四机并联发动机低频动态特性分析

为了获得发动机结构的低频动态特性，采用有限元方法进行了液体火箭一级四机并联发动机(含机架)的计算模态分析。由于发动机为复杂的非对称结构，建模时按质量和刚度等效原则将推力室的夹层结构简化成单层板，其余结构大都按空间梁简化，通过改变材料密度保证了模型质量与发动机稳态工作时的质量一致。简化后的计算规模适中，既反映了结构的主要特征又不浪费计算机资源和时间。计算结果表明了四机并联发动机系统中有多阶轴向运动较大的模态值得注意，需避免它们和发动机的低频脉动及箭体的低频振动耦合。

Low Frequency Dynamic Characteristics of Four Parallel Connected Engines

In order to obtain low frequency dynamic characteristics of engine structure, a computing modal analysis model was set up for finite element method modal analysis of the four parallel connected liquid rocket engines. To avoid some unnecessary complexities caused by the unsymmetric characteristic of some engine structures, according to the principles of mass and stiffness equivalence, sandwich plate structure of thrust chambers was simplified into monolayer plates. This makes it easier to modeling. The most rest structures were modeled into space beams. The size of simplified computing model is moderate. It reflects primary characteristics of engine structures without waste the computer resources and computing time. The nature frequencies and modes of four parallel connection engines have been obtained. Many of these modes have large axis motion, the coupling between these modes and low frequency pressure oscillations of feedline and low frequency modal vibration of rocket should be avoided.