while others offer capabilities that are specifically designed for certain applications like electronics, turbo machinery, and offshore structures. Some can be used to perform all steps of a finite element analysis while others offer support for a specific stage of analysis like solid modeling or meshing. Some products use the same underlying technology but access it through different (or multiple) user interfaces. Finally, some products are built on the same platform but have different capabilities depending on the licensing options. This book provides an introduction to the family of products offered by ANSYS, Inc. that evolved from the original ANSYS finite element software program. Throughout this book, the term “ANSYS” is used to refer to any (or all) of the ANSYS, Inc. commercial and academic products that provide access to the general-purpose structural, thermal, and/or multiphysics finite element simulation capabilities via the original (non-Workbench) user interface. Collectively, this group is known as the ANSYS Mechanical APDL family and is referred to as such in the program documentation. Today, the ANSYS Mechanical APDL family includes ANSYS Mechanical Enterprise, ANSYS Mechanical Premium, and ANSYS Mechanical Pro. It also includes versions of the program intended for university use, such as ANSYS Student, ANSYS Academic Teaching, ANSYS Academic Research, and ANSYS Academic Associate. The ANSYS Mechanical APDL product portfolio and the names of those products are constantly evolving. Therefore, this part of the book will always be out of date. For up-to-date product information, please refer to the company website (http://www.ansys.com). The exercises in this book are limited to structural and thermal analyses. However, the information in the book is equally valid for analyses that use other physics (fluid, electric, magnetic, and low-frequency electromagnetic) and multiphysics (thermal-fluid, piezoelectric, acoustic- structural, electromagnetic-thermal-structural, etc.) capabilities. As a result, information related to these capabilities will be referred to in the text. 5 Chapter 1 - Introduction to ANSYS and Finite Element Modeling Because explicit dynamics capabilities can be accessed through the ANSYS Mechanical APDL family of products (with an appropriate license), we will make occasional references to ANSYS LS-DYNAs in this book. It will be referred to as “LS-DYNA” for simplicity. Because much of the underlying technology is the same, a considerable amount of the information presented in this book is still relevant to products like ANSYS DesignSpaces that exclu- sively use the ANSYS Workbench environment. However, this book does not address the Workbench environment in any detail. 1.7. ANSYS Licensing As noted above, access to ANSYS, Inc. products is based on product licenses. You can down- load and install all of the software that ANSYS, Inc. offers from the ANSYS Customer Portal. (See chapter 2 for more details.) However, you cannot run any ANSYS, Inc. products without a valid license. Each ANSYS license specifies which ANSYS, Inc. products or capabilities can be used, the maximum number of elements that may be included in a model, and how many people can use the software at the same time. It may also limit the physical distance that you may be from the license server while using the software or impose other restrictions. The software in the ANSYS Mechanical APDL family is basically the same for all products. Only the licenses are different. 1.8. Functionality and Features of the ANSYS Mechanical APDL Family The features of the products in the ANSYS Mechanical APDL family are constantly evolving and new capabilities are added regularly. This section outlines some of the functionality and features that you can expect in the full multiphysics version of the program. 1.8.1. Can ANSYS. . .? New users often want to make sure that the program can be used for their intended application(s) so the very first question that they usually ask is “Can ANSYS do. . .?”. As long as you want the program to do engineering analysis (and not the dishes), the answer is usually “Yes.” It may not be quick or easy. You may need licenses for additional ANSYS, Inc. products. You might need a more powerful computer. You might need to write some code. You might even need to recompile or relink the program. But there is very little engineering analysis that ANSYS can’t do given enough time, resources, and creativity. 1.8.2. Steady-State and Time-Dependent Analyses ANSYS supports a variety of steady-state and time-dependent analyses. These include static analyses where inertia effects are not included and dynamic analyses where inertia effects are important. It permits two types of static analyses: single step analyses where all loads are applied at the same time and multistep static analyses where different loads can be applied or removed with each load step. Multistep analyses allow multiple combinations of loads to be solved in a single run. They also allow loads to be applied gradually in nonlinear analyses, such as creep analysis, where time is important but mass effects are not. ANSYS permits nonlinear transient dynamic analysis where the response of the system is time dependent due to changing loads and other system nonlinearities, mode-frequency analyses where the outputs are the natural frequencies (eigenvalues) and mode shapes (eigenvectors) of the system, spectrum analyses to model phenomena such as earthquakes where the loads applied to the system are frequency dependent, harmonic analyses where the excitation loads are harmonic (sinusoidal), and analyses with random vibrations. 