ABSTRACT:

The impact of model uncertainty on the accuracy of a nondestructive damage detection technique when applied to an offshore jacket platform is assessed. First, a nondestructive algorithm to locate and size damage from a few mode shapes of structures is outlined. Next, numerical damage localization and severity estimation exercises are performed for an example of an offshore jacket platform. Finally, the accuracy of damage localization and severity estimation results in the numerical example is assessed as a function of model uncertainties for the structure.

INTRODUCTION

During the past decade, a significant amount of research has been conducted in the area of nondestructive damage detection via changes in modal responses of structures (Cawley and Adams, 1979; O'Brien, 1980; Gudmunson, 1982). In "offshore applications, research efforts have been made to detect" changes in structural integrity of offshore platforms by monitoring changes in modal frequencies (Kenley and Dodds, 1980; Crohas and Lepert, 1982; Nataraja, 1983), or by monitoring changes in mode shapes of the structures (Rubin and Coppolino, 1983; Shahrivar and Boukamp, 1986; Idichandy and Ganapathy, 1990). Subsequent studies focused on using changes in mode shapes of offshore structures to locate and estimate severity of damage (Kim and Stubbs, 1995). Despite the" combined research efforts, there are still outstanding needs to detect damage in offshore jacket structures with limited modal information and to evaluate the damage in an environment of uncertainty due to modeling. and modal response measurement errors. In this study, model uncertainty for nondestructive damage detection (NDD) encompasses the uncertainty due to modeling errors in the choice of structure (or structure member) types. The objective of this paper is to evaluate the impact of model uncertainty on the accuracy of damage detection techniques when applied to jacket-type platforms for which only few modal response parameters are available.

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