Optimization of composite stiffened panels subject to compression and lateral pressure using a bi-level approach

Composite stiffened panel optimization is typically a mixed discrete-continuous design problem constrained by buckling and material strength. Previous work applied a bi-level optimization strategy to the problem by decomposing the mixed problem to continuous and discrete levels to reduce the optimization search space and satisfy manufacturing constraints. A fast-running optimization package, VICONOPT, was used at the continuous optimization level where the buckling analysis was accurately and effectively performed. However, the discrete level was manually adjusted to satisfy laminate design rules. This paper develops the strategy to application on continuously long aircraft wing panels subjected to compression and lateral pressure loading. The beam-column approach used to account for lateral loading for analysis during optimization is reported. A genetic algorithm is newly developed and applied to the discrete level for automated selection of laminated designs. The results that are presented show at least 13% weight saving compared with an existing datum design.     

Optimum cost design of welded box beams with longitudinal stiffeners using advanced backtrack method

The use of longitudinal stiffeners in box girders loaded in bending results in savings in weight and cost. To study these savings the optimized box beams without and with stiffeners are compared to each other. The minimum cross-sectional area design can be solved analytically. A cost function is defined containing material and fabrication (welding) costs. This function is nonlinear in the structural dimensions to be optimized, therefore an advanced backtrack method is worked out and applied. An illustrative numerical example shows the savings. Received June 30, 1999     

Optimization of anisotropic composite panels with T-shaped stiffeners including transverse shear effects and out-of-plane loading

A two-step method to optimize anisotropic composite panels with T-shaped stiffeners, including a new formulation of the transverse shear properties and an approximation of the ply contiguity (blocking) constraints as functions of the lamination parameters is provided. At the first step, a representative element of the stiffened panel (superstiffener) is optimized using mathematical programming and lamination parameters subjected to combined loading (in-plane and out-of-plane) under strength (laminate or ply failure), buckling and practical design constraints. Ply blocking constraints are imposed at this step to improve convergence towards practical laminates. At the second step, the actual superstiffener’s laminates are obtained by using a genetic algorithm. Results, for the case considered, show that the inclusion of transverse shear effects has an associated 2.5% mass penalty and that neglecting its effects might invoke earlier buckling failure. In addition, the influence of designing for failure strength at laminate or ply level is assessed.     

Maximization of buckling loads of composite panels using flexural lamination parameters

Unstiffened composite panels are optimized by using flexural lamination parameters as continuous design variables for the case in which the amounts of 0°, ±45°, and 90° plies are given. It is shown that for this case, the lamination parameters are located in a hexagonal domain. Continuous optimization is compared with genetic optimization for the stacking sequence that accounts for the discreteness of the design space and constraints on the number of contiguous plies of the same orientation. It is shown that only for very thin panels with low aspect ratios is there a significant difference between the continuous and discrete solutions.     

Discrete cost optimization of composite floor system using social harmony search model

This paper presents a social harmony search algorithm model for the cost optimization of composite floor system with discrete variables. The total cost function includes the costs of concrete, steel beam and shear studs. The design is based on AISC load and resistance factor design specifications and plastic design concepts. Here, six decision variables are considered for the objective function. In order to demonstrate the capabilities of the proposed model in optimizing composite floor system designs, two design examples taken from the literature are studied. It is shown that use of the presented model results in significant cost saving. Hence, it can be of practical value to structural designers. Also the proposed model is compared to the original harmony search, its recently developed variants, and other meta-heuristic algorithms to illustrate the superiority of the present method in convergence and leading to better solutions. In order to investigate the effects of beam spans and loadings on the cost optimization of composite floor system a parametric study is also conducted.     

Optimal plastic design of a bar under combined torsion, bending and shear

Optimal plastic design of a bar or beam under torsion with superposed bending and shear is obtained via the boundary perturbation method. Effects of bending and shear are expressed by a small parameter α. The results of optimization of solid bars and of hollow bars are shown. Received May 15, 2000     

Nonparametric cost and revenue functions under constant economies of scale: an enumeration approach for the single output or input case

This article shows how the linear programs needed to compute cost and revenue functions under constant returns to scale and a single output or input, respectively, can be replaced with a more efficient enumeration algorithm.     

子母式穿梭车仓储系统配置优化问题研究

针对仓库资源配置涉及因素众多难以优化问题,提出平均吞吐时间和成本集成的配置优化方法,从提升机和穿梭车两个维度分析,结合子母式穿梭车仓储系统运作特点,考虑穿梭车跨层作业,以平均吞吐时间和成本为目标函数,以货架数量、层数、列数、排数以及设备的数量及运行参数为决策变量,构建子母式穿梭车仓储系统配置多目标优化模型.采用非支配排...     

切换拟对称组合系统的降阶方法及稳定性分析

切换拟对称组合大系统其结构上的特殊性,为这种切换系统的简化降阶提供了有效方法.从简化后的切换系统入手,可方便地研究原系统的稳定性问题:a)在任意切换律下,切换拟对称组合系统二次稳定;b)构造切换律,使切换拟对称组合系统二次稳定.最后,通过仿真验证文中结论的正确性.这对于某些实际问题,如大型电力供应系统、军事系统中的舰队护航、多直升机吊物系统及大范围动物种群生态系统等有着重要的理论与应用价值.     

