应力和位移约束下桁架拓扑优化的有无复合体方法

按照独立连续拓扑变量的思想,将有无复合体模型由构造应力约束问题发展为应力与位移约束问题,用于桁架结构拓扑优化.基于该文提出的位移约束与拓扑变量关系的近似显式,建立了具有应力、位移约束下桁架结构拓扑优化的有无复合体模型,用序列二次规划算法求解.数值结果令人满意.这一工作表明独立连续拓扑变量的提出对于结构拓扑优化的研究是有价值的.     

空间桁架结构大位移问题的有限元分析方法

本文基于总体拉格朗日坐标描述法,采用Ｋｉｒｃｈｏｆｆ应力张量和Ｇｒｅｅｎ应变张量定义,导出了严格意义下的杆单元增量列式,计算表明本文方法可以有效用于空间桁架结构大位移问题分析。     

自适应超静定桁架强度控制能力的提高

利用作动器的调节功能和超静定桁架的内力耦合特性,提高了自适应超静定桁架结构的承载能力,获得了更加合理的结构工作状态,有效地解决了文[8]中当作动器刚度较小时调控能力受限的问题。计算结果比文[8]模型的结果更令人满意。     

具有坐标变量和稳定性约束的桁架结构优化

本文讨论以结构重量为目标函数,以杆件截面积和节点坐标为设计变量,以杆件应力和稳定性为约束条件的桁架优化设计,利用乘子法修改杆件截面积和拉格朗日乘子,以梯度法修改节点坐标。梯度法的步长则以满应力法确定。算例表明,本文方法是比较有效的。     

采用自动分组遗传算法的频率约束下桁架拓扑优化

研究了带有频率约束的桁架结构拓扑优化问题.首先比较了同为铰结情况下采用两种不同单元-杆单元和梁单元模拟对频率计算结果的影响,发现杆模型会丢失杆件弯曲振动模态,得到的最大自振频率设计往往含有很细截面的杆件,而实际上具有很低的频率.为克服这一困难,并考虑到实际工程结构的结点具有一定的刚性,建议此类优化问题可以采用刚架模型进...     

自适应桁架结构天线形状最优控制

给出了两种含压电作动杆的自适应桁架抛物面天线的形状最优控制方法,分别以天线表面点相对原设计抛物面和最佳吻合抛物面(BFP)的光程差为精度指标,建立了同时考虑精度和能耗的综合控制目标。控制考虑杆件轴力与作动电压限制,以作动电压为被控量。利用桁架力学量及天线精度与作动电压的关系,将控制问题精确表达为显式数学规划问题。理论分析和仿真结果均说明基于BFP的控制方法在天线精度和能量消耗方面的优越性,最后通过仿真算例讨论了结构受载形式和电压限设定对天线形状控制能力的影响。     

应力和位移约束下连续结构的有效拓扑优化方法

为了解决在拥有位移与应力多个约束条件下,以减少结构重量为目标函数的拓扑优化中多约束难处理的问题,本文研究了以位移约束、应力约束、应变能约束重量最小化为目标的拓扑优化关系.通过对目标函数与约束函数的解析敏度推导,证明了它们之间的等价性.得到的准则方程表明:在最优结构中,单元质量与该单元应变能之比等于结构总质量与结构总应变能之比.由于迭代准则方程中的各项都可以在 ANSYS 有限元分析中直接提取,也不必计算乘子,从而减少了优化过程中的函数调用次数,加快了优化速度.两个算例说明了该方法的简单、高效与适用性.     

平稳随机激励下随机智能桁架结构振动主动控制中的优化

研究了平稳随机激励下随机智能桁架结构振动主动控制中主动杆的配置位置和闭环控制系统增益的优化问题。考虑结构物理参数、几何尺寸、阻尼同时具有随机性以及作用荷载为平稳随机激励,基于系统最小储存能,构建了具有位移响应均方值、应力响应均方值可靠性约束的主动杆配置和控制增益的优化模型;并对结构平稳随机动力响应的数字特征进行了推导。通过算例,验证了该优化配置模型的合理性和有效性,获得了若干有意义的结论。     

自适应超静定桁架结构强度控制的研究

以超静定桁架结构为背景研究了自适应结构的承载能力.探讨作动器和杆单元的共同工作,用以进行结构分析和控制结构承载能力.后者意指通过作动器的主动变形调控结构的内力分布以获得更加合理的工作状态.     

