AEROELASTIC OPTIMIZATION DESIGN OF COMPOSITE WING WITH CONSIDERATION OF STRUCTURAL INSTABILITY

从工程数学求解和有限元分析角度对复合材料结构的稳定性分析方法进行研究,基于这两个方面分别建立了同时考虑壁板稳定性约束和气动弹性约 束的气动弹性优化技术,并以大展弦比复合材料机翼为对象,进行气动弹性综合优化设计。研究表明,机翼气动弹性优化中若不考虑稳定性约束条件,虽然可以获得较小结构重量,但往往不满足稳定性要求;相比从有限元角度考虑结构失稳特征的气动弹性综合优化设计方法,通过工程数学方法对机翼结构进行分区失稳分析优化可以更加精准地控制变量,在满足各项性能指标,特别是稳定性约束的同时,进一步减轻了结构重量,提高了结构失稳因子。     

考虑几何非线性的复合材料机翼气动弹性分析

本文研究结构几何非线性与气动力非平面效应对大展弦比复合材料机翼的气动弹性行为的影响．将非线性有限元法与曲面涡格法结合，计算机翼静气动弹性变形；通过曲面偶极子格网法结合静气动弹性平衡位置处的结构切线刚度，建立气动弹性方程并求解得到机翼颤振速度．针对板模型机翼，分析了迎角对机翼几何非线性气动弹性特性的影响．结果表明：本文复合材料板模型机翼的颤振形式不受水平弯曲模态影响，属于经典弯扭颤振；在几何非线性的影响下，机翼扭转频率随结构变形增大而明显减小，颤振速度随迎角增大而减小．     

轻型飞机机翼气动/结构协同优化研究

探讨用协同优化方法能否有效地解决机翼气动／结构一体化设计优化问题。首先对基本的协同优化和基于响应面协同优化两种方法的特点进行了探讨,然后以轻型飞机机翼气动／结构一体化设计为例,着重研究如何用协同优化方法建立机翼气动／结构一体化设计的优化模型。研究结果表明,基本的协同优化算法不能有效地解决该机翼气动／结构一体化优化问题,而基于响应面的协同优化方法在求解这一问题时具有较好的鲁棒性。     

遗传算法求解可行域分离的结构优化问题

应用遗传算法求解了两类可行域分离的结构优化问题：局部屈曲约束的桁架拓扑优化问题和动力响应约束优化问题．对第一类问题，提出了新的数学表达式，适合于遗传算法求解．采用了改进的适应度函数及约束处理方法、约束凝聚选择、交叉操作改进和竞争最优保留，提高了遗传算法的效率和可靠性．算例说明，该方法能够克服可行域分离给传统优化算法带来的困难，有效地在多连通可行域中搜索全局最优解．     

基于传递函数法的带多个外挂机翼颤振分析

基于带外挂机翼结构和气动特点，使用带有半解析半数值特性的传递函数方法进行处理．首先，通过机翼的运动微分方程、二元机翼非定常气动力Therdorson 模型、结合外挂挂载处的内力平衡与位移状态条件，得到了三维的带多个外挂大展弦比机翼的颤振微分方程．进而，使用传递函数方法，先将颤振计算方程整理成为状态空间方程形式，结合求解复特征值的方法，完成了带多个外挂大展弦比机翼的动气动弹性稳定性分析．对比已有文献的计算结果以及通过有限元方法进行的仿真结果，证实了文章所提计算方法的准确性和高效性，结合传递函数方法的优势，进一步将文章方法拓展到机翼的固有频率和发散速度求解．文章结尾，分析了外挂数量、外挂质量、转动惯量及位置分布等变量对带多个外挂大展弦比机翼的动气动弹性稳定性的影响．     

基于卷积神经网络和松鼠优化算法的机翼结构混合优化设计#br#

针对大展弦比机翼的结构轻量化优化设计,提出了一种高效的布局和尺寸混合优化方法．在CFD/CSD气动弹性计算的基础上,对不同的结构变量进行统一编码,使用一维卷积神经网络建立代理模型,并使用松鼠优化算法建立了混合优化模型进行搜索寻优．以某型太阳能无人机的机翼结构优化为例,优化结果表明翼肋的布局变量和翼梁的尺寸变量之间存在着耦合关系,使用松鼠优化算法相比于遗传算法节省了35 %~45 %的计算成本,且混合优化后的结构比原始结构减重4.1 %,验证了该方法的有效性．     

