Modeling damping with solid elements in nonlinear FEA transient analysis

[Kevin071586]

Hi All,
I'm wondering what options, other than Rayleigh damping, are available for modeling damping in nonlinear FEA (explicit transient analysis). It's easy to add damping to linear structural models (e.g., mass, stiffness, and damping matrices) by using modal damping, rayleigh damping, or structural damping. I've had less experience with damping in fully nonlinear models. In a fully nonlinear analysis with solid/hex elements that may experience large deformation, is there an option that is similar to modal damping that can be used in codes like LS-DYNA and ANSYS? Rayleigh damping is not an option, since mass proportional damping affects rigid body modes and stiffness proportional damping causes the stable time step to decrease too much.

Plasticity and friction are two sources of energy loss, but ideally I'd like to apply something like modal damping -- say 5% damping to all frequencies -- so that a vibrating solid tends to lose energy.

Thanks,
Kevin

 

[grogannc]

You can apply global damping to the whole modal or part damping to individual parts in LS-DYNA. The *DAMPING command is what you will use. You need to do an implicit run probably to get the period of the structure. You can use the same model and run an implicit eigenvalue solution to get the freq of the first mode. The input for damping is based on 4pi/T so if you want 5% critical, the value in the parameter would be 0.2pi/T.

I think you will find though that the plasticity and friction will damp out the structure much better than traditional damping.