ALE simulations: local fluid force on specific rigid body positions

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daniele
Posts: 91
Joined: Wed Feb 01, 2017 11:42 am

Re: ALE simulations: local fluid force on specific rigid body positions

Post by daniele » Fri Nov 29, 2019 2:33 pm

Dear Luciano,

Thanks a lot, you are right, the correct field is iforbr.
I am now able to calculate the Stress on the cell surfaces.
I still have one problem. In order to obtain the force, I have to multiply the Stress by the boundary surface of the cell.
The surface value is given by surfbn(ifac) if I am not wrong.
To check the consistency, I performed the following test to calculate the total boundary surface:

Code: Select all

s_tot = 0.d0
 call getfbr('STRUCTURE_WALL', nlelt, lstelt)
    do ilelt = 1, nlelt
       ifac = lstelt(ilelt)
       s_tot=s_tot+surfbn(ifac)
    enddo
Post-processing "s_tot" at every time step, I always have s_tot=0.
Is surfbn the right field to get the face surface?

Thank you very much in advance.
Best regards,
Daniele

Luciano Garelli
Posts: 239
Joined: Fri Dec 04, 2015 1:42 pm

Re: ALE simulations: local fluid force on specific rigid body positions

Post by Luciano Garelli » Fri Nov 29, 2019 3:26 pm

Hello,

You can check the user example cs_user_extra_operations-global_efforts.f90 file. You don't need to multiply by the face area.
Are you running in parallel or serial? Because if you run in parallel you have to do a parallel sum of this variable and the same for the forces.

Regards,
Luciano

daniele
Posts: 91
Joined: Wed Feb 01, 2017 11:42 am

Re: ALE simulations: local fluid force on specific rigid body positions

Post by daniele » Fri Nov 29, 2019 5:13 pm

Hello,

I agree with you about the example.
Nevertheless, in code_saturne doxygen "iforbr" is described to be "field id of the stresses at boundary".
That's why I am confused. It looks as if iforbr was just mu*du_i/dx_i.
Moreover, are pressure forces taken into account inside iforbr?
I did a test to double check: I calculated the sum of iforbr (along a given direction) for the "internal coupling" wall. The obtained value is completely different from the one printed inside the "probes_str_force_i.dat".

I should maybe try to look inside the source what iforbr is exactly...

Have you ever used this field to postprocess forces?

Thank you very much!

Best regards,

Daniele

Luciano Garelli
Posts: 239
Joined: Fri Dec 04, 2015 1:42 pm

Re: ALE simulations: local fluid force on specific rigid body positions

Post by Luciano Garelli » Fri Nov 29, 2019 6:10 pm

Hello,

Both are taken into account, pressure and viscous forces. You can check the file post_util.f90. In this file the forces are used to compute normal and tangential stresses to be the post-processed in salome.

Also I guess that in the forum there are several post about the force posprocessing.

Regards,
Luciano

daniele
Posts: 91
Joined: Wed Feb 01, 2017 11:42 am

Re: ALE simulations: local fluid force on specific rigid body positions

Post by daniele » Wed Dec 04, 2019 11:07 am

Dear Luciano,

Thanks to your help, I managed to calculate the forces on the faces I wanted to.

Thank you very much!

Best regards,

Daniele

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