Encyclopaedia Index
### Sub-grids, setting of

(see SUBGRD command)
SUBGRD: The SUBGRD extension to GRDPWR

SUBGRD facilitates the distribution of grid intervals for a
succession of segments in each direction. All the user has to do
is to insert a series of SUBGRD commands.

This feature is especially useful when the grid has to accord with
the geometric positions of the corners of solid bodies placed
within the flow domain. The user can start by concentrating his
attention on these locations, and defining his boundary-condition
and source patches in terms of the corner indices, expressed in
symbolic terms.

When all that is done, he can consider what values he wishes to
ascribe to the indices and exponents in order to produce the
required fineness and distribution of grid.

The syntax is : SUBGRD(DIR,L1,L2,DIST,POW)

This sets GRDPWR-type grids over a portion of the grid. DIR is the
direction, and may be X,Y,Z or T. L1 and L2 are the first and last
cells in the section of sub-grid. L1 must always be (L2+1) of the
previous section. SUBGRD automatically resets NX,NY,NZ or LSTEP to
the current running total number of cells. DIST is the distance
over which the current sub-grid extends. XULAST, YVLAST, ZWLAST or
TLAST are reset internally to the new total distance, and the
corresponding FRAC array is rescaled to be between 0 and 1.

See GRDPWR for further information.

Symmetrical power-law grids can be obtained by setting L2 to be
negative.

SUBGRD has now been superseded by GRDPWR used in conjunction with
NREGT and IREGT; however, it is still available, for compatibility
with Q1 files written for version 1.5.

wbs