索网天线找形分析的参变量变分有限元法

针对柔性空间索网天线的非线性特点,建立了基于参变量变分描述索网拉压非线性和共旋列式描述几何非线性的有限元控制方程,应用Lernke与改进牛顿法进行求解.通过对索网预张力平衡计算,证明改进牛顿法比Newton-Raphson法具有更强的收敛能力.进一步将力密度法迭代原理与有限元法结合应用于索网天线的非线性找形分析中,获得了理想的索网构型.本文的索网找形方法可广泛应用于空间索网天线结构的设计.     

预应力索网天线结构优化设计

索网预拉力设计是索网天线结构设计的一个重要内容.针对三向网格旋转抛物面索网天线结构,首先在不计桁架结构受力变形的条件下,从索网节点的力平衡方程出发,以索网结构的结构特征为依据,以网面索段最大拉力比最小为设计目标,给出了索网结构预拉力优化设计的有效方法;其次,考虑到在索网结构的拉力作用下,桁架结构的微小变形将导致网面索段的拉力均匀性变差,通过调节索网挂接节点的位置,对桁架结构的受力变形进行了有效补偿,改进了预应力索网天线结构的整体设计方案.算例分析结果表明,天线结构网面索段的实际设计最大拉力比为1.30,验证了方法的正确性及有效性.     

矩形平面预应力索网大变形静力计算的级数迭代法

根据平衡荷载与索网变形及索拉力之间的关系给出了索网结构平衡的微分方程,得到了矩形平面预应力索网在均布荷载、均布拉力下不考虑几何非线性的变形曲面的一种级数解;通过对变形后索拉力的改变得到了近似考虑索网结构大变形几何非线性影响的级数迭代法,给出了修正的级数迭代法使计算收敛更加迅速;该方法应用在中关村文化商厦30m×70m平面索网的设计计算中,与非线性有限元计算结果比较验证了级数迭代法计算索网变形和索拉力大小的准确性,计算精度完全可以满足工程设计的需要.     

索网大变形广义余能原理及工程实践

杭州市的体育馆是一个80m×60m椭圆平面的马鞍形索网屋盖结构。其设计计算分两阶段。第一阶段,采用伽辽金变分法对索网单独进行计算,其边界假定为刚性。进一步的研究发现,边界的水平位移对索网计算影响颇大,特别是对索网的挠度影响很大,必须把索网与其边界合起来计算。这就使我们进入设计计算第二阶段,将索网、空间环梁、水平拉杆和外柱组合成一个整体力学问题。除了索网以外,水平拉杆也是大变形,     

“小震”作用下索网结构可靠指标β的计算方法

本文将Ｗｉｌｓｏｎ－θ法与Ｊ·Ｃ方法相结合，建立了“小震”作用下索网结构各单元承载能力可靠指标与索系正常使用可靠指标的计算方法。考虑了索网结构的几何非线性特性以及静载的影响。可求出索网结构在“小震”过程中任意时刻单元承载能力可靠指标与索系正常使用可靠指标。本文方法尚可推广用于分析“小震”作用下考虑索系材料非线性时索网结构的可靠度     

索网结构可靠指标β的计算方法

以索网结构内力分析的结点位移法和结构可靠度分析的验算点法为基础,给出了索网结构中索系可靠指标β的计算方法。     

大型索网天线机电耦合动力学建模与主动变形控制

索网天线因其折叠收纳比高、质量轻以及口径大等优点,成为众多空间任务的首选天线形式,但反射面精度较低限制了大型索网天线的在轨性能指标。在索网天线竖向张力索中加入压电陶瓷堆(PZT)作动器,通过主动控制提高反射面的形面精度。首先,将张紧的索网天线分为含有作动器的主动索单元和不含作动器的被动索单元,通过压电本构方程、几何方程和哈密顿原理推导出主动索单元的动力学模型,并与被动索单元一起组装得到索网天线的机电耦合动力学模型。然后,根据天线反射面的初始形面误差和所建立的天线机电耦合动力学模型,基于模型预测控制(MPC)方法计算出各作动器的控制输入电压曲线。最后,以一个10m口径的索网天线为算例,验证本文所建立的模型和控制方法的有效性。     

环形桁架展开天线索网的预拉力优化技术及工程应用

针对环形桁架展开天线抛物面索网预拉力配置问题,提出了一种寻找预拉力最优配置的方法,该方法基于抛物面索网结构的平衡矩阵奇异值分解,并采用含线性不等式约束及线性等式约束的线性规划方法,寻找抛物面索网最优预拉力配置,文中对抛物面索网结构平衡矩阵的形成、奇异值分解、线性约束优化方法的数学模型、约束矩阵的集成等关键技术进行了详细的推导说明,同时,根据理论推导编写了相应的分析程序,进行了算例分析,并采用非线性有限元法对分析结果进行了验证,证明该方法的正确性.最后,通过实际的天线结构工程的设计分析,对文中提出方法的工程应用可行性进行了论证.     

