Uniform (over the whole field) initial values for any variable are set by:
FIINIT(phi) = value
where phi is any SOLVEd or STOREd variable.
Initial values can also be set over parts of the domain by combinations of PATCH and INIT commands. These have the format:
INIT(name, phi, 0.0, value)
|name||- is a unique name, up to 8 characters long, identifying the PATCH|
|INIVAL||- signifies that the PATCH is setting initial values|
|IXF,..||- the first and last cells in X, Y and Z, defining the block of cells. ITF, ITL have no significance, and should be set to 1.|
|phi||- is any SOLVEd or STOREd variable|
|value||- is the value required|
If it is required to set a different value in each cell of a block, then 'value' in the INIT command can be set to one of the ground flags, GRND, GRND1 ... GRND10, to activate coding in Group 11 of GROUND.
The PATCH limits can be set in terms of region numbers by specifying them as #IXF,#IXL etc.
Although the final solution is usually independent of the initial guesses supplied (via FIINIT or PATCH and INIT) by you, these guesses can influence both the time taken to attain the solution, and indeed whether the solution is reached at all, as has been mentioned in sub-Section 5.8 above.
It is therefore a good rule to seek always to supply initial guesses which are as close as possible to the values to be expected in the final solution. Thus, they should have the right sign, and be of the correct order of magnitude; and the velocity fields should satisfy continuity.
If this is not done, PHOENICS will normally attain the correct solution, but at a greater cost in computer time than is necessary; and sometimes the initial guess can be so far from the solution that divergence occurs.
>>> See the Encyclopaedia entry 'INITIAL VALUES'.
(see GROUP 11)
(see LINVLX, LINVLY, LINVLZ)