Damage identification of cables via Virtual Distortion Method

The present paper deals with the problem of identifying defects in cable type structures and structural members. For numerical simulation of the structural response the so-called Virtual Distortion Method (VDM), which may be viewed as an extension of the common FEM, is used. For the re-computation of the dynamic response an impulse influence matrix D is built which stores the effects of structural parameter changes in elements on the response at selected DOFs. Based on this record the VDM supplies the analytic gradients of the system response to defined model variables. The whole methodology is applied to the case of piezodiagnostics, where one or a net of piezoceramic sensors is used to pick up elastic wave signals induced by a piezo-actuator. With the measured signal at hand the identification is then formulated as least squares minimization problem. Thus the gradients of the objective function can be calculated very accurately in analytical form and a gradient-based optimization technique may be applied. The computational demand of the high accuracy gradients is however quite restricting at an, early identification phase, so a fast, simple algorithm is proposed to redeem this computational burden. Afterwards a successful laboratory experiment is carried out to validate the proposed methodology.