I have some question in a MODAL Analysis .

I was doing the model setup in ANSA , In that I have modelled the throttle with a lumped mass  and that mass point is connected to the main body through KINEMATIC COUPLING as shown below image.

There are two cases –

1. In the first case, I am adding the Moment of inertia (MI) for the lumped mass .
2. In the second case, I am not adding the Moment of inertia (MI) for the lumped mass.

There is a significant change in the first MODE  .

With Inertia: 25.896  Hz

Without Inertia: 106.01 Hz

SO , Please tell me the possible reason of this significant variation in MODES . how abacus is solving ?

 With INERTIA                                                                                                                                                                                   Without INERTIA