复合材料壁板铺层参数对大展弦比机翼气动弹性优化的影响

开展了大展弦比复合材料机翼气动弹性综合优化设计研究,以复合材料层合板铺层厚度为设计变量,以多种气动弹性约束与强度/应变约束为限制条件对结构进行优化设计,从铺层比例和铺层非均衡两方面分析了蒙皮铺层参数的影响。研究表明: 在满足综合约束的条件下,随着0°铺层比例的增加,翼尖变形略微减小,颤振速度略有下降,副翼效率变化不大; 蒙皮铺层非均衡程度主要影响机翼静气动弹性能,随着蒙皮非均衡引起的机翼刚轴绕翼根向前缘逐渐偏转,翼尖垂直变形变化不明显,但翼尖负扭转变形的绝对值加大,副翼效率下降。     

翼面复合材料结构气动弹性剪裁设计和工艺技术

为实现机翼翼尖扭角增量的设计要求,达到改善飞机气动弹性特性的目的,利用复合材料的弯扭耦合特性,着重对复合材料非均衡铺层设计和工艺技术进行了研究,提出了对翼面复合材料结构弯扭耦合特性进行设计的工程解决方法,并开展了对比试验研究。试验结果表明,经剪裁设计后,模拟机翼盒段外洗效果明显,在不同载荷作用下,翼尖扭角增量降低10％～45％。     

非均衡铺层壁板复合材料机翼气动弹性分析

对上下壁板采用非均衡铺层的大展弦比复合材料机翼进行了气动弹性分析。建立了不同掠角和壁板铺层非均衡程度的气动弹性模型 , 并考虑了壁板铺层非均衡程度的变化。分析了严重载荷情况下 , 机翼变形、 升力特性弹性修正等随壁板铺层非均衡程度的变化 , 并分析了固有振动特性和发散/颤振速度随壁板铺层非均衡程度的变化趋势 , 以期为进行这类结构的设计提供参考。研究结果表明 : 壁板铺层的非均衡程度对于所研究机翼的固有振动频率、 颤振速度影响较小 , 但对发散速度和机翼的静气动弹性性能影响较大。      

基于几何因子的复合材料层合板颤振特性

首先实现了基于几何因子的复合材料层合板建模方法,解决了几何因子与Natran的参数输入问题,并通过一个简单算例进行验证。其次,在基于几何因子的层合板建模方法的基础上,采用p-k法计算颤振速度和发散速度,进行基于几何因子的悬臂复合材料层合板颤振和发散特性分析研究,重点研究了主轴刚度和弯扭耦合效应对颤振速度的影响。分析结果表明:相对于弯曲刚度,扭转刚度的改变对颤振速度的影响更显著,且扭转刚度越小,颤振速度越低;颤振模式随着刚度特性的改变有可能发生转变,导致颤振速度的突然变化和几何因子空间内颤振速度等高线的不连续;在正则化刚度矩阵不变的情况下,层合板厚度增加会同时提高颤振速度和发散速度,且颤振速度与发散速度与厚度大致呈线性关系。     

基于遗传算法的复合材料层压板固有频率的铺层顺序优化

本文提出了一种用于组合优化的译码方式和遗传算子.对给定铺层的复合材料层压板在满足固有频率的要求下,采用遗传算法进行了铺层顺序的优化.算例的计算表明:采用本文所述方法,只要搜索解空间的一小部分就能收敛到组合优化问题的最优解.      

基于现代优化方法的气动弹性建模与设计技术

通过六种在工程设计上应用的实例,阐述国内飞机设计单位当前在飞机设计的各个阶段,利用现代优化技术所开展的气动弹性优化工作。内容涵盖机翼、尾翼、全机、常规金属结构、复合材料结构气动弹性优化建模和优化设计方面的问题;涉及飞机初步设计、详细设计和改型设计等多个阶段。应用结果表明:使用作者提出的基于遗传/敏度混合优化方法的现代优化技术,可以很好地解决现代飞机设计各个阶段的气动弹性建模和结构优化问题,达到提高设计效率、提升设计水平的效果。     

