Difference between revisions of "HowTo blockMesh with m4"
m (Moved this from the FAQ) |
(→How to quickly change the mesh with blockMesh) |
||
Line 24: | Line 24: | ||
The first four line of codes simply define a calculator, sets a variable <i>VCOUNT = 0</i> and defines a new way of defining vertices. The last four are for defining 2D cells, as well as patches for the boundaries. The b is short for the bottom and t for top, that is the bottom and top of the 2D cell set. | The first four line of codes simply define a calculator, sets a variable <i>VCOUNT = 0</i> and defines a new way of defining vertices. The last four are for defining 2D cells, as well as patches for the boundaries. The b is short for the bottom and t for top, that is the bottom and top of the 2D cell set. | ||
− | So imagine we want to create a | + | So imagine we want to create a 2D channel with an inlet outlet and wall boundary conditions, first off we define the coordinates of the channel: |
<cpp> | <cpp> | ||
− | + | define(side, 100.0) | |
− | + | define(height, 300.0) | |
− | + | define(nrcellsx, 10) | |
− | + | define(nrcellsy, 30) | |
+ | define(origox, 0.0) | ||
+ | define(origoy, 0.0) | ||
+ | define(coordinatesidex, calc(origox+side)) | ||
+ | define(coordinatesidey, calc(origoy+height)) | ||
+ | |||
+ | define(Z1, 0.0) | ||
+ | define(Z2, 1.0) | ||
</cpp> | </cpp> | ||
− | + | Then we want to define the actual vertices: | |
− | + | ||
<cpp> | <cpp> | ||
− | + | ||
− | + | ||
− | + | ||
vertices | vertices | ||
( | ( | ||
− | + | (origox origoy Z1) vlabel(a1b) | |
+ | (coordinatesidex origoy Z1) vlabel(a2b) | ||
+ | (coordinatesidex coordinatesidey Z1) vlabel(a3b) | ||
+ | (origox coordinatesidey Z1) vlabel(a4b) | ||
+ | |||
+ | (origox origoy Z2) vlabel(a1t) | ||
+ | (coordinatesidex origoy Z2) vlabel(a2t) | ||
+ | (coordinatesidex coordinatesidey Z2) vlabel(a3t) | ||
+ | (origox coordinatesidey Z2) vlabel(a4t) | ||
) | ) | ||
</cpp> | </cpp> | ||
− | + | ||
+ | We can now define the block: | ||
<cpp> | <cpp> | ||
blocks | blocks | ||
+ | ( | ||
+ | // block0 | ||
+ | hex2D(a1, a2, a3, a4) | ||
+ | (nrcellsx nrcellsy 1) | ||
+ | simpleGrading (1 1 1) | ||
+ | ); | ||
+ | |||
+ | </cpp> | ||
+ | Then, the boundary conditions is simply: | ||
+ | |||
+ | <cpp> | ||
+ | patches | ||
+ | |||
+ | ( | ||
+ | patch inlet | ||
( | ( | ||
− | + | quad2D(a1,a2) | |
) | ) | ||
+ | |||
+ | patch outlet | ||
+ | ( | ||
+ | quad2D(a3,a4) | ||
+ | ) | ||
+ | |||
+ | empty back | ||
+ | ( | ||
+ | backQuad(a1,a2,a3,a4) | ||
+ | ) | ||
+ | |||
+ | empty front | ||
+ | ( | ||
+ | frontQuad(a1,a2,a3,a4) | ||
+ | ) | ||
+ | |||
+ | wall | ||
+ | wall | ||
+ | ( | ||
+ | quad2D(a1,a4) | ||
+ | quad2D(a2,a3) | ||
+ | ) | ||
+ | ); | ||
+ | |||
</cpp> | </cpp> | ||
Revision as of 10:47, 1 February 2006
How to quickly change the mesh with blockMesh
The Gnu preprocessor m4 is handy for parametric refinement to the mesh. It is also possible to change position of multiple vertices at the same time, thus reducing the possibility of errors when altering the mesh.
Example:
changecom(//)changequote([,]) define(calc, [esyscmd(perl -e 'printf ($1)')]) define(VCOUNT, 0) define(vlabel, [[// ]Vertex $1 = VCOUNT define($1, VCOUNT)define([VCOUNT], incr(VCOUNT))]) define(hex2D, hex ($1b $2b $3b $4b $1t $2t $3t $4t)) define(quad2D, ($1b $2b $2t $1t)) define(frontQuad, ($1t $2t $3t $4t)) define(backQuad, ($1b $4b $3b $2b))
The first four line of codes simply define a calculator, sets a variable VCOUNT = 0 and defines a new way of defining vertices. The last four are for defining 2D cells, as well as patches for the boundaries. The b is short for the bottom and t for top, that is the bottom and top of the 2D cell set.
So imagine we want to create a 2D channel with an inlet outlet and wall boundary conditions, first off we define the coordinates of the channel:
define(side, 100.0) define(height, 300.0) define(nrcellsx, 10) define(nrcellsy, 30) define(origox, 0.0) define(origoy, 0.0) define(coordinatesidex, calc(origox+side)) define(coordinatesidey, calc(origoy+height)) define(Z1, 0.0) define(Z2, 1.0)
Then we want to define the actual vertices:
vertices ( (origox origoy Z1) vlabel(a1b) (coordinatesidex origoy Z1) vlabel(a2b) (coordinatesidex coordinatesidey Z1) vlabel(a3b) (origox coordinatesidey Z1) vlabel(a4b) (origox origoy Z2) vlabel(a1t) (coordinatesidex origoy Z2) vlabel(a2t) (coordinatesidex coordinatesidey Z2) vlabel(a3t) (origox coordinatesidey Z2) vlabel(a4t) )
We can now define the block:
blocks ( // block0 hex2D(a1, a2, a3, a4) (nrcellsx nrcellsy 1) simpleGrading (1 1 1) );
Then, the boundary conditions is simply:
patches ( patch inlet ( quad2D(a1,a2) ) patch outlet ( quad2D(a3,a4) ) empty back ( backQuad(a1,a2,a3,a4) ) empty front ( frontQuad(a1,a2,a3,a4) ) wall wall ( quad2D(a1,a4) quad2D(a2,a3) ) );
When the file is finished, assuming it's called blockMeshDict.m4, one simply types
m4 blockMeshDict.m4 > blockMeshDict
Before running blockMesh as usual.