FREQUENCY DOMAIN CALCULATION METHOD FOR WIND-INDUCED RESPONSE OF MONOLAYER CABLE NET

以随机振动理论为基础,采用频域法对单层索网结构风振响应进行了研究,主要探讨不同计算方法和空间相干函数的选取等问题对索网结构风振响应的影响. 依据不同的计算方法和空间相干函数,建立了3 种分析模式进行了分析. 分析结果表明：对于频率密集的索网结构,需要考虑模态交叉项对计算结果的影响;空间相干函数的选取对计算结果影响较大,采用与风频率相干的空间相干函数更为合理.     

地面重力环境下可展开天线索网结构形态分析

为了模拟在地面环境测试时重力对可展开天线索网结构形面精度的影响和索网在天线展开过程中的内力变化情况,本文引入悬链线单元对天线索网结构进行了重力作用下的形态分析和计算。文中首先使用平衡矩阵线性分析方法计算出了天线索网结构各索段在无重力作用下的预张力值和索段原长;然后在不改变索段原长的条件下以悬链线单元模拟了可展开天线的上、下弦索网,以两节点直杆单元模拟天线的纵向索网,计算得到了索网结构在地面重力环境下的形状和内力分布,并仿真模拟了天线索网在展开过程中的形态和内力变化情况。基于文中的数值算例对可展开天线索网结构在重力作用下的形面精度以及在展开过程中的形态变化进行了仿真计算和分析。算例计算结果表明,自重作用下的天线索网形态与无重力作用下的索网形态差别很小,但天线索网结构在重力作用下的展开过程中,其内部各个索单元的张力表现出了强烈的非线性变化特征。     

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本文建立了二自由度1/4车体液压悬架的数学模型，介绍了利用模糊控制工具箱设计汽车液压半主动悬架模糊控制器的方法，通过应用MATLAB/Simulink对比仿真，得出了具有模糊控制器的液压半主动悬架的控制效果明显优于被动悬架，为半主动悬架在车辆上的应用提供了成功的范例。     

Sedimentation of bidisperse suspensions

The average settling velocity of a suspension of identical particles through otherwise quiescent fluid is smaller than the settling velocity of a single particle in an unbounded fluid. When a suspension settles out to form a deposit, this hindered settling effect may lead to complicated sedimentation behaviour, even if the initial suspension is uniformly distributed. This study analyses the bulk sedimentation of bidisperse suspensions and calculates the evolution of the volume fraction of each species from an initially vertically uniform state through to the final steady state where both species have fully settled out of suspension and have formed a deposit. These calculations are analytical and employ the method of characteristics to reveal how both particle species evolve. The profiles often include ‘shocks’, across which discontinuous changes in volume fraction occur. Rarefaction fans may also be found across which the gradients of volume fraction are discontinuous. These new analytical solutions reveal the evolving composition of the suspension and the deposit and may be compared to experimental observations. They also provide test cases that can be used to verify recent numerical techniques for computing the bulk sedimentation behaviour of polydisperse suspensions.     

On co-rotational and other rate type constitutive equations

We derive expressions for the dilatational properties of suspensions of gas bubbles in incompressible fluids, using a cell model for the suspension. A cell, consisting of a gas bubble centered in a spherical shell of incompressible fluid, is subjected to a purely dilatational boundary motion and the resulting stress at the cell boundary is obtained. The same dilatational boundary motion is prescribed at the boundary of an “equivalent” cell composed of a one-phase, uniformly compressible fluid with unknown dilatational properties. By specifying that the stress at the boundary of the one-phase cell is equal to the stress at the boundary of the two-phase suspension cell, we obtain expressions for the unknown dilatational properties as a function of observable properties of the suspension. The dilatational viscosity of a suspension with a Newtonian continuous phase and the analogous properties for suspensions with non-Newtonian continuous phases are obtained as functions of the boundary motion, volume fraction of gas, and properties of the incompressible continuous phase. Results are presented for continuous phases which are Newtonian fluids, second-order fluids, and Goddard—Miller model fluids.     

