applying finite-element analysis1 Mar, 2003 By: Don LaCourse
FEA (finite-element analysis) is easier to use than ever before as it becomes more closely integrated with the 3D modeling system. Designers, not just engineering analysts, can now use FEA. We'll discuss this and other issues such as applications, recent advancements, and future trends with four leading FEA application developers.
FEA began back in the 1940s with R. Courant, who used numerical analysis and variational calculus methods to derive approximate solutions to various vibration system problems. A much broader definition that encompassed the stiffness and deflection of complex structures emerged in the 1950s. Today, you generally generate a 3D or 2D finite-element mesh that approximates stresses based on case loads and boundary constraints you assign. For the basics of FEA, see "Finite-Element Analysis and Solid Modeling" (Cadalyst, February 2001).
FEA is just one of many analysis types you can perform on 2D and 3D surface and solid models. For the full range of options, see "Validate Designs with Today's CAE Options" (Cadalyst, July 2002).
WITHIN THE PAST FIVE YEARS, WHAT TECHNICAL ADVANCEMENTS IN FEA DEVELOPMENT HAVE IMPROVED ITS APPLICATION IN THE MCAD INDUSTRY?
CAD integration. New releases of MCAD applications often incorporate features and functionality that were previously provided by dedicated third-party applications. FEA analysis still requires a third-party application, but the distinction between the 3D modeling application and the FEA program is blurring. Many FEA applications now include modeling functionality, and many 3D modeling applications more tightly integrate with analysis applications.
All of our respondents agree that the integration of analysis tools within the modeling environment is the most significant technical advancement in recent years (figure 1).
Figure 1. ALGOR and Pro/ENGINEER work in tandem to conduct a parametric FEA study of inflation pressure and stresses in a common wheel design for Goodyear. Laboratory tests correlated well with linear static stress analysis results.
As Suchit Jain of SolidWorks put it, "Because there is only one interface, and no data translation issues, the learning curve is shortened, making the analysis tasks much easier to assimilate. This allows engineers to perform analysis earlier in the product design cycle."
Barry Christenson of ANSYS lists the ways in which FEA applications take advantage of this openness to the CAD system: "Accessing geometry is easier-parameters can be exposed and users can better control the CAD data-all of which leads to easier model updating."
ALGOR's Bob Williams attributes the tighter integration to technical advances in CAD support options, improvements in ease of use for all analysis types, modern user interfaces, and overall capability to perform multiphysics on CAD geometry.
Figure 2. MSC.visualNastran 4D evaluates stress in the trailing arm of this motorcycle during a drop test.
For loading, he says that most companies outside the automotive and aerospace industries use one of the following methods:
- run through a set of hand calculations to calculate the load (which leaves them vulnerable to error)
- overestimate the specific loading
- conduct a physical test to derive the load
- just guess
There are several problems with this process. For example, one reason to use simulation is to reduce the time it takes to evaluate a design. Performing hand calculations, while useful, is not usually the most efficient method. Loading can change due to changes in the overall product geometry. Make one design change, and you need to run through the calculations again.
Another reason to perform simulation is to reduce the number of physical evaluations in the design process. If you need to do a physical evaluation to derive the load, running the simulation itself is self-defeating-"you don't give yourself the opportunity to save the time you are trying to save," says Brewster.
Williams adds that MES (mechanical event simulation) combines large-scale motion and stresses and supports built-in linear and nonlinear material models. The combination of motion and stress analysis that considers full inertial effects enables engineers to see motion and its results, such as impact, buckling, and permanent deformation and displacement.
"MES results are based on physical data, including dynamic or contact forces, rather than calculated or assumed loads and constraints, thus eliminating the need for extensive knowledge of nonlinear or dynamic theory," Williams says. This makes FEA technology accessible to more CAD users.
Interface improvements. This FEA discussion yields additional evidence that MCAD user interfaces are becoming easier to use and less of a hindrance to quick, efficient design. For details on how this is happening, see "Design Optimization, Part 1-MCAD developers optimize the user interface" (Cadalyst, July 2002).
WHAT STEPS HAVE FEA DEVELOPERS TAKEN TO DISPEL THE VIEW THAT FEA IS ONLY FOR ANALYTICAL ENGINEERS? HOW HAVE YOU MADE FEA APPLICATIONS MORE USER FRIENDLY FOR DESIGNERS?
My hands-on introduction to an FEA application occurred in the early 1990s when I was a design engineer for a Tier 1 automotive design and manufacturing company. FEA was a prerequisite for supplier certification. Windows and CAD integration did not exist at the time. The FEA program was overly complex and downright unfriendly. Needless to say, we fired the product up only for annual supplier certification reviews: "Yeah, we have FEA capability."
