Use of reciprocal modal vectors for nonlinearity detection

This paper seeks to exploit the reciprocal modal vector orthogonality betwe en experimentally-derived mode shapes and the corresponding measured freque ncy response functions in order to derive a criterion for the detection of structural non-linearities. Being based on the use of measured data and exp erimentally-derived quantities only, the method is directly applicable to p ractical engineering cases for which there are usually no spatial descripti ons. A brief outline of the reciprocal modal vector theory is given first, followed by a short description of a frequency-domain nonlinear response si mulation technique using a harmonic balance approach. A detailed study of a 4-DOF system with cubic stiffness and friction damping nonlinearities is p resented next. It is shown that the proposed nonlinearity detection criteri on is relatively insensitive to measurement noise. It is concluded that the method is effective for detecting nonlinear behaviour in a consistent and quantitative fashion.