FRF measurement of rotational DOFs by T-block approach (improvement of accuracy for random noise and application to a car body)

The importance of rotational FRF was recognized widely, and many attempts have been made to measure those FRFs experimentally, but the satisfactory results can hardly be seen. The authors have proposed an estimation method of FRF on rotational degrees of freedom (DOFs) by adding a T-block to the structure's measurement point. In this paper the measurement noise is considered, and the noise effective approach is presented, which lead to good estimate of rotational FRF. The proposed method is applied to estimate cross FRFs of a car body. A new T-square-block (T²-block) for measurement of six DOFs (three DOFs in translation and three DOFs in rotation) is designed. Two T²-blocks are attached to the measurement points of the sub frame of a passenger car: the T²-blocks are excited by the impact hammer, respectively; and cross FRFs of the car body are obtained. The validity of the method is investigated by comparing the experimental model and the FE model. The estimated rotational FRFs of car body are used for structure synthesis approach.