双稳态复合材料层合结构的黏弹性模型

为探明双稳态复合材料层合结构在复杂环境条件下的应用,对双稳态复合材料层合结构的黏弹性行为进行了研究。首先,将纤维简化为弹性材料,考虑基底材料的黏弹性行为。然后,根据纤维和基底的材料属性,通过理论分析得到了双稳态复合材料层合结构的黏弹性材料属性;根据经典层合板理论、最小应变能原理和Maxwell黏弹性模型建立了双稳态复合材料层合结构的黏弹性模型,通过理论分析得到其第二稳态主曲率与扭曲率随加载时间和温度的变化关系。同时,利用有限元软件ABAQUS及其子程序UMAT建立了相应的有限元模型,研究了加载时间和温度对层合结构第二稳态性能的影响。理论与模拟结果均表明:层合结构第二稳态主曲率随加载时间的延长和温度的升高而增大;扭曲率随加载时间的延长而减小,一般情况下随温度的升高而增大,但在加载时间较长且温度较高时,可能会出现扭曲率随温度升高而减小的情况。理论计算结果与有限元模拟结果的比较显示两者吻合较好,可以通过有限元模拟对双稳态复合材料层合结构的黏弹性行为进行研究。      

Hierarchical optimization for topology design of multi-material compliant mechanisms

Multi-material topology optimization enables potential design possibilities in the multiphysics and structural designing fields. In this article, a bi-level hierarchical optimization method is introduced to address the multi-material design of compliant mechanisms. The hierarchical optimization develops decomposition approaches allowing the original complex multi-material optimization problem to be reduced to set of low-order single-material optimization sub-problems. The solution of the complex multi-material problem is found as a vector of the single-material sub-problems solutions. All the local sub-problems are solved with the solid isotropic material with penalization method independently, and a stiffness spreading technique is worked out to coordinate components of the global solution of the original problem. Several numerical examples are presented to demonstrate the validity of this method.     

变体机翼大变形梯形蒙皮结构研究

首先介绍了变体机翼及蒙皮结构的发展研究现状,提出了大变形梯形蒙皮结构的构想.随后,建立了梯形蒙皮结构的力学分析数学模型,与有限元仿真分析结果进行了比较和分析,验证了所建立数学分析模型的正确性,为进一步开展制备和实验研究奠定了理论基础.     

Topology optimization of compliant mechanisms using pairs of curves

The structural topology optimization approach can be used to generate compliant mechanisms for some desired input–output requirements. The success of the optimization depends on the structural geometry representation scheme used. In this paper, a novel representation scheme is proposed. The representation scheme is characterized by pairs of curves that are used to connect Input/Ouput (I/O) regions of the structure. Each pair of curves includes a normal curve and a fat curve. The areas bounded by the pair of curves define the material distribution between them. All I/O regions are connected to one another (either directly or indirectly) by pairs of curves in order to form one single connected load-bearing structure. A genetic algorithm for constrained and multiobjective optimization is then applied with the representation scheme of the structure in the form of a graph. Simulation results from a displacement inverter and a displacement redirector indicate that the presented representation scheme is appropriate.     

基于GA-NLP的剪刀式折叠桥梁展桥机构多目标优化设计

针对新型剪刀式折叠桥梁展桥机构的优化设计问题,首先建立了展桥机构的运动学和静力学模型,然后以展桥机构关键铰点位置和岸桥节与竖直方向所成夹角为优化设计变量,以展桥机构的空间位置为主要约束条件,以展桥油缸、连杆、关键铰点受力峰值最小为优化目标,通过正规化和加权处理构造了展桥机构多目标优化分析模型,并采用遗传算法（genetic algorithm, GA）和非线性规划(nonlinear programming, NLP)混合算法对该优化分析模型进行求解。最后,利用ADAMS（automatic dynamic analysis of mechanical systems,机械系统动力学自动分析）软件验证了展桥机构多目标优化分析模型的正确性。结果表明,优化后展桥油缸承载的拉力与推力峰值分别减小了57.9%和25.3%,连杆承载的拉力与压力峰值分别减小了26.1%和55.2%,展桥机构2个关键铰点受力峰值分别减小了23.5%和26.8%。研究结果可为展桥机构的改进设计提供理论依据。     

