机翼柱面梳状接头设计和参数优化

为解决工程实际中常规机翼梳状接头应力严重、结构偏重的问题,设计一种用于机翼结构对接的柱面梳状接头,并借助试验设计和Kriging代理模型技术提出其细节参数优化方法,应用试验设计法选取样本点,通过非线性有限元接触分析得到该样本点的响应,以此建立Kriging代理模型,并采用更新技术提高Kriging代理模型的精度;应用多岛遗传算法优化该代理模型并获得最优解.算例表明:采用该方法,机翼减重效果明显,优化效率提高.     

带控制截面机翼结构基于非线性能量阱的颤振抑制

二元刚性机翼结构简化为三自由度结构,在浮沉位移和俯仰位移方向的非线性刚度简化为立方非线性,对于控制截面存在间隙采用双线性刚度代替.基于靶能量转移的原理在机翼结构耦合非线性能量阱,实现对机翼颤振的抑制.考虑准定常气流,建立机翼减振前后的运动方程,通过数值模拟构造减振前后峰值-峰值图,初步反应其整体的减振效果.通过弧长数值连续法和结合Floquet算子构造减振前后的分岔图,并研究其稳定性.通过分岔图结合数值模拟的峰值图,讨论在不同风速下的减振效果,结果表明机翼结构颤振可以部分甚至全部抑制.     

基于Marc的空气弹簧横向特性分析

为实现空气弹簧的横向特性和强度分析,基于有限元非线性接触技术,用Marc对空气弹簧的非线性横向刚度特性进行数值模拟,分析最大横向力作用下空气弹簧各部分的应力分布,横向刚度计算结果与试验结果基本一致,表明空气弹簧的建模与仿真方法的合理性,为空气弹簧优化设计和特性分析提供参考.     

基于CFD-CSD耦合的机翼跨音速颤振计算

采用CFD-CSD耦合计算是预计机翼跨音速颤振特性的主流方法。以跨音速颤振国际标准模型AGARD 445.6机翼为研究对象,利用ANSYS.MFX多场耦合求解器对Euler方程进行求解来获得作用在机翼表面上的非定常气动力;对结构振动方程采用HHT方法直接数值积分以获得结构响应。通过CFD和CSD的耦合,计算了AGARD 445.6机翼的跨音速颤振特性。数值模拟结果与NASA风洞实验结果符合良好,表明利用ANSYS.MFX计算机翼跨音速颤振问题是可行的。     

T形异形柱的非线性有限元分析

分析了T形异形柱的受力问题,利用ABAQUS有限元软件对T形异形柱进行了弹塑性非线性有限元分析.着重从混凝土的非线性本构关系和破坏准则,受拉开裂后的行为,钢筋的本构关系几方面进行分析,通过计算绘制出了梁柱混凝土的应力云图、裂缝图及钢筋的应力云图.用ABAQUS计算所得的裂缝图与拟静力试验结果裂缝进行比较,两者结果吻合.结果表明:应用ABAQUS对异形柱进行非线性分析是可靠的,从而论证了软件的实际应用能力,也为进一步进行更复杂的非线性分析打下了基础.     

飞机平尾升降舵接头耳片承载能力分析与试验

为给飞机平尾升降舵接头耳片极限承载能力试验提供参考依据,指导试验方案设计,采用非线性有限元法,将运动约束和节点力作为边界条件直接施加在产生接触的节点上,将加载棒作为刚体,将耳片作为变形体,运用MSC Patran和MSC Marc分析某飞机平尾升降舵铰链接头耳片在轴向0°,斜向45°和横向90° 3个方向的承载能力,并给出对应的极限承载能力和应力分布情况,用于指导试验加载方案和应变片布置. 通过接头耳片有限元计算得到的载荷-位移曲线与试验曲线大致吻合,预测出的试件破坏最大应力值和最易破坏部位与试验结果也相符合.     

