液体火箭POGO振动缩聚模型研究

POGO vibration reduced model for liquid rockets

针对液体火箭POGO模型中推进系统模型难以降阶的问题,提出了一种POGO模型缩聚的方法。利用广义逆迭代法只对输送管路的有限元模型模态分解,选取管路任意阶次模态方程与其余部件的方程组合得到推进系统的缩聚模型,进而与结构系统模态方程耦合得到POGO振动缩聚模型。当蓄压器作为纯柔性元件或非纯柔性元件时,缩聚模型的维度由管路的模态变量、结构模态变量再加1或2组成。模型的维度大大降低且算例表明其具有很高的精度。基于缩聚模型研究了某液体火箭蓄压器能量值和惯性对POGO稳定性的影响。研究得出,对于纯柔性或非纯柔性的蓄压器设计,能量值和惯性对不同时刻耦合模型稳定性具有不同的、非单调的影响规律。当耦合而导致结构系统频率大幅降低时,合理的调节蓄压器的能量值或惯性可以显著的增大结构耦合阻尼比,增强结构的稳定性。

Aiming at the order of the propulsion system model being difficult to be reduced in liquid rockets’POGO model,a POGO reduced model method was proposed.The generalized inverse iterative method was used to do modal decomposition only for the transfer pipeline’s finite element model to choose the any order modal equation of the transfer pipeline combined with other parts’equations to obtain the reduced model of the propulsion system.The POGO vibration reduced model was obtained by coupling the structure system’s modal equations and the propulsion system reduced model.When the accumulator was taken as a pure flexible element or a non-pure flexible one,the dimension of the POGO vibration reduced model was composed of the transfer pipeline’s modal variables,the structure’s modal variables plus 1 or 2.The model’s dimension was largely and the calculation examples showed that the POGO vibration reduced model has a high precision.Based on this reduced model,the effects of the accumulator’s energy value and inertia of a certain liquid rocket on its POGO stability were studied.The results showed that for a pure flexible accumulator or a non-pure flexible one,its energy value and inertia have different and non-monotonic influences on the coupled model’s stability at different time instants;when the structure system’s frequency drops obviously due to the coupling effect,a reasonable adjustment of the accumulator’s energy value or inertia can significantly increase the structure’s coupled damping ratio to enhance the structure’s stability.