基于刚度与应力问题的多相材料双尺度拓扑优化研究

本文针对双尺度晶格结构的优化设计，在质量约束条件下，提出了一种将均匀化方法与快速非支配排序遗传算法(NSGA-Ⅱ)相结合的拓扑优化方法，并引入双向渐进(BESO)思想指导单元的增删．对于双尺度优化设计，利用均匀化理论实现了微观尺度与宏观尺度的耦合．为了解决工程应用中的多相材料布局以及结构刚度、应力双目标优化问题，引入带有加权因子的材料插值方案，利用改进的密度插值函数推导出带惩罚因子的灵敏度计算公式，利用全局p范数应力方案消除应力的局部行为．为了使多相微观结构具有较强的边界连通性，对微观单元进行基于密度的边界设计．最后，对经典的L型梁与二维支撑结构进行优化设计，分析了p范数应力参数对优化结果的影响．结果表明，所提出的算法可以有效地使双目标达到最优解的平衡状态．此外，通过与经典的均匀化算法以及相关领域研究的结果进行对比，证明了所提出算法在多相材料以及双目标优化问题中的优越性，为未来双尺度优化解决工程问题提供了一定的理论基础．     

基于遗传算法的机翼柔性蒙皮全参数优化设计

为解决变弯度机翼前缘柔性蒙皮结构设计问题,提出基于遗传算法的柔性蒙皮全参数优化方法。采用"刚度剪裁"设计理念,以大型远程飞机前缘为研究对象,通过优化变量缩减、设计区域规划和边界条件位移等效,对柔性蒙皮结构进行工程简化,在保证变形精度的同时达到降低模型复杂度的目的;基于遗传算法对蒙皮结构进行全参数同步优化,以获得混合优化变量的全局最优解。研究表明,该方法在兼顾优化效率和制造可实现的基础上,使前缘蒙皮变形的最小二乘误差(LSE)降低60%,最大偏移误差降低64%,可显著提高变形精度。     

基于径向基函数的机翼二维气动代理模型设计

采用多学科设计优化方法进行机翼气动/结构优化时,结构学科的优化需要气动学科提供机翼压力分布的代理模型。本文引入了等参单元形函数的几何变换思想,利用径向基函数,解决了复杂形状机翼的二维气动代理模型的构造问题,进行了某巡航导弹弹翼考虑结构变形的气动力代理模型的构建。算例结果表明,本文所用代理模型构造方法简单易行,预测结果的精度很好。     

地震作用下结构的AMTMD主动控制策略

提出了一种新的控制策略——主动多重调谐质量阻尼器(AMTMD)．AMTMD控制系统频率呈线性分布．AMTMD保持相同的刚度和阻尼但质量变化．AMTMD的主动控制力采用Roorda(1975)提出的生成模式．基于结构的广义振型模型，导出了设置AMTMD时结构的动力放大系数(DMF)．于是AMTMD优化准则选择为结构最大动力放大系数的最小值的最小化．分别使用位移、速度和加速度传感器，通过最优搜寻，研究了反映AMTMD有效性和鲁棒性的参数．这些参数包括：频率间隔、平均阻尼比、调谐频率比、Min．Min．Max．DMF、标准化反馈增益系数和环增益系数．为比较，同时考虑了多重调谐质量阻尼器和主动调谐质量阻尼器．而且，数值结果表明：AMTMD比MTMD具有更高的有效性和鲁棒性且ATMD也有更高的有效性．     

Design enhancements for stress relaxation in automotive multi-shell-structures

Recent attempt to enhance the safety against collision has reshaped the simple single-shell structure into the integrated multi-shell structure. Moreover, due to various regulations continuously tightened for environment, weight reduction of automobile becomes an increasingly important issue. Weight reduction is mainly accomplished by better redesign, adoption of lighter materials, and small-sizing of auto (parts). Focusing on the local redesign among three, we suggest local patching methods. We also present, as another way, a method of determining thicknesses of subpart-shells in an integrated multi-shell structure. Those redesign methods successfully bring a preset amount of stress relaxation. More specifically, we first select a cross member as local patching model. Based on the finite element stress calculations, we relieve the stress of cross member by patching in two ways––non-uniform thickness patching and optimized uniform thickness patching. The latter is more effective and practical. Selecting a box type subframe as other redesign model, we determine the thickness of each subpart-shell by axiomatic design approach. The patching methods and the axiomatic approach of this work can be extended to the other multi-shell structures such as center member and lower control arm.     