用于变形机翼夹心式柔性伸缩蒙皮的梯形蜂窝支撑结构

变形机翼技术的实现离不开柔性蒙皮技术的支持,提出了一种应用于变形机翼夹心式柔性伸缩蒙皮的面内褶皱型梯形蜂窝蒙皮支撑结构。通过理论分析研究了该支撑结构的面内伸缩特性,得到其面内横向无量纲化等效弹性模量大小与3个参数(形状系数k、宽度系数t和高度系数h)之间的关系:其等效弹性模量随k增大而减小,随t增大而增大,随h增大而减小。利用ANSYS软件对其进行了有限元分析并通过实验对其面内力学特性进行了验证。结果表明:理论分析、有限元结果与实验结果基本吻合。通过选择合适的结构参数,其面内横向等效弹性模量可达到原材料弹性模量的10-4,比同等参数下手风琴式支撑结构的面内横向等效弹性模量更小,变形能力更强。相比传统蒙皮支撑结构,该结构可以减小变形过程中的驱动力与能量消耗,提高柔性蒙皮的变形效率。     

Analysis,design, and optimization of structures with integral compliant mechanisms for mid‐frequency response

A multi‐scale paradigm is proposed that utilizes periodic, small‐scale, integral compliant mechanisms within larger‐scale structures for the attenuation of vibro‐acoustic response. Amplification principles serve as the basis for the design of these mechanisms in achieving reduced energy transmission. The spectral finite element method is exploited for a force–velocity and energy flow analysis of the resultant truss‐like structures. A genetic algorithm is employed to optimize structure size for greatest effectiveness in the frequency range of interest. This study demonstrates that a significant decrease in structural vibration is achievable and suggests promising applications including the design of acoustic isolation panels for broadband vehicle noise reduction. Copyright © 2007 John Wiley & Sons, Ltd.     

A Study of Bistable Laminates of Generic Lay‐Up for Adaptive Structures

Abstract: Asymmetric laminates are known to exhibit two stable cylindrical states and one unstable saddle state. Such bistability has attracted attention in aerospace applications because of the potential low energy requirement to achieve a large deflection or change in shape. This paper presents experimental observations of a generic asymmetric [?30/60] laminate with and without piezoelectric actuation and compares against both energy‐based analytical and finite element (FE) models. It is observed that the analytical model offers a qualitative understanding of bistable behaviour, degree of curvature and overall shape but is unable to model the distinctive curvature changes near the boundaries which can be captured by the FE model. The investigation also presents the use of piezoelectric actuation to achieve snap‐through in both analytical and FE models, which is compared and validated with experimental characterisation.     

Topology and sizing optimization of discrete structures using a cooperative coevolutionary genetic algorithm with independent ground structures

This article proposes a method called the cooperative coevolutionary genetic algorithm with independent ground structures (CCGA-IGS) for the simultaneous topology and sizing optimization of discrete structures. An IGS strategy is proposed to enhance the flexibility of the optimization by offering two separate design spaces and to improve the efficiency of the algorithm by reducing the search space. The CCGA is introduced to divide a complex problem into two smaller subspaces: the topological and sizing variables are assigned into two subpopulations which evolve in isolation but collaborate in fitness evaluations. Five different methods were implemented on 2D and 3D numeric examples to test the performance of the algorithms. The results demonstrate that the performance of the algorithms is improved in terms of accuracy and convergence speed with the IGS strategy, and the CCGA converges faster than the traditional GA without loss of accuracy.     

