MODAL v7n4 - Measurement and Application of Experimental Rotational Degrees of Freedom for Mode Shape Refinement

ABSTRACT

The measurement and utilization of rotational degrees of freedom for experimental modal analysis applications is presented in this work. The experimental data is obtained with a novel noncontacting measurement approach capable of simultaneously sensing dynamic translation (y) and two dynamic rotations (Ox, Oz) of a vibrating surface. The paper briefly discusses transducer operation and its performance. The transducer is utilized for the modal analysis of two structures (a cantilever beam and a printed circuit board) providing estimates of both the translation and the rotation modal residues at each measurement test position. Several methods to combine the estimated translation and the rotation modal residues to refine the description of the mode shapes are presented and compared. The integration focuses on the use of polynomial curve fitting methods incorporating both translation (translational residues) and slope (rotational residues) at each test location to define the mode shapes. The results show that combined use of translational and rotational degrees of freedom reduces the effects of experimental measurement uncertainty and provides a significantly improved spatial description of mode shapes.