Finite Element Analysis Sails into the Mainstream
Improvements in latest finite element analysis (FEA) software help speed engineering analysis
By Patrick Waurzyniak
Long the domain of engineering specialists, finite element analysis software is reaching a wider audience as the tools become easier to use and more accessible to non-expert users. Improvements in FEA software, coupled with the faster multicore processors available today, also make it feasible to run these highly complex compute-intensive simulations on an ordinary desktop or laptop computer.
With FE modeling and analysis, product development engineers use mathematical-based modeling techniques to accurately describe how an automotive structural component or an aircraft engine or airframe will perform in the real world. While FEA may never eliminate the need for real-world testing, advances in FEA and other types of simulations have dramatically reduced the number of physical prototypes required for product development and cuts costs.
Companies like General Motors have eliminated prototypes for iterative development testing, said Keith Meintjes, practice manager, Simulation and Analysis, CIMdata Inc. (Ann Arbor, MI). "The development iterations are the evil prototypes you want to rid of," he stated. "They’re the ones that are expensive, and there are all kinds of issues because they’re hand-built."
Virtual automotive crash-test dummies are another major application where FEA software has been speeding testing. Performance gains with higher-fidelity simulations and faster hardware also now allow developers to do more virtual testing much earlier in the process, and to rely on less physical prototypes than in the past.
"The traditional application of finite elements and simulation in general has been to validate completed designs, or proposed designs, and that’s usually towards the end of the cycle, when the CAD is done and then people are essentially validating the designs," Meintjes said. "And that’s extremely important, but for many companies that has become very routine. They do the simulations and they’ve greatly reduced physical testing."
Finite element software traces its lineage back to the 1960s, when the US government developed the original NASA Structural Analysis System (NASTRAN) code for CAE simulation before releasing it into the public domain, noted Meintjes, who spent 30 years at GM in product engineering development. At CIMdata’s recent PLM Road Map event in Plymouth, MI, in October, Meintjes cited this "democratization" trend in CAE moving simulation to the masses, with software developers making FEA systems easier to use and more widely available in CAD-embedded versions.
"They’re getting faster, better, and easier to use, so you can spread it around to more users," Meintjes said. "In other words, you can embed it in the tools that people are using. The software is vastly better than it used to be. People discount that or don’t appreciate that, but the software is really very capable."
Automating and simplifying simulation processes has broadened the tools’ use, noted Jeff Brennan, chief marketing officer, Altair Engineering Inc. (Troy, MI), who spoke on a simulation panel at CIMdata’s conference. Altair recently added Basic FEA, a user profile that exists on top of its HyperWorks software. "We’re investing a lot in new user experiences, both on the direct modeling side but also on integrated tools like topology optimization," Brennan said. "Our next-generation interface is made quite simple, showing topology results that are then pushed into CAD."
Building the Mesh
Automation improvements also have made FEA meshing easier. With Siemens PLM Software’s Femap and NX Nastran, users can clean up geometry in the model within Femap before NX Nastran creates the FEA simulation, noted Al Robertson, product marketing manager, Siemens PLM Software (Plano, TX). "These programs work with each other, with Femap being the pre-processor and postprocessor, and Nastran is the actual solver."
Problems with CAD models create havoc when building the mesh in FEA software. "There are many aspects of how CAD models can be built that can be a problem to the simulation world," Robertson said. "With finite element analysis, you break the model into literally finite pieces, each with a kind of mapped stiffness. You’re building up this CAD model, breaking it into a finite element model, and the process of doing that is called meshing, creating a finite element mesh. If you have problematic geometry, that can be a real problem."
With Femap, users employ an array of tools that help to clean up geometry and help build a finite element model, he noted, and recent Femap releases added more automation to speed up the process. "If you’ve got a lot of thin-wall sections, rather than model them with solid elements, you can actually take the mid-plane and model them with two-dimensional elements—literally squares or triangles—and that really cuts down on the model size, without compromising accuracy," Robertson added. "To go a stage further, if you’ve got long slender components in the model, you can get away with modeling them as one-dimensional beam elements, rather than many, many solid elements. That process we call idealization, and Femap does that as well."
"The focus is on ease of use, so that you don’t have to have a strong engineering background to make those kinds of decisions. You can make these decisions automatically, but really the best place for that to be done is by the engineer," noted Mitch Muncy, director of engineering, NEi Software (Westminster, CA), developer of NEi Nastran and a Femap reseller. "Where a tool like Femap comes in handy, you’re pretty much trying to destroy the CAD model to come up with the best mathematical model to represent what you’re trying to build—you want the most accurate answer that you can possibly have, so when you go and test a product, it’s going to behave exactly how you had predicted it."
Robust Design and Topology Optimization
Some leading FE software developers offer tools for robust design and topology optimization that allow running many more simulations than previously done. "Back a decade or two ago, people created a nominal design, with the basic design dimensions, then analyzed that design," Meintjes said. "Today, people are looking at variation and tolerancing, manufacturing capability, material properties and thicknesses, and doing robust design by analyzing random variations of these things that do vary, due to manufacturing, to come up with designs that aren't sensitive to manufacturing parameters."
With topology optimization, software like Altair's HyperWorks OptiStruct can take a volume, analyze loads and forces the structure needs to carry, and derive an optimum structure to carry those loads, Meintjes noted. "OptiStruct uses FEA, but sort of an inverse of the usual problem, which is give me a design and I’ll tell you if it can carry the load. What OptiStruct says is ‘Give me the loads, and I’ll show you a design that can carry them.’ So the geometry is not an input."
Improving Simulation Workflow
The Simulia Isight and Abaqus software from Dassault Systèmes (Vélizy-Villacoublay, France) enable users to link simulations including FEA to meet constraints and derive optimum designs. "The real claim to fame is our ability to glue together disparate tools in a workflow," noted Mark Bohm, senior sales director, Simulia. The Isight 5.7 software is an application for simulation process automation and design optimization, and Abaqus 6.12 is the latest version of the company’s FEA for multiphysics, modeling and meshing.
Simulia’s software is applied in aerospace/defense, automotive, and construction. "There are instances where we’ve provided simulation technology on the shop floor for people who are not familiar with FEA," Bohm noted. "One was for a steel producer to develop a virtual roll-pass design system, for heavy sections of steel mostly used for civil engineering."
Modeling the Human Body
Multiphysics combining FEA with computational fluid dynamics (CFD) have made great strides in biomedical applications, said Thierry Marchal, industry director, healthcare, construction and consumer products, Ansys Inc. (Canonsburg, PA). Simulation offerings from Ansys include its Structural and Polyflow packages, Marchal noted, and users are employing simulations using more of a systems-engineering approach.
In biomedical, researchers have used both FEA and CFD simulation systems to model how pacemakers interact with the heart and the overall cardiovascular system. "This is huge work, but we are taking a systems-level approach," Marchal added.
Researchers for the Foundation Leducq in Paris, France, have simulated surgeries to help treat congenital heart defects in small infants. "Most of the time when you manufacture a part, you don’t just run a simulation once," he said. "Each time you need to re-run the simulation. With a full 3-D model, you want to run that very effectively. There was a wonderful example by the Foundation Leducq where doctors in Italy were able to save the life of a newborn by modeling the entire heart and cardiovascular system of the baby."
With a systems approach, this type of modeling can be done very quickly, Marchal stated, and in some cases, it may even replace some clinical testing. ME
This article was first published in the December 2012 edition of Manufacturing Engineering magazine. Click here for PDF.