折叠结构几何非线性分析

本文提出了一种推导折叠结构宏单元刚度矩阵的新方法,即在所假设普通单元位移模式的基础上直接引入位移约束条件,得到宏单元的形函数矩阵,进而给出宏单元的力与位移间关系。利用该思路,文中简捷地推导出剪式单元三节点梁大位移小变形的几何非线性切线刚度矩阵,并给出了线性刚度矩阵的显式。算例表明,分析折叠结构承载能力和自稳定结构的展开或收纳过程,考虑几何非线性的影响是必要的。     

Numerical approach for detecting bifurcation points of the compatibility paths of symmetric deployable structures

New internal mechanisms of a deployable structure could be generated, when the structure undergoes significant transformations along its compatibility path. Because of such kind of kinematic bifurcation, the structure might not transform into the desired configuration. To design novel deployable structures, it is necessary to detect all possible bifurcation points of the compatibility paths and study the bifurcation behavior. Here, on the basis of the nonlinear prediction–correction algorithm with variable increment size, we will propose an efficient approach to detect all the possible bifurcation points of the compatibility path for a symmetric deployable structure. Null space of the Jacobian matrix is studied iteratively, to follow the complete compatibility path. The variable increment size at each step is determined by evaluating whether the configuration is close to the singular configuration. Numerical examples of several 2D and 3D symmetric deployable structures are presented, to verify the feasibility and computational complexity of the proposed approach. The results show that the proposed method is computationally efficient, and could detect different bifurcation points of the compatibility path. Further, it turns out that all the analyzed symmetric structures experience kinematic bifurcation on certain conditions.     

Optimization of high-speed railway pantographs for improving pantograph-catenary contact

A crucial system for the operation of high-speed trains is the pantograph catenary interface as it is the sole responsible to deliver electrical power to the train. Being the catenary a stationary system with a long lifespan it is also less likely to be redesigned and upgraded than the pantographs that fit the train vehicles. This letter proposes an optimization procedure for the improvement of the contact quality between the pantograph and the catenary solely based on the redesign of the pantograph head suspension characteristics. A pantograph model is defined and validated against experimental dynamic characteristics of existing pantographs. An optimization strategy based on the use of a global optimization method, to find the vicinity of the optimal solution, followed by the use of a deterministic optimization algorithm, to fine tune the optimal solution, is applied here. The spring stiffness, damping characteristics and bow mass are the design variables used for the pantograph optimization. The objective of the optimal problem is the minimization of the standard deviation of the contact force history, which is the most important quantity to define the contact quality. The pantograph head suspension characteristics are allowed to vary within technological realistic limits. It is found that current high-speed railway pantographs have a limited potential for mechanical improvements, not exceeding 10%–15% on the decrease of the standard deviation of the contact force.     

高速列车受电弓风洞试验研究

为了研究高速列车受电弓在较高速度下的整体气动特性、弓网接触压力以及受电弓对支持绝缘子的作用力等综合性能,在FD-09低速风洞中进行了测力试验。试验采用测力天平和力传感器进行测量。通过在FD-09风洞试验段内安装收缩地板的方式首次将受电弓试验风速提高到了380km/h,可以满足高速列车受电弓高速性能研究的需求。研究结果表明：受电弓相对列车运行方向对受电弓升力特性有显著的影响,对弓网接触压力也有较大的影响;通过调节导风板的角度可以有效控制弓网接触压力;受电弓对支持绝缘子的作用力表现为前面拉力后面压力。     

基于能量原理的双稳态各向同性柱壳力学特性研究

双稳态结构可以在伸展和卷拢两种状态下均保持稳定,作为一种新型可展开空间结构,其在航空航天等领域具有广阔的应用前景。选取各向同性材料作为研究对象,并假定该材料为理想弹塑性材料。建立柱壳的力学计算模型,推导结构变形时应变能的解析表达式,基于能量原理导出柱壳在两个稳定状态下的卷曲半径。结果表明,基于全量理论和增量理论的模型均能反映结构的双稳态特性,但后者能更准确地预测两个稳态对应的卷曲半径的大小。对于文中给定的柱壳,全量理论导出的卷曲半径R3x相对于增量理论结果误差为5.2%~11.6%,R5y相对误差为29.8%~41.3%。另外,应用有限元软件ABAQUS对各向同性柱壳结构的双稳态过程进行数值模拟,数值结果与增量理论结果的相对误差为0.9%~13.2%,二者吻合较好。     

