FEA-Based Simulation Technologies are Defining Virtual Prototyping

Michael L. Bussler
President and CEO
ALGOR, Inc.
Pittsburgh, PA

Since the mid-1990s, the computer-aided engineering (CAE) industry has focused on making it easy to create increasingly realistic simulations of events. Developments that have contributed to this trend include the creation of easy-to-use user interfaces, full associativity with CAD solid modelers, new tools for handling combined motion and stress analysis and the consideration of a wider range of environmental factors. These developments are already making CAE software accessible to a growing number of engineers and scientists. As these trends progress, users will be able to create more accurate design representations and replicate the actual behavior of a product through realistic virtual prototypes.

The Development of CAE Technologies

In the past, various types of structural analysis have been called “simulation” including rigid-body kinematics, static finite element analysis (FEA) and FEA based on loads calculated by kinematics software.

Rigid-body kinematics software has traditionally been used to enable engineers to view the motion produced within a fully coupled mechanism. While this technology enables engineers to simulate motion in order to check for interference between parts, it does not automatically produce stress results. There are also many design scenarios that rigid-body kinematics software cannot consider, such as the effect of flexible joints and links within a mechanism.

FEA has traditionally been performed using static stress analysis to calculate the effects of structural or mechanical loads within a factor of safety. While applying loads in static FEA is not difficult, significant expertise may be required to properly estimate their magnitude and direction, particularly when modeling a part or assembly that is undergoing large-scale motion or is involved in contact and impact. In addition, this type of simulation requires that the engineer know how to interpret the results. Static FEA yields results at only a single moment in time. If the worst-case scenario that a design is likely to encounter involves motion, static results provide limited insight. Furthermore, static FEA is often performed on only part of a design, sometimes with simplified geometry, in order to save computing time and resources.

To solve the problem of how to calculate static stresses for parts involved in motion, many CAE vendors use a two-step approach that uses rigid-body kinematics software to obtain loads (reaction forces and moments at joints), which are meant to represent the effects of motion. Then, static FEA is used to obtain the stresses based on those loads. In this approach, the limitations of both rigid-body kinematics and static FEA still apply. Thus, the application of this technology is limited to fully coupled mechanisms and the static FEA results need to be interpreted by an experienced engineer.

The Development of User Interfaces for Simulation Technologies

All of these types of simulation have typically been performed by analysts using software and user interfaces that were time-consuming to learn. Over the last decade, CAE software has become more widely used as user interfaces have become more intuitive. The ease-of-use trend began when the CAE industry embraced Windows and its guidance on user interface design. Today’s modern user interface includes easy-to-use, Windows-style features such as right-click functionality for loads, constraints and FEA properties, tree views that visually guide users to provide all necessary information, wizards that help users perform common tasks, multiple view windows, docking toolbars and context-sensitive menus that are tailored to particular steps in the analysis process.

Through the use of standard engineering terminology and guidance provided by features such as tree views, user interface enhancements also support the broader application of simulation software. This is because the user can focus on the physics of a part or assembly, rather than having to learn the process and terminology of a particular software package. This broadens the usability of CAE software from analysts to designers, scientists and even non-engineers.

The CAD preference these new users bring with them is being supported by full associativity with multiple CAD solid modelers. This advancement in CAD support enables engineers and scientists to use their choice of modeling tools. Associativity with leading CAD packages makes CAE software more readily available to design engineers.

In addition to supporting a variety of CAD solid modelers, modern CAE interfaces incorporate a wide range of modeling tools including parametric solid modeling, midplane meshing and FEA mesh generation with automatic mesh refinement. The latter two tools are especially helpful to users who are new to CAE software because they automate finite element mesh generation tasks that previously required expertise and extensive user intervention.

Furthermore, CAE user interfaces now include a wide range of analysis options including motion and dynamics, structural including linear and nonlinear material models, heat transfer, fluid flow and electrostatics. These capabilities enable users to consider numerous environmental factors. These interfaces often include easy-to-use tools for applying the results of one analysis type to another to enable multiphysics analyses, which are important because real-world product behavior is often the result of several physical factors acting simultaneously.

This ALGOR Mechanical Event Simulation of a conveyor belt assembly uses a nonlinear hyperelastic material model for the belt. This simulation enabled engineers to study the response of the conveyor belt during tensioning.

Simulation’s Leading Edge

Currently, the most comprehensive simulation tool involves combining motion and stress simulation with multiphysics support. The combination of motion and stress analysis considering full inertial effects enables engineers to see motion and its results, such as impact, buckling and permanent deformation. This technology eliminates the limitations and assumptions inherent in rigid-body kinematics, static FEA and FEA based on loads calculated by kinematics software and can include the effects of a variety of environmental factors.

This Bourdon tube pressure gauge utilizes ALGOR’s surface-to-surface contact between its gears to replicate the motion of the indicator needle as pressure is increased within the tube.

Motion and stress simulation with multiphysics support accounts for the bending, twisting, stretching, squashing and inertial effects of a model while simultaneously calculating rigid- and flexible-body motion. The results are based on physical data, rather than calculated or assumed loads and constraints, including dynamic or contact forces. Motion and stress simulation with multiphysics support does not require the user to input constraints that do not exist in the real world (i.e., free falling objects). Rather, it accounts for flexible joints and links, includes linear and nonlinear material behavior and can incorporate environmental factors such as heat, electrostatics and the effects of fluids.

