Abstract: A two-level approaching method for structural optimal design is proposed. Based upon the values and the first-order derivatives of the critical constraint functions at the points obtained in the procedure of optimization, the explicitly approximate functions approaching the primal constraint functions have been made up, and the nonlinearity of them is controlled to be near to those of the constraint functions in their expansive domains with a adaptive method, from the above principle the first-level nonlinearly explicit approximate problems approaching the primal problem are established. In order to handle each of them, the second-level approximate problems is formed, which are then solved by using dual theory. The results of given examples show that the present method is of a rapidly stable convergence.

Key words: structural synthesis, optimization, CAD