The reliability-based design optimization and safety factor method is compared for the optimization result and process. The reliability-based design optimization method including probabilistic reliability and nonprobabilistic reliability are given. The viewpoint is illustrated by two numerical examples including a two-bar truss and a supersonic wing structure.Abstract: Reliability-based design optimization theory has been widely acknowledged as an advanced and advantageous methodology for complex structural system design. Comparatively, the traditional safety factor design method has fallen out of favor with designers since it is simply just a comprehensive expression of all the uncertainties existing in a practical engineering structure, which has been verified to be unreasonable. Moreover, there is no description of the method for searching for the optimal design. In this paper, a comparison of the two approaches is performed for the optimization results and process. It is demonstrated that the weight of the designed structure by the reliability-based optimization is not heavier than that by the safety factor design method under the same reliability requirements. The time efficiency, error estimates and sensitivity analysis are also compared to discuss the advantages and disadvantages of the two approaches.Eventually, the advancement of the reliability-based design optimization is illustrated with optimization designs of a two-bar truss and one practical supersonic wing.
Linkage mechanisms are typically designed to generate a specific functional relationship or path. Because the uncertain dimensions and joint clearances severely affect the output motion accuracy, designers urgently need a reliability-based design approach with high confidence and efficiency. However, the traditional kinematic reliability synthesis, which focuses on several discrete time points, cannot satisfy the accuracy requirement over a continuous time interval. Accordingly, to ensure high accuracy over a time period, this study presents a reliability synthesis approach that considers the time-dependency effect of motion error. The exact statistical characteristics of clearances and dimensions may be unavailable because of the limited sample information in practical engineering. Thus, by qualifying the uncertainties as unknown but bounded variables, the time-dependent reliability index is assessed based on a combination of the nonprobabilistic interval process and first-passage theories. Two engineering examples are presented to demonstrate the validity and applicability of the developed methodology.
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