Page 179 - Process Modelling and Simulation With Finite Element Methods

166 Process Modelling and Simulation with Finite Element Methods

AddIEdit Expressions
Name I Type I Defined I Expression
I uinlet I boundary I geom2: bnd 1 I Ufeed+f*ue
vinlet I boundary geom2: bnd 1 I Vfeed+f*ve
supvel geometry geom2: bnd 1 I 0.5*(uinlet+vinlet)/(Ufeed+Vfeed)
APPlY
OK

Pull down the Mesh menu and select Parameters.

Mesh Mode (cd2, geom2)
>>More
Number of Elements in Subdomain: 1 1000
Apply
OK

This results in a 1000 element meshing. Now change the output times on the
Solver Parameters time stepping tab to 0:0.1:1, Now doubt you are shortly
visited with the error message "Unknown variable or function u" - the same fault
line as before. We found that the convection velocity in a 1-D convection-
diffusion model must be a geometry-wide expression to pass this hurdle. The
workaround is to set u=0.5 (say), run the time integration long enough to get a
solution. Save a model m-file, flowsheet2.m, and edit the coupling variable lines
as follows:
elerncpl 5).elem=elcp~sca~ar;
elerncpl 5).src.g=2;
e 1 emcpl 5].src.bnd.gporder=(l};
elemcpl 5) . src. bnd.var= { 'u0 , { supvel 1 } ] ;
elemcpl 5}.src.bnd.ind=(l};
elemcpl 5].dst.g=2;
%elemcp (5).dst.equ.ind=(l};

Commenting out the destination makes u0 available throughout geometry 2. For
good measure, I also edited the convection velocity variable line to read

equ.u={ { {'uO'},{'uO'},{'uO'},{'O'],{'O'},{'O'}]];
which replaced the hardwired u0=0.5 with the coupling variable. Now we read
in the model m-file (File Menu, Open command), which computes the solution.
Not surprisingly, the time dependent solution is visually invariant from the initial
conditions, which were created as a solution to the no recycle problem. Two
percent recycle does not make a major impact on the solution.