A FINITE ELEMENT SOLVER FOR NAVIER-STOKES EQUATIONS VIA VORTICITY AND VELOCITY

INTRODUCTIONThe stationary incompressible Navier- Stokesequations in the primitive variables( velocity uand pressure p)- vΔu + u . u + p =f . u =0u =g　inΩinΩonΓ( 1 )whereΩ is a set of R2 ,Γ its boundary,v thekinematic viscosity of the fluid,f a field of givenbody forces,and g a given field defined onΓ sa-tisfying the global conservation property∫Γg . n =0 ( 2 )n denotes the unit outer normal vector toΓ.The vorticity- velocity system of Eq.( 1 ) ,byintroducing the vorticityω…     

复合材料迭层板孔边应力集中分析

采用平面４节点等参元方法，研究含中心圆孔复合材料迭层板孔边应力分布规律，对比分析了边距、铺层、材料性能常数、外载等因素对孔边应力集中的影响。     

基于正弦基础激励的航天器结构模型修正方法

正弦振动试验是航天器系统级和单机产品需要开展的常规试验,充分利用工程中积累的正弦试验数据进行结构模型修正具有重要的工程意义。文章首先介绍了基础激励下结构模型修正方法,通过矩阵分块、待修正参数归一化、参与修正的频率点选择等步骤,推导出基于基础激励的模型修正公式;然后对国际通用算例GARTEUR桁架结构的有限元模型进行修正,分析修正后模型在修正频段内和修正频段外计算所得模态频率,验证修正后模型对模态频率的复现和预示能力,通过对比试验模型、分析模型和修正后模型中4个典型节点的响应曲线,检验修正后模型精度。结果表明:修正后模型的模态频率和响应曲线均与试验模型趋于一致,证实了该修正方法对GARTEUR结构修正的有效性。     

基于任务科目的直升机飞行品质评定试飞技术研究

主要对ADS-33E中飞行品质评定的要求进行分析,从任务科目、响应类型和可用感示环境3个维度进行飞行品质的等级评定研究,提出了直升机飞行品质综合评定的试飞技术研究思路,并对某型号直升机的试飞结果和有关问题进行了初步分析。     

铝合金T型材拉弯成形的有限元模拟

针对目前拉弯成形中的问题,采用有限元模拟的方法,对带下陷拉弯过程进行计算机仿真,得到优化后的工艺参数,避免了盲目的试拉,提高了加工效率,降低了拉弯成本,积累了带下陷拉弯成形的经验,提高了公司拉弯工艺水平。     

跃变型介质中原油渗流有限元计算

本文建立跃变型介质中原油渗流的数学模型,可用来描述油层(尤其是低渗透层)超高压注水条件下的不稳定渗流过程及其特征。用Galerkin有限元法进行了数值计算,讨论了介质跃变的影响。     

材料非线性有限元分析的一种有效方法——预测割线刚度变刚法

 材料非线性有限元增量解法中如何减少加载次数,保证精度是两个重要的问题;而误差估计也是与之密切相关的问题,特别是对每次加载不进行迭代的增量变刚法。本文针对这些问题提出预测割线刚度变刚法。     

基于有限Fourier级数的航天器转移轨迹设计

针对航天器小推力转移轨迹的初始设计问题，利用基于三阶Fourier级数的设计方法实现了航天器小推力的多圈转移。同时，基于有限Fourier级数的形状法，对具有多个约束条件的小推力多圈转移轨迹进行了优化设计。选取了共面同轴同偏心率的初始和末端轨道位置，对所提出的方法进行了仿真验证。结果表明：与改进逆五阶多项式形状法相比，所提出的方法虽然增加了转移时间，但当转移圈数为5圈、有限Fourier级数的项数为10时，可减少将近75%的转移速度增量，同时大大减小了所需的最大推力加速度的值。     

Cutting path-dependent machinability of SiCp/Al composite under multi-step ultra-precision diamond cutting

Particle-tool interactions, which govern the synergetic deformation of SiC particle reinforced Al matrix composites under mechanical machining, strongly depend on the geometry of particle position residing on cutting path. In the present work, we investigate the influence of cutting path on the machinability of a SiCp/Al composite in multi-step ultra-precision diamond cutting by combining finite element simulations with experimental observations and characterization. Be consistent with experimentally characterized microstructures, the simulated SiCp/Al composite is considered to be composed of randomly distributed polygonally-shaped SiC particles with a volume fraction of 25vol%. A multi-step cutting strategy with depths of cut ranging from 2 to 10 μm is adopted to achieve an ultimate depth of cut of 10 μm. Intrinsic material parameters and extrinsic cutting conditions utilized in finite element simulations of SiCp/Al cutting are consistent with those used in corresponding experiments. Simulation results reveal different particle-tool interactions and failure modes of SiC particles, as well as their correlations with machining force evolution, residual stress distribution and machined surface topography. A detailed comparison between numerical simulation results and experimental data of multi-step diamond cutting of SiCp/Al composite reveals a substantial impact of the number of cutting steps on particle-tool interactions and machined surface quality. These findings provide guidelines for achieving high surface finish of SiCp/Al composites by ultra-precision diamond cutting.     

Inverse identification of constitutive parameters of Ti2AlNb intermetallic alloys based on cooperative particle swarm optimization

Ti₂AlNb intermetallic alloy is a relatively newly developed high-temperature-resistant structural material, which is expected to replace nickel-based super alloys for thermally and mechanically stressed components in aeronautic and automotive engines due to its excellent mechanical properties and high strength retention at elevated temperature. The aim of this work is to present a fast and reliable methodology of inverse identification of constitutive model parameters directly from cutting experiments. FE-machining simulations implemented with a modified Johnson-Cook (TANH) constitutive model are performed to establish the robust link between observables and constitutive parameters. A series of orthogonal cutting experiments with varied cutting parameters is carried out to allow an exact comparison to the 2D FE-simulations. A cooperative particle swarm optimization algorithm is developed and implemented into the Matlab programs to identify the enormous constitutive parameters. Results show that the simulation observables (i.e., cutting forces, chip morphologies, cutting temperature) implemented with the identified optimal material constants have high consistency with those obtained from experiments, which illustrates that the FE-machining models using the identified parameters obtained from the proposed methodology could be predicted in a close agreement to the experiments. Considering the wide range of the applied unknown parameters number, the proposed inverse methodology of identifying constitutive equations shows excellent prospect, and it can be used for other newly developed metal materials.