The geometry input handles the dimension and the numerical resolution of the simulation domain, i.e. the user has to specify the number of numerical grid cells in each direction and the grid spacing. In this context, the user decides whether to perform a 1D, 2D or a 3D simulation. Here, the x, y and z direction are not completely equivalent: temperature gradients or profiles e.g. can only be defined in z-direction (except for temperature coupling, see below). Therefore, for 1D simulations, the number of cells in x and y direction (CellsX and CellsY) should be set to 1. For 2D simulations, CellsY must be set to 1. The definition of a 2D calculation domain is shown in the driving file section below.
The grid spacing is specified in microns. It is one of the most important numerical parameters as it determines the numerical resolution. The grid resolution should be high enough to resolve the diffusion profiles, depending on the diffusion coefficients and the growth velocity of the interface, and the curvatures of the finest expected microstructures. On the other hand, the simulation time is strongly determined by the grid resolution, so that in practice always a compromise must be found between grid resolution and calculation time.
As an optional parameter, a rescaling factor for the graphical outputs can be given if the result files otherwise would be too big. If as rescaling factor is specified, the outputs are written with a correspondingly smaller resolution. The simulation itself is not affected by this parameter.
Example: Geometry settings for a 2D simulation
... # Geometry # ------------- # Grid size? # (for 2D calculations: CellsY=1, for 1D calculations: CellsX=1, CellsY=1) # Cells in X-direction (CellsX): 300 # Cells in Y direction (CellsY): 1 # Cells in Z direction (CellsZ): 300 # Cell dimension (grid spacing in micrometers): # (optionally followed by rescaling factor for the output in the form of '3/4') 2.0000 ...