基于显式几何更新算法的地下管道自动形状优化

基于计算力学中的结构优化思想,应用一种新型的显式几何更新算法,自行编制C++程序,实现地下管道形状设计的自动优化。管道内的流体假设为牛顿不可压缩流,并考虑惯性项。优化区域主要为管道竖直方向和水平方向的过渡段。形状优化的设计变量是几何边界的有限元节点坐标,优化目标是实现流体黏性能耗散的最小化。优化过程基于形状梯度,即通过形状敏感度分析来求解目标函数相对于设计变量的偏导数。所使用的显式几何更新算法既可以通过网格清晰描述形状,也可以大范围地自动更新网格。详细介绍了地下管道自动形状优化过程的关键步骤。通过数值算例探讨了不同注入速度、密度和黏度对其最优形状的影响。     

Cosserat连续体模型中本构参数对应变局部化模拟结果影响的数值分析

基于所发展的压力相关弹塑性Cosserat连续体模型及相应的数值方法,以一维剪切层及二维平板压缩问题为例,数值分析了Cosserat连续体模型中的本构参数Cosserat剪模、软化模量及内部长度参数对应变局部化数值模拟结果的影响.结果表明在一定取值范围内,Cosserat剪模对数值模拟结果几乎没有影响,并给出了具体数值计算时的取值范围;软化模量绝对值越大,后破坏段的荷载-位移曲线越陡,计算得到的剪切带宽度越窄;内部长度参数越大,后破坏段的荷载-位移曲线越平缓,计算得到的剪切带越宽.     

基于拓扑与形状优化的小型化金属天线设计方法

天线小型化设计需要基于先进的设计方法,基于拓扑优化的设计往往存在灰度单元,因此设计结果无法直接应用,需要进一步规整设计。而对于电磁金属结构,粗糙的规整方法会引起结构性能的很大变化以致偏离最优结果。提出一种拓扑优化和形状优化相结合的方法,用于金属天线结构的小型化设计。该方法通过拓扑优化获得金属天线结构的概念构型,进而利用形状优化对概念构型进行边界规整和精细化设计。形状优化方法采用多控制点贝塞尔曲线描述拓扑概念构型,通过贝塞尔曲线控制点的移动实现天线构型的调控。给出了贝塞尔曲线控制点的设置原则,基于拓扑优化得到场量分布结果,利用较少的贝塞尔曲线控制点实现天线拓扑构型结构特征的有效调控。该方法可以获得无灰度单元残留的拓扑结果,同时可有效避免密度阈值规整方法中天线性能改变的问题,并且获得的拓扑构型边界光滑。数值算例表明拓扑优化和形状优化相结合方法的有效性。此外,该方法可拓展到其他类型电磁器件的优化设计中。     

基于物理的变形曲线在结构形状优化中的应用

用各向异性模型定义NURBS曲线的变形能,基于所提出的变形能模型,用有限元法对NURBS曲线表达的设计边界进行模态计算,然后,将设计边界用模态向量的线性组合参数化表示。将这种基于边界特征向量的几何形状表示方法应用于优化参数定义．提出了一种适用于结构形状优化的自适应几何精化方法,它有效地将户型有限元分析、优化方法和设计边界的形状表达集成在一起。     

连续体结构的拓扑与形状集成优化算法

以连续体结构的拓扑与形状优化设计技术作为研究对象,将拓扑优化、形状优化、有限元分析和计算机辅助设计有机地集成在一起,构建了优化设计模型;研究了用B样条曲线曲面逼近拓扑优化后的结构体边界,进行边界光滑处理;在形状优化中,设计变量定义为B样条曲线或曲面的控制顶点的运动,建立了边界节点移动速度场计算方法和边界形状调整方法及模型更新理论,有效地控制节点的运动,给出了相应的算法和计算表达式,寻求较快的搜索方向,以合理速度分布尽快使形状变为最佳。设计实例的结果表明了本文所建立的模型的合理性和方法的有效性。     

结构形状优化设计数值方法的研究和应用

本文论述了连续体结构形状优化设计数值方法的研究和应用进展,讨论了结构模型化、灵敏度分析、优化方法改进、优化实用软件开发以及同CAD技术相结合等问题,介绍了在结构优化设计软件MCADS中采用的方法,并通过工程实例说明了结构形状优化设计的应用及其价值。     

