Estimation of frequency response function on rotational degrees of freedom of structures (cross FRFs estimation and measurement of 6-DOF FRFs)

Rotational FRFs have not been measured in experimental modal analysis even though the importance of rotational FRFs have been recognized recently. Consequently it is difficult to utilize the FRFs on the basis of vibration testing for the structure modification analysis. The authors have proposed an estimation of the auto FRFs in rotation of structures. In the method a T-shaped rigid block whose inertia properties were known was attached to the measurement point on the structure. The estimation of three-degree-of-freedom (3-DOF) FRFs (one DOF in rotation and two DOFs in translation) of the beam structure using the T-shaped rigid block was demonstrated. The effect of estimated rotational FRFs against the random noise of measured FRFs were evaluated as a Reliability Factor. In this paper the estimation method of the cross FRFs in rotation and the reliability of the estimated FRFs are presented. A new rigid block whose overview is the cross-shape is designed for measuring 6-DOF FRFs. The 6-DOF FRFs of the beam structure is estimated. The structure modification analysis of 3D-rahmen structure based on experimental data is carried out.