Isolation and Expansion of Gyroscopic Effects Using Frequency-Based Substructuring

Due to gyroscopic effects, the dynamics of rotating machinery depend on the rotational speed. In order to experimentally determine a machine’s dynamics, measurements for each rotational speed are required. A method using frequency-based substructuring to extrapolate the speed-dependent dynamics is presented for a system with gyroscopic forces. In an isolation step, the dynamics of the rotating system are decoupled from the dynamics of the nonrotating system, which yields the gyroscopic terms. In an expansion step, the isolated gyroscopic terms can be extrapolated to an arbitrary speed. This is coupled with the dynamics of the nonrotating system for the dynamics of the rotating system at an arbitrary speed. Here, the frequency response function must only be measured for the rotor at standstill and at one rotational speed. The FBS method gives good results as long as the interface is rigid enough. Also, another method that divides the dynamic stiffness into symmetric and skew-symmetric parts is presented, which only needs FRFs at one rotational speed. It gives slightly worse results than the FBS method in the current implementation.