Simplifying the Geometry Using Boundary Conditions
An important technique to minimize the problem of size is to use efficient boundary conditions. Truncating the geometry without introducing large errors is one of the great challenges in modeling. Following are some ideas of how to do this in both 2D and 3D problems.
Does the solution only undergo small changes?
When a model extends to infinity, it might have regions where the solution only undergoes small changes. This problem is addressed in two related steps. First, truncate the geometry in a suitable position. Second, apply a suitable boundary condition there. For static and quasi-static models, it is often possible to assume zero fields at the open boundary, provided that this is at a sufficient distance away from the sources.
Can you replace the thin layers with boundary conditions?
There are several types of boundary conditions in COMSOL Multiphysics suitable for such replacements. You can, for example, replace materials with high conductivity with the shielding boundary condition, which assumes a constant potential through the thickness of the layer. If you have a magnetic material with a high relative permeability, you can also model it using the shielding boundary condition.
One-Sided Magnet and Plate: Application Library path ACDC_Module/Magnetostatics/one_sided_magnet
Use boundary conditions for known solutions.
A body with a high conductivity at high frequency has the current density confined to a thin region beneath the surface of the wire. You can often replace the current in the body by either a surface current boundary condition or an impedance boundary condition.
Eddy Currents: Application Library path ACDC_Module/Inductive_Devices_and_Coils/eddy_currents