Estimation of Frequency Response Function on Rotational Degrees of Freedom of Structures: Estimation of Auto FRFs and Its Fundamental Investigation

In conventional vibration testing, measurement of frequency response function (FRF) has been limited to translational degrees of freedom (DOF). Rotational DOFs have not been treated in experimental analysis. However, the rotational DOF is indispensable in further analysis, such as substructure synthesis, prediction of structural dynamics modification, etc. FRF measurement on rotational DOF is essential for expanding applicability of experimental modal analysis. This paper proposes a new method for FRF estimation on rotational DOF of structures. The following is the estimation procedure: a rigid block is fixed on the measurement point of structure; the block is excited by conventional impact hammer, the inner force and the response of the connection point are estimated; and lastly, the FRF including rotational DOF at the connection point of the structure is obtained. The feasibility of the method is investigated experimentally by applying it to a beam structure. The method is applied to structure synthesis approach by using experimental models.