【作者】 吕畅；

【导师】 余晓容；

【作者基本信息】 郑州大学 ， 材料加工工程， 2012， 硕士

【摘要】 粘度是聚合物流体的一个重要表征参数,也是聚合物加工成型性能的重要影响因素。在进行传统的聚合物流动有限元模拟过程中,获得揭示材料物性的本构方程(粘度函数)已经成为了模拟的关键。通过微观模拟或介观模拟的方法来获得一定条件下的应力应变关系,从而避免封闭本构方程是实现复杂流体模拟的重要方向。聚合物流体由于分子链的长链结构,尺度跨度比较大,单尺度模拟往往难以实现。在本文中,我们采用了将微观的分子动力学模拟和介观的耗散粒子动力学模拟相结合的方法进行了聚乙烯熔体的非平衡态模拟,考察了在我们建立的模拟体系中的粘度随剪切速率的变化情况。本文的主要工作如下：1)建立了450K、latm下40条链长为96的聚乙烯体系的分子模型,并进行了分子动力学的模拟。通过径向分布函数、均方回转半径、密度、以及均方位移来对聚乙烯模型进行表征,获得平衡态下该模型结构和动力学信息。经过与实验结果的对比分析,发现在所给的条件下,所建立的分子模型及模拟方法是合理的。2)采用基于径向分布函数的方法建立了耗散粒子动力学模拟保守势能,实现了从分子动力学模拟到耗散粒子动力学模拟的贯通连接。考察了几个关键模拟参数对模拟结果的影响,将DPD模拟结果与分子动力学模拟结果进行对比,选择了合适的参数作为进一步模拟的参数。3)建立了平板拖拽流和反转泊萧叶流两种不同的模型对聚合物流体的流动进行了模拟,通过计算得到了流动过程中的速度分布、剪切应力的分布以及剪切粘度,并将所得的结果与理论分析的结果进行了对比分析,发现两种模型的速度分布以及剪切应力的分布都具有与理论分析的结果相同的变化趋势。更多还原

【Abstract】 Viscosity is one of the most important characteristics of the polymer fluids, and it is also a key influence factor of polymer material processing.Getting the constitutive equation that reveals material property has become the key to caryy out polymer processing simulation with traditional finite element simulation. It has become an important reserch direction to obtain the stress-strain relationship of complex fluid under certain conditions through the microscopic simulation or mesoscopic simulation method, so as to avoid the constitutive equation.The simulation of polymer fluid is often difficult to achieve only through single scaling simulation,due to its long chains of chain structure and big scale span.In this paper,we conduct a nonequilibrium simulation about polymer fluid through a connection of microscale molecular dynamic simulation and mesoscale dissipative particle dynamics simulation.And we focus on the viscosity in our simulation mold. The main work in this paper are as follows:1) We set up the molecular simulation model of polyethylene, and implement the molecular dynamics simulation with the software lammps. Structure information, thennodynamic properties, and transport properties are analyzed in detail under the condition of450K,1atm,with the system of96PE chains,one of which contain96union atoms. The radial distribution function, mean square rotary radius, density, and orientation of polyethylene are used to characterize the model.2) Through the method that based on the radial distribution function,we set up DPD simulation of conservative potential energy, and realizes the connection between molecular dynamics simulation and dissipation particle dynamics simulation. Several key parameters have been investigate to obtain the proper simulation parameters through comparing with the result of MD simulation.3) We set up two kinds of different models of polymer fluid flow, and calculated the velocity distribution, shear stress distribution and shear viscosity in the process of flow, then the result with the simulation are compared with results of the theoretical analysis, which show that both of the models indicate the same variation tendency in velocity distribution and stress distribution.更多还原