REMOTE IDENTIFICATION OF IMPACT FORCES ON LOOSELY SUPPORTED TUBES - PART 1 - BASIC THEORY AND EXPERIMENTS

Flow-induced vibration of heat-exchanger tube bundles is an important issue, concerning component life and plant availability. Predictive me thods have been developed to analyze heat-exchanger tube responses and wear, for realistic multi-supported tubes and flow configurations. Ex perimental validation of these methods is currently pursued by several research groups, with considerable success. However. experiments on v ibro-impacting tubes involve very carefully instrumented test tubes an d tube-supports, which is seldom possible in real field components, du e to space limitations and severe environment conditions. Hence, there is a need for identification techniques that enable the diagnostic an d field monitoring of tube-support interaction under real operating co nditions, using information from motion transducers located far from t he impact locations. In this paper, the basic theory for the propagati on of flexural waves is briefly reviewed, and techniques are developed for the experimental identification of the wave path propagation para meters and impact forces, from tube response measurements at remote lo cations. These inverse problems are quite sensitive to the noise conta mination of measurements. Optimization techniques are used to overcome these difficulties, and their merits are accessed using extensive num erical simulations. Then, experiments performed on a long steel beam a re presented. A simple method is developed to deal with the boundary r eflections of a wave generated by a single impact. Experimental identi fication of the wave-path properties, of isolated impact forces and al so of impact locations is performed. Overall, quite good agreement was found between directly measured and remotely identified quantities. ( C) 1998 Academic Press.