Free vibration not correct

[xieyazhou]

Hi All,

I conducted a free vibration analysis of a rocking column with no damping included, geometric nonlinearity is modeled as corotational transformation and corotational truss elements at rocking supports. Newmark method is used as the integrator. However, the amplitude of the free vibration differs in every circle. Does anyone know the reason? Ideally free vibration amplitude should be constant since no damping is modeled.

Thanks in advance,
Yazhou

[fmk]

i suggest you start with a linear transformation and ensure the answers you get are correct. if not your model is incorrect to start with,