基于有限元分析的重型卡车车架铆钉应力精确计算法

针对某重型卡车在行驶过程中铆钉脱落的问题,提出基于有限元分析的车架及其连接铆钉应力计算方法．在对整体车架进行结构强度分析时,先用梁单元离散铆钉并进行线性分析,再对感兴趣的部分划分边界,建立详细的铆钉接触子模型,做非线性分析．通过施加边界条件和进行非线性求解,得到铆钉上详细的应力分布情况．由接触子模型计算得到的22颗铆钉应力值,符合重型卡车在行驶过程中铆钉脱落的实际情况,表明该方法切实可行．深入分析22颗铆钉的应力情况,给出重型卡车车架铆钉的非线性计算结果与线性计算结果的比例因数0．285（铆钉连接的板壳有应力集中处为0．35）,为解决同类问题提供简单易行的方法．     

混凝土楔入劈拉破坏的损伤塑性模拟

针对混凝土在微观上产生的损伤或者断裂,长期积累下来会导致在宏观上破坏的问题,基于试件表面的数字图像,建立反映真实骨料形状和分布的二维有限元模型,并通过混凝土损伤塑性模型进行楔入劈拉试验中混凝土非线性破坏的数值模拟.模拟结果与试验结果非常吻合,很好地反映混凝土试件的破坏区域和损伤发展的路径.     

立足技术稳发展着眼实际拓市场——ABAQUS 2007城市巡回研讨会有感

真实世界的实际问题不同程度都是非线性的,结构大变形、材料非线性以及接触非线性在实际动力分析问题中几乎无处不在,因而要准确地模拟分析复杂结构和装配系统以及过程的力学特性,非线性有限元技术是不可或缺的.     

高混凝土重力坝孔口应力非线性数值模拟

为准确描述重力坝孔口应力分布,提出高混凝土重力坝孔口应力的非线性数值计算分析整体方案．首先对坝体进行线性计算获得孔口应力分布规律及峰值以便于配筋,然后基于损伤塑性模型对孔口剖面作非线性应力应变分析,考察钢筋应力及其止裂效果．以某钢筋混凝土重力坝工程为背景,依据规范简化混凝土单轴应力一应变曲线,在Abaqus平台上对中孔的3个剖面进行非线性有限元分析,考察中孔在坝体自重和内水压力作用下的结构特性和损伤分布规律等,并重点探讨损伤区域的演化及钢筋应力等问题．结果表明数值模拟结果与模型试验有较好的一致性,可为同类型工程的数值计算和设计提供一定借鉴．     

Development of a variable stiffness joint drive module and experimental results of joint angle control

Two prototypes of variable stiffness joint drive modules imitating a human joint structure are presented. A human joint is driven by a pair of flexor and extensor muscles that work antagonistically. The stiffness of the joint is adjusted by their co-contraction. Such a structure was given to the joint drive module so that it could achieve a variable stiffness property. The joint is driven by two wires with nonlinear springs. Thanks to the nonlinearity of the springs, the stiffness of the joint can be adjusted by quasi-co-contraction of the wires. With the first prototype, the stiffness adjustability of the joint was empirically confirmed. Regarding joint angle control, a three-layered proportional integral derivative (PID) control algorithm was implemented in the second prototype, and it was verified that the control algorithm worked properly.     

Nonlinear behavior of R/C frames

The nonlinear behavior of reinforced concrete frames under gravity and/or lateral loads is investigated. The geometric and material nonlinearities together with the joint flexibility are considered in the present analysis. Material nonlinearity is found to be the most influential factor on the behavior of frames. The assumption of a rigid joint in the usual structural analysis appears to be reasonable compared with the flexible joint in a practical application. Geometric nonlinearity plays a more significant role in the case of the lateral loads.     

Position Control of Robots by Nonlinearity Estimation and Compensation: Theory and Experiments

To improve the performance of position controllers of robots, a designapproach using the method of nonlinearity estimation and compensation ispresented. The controller designed has a similar structure to that of thelinear independent joint control. Nonlinearities in the robot dynamics areestimated by a state observer based on approximate linear models of thesystem, and then compensated by an appropriate feedback. The paper presentsthe theory how to design such a controller as well as the experimentalresults verifying its performance.     

Nonlinear analysis and optimal design of structures via force method and genetic algorithm

In this paper analysis, design and optimization of structures are performed considering material and geometric nonlinearity. For this purpose, the force method, energy concepts and genetic algorithm are employed. The first part of this paper contains the formulation of the problem based on the force method and energy principles using linear analysis. In this method, the material nonlinearity is also included. The formulations are examined by simple illustrative examples. Reduction of the complementary energy is efficiently incorporated in this approach. The second part of the article combines the process of the analysis and design to achieve specified stress ratios for the members of the structure. This problem is especially important in the seismic deign of structures. Geometric nonlinearity is then formulated, in the third part by employing two approaches. Considering the energy term next to the weight of the structure, optimal dimensions of the structures are selected. In each part, the efficiency of the methods is illustrated by means simple examples.     

