Theoretical aspects of selecting repeated unit cell model in micromechanical analysis using displacement-based finite element method

Repeated Unit Cell(RUC)is a useful tool in micromechanical analysis of composites using Displacement-based Finite Element(DFE)method,and merely applying Periodic Displacement Boundary Conditions(PDBCs)to RUC is almost a standard practice to conduct such analysis.Two basic questions arising from this practice are whether Periodic Traction Boundary Conditions(PTBCs,also known as traction continuity conditions)are guaranteed and whether the solution is independent of selection of RUCs.This paper presents the theoretical aspects to tackle these questions,which unify the strong form,weak form and DFE method of the micromechanical problem together.Specifically,the solution’s independence of selection of RUCs is dealt with on the strong form side,PTBCs are derived from the weak form as natural boundary conditions,and the validity of merely applying PDBCs in micromechanical Finite Element(FE)analysis is proved by referring to its intrinsic connection to the strong form and weak form.Key points in the theoretical aspects are demonstrated by illustrative examples,and the merits of setting micromechanical FE analysis under the background of a clear theoretical framework are highlighted in the efficient selection of RUCs for Uni Directional(UD)fiber-reinforced composites.     

考虑不确定性的复合材料加筋壁板后屈曲分析模型验证方法

复合材料加筋壁板在结构轻量化设计中,由于材料组分、几何尺寸具有不确定性,导致了壁板结构在服役条件下承载特性的不确定性。针对上述问题,提出了一种考虑参数不确定性的复合材料加筋壁板后屈曲模型验证方法。首先基于正交试验设计方法进行了不确定性参数的显著性分析,然后采用Kriging模型构建了能够表征后屈曲特性的代理模型,利用蒙特卡洛随机模拟获得加筋壁板后屈曲载荷概率分布,最后通过壁板结构在典型承载条件下的力学实验数据验证了分析模型的准确性。该分析方法对于壁板件在实际工程中的应用具有一定指导意义。     

The finite element analysis of shells of revolution with a branching meridian

We present an algorithm for calculating the shells of revolution with the branching meridian using the triangular finite elements, the rigidity matrices of which are formed based on the vector method of displacement interpolation [1]. The correct kinematic and static conditions of shell conjugation on the line of their coupling have been developed. The shell structure consisting of a cylinder and adjacent shells is calculated under various conditions of support.     

A new analysis model for the effective stiffness of stiffened metallic panels under combined compression and shear stress

The paper deals with the analysis of the effective stiffness of stiffened metallic panels under combined compression and shear stress as used, e.g. in aircraft fuselages. An important criterion for sizing and certification of aircraft fuselages is the local and global buckling behaviour. For optimisation of stiffened metallic panels it is necessary to know the buckling and postbuckling behaviour as accurately as possible. Due to the fact that nonlinear FE analyses of a whole aircraft fuselage are too time consuming, a very fast quasi nonlinear FE analysis with a coarse mesh under consideration of semi-empirical methods for the effective skin-stiffness are used. At this point the effective stiffness method derived in this paper is used. Admittedly previous semi-empirical methods like the effective width method [J. Wiedemann, Leichtbau 1: Elemente, second ed., 1996; M.C.Y. Niu, Airframe Stress Analysis and Sizing, second ed., Commilit. Press Ltd., 1999] (only for pure compression load) or the method of Kuhn [P. Kuhn, J.P. Peterson, L.R. Levin, A summary of diagonal tension part I – methods of analysis, Technical Note 2661, NACA, 1952] (only for pure shear load) have disadvantages for the general combined compression and shear load case. This is improved in the current method.The first part of the paper deals with the realisation of the compression and shear test facility in a finite element model. The verification of the finite element model is important for subsequent parameter variations. The second part of the paper presents the approach of how to assess the effective skin-stiffness. In comparison to the paper in [M. Heitmann, P. Horst, D. Fitzsimmons, Effective stiffness of postbuckled stiffened metallic panels under combined compression and shear stress, J. Strain Anal. 38 (6) (2003) 534–555] many new parameters have been analysed. Therefore the new approach for the geometrically nonlinear analysis derived from the finite element results for combined compression and shear stress is considerably improved. At the end of the paper the great benefit of the new approach is shown. The results of very fast quasi nonlinear FE analyses under consideration of the new approach for the effective skin-stiffness on a coarse panel mesh agree well with the results of time expensive nonlinear FE analysis on a very fine panel mesh. Further studies are necessary to expand the new method to the influence of plasticity.     

