New FEA Tools for Engineering Analysts

CAD/CAE interoperability tools, new elements, additional material models, faster solvers, and innovative training techniques make the latest finite element field worth a closer look.

Bob Williams
Development Manager
Algor, Inc.
Pittsburgh, PA

Finite element technology is changing so fast that analysts who keep their noses to the grindstone may miss out on many of the recent, useful developments. For example, an actuator element, just one of several new inventions, simulates the motion of hydraulic, pneumatic and electric cylinders and solenoids. This element lets designers analyze complex mechanical events that would have been nearly impossible even just a few months ago.

What's more, FEA companies consistently improve their solvers in order to reduce solution times. They have to. The ever-increasing memory and disk space capacities on today’s computers encourage finite element analysts to work with larger and larger models.

These trends and developments make it useful to occasionally step back from the daily grind for a better view of what's cropping up in the industry.

What's new in preprocessing?

Shown here, Algor’s InCAD DesignPak captures geometry directly from CAD solid modelers for linear static stress analysis in Algor. InCAD DesignPak provides an introductory step into the FEA realm, but provides the flexibility and extensibility to add additional analysis capabilities by utilizing the same user interface as all of Algor’s product line.

Success using universal files, such as IGES, to transfer geometry from a CAD solid modeler to FEA software has been so intermittent that companies began integrating their FEA programs inside CAD programs. This arrangement was intended to provide CAD/CAE interoperability with entry-level FEA tools for design engineers who typically desire quick verification of their product design. Although this software arrangement has solved the problem of geometry transfers, extending the software for new analysis tasks is often quite difficult or impossible.

For example, limiting the number of available element types in order to simplify FEA programs also significantly limits what can be modeled. Engineers and analysts realized that the lack of other element types, such as beam, truss, or brick elements, in such a product keep them from analyzing even moderately complex parts or mechanisms.

Some FEA companies now recognize that a better approach is to reside just "one window away" from the CAD system while still directly transferring geometry through memory. Communication with the CAD solid modeler remains direct, but upgrades and expansions to the analysis program are easy.

InCAD^Plus from Algor provides an example of a full-featured CAD/CAE interoperability solution. Like InCAD DesignPak, the software works directly with CADKEY, Pro/ENGINEER for Windows, Mechanical Desktop, SolidWorks, and Solid Edge using the same interface regardless of the CAD system or analysis type involved. However, InCADPlus provides Algor’s full range of finite element modeling capabilities, including the ability to combine multiple element types; solid FEA brick, tetrahedral or hybrid meshing; and midplane meshing.

It’s also easier on analysts when they are presented with a consistent user interface regardless of the type of analysis being performed. A consistent user interface saves users from mastering a different GUI just because the analysis needs to be changed. In addition, the interface is the same no matter which CAD package you use.

Another trend is the increasing level of expectations for engineering software. There was a time when engineers were comfortable working through a command-line prompt or an unfriendly technical terminal. Engineering software was almost expected to be difficult.

That is no longer the case. A modern graphic user interface with user-friendly dialogs and wizards are features analysts now expect in FEA software. For example, Algor’s effort to meet this demand has delivered additional ease-of-use features such as context-sensitive help, which calls up relevant written information no matter where you are in the program. In addition, Algor interfaces with Microsoft Office so users can, for example, import load curve data from an Excel spreadsheet.

Furthermore, a single consistent interface across low-end, intermediate, and high-end analysis capabilities means users aren’t confused when they add other capabilities in order to perform different analyses. So whether working on problems involving heat transfer, electrostatic, linear static stress, linear vibration, fluid flow, or analyzing mechanical events, users work within the same FEA interface.

Meshing a model with solid elements makes sense when the part has a substantial thickness. But meshing a thin-wall part, such as the housing on the left, with solid elements can often produce a large number of elements and cause long solution times. Algor’s automatic midplane meshing capability can simplify the problem by generating the midplane surface and, therefore, replace the solid elements with plate/shell elements, as shown to the right. The plate/shell model will solve more quickly and encourages more what-if studies.