Simultaneous optimization of the material properties and the topology of functionally graded structures

A level set based method is proposed for the simultaneous optimization of the material properties and the topology of functionally graded structures. The objective of the present study is to determine the optimal material properties (via the material volume fractions) and the structural topology to maximize the performance of the structure in a given application. In the proposed method, the volume fraction and the structural boundary are considered as the design variables, with the former being discretized as a scalar field and the latter being implicitly represented by the level set method. To perform simultaneous optimization, the two design variables are integrated into a common objective functional. Sensitivity analysis is conducted to obtain the descent directions. The optimization process is then expressed as the solution to a coupled Hamilton-Jacobi equation and diffusion partial differential equation. Numerical results are provided for the problem of mean compliance optimization in two dimensions.     

热力载荷作用下复合材料板-铝合金板接头 钉载分配与钉孔周边应力分布

采用试验和有限元方法研究复合材料板 铝合金板单搭接接头在热和力载荷共同作用下的钉载分配和钉孔周边应力分布。将仿真模型得到的钉载分配结果与试验结果进行对比发现：温度升高后,靠近加载端承载最大的螺栓载荷分配比例增大,相应位置钉孔周边应力水平也有较大幅度的增加。对比未考虑热残余应力模型发现：考虑热残余应力模型与试验结果最相近;同样温度时热残余应力的存在使应力水平提高10%左右,说明在热载荷作用下考虑热残余应力的必要性。复合材料与金属接头钉孔周边应力分布呈“枫叶”状。     

On the cost of sequential and parallel algorithms for solving linear system of equations

In this paper two parallel algorithms for solving dense linear equations are discussed. The algorithms are based on LU-decomposition followed by forward and backward substitutions. The algorithms are numerically stable and have been tested on the Sequent Balance Machine with efficient utilization of all processors.     

多种结构框架在拉压试验机中的应用研究

现代工业的发展对拉压试验机的应用范围和实验性能提出了越来越高的要求。文中介绍了拉压试验机常见的立式和卧式框架结构,分析了其结构形式、应用场合及基本应用方法,并将拓扑优化设计方法引入到拉压试验机的设计中,最终减轻了结构重量,改进了结构的强度、刚度等特性。     

固化冷却过程中复合材料参数对其应变的影响

为有效降低某复合材料固化冷却过程中的应变水平,以某圆柱形复合材料为例,利用有限元分析软件MSC Nastran,研究固化冷却过程中复合材料参数对其应变的影响.计算得到复合材料最大von Mises应变值和分布位置,分析弹性模量、泊松比、线膨胀系数、密度等参数对其应变的影响.     

理想物系内部热耦合精馏塔操作费用的估计与优化

给出了理想物系内部热耦合精馏塔操作费用和费用节省的估计方法.首次建立了过程操作费用的优化数学模型,并以苯-甲苯物系作为实例进行了操作费用节省的优化研究.研究结果揭示出理想物系内部热耦合精馏塔巨大的操作费用节省潜力,同时得到了最大操作费用节省目标下的过程最优操作条件.     

船用复合材料螺旋桨性能数值预报工具开发和应用

为进行船用复合材料螺旋桨性能的数值预报,用Python和MATLAB程序编程,通过有限元法和涡格法(Vortex Lattice Method,VLM)相结合的方法,开发考虑螺旋桨桨叶变形与流体之间相互影响的复合材料螺旋桨水动力性能预报工具.用网格算法生成结构化网格,进行变形和压力插值交换和迭代计算,解决复杂几何螺旋桨的快速精确建模问题以及结构变形计算与水动力性能预报之间的数据交换问题,实现船用复合材料螺旋桨的性能预报.     

Simultaneous design of components layout and supporting structures using coupled shape and topology optimization technique

The purpose of this paper was to study the layout design of the components and their supporting structures in a finite packing space. A coupled shape and topology optimization (CSTO) technique is proposed. On one hand, by defining the location and orientation of each component as geometric design variables, shape optimization is carried out to find the optimal layout of these components and a finite-circle method (FCM) is used to avoid the overlap between the components. On the other hand, the material configuration of the supporting structures that interconnect components is optimized simultaneously based on topology optimization method. As the FE mesh discretizing the packing space, i.e., design domain, has to be updated itertively to accommodate the layout variation of involved components, topology design variables, i.e., density variables assigned to density points that are distributed regularly in the entire design domain will be introduced in this paper instead of using traditional pseudo-density variables associated with finite elements as in standard topology optimization procedures. These points will thus dominate the pseudo-densities of the surrounding elements. Besides, in the CSTO, the technique of embedded mesh is used to save the computing time of the remeshing procedure, and design sensitivities are calculated w.r.t both geometric variables and density variables. In this paper, several design problems maximizing structural stiffness are considered subject to the material volume constraint. Reasonable designs of components layout and supporting structures are obtained numerically.     

A novel combined forecasting system for air pollutants concentration based on fuzzy theory and optimization of aggregation weight

Effective forecasting of the air pollutant concentration is crucial for a robust air quality early-warning system and has both theoretical and practical significance. However, the accidental and cognitive uncertainty in the model selection or parameter setting of a single system will result in inaccurate and unstable forecasting results. Thus, in this paper, a novel fuzzy combination forecasting system based on the data preprocessing, fuzzy theory, and advanced optimization algorithm is proposed to improve the accuracy and stability of forecasting results. Based on the fuzzy theory and decorrelation maximization method, our proposed forecasting system can considering more information and maintaining the diversity of models. Moreover, Cuckoo Search algorithm applied in the system can determine the optimal weights for models aggregation. Several experiments based on PM${}_{\mathrm{2.5}}$ and PM₁₀ datasets in three cities are analyzed and discussed to verify the excellent performance of our proposed forecasting system, and the results indicate that the forecasting system outperforms others with respect to the accuracy, stability and generalization capabilities which are the basis of a robust air quality early-warning system in practice.