【作者】 夏鸿建；

【导师】 陈立平； 王波兴；

【作者基本信息】 华中科技大学 ， 机械设计及理论， 2008， 博士

【摘要】 机械系统虚拟样机技术是计算机辅助分析的重要分支之一,对缩短产品设计周期,降低产品开发成本,提高产品设计质量均有着显著意义。借助这项技术,可通过建立机械系统数字模型,模拟现实环境下机械系统的运动学和动力学特性。本文从虚拟样机建模和动力学数值求解等方面对机械系统虚拟样机技术进行了深入系统的研究。首先阐述了机械系统虚拟样机技术的基本概念和体系结构,提出一个支持模型数据共享和求解器兼容的软件平台框架。通过对模型元素表达和管理进行研究,归纳了模型元素关联关系和模型操作传播方式,并据此提出了模型元素更新机制,以实现模型编辑时的内部关系一致性维护与管理。机械系统虚拟样机建模是样机动力学分析的基础。为了便于模型修改、融合领域工程设计知识并支持功能优化分析,提出了适用于机械系统建模的参数化技术。通过分析机械系统模型参数类型、参数特性和工程约束种类,结合元素关联关系,建立有向二分图表达的模型参数完整约束网络。根据约束网络描述的参数偏序关系,给出了模型参数推理求解序列生成方法,并结合模型元素更新机制,实现样机模型参数化驱动。针对机械系统虚拟样机建模效率低、模型重用困难等问题,提出了面向复杂机械系统建模的子系统技术。基于机械系统模型结构特点,引入虚部件定义子系统外部拓扑连接关系,通过主控参数封装模型设计知识和内部参数信息,使用子系统坐标系解耦空间位姿关系,从而建立自顶向下的层次化子系统模型结构;根据层次结构特点和主控参数关联关系,提出了子系统装配算法和参数化求解算法,并在此基础上讨论了模型重用和子系统建模流程。机械系统虚拟样机技术的主要功能是实现样机模型的运动特性仿真分析。为提高运动方程组装效率,在综合全局建模法和拓扑建模法优点的基础上,提出了运动方程混合建模方法。通过分析相邻构件的位姿关系,推导了系统运动方程递归关系式和约束雅可比矩阵;然后根据约束对运动方程求解效率的影响,建立了模型拓扑带权图,并研究了闭环系统最大求解效率派生树生成算法和无根开环系统基点选取算法。基于模型拓扑结构和递归关系式,推导了笛卡尔坐标空间到铰坐标空间的转换关系式,实现了递归组装运动方程的混合建模算法。分析了机械系统动力学数值求解存在的主要问题。提出切空间扰动法甄别系统冗余与矛盾约束。通过扩展惩罚因子法,处理构形奇异和变拓扑情况的动力学数值求解,并伴随广义参数投影校正,避免约束违约。对于存在刚性特性的机械系统,为了提高数值算法稳定性,直接采用隐式积分格式离散运动方程,并推导了近似雅可比矩阵和方程残量计算公式,提高算法效率。考虑到整体求解算法效率低,求解并行差的问题,基于模型拓扑耦合关系,研究了子系统综合和分治算法。最后,在上述理论研究成果的基础上,研制开发了机械系统虚拟样机软件平台—InteDyna,并给出了汽车建模和分析实例以验证本文研究内容的有效性和正确性。更多还原

【Abstract】 As one of the important branches of computer aided engineering, mechanism system virtual prototyping (MSVP) is expected to reduce product design cycle with lower life-time cost, and has great significance to improve product quality. In virtue of this technology, engineers can simulate the characteristic of kinematics and dynamics of mechanical system on realistic condition by its digit model. In the dissertation, several key issues of developing an applicable MSVP including prototype modeling and dynamic numerical solution are addressed.At first, the basis concept and main task of MSVP are discussed, an architecture of software platform is proposed which can be compatible with various numerical solvers and support data exchange with different software. Furthermore, the associated relationships of model elements and the operation spreading are also concluded according to the model representation, an event-driven update mechanism is presented to implement model management and element relationship maintenance.Virtual prototype modeling is a basic problem in dynamic simulation of mechanism system. To facilitate model modification, integrate engineering design knowledge and support optimization analysis of model, a parametric modeling technique for MSVP is studied. According to the parameter trait, engineering constraint and associated relationship, a directed bi-partite graph is utilized to express parameter constraints. In terms of the partially ordered relationship of parameters, a solving sequence of reasoning is formulated. With the update mechanism, a parametric modeling method is proposed.To improve modeling efficiency and reuse of models, subsystem modeling techniques for complicated mechanism systems are addressed. According to the characteristic of model structure, virtual parts are presented to define the topological relationship among the subsystems, main control parameters are introduced to encapsulate the design knowledge and the internal parameters, the reference frames of subsystem are used to position. Consequently, a top-down hierarchical architecture is constructed. In terms of the hierarchical architecture and main control parameters, the algorithms are also presented to assemble the subsystems and solve the parameter constraints. Based on these techniques, the complicated model can be decomposed into smaller and simpler subsystems to construct and reuse.The kinematics and dynamics analysis is the essential function of MSVP. To improve the computationally efficiency of assembling equation of motion, a hybrid algorithm is presented by combination of global method and topological method. Firstly, the recursive formulations and Jacobian matrix are obtained by the kinematics relationship between reference frames of adjacent bodies, and then, according to the computational effect of cut joint, a weight graph is constructed to represent the topology of model. Based on this weight graph, the algorithms of the spanning tree generation with best efficiency and selection of base body are also proposed. Furthermore, the transformation formulation of Cartesian coordinates space to joint coordinates space is developed by model topology and recursive formulation, and an hybrid algorithm for assembling equation of motion is obtained.The main problems of dynamic numerical solution of mechanism system are discussed. Firstly, a perturbation on tangent-plane algorithm is proposed to distinguish the redundant constraint, and then a modified penalty numerical method is applied to dynamic analysis of mechanism system with singular configuration and topology change. To eliminate the constraint violation, the project correction of general coordinates is utilized. For the system with stiffness characteristic, an implicit integration scheme is adopt to directly discrete the equation of motion. To improve the computational efficiency, the residual of equation and approximated Jacobian matrix are also computed by the recursive formulations. In the end, the subsystem synthesis algorithm and divide-and-conquer algorithm is also studied to improve the computational efficiency and parallel of dynamic analysis.On the basis of the above proposed algorithms, a MSVP named InteDyna has been developed. Finally, the feasibility and validity for this research is testified using a whole vehicle modeling and simulation.更多还原