固体火箭发动机模态分析中的推进剂建模研究

FEM modeling of solid rocket motor with propellant in modal analysis

应用有限元软件Marc建立了某固体发动机有限元计算模型,对其中难以用有限元模型准确描述的推进剂,采用了两种简化建模方法。一种是仅仅考虑推进剂质量,忽略其刚度等属性,将推进剂简化为均匀附加在发动机壳体有限元模型节点上的集中质量;另一种是将推进剂作为几何实体,考虑其质量和刚度,建立推进剂实体模型。模态计算结果与试验比较表明:推进剂的壳体节点集中质量模型,能较好地模拟发动机的弯曲特性,由于忽略了推进剂刚度,对于呼吸振动特性的模拟不太理想;相比之下,推进剂的实体模型,由于同时考虑质量和刚度,对弯曲和呼吸振动特性的模拟较好一些。计算还表明,要逼近高阶振型,需要将推进剂弹性模量修正得更高一些。

Modal analysis of solid rocket motor is carried out in FEM with MSC/Marc.Two models to simplify the characters of the propellant,which is difficult to be described in FEM,are adopted.In the first model,only mass of the propellant is considered,and treated as concentrated mass distributing on FEM nodes of the motor's case,other attributes,such as stiffness,are ignored.Another model is a 3D FEM model according to the propellant's geometry,mass and stiffness are considered.FEM modal analysis and modal test are compared,and found that, the fist model can simulate the bending vibration characteristics of the motor, except that the breathing vibration characteristics for the ignoring of the stiffness.The second model is ideal for both bending and breathing vibration characteristics.And it is found that calculation error increase for higher order mode,so the elastic modulus of the propellant must be modified larger to get the calculation more closely correlated with the test results.