陡峭山坡风场数值模拟方法研究

地形起伏是造成山地风场复杂多变的主要原因,其风场特性与基于均匀粗糙平面的风场有很大的区别.为准确模拟山坡地形风场,以坡角45°的简化陡峭山坡为研究对象,采用CFD数值模拟方法进行了流场分析,通过与风洞试验和各国规范对比,详细分析了网格分辨率、湍流模型和坡顶局部光滑处理等因素对数值模拟风场精度的影响.结果 表明,采用基本网格尺度布置以及Realizable k-ε湍流模型,在坡顶位置的风压系数值与风洞试验存在一定偏差;在坡顶分离点处采用具有二阶连续性的曲线进行局部光滑,可使得数值模拟所得风速比和风压系数与试验结果更好地吻合,且光滑曲线的过渡段水平距离越短,模拟效果相对越好,坡顶位置的地形加速效应模拟结果与文献试验、中国以及澳大利亚规范具有更好的一致性.     

飞行器船尾设计对亚声速底阻影响及风洞试验验证

减小阻力尤其是底部阻力,是飞行器增加航程的重要手段,而船尾布局则是减小底部阻力的有效措施．为研究船尾修型设计在亚声速段对飞行器阻力的影响规律,对某飞行器外形开展船尾修型设计并进行数值模拟,分析了不同船尾形状和船尾角度对飞行器阻力的影响情况,并开展了风洞试验验证．结果表明,船尾修型设计可以有效减小底部阻力;船尾采用曲线过渡的减阻效果优于直线过渡;在限定船尾过渡段尺寸（轴向长度80 mm、法向高度40 mm）的情况下,船尾角度超过45°的修型设计,对底部的减阻效果更为明显;风洞试验结论与数值分析结果一致．     

基于3D细观模型的混凝土动态压缩行为分析

通过建立混凝土的3D细观模型,在细观尺度上分析动态压缩荷载作用下混凝土材料内部裂缝的产生和发展、损伤演化和动态强度及其影响因素。首先,基于传统的“生成-投放”法生成粒径、形状和空间分布均随机的凸多面体粗骨料模型,并通过骨料沉降和粒径缩放实现粗骨料的大体积率（达50%）和可调控;使用四面体网格划分骨料和砂浆表征其真实物理形状;使用界面粘结接触表征界面过渡区（ITZ）提升计算效率。进一步通过对比不同粗骨料粒径混凝土的分离式霍普金森压杆（SHPB）试验数据与模拟结果,如杆上应变时程、试件动态应力-应变曲线和试件损伤破坏模式,验证了建立的混凝土3D细观有限元模型、参数确定方法和数值仿真方法的准确性。最后,分析了30～100 s-1应变率范围内骨料粒径（4～8、10～14和22～26 mm）、体积率（20%、30%和40%）和类型（石灰岩、花岗岩和玄武岩）对混凝土动态压缩强度的影响。结果表明：粗骨料粒径增大,混凝土动态压缩强度先增大后减小;粗骨料体积率越高,混凝土动态压缩强度越大;混凝土动态压缩强度随粗骨料强度的增加而提高。     

记录介质的非线性响应对粒子场同轴全息再现像的影响

建立粒子场同轴全息非线性记录对再现像影响的数值模拟模型，模拟了不同形状粒子在非线性段记录时再现像。并通过实验验证了数值模拟模型，实验上得到非线性记录下不同形状粒子的再现像。     

固定网格下基于光滑变形隐式曲线的孔形优化设计方法

孔形优化设计是减缓开孔结构孔边应力集中的有效手段，其对应力分析精度和孔边曲线的几何表达能力都有着较高的要求．论文针对现有固定网格孔形优化方法分析精度较低和/或孔边曲线变形能力有限等不足，采用有限胞元方法在固定网格下对开孔结构进行高精度的力学性能分析，采用能够自由光滑变形的隐式曲线描述待优化的孔洞边界，进而建立优化模型并推导出相应的解析灵敏度计算公式，形成了固定网格下开孔结构孔形优化设计新框架．通过对不同载荷边界条件下的开孔平板结构进行孔形优化设计，表明本方法无需网格更新、灵敏度推导简便、力学分析精度高且优化设计空间大，能够有效降低孔边应力集中程度．     

Optimization of high-speed railway pantographs for improving pantograph-catenary contact

A crucial system for the operation of high-speed trains is the pantograph catenary interface as it is the sole responsible to deliver electrical power to the train. Being the catenary a stationary system with a long lifespan it is also less likely to be redesigned and upgraded than the pantographs that fit the train vehicles. This letter proposes an optimization procedure for the improvement of the contact quality between the pantograph and the catenary solely based on the redesign of the pantograph head suspension characteristics. A pantograph model is defined and validated against experimental dynamic characteristics of existing pantographs. An optimization strategy based on the use of a global optimization method, to find the vicinity of the optimal solution, followed by the use of a deterministic optimization algorithm, to fine tune the optimal solution, is applied here. The spring stiffness, damping characteristics and bow mass are the design variables used for the pantograph optimization. The objective of the optimal problem is the minimization of the standard deviation of the contact force history, which is the most important quantity to define the contact quality. The pantograph head suspension characteristics are allowed to vary within technological realistic limits. It is found that current high-speed railway pantographs have a limited potential for mechanical improvements, not exceeding 10%–15% on the decrease of the standard deviation of the contact force.     

