Two mathematical programming procedures for treating nonlinear problems involving mixed variables are presented. One involves a relatively simple concept. First an optimum is located treating all variables as continuous. Adjacent discrete points are then evaluated in order of increasing distance from the all-continuous optimum, each evaluation requiring an optimization of the continuous variables, if any, until a satisfactory design is found. The other method utilizes an optimal discrete search to locate the optimum. These procedures are applied to the minimum weight design of stiffened, cylindrical shells where they prove to be effective.
The stress distribution in a ring of nonuniform cross section under the action of a uniform radial line load is obtained. The solution is an approximation to the exact interaction problem of a reinforced circular cylindrical shell under hydrostatic pressure. The ring is fabricated in three segments; one segment, whose cross-sectional area varies according to a power function, connects two uniform segments. By a proper choice of parameter values the ring geometry can be reduced to two segments, one of uniform depth, the other of continuously varying depth. Several sets of parameters are chosen for numerical calculations. Within these sets only the length of the transition section changes. Thus an appraisal of the importance of the transition section in reducing the maximum stress is made. The stress distribution in a frame with different lengths of transition section is obtained.
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