Hi,
I am running an explicit dynamic analysis with Ls dyna using a constant time step. I entered my initial time step of 2.75e-5 using the control implicit general card; however, Ls dyna chooses to evaluate the problem with a larger time step. I invoked DTMax as recommended by the ls-dyna user's manual but the software appears to ignore it. Is there another way to make Ls dyna use a particular time step throughout the analysis run time?
Hi @kingoz79,
I'm a bit confused because you say you are running an explicit analysis but are trying to use a *control_implicit card to control your timestep? And you want to make the timestep smaller? Generally, you'd want to increase the timestep if you had something like long runtimes, by defining a minimum timestep as DT2MS in *Control_timestep. This would invoke mass scaling at regions of you analysis where the timestep fell below this cutoff.
https://www.dynasupport.com/howtos/general/mass-scaling
Sorry, I'm just a little confused.
Hi @Negative Volume,
Thanks for reaching out. In the Control_Implicit_auto, I have set IAUTO = 0 to ensure a constant time step. I have also specified DTMIN = 1.2e-7sec and added a table to control DTMAX. In Control_implicit_general, IMFLAG = 0 for explicit analysis. Perhaps, it is not clear to me how Ls Dyna works. For the purpose of my research, I need to have constant time step for the results to be accurate. If Ls Dyna skips a several time steps, the results may be incorrect. Thus, I would like to control the maximum timestep.
@Negative Volume,
Thanks for the clarification. Your explanation helped and was similar to that provided by Ansys Ls Dyna support staff.
@kingoz79 okay so did you get everything figured out?