大展弦比复合材料机翼气动弹性优化

使用遗传/ 敏度混合优化算法对大展弦比复合材料机翼进行气动弹性优化设计研究。在满足强度、位移、发散速度和颤振速度等约束条件的前提下, 以机翼各部件复合材料铺层的厚度为设计变量, 对结构进行重量最小化设计。研究表明: 弯曲变形严重影响最终的优化重量, 是设计大展弦比复合材料机翼结构时应该重点考虑的问题; 按照应力设计准则对这类结构进行设计, 往往很难满足弯曲变形的要求; 使用遗传/ 敏度混合优化算法对大展弦比复合材料机翼进行气动弹性优化设计能够在可以接受的计算耗费下获得满意的结果。      

悬臂的复合材料层压板的振动与颤振

本文在一个复合材料层压板上,通过不同的铺设方式和不同的偏轴角,对其振动特性及颤振特性作了详细的计算,得出了一系列有益的、并能说明复合材料层压板可剪裁性的数据。为了进行上述振动特性的计算,在国内尚没有面外载荷弹性模量的情况下,通过振动试验实测结果,再由振动计算试凑出切实可用的面外载荷弹性模量。最后,在三种不同铺设的复合材料层压板上作了风洞颤振试验,并取得了与理论计算相一致的结果。      

考虑屈曲的复合材料加筋壁板铺层顺序优化

提出了一种考虑屈曲的复合材料加筋壁板铺层顺序优化方法。基于复合材料加筋壁板屈曲载荷求解的能量法,系统推导了轴压载荷作用下复合材料加筋壁板蒙皮、筋条局部屈曲载荷的显示表达式,考虑了加筋壁板各板元之间的弹性支持作用及筋条下缘条的影响,引入工程法求解了加筋壁板整体屈曲载荷。基于国产自主结构分析软件HAJIF中的复合材料铺层工程数据库,以铺层参数为中间变量,利用本文提出的复合材料加筋壁板屈曲载荷求解方法,构建了考虑屈曲的复合材料加筋壁板铺层顺序优化设计流程并完成程序实现,将最小二乘法用于最优铺层顺序与工程铺层数据库的匹配。相比于传统有限元计算方法,本文提出的复合材料加筋壁板屈曲载荷求解方法具备较好的求解精度及求解效率。复合材料加筋壁板优化算例表明,采用本文提出的加筋壁板屈曲载荷分析及其优化方法,在结构重量不变的前提下,屈曲载荷提高约17%,且铺层顺序优化结果可直接从铺层工程数据库中提取并用于工程实际。      

基于遗传算法的复合材料结构-声辐射优化研究

研究了外载荷作用下的复合材料结构振动响应和声辐射问题。在此基础上,分析了复合材料的结构一声辐射优化设计模型,基于遗传算法进行了对称型复合材料板结构的结构一声辐射铺层几何优化分析。数值算例表明,复合材料板结构的铺层数、铺层厚度和铺层角度等参数优化,可以有效降低结构的振动和声辐射。数值算例结果验证了优化方法的有效性。     

Optimization of aeroelastic composite structures using evolutionary algorithms

The flutter/divergence speed of a simple rectangular composite wing is maximized through the use of different ply orientations. Four different biologically inspired optimization algorithms (binary genetic algorithm, continuous genetic algorithm, particle swarm optimization, and ant colony optimization) and a simple meta-modeling approach are employed statistically on the same problem set. In terms of the best flutter speed, it was found that similar results were obtained using all of the methods, although the continuous methods gave better answers than the discrete methods. When the results were considered in terms of the statistical variation between different solutions, ant colony optimization gave estimates with much less scatter.     

Probabilistic optimal design of laminates using improved particle swarm optimization

A new approach to the particle swarm optimization (PSO) is proposed for the solution of non-linear optimization problems with constraints, and is applied to the reliability-based optimum design of laminated composites. Special mutation-interference operators are introduced to increase swarm variety and improve the convergence performance of the algorithm. The reliability-based optimum design of laminated composites is modelled and solved using the improved PSO. The maximization of structural reliability and the minimization of total weight of laminates are analysed. The stacking sequence optimization is implemented in the improved PSO by using a special coding technique. Examples show that the improved PSO has high convergence and good stability and is efficient in dealing with the probabilistic optimal design of composite structures.     

