Page 194 - Process Modelling and Simulation With Finite Element Methods

Simulation and Nonlinear Dynamics 181

Boundary Mode
Select domain 1
Use the multiphysics pull down menu to select the IC NS mode
Set boundaries 1& 4 with slip/symmetry and 2&3 as no-slip
0 Use the multiphysics pull down menu to select the CC mode
Set bnd 2 with T=l; bnd 3 with T=O; keep 2 and 4 no flux

Now pull down the Subdomain menu and select Subdomain settings.

Subdomain Mode
Select domain 1
0 Use the multiphysics pull down menu to select the IC NS mode
Set p=l; ‘fl=Pr; F,=O; F,=Ra*Pr*T
0 Use the multiphysics pull down menu to select the CC mode
Set p=l; K=l; c=l; U=U; V=V
Select the init tab; set T(tO)= 1-y
APPlY
OK
Now pull down the Mesh menu and select the Parameters option.

Mesh Parameters
0 Select more>>
Max edge size general: 0.1
Remesh
0
OK
There should be 1028 elements. If you click on the = button on the toolbar to
Solve you will find that the solution is poorly convergent. There are two
contributions to this poor convergence. The first is the lack of a pressure datum.
This problem has no imposed pressure on the boundary, so the solution is unique
up to an arbitrary additive pressure constant. The pressure equation

(5.9)

is therefore singular. A pressure datum is readily set by following a recipe
discovered by Jerome Long of COMSOL UK Ltd.