Comparative study between random vibration and linear static analysis using Miles method for thruster brackets in space structures

摘要

Random vibrations occur during the launch at the fastening interface between thruster brackets and basic support of satellite. These are generated in the launcher by the motion of some mechanical parts, combustion phenomena or structural elements excited by the acoustic environment. The goal of this comparative study is to find a simplified and efficient validation method using FEM PATRAN-NASTRAN software for thruster brackets in the random vibrations environment for space applications. The random vibration analysis requests complex pre/ post processing efforts and large hardware resources for various geometrical shapes. The PATRAN-NASTRAN random vibration analysis consists of frequency response analysis (111 solver) and Acceleration Spectral Density (ASD) diagram, taking into account the natural frequencies of the bracket. The Miles method computes the root mean square acceleration (aRMS) using the natural frequencies and the ASD diagram as input. As a conservative hypothesis in the random analysis, the three sigma standard deviation criteria in normal Gaussian distribution is applied at these RMS acceleration values, which means to multiply the aRMS by a load factor of three. Simplified method consists of using linear static PATRAN-NASTRAN analysis (101 solver) where the aRMS are introduced as loads. For validation of the simplified method, a comparative study was made between the random vibration and the linear static analysis. The final results are presented in detail in this article.