Structural Optimization Under a Multiple Loading Condition Based on the ASME Code Section III Stress Categories

Abstract

The structural optimization technique is well known as one of the tools to achieve a better design. Recently, it has been applied to the design of nuclear components for the purpose of a design evolution and enhancement. When it is applied to nuclear components, there are a couple of points to be considered. The ASME code section III, design by analysis, provides stress criteria for nuclear components, which is quite different from the general stress constraints for a typical optimization process. Based on the ASME code section III, stresses are categorized into three types with different stress limits. The stress limits change in accordance to corresponding service levels. Since the types of stresses and the service levels introduce different stress, the multiple loading conditions should be utilized during an optimization. And the general stress constraints during an optimization are the maximum nodal stresses applied to the concerned points rather than the concerned section. On the contrary, the failure condition of the ASME code section III can be evaluated by comparing the stress intensity, which was created by the stress linearization procedure at the concerned section, with the prescribed one. So, the linearized stresses such as the stress intensities are used as stress constraints during an optimization for nuclear components. In order to adopt the stress linearization procedure to the constraints during an optimization, an extra data manipulation such as calculating a linearized stress and a derivative of the linearized stress needs to be conducted. In this paper, a structural optimization technique is proposed for an optimization application of a nuclear-related structure. This proposed optimization technique mainly includes a multiple loading condition and a stress linearization procedure to satisfy the requirements of the ASME code section III. To validate the ideas, one of the nuclear-related structures is selected and optimized under multiple loading conditions with linearized stress constraints.