传统的三螺杆挤出机流体流动和混合机理研究主要基于欧拉观点的静态物理参数表征，难以揭示三维拓扑流场的动力学本质。本课题更新思路，拟探究基于拉格朗日理论框架的三螺杆挤出机流体输运和混合动力学新机理。内容包括：①分别采用有限元法和光滑粒子流体动力学法(SPH)，对三螺杆挤出机三维流场进行精确计算，并探索出一套适于螺杆挤出机三维动态复杂流场的有限时间李亚普诺夫指数(FTLE)和拉格朗日拟序结构(LCS)的计算方法。②利用FTLE、LCS 和Lobe动力学理论，结合可视化实验，给出三螺杆挤出机流体输运和混合的动力学边界识别和控制方法；提出双曲周期点触发和控制流体输运和混合的动力学新机制。③设计和制造新型高效的非对称三螺杆挤出机，给出基于拉格朗日框架三螺杆挤出机三维几何造型的解析表征方法。研究意义：为高分子加工设备流体力学研究提供新思路，拓展和丰富螺杆挤出机设计的理论体系。

The traditional studies about the flow and mixing mechanisms in tri-screw extruders are mainly focus on the analysis of static physical parameters from the Euler viewpoint. Due to lack of the dynamic mechanism description, it is difficult to reveal the dynamic nature of the 3D topological flow field in tri-screw extruders. In this project, the new mechanisms of fluid transport and mixing in tri-screw extruders are explored based on the framework of Lagrangian theory. The project contents cover: The 3D flow fields in the tri-screw extruders will be calculated accurately by using the finite element method and smoothed particle hydrodynamics method (SPH), respectively. Moreover, a set of suitable method to calculate the Finite time Lyaponuv exponent (FTLE) and Lagrangian coherent structures (LCS) of three-dimensional dynamic complex flow field in tri-screw extruders will be put forward. Based on the FTLE, LCS and Lobe dynamics theory, combining visualization experiment, a method of identifying and controlling the dynamic boundary for fluid transport and mixing in tri-screw extruders will be presented. Moreover, the transport and mixing mechanism triggered and controlled by the hyperbolic periodic point in flow field of tri-screw extruders will be proposed from . ③A new high-efficient tri-screw extruder with three asymmetric screws will be devised and manufactured based on the chaotic dynamics theory. And the analytical equations for describing the geometric modeling of the asymmetric screws will be put forward. The significance of this project covers: the new theory system of designing the screw extruders will be enlarged based on the framework of Lagrange theory. An important theoretical foundation will be provided to achieve the precision control of extrusion process.