TMAP8 User Notes
The following page is dedicated to various notes concerning TMAP8 functionality that might be helpful to both new and seasoned uers. This page will be updated periodically, so check back often!
Scaling
Dimensions in TMAP simulations can have dramatically different scales, e.g. number densities can be of order Avogadro's number while length and time scales are closer to unity when using SI units. Morever, multiple species, whether different chemical species or the same chemical species in different phases (e.g. solute vs. trapped), can have significantly different concentration levels. In order to have robust nonlinear and linear solves, we often have to perform scaling operations to bring different quantities closer to order unity.
One example of scaling is exemplified by the trap_per_free parameter that is present in the TrappingNodalKernel object (as well as other objects in TMAP8). Trapping concentrations may be larger than solute concentrations for a given chemical specie. However, for a good multiphysics multivariable solve, we want the numerical concentrations of the two species to be about the same. If for instance, the concentration of the trapped specie is roughly 1000 times larger than the mobile specie, we can specify trapped_per_free = 1000. This is effectively changing the concentration of the trapped specie from being measured in #/volume to k#/volume where 'k' indicates kilo. After this transformation, the numerical concentrations of the trapped and mobile species are on the same order of magnitude.