Engineers at SiWave, Inc. examined the dynamic response of this MEMS optical switch using ALGOR’s Mechanical Event Simulation. The simulation was performed to assure that the device would be in compliance with Telcordia shock loading standards.

The user can perform a motion and stress simulation using a full CAD assembly because this technology is available within the same Windows-native user interface that is used for other types of CAE. The resulting dynamic visualization displays the product’s behavior and analysis results on the exact CAD geometry during or after the event. The result is a true virtual laboratory.

The Applicability of Simulation

The most common application of CAE software is new and existing product design. Engineers in industries such as automotive, aerospace, medical, consumer products, military, electric power, petroleum, large structures, micro electro mechanical systems (MEMS) and more continue to represent the largest market for CAE software. These engineers are receptive to leading-edge technologies such as simulation tools that couple motion and stress analyses with multiphysics support because it enables them to speed up time to market and make better, safer products at a lower cost.

Engineers at Hewlett-Packard Company performed a Mechanical Event Simulation with ALGOR software on a new back-up tape drive design to optimize the tape path stability in order to maximize the durability of the back-up tape.

We have recently seen many exciting uses of CAE software in industry. For example, Gyrus Medical, Ltd. analyzed instruments used to perform arthroscopic surgery. The Goodyear Tire & Rubber Company verified a standard wheel design for "run flat" tires. Hewlett-Packard Company analyzed the behavior of a magnetic recording tape as it wound through an HP Ultrium tape drive.

Scientific researchers have also embraced CAE software, especially as it has become easier to use. Scientists have found these newer simulation tools very intuitive since they eliminate the limitations, assumptions and need for specialized knowledge required by previous technologies. Archaeology, geology, biomechanics, veterinary science and MEMS are just a few of the areas of scientific research in which CAE software is being used today.

We collaborated with University of Alberta researchers to perform a MEMS simulation to study thermal stresses on an experimental automotive gas sensor. On the medical front, a researcher from Tufts University School of Medicine simulated the motion and stresses generated in the human eye as it undergoes a rapid point-to-point rotation of 30 degrees in the hopes of improving techniques for the repair and prevention of retinal detachments. Researchers at the New York Institute of Technology simulated chewing in the skull of a crab-eating macaque monkey to examine the functional anatomy and evolution of the facial skeleton in primates.

Researchers at the Tufts University School of Medicine used ALGOR’s Mechanical Event Simulation to determine the peak stresses generated in the human eye as it undergoes a rapid point-to-point rotation of 30 degrees. This research could lead to improved techniques for the repair and prevention of retinal detachments.

Many university researchers carry their use of CAE software with them into the classroom. Learning CAE software in the classroom provides students with the tools necessary to properly prepare for professional careers in engineering and enables them to experience the entire engineering design process from conception to market. One Oxford University professor has observed that by using CAE software, physics students gain understanding about how materials and structures behave during the course of a simulated experiment.

CAE simulation technologies are also used in engineering competitions. Educational competitions, such as Formula SAE®, SAE Mini Baja®, various solar car competitions, robotics competitions and others, are designed to give students experience on an engineering project as well as the opportunity to work in a dedicated team effort. These competitions involve conceiving, designing and fabricating a competition entry. During the design phase, teams may use CAE to optimize parts of their entries. ALGOR has granted software to many teams over the years including Carnegie Mellon University, Massachusetts Institute of Technology, Queen's University and the University of California at Berkeley.

In addition, CAE software is frequently used to optimize entries for other competitions, such as automotive races. For example, engineers at Triple Eight Race Engineering used CAE software to optimize a variety of load-bearing components on their Vauxhall Astra Coupe race cars. Their efforts were rewarded with the driver, team and manufacturer titles in the British Touring Car Championship for both 2001 and 2002.

Virtual Prototyping

In the future, current simulation technologies will lead to true virtual prototyping, in which CAD assemblies of entire products or mechanisms are used in simulations including all of the environmental factors a product may experience.

With the ever-increasing power of computer hardware, future CAE users will have no need to simplify CAD geometry and will instead focus on the accurate representation of products. Growing computing power will also speed up the processing of simulations and enable users to see results in real time. User interfaces will undoubtedly continue to become easier to use, perhaps even utilizing virtual reality technologies.

In additition, multiphysics analysis capabilities will be more tightly integrated into a single process so that engineers can simulate an entire scenario that incorporates the whole product and the environment in which it will be used. By avoiding assumptions about the effects of multiple physical phenomena, engineers will be able to produce more accurate and comprehensive simulations. Animated results of virtual prototypes will show a product’s behavior in a particular scenario, rather than just producing numerical results that need to be interpreted. As computer graphic technologies become more realistic, virtual prototypes will look increasingly like a video of a physical prototype test.

By seeing the behavior of a design on the computer, engineers will develop useful, real-world insights into their designs and reduce expensive and time-consuming physical prototype testing, thus lowering cost and time to market.