Machine Design

Multidiscipline analyses made easier

Most engineering problems involve at least two disciplines such as stress from physical loads and thermal changes. But for simplicity, disciplines are usually examined separately and merged into hopefully meaningful results.

Femlab's GUI includes ready-to-use applications in a variety of disciplines, and with free-equation modeling. The muffler model comes from ready-to-use acoustic applications in the software. Variables can be changed for new studies. The figure shows pressure amplitude and energy flow at selected frequencies.

Although many FEA programs accurately handle multiple disciplines, Femlab software allows perhaps the widest range of simultaneous simulations. It couples mechanical, electrical, chemical, fluid, and acoustic phenomena, according to the developer. And if you know the partial differential equations for other phenomena, they can be typed in and simultaneously applied as well.

The software resembles other FEA programs in that models are meshed, solved, and postprocessed. The differences come after meshing when selecting the analysis. "Users check off phenomena and the software shows the partial differential equations that apply with each selection," says Bjorn Sjodin, vice president of engineering at developer Comsol Inc. "For instance, analyzing a fuel cell might involve chemical reactions, electrical currents, fluid dynamics, and heat transfer."

In the recent release, V3, solver speed and memory efficiency are increased letting the software tackle larger problems. And a Java-based user interface makes more drawing tools accessible. Previous versions required Matlab from MathWorks Inc. to run, but no more. "V3 is written in C++ and Java," says Sjodin. "It solves some models in as little as 5% of the time and with 5% of the memory previously needed. Pentium II-based PCs are adequate for many problems," he adds. In addition, accelerated Java graphics are displayed in less than 4% of the time once needed.

The software lets users run it alone or coupled into Matlab with Simulink providing a graphics-based way to simulate control systems.

The software includes a library of more than 200 completely solved and documented models of frequently encountered systems such as wave guides, antennae, fuel cells, biochips, and MEMS (microelectromechanical systems). These models can be used as starting points by modifying the geometry and equations. Users can name variables, define their values, and modify accompanying equations with tables and text boxes.

"A built-in CAD editor lets users draw 2D and 3D parts," says Sjodin, "So the software can be used farther upstream in the design process where part geometry is not available." After selecting the discipline, the software sets up appropriate equations. Or users enter their own equations by typing them into a dialog box. "Few programs allow entering PDEs in a familiar form," he adds. After completing a model, the software selects an optimal solver from several. Users can fine-tune solver settings for special circumstances.

The developer says the software handles problems with as many as a million degrees of freedom. "Solution time in these cases typically ranges from 15 min to a couple hours, depending on solver technique and computer speed. Postprocessing often takes only seconds, and model rotations seem instantaneous. Animations provide insight into dynamic processes, and AVI or QuickTime movies of results can be sent to colleagues.

Femlab 3.0 runs under Windows 98, 2000, NT 4.0, and XP, as well as Linux, Solaris, and HP-UX. A minimum system includes 256-Mbytes RAM (512 Mbytes recommended) and an OpenGL-compatible graphics card. A single-user perpetual license lists for $6,995, including support and automatic upgrades for 12 months. Femlab 3.0 comes from Comsol Inc., 8 New England Executive Park, Suite 310, Burlington, MA 01803, (781) 273-3322,

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