绳驱桁架结构伸展臂的主动振动控制

伸展臂由于受到空间温度变化和卫星机动动作的影响,不可避免地会产生振动。在阻尼较低的空间环境中,这种振动衰减较慢,影响伸展臂的正常工作。因此,合适的振动控制方法对于伸展臂的正常工作至关重要。本文采用拉绳作为作动器的空间桁架结构伸展臂,研究其作动绳上铰链串联顺序的优化和模型预测控制律的设计,这两部分内容均考虑了作动绳的单边约束和饱和约束。首先,通过ANSYS软件获取结构的模态信息;然后结合系统可控性原理和遗传算法计算出作动绳上铰链串联最优顺序;最后,在数值仿真中,通过设计的控制率对一个由四个单元组成的桁架结构伸展臂的振动控制过程进行仿真分析。结果表明,提出的作动绳串联铰链的方式能够有效抑制伸展臂的振动。     

CED400型高速受电弓精细动力学 模型影响因素研究 1)

受电弓精细动力学建模及固有振动特性分析对于进行结构优化设计,提高装备性能具有重要意义。对于结构可靠和性能优良的高速受电弓,不仅取决于整体动力学特性,局部振动特性也成为其中的关键环节。本文对受电弓精细动力学建模方法进行了研究,讨论了不同影响因素对受电弓固有振动特性的影响。研究表明,受电弓主要部件适当的质量分布和连接设置特性是获得符合实际结构固有振动特性的重要保证。     

含刚性体可展开结构的展开过程动力学分析方法

在可展结构中设置刚性体可以有效提高展开效率,保证形状精度,因此含刚性体可展结构具有较高的实用价值。刚性体按需要可为刚性曲板等,一般形状复杂且形式多样,含任意形状刚性体可展结构的展开过程动力学分析比较困难。本文以笛卡尔坐标系下节点坐标及位移为变量,利用广义逆矩阵建立了一种通用的刚性体动力学方程,给出了利用Newmark—...     

Three-Dimensional Large Deformation Analysis of the Multibody Pantograph/Catenary Systems

To accurately model the nonlinear behavior of the pantograph/catenary systems, it is necessary to take into consideration the effect of the large deformation of the catenary and its interaction with the nonlinear pantograph system dynamics. The large deformation of the catenary is modeled in this investigation using the three-dimensional finite element absolute nodal coordinate formulation. To model the interaction between the pantograph and the catenary, a sliding joint that allows for the motion of the pan-head on the catenary cable is formulated. To this end, a non-generalized arc-length parameter is introduced in order to be able to accurately predict the location of the point of contact between the pan-head and the catenary. The resulting system of differential and algebraic equations formulated in terms of reference coordinates, finite element absolute nodal coordinates, and non-generalized arc-length and contact surface parameters are solved using computational multibody system algorithms. A detailed three-dimensional multibody railroad vehicle model is developed to demonstrate the use of the formulation presented in this paper. In this model, the interaction between the wheel and the rail is considered. For future research, a method is proposed to deal with the problem of the loss of contact between the pan-head and the catenary cable.     

高速电动列车悬链线——导电架的动力分析

在过去几年中，电动列车的速度已高达３５０ｋｍ／ｈ以上。为能成功地设计高速列车的导电架，需要对悬链线－导电架耦合系统进行计算机模拟。兹采用模态分析技术描述悬链线的分布参数系统。而导电架则在大多数应用中表示为两质量的集总参数系统。由于移动的导电架与悬链线间的耦合作用，系统用具有时变系数的向量常微分方程表示。导电架触端高度与接触力的模拟结果用计算机程序ＦＡＳＴ在时速直至３６０ｋｍ／ｈ的情况下得到。该模拟     

Vertical dynamics of a pantograph carbon-strip suspension under stochastic contact-force excitation

In electric trains, a pantograph is mounted on the roof of the train to collect power through contact with an overhead catenary wire. The carbon-strip suspension of a pantograph, along which contact with the catenary occurs, is subjected to harmonic and stochastic contact-force excitations. In this paper, vertical dynamics of the carbon-strip suspension is studied with an aim of improving the reliability and safety of running trains. A single-degree-of-freedom model of the carbon-strip suspension with nonlinear stiffness is developed using parameter values of the DSA X pantograph. Through stochastic averaging, a Fokker–Planck–Kolmogorov equation governing the stationary response of the carbon-strip suspension is set up. Based on the transition probability density of the stationary response, it is found that random jumps and bifurcations in the carbon-strip motion can occur. The possibility of motion bifurcations and the frequency of random jumps warrant consideration in advanced design of carbon-strip suspensions.     

