Evaluation of the Probabilistic Design Methodology and Computer Code forComposite Structures

摘要

This report presents the results of an independent evaluation on the numericalaccuracy and computational efficiency of a probabilistic design methodology for composite aircraft structures. The methodology was developed by Northrop-Grumman Commercial Aircraft Division (NGCAD) under the Federal Aviation Administration (FAA) funding through Interagency Agreement DTFA03-94-A-40021, while the associated PC-based computer code MONTE was developed through FAA Grant 96-G-0036 with the University of Texas at Arlington. The probability calculation of NGCAD's probabilistic methodology is based on the conditional expectation method (CEM) to determine the failure probability of a specified failure event. This methodology was first verified by traditional Monte Carlo simulation (MCS) method using the computer code NESSUS developed by the National Aeronautical and Space Administration (NASA). Since Monte Carlo simulation is not efficient for small probability calculation, a mixed probabilistic method (MPM) was developed in this study to verify the results from MONTE in the 10 (sup -6) or less probability level. The mixed probabilistic method requires a decomposition of the overall failure function into several conditional failure functions. The probability of failure for conditional failure functions is first calculated using the CEM. The overall failure probability is then computed using the probability integration method (PIM). The mixed probabilistic method is implemented in the computer code NESSUS.