解决约束违背问题的一种自适应调整方法

带约束的优化问题的目的是要找到满足等式或者不等式约束的最优点。在某些情况下,优化求解得到的"最优点"可能会使得某个或某几个约束条件超出目标约束限,或者在所有约束条件中的最大值远远小于目标约束限。针对这一类问题,本文提出一种在寻优过程的每一次迭代中自适应调整约束限的方法,通过动态调整迭代过程中迭代模型约束限的值,将约束条件中最大值的约束条件变为等式约束,使得迭代解始终在可行域范围内,且收敛后的最优解不违背任何约束条件。本文将该方法成功应用于位移约束下结构重量最小化拓扑优化模型,原来不满足约束条件的情况在使用该方法后都能使约束得到满足,解决了约束条件被违背的问题。     

Characteristics of strength control of adaptive structure with electromechanical coupling

Based on the programming method, an electromechanical coupling adaptive statically indeterminate truss structure is controlled for increasing its load capacity. Several main parameters during the process of design of the adaptive structure are selected for a study of its characteristic during the control stage. The curves of each parameter for the effect of control results are plotted and corresponding conclusions are drawn. Thus, the theoretical basis is presented for optimal design, manufacture and control of the adaptive structure. Project supported by the National Natural Science Foundation of China (10072005), Beijing Educational Committee (99LG-11) and Beijing Natural Science (3002002) Foundation.     

On the effect of constraint parameters on the generalized displacement control method

In this work, we investigate the generalized displacement control method (GDCM) and provide a modification (MGDCM) that results in an equivalent constraint equation as that of the linearized cylindrical arc-length control method (LCALCM). Through numerical examples, we illustrate that the MGDCM is more robust than the standard GDCM in capturing equilibrium paths in regions of high curvature. Moreover, we also provide a geometric and physical interpretation of the method, which sheds light on the general class of path following methods in structural mechanics.     

APPROACH FOR LAYOUT OPTIMIZATION OF TRUSS STRUCTURES WITH DISCRETE VARIABLES UNDER DYNAMIC STRESS, DISPLACEMENT AND STABILITY CONSTRAINTS

A mathematical model was developed for layout optimization of truss structures with discrete variables subjected to dynamic stress, dynamic displacement and dynamic stability constraints. By using the quasi-static method, the mathematical model of structure optimization under dynamic stress, dynamic displacement and dynamic stability constraints were transformed into one subjected to static stress, displacement and stability constraints. The optimization procedures include two levels, i.e., the topology optimization and the shape optimization. In each level, the comprehensive algorithm was used and the relative difference quotients of two kinds of variables were used to search the optimum solution. A comparison between the optimum results of model with stability constraints and the optimum results of model without stability constraint was given. And that shows the stability constraints have a great effect on the optimum solutions.     

具有动应力和动位移约束的离散变量结构形状优化设计方法

讨论了动应力、动位移约束下离散变量状优化设计问题。首先用拟静力算法,将结构惯性力极值作为静载荷施加到结构上,求得结构的动位移和动内力,然后将考虑动应力约束和动作移约束的离散变量结构优化设计问题化为静应力和静位移约束的优化问题。在求解过程中,将单元内力作了一阶近似,并将多约束问题转化为单约束问题,然后利用两类变量统一考虑的离散变量结构形状优化设计的综合算法进行求解。     

Dynamics and adaptive control of a dual-arm space robot with closed-loop constraints and uncertain inertial parameters简

A dynamics-based adaptive control approach is proposed for a planar dual-arm space robot in the presence of closed-loop constraints and uncertain inertial parameters of the payload. The controller is capable of controlling the po- sition and attitude of both the satellite base and the payload grasped by the manipulator end effectors. The equations of motion in reduced-order form for the constrained system are derived by incorporating the constraint equations in terms of accelerations into Kane＇s equations of the unconstrained system. Model analysis shows that the resulting equations perfectly meet the requirement of adaptive controller design. Consequently, by using an indirect approach, an adaptive control scheme is proposed to accomplish position/attitude trajectory tracking control with the uncertain parameters be- ing estimated on-line. The actuator redundancy due to the closed-loop constraints is utilized to minimize a weighted norm of the joint torques. Global asymptotic stability is proven by using Lyapunov＇s method, and simulation results are also presented to demonstrate the effectiveness of the proposed approach.     

用ICM法拓扑优化静位移及频率约束下连续体结构

用ICM方法建立了静位移及频率约束下、重量最小为目标的连续体结构拓扑优化模型。采用独立于截面及形状参数的连续拓扑变量,借助于过滤函数,位移约束用莫尔定理显式化,频率约束用瑞利商求导数借助模态动能及模态应变能近似显式化。用图形过滤处理的方法解决了棋盘格及网格依赖问题。通过构造适当的过滤函数有效地防止了局部模态问题。动态引入防止模态交换的频率约束条件,使迭代过程不发生振荡。算例表明:用ICM方法建立的模型在处理多工况静位移约束、多频率约束及解决局部模态及模态交换等问题上有优势。     

Robust adaptive control of nonholonomic systems with uncertainties

Robust adaptive control of nonholonomic systems in chained form with linearly parameterized and strongly nonlinear disturbance and drift terms is dicussed. The novelty of the proposed method is a combined use of the state-scaling and the back-stepping procedure.     

Neural network-based adaptive control of a class of uncertain nonlinear systems

I.ProblemF0muIationandAssumptionsConsiderthenonlinearsystemfwhereeeR-isthestate,andavailableformeasurement,'.ERistheinput,geRistheoutput.hisasmoothfunctiononR-withh(0)=O,andthevectorfieldsI',g"aresmo0thonR-withg'(x)*O,VxeR--andI'(O)-O.ForcIarity0fexpositi…