NewmarkHHT algorithm in Code_Saturne
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NewmarkHHT algorithm in Code_Saturne
Hello,
I am dealing with FSI calculations with Code_Saturne through an internal code coupling. The code uses as mentioned in the documentation a NewmarkHHT 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
I am dealing with FSI calculations with Code_Saturne through an internal code coupling. The code uses as mentioned in the documentation a NewmarkHHT 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

 Posts: 230
 Joined: Fri Dec 04, 2015 1:42 pm
Re: NewmarkHHT algorithm in Code_Saturne
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
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
Re: NewmarkHHT algorithm in Code_Saturne
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
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

 Posts: 230
 Joined: Fri Dec 04, 2015 1:42 pm
Re: NewmarkHHT algorithm in Code_Saturne
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
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
Re: NewmarkHHT algorithm in Code_Saturne
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
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

 Posts: 230
 Joined: Fri Dec 04, 2015 1:42 pm
Re: NewmarkHHT algorithm in Code_Saturne
Hello,
To what specific set of values do you refer? alpnmk, betnmk, gamnmk?
Regards,
Luciano
To what specific set of values do you refer? alpnmk, betnmk, gamnmk?
Regards,
Luciano
Re: NewmarkHHT algorithm in Code_Saturne
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
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.

 Posts: 230
 Joined: Fri Dec 04, 2015 1:42 pm
Re: NewmarkHHT algorithm in Code_Saturne
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 subiterations for implicit coupling (NALIMX)?
Regards,
Luciano
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 subiterations for implicit coupling (NALIMX)?
Regards,
Luciano
Re: NewmarkHHT algorithm in Code_Saturne
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 Fluidstructureinteraction tutorial.
Regards,
So_nuc
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 Fluidstructureinteraction tutorial.
Regards,
So_nuc
Re: NewmarkHHT algorithm in Code_Saturne
Hello,
I think I get the issue relating to the mass structure: I indeed simulate a 2Dlike simulation (height of 1e6m) and I entered before the linear mass instead of the real mass within the height 1e6m. 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
I think I get the issue relating to the mass structure: I indeed simulate a 2Dlike simulation (height of 1e6m) and I entered before the linear mass instead of the real mass within the height 1e6m. 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