Modification of calculation methods for the stiffened shells

using the experimental data

V.V.Chekanin

State Rocket Centre V.P.Makeyev Design Bureau>

The existing methods of solution of direct and inverse optimization problems for the orthogonally stiffened shells sustaining compressing loads provide efficient synthesis of these constructions allowing for the system of active constraints and loading conditions. Simplified methods of critical loads calculation that provide high rate of generation of design versions with low accuracy are very popular for the practical application of optimization methods for the stiffened shells. However, the accuracy of calculation methods essentially influences the design and mass features of the shell construction and eventually its functional quality. Therefore verification of calculation methods and choice of the most accurate experimental dependencies relative to the theoretical ones (according to the minimal variation coefficient) are of great importance.

Representative sets of experimental results on stability of the stiffened shells accumulated during a long period of shell operation together with their stable technology prepared the foundation for the modification of the calculation methods on the basis of statistical handling of empirical data aimed at improved correlation between theoretical and experimental relations.

This work is representing the author's method. The submitted method based on comparison of the curves of objective mass function of the stiffened shells plotted for the overall stability in the design space for the functions of critical loads that differ in accuracy, allows revealing the reasons for the raised scatter of experimental data and high variation coefficients for the less accurate calculation relations. Besides, the method enables to demonstrate an essential influence of relations for critical loads calculation on performance of the stiffened shell.

The submitted composition of correction function parameters provides similar accuracy of critical loads calculation for different methods. This accuracy is limited by the existing level of technology (i.e. mechanical milling). This result is important from the practical point of view and enables to use simplified calculation methods for efficient synthesis of design versions of the stiffened shells.

The empirical dependencies of the critical load of the stiffened shell on its mass thickness, obtained during the statistical analysis of experimental data, can be also useful for approximate evaluation of the shell masses.