Encyclopaedia Index

### (k) Block-location Indices (LB's); BFC Geometrical Quantities

The body-fitted-coordinate geometrical variables which can be
accessed from GROUND are those in the GRDBFC COMMON block BFCINT.

The zero-location indices of all these variables are stored in the
array L0B(106), which also appears in the file GRDBFC.

The majority of BFC geometrical variables are stored in the same
manner as whole-field solver variables, ie in segments NX*NY*NZ
long. Therefore, the value of, say, the east projected area at cell
IX, IY and IZ is given by:

LF=L0B(APROJE)+IY+NY*(IX-1)+NX*NY*(IZ-1).

The cell-corner coordinates, namely XCORNR, YCORNR, ZCORNR, and (for
the earlier time interval) XCORNO, YCORNO and ZCORNO, are also
stored in continuous segments of the F-array; but the length of each
segment is: (NX+1)*(NY+1)*(NZ+1).

The reason is that, the convention being that the stored coordinates
are those of the low-south-west corners, an extra location is needed
in order that the corners on the high, north and east faces should
also be stored. Thus, where NX, NY and NZ all equal to unity, there
would still be a necessity to store the coordinates of eight corner
points, in order to describe the cell.

To facilitate access to the corner coordinates, the following
INTEGER FUNCTIONs are provided:

ICORN(I,J,K)=J+(NY+1)*[I-1 +(NX+1)*(K-1)]

XC(I,J,K)=F(L0B(XCORNR)+ICORN(I,J,K))

and corresponding ones for YC, ZC, XCO, YCO and ZCO.

Also available for calling by the user are, among other subroutines:

- SECORN (corner index, I, J, K, value), which sets the low-south-
west corner of the cell to value; and
- PRCORN(corner index, K), which prints out the values of the
corner coordinates for the slab with index K (ie, IZ).

It should be noted that the user of PHOENICS is permitted to re-
calculate corner coordinates in the course of the solution,
following that recalculation by calls to BGEOM(1) and BGEOM(2) in
order to ensure that all the dependent geometrical features are also
re-calculated.
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