Page 139 - Process Modelling and Simulation With Finite Element Methods

126 Process Modelling and Simulation with Finite Element Methods
Pull down the options menu and select Add/Edit constants. The AddEdit
constants dialog box appears.

Add/Edit Constants
Assign Pe, Bz, nlim, and q with the values
from Table 3.2

Now pull down the Subdomain menu and select Subdomain settings.

Subdomain Mode
0 Select domain 1
Set u=Pe; R= B2*(nlim-c)*exp(-QQ/c)
Apply
Select the init tab; set c(t0)=1.656

Now Pull down the Subdomain menu and select View as PDE Coefficients,
then reselect Subdomain settings. We will tackle the steady state solution
first. We could put d,=O as the mass coefficient now, but in fact the selection of
the Solver (Stationary nonlinear or Time Dependent) will make the
appropriate choice for us.
The mesh is extremely important here, as rapid variations near the boundary
conditions are expected. Pull down the Mesh menu and select Parameters. By
creating symmetry boundaries, the endpoints become equivalent.

Mesh Mode
>>More
Max size near vertices: 1 0.0001 2 0.0001
0
0 Number of Elements in Subdomain: 1 1000
APPlY
0 OK
This results in a 1312 element meshing. Note that “Max size near vertices” takes
a vector entry with each pair of elements of the form: vertex number followed
by maximum size. This constrains the elliptic mesh generator to give
appropriately large or small elements as directed. Similarly, “Number of
elements in subdomain” can be set by a MATLAB vector entry. Since there is
only one subdomain here, only one pair (subdomain number, number of
elements) can be specified.