基于绝对节点坐标法的流体单元建模及在载液列车中的应用

For the liquid sloshing, the conventional Computational Fluid Dynamics (CFD) has its limits in the fluid free surface description, boundary definition, rigid-flexible-fluid coupled multibody system modelling, and high computational cost. In this work, a new fluid element based on the Absolute Nodal Coordinate Formulation (ANCF) is proposed to resolve the complicated boundaries and nonlinear behavior (compared with the Mass-Spring and Pendulum models), large-scale deformations (compared with the conventional CFD methods), small number of degrees of freedom (compared with Smoothed Particle Hydrodynamics method, SPH), and the unified coordinate system (Lagrangian based formulation). The presented ANCF fluid element can provide an efficient and high accuracy modelling and algorithm for the rigid-flexible-fluid coupled multibody dynamics (MBS) system. A thoroughly kinematic definition of the ANCF fluid element is presented as well as the constitutive formulations and incompressible control equations. In order to extend the fluid element type including two- and three-dimensional elements, their application conditions and validations are carefully provided. For the container has nonlinear shapes or considering its flexibility, the constraints equations and penalty method are applied to the present the fluid-container contact, which are used to construct the rigid-flexible-fluid coupled MBS equations. Then the liquid sloshing behavior for the railway tank cars are examined in the curve negotiation and braking scenarios, and their effects on the vehicle dynamics are summarized. Followed by the suspension parameters optimization for the vehicle or equipment on the vehicle with liquid are conducted.

对于液体晃动问题，其自由表面的大变形描述、运动边界表达、刚柔液耦合系统的统一建模、高效计算方法等问题，制约着现有传统计算流体动力学方法的应用。本项目拟建立一种基于绝对节点坐标法（ANCF）的流体单元，能够处理复杂边界及非线性晃动问题（相对于等效简化模型）、具有大变形能力（相对于传统有限元方法）、自由度少（相对于光滑粒子方法）、与多体系统建模体系相同（均为拉格朗日描述），能够为含自由表面的刚柔液耦合多体系统提供高效高精度的建模及求解方法。理论推导ANCF流体单元的运动学描述、本构方程、不可压控制方程，扩展流体单元类型，进行适用性分析和验证；针对容器具有规则或任意形状、考虑结构柔性情况，提出基于约束方程和罚函数的流固耦合关系描述方法，并组建刚-柔-液耦合柔性多体系统；针对铁路载液列车，研究曲线通过、制动等工况下的液体晃动行为及其对车辆动力学性能的影响，提出载液车辆、含液设备的悬挂参数优化方法。

项目针对液体晃动模拟过程中的自由液面大变形描述、运动边界表达、刚柔液耦合多体系统在拉格朗日坐标系下统一描述等问题展开深入研究，完成了任务书预期目标。首先，开展了基于绝对节点坐标法（ANCF）的流体单元建模方法研究，建立了ANCF三维实体和二维平面矩形流体单元，构建了单元内部粘性力表达式、体积不可压缩条件方程和流体运动微分方程组。分析了二维矩形容器和三维罐体内的流体单元网格划分方法，实现不同充液比下流体网格参数化划分。然后，分析了ANCF流体单元的适用性，对比了三维实体单元和平面矩形单元的计算效率和精度，研究了矩形、球形和椭球形容器内的液体晃动行为。再有，基于约束方程和罚函数方法表征流体与容器之间的耦合关系，并通过悬挂将容器连接至车体，搭建了载液列车液体晃动行为动力学仿真平台。进而，分析了液体晃动对列车曲线通过安全性的影响机理，以及牵引制动过程中轮重增减载和车钩力变化规律。在上述理论和模型研究基础上，拓展研究了高速车辆动力学建模技术和台架与线路试验研究方法等，初步掌握了车辆动力学行为随车轮磨耗、线路状态等边界条件的演化规律，以及国内外铁道车辆动力学评价标准的差异。