多元统计分析线性模型主成分筛选准则研究

对多元统计分析线性模型中系数β估计时，如果观测值矩阵出现多重共线性，常规的最小二乘法会因均方误差太大而失效。本文的研究表明把RMS和AIC准则用作主成分评判标准，可降低多重共线性，减少均方误差，提高估计的稳定性和模型的拟合精度。     

带副翼的翼身组合体的数值模拟

利用NUMECA公司的 FINE软件对带副翼的翼身组合体进行数值模拟,在副翼和主翼的两个交界面分别形成结构化网格,利用FINE中的FNMB功能进行计算.通过与文献中此类工作的对比,认为FINE软件完成网格自动拼接是行之有效的.用不同网格数进行验算分别得到文献[1]和文献[2]的压力曲线,由此证明两者的区别源于网格数的不同.     

复合材料加筋板剪切后屈曲分析与优化设计

为了充分利用复合材料加筋板的后屈曲承载能力,针对复合材料加筋板的后屈曲行为开展优化设计方法的研究具有重要意义。详细探讨了筋条尺寸及密度等参数对承受面内剪切载荷作用下的复合材料双向加筋板屈曲后屈曲的影响规律。建立了复合材料加筋板考虑后屈曲响应的结构分级优化方法:在一级优化中以结构几何尺寸为设计变量,使用响应面法(RSM)拟合出结构后屈曲响应的全局近似函数,结果显示,加筋缘条的宽度及加筋的密度对屈曲承载能力有重要影响;在二级优化中采用遗传算法(GA)对复合材料铺层顺序进行优化,经过两级优化后的复合材料加筋板相比于初始设计在质量减少了3%的同时,线性屈曲位移提高了8.86倍,线性屈曲模态由局部屈曲改善为整体屈曲,同时结构的后屈曲承载能力提高了8.7%。基于解决旅行商问题(TSP)的遗传算法被调整用于固定铺层厚度的复合材料铺层顺序优化问题,经优化,结构线性屈曲特征值提高了12.76%,表明了优化方法的可行性。     

简单转子系统油膜稳定界限的计算分析

对简单转子支承系统的油膜稳定区进行了计算研究.通过建立包含支承阻尼和转子外阻尼在内的弹性支承滑动轴承系统模型,计算了该转子系统的油膜稳定界限,并对稳定界限进行分析,讨论了提高转子系统稳定性的措施.分析结果表明:减小转子系统的刚度,是提高系统油膜稳定性的有效办法.     

混料线性对数比模型的D-最优试验设计

混料问题我们可以在医药、化工、农业等诸多领域中经常遇到。对于该问题在1984年由Aitcison和Bacon-Shone提出了线性对数比模型。针对设计空间为的线性对数比模型，已有D-最优设计的分析形式的解并由关颖男教授给出了A-最优设计。作者针对另一个设计空间的混料线性对数比模型，给出了D-最优设计以及最优配置件。并利用D-最优准则讨论了该线性对数比模型的最优解是在Z集合的顶点处取得。     

Crushing of conical composites shells: a numerical analysis of the governing factors

A numerical and experimental analysis comparing the influence of specimen geometry, material composition and loading conditions on the crushing response of truncated conical shells is presented. The analysis is based on a new multi-layered numerical modelling composed of shell and solid elements. A material model appropriate for balanced fabrics has been developed including in-plane failure, delamination failure and resulting degradation models.     

顾客满意指数的结构方程模型与应用

分析了经典的顾客满意指数的结构关系模型的基本原理;结合企业顾客满意指数测评的实际案例,给出了结合偏最小二乘回归(PLS)方法的顾客满意指数测评的线性结构关系(LISREL)路径分析的实施途径。此外,还通过控制某些中间变量的作用,研究了原因变量对结果变量影响作用分解的一般模式。     

涡轮叶片型面气膜冷却效率的计算模型

研究并发展了以低雷诺数k ε紊流模型为基础的气膜冷却效率计算方法,将前人针对平板气膜冷却提出的掺混模型推广应用于涡轮叶片型面。计算结果表明,导向叶片型面存在四个典型区域,每个区域自气膜孔喷出的冷气射流与主流的相互作用的规律不同,对于四个典型区域分别建立质量喷出率φ和三维掺混系数γ两个经验参数随冷气吹风比变化的规律,并用所得的规律计算叶片上单排气膜孔下游的冷却效率,与实验数据符合良好。     

An improved numerical method for constructing Halo/Lissajous orbits in a full solar system model

An improved numerical method that can construct Halo/Lissajous orbits in the vicinity of collinear libration points in a full solar system model is investigated. A full solar system gravitational model in the geocentric rotating coordinate system with a clear presentation of the angular velocity relative to the inertial coordinate system is proposed. An alternative way to determine patch points in the multiple shooting method is provided based on a dynamical analysis with Poincare′sections. By employing the new patch points and sequential quadratic programming, Halo orbits for L_1, L_2, and L_3 points as well as Lissajous orbits for L_1 and L_2 points in the EarthMoon system are generated with the proposed full solar system gravitational model to verify the effectiveness of the proposed method.     

