2008

Multiphysics Modeling Simplifies Analysis of Electrical and Electromagnetic Effects

Effects of lightning strikes and electromagnetic fields are simulated and modeled easily.

The Saab Group has 17 business units, which are split into defense and security, systems and products, and aeronautics. Over the years, the company has taken advantage of the many paradigm shifts that have taken place in engineering analysis. One example is implementing comprehensive engineering methodologies that combine traditional experiments and testing with newer tools such as computer modeling and simulation. In the 1980s, Saab began applying largescale computer simulations, which were used to verify the lightning-protection components in the wings of the Gripen fighter aircraft.

One of the Saab divisions was working with the Swedish Defense Material Administration, and engineers in that division were asked to perform a conceptual study on what happens to airplane materials when struck by lightning. Because weight is a major consideration in aeronautic design, these wings are made of lightweight, yet strong, composite materials. These materials are made up of several layers of different composites, and in these layers, the materials often have a different orientation to increase strength. But, because modern composites exhibit strongly anisotropic electrical and thermal conductivities, and because they have low conductivity compared to metals, when the high electric currents due to a lightning strike flow through them, they experience a high temperature rise and are vulnerable to heating damage. The heat flowing through the composite structure also has an effect on aircraft parts close to the location of the strike.

The anisotropic, layered nature of these composites demands a 3D analysis. In addition, the underlying physics are strongly coupled because the heating, and thus temperature, depends on the current distribution, which in turn is influenced by the fact that the composites’ electrical conductivity is temperature- dependent. Any attempt to analyze the temperature rise becomes a non-trivial multiphysics problem.

In initial attempts at modeling this effect, engineers tried manipulating inhouse codes and commercial codes to include these multiphysics phenomena. However, this proved extremely difficult because none of the codes were built for simultaneously solving the electromagnetic and temperature fields together.

In 2002, Saab learned of COMSOL Multiphysics, a simulation tool whose fundamental structure was built around coupling physics and solving them together easily and intuitively. This was, at the time, almost unheard of in codes for electromagnetic simulations, which basically analyzed just the electromagnetic fields; if other physics were to be involved in the modeling application, their effect had to be integrated in an empirical or approximate fashion.