Finite element analysis of edge lamination during hot rolling process of aluminium alloy

Summary The rigid-plastic finite element method is applied to the analysis of the three-dimensional deformation behaviour, in particular the forming of edge lamination during the multi-pass hot roughing process of aluminium. the calculation is carried out for various rolling conditions and reduction schedules, and their influence on the edge lamination is examined. The results suggest that the crop loss due to the edge lamination can be reduced by increasing the roll diameter, the reduction per pass and the initial width of the slab.     

秦沈客运专线高速列车构架蛇行波标准差的试验研究

国内外大多采用轨道横向不平顺作为列车—桥梁(轨道)时变系统横向振动的激振源。实际上，引起此系统横向振动的因素很多，诸如轨道横向不平顺、车轮踏面锥度、轮轨缺陷、车轮与钢轨的制造误差、车辆质量及其载重的偏心等。仅仅考虑轨道横向不平顺，会忽略其他很多因素的影响。相反，机车车辆构架蛇行波反映了引起此系统横向振动所有因素的影响，同时还反映了轮轨实际接触状态。研究证明，构架蛇行波标准差是输入此系统横向振动的能量，因此，有关它的研究十分重要。本文根据秦沈客运专线高速列车(中华之星)构架蛇行波现场测试结果，采用工程概率数值分析方法，对高速列车构架蛇行波标准差进行了统计分析，得出具有99％概率水平的高速列车构架蛇行波标准差与车速的关系曲线，为高速列车—桥梁(轨道)时变系统横向振动随机分析激振源的确定提供了基础资料；同时还列出了具有代表性的高速列车构架蛇行波实测波形图。     

A biarc-based shape optimization approach to reduce stress concentration effects

In order to avoid stress concentration, the shape boundary must be properly designed via shape optimiza- tion. Traditional shape optimization approach eliminates the stress concentration effect by using free-form curve to present the design boundaries without taking the machin- ability into consideration. In most numerical control （NC） machines, linear as well as circular interpolations are used to generate the tool path. Non-circular curves, such as non- uniform rotational B-spline （NURBS）, need other more ad- vanced interpolation functions to formulate the tool path. Forming the circular tool path by approximating the opti- mal free curve boundary with arcs or biarcs is another op- tion. However, these two approaches are both at a cost of sharp expansion of program code and long machining time consequently. Motivated by the success of recent researches on biarcs, a reliable shape optimization approach is pro- posed in this work to directly optimize the shape boundaries with biarcs while the efficiency and precision of traditional method are preserved. Finally, the approach is validated by several illustrative examples.     

Determination of the mechanical constants of ZnS nanobelt by combining nanoindentation test and finite element method

The single nanobelt simplified as transversely isotropic is modeled by three dimension element during the modeling of finite element method (FEM), and the mechanical constants of ZnS nanobelt are obtained by combining nanoindentation test and FEM. In the forward analysis, the numerical loading curves at the appropriate penetration depth are simulated by using the purely mechanical indentation (PMI) and piezoelectric indentation (PI) modes to extract the numerical maximum indentation load and numerical loading curve exponent, and they are used to establish the dimensionless equations related with the mechanical constants of nanobelt by fitting the mechanical constants vs numerical maximum indentation load and numerical loading curve exponent curves. In the reverse analysis, the experimental indentation curve performed on ZnS nanobelt is fitted as the power function to obtain the maximum indentation load and the loading curve exponent and they are substituted into the dimensionless equations to solve the mechanical constants of the nanobelt. In order to verify the validity, the mechanical constants are inputted into ABAQUS software to obtain the computational loading curves under PMI and PI modes, and they are in good agreement with the experimental indentation curve of ZnS nanobelt. The combination solutions of mechanical constants under PMI mode is of larger total error than those under PI mode, and it indicates that the piezoelectric effect should be reasonably considered into the developed method, which is effective to determine the mechanical property of single nanobelt.     

