Encyclopaedia Index

### INFORMATION-SEEKING PIL COMMANDS

INITIAL VALUES of SOLVEd and STOREd variables, whether starting- time values for a transient phenomenon or first guesses for a steady one, are needed by EARTH at the start of the solution process.

If the variable is being stored but not solved for (which is usually true of porosities and of PRPS, the initially-set values will be retained throughout the calculation.

### (a) Setting the initial values

Initial values may be set in one or more of the following ways:-

• A uniform initial value may be supplied for each variable, for the whole integration domain, by setting FIINIT(variable_name) in the Q1 file. Alternatively the default values of FIINIT, usually 1.0e-10), may be accepted.
• A PATCH can be used to define sections of the domain over which further settings are to be made, with "type" INIVAL, LINVLX, LINVLY or LINVLZ, followed by appropriate INIT commands.

For example,
PATCH(MIDDLE,INIVAL,NX/4+1,3*NX/4,NY/4+1,3*NY/4,1,1,1,1)
INIT (MIDDLE,H1,0.0,100.0) sets the values of H1 in the centre of the IZ=1 slab to:
FIINIT(H1) + 100.0, if INIADD = T, or to:
100.0, if INIADD = F .

The default value of INIADD is T. Use of this value, especially in conjunction with the use of other types than INIVAL, permits complex initial-value patterns to be created by the use of multiple partly-overlapping PATCHes.

When INIADD=F, by contrast, the effect of any PATCH-INIT combination is simply to overwrite the value already set.

If it is desired to give the variable initial values which vary linearly with x, y or z, the following steps should be taken:

1. the PATCH type should be LINVLX, LINVLY or LINVLZ;
2. the third argument of INIT should be given the value of the multiplier of x, y or z (ie. the gradient);
3. the fourth argument of INIT should be given the value of the additive constant, i.e. the value in the first cell.

When porosities ( eg. NPOR ) fields are being set, it is important to remember to put FIINIT(NPOR)=1.0, so that no blockage is present in sections of the domain not identified by PATCH.

For more complicated variations of the initial fields than those provided by the above options, the fourth argument of INIT should be set to GRND. This causes EARTH to visit group 11 of GROUND for an array of GROUND-set VALues for each cell in the PATCH. For example,

PATCH(DOMAIN,INIVAL,1,NX,1,NY,1,NZ,1,1)
INIT(DOMAIN,H1,0.0,GRND)

requires the user to provide in group 11 of GROUND a sequence which fills the EARTH array referred to by the index VAL for INDVAR=H1 at each IZ slab of the domain.

### (b) Checking the initial values

To check that the initial fields are correctly set, the user should set INIFLD=T to cause EARTH to print out the initial fields at the beginning of the calculation.

### (c) Velocities in BFC grids

In BFC grids, uni-directional flows can be initialized by means of the special PATCH names starting IBFC that causes group 11 of GREX to call subroutine GXBFC. The following commands result in a uniform initial flow at 99.0 m/s, parallel to ZC in a body-fitted grid,
PATCH(IBFC,INIVAL,1,NX,1,NY,1,NZ,1,1)
INIT(IBFC1,U1,0.0,GRND1)
INIT(IBFC1,V1,0.0,GRND1)
INIT(IBFC1,W1,0.0,GRND1)
INIT(IBFC1,UCRT,0.0,0.0)
INIT(IBFC1,VCRT,0.0,0.0)
INIT(IBFC1,WCRT,0.0,99.0)

See PATCH, TYPE and INIVAL, for further information.

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