Modal Analysis missing rotational DOF participation factor

- September 8, 2025 at 1:54 am
  
  Dennis Chen
  Subscriber
  
  Hello, I am doing a comparison between Ansys Mechanical and LS-Dyna for their modal analysis. Everything is basically the same except in LS-Dyna, the rotational DOF has 0 participation factors for the 1st 10 modes.
  I first thought that 1) it's because of the scaling of rotscl from implicit_control_eigenvalue but that doesn't check out and 2) it's because it's all solid elements but that it's also solid elements in Ansys Mechanical side.
  Both tool are using block Lanczos mode extraction methods. Can anyone think of a reason why I get 0 participation factor in rotational DOF in dyna?
  However, the same problem in Ansys Mechanical returns rotational DOF
- September 8, 2025 at 3:42 pm
  
  Erik Kostson
  Ansys Employee
  
  Hi
  It is as you say - in LS-Dyna there are no rot dof in solid model and hence zeros for PF.
  
  In MAPDL it is the same but rot PF are calculated - for details on PF see the ansys mapdl help manual where it is shown - D matrix has also rotations - LS-Dyna does not have/do that.
  
  All the best
  
  Erik