航天器典型防护结构节点分离FEM的数值模拟

建立了一种航天器防护结构超高速碰撞数值模拟的节点分离有限元方法。通过重合节点网格转换和添加节点集约束建立了节点分离有限元模型。在显式积分迭代中，将达到断裂判据的节点集解离，从而生成裂纹。对网格畸变问题进行分析，并建立了几何识别方法，进而删除畸变单元，改善了算法的稳定性。应用节点分离方法模拟了单层板超高速撞击问题，并分析了撞击速度对弹丸变形程度和碎片云形状的影响。应用节点分离方法对Whipple防护结构、填充式防护结构和多层网结构进行了模拟，获得了与实验一致的结果。多种算例表明，节点分离有限元方法改善了以往断裂侵蚀有限元方法处理网格畸变、碎片云模拟以及二次碎片云碰撞等方面的能力，对典型防护结构模拟具有很好的适用性，能够成为光滑粒子流体动力学(SPH)方法的有效补充和替代。

Node Separation FEM Simulation of Typical Spacecraft Protective Structure

A node separation finite element method (FEM) for spacecraft protective structure hypervelocity impact simulation is developed in this paper. By the conversion of the mesh into coincident node mesh and adding set constraints, a node separation FEM model is built. In the explicit integration iteration, the node sets which meet the fracture criteria are released, and then the crack is generated. By the analysis of the mesh distortion, a geometric identification approach is built. The distorted elements are deleted from the model and the stability of the method is improved. Node separation FEM is applied to simulate the single plate hypervelocity impact problem and to analyze the influence of the impact velocity on the deformation of the impactor residual and the debris cloud shape. The node separation FEM is also applied to simulate Whipple shield, Stuffed shield and Multilayer mesh shield. The simulated result shows good agreement with the experimental test. Various simulation examples indicate that the node separation FEM improves the mesh distortion treatment, debris cloud simulation and secondary debris contact compared with the traditional fracture erosion FEM. The node separation FEM is well adapted to typical spacecraft protective structure, it can be an available supplement and surrogate of Smoothed Particle Hydrodynamics (SPH) method.