Newmark-HHT algorithm in Code_Saturne

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So_nuc
Posts: 45
Joined: Wed Sep 05, 2018 12:16 pm

Newmark-HHT algorithm in Code_Saturne

Post by So_nuc » Mon May 20, 2019 11:47 am

Hello,

I am dealing with FSI calculations with Code_Saturne through an internal code coupling. The code uses as mentioned in the documentation a Newmark-HHT algorithm to determine the structure displacement. However, it seems to have no information about the numerical scheme to calculate the structure acceleration and velocity. Moreover, the frequency of structure displacement in my case depends on the dtstr value, which is not acceptable. What would you propose regarding this issue please ?

Thank you in advance.

Best regards,

So_nuc

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

Re: Newmark-HHT algorithm in Code_Saturne

Post by Luciano Garelli » Mon May 20, 2019 12:35 pm

Hello,

I don't understand very well your question, but did you check the file newmrk.f90. In this subroutine are computed the accelerations, velocities and displacements of the structure.

Regards,

Luciano

So_nuc
Posts: 45
Joined: Wed Sep 05, 2018 12:16 pm

Re: Newmark-HHT algorithm in Code_Saturne

Post by So_nuc » Mon May 20, 2019 2:04 pm

Hello,

Thank you for your reply.

I meant that there only seems to have the details of the numerical scheme for the predicted displacement and forces driven by the coefficients aexxst, bexst and cfopre (on the file example "cs_user_fluid_structure_interaction.f90").

Then, how to handle the coefficients of the Newmark algorithm (alpnmk, betnmk, gamnmk) within a FSI calculation (done by means of the internal coupling of Code_Saturne) ?

Thank you in advance.

Best regards,

So_nuc

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

Re: Newmark-HHT algorithm in Code_Saturne

Post by Luciano Garelli » Mon May 20, 2019 3:09 pm

The parameter alpnmk is initialized in iniini.f90 and the paremeters betnmk and gamnmk a defined in modini.f90. I think that you can copy the newmrk.f90 or strdep.f90 to the SRC directory and change the values.

I don't known if the values of the alpnmk, betnmk, gamnmk can be accessed from another user function like cs_user_paremeters. If it is possible will be better solution

Regards,

Luciano

So_nuc
Posts: 45
Joined: Wed Sep 05, 2018 12:16 pm

Re: Newmark-HHT algorithm in Code_Saturne

Post by So_nuc » Mon May 20, 2019 4:06 pm

Hello,

I have included the use of alstru module in the "cs_user_paramters.f90" file. However, the structure displacement depends on the structure time step used within the internal coupling. Would you require a specific set of values to get accurate results ?

Thanks in advance.

Regards,

So_nuc

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

Re: Newmark-HHT algorithm in Code_Saturne

Post by Luciano Garelli » Mon May 20, 2019 4:27 pm

Hello,

To what specific set of values do you refer? alpnmk, betnmk, gamnmk?

Regards,

Luciano

So_nuc
Posts: 45
Joined: Wed Sep 05, 2018 12:16 pm

Re: Newmark-HHT algorithm in Code_Saturne

Post by So_nuc » Mon May 20, 2019 4:50 pm

Hello,

The set of values (aexxst, bexxst, cfopre, dtstr, alpnmk, betnmk, gamnmk). By changing dtstr for fixed values of the other parameters, I indeed get different frequencies of the structures displacement from the internal coupling.

Thanks in advance.

Regards,

So_nuc
Last edited by So_nuc on Mon May 20, 2019 5:56 pm, edited 1 time in total.

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

Re: Newmark-HHT algorithm in Code_Saturne

Post by Luciano Garelli » Mon May 20, 2019 5:32 pm

Hello,

I don't known what kind of FSI problem are you solving. The time integration is implemented like in the paper"Improved Numerical Dissipation for Time Integration Algorithms in Structural Dynamics, Hilber, H.M, Hughes,T.J.R and Talor, R.L.". The change in the parameters will modify the behavior of the algorithm and the numerical damping added. Sometime some numerical damping should be added (alpha>0) in order to stabilized the simulation.

Did you try to increase the number of sub-iterations for implicit coupling (NALIMX)?

Regards,

Luciano

So_nuc
Posts: 45
Joined: Wed Sep 05, 2018 12:16 pm

Re: Newmark-HHT algorithm in Code_Saturne

Post by So_nuc » Mon May 20, 2019 6:03 pm

Hello,

Thank you for these details. I am actually dealing with the simulation of structures in a fluid. I should observe the added mass effect through a reduced frequency of structures displacement but the result does not exhibit any effect (the structure oscillates with its natural frequency). I have also tried with the "nalimx" and "epalim" values of the Fluid-structure-interaction tutorial.

Regards,

So_nuc

So_nuc
Posts: 45
Joined: Wed Sep 05, 2018 12:16 pm

Re: Newmark-HHT algorithm in Code_Saturne

Post by So_nuc » Tue May 21, 2019 8:29 am

Hello,

I think I get the issue relating to the mass structure: I indeed simulate a 2D-like simulation (height of 1e-6m) and I entered before the linear mass instead of the real mass within the height 1e-6m. Nevertheless the structure mass is now very low and leads to calculation instability despite of the parameters of the Newmark algorithm which should ensure calculation unconditional stability.

Regards,

So_nuc

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