From two-dimensional model networks to microcapsules

The synthesis of microcapsules for technical, cosmetic, and pharmaceutical purposes has attracted much interest in recent years. The design of new capsules requires profound knowledge of their mechanical properties. Rheological studies provide interesting information on intrinsic membrane features and they can also be used to obtain information on bursting processes and shear-induced release of encapsulated compounds. In this article we shall discuss the basic rheological properties of different types of ultra-thin membranes, which can be used to form stable capsules walls. We have also analyzed the typical structures of these cross-linked films using Brewster-angle microscopy. Tiny oil or water droplets, which are surrounded by ultra-thin membranes, form simple types of microcapsules. In addition to the interface shear rheology, we have measured the Young's modulus (elongational modulus) and the Poisson ratio using a modified spinning drop apparatus. The shear-induced deformation and orientation of microcapsules was investigated in optical rheometers (rheoscopes). In the regime of small deformations the results were in fairly good agreement with a theoretical model recently proposed by Barthès-Biesel. Due to the simple synthesis and well-defined structure, microcapsules can also serve as model systems to understand the complicated flow properties of red blood cells (erythrocytes).     

On Fiber Dispersion Models: Exclusion of Compressed Fibers and Spurious Model Comparisons

Fiber dispersion in collagenous soft tissues has an important influence on the mechanical response, and the modeling of the collagen fiber architecture and its mechanics has developed significantly over the last few years. The purpose of this paper is twofold, first to develop a method for excluding compressed fibers within a dispersion for the generalized structure tensor (GST) model, which several times in the literature has been claimed not to be possible, and second to draw attention to several erroneous and misleading statements in the literature concerning the relative values of the GST and the angular integration (AI) models. For the GST model we develop a rather simple method involving a deformation dependent dispersion parameter that allows the mechanical influence of compressed fibers within a dispersion to be excluded. The theory is illustrated by application to simple extension and simple shear in order to highlight the effect of exclusion. By means of two examples we also show that the GST and the AI models have equivalent predictive power, contrary to some claims in the literature. We conclude that from the theoretical point of view neither of these two models is superior to the other. However, as is well known and as we now emphasize, the GST model has proved to be very successful in modeling the data from experiments on a wide range of tissues, and it is easier to analyze and simpler to implement than the AI approach, and the related computational effort is much lower.     

基于耦合算法的三维复杂结构冲击动力学特性

光滑粒子流体动力学-有限元耦合算法（SPH-FEM）较好地结合了SPH和FEM的优势,近年来逐渐被引入冲击动力学相关问题研究中。然而早期的研究对象多为单一材料的简单结构,所取得的研究成果距离实际工程应用仍有一定差距。为此,在总结前人工作的基础上,对SPH-FEM耦合算法进行适当改进,通过引入复合材料损伤模型,对复合材料蒙皮结构飞行器舱段结构进行建模计算,分析其在爆炸冲击激励下的冲击动力学特性。将数值计算结果与试验结果进行对比分析,验证该算法和模型的有效性和准确性,初步实现SPH-FEM的工程实际应用。最后总结了复合材料蒙皮结构飞行器在爆炸冲击激励下的一系列结构动态响应规律,以期为航天飞行器结构设计与防护提供参考。     