考虑迟滞非线性的高超声速飞行器颤振分析

为给飞行器颤振控制及结构设计等提供支持,利用适合复杂结构建模的动态子结构方法中的自由界面模态综合法,考虑飞行器在超声速飞行状态下高超声速流和飞行器自身结构的特点,将整个飞行器分成多个子结构;考虑飞行器机身与机翼之间相互连接构件的实际工作状况和制造工艺情况,带有间隙非线性与立方非线性相互作用所产生的迟滞非线性特性,以及阻尼因子对非线性的影响,用有限元计算软件计算各子结构的动力学特性参数和气动力分布情况,建立飞行器整机的振动微分方程以分析颤振特性．对得到的飞行器在所设工况下的振动和颤振特性及颤振临界状态进行分析,实现全机气动弹性问题的仿真计算．分析结果表明,该方法拓展高超声速飞行器颤振的计算,可为动态子结构方法应用于颤振研究提供参考．     

Finite element analysis of interlocking mortarless hollow block masonry prism

Interlocking mortarless masonry system has been developed as an alternative system for the conventional bonded masonry. This paper covers the analysis of interlocking mortarless hollow concrete block system subjected to axial compression loads using FEM. An incremental-iterative finite element code is written to analyze the masonry system till failure. The stress-strain relation obtained from test is employed and equivalent uniaxial strain concept is used to account for the material nonlinearity in the compression stress field. The developed program is also capable of simulating the nonlinear progressive contact behaviour (seating effect) of dry joint taking into account the block bed imperfection. The comparison shows a good agreement between the developed FE program and the experimental test results.     

方膜上横向压阻压力传感器的非线性研究

本文对方膜的硅压力传感器结构进行了应力非线性的计算分析,得出了应力-压力关系非线性与压力量程、膜的几何参数以及器件位置的关系,并给出了实现线性最佳化设计的结果.实验与理论结果的比较表明:(1)压阻效应非线性很小,压力传感器的非线性主要决定于应力非线性;(2)方膜边缘的四端力敏电阻设计不仅灵敏度高,而且有较好的线性;(3)进一步改进压力传感器精度的方法是选用应力线性优良的结构.     

格构柱非线性全过程分析与试验

针对细长臂架结构非线性效应突出、传统的线性分析已不能对其性能进行准确评估的问题,对5节空间格构柱进行有限元仿真和试验,检验仅考虑几何非线性、仅考虑材料非线性以及同时考虑几何与材料的双重非线性等3种全过程有限元分析所反映的实际意义。研究结果表明：双重非线性全过程有限元分析结果与试验得到的极限载荷相近,破坏过程一致,可为起重机设计优化和评估提供依据。     

Nonlinear joint state and parameter estimation: Application to a wastewater treatment plant

A systematic approach to joint state and time-varying parameter estimation for nonlinear systems is proposed in this paper. Applying the sector nonlinearity transformation to both the system nonlinearities and the time-varying parameters, the original system is equivalently rewritten as a Takagi–Sugeno system with unmeasurable premise variables. A joint state and parameter observer whose parameters are designed by solving an LMI optimization problem is then proposed. The target application is a realistic model of an activated sludge wastewater treatment plant, being an uncertain nonlinear system affected by a time-varying parameter.     

Detection of asymmetric control valve stiction from oscillatory data using an extended Hammerstein system identification method

The study in this paper is motivated by the detection of control valves with asymmetric stiction resulting in oscillations in feedback control loops. The joint characterization of the control valve and the controlled process is formulated as the identification of a class of extended Hammerstein systems. The input nonlinearity is described by a point-slope-based hysteretic model with two possibly asymmetric ascent and descent paths. An iterative identification method is proposed, based on the idea of separating the ascent and descent paths subject to the oscillatory input and output. The structure of the formulated extended Hammerstein system is shown to be identifiable, and the oscillatory signals in feedback control loops are proved to be informative by exploiting the cyclo-stationarity of these oscillatory signals. Numerical, experimental and industrial examples are provided to illustrate the effectiveness of the proposed identification method.