Rotational frequency response functions: Model based estimation and experimental assessment

Measured and simulated data are often not compatible in terms of the number and the type of degrees of freedom (DOFs). While one can obtain a full data set by finite element modelling, the conventional vibration testing is usually limited, as one can only measure a portion of the receptance matrix (translational DOFs due to applied forces). Therefore, the experimental frequency response functions (FRFs) do not contain information related either to rotational DOFs or to pure moment excitations. In this work, one proposes the expansion of a set of translational FRFs, conventionally measured, to estimate the entire receptance matrix. The expansion process is based upon a modified Kidder's method and the principle of reciprocity, and it has the advantage of avoiding modal identification. The accuracy of the estimated FRFs is assessed by the use of experimental data collected at a simple structure. Note that the use of a T-block is considered to obtain experimental rotational FRFs, which are only used for accuracy assessment purposes.