How to adjust the time step during calculation?

[LiuTingy]

Hello everyone:
I am using Anura3D 2022 version. There exists some numerical oscillation in my calculation. The incipient calculation results are in line with expectations, but distortion occurs when the deformation reaches a certain degree. I'm wondering if there is an option to adjust the critical timestep during dynamic analysis. I don't see any tips in the manual tutorial.
I hope someone can help me to solve the problem, thank you very much!

[LiuTingy]

Maybe I can reduce the courant number to reduce the time step, so as to reduce the numerical oscillation, but I don't know whether it‘s feasible for dynamic analysis and what's the appropriate range taking into account of the calculation efficiency and accuracy.

[ayerrocolom]

You can indeed modify the time step by decreasing the Courant number, which is a factor that multiplied the "critical time step" calculated intrinsically in Anura3D based on established criteria (e.g., CFL condition). The size of the time step will not directly affect the dynamics of the problem. Usually, a time step with a Courant number slightly less than 1 is enough for solution convergence. However, in some cases, when the problem is more complicated (e.g., tricky meshes, complex geometries, very different materials, contact algorithms, multi-phase formulations.... all together), the Courant number needs to be decreased. There is no "good"range, it depends on the problem, and the user should assess that based on solution convergence and calculation efficiency.

[LiuTingy]

Thank you so much for the explanation. I will try to find an appropriate number for my model. And I guess if we can plot the courant number field, or will you guys include it in the next development plan? Because in some CFD simulations, users can visually observe the distribution area and size of the number, thus facilitating the personalized adjustment of their models.

[ayerrocolom]

The Courant number is selected by the user, not by the code, and it is a constant number across the mesh and during the full calculation.