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#1 |
Member
David Hora
Join Date: Mar 2009
Location: Zürich, Switzerland
Posts: 63
Rep Power: 16 ![]() |
Hi all
I encountered a problem with the forces functionObject. I have a simulation with different patches in the domain. Some of the patches have similar names, e.g.: BLADE HUB-BLADE SHROUD-BLADE I wanted to calculate the forces acting on the patch "BLADE". Unfortunatelly the forces functionObject adds the forces of all patches with the string "BLADE" in its name. Additionally I have a question concerning the moments. As far as I understand the code, the moments are calculated with the cell centers: vectorField Md = mesh.C().boundaryField()[patchi] - CofR_; vectorField pf = mesh.Sf().boundaryField()[patchi]*p.boundaryField()[patchi]; fm.first().first() += rho(p)*sum(pf); fm.second().first() += rho(p)*sum(Md ^ pf); Wouldn't it be better to use the face centers (mesh.Cf())? Thanks a lot & best regards David |
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#2 |
Senior Member
Join Date: Mar 2009
Posts: 854
Rep Power: 21 ![]() |
I will look into the patch name issue.
mesh.C().boundaryField()[patchi] returns the face centres the same as mesh.Cf().boundaryField()[patchi] H |
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#3 |
Senior Member
Mattijs Janssens
Join Date: Mar 2009
Posts: 1,419
Rep Power: 25 ![]() |
Thanks for the report. I corrected the wild-card matching (in 1.5.x). Now BLADE will match only BLADE. Use "BLADE.*" to match all patches starting with BLADE.
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#4 |
Member
Greg Givogue
Join Date: Aug 2010
Location: Ottawa Canada
Posts: 57
Rep Power: 15 ![]() |
Hi,
I realize this is an old post but I'm pretty desperate! I'm having some trouble understanding why I cannot calculate a reasonable centre of pressure when I use the forces and moments function. It is my understanding that centre of pressure (x y z) should be located on the body and that it is related by; Mx=Fy*z+Fz*y My=Fx*z+Fz*x Mz=Fx*y+Fy*x When I use these relationships I end up with x y z far from the body... I have also ran the patchIntegrate command for p over the body and it produces a different force than the force function (pressure component)? I have posted this question http://www.cfd-online.com/Forums/ope...aero-body.html but I haven't received any useful feedback. I appreciate any pointers you can give! Please help. Greg |
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