Running list of assumptions/approximations to be revisited

[stvdwtt]

• When the heat source is incident on a part of the domain that is lower than the nominal height of the build (currently defined as the highest active part of the mesh), the heat from the heat source is lost -- the analytic function puts it in the inactive part of the mesh. The expected behavior is that the heat source is translated downward until it reaches active material.
• For wire/DED, a fairly typical approximation is used that the material is deposited as an extruded rectangular box. This ensures full coverage for each layer. However, the actual deposition profile is closer to hemispherical with overlap between passes.
• Currently the governing equations ignore the chain-rule terms that result from spatial variation in the thermal conductivity and heat capacity due to their dependence on the (spatially varying) temperature.
• ~All boundary conditions are adiabatic.~ Fixed by #101