The additional source terms which bring about the different convection schemes are activated by means of PATCH and COVAL commands in which
PATCH commands contain the special names, types and can cover the computational domain in user prescribed order.
To activate any of the schemes available, the patch name must start with four characters CONM. A fifth character controls the coordinate direction in which the scheme is to be applied, as follows:-
| PATCH name | Scheme in the direction | |
| CONM2 | All | |
| CONM3 | X | |
| CONM5 | Y | |
| CONM7 | Z |
However, if the sixth character of the patch name is the letter D, then it signifies the choise of the one of the local oscillation- damping algorithms, i.e SOLD or CDLD, depending on the GRNDn number in the value argument of the COVAL command, as will be explained in the next section. The letter C in the sixth character of the patch name determines the CSOB scheme to be used. In the latter case two different PATCH'es with the names ending with C0 and C4 followed by corresponding COVAL commands must be specified for each variable.
The patch type must be CELL.
The extent of the patch does not need to be the whole computational domain, but will determine the region over which the scheme is applied.
Note that convection terms are modified only over the cell surfaces internal to the patch.
The COVAL command has the general format
COVAL ( CONM***, phi, FIXFLU, GRNDn )
where
(i) phi is a scalar variable;
(ii) The GRNDn number in the value argument determines the scheme to be used, according to the following table:
| Value | PATCH name | Scheme | |
| GRND | CONM* | Implicit SOUD | |
| GRND4 | CONM* | Implicit CDS | |
| GRND4 | CONM*D | Implicit CDLD | |
| GRND | CONM*D | Implicit SOLD | |
| GRND | CONM*C0 | Implicit CSOB | |
| GRND4 | CONM*C4 |
Users may choose to employ different schemes for different variables; they may do so simply by setting different GRND numbers in their corresponding COVAL statements. The coefficient argument of the COVAL is always FIXFLU.
For example, a Q1 file which invokes the fully implicit SOLD algorithm over the whole integration domain for a variable UC1 would include the statements:
PATCH ( CONM2D, CELL, 1,NX,1,NY,1,NZ,1,LSTEP)
COVAL ( CONM2D, UC1, FIXFLU, GRND )
But, the PATCH and COVAL commands to activate the CSOB in X- direction would be , as follows :
PATCH(CONM3C0,CELL,1,NX,1,NY,1,NZ,1,LSTEP)
PATCH(CONM3C4,CELL,1,NX,1,NY,1,NZ,1,LSTEP)
COVAL(CONM3C0,VC1,FIXFLU,GRND)
COVAL(CONM3C4,VC1,FIXFLU,GRND4).
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