基于改进链码法的LuGre摩擦模型动态参数辨识

针对现有LuGre摩擦模型动态参数辨识方法辨识精度不高,收敛性难以保证及参数初值难以确定等不足,提出了一种基于改进链码特征识别法的参数辨识方法。首先,研究LuGre摩擦模型中两个动态参数-鬃毛刚度系数与阻尼系数之间的关系,以及鬃毛刚度系数与预滑动阶段位移-摩擦力曲线形状之间的对应关系;然后,改进现有Freeman链码的采样方式和码间距,利用改进的链码结合傅立叶描绘子提取位移-摩擦力曲线的形状特征并形成特征向量;最后,以加噪声原始位移-摩擦力曲线和仿真位移-摩擦力曲线的特征向量为参数建立度量两曲线相似程度的欧氏距离,寻优得到使欧氏距离满足给定误差的仿真位移-摩擦力曲线,该曲线对应的鬃毛刚度系数即为其辨识值,进一步可计算出阻尼系数。文末给出的辨识实例验证了提出方法的正确性和有效性。     

A Numerical Approach for Non-Linear Moisture Flow in Porous Materials with Account to Sorption Hysteresis

A numerical approach for moisture transport in porous materials like concrete is presented. The model considers mass balance equations for the vapour phase and the water phase in the material together with constitutive equations for the mass flows and for the exchange of mass between the two phases. History-dependent sorption behaviour is introduced by considering scanning curves between the bounding desorption and absorption curves. The method, therefore, makes it possible to calculate equilibrium water contents for arbitrary relative humidity variations at every material point considered. The scanning curves for different wetting and drying conditions are constructed by using third degree polynomial expressions. The three coefficients describing the scanning curves is determined for each wetting and drying case by assuming a relation between the slope of boundary sorption curve and the scanning curve at the point where the moisture response enters the scanning domain. Furthermore, assuming that the slope of the scanning curve is the same as the boundary curve at the junction point, that is, at the point where the scanning curve hits the boundary curve once leaving the scanning domain, a complete cyclic behaviour can be considered. A finite element approach is described, which is capable of solving the non-linear coupled equation system. The numerical calculation is based on a Taylor expansion of the residual of the stated problem together with the establishment of a Newton–Raphson equilibrium iteration scheme within the time steps. Examples are presented illustrating the performance and potential of the model. Two different types of measurements on moisture content profiles in concrete are used to verify the relevance of the novel proposed model for moisture transport and sorption. It is shown that a good match between experimental results and model predictions can be obtained by fitting the included material constants and parameters.     

基于机电阻抗技术的管道法兰结构健康监测实验研究

基于机电阻抗技术,采用一种新型压电陶瓷纤维复合材料MFC(Macro-fiber composite),对管道连接处法兰的螺栓工况进行监测实验研究。首先,研究了螺栓扭矩大小对管道法兰结构的阻抗的影响程度。在对螺栓开始施加扭矩时阻抗值变化明显,当扭矩增大到一定程度后,阻抗变化减缓。同时进一步研究了松动螺栓数量与管道法兰结构的阻抗变化之间的关系。结果显示,结构的损伤值随松动螺栓个数的增加呈线性增长。采用均方根偏差统计算法,对在不同工况条件下管道法兰结构处测得的阻抗值进行了有效的分析和处理。结果表明,采用MFC作为压电敏感元件的机电阻抗法,用于管道法兰结构健康监测具有较好的稳定性和应用潜力。     

岩体原位流变荷载试验的力学参数与模型反演

根据现场岩体原位测试的60m和70m处两试验点的流变变形曲线,首先通过曲线特征筛选出了能够描述其变形特性的流变模型(三参量固体模型,Burgers模型),基于粘弹性分析理论及两步反分析法思路,建立了荷载试验的三参量固体模型、Burgers模型的位移优化反演格式,利用分级加载所获得的瞬时弹性位移,反算出了两试验点处的岩体弹性体积模量K、剪切模量G0和变形模量E0,并由优化反演方法获得了两模型的所有流变参数G1,η1,η2和E1以及长期弹性模量E∞。利用所获得的粘弹性参数分别计算出了在不同载荷下两种模型的理论解析曲线,并与实测曲线进行了分析对比,最终获得了能够较真实地描述试验区域岩体流变变形特性的最佳模型,即三参量固体模型。通过对比分析验证了所用思路及方法的正确性和实用性,文中方法虽然应用于流变荷载实验情况,但其具有一定的普遍意义,可应用于不同状况的流变实验的参数确定和模型反演。