Structural Modeling Reflected Nonlinearity for Longitudinal Dynamic Instability (POGO) Analysis of Liquid Propellant Launch Vehicles in Preliminary Design Phase

Abstract

The longitudinal dynamic instability (POGO) of liquid propellant launch vehicle results from the complex interaction between the vehicle structural vibration in the longitudinal direction and liquid propellant feeding system. In the preliminary design phase of a launch vehicle, accurate prediction of the lower-mode longitudinal natural vibration characteristics enables to avoid pogo instability efficiently. In this paper, a complete vehicle including the liquid propellant tanks is analytically modeled for pogo instability analysis, focusing on the longitudinal lower natural frequencies. Moreover, liquid propellant tank modeling methods are established by use of an advanced one-dimensional mass-spring model to refine the complete vehicle model. By using these methods, parametric studies for the hydroelastic effect, evaluations of modal analysis, and pogo estimation were conducted. Consequently, the numerical results obtained by the orthotropic liquid tank modeling method were found to be in good agreement with natural vibration characteristics by the previous analyses and experiments. And, the target vehicle showed the pogo estimated areas at the first structural mode. Thus, the present simplified structural modeling and modal analysis procedure can be used to identify pogo occurrence areas and provide design criteria for pogo instability in the preliminary design phase.