Shape morphing of laminated composite structures with photostrictive actuators via topology optimization

In this paper, a new design method is presented for achieving remote wireless shape morphing of laminated composite structures using topology optimization methods. A recently emerging family of smart materials, photostrictive materials, is introduced as the actuation discipline to implement the active control of optical structures by utilizing the photostriction mechanism, which arises from the superposition of photovoltaic effect and converse piezoelectric effect when exposed to the illumination of near ultraviolet light. In terms of the Mindlin plate theory of first-order shear deformation, a finite element formulation including multiphysics effects of photovoltaic, pyroelectric and thermal expansion is developed to model composite structures of ferroelectric materials polarized in 0–1 and 0–3 directions, respectively. The design is formulated as a multi-constrained optimization problem with a least square objective function to minimize structural shape errors. The topology optimization method is used as a systematic design approach to seek the optimal topologies of material layouts for both the photostrictive and host layers as well as the actuator light distribution. In terms of design sensitivity analysis, many gradient-based optimization algorithms can be applied to solve the problem effectively. Numerical examples are presented to demonstrate the effectiveness of this method in the field of active photonic control of laminated composite structures.     

Bidirectional evolutionary structural optimization for nonlinear structures under dynamic loads

This study aims to develop efficient numerical optimization methods for finding the optimal topology of nonlinear structures under dynamic loads. The numerical models are developed using the bidirectional evolutionary structural optimization method for stiffness maximization problems with mass constraints. The mathematical formulation of topology optimization approach is developed based on the element virtual strain energy as the design variable and minimization of compliance as the objective function. The suitability of the proposed method for topology optimization of nonlinear structures is demonstrated through a series of two- and three-dimensional benchmark designs. Several issues relating to the nonlinear structures subjected to dynamic loads such as material, geometric, and contact nonlinearities are addressed in the examples. It is shown that the proposed approach generates more reliable designs for nonlinear structures.     

The universal scissor component: Optimization of a reconfigurable component for deployable scissor structures

Deployable scissor structures are well equipped for temporary and mobile applications since they are able to change their form and functionality. They are structural mechanisms that transform from a compact state to an expanded, fully deployed configuration. A barrier to the current design and reuse of scissor structures, however, is that they are traditionally designed for a single purpose. Alternatively, a universal scissor component (USC)—a generalized element which can achieve all traditional scissor types—introduces an opportunity for reuse in which the same component can be utilized for different configurations and spans. In this article, the USC is optimized for structural performance. First, an optimized length for the USC is determined based on a trade-off between component weight and structural performance (measured by deflections). Then, topology optimization, using the simulated annealing algorithm, is implemented to determine a minimum weight layout of beams within a single USC component.     

索杆式伸展臂的结构设计与分析

 对国内外伸展臂的研究现状进行了总结，说明了索杆式伸展臂具有的高精度、高刚性、高收纳率的特点．结合一种索杆式伸展臂的模型制作，介绍了该类伸展臂的技术要求，其中包括：高收纳率、高刚性、展开的高可靠性、轻质量、高重复展开精度以及满足空间环境要求等．同时，总结了伸展臂展开与收纳机理和设计方法．最后，对伸展臂展开后的结构进行了动力分析，包括模态、频率响应和冲击响应分析．动力学分析的结果可以作为伸展臂实际应用时的参考．     

Application of manufacturing constraints to structural optimization of thin-walled structures

Topology optimization can be a very useful tool for creating conceptual designs for vehicles. Structures suggested by topology optimization often turn out to be difficult to implement in manufacturing processes. Presently, rail vehicle structures are made by welding sheet metal parts. This leads to many complications and increased weight of the vehicle. This article presents a new design concept for modern rail vehicle structures made of standardized, thin-walled, closed, steel profiles that fulfil the stress and manufacturing requirements. For this purpose, standard software for topology optimization was used with a new way of preprocessing the design space. The design methodology is illustrated by an example of the topology optimization of a freight railcar. It is shown that the methodology turns out to be a useful tool for obtaining optimal structure design that fulfils the assumed manufacturing constraints.     

Solving structural optimization problems with genetic algorithms and simulated annealing

In this paper we study the performance of two stochastic search methods: Genetic Algorithms and Simulated Annealing, applied to the optimization of pin‐jointed steel bar structures. We show that it is possible to embed these two schemes into a single parametric family of algorithms, and that optimal performance (in a parallel machine) is obtained by a hybrid scheme. Examples of applications to the optimization of several real steel bar structures are presented. Copyright © 1999 John Wiley & Sons, Ltd.     