Lonsdaleite Model of Open-Cell Elastic Foams: Theory and Calibration

We formulate a unit-cell model of open-cell elastic foams. In this model, a foam consists of four-bar tetrahedra arranged in the hexagonal diamond structure known as Lonsdaleite. The parameters of the model are the Young??s modulus of the bars and a few geometric parameters, the values of which may be roughly estimated for any given foam. We use the model to simulate a set of experiments in which elastic polyether polyurethane foams in a broad range of densities were tested under five loading conditions, namely tension along the rise direction; compression along the rise direction; compression along a transverse direction; simple shear combined with compression along the rise direction; and hydrostatic pressure combined with compression along the rise direction. With a suitable choice of values of the parameters of the model, the stress?Cstretch curves that we compute using the model compare favorably with the stress?Cstretch curves that were measured in the experiments. In some of the experiments a stress plateau in the stress?Cstretch curve was accompanied by heterogeneous stretch fields, even though the attendant stress fields were homogeneous. For these experiments we show that the model can be used to predict the occurrence of a second-order phase transition, so that the plateau stress can be interpreted as a Maxwell stress and the attendant heterogeneous stretch fields as two-phase fields, consistent with the experimental evidence. In other experiments the stress?Cstretch curve evinced a sudden and pronounced loss of stiffness, but no genuine stress plateau, and the attendant stretch fields remained homogeneous. For these experiments we show that the model can be used to predict the occurrence of a bifurcation of equilibrium in which the stress keeps rising as the deformation continues to increase in the post-buckling stage, so that the stretch fields remain homogeneous throughout, consistent with the experimental evidence. In general, to appraise the goodness of our model we put emphasis on the relation between the stress?Cstretch curve measured in an experiment and the nature of the attendant stretch fields. We submit that this emphasis should remain a guiding methodological trait in the appraisal of constitutive models of open-cell elastic foams.     

Analysis of pipe flow transition. Part II. Energy transfer

The present article describes the results from a study of nonlinear mechanisms at work during the process of transition to turbulence in pipe flows. Using an accurate hybrid finite-difference code for the simulation of unsteady incompressible pipe flow, we have performed a direct numerical simulation designed to model experiments performed by Han, Tumin and Wygnanski [12]. Based on these numerical data, we have conducted a meticulous investigation of the dynamic interactions of the structures and flow modes that can be observed during this process. Based on this study, we can paint a detailed picture of the dynamical interactions of flow structures during both the linear and nonlinear stages of pipe flow transition. While this picture does have some similarities to earlier proposed mechanisms, we find that even for the simple cases considered here the structure of the pertinent interactions is much richer than suggested by these earlier models.     

悬挂式偏心欹器的分析与制作

为制作出结构简单、易于加工的欹器,设计了一种悬挂式偏心的方案.使用MATLAB和Pro/E软件分别建立了数学模型与三维实体模型,对欹器的重心位置变化进行了仿真,在此基础上提出可行悬挂区域的概念,同时分析了若干重要结构参数对悬挂区域面积大小的影响,从机械制造的角度对欹器进行了设计和参数优化,采用机械加工方法加工出实物,并通过注水试验达到预期效果.     

THE DISLOC ATION EQU ATIONS OF A SIMPLE CUBIC CRYSTAL IN THE ISOTROPIC APPROXIMATION-A SOLVABLE MODEL

The dislocation equations of a simple cubic lattice have been obtained by using Green's function method based on the discrete lattice theory with the coefficients of the secondorder differential terms ...     

Rheological constitutive equation of solids: a link between models based on irreversible thermodynamics and on fractional order derivative equations

In this paper we focus on the rheological problem of defining a constitutive equation for viscoelastic materials. In this simple case, we show that writing the dissipative component of the observable response to a given excitation as the result of multiple internal processes working for equilibrium recovery (flux of internal hidden variables), can yield a recursive series in time. This can be obtained when use is made of the theorem of created entropy equipartition as a model for fluctuation regression. A distribution (spectrum) for relaxation times naturally follows. The model thus obtained reflects the concept of a hierarchically constrained dynamic behavior. The conclusion is that the operator of non-integer differentiation in time applied to field variables can also be recovered from pure thermodynamic considerations.     

Quantum field induced strains in nanostructures and prospects for optical actuation

We develop the mechanics theory of a phenomenon in which strain is induced in nanoscale structures in the absence of applied stress, due solely to the presence of quantum mechanical confinement of charge carriers. The direct effect of strain on electronic structure has been widely studied in recent years, but the “reverse coupling” effect that we investigate, which is only appreciable in the smallest structures, has been largely ignored even though its effects are present in first principles atomistic calculations. We develop a simple effective mass approach that can be used to model this universal physical phenomenon allowing a transparent scheme to identify its occurrence. We relate quantum field induced strain to acoustic polarons and identify the presence of this effect in density functional theory calculations of strain and quantum confinement in free-standing Si and GaAs quantum dots. Finally, we discuss the use of this quantum confinement induced strain as a mechanism for universal optical actuation in nanowire structures in the context of recent experimental results on carbon nanotubes.