Another one of our recent developments has been the expanded use of the 20-node brick element in linear static stress problems. The element is modeled as a standard eight-node brick, but includes mid-side nodes. Although 20-node brick elements are not new, they have been available mostly in more expensive nonlinear, FEA programs. Brick elements are generally regarded as more efficient than tetrahedral elements in that fewer brick elements are necessary to obtain a similar level of accuracy in a particular model.

The additional nodes allow it to capture bending more accurately than eight-node elements or tetrahedra. Another way to capture bending involves the use of a large number of elements. The new element also avoids this latter tactic. The 20-node element works with isotropic and orthotropic material models, and can be temperature-dependent, making it applicable to a wide range of linear material models.

Analysts should need only one library to maintain all known material property data. Algor’s software is delivered with a material library and manager that enables engineers to quickly access standard material properties or to define customized material property libraries for use with all analysis types.

Additionally, a piezoelectric material model is available for the new brick element. In the same way that heat generates stress in a temperature-dependent element, voltage generates stress in the piezoelectric material model.

New material models are enabling analysts to handle multiphysics applications more easily. Recently, Algor introduced a new piezoelectric material model that produces stress results based on voltage loads. An electrostatic analysis can be used to calculate voltage results, which are then automatically transferred via the global data input screen in Superdraw III to a linear static stress model. The final stress results are shown at the right.

Composite elements are available for wider application use than ever before. These elements are modeled in the same manner as plate/shell elements. The data input screen for a composite element lets users assign the number of plies that make up the laminate. Each ply gets assigned a thickness, an orientation angle that positions the plies with respect to each other, and a material for that ply. This is accomplished in Algor through a simple three-column spreadsheet that tracks the user-defined data.

Composite elements have been available for many engineering conditions, such as vibration analyses and linear static stress. More recently, they have been extended to model linear critical buckling. This type of analysis uses Euler approximations to find a buckling load multiplier. The composite element is also proving useful in simulations of mechanical events, including those involving large-scale motion.

Kinematic elements, another recent invention, assist with large models by transmitting loads, motion, and displacements, but are not considered when calculating stresses. These elements are ideal for large models with small areas of engineering concern.

Kinematic elements were used in conjunction with Algor’s Mechanical Event Simulation software to perform motion analysis and simulation of this landing gear assembly. Flexible elements were defined at the joints to determines stresses (see inset) while kinematic elements were used on the remainder of the model to speed processing times.

A more general development, communication links between different analysis modules, adds even more capability. Integrating different analyses together more directly lets the user model the multiple physical phenomena affecting parts in the real world. For instance, the link will let users perform an electrostatic analysis to determine unknown voltages and then automatically apply the calculated results to a linear static stress model utilizing the piezoelectric material model to find the stress from those voltages.

What's new in solvers?

Analysts probably expect to see new elements and features in preprocessors since that is where they spend most of their analysis time. But some of the developments they don't see, such as solvers, can be equally impressive.

Recent solver development has focused on sparse matrix and iterative technology. While aerospace companies have made frequent use of this technology in the past, a growing number of analysts from all industries are now taking advantage of the solvers due to the processing speed gains that are possible when analyzing large models. In the recent past, users would ask themselves: How can I simplify a model so that it runs faster? But the recent trend is to analyze the real thing -- a more complete model. This trend has encouraged increased model size and the need for faster solvers, such as the sparse matrix and iterative versions.

Sparse solvers are based on the fact that zero terms in the stiffness matrix do not need to be considered. The iterative solver is often the fastest for analyzing large solid models, but there is a price for its speed -- it does not always converge. The iterative technology uses extrapolation techniques so it’s not actually solving for every instance. Therefore, any intermediate results in a linear static stress analysis are not meaningful.

Because it’s important to tell whether or not a solution is converging or how it is converging, users can watch the progress of the analysis through a monitor program that generates real-time plots of convergence. This is also important when simulating moving mechanisms. For example, if a large mechanism is not converging due to geometry issues, such as widely varying stiffnesses throughout the model, analysts can switch to the sparse solver, which will converge. In addition to the sparse solver, analysts can always choose reliable skyline or banded solvers for more general scenarios. Both of these are stable, direct solvers that do not have convergence issues that are inherent in the iterative solver.

Iterative solvers are perfect candidates for fluid-flow problems, which traditionally involve large models where the results are not significantly changing from one timestep to another. Expect to see big changes in this analysis arena in the next few months.