Optimum weight design of fiber composite plates in flexure based on a two level strategy

This paper offers a method for weight optimization of multilayer fiber composite plates under the action of lateral loadings. The objective is to design a fiber composite plate of minimum thickness which can sustain multiple static loadings applied normal to its surface without exhibiting failure based on Tsai-Hill criterion in any of its layers. In this investigation, fiber orientation angles are treated as discrete variables, which can vary only by pre-assigned increments, while thicknesses of layers are treated as continuous variables. The optimization procedure is based on a two stage strategy; in the first of which only the fiber orientation angles for the layers are treated as variables, and in the second, only the layer thicknesses. A powerful criterion based on a load factor has been defined to find the best angle for a new layer in the first stage, and the method of center points has been used for thickness optimization in the second stage. After any angle and thickness optimization has been done, a new layer is added to the thickness and the procedure is repeated for other new layers. The end of the two stage procedure is signaled whenever the thickness of the new layer in the optimization process approaches zero; meaning that no new layers would improve the set of layers already found. In this way at the end of the optimization procedure the plate thickness would be made of a minimum number of layers whose fibers are optimally oriented, and whose thicknesses are minimal. A poor choice of layers in the stack produce near zero thickness for the respective layer, and are thus deleted from the set. A repeat process is performed after each cycle, to modify layer angles in order to compensate for errors due to approximations involved. The priorities exercised in the choice of new layers for inclusion in the set and exclusion of all the un-necessary ones, allow an optimal state of stacking sequence to be achieved. Several examples are given to demonstrate the operation of the algorithm.     

Analysis of various thick-walled cross-ply composite cylindrical shells subjected to lateral pressures

A simple and accurate finite cylindrical element method was formulated by the authors to determine stresses and deformations in laminated thick-walled cylindrical composite shells. This method reduces the overall problem to a one-dimensional one. In the previous study it was found that significant tensile radial strains occur near the inner shell surface, when the shell is subjected to external pressures. These radial tensile strains are of the same magnitude as the failure strains for the composite shells for shell dimensions and pressures of practical use. In the present study various stacking sequences are investigated to determine the one resulting in the lowest radial tensile strains. Using this optimum stacking sequence, results are obtained for shells composed of E-glass/epoxy, T300/SP-286 graphite/epoxy, and Kevlar 49/epoxy. In addition, two hybrid composite systems consisting of graphite/epoxy and glass/epoxy are studied.     

Recent progress in dynamics and aeroelasticity

With the emphasis on higher performance, modern aircraft designs aim at lower structural weight, aerodynamically efficient thinner configurations, and reduced or even negative stability margins augmented by automatic flight control systems. These design considerations lead to highly flexible structural designs with associated problems of dynamic and aeroelastic interactions which need to be considered at the preliminary design stage itself. Advent of advanced composites and active control techniques have given the aircraft designer the freedom to use aeroelastic interactions in an advantageous way. This paper reviews the recent research and development efforts in the areas of aeroelastic tailoring, structural optimisation with aeroelastic constraints and aeroservoelasticity, and applications of the same in practical designs. The developments and applications in India in these areas are also highlighted.     

基于遗传算法的大型风机复合材料叶片根部强度优化设计

为了提高复合材料叶片承担载荷的能力, 尤其是承受最大弯矩的叶片根部的承载能力, 研究了遗传算法的优化原理并将遗传算法应用到复合材料叶片根部铺层的优化设计中。针对复合材料层压结构遗传算法优化设计中, 层压结构参数具有离散型的特点, 提出了适合复合材料层压结构遗传算法优化设计的整数编码策略, 以整数来表征层压结构参数。在分析层压结构强度的基础上, 针对结构强度优化的目标构造了可用于遗传算法的适应度函数。同时参考了一定的铺层规则, 在铺层角度限制为工程中常用的四种角度的前提下, 应用遗传算法对叶片根部进行了铺层优化设计。结果表明, 由于遗传算法特有的处理离散型问题的优势, 在叶片根部的铺层优化设计中应用遗传算法是可行和可信的。