Introduction

This book addresses the problem of updating a numerical model by using data acquired from a physical vibration test. Modern computers, which are capable of processing large matrix problems at high speed, have enabled the construction of large and sophisticated numerical models, and the rapid processing of digitised data obtained from analogue measurements. The most widespread approach for numerical modelling in engineering design is the finite element method. The Cooley-Tukey algorithm, and related techniques, for fast Fourier transformations have led to the computerisation of long established techniques, and the blossoming of new computer intensive methods, in experimental modal analysis. For various reasons, to be elaborated upon in the chapters that follow, the experimental results and numerical predictions often conspire to disagree. Thus, the scene is set to use the test results to improve the numerical model. It would be superficial to imagine that updating is straightforward or easy: it is beset with problems of imprecision and incompleteness in the measurements and inaccuracy in the finite element model. In model updating the improvement of an inaccurate model by using imprecise and incomplete measurements is attempted. But by what means can the proverb of two wrongs not making a right be defied?