Robust Design Optimization by First Design Method

摘要

Launch vehicles are subjected to severe vibratory conditions during takeoff and flight ascent. The loads are notnwell known at the very beginning of a project, and, even at the end, some uncertainties still prevail. In spite of this, thenpreliminary design has to be robust with regard to the vibration levels encountered at the payload/launch vehicleninterface. This paper presents a new robust design methodology called the First Design Method. This methodologynhas been applied to a typical launch vehicle excited by a low-frequency transient load. The First Design Methodnoptimizes the natural frequencies of the structural configuration of interest and, subsequently, designs the structuralnconfiguration with the modes provided by the optimization procedure. Furthermore, the method, which is based onnenergy conservation for integrating uncertainties about excitation, is compliant with the laws of physics. In thenindustrial case investigated in this paper, the First Design Method has been used to design a typical launch vehiclenwith a very satisfactory behavior as far as the mass and vibration levels at the payload/launch vehicle interface arenconcerned.