Multiphysics for the everyday engineer

Fall has hit hard in the Boston area -- cool breezes and colorful leaves. COMSOL INC. is holding its COMSOL 2009 Conference here. As you might know, the company provides multiphysics software for the modeling of complex phenomena such as flow and mixing in the liquid between bubbles, effects of antenna polarization relative to tunnel orientation in underground tunnels, and turbulent flow in HEV static mixers. Until fairly recently, the software targeted academic institutions, government agencies, and research groups. The recent v4 aims for the everyday design engineer. For advanced users, it's still possible to get under the hood, connect to, say, Matlab, and call legacy C or Fortran code. A new modeling tree (similar to a history tree in CAD) walks newer users intuitively through all the steps to building and solving a model. The new GUI is clean and elegant. A COMSOL representative told me that a creative design firm helped design the interface, and this really shows in the unobtrusive yet aesthetically pleasing GUI and icons.

In one session, the presenter explained a new transient segregated solver (for physics systems such as EM problems that are not tightly coupled). He says the solver works by first determining the initial conditions. Then, for each time step, it: (1) determines the material properties; (2) computes electric fields; (3) computes resistant heating; (4) determines appropriate next time step; and, (5) repeats these steps until finished. Because the orders of time for thermal and electrical problems are completely different, the solver might, for instance, take a large thermal step, takes many little electromagnetic steps, take a huge thermal step, and take a lot of tiny electromagnetic steps, until conversion. The advantage for these kinds of problems is that the solver take 1/16 of the memory of fully-coupled transient solvers.

Another session explained equation-based modeling, which can involve numeric as well as symbolic mathematics. The so-called Weak Form PDE is the foundation of all the FEM that goes on in the software. That's because it's possible to ignore or add elements to it for the solving of almost any kind of multiphysics problem. COMSOL uses the FEM to approximate a solution's equation written in what's called the "complex vector analysis form." Shorter and "cleaner" looking than coefficient equations, this makes it easier for designers to wrap their heads around solving PDEs, ODEs, and even algebraic equations.

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