STATIC AND DYNAMIC RELIABILITY ANALYSIS OF INTEGRAL SATELLITE IN VIEWOF LOW FAILURE PROBABILITY

摘要

In conventional safety-factor based design the un-certainty about structural and loading parameters isaccounted for by means of safety factors which areapplied in combination with the results of a deter-ministic analysis. In this case, however, the resultingdegree of conservatism remains unquantified.This shortcoming is avoided in a probabilistic frame-work, where the uncertainties in material and geo-metric properties and in the loading are quantifiedin terms of probability distributions and propagatedto the structural responses upon which the design isbased (e.g. stresses).The application of probabilistic methods to struc-tural design of large-scale structures remains a chal-lenging task, because high levels of reliability implythe necessity to calculate very low failure probabili-ties. The associated difficulties increase in the pres-ence of a high number of uncertain structural pa-rameters, e.g. in the case of FE models of large-scale structures with many thousands DOF's, theperformance of traditional methodologies for relia-bility analysis quickly deteriorates.Recently, a novel method for the estimation oflow failure probabilities has been introduced. Themethod has been termed 'Line Sampling' and hingeson the efficient, approximate estimation of the gra-dient in the space of uncertain parameters and theevaluation of samples along lines that are parallel tothe approximate gradient. With this approach theestimation of sufficiently low failure probabilities (inthe range of 10-6) is feasible at a tolerable compu-tational cost.In the present paper, the application of this newlydeveloped variance reduction technique is demon-strated in connection with ESA's INTEGRAL satel-lite. The FE model consists of roughly 120,000 DOF's and the number of uncertain structural pa-rameters amounts to approximately 1300. Two loadcases are considered in the present study: the firstis a static load case, in which the critical responsequantity is given by the force between the satelliteand its solar panels; the second load case is dynamicand involves the frequency response of the satellite toharmonic excitation in the range between 5 and 100Hz. The obtained results are very significant in thatthey show the feasibility of a full scale probabilisticreliability analysis, in a design context for aerospacestructures.