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Ansys Learning Forum › Forums › Discuss Simulation › LS Dyna › A question about quasi-static loading and oscillating response › Reply To: A question about quasi-static loading and oscillating response

May 3, 2024 at 1:24 pm
Alex R.
Ansys Employee

Hello Andreas,

In any explicit simulation some degree of dynamic effects will be present, even if the ratio of kinetic energy to internal energy falls below 5%. There are couple of options that you could try: 

  1. Include damping in your simulation.
  2. Check the material models, if all of them are elastic and there is no damping, the system will oscillate more than a physical one. Please check if there are materials with viscoelastic properties in the model. 
  3. Incorporate a dynamic relaxation phase in your simulation. Please check: https://ftp.lstc.com/anonymous/outgoing/jday/bolt_preload3.pdf
  4. If you are not interested in dynamic events at all, the implicit solver can be used to solve the model.

Regarding your follow up question. It is hard to define what is a quasi-static condition for an explicit model. The 5% threshold is also just a rough estimate, not a specific threshold value. It  might not be applicable to some models. The question that should be asked if the rigid body would have a 0 acceleration will the result change, by how much? If the answer is that it will change too much then yes, the 0 acceleration should be pursued. 

Please let me know,

Thank you,
Alex