One of the most significant changes is the capability to analyze moving events in a finite element analysis using Mechanical Event Simulation software. The concept is simple: things move, they collide, and sometimes they break. However, FEA technology for linear static analysis models only stationary objects, often requires input of approximated loads, and is unreliable for large deformations. True-to-life simulations, on the other hand, let users analyze true events, including those involving small and large-scale motion.

An automatic time-stepping feature in the Mechanical Event Simulation software makes it possible to simulate actual events. During periods of relative inactivity in an analysis, for example, a car headed toward a telephone pole, nothing is happening so the software assigns a large timestep to the event. But when contact is imminent, the software reduces the timestep to fractions of a second to capture the detail during the actual impact.

Algor’s Mechanical Event Simulation software can be used to simulate the actual impact of independent objects. For example, engineers at West Coast Engineering, Ltd., the largest Canadian pole manufacturer, analyzed the impact of a car into a pole to assess the performance of the transmission pole under extreme dynamic loading.
Model courtesy of West Coast Engineering, Ltd., British Columbia, Canada.

This kind of automation in software is showing up in other places as well. Not long ago, engineers measuring the motion characteristics of a mechanism would manually transfer loads from one program to another. According to more recent thinking, if the engineer should choose to perform a static stress analysis instead of the dynamic event, than let the software perform the load transfers to an FEA program.

This idea has resulted in what’s called an Inertial Load Transfer module. The capability expands upon recent geometry-transfer techniques that bring over an entire assembly and turn it into an FEA model comprised mainly of kinematic elements. After an analysis reveals the motion, the Inertial Load Transfer module automatically transfers loads to a linear or nonlinear stress analysis and performs an analysis on one or more parts to get the resulting stresses. Older systems would require working in a kinematics package on a separate kinematic model. Results would often be transferred manually, a process that invites error. In addition, the kinematic model is based on assumed joint stiffnesses and rigid-body motion, not flexible-body motion.

What's coming?

FEA companies are paying more attention to simplifying the application, modification, and removal of loads and constraints to models. With this technology, FEA users can right-click on a model location to apply constraints or loads, or right-click on an existing one to alter its magnitude. In addition, this technology is available for all analysis types. Because FEA is an iterative process with one analysis often leading to another, efforts in this area will increase the user’s overall efficiency by enabling quicker, easier modification of model properties. That is, the user can quickly review the results and then change the model and begin another analysis, if necessary.

Right-click application also introduces more types of common loads, constraints, and ways of connecting parts. These are especially critical for motion studies, which require engineers to identify where and how links are jointed. For example, a piston and rod are connected at a joint that should not translate from side to side, but must rotate about a connection point. It’s important to define the joint properly to capture the true motion of the mechanism.

To quickly model such connections, expect to see kinematic pivots, which enable kinematic elements to rotate in different relationships to each other. Kinematic pivots are the first of a series of joints that accurately model movement for analysis using Mechanical Event Simulation.

Also, look for more dynamic postprocessing capabilities, real-time monitoring, and presentation capabilities. For example, users should be able to dynamically rotate, pan or zoom in on a model in order to quickly examine von Mises stresses or other results regardless of where they reside on the model. In addition, analysts can take advantage of timesaving monitoring capabilities, which make results available graphically during the analysis of time-dependent analyses like transient heat transfer and Mechanical Event Simulation. Engineers do not need to wait for an analysis to finish before evaluating the results to determine if modifications are necessary.

Once analysts have completed their analyses, the task of presenting the results remains. Report Wizards generate fully customizable HTML reports of the FEA model data that can include VRML, AVI, JPG, TIF, PNG, TGA and PCX graphic files. The reports can be printed or distributed via an Intranet or the Internet.

Algor’s HTML Report Wizard automatically generates an analysis report that can be printed or distributed via an Intranet or the Internet. The report includes detailed model data, graphics and multimedia files and user-specified information that can be transmitted to a client or supervisor through any web browser.

Users should not be surprised to learn that most ideas for new features come from them. Many of these new features stemmed from customer feedback. If you have an idea for a new software feature, contact Algor or the developer of your FEA software package.