Ansys

Hi,

I have a three freedom vibrational system that has complex eigen values . I want to earn natural frequencyes it with Ansys .analytic solution system is condition space method(General Damping). In Ansys after choice Modal property in Analysis Taype,I choiced block lanczos as solution method but responses don't agree with analytic solution!! I used from Reduce,Damping,QR Damping as solution method too but natural frequencyes don't agree with analytic solution again. subspace property doesn,t exist among propertyes so I 

couldn't use It . please help me . how earn natural frequencyes this system.