Extrapolation-Boundary-Condition

Extrapolation Boundary Condition is implemented in OpenFOAM. This boundary condition is strongly recommended to use at the outlet of the flow domain. Any flow properties can be extrapolated from the internal field (p, U, T, alpha .. etc).
Extrapolation boundary condition doesnot take any inputs from the user and hence can be simply implemented as, \

patch_name 
{
    type      extrapolation;
}

For more details please have a look into into the initial comments on extrapolation/extrapolationFvPatchField.H file.

Compilation and linking as library

1. create a Make folder outside the extrapolation directory containing "files" and "options" files.
2. files

extrapolation/extrapolationFvPatchFields.C

LIB = $(FOAM_USER_LIBBIN)/libextrapolation

3. options

EXE_INC = \
    -I$(LIB_SRC)/fileFormats/lnInclude \
    -I$(LIB_SRC)/surfMesh/lnInclude \
    -I$(LIB_SRC)/meshTools/lnInclude \
    -I$(LIB_SRC)/dynamicMesh/lnInclude \
    -I$(LIB_SRC)/finiteVolume/lnInclude

LIB_LIBS = \
    -lOpenFOAM \
    -lfileFormats \
    -lsurfMesh \
    -lmeshTools \
    -lfiniteVolume

4. Run wmake
5. Last line of the successful compilation will be,

-lOpenFOAM -lfileFormats -lsurfMesh -lmeshTools -lfiniteVolume  -o $WM_PROJECT_USER_DIR/platforms/linux64GccDPInt32Opt/lib/libcustomfiniteVolume.so

Linking library through Control Dict

To link this library with the case files of OpenFOAM, Open ControlDict file and add the following line at the end of the file,

libs ("libextrapolation.so");