6 ANSYS Mechanical APDL for Finite Element Analysis 1.8.3. Physics Capabilities* The full multiphysics version of ANSYS offers structural, thermal, fluid, electric, magnetic, and electromagnetic physics capabilities. Structural analyses may include linear and nonlinear buckling; fracture; composites; fatigue; and contact with and without friction, gaskets, joints, pretension, and spot welds. They can involve geometric nonlinearities such as large strain and large deflection, and may use linear and nonlinear material models including rate-dependent and rate-independent plasticity, hypere- lasticity, viscoelasticity, and creep. Structural analyses where time is important but time steps are very short, such as high-speed impacts and explosions, should be performed using one of the ANSYS explicit dynamics products such as ANSYS LS-DYNAs or ANSYS AUTODYNs. Pure thermal analyses may include conduction, convection, radiation, phase change, or some combination of the four. Fluid analyses may include laminar and turbulent compressible and incompressible flow, multi- phase flow, free surfaces, porous media, fans or pumps, smooth or rough walls, cavitation, multiple species transport, particle tracing, and swirl. Other types of fluid analyses should be performed using one of the ANSYS CFD products, such as ANSYS CFDs, ANSYS Fluents, ANSYS CFXs, ANSYS CFD-Flot, or ANSYS Polyflows. Electromagnetic analyses may include electric fields, magnetic fields, alternating current (AC), direct current (DC), far fields, and electric circuits. Other types of electromagnetic analyses, especially those involving high-frequency analysis, should be performed using an ANSYS Electronics product such as ANSYS HFSSt or ANSYS Maxwells. Finally, analyses using multiple (coupled) physics are possible. The ANSYS Mechanical APDL family supports acoustic, acoustic-structural, electromagnetic, electromagnetic-fluid, electromagnetic-thermal (for induction heating), electromagnetic-thermal-structural (for MEMS), electrostatic-structural, fluid-structural, magnetic-structural, piezoelectric (for ultra- sonic transducers), piezoresistive, thermal-electric (for resistive heating), thermal-fluid, thermal- structural, and thermal-electric-structural analyses. Coupled analyses using thermal-electric- fluids and electromagnetic-thermal-fluids can only be performed using ANSYS Fluent at this time. Access to these features depends on your license and new features may be added at any time. For up-to-date information, contact your local ANSYS representative or see the company website for more details. 1.8.4. Special Features Members of the ANSYS Mechanical APDL family offer some or all of the following special features: APDL, probabilistic design, optimization, submodeling, substructuring, user materials, and user programmable features. The ANSYS Parametric Design Language (APDL) is one of the most powerful features of ANSYS. It allows you to define some or all parts of your model (geometry, material properties, loads, etc.) as parameters. Creating and solving a new variation of a parameterized model is as simple as changing a few parameter values and rerunning the model. This makes ANSYS a powerful tool for engineering analysis, optimization, root cause analysis, and for the design of new systems and technologies. APDL also allows you to build and execute macros, run macros as ANSYS commands, operate on parameter arrays, and do simple logic (if, then, else, do, repeat, etc.). 7 Chapter 1 - Introduction to ANSYS and Finite Element Modeling Probabilistic design allows you to randomly vary certain input parameters in order to model indeterminate features such as surface finish. Optimization allows you to automate the process of varying model parameters and rerunning the solution in order to identify the best design for a given situation. Optimization in Mechanical APDL requires a parameterized input file. Submodeling is a two-step process in which the results from a large model with a coarse mesh are used as the boundary conditions for a small model with a fine mesh. This is useful for problems (like those involving stress concentrations) where the inclusion of a sufficiently refined mesh in the large model would make the solution prohibitively expensive. For submodeling, two solutions are required. The first solution is needed to obtain the results for the coarse model. These results are then used as boundary conditions in the second model to obtain results in the area of interest. The creation of the boundary conditions for a submodel, which requires the interpolation of the results from the coarse model, is done by ANSYS and does not require man- ual calculations by the user. Substructuring is a technique in which a stiffness matrix is used to replace a large section of a finite element model in order to reduce the overall cost of the analysis. Substructures were originally called superelements and should be thought of as such. To perform an analysis using substructuring, first a finite element model is created for the substructure. The master degrees of freedom are identified and the model is solved to create the substructure matrix. Next, the substructure is defined and used as an element in the larger model. Finally, the detailed response of the substructure can be expanded using the analysis files from step 1 and the results file from step 2 if desired. Substructures remain linear for the entire analysis but can be used with other nonlinear elements in nonlinear analyses. ANSYS also includes a number of user programmable features that allow you to create a customized version of ANSYS. User programmable features include customized elements, load- ing conditions, material models, and commands. For example, ANSYS users are not restricted to the material constitutive models contained in the ANSYS material library. You can create your own material models from handbook values, experimental values, or tabulated data. All ANSYS user programmable features require you to relink the program. This means that you will need the Fortran, C, and C11 compilers used to create the ANSYS release version of the program that you are using. Details may be found in the Guide to ANSYS User- Programmable Features, which has been incorporated into the Mechanical APDL Programmer’s Reference. The combination of APDL, user materials, and user programmable features allows ANSYS users to develop custom applications and macros. Applications and macros are collections of ANSYS commands that can be used to solve a particular class of problems or perform a certain set of commonly used functions. Both applications and macros accept parameterized arguments as part of the input. This makes them very flexible and powerful tools. 1.9. ANSYS: Backward Compatibility and Legacy Code Applications, macros, and customized versions of ANSYS can be and are created by all types of users. However, they are most commonly associated with large corporations that have the resources to invest in their creation and enough product variations to justify the investment. Some industrial applications contain a large number of ANSYS commands, are well verified, and have been used for years (or decades) by the analyst or the company. If the ANSYS development team were to delete an element or a feature that is used in an application (or an input file), either the model would no longer run or it would produce meaningless 8 ANSYS Mechanical APDL for Finite Element Analysis