Two-level approximation method for stress constraints in structural optimization

This paper presents a two-level scheme for stress constraints in structural optimizations, which uses both the force approximation and the direct- stress approximation methods. At the second stage of the approximation procedure, the stress constraints are directly expanded in Taylor series with respect to the shape variations. This approximation is nested within the original force approximation. These nested approximations, along with constraint deletion techniques of this method, reduce the computational effort significantly. Compared to the one-level approximation approach, the present method converges at a slightly higher objective function. This difference is considered to be within the convergence tolerance of the method. (I.S.)