Multiobjective design of actively controlled structures using a hybrid optimization method

A multiobjective approach to the combined structure and control optimization problem for flexible space structures is presented. The proposed formulation addresses robustness considerations for controller design, as well as a simultaneous determination of optimum actuator locations. The structural weight, controlled system energy, stability robustness index and damping augmentation provided by the active controller are considered as objective functions of the multiobjective problem which is solved using a cooperative game-theoretic approach. The actuator locations and the cross-sectional areas of structural members are treated as design variables. Since the actuator locations are spatially discrete, whereas the cross-sectional areas are continuous, the optimization problem has mixed discrete-continuous design variables. A solution approach to this problem based on a hybrid optimization scheme is presented. The hybrid optimizer is a synergetic blend of artificial genetic search and gradient-based search techniques. The computational procedure is demonstrated through the design of an ACOSS-FOUR space structure. The optimum solutions obtained using the hybrid optimizer are shown to outperform the optimum results obtained using gradient-based search techniques.     

Cyclical parthenogenesis algorithm for layout optimization of truss structures with frequency constraints

Structural optimization with frequency constraints is seen as a challenging problem because it is associated with highly nonlinear, discontinuous and non-convex search spaces consisting of several local optima. Therefore, competent optimization algorithms are essential for addressing these problems. In this article, a newly developed metaheuristic method called the cyclical parthenogenesis algorithm (CPA) is used for layout optimization of truss structures subjected to frequency constraints. CPA is a nature-inspired, population-based metaheuristic algorithm, which imitates the reproductive and social behaviour of some animal species such as aphids, which alternate between sexual and asexual reproduction. The efficiency of the CPA is validated using four numerical examples.     

The harmony search heuristic algorithm for discrete structural optimization

Many methods have been developed and are in use for structural size optimization problems, in which the cross-sectional areas or sizing variables are usually assumed to be continuous. In most practical structural engineering design problems, however, the design variables are discrete. This paper proposes an efficient optimization method for structures with discrete-sized variables based on the harmony search (HS) heuristic algorithm. The recently developed HS algorithm was conceptualized using the musical process of searching for a perfect state of harmony. It uses a stochastic random search instead of a gradient search so that derivative information is unnecessary. In this article, a discrete search strategy using the HS algorithm is presented in detail and its effectiveness and robustness, as compared to current discrete optimization methods, are demonstrated through several standard truss examples. The numerical results reveal that the proposed method is a powerful search and design optimization tool for structures with discrete-sized members, and may yield better solutions than those obtained using current methods.     

Design optimization of laminated composite structures using distributed grid resources

Parameter studies, genetic algorithms and Monte Carlo type calculations are examples of pleasantly parallel computational tasks. Pleasantly parallel computational tasks can be effectively calculated in computer clusters or grids. In this work, we consider a weight minimization problem of a laminated composite structure in the post-buckling region. The design variables are the number of layers and the layer orientations given in a discrete set of allowable angles for layer orientations. Optimization is carried out using a deterministic search process, where the lay-up configurations are generated iteratively in the design space from the selected design points of the population at the preceding cycle. Computation is performed using NorduGrid grid computing platform. In this work, we briefly go through some general grid concepts and the use of grid in optimization of laminated composite structures.     

聚脲柔性减阻材料的制备及性能

以喷涂聚脲弹性体技术为依托,合成NCO%在13~14的芳香族聚脲半预聚物(A组分),在B组分中引入适当比例的长链氨基聚醚和位阻型胺类扩链剂,设计合适的工艺参数制备出一种低模量、高伸长率的聚脲柔性减阻涂层。与传统的硅胶、PVC、聚氨酯、丙烯酸等减阻涂层相比,该涂层具:①耐冲击,附着力好;②密度与水基本相同;③模量低,阻尼小;④涂层致密,不透水等重要特点。经中国船舶科学研究中心测试,在3 m/s~10 m/s时平板上1 mm的柔性减阻涂层可降低阻力6%以上。