高速弓网系统动力学参数敏度分析及优化

随着高速列车运行速度的提升, 弓网关系这一基础力学问题备受关注. 良好的弓网关系是确保列车安全高效运行、稳定可靠受流、降低接触线与受电弓滑板磨耗等的基本前提. 其中, 受电弓和接触网的动力学参数对弓网耦合作用起至关重要的作用. 本文采用弓网接触力随机统计特征作为优化目标函数,进行受电弓动力学参数的敏度分析和优化设计. 首先, 建立了二维弹性链悬挂接触网-三质量块受电弓动力学模型,根据EN50318: 2018标准验证了动力学建模和分析结果的正确性. 然后, 基于高速弓网系统的动力学仿真, 进行了DSA380型高速受电弓三质量块参数的动力学敏度分析, 确定了9个动力学参数的敏感度级别, 弓头等效质量敏度评级最高,下框架等效阻尼次之, 下框架等效质量和上框架等效阻尼第三. 最后, 研究了弓头等效刚度和等效阻尼联合变化对弓网耦合动力学性能的影响,给出了提升弓网耦合性能的弓头双参数优化方案, 建议同时减小弓头等效阻尼和增大弓头等效刚度, 能够实现比单参数优化更好的弓网耦合性能.      

Two-fold symmetrical 6R foldable frame and its bifurcations

In this paper, we have discovered that a type of two-fold symmetrical 6R foldable frame proposed as a deployable core structure to support solar blankets in space applications is actually a line and plane-symmetric Bricard linkage. Using the singular value decomposition of the Jacobian matrix of closure equations, we are able to show that bifurcations exist during deployment of the frame. And the bifurcations cannot be avoided in current designs. However, we also identified a feasible area for design parameters in which bifurcations can be completely removed. A physical model has been made which proves that our conclusion is correct.     

Deployable lenticular stiffeners for origami-inspired mechanisms

Light-weight origami-inspired mechanisms can provide advantages in deployable space systems and other applications. However, a significant challenge in their design is ensuring that they are su?ciently stiff. Compliant, deployable stiffeners utilizing a profile that approximates the Euler Spiral are proposed as one possible solution. It is shown that a structure with this specific profile, called a lenticular stiffener, permits stiffeners to be flattened using a force applied at their edge. Formulas for calculating the increase in stiffness are developed. Relations needed to design the deployment behavior of the stiffeners are also derived. Finally, advantages of different configurations of stiffeners are evaluated. These results are verified through simulation and experiments.     

Dynamics of a System of Bodies with Program-Variable Configuration

The dynamics of a system of rigid bodies with program-variable configuration is analyzed. A mathematical model is constructed using methods of analytical mechanics. The behavior of a microsatellite with a deployable gravity-gradient boom is analyzed as a numerical example     

Dynamics of the orbital deployment of an elastic ring-shaped antenna

A generalized mathematical model of an unguided spacecraft that carries an elastic body of variable geometry (a deployable ring-shaped antenna) is constructed. Its dynamics is simulated numerically     

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.     

A necessary condition for stability of kinematically indeterminate pin-jointed structures with symmetry

Stability conditions are the key to transform kinematically indeterminate structures into prestressed structures or deployable structures. From the viewpoint of symmetry, a necessary condition is presented for the stability of symmetric pin-jointed structures with kinematic indeterminacy. The condition is derived from the positive definiteness of the quadratic form of the tangent stiffness matrix. Numerical examples verify that the proposed necessary stability condition is in accord with the conventional theory of structural rigidity, and is considered to be more comprehensible. It is robust and easy to implement. Results show that a symmetric prestressed structure is guaranteed to possess integral prestress modes, if the necessary condition is satisfied. Further, a pin-jointed structure with fully symmetric mechanism modes is proved to be unstable, if it does not satisfy the condition.     

On aerodynamic noises radiated by the pantograph system of high-speed trains

Pantograph system of high-speed trains become significant source of aerodynamic noise when travelling speed exceeds 300 km/h. In this paper, a hybrid method of non-linear acoustic solver （NLAS） and Ffowcs Williams-Hawkings （FW-H） acoustic analogy is used to predict the aerodynamic noise of pantograph system in this speed range. When the simulation method is validated by a benchmark problem of flows around a cylinder of finite span, we calculate the near flow field and far acoustic field surrounding the pantograph system. And then, the frequency spectra and acoustic attenuation with distance are analyzed, showing that the pantograph system noise is a typical broadband one with most acoustic power restricted in the medium-high frequency range from 200 Hz to 5 kHz. The aerodynamic noise of pantograph systems radiates outwards in the form of spherical waves in the far field. Analysis of the overall sound pressure level （OASPL） at different speeds exhibits that the acoustic power grows approximately as the 4th power of train speed. The comparison of noise reduction effects for four types of pantograph covers demonstrates that only case 1 can lessen the total noise by about 3 dB as baffles on both sides can shield sound wave in the spanwise direction. The covers produce additional aerodynamic noise themselves in the other three cases and lead to the rise of OASPLs.     

Nonlinear Dynamic Behaviour of Coupled Suspension Systems

