Meshing and Solving
Mesh Resolution
The finite element method approximates the solution within each element, using some elementary shape function that can be constant, linear, or of higher order. Depending on the element order in the model, a finer or coarser mesh is required to resolve the solution. In general, there are three problem-dependent factors that determine the necessary mesh resolution:
Is the variation in the solution due to geometrical factors?
The mesh generator automatically generates a finer mesh where there is a lot of fine geometrical details. Try to remove such details if they do not influence the solution because they produce a lot of unnecessary mesh elements.
Is the skin effect or the field variation due to losses?
It is easy to estimate the skin depth from the conductivity, permeability, and frequency. You need at least two linear elements per skin depth to capture the variation of the fields. If you do not study the skin depth, you can replace regions with a small skin depth with a boundary condition, thereby saving mesh elements.
What is the wavelength?
To resolve a wave properly, it is necessary to use about 10 linear (or 5 2nd-order) elements per wavelength. Keep in mind that the wavelength might be shorter in a dielectric medium.
Selecting a Solver
In most cases the solver that COMSOL Multiphysics suggests can be used. The choice of solver is optimized for the typical case for each physics interface and study type in the AC/DC Module. However, in special cases the solver settings might need fine tuning. This is especially important for 3D problems because they use a large amount of memory. For large 3D problems, a 64-bit platform might be required.
It is of great importance to make sure the formulation defined by the physics interface is compatible with the solver. For example, in the Electrostatics or the Electric Currents interface, a ground boundary condition is usually required to make the model be solved with a direct solver.
In the
COMSOL Multiphysics Reference Manual
:
•
Meshing
•
The Gauge
•
Studies and Solvers
