Jack of all trades
Femlabstacks up well against more complex simulation software

Jack of all trades and master of none, goes the saying – but Femlab breaks the rules. Two university-based research groups who benchmarked three leading simulation packages found that Femlab rivals its more specialized competitors. Clearly, flexibility and ease of use don’t have to mean a sacrifice in performance.

Scientific-modeling software packages are conventionally optimized to solve certain types of problems in particular fields of engineering. You might therefore assume that speed and accuracy
would be lost when one flexible and easy-to-use software package is employed to tackle specialized these “single-physics” problems. Not so: Femlab 3.0a, the latest release of the popular “multiphysics” simulator from Swedish software company Comsol, compares well with more specialized simulators in terms of speed and accuracy. Independent benchmark tests confirm that this software closes the speed and accuracy gap that previously separated multiphysics and niche software classes.
After all it is a multiphysics package capable of modeling any physical phenomenon that can be described with partial differential equations (PDEs). It is this emphasis on solving PDEs that makes Femlab effective within and between widely-ranging disciplines. “We saw no reason why being general and flexible should
mean giving up the efficiency and computational performance of software designed specifically for solving one-type physics problems”, explains Svante Littmarck, CEO of Comsol. “After all, the heart of modeling a problem in structural analysis, fluid flow, electromagnetics, or acoustics is solving a PDE.”
Femlab uses state-of-the-art solvers developed primarily within the academic research community to address both single- and multi-physics problems. Most dedicated physics packages employ similar solvers. “Because these codes share the same core algorithms for the computationally-intensive tasks”, continues Littmarck, “we believed we could make our general-purpose package just as fast, accurate, and memory-efficient as specialized programs.”

The benchmark evaluation
The benchmark evaluation was conducted by two independent research groups — The Parallel and Scientific Computing Institute at The Royal Institute of Technology (Stockholm, Sweden) and the Centre for Mathematical Sciences at the Lund Institute of Technology (Lund, Sweden). The two groups compared Femlab 3.0a with the dedicated-physics packages Ansys and Fluent.
The testing centered on well-known problems in which clear and definite parameters exist as reference metrics. Structural mechanics capabilities of Femlab and Ansys were evaluated using standardized problems from NAFEMS (National Agency for Finite Element Methods and Standards) as well as examples directly from the Ansys manuals. Fluid-dynamics capabilities of Femlab and Fluent were tested using classic models from the scientific literature.
Results of the testing have been reported and are available to the public. In the reports, examiners define problems, explain procedures, and provide data with sufficient detail for readers to reproduce and verify the results. The complete academic reports are available on the web (see InfoClick at the end of the article).
Bridging the gap
The shown tables give an overview of selected results from the benchmark studies. Parameters of particular interest are accuracy, execution time and peak memory usage. Accuracy is shown as the negative logarithm of the relative deviation from a reference value: an accuracy value of 1.0 corresponds to 90% of the exact value; a value of 2.0 equals 99%, 3.0 equals 99.9%, and so on. The number of degrees of freedom (DOF) measures the problem size. The results at a glance:
-Tab. 1: Here the problem size and CPU time for Femlab and the single-physics product are roughly equal, but Femlab consumes less memory to achieve higher accuracy.
-Tab. 2: Here the problem sizes are almost identical. Compared with its competitor, Femlab achieves the same accuracy for principal stress, greater accuracy for displacement, far less memory consumption and roughly comparable CPU times.
-Tab. 3: The cylinder is slightly offset
from the center of the channel. This results in a lifting force, measured as the lift coefficient. The drag on the cylinder is
measured as the drag coefficient. Problem sizes in this comparison are roughly equal. While the Femlab model consumes greater memory than the single-physics package, the results are far more accurate and require less computing time than the single-physics product.