一种高精度夹具的设计原理

通过对定位精度高达２μｍ,又非常便捷装卸的瑞士ＥＲＯＷＡ夹具结构原理的介绍,以引起国内同行的关注,旨在推广应用于我国航空精密零件及工模具生产中,以期解决长期困惑我国的高位置精度问题。     

旋转带肋U型通道内流动与换热的数值模拟

为了获得能够模拟高参数涡轮叶片内冷通道换热效果的模型，数值模拟了旋转状态下U型通道内的流场和温度场，比较了数值模拟与实验的结果。结果表明：所采用的计算程序和模型与实验结果吻合。旋转状态下，通道内各面换热的变化是和通道内流场的变化密切相关的；哥氏力在垂直于旋转半径截面上的不均匀分布引起流动较大变化，对通道内各面换热的影响比较大。哥氏力的作用较大幅度强化指向面换热，小幅强化两侧面换热，而弱化背向面换热。对于带肋通道，总体上阻力系数随着旋转速度的增加而升高。     

Algorithms of constructing a neural network model for a dynamic object of control and adjustment of PID controller parameters

The paper presents an algorithm for constructing a neural network model for a dynamic object of control based on the data sample obtained as a result of the object operation. The algorithm being considered applies a neural network approach and a genetic algorithm. An algorithm is presented for determining a domain of possible values for a proportional-integral-derivative controller (PID controller) based on application created neural network model of the controlled object.     

基于有限元/边界元耦合方法的管道进口声传播及声辐射模型

发展了一种基于有限元和边界元耦合方法的管道进口声传播及声辐射计算模型.该模型将整个声场分为内部有限域和外部无界域,分别用有限元和边界元方法求解控制方程,在两者之间的界面上使用具有物理意义的声阻抗参数进行匹配,并通过一种快速迭代方法实现全声场求解.这种迭代方法可以保证有限元刚度矩阵等带宽以及对称的特性不被破坏,有助于提高计算效率.该模型先得到了Levine-Schwinger标准解的检验,进而在无流动情况下对于简化的航发短舱进口管道模型进行了噪声辐射现象的数值模拟,最后基于计算结果分析了声衬对远场声辐射的影响.      

悬停旋翼无粘流场数值模拟中的多重网格方法

发展了一种基于不同空间离散格式的多重网格算法,并应用于悬停旋翼无粘绕流的Euler方程数值模拟。由于悬停旋翼流场中存在不可压区域,同时旋翼尾涡系统的发展需要较长的时间,使得旋翼流场的收敛速度远低于固定翼流场,因此研究旋翼流场的多重网格算法具有重要意义。空间离散采用了Roe s FDS格式和Jameson中心有限体积格式,时间推进应用了五步Runge-Kutta方法。采用多重网格V循环方式,对一跨声速悬停旋翼无粘流场进行了数值计算。计算结果表明:多重网格算法可以显著加速悬停旋翼无粘流场的数值计算收敛速度;无论在激波分辨率还是在计算精度上,Roe s FDS格式都优于JST格式。     

微机械陀螺正交耦合误差静电力抑制的有限元仿真研究

微机械陀螺的正交耦合误差是敏感结构振动模态间的刚度耦合引起的检测模态输出偏量,是影响陀螺性能的关键误差源之一。静电力抑制是一种采用静电力调节驱动模态的主轴偏量,使用直流电压进行正交耦合误差抑制的方法,该方法具有片上实时抑制能力,能够有效抑制正交耦合误差。从静电力抑制正交耦合误差的基本原理出发,运用有限元仿真,对硅基音叉陀螺正交耦合误差的静电力抑制进行了仿真分析,并通过实物测试数据进行了验证。     

计算流体力学中有限元的强间断处理

本文首次提出了无波动，无自由参数的有限元离散方法，它是基于矢通量分裂后其物理传播特性，利用差分格式构造过程中对激波上下游不同性质的分析，对一维Ｅｕｌｅｒ方程进行了仔细分析，并将其推广到二维，轴对称的无粘，有粘方中，从计算实践看，这种方法简便、实用，对激波，分离，激波与边界层干扰的复杂流场有较好的分辨能力和计算稳定性，比以往的迎风有限元，加入Ｌａｐｄｉｕｓ人工粘性修正的有限元有更好的流场分辨能力，使