Inverse Algorithm for Impact Force Identification on Engineering Structures

Abstract

This thesis focuses on applications of the model-based techniques for impact force identification on engineering structures. The thesis first presents impact force reconstruction on a concrete deck based on dynamic signals captured using accelerometers. The effects of the locations of impact and measurement points, characteristics of the reference impact force and the stiffness of impact hammer head have been studied. Simultaneous estimation of location and force history of an impact is investigated through minimisation of an extended matrix form of the convolution integral. As the first case study, impact forces are applied on a lattice truss core sandwich panel and the velocity signals are collected by a scanning laser Doppler vibrometer. It is shown that the superposition approach recognises the actual impact location based on some qualitative and quantitative evaluating criteria. It is found that different arrangements of measuring points all lead to identification of the location and magnitude of the impact force, though the use of four evenly distributed measurement points seems to be most effective. As the second case study for the simultaneous estimation of the location and force history, the dynamic signals captured by a single piezoelectric (PZT) sensor installed on a rectangular carbon fibre-epoxy honeycomb composite panel are utilised to identify the impact forces. It is revealed that impact forces occurred at any location amongst four possible locations can be well identified. An algorithm based on wavelet analysis is developed for automatically estimating the location and magnitude of impact forces. To assess the effect of a dent or damage in a structure on the accurate reconstruction of impact forces, a rectangular thin aluminium plate is considered. The impact damage in the plate is assessed and the necessity for updating the transfer function of the system is investigated.