These types of experiences promote the idea that FEA is just for analytical engineers.
Figure 3. This machining center component from the specialty machinery industry was analyzed using ANSYS DesignSpace and its Windows-style interface. Analysis indicated that a stress concentration that could lead to failure was found in the mounting area.
Christenson adds, "Experience has shown us that basic tasks can be automated. ANSYS has identified these areas and has taken complicated FEA and packaged it for designers and engineers (the new type of user in the FEA community)."
Brewster cites the importance of automated mesh generators. FEA/CAD integration, easily accessible materials libraries, and lower price points for mid-market products also appear
Figure 4. COSMOSWorks 2003 generates eDrawings of analysis results. You can view results in 3D, rotated and zoomed in and out, using the SolidWorks eDrawings viewer.
Williams points to improvements in the FEA user interface, such as wizards that guide you through common procedures, built-in data checking, and context-sensitive help accessible by right-clicking. The familiar Windows-native environment (figure 3) includes tools such as tree views, multiple views, and docking toolbars. Material library managers let you import or create customized libaries. Results evaluation and presentation capabilities (figure 4) automated creation of contour plots, graphics output formats, animation output formats, and HTML reporting output.
THE FEA USER BASE IS EXPANDING. WHAT ARE SOME NEW AND UNIQUE WAYS IN WHICH USERS APPLY FEA?
FEA has traditionally been used in the aerospace and automotive industries, but today is found across all industries, including consumer products, medical, electronics, and biomedical. "You see many neat applications of FEA from design of prosthetic limbs and artificial jaws to car seat designs and cell phone designs," says Jain.
Christenson adds that "a lot of 'out-of-the-box' automation exists in areas such as mesh quality, solution settings and convergence, load application, and CAD geometry integration. Users can concentrate on custom applications that are more tailored around processes."
Brewster adds that nonlinear FEA enables modeling and testing of manufacturing processes and production lines.
"Many times, solutions can't be obtained for nonlinear and contact problems without some user adjustments during the solve process. These adjustments require an in-depth knowledge of the mathematics and physics that exist in the simulation. We are working on ways to eliminate this user interaction," says Christenson. "Also, the ability to develop integrated finite-element and optimization programs enables designers to achieve a greater level of innovation by evaluating multiple designs at one time."
Williams notes that ALGOR's products are even used in biomechanical research: "A retinal surgeon has simulated eye movement and the resultant stresses with ALGOR's MES software in the hope of discovering more about retinal detachments (see sidebar)."
WHAT ARE CURRENT TRENDS IN FEA APPLICATION DEVELOPMENT, AND WHAT CAN DESIGNERS EXPECT TO SEE IN THE NEXT FIVE YEARS?
Simplify, simplify, simplify, our chorus of developers chants. Jain predicts that analysis will be easier than ever before: "Analysis concepts will be simplified further so that people don't have to think in terms of loads and boundary conditions. Industry-oriented wizards will ask the right questions and then automatically create loads and boundary conditions."
Christensen expects that FEA applications will be able to handle larger model sizes. Designers can analyze entire complex assemblies rather than isolated components.
Williams foresees improvements in the capability to perform multiphysics analyses on CAD geometry: "Real-world mechanical behavior is often the result of several physical factors acting simultaneously. Multiphysics software enables engineers to simulate a product's behavior when those multiple physical factors interact."
Christensen also points to probabilistics as a fertile area for development. While most FEA analyzes for a specific solution in a linear fashion, probabilistics investigates a cloud of solutions, enabling an engineer to pick the best solution for a given problem, he says. "Probabilistics is moving out of the theoretical and into the engineering department because the processing power required is becoming affordable."
Clearly, FEA has come a long way from the cumbersome products of the 1980s. Advances in user interface development, integration with 3D modeling applications, lower costs, and faster computers combine to offer more designers the benefits of FEA. A special thanks to our FEA application developers for taking the time to participate in this discussion.
Note that we selected a sampling of vendors to participate in our discussion. Many more companies offer FEA software. For a list, visit the International Association for the Engineering Analysis Community.
Autodesk Technical Evangelist Lynn Allen guides you through a different AutoCAD feature in every edition of her popular "Circles and Lines" tutorial series. For even more AutoCAD how-to, check out Lynn's quick tips in the Cadalyst Video Gallery. Subscribe to Cadalyst's free Tips & Tools Weekly e-newsletter and we'll notify you every time a new video tip is published. All exclusively from Cadalyst!