Effectiveness evaluation of hydro-pneumatic and semi-active cab suspension for the improvement of ride comfort of agricultural tractors

Advances have been made to agricultural tractors to improve their ride comfort. However, the ride comfort of tractors is relatively low compared to that of passenger vehicles. Many researchers have developed various types of suspension for tractors. While most studies have focused on the geometry of the suspension, few studies have been carried out on the development of a control algorithm for tractor suspension.In this paper, to improve the ride comfort of an agricultural tractor, a hydro-pneumatic suspension model with a semi-active suspension control is developed with computer simulation, and the effectiveness of the suspension is evaluated before the vehicle is equipped with the suspension and placed into production.An optimal control algorithm for the semi-active suspension of the tractor is developed using a linear quadratic Gaussian. In the simulation, a hydro-pneumatic suspension system model is developed using SimulationX and is applied to a full vehicle model using MATLAB/Simulink. The suspension is assessed by experiments and simulations. The ride comfort using the ride comfort index according to ISO 2631 is evaluated by comparing a vehicle with a passive cab suspension to that with a hydro-pneumatic suspension applied with the semi-active control.     

Asymptotic stability boundaries for the equilibrium positions of a double pendulum with vibrating point of suspension

The mechanisms whereby a double pendulum with vibrating point of suspension loses stability in equilibrium positions are studied. Stability conditions for the equilibrium positions in critical cases are established __________ Translated from Prikladnaya Mekhanika, Vol. 44, No. 7, pp. 120–133, July 2008.     

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在仿真研究1/4车体二自由度液压半主动悬架的基础上,设计了一种 用于1/2车体的液压半主动悬架的参数自整定模糊PID控制器,并利用模糊控制规则对 PID参数进行在线修改. 以正弦信号路面、脉冲信号路面和C级路面3种典型路面作为输入 信号,应用MATLAB/Simulink控制系统仿真软件对该半主动悬架模型进行的计算机仿真表明, 具有模糊PID控制器的半主动悬架在提高车辆乘坐的舒适性方面要明显优于一般的模糊控制 悬架,具有更好的自适应能力.     

Stochastic optimal active control of a half-car nonlinear suspension under random road excitation

The random response analysis and the stochastic optimal active control of a half-car model with nonlinear suspension stiffness and damping traversing a rough road are studied in this paper. The road roughness height is modeled as the output of a first-order linear filter to Gaussian white noise. Considering the hysteretic nonlinear stiffness and the square damping of the vehicle model, the response statistics of the nonlinear suspension with active control are obtained by using the equivalent linearization method. The performance indexes of the active suspension are evaluated and compared with those of the corresponding passive suspension. It is found that the nonlinear active suspension gives a better vehicle performances like ride comfort, suspension stroke and overall performance. Finally, the theoretical results are verified through Monte Carlo simulation.     

静电支承球形转子的恒速控制

本讨论静电支承球形转子的恒速控制问题。首先,介绍静电支承系统的基本工作原理,其次,建立静电支承系统的动力学模型。第三,分析采用PID控制器的支承刚度,第四,阐述形成静电旋转力矩的原理。最后,提出利用静电力恒速的方案与基本限制条件。     

A study of the hydraulically interconnected inerter-spring-damper suspension system

A new hydraulically interconnected inerter-spring-damper suspension (HIISDS) is developed to compensate for traditional passive suspension limitations, such as the imbalance of ride performance and handling stability. In this article, the structure and mechanism of the HIISDS system is briefly introduced at first, and compiled with hydraulically interconnected suspension (HIS) mode and hydraulic inerter-spring-damper (ISD) suspension mode. A vehicle dynamic model of HIISDS system is then derived through these two suspension modes by using Matlab/Simulink. Two different road excitations are used to validate the adaption of the two suspension modes. The effectiveness of HIISDS has been verified by simulation results, in which vehicle ride comfort and handling stability are effectively coordinated through the HIISDS model switch. Finally, an HIISDS suspension prototype is designed based on Simulink results, and test results reconfirm the partial performances of HIISDS modes effectively.     

吊篮悬挂机构的力学分析

高处作业吊篮是一种高层建筑外墙装修施工的设备,吊篮悬挂机构是架设在高层建筑顶面,通过钢丝绳承受悬吊平台、额定载荷的钢结构架.该文通过吊篮悬挂机构的力学分析,基于一个非常简单的组合杆件展示了杠杆平衡、杆件强度合理设计、安全性评估等多方面内容.这种在日常生活中随处可见的实例不仅可以作为基础力学教学的素材,更可成为学生课程设计极好的题目:培养学生认真观察、独立思考、综合运用相关知识分析与解决工程实际问题的能力.