[pad]

Hi all,

I have tried searching for a solution to my "problem" but so far I only came across Possible to sum across different patches? which seems clutter my code with similar expressions

I have a number of patches which might change in number so to avoid too much editing of code from simulation to simulation with the risk of missing something I would like to go from

"pressure{patch1}=p*rho*normal()*area();"
...
"pressure{patchN}=p*rho*normal()*area();"

to something like

										
grouped_patches
(
    patch1
    ...
    patchN
)
"pressure{grouped_patches}=p*rho*normal()*area();"

Does anyone know if this is possible in swak4foam to do it directly in the external expressions? I looked through the reference but couldn't find a solution.

Any help is appreciated

[pad]

So it seems creating a faceSet with topoSet for all the patches I want would do the job in this particular case.

"pressure{faceSet'grouped_patches}=p*rho*normal()*area();"

However, when it comes to extracting viscous forces I have come to another hold since

"viscous{faceSet'grouped_patches}=sum(-nu*snGrad(U)*area());"

doesn't work due to the field snGrad(U) is not existing or of wrong type. So snGrad(U) cannot be used on a faceSet. Does anyone know how to work around this?

Also, doing the following gives a similar missing field error on the density.

"density=997;"
"pressure_forces{faceSet'grouped_patches}=density*sum(p*normal()*area());"

while

"density=997;"
"pressure_forces{faceSet'grouped_patches}=sum(p*normal()*area());"
"pressure_forces_density=density*pressure_forces;"

seems to work OK. Have I completely misunderstood how variables are defined or is there a bug in swak4foam when it comes to the last field error with density?