基于ANSYS的浮空器组阵结构屈曲分析及优化设计

针对空间太阳能电站地面演示系统,提出了一种空间大型浮空器组阵结构,利用ANSYS有限元软件建立其桁架结构的三维模型并进行结构屈曲分析,判断桁架结构的稳定性.以第1阶临界屈曲载荷为约束条件,对桁架梁截面的型材进行尺寸结构优化.通过响应曲面分析和多目标遗传优化算法找到设计优化点,使优化后的桁架结构在保证结构稳定的前提下实现...     

Optimum design of structures with stress and displacement constraints using the force method

A new structural analysis and optimization algorithm is developed to determine the minimum weight of structures with the truss and beam-type members under displacement and stress constraints. The algorithm combines the mathematical programming based on the sequential quadratic programming (SQP) technique and the finite element technique based on the integrated force method. The equilibrium matrix is generated automatically through the finite element analysis while the compatibility matrix is obtained directly using the displacement–deformation relations and the single value decomposition (SVD) technique. By combining the equilibrium and compatibility matrices with the force–displacement relations, the equations of equilibrium with the element forces as variables are obtained. The proposed method is extremely efficient to analyze and optimize the truss and beam structures under stress and displacement constraints. The computational effort required by the force method is found to be significantly lower than that of the displacement method. The effect of the geometric nonlinearity in the structural optimization problems under the stress and displacement constraints were also investigated and it is illustrated that the geometric nonlinearity is not an important issue in these types of problems and hence, it does not affect the final optimum solution significantly. Four examples illustrate the procedure and allow the results to be compared with those reported in the literatures.     

基于响应面法的桥梁主桁架结构优化设计

对复杂结构进行优化设计和可靠性设计时,利用传统的设计方法可能会遇到计算量太大的困难,应用响应面法是有效地解决该问题的途径之一.文中将响应面法和有限元技术相结合,建立了桥梁主桁架的挠度、弯曲应力与结构尺寸的函数表达式,继而对主桁架进行了结构优化设计,最后对优化结果进行了有限元分析和验证.设计计算结果表明,对于桁架结构设计这类问题,响应面优化设计具有很好的应用价值.     

Reliability-based design optimization via high order response surface method

To reduce the computational effort of reliability-based design optimization (RBDO), the response surface method (RSM) has been widely used to evaluate reliability constraints. We propose an efficient methodology for solving RBDO problems based on an improved high order response surface method (HORSM) that takes advantage of an efficient sampling method, Hermite polynomials and uncertainty contribution concept to construct a high order response surface function with cross terms for reliability analysis. The sampling method generates supporting points from Gauss-Hermite quadrature points, which can be used to approximate response surface function without cross terms, to identify the highest order of each random variable and to determine the significant variables connected with point estimate method. The cross terms between two significant random variables are added to the response surface function to improve the approximation accuracy. Integrating the nested strategy, the improved HORSM is explored in solving RBDO problems. Additionally, a sampling based reliability sensitivity analysis method is employed to reduce the computational effort further when design variables are distributional parameters of input random variables. The proposed methodology is applied on two test problems to validate its accuracy and efficiency. The proposed methodology is more efficient than first order reliability method based RBDO and Monte Carlo simulation based RBDO, and enables the use of RBDO as a practical design tool.     

Fast and accurate NURBS fitting for reverse engineering

Fast and accurate fitting of non-uniform rational B-spline (NURBS) curves and surfaces through large sets of measured data is an important problem in applications such as reverse engineering and geometric modelling. This paper presents a method for realising significant improvements in the computational efficiency of this task. The basic idea is that the sparsity structures of the relevant matrices that are specific to the problem of NURBS fitting can be precisely defined and that full exploitation of these structures leads to significant savings in both computational and storage requirements. These savings allow for a large number of control points to be used in order to define the surface and consequently to improve the accuracy of shape representation. The achieved computational complexity is linear in both the number of measured points and the number of control points while the storage requirements of the algorithm are linear with the number of control points only. The complexity analysis, as well as the analysis of actual running times is presented. The results demonstrate that, using this approach, highly complex shapes may be modelled accurately with a single NURBS surface.     

A contribution on the optimization strategies based on moving least squares approximation for sheet metal forming design

Computer-aided procedures to design and optimize forming processes are, nowadays, crucial research topics since industrial interest in costs and times reduction is always increasing. Many researchers have faced this research challenge with various approaches. Response surface methods (RSM) are probably the most known approaches since they proved their effectiveness in the recent years. With a peculiar attention to sheet metal forming process design, RSM should offer the possibility to reduce the number of numerical simulations which in many cases means to reduce design times and complexity. Actually, the number of direct problems (FEM simulations) to be solved in order to reach good function approximations by RSM is a key aspect of their application in sheet metal forming operations design. In this way, the possibility to build response surfaces basing on moving least squares approximations (MLS) by utilizing a moving and zooming region of interest can be considered a very attractive methodology. In this paper, MLS is utilized to solve two optimization problems for sheet metal forming processes. The influence on the optimization results was analyzed basing on MLS peculiarities. The idea is to utilize these peculiarities and make the MLS approximation as flexible as possible in order to reduce the computational effort of an optimization strategy. An innovative optimization method is proposed and the results show it is possible to strongly reduce the computational effort of sheet metal forming processes optimization. In particular, the advantages, in terms of computational effort reduction, with respect to classical RSM approaches have been demonstrated and quantified.     

Natural frequency and mode shape analysis of structures with uncertainty

Two methods called random factor method (RFM) and interval factor method (IFM) for the natural frequency and mode shape analysis of truss structures with uncertain parameters are presented in this paper. Using the RFM, the structural physical parameters and geometry can be considered as random variables. The structural stiffness and mass matrices can then, respectively, be described by the product of two parts corresponding to the random factors and the deterministic matrix. The structural natural frequencies, mode shapes and random response can be expressed as the function of the random factors. By means of the random variable's algebra synthesis method, the computational expressions for the mean value and standard deviation of natural frequencies and mode shapes are derived from the Rayleigh quotient. Using the IFM, the structural parameters can be considered as interval variables and the computational expressions for the lower and upper bounds of the natural frequency and mode shape are derived by means of the interval operations. The effect of uncertainty of individual structural parameters on structural dynamic characteristics, and the comparison of structural natural frequency and mode shape using the RFM and IFM are demonstrated by truss structures.     

Two-step Structural Design of Mesh Antennas for High Beam Pointing Accuracy

A well-designed reflector surface with high beam pointing accuracy in electromagnetic performance is of practical significance to the space application of cable mesh reflector antennas. As for space requirements, circular polarizations are widely used in spaceborne antennas, which usually lead to a beam shift for offset reflectors and influence the beam pointing accuracy. A two-step structural design procedure is proposed to overcome the beam squint phenomenon for high beam pointing accuracy design of circularly polarized offset cable mesh reflectors. A simple structural optimal design and an integrated structural electromagnetic optimization are combined to alleviate the beam squint effect of circular polarizations. It is implemented by cable pretension design and adjustment to shape the offset cable mesh surface. Besides, in order to increase the efficiency of integrated optimization, an update Broyden-Fletcher-Goldfarb-Shanno (BFGS) Hessian matrix is employed in the optimization iteration with sequential quadratic programming. A circularly polarized offset cable mesh reflector is utilized to show the feasibility and effectiveness of the proposed procedure. A high beam pointing accuracy in order of 0.0001º of electromagnetic performance is achieved.     

Damage detection of truss structures using two-stage optimization based on micro genetic algorithm

A simple and efficient two-stage optimization procedure is proposed to properly identify the sites and the extent of multiple damages in truss structures. In the first stage, the most potentially damaged elements are identified using an anti-optimization (AO) technique. In the second stage, a micro genetic algorithm (MGA) is performed to accurately determine the actual damage extents based on a priori knowledge from the first stage. The correctness and effectiveness of the proposed algorithm are proved by two illustrated test examples: the planar and space truss models with the numerically simulated data. The numerical results show the computational advantages of the proposed method to precisely determine the sites and the extent of multiple damages of truss structures.     

随机智能桁架结构闭环控制平稳随机响应分析

研究平稳随机激励下随机智能桁架结构的闭环动力响应问题。同时考虑智能桁架结构的物理参数、几何尺寸和阻尼的随机性，利用矩法和代数综合法，从结构平稳随机响应在频域上的表达式出发，分别导出随机智能桁架结构在平稳随机激励下闭环位移响应均方值和应力响应均方值的均值、方差的计算表达式。通过算例考察结构物理参数、几何尺寸和阻尼的随机性对结构位移响应均方值与应力响应均方值随机变量随机性的影响，并获得若干有意义的结论。     

空间太阳望远镜镜筒桁架的优化

空间望远镜的镜筒桁架结构优化以构件总质量等于常数为约束条件,以横向摆振频率最高为优化目标。优化分两步进行:首先以瑞雷方法和简化模型为基础,在较大范围内对可能的模型进行筛选,得出桁架分层数和每层斜杆数的最优解;然后用ANSYS软件对桁架杆、梁截面参数进行优化,得到比较满意的结果。此方法也适用对其他类似的筒状桁架的优化。     

运用波传播和子结构技术检测结构损伤

提出了一种基于波传播和子结构技术来检测大型周期结构损伤的方法,分析了存在单一扰乱单元的有限周期结构的自由波传播,讨论了单元柔度变化对结构自振频率变化的敏感性。通过求解敏感性方程,用测得的自振频率的变化检测了大型周期结构的损伤位置和程度,并通过与子结构方法的结合,进一步提高了大型周期结构损伤检测的准确性和计算效率。对周期弹簧－质量结构损伤识别的数值结果说明,该方法不仅对结构损伤的位置和大小能够作出良好地预测,而且不需要知识未损伤结构的原始信息,只需要测得结构损伤前后的少数几个自振频率的变化,这对于实际的工程运用具有一定的吸引力。     

基于深度学习的传感器优化布置方法

针对传感器优化布置(optimal sensor placement,简称OSP)问题,提出了一种新的使用深度神经网络的解决方案,并以简化的桥梁形状的桁架结构中的振动测试传感器优化为例进行了验证。首先,选择一种传统的传感器优化布置方法,对自动化生成的大量不同的桁架结构分别进行传感器优化布置计算,将所得优化布置结果在进行数据预处理后构建出深度学习方法所需要的训练集与验证集;其次,使用Python语言和深度学习框架TensorFlow设计实现与本研究问题适配的深度神经网络模型并训练;然后,随机生成了新的桁架结构参数;最后,将深度神经网络输出的传感器布置结果和传统方法的计算结果进行了比较,验证了本研究方法的有效性以及在速度上、可移植性与可扩展性方面的性能优势。     

Design optimization of truss bridge structures of composite materials

In this paper the problem of optimizing a distribution of carbon fiber content in hybrid glass/carbon fiber reinforced (GFRP/CFRP) structural elements of plane, statically determinate regular elastic truss structure is discussed. A modification of genetic algorithm combined with the method of mathematical induction is proposed. A criterion of structural materials cost minimization while satisfying elastic strength requirements is used as an optimality criterion.     

A general optimality criterion for strength and stiffness of dual-material-property structures

An optimality criterion is established for combined strength and stiffness requirements per unit weight of structures utilizing materials which may have different strength, stiffness or density for the tension and compression members. In the extreme case this covers the use of different materials for tension and compression members; referred to here as dual-material structures. It is shown that additional considerations are required for statically determinate structures and proof of optimality is given for statically indeterminate and statically determinate cases. In all cases, the optimal structures are based on Michell structural layouts, in which the cross-sectional areas of the structural members are determined to give constant strain energy per unit mass. Material density may be replaced by material cost per unit volume to optimize combined strength and stiffness requirements for minimum material cost.     

Technical note: Coherence analysis of the transfer function for dynamic force identification

Identifying dynamic forces with structural response signals is important when direct measurement is difficult or impossible. The minimized condition number method was introduced to reconstruct the forces with selected spatial distribution of response locations. This paper presents another way to optimize the selection of the response locations. The coherence of transfer function matrix is analyzed and the coherence factor of the transfer function matrix is introduced to optimize the response locations. Numerical simulations of the coherence analysis show that it is effective and requires less computational effort than the condition number method. The validity of the analysis is verified by applying it to the identification of the suspension forces on a vehicle cab.     

多指抓取的实时力优化算法

根据非线性摩擦约束与特定结构矩阵正定性之间的等价性,将多指抓取力规划问题描述为线性约束正定矩阵对应的平滑流形最优化问题,并且采用线性约束梯度流方法计算得到最优的抓取力。当手指数目较多时,高维描述矩阵限制了传统线性约束梯度流表达式的计算速度,为了解决该问题,基于力优化过程中描述矩阵的仿射约束特性,提出一种适合实时应用的基于抓取力矢量的线性约束梯度流算法。该算法取代描述矩阵,采用抓取力矢量表示线性约束梯度流,大大降低了线性约束梯度流表达式的维数和计算量。以摩擦点接触情况下的四指灵巧手为对象, 采用该算法进行抓取力计算,分析权重因子和步距因子对于计算结果和收敛速度的影响,证明该算法的正确性和实时性。     

基于轮廓约束点的B样条曲面拟合算法

提出了一种面向截面测量数据的B样条曲面拟合算法。首先对原始数据点列进行降噪处理,然后遴选出曲率优势点,并将其作为初始的轮廓约束点,得到插值于约束点的初始曲线。再在需改善拟合精度的区域增加约束点,直至获得满足精度要求的B样条曲线。最后以约束点数目最多的曲线为准,在其余的曲线上增加差额数目的约束点,并进行平均弦长参数化,构造出B样条曲线簇,最终获得B样条拟合曲面。仿真实验结果表明,该方法可显著压缩曲面模型的控制顶点数目,具有较高的曲面重构效率。     

大射电望远镜精调平台结构参数优化设计

精调平台的结构参数对其运动性能有极为重要的影响。本文首先推导了并联型平台的 Jacobian矩阵 ,然后论述了选择 Jacobian矩阵的条件数作为优化设计目标函数的合理性 ,并以 Jacobian矩阵的条件数为优化设计目标函数 ,优化了精调平台的结构参数 ,得到了较为合理的结果     

Development of high speed computation algorithm for transient analysis of rectangular plates

A new transient analysis method for a rectangular plate structure comprised of a large number of plate elements was developed in order to significantly reduce computational time and memory. This algorithm was derived from the combination of the transfer technique of the transfer mass coefficient method, the modeling technique of the finite element method, and the numerical integration technique of Newmark’s method. In this paper, the algorithm for the transient analysis of a rectangular plate structure is formulated by the proposed method. In order to verify the computational accuracy and efficiency of the proposed method, the results obtained by the proposed method were compared with those obtained by the finite element method and the finite element-transfer matrix method. The proposed method, the finite element-transfer mass coefficient method, could considerably reduce the computation time without the loss of accuracy, in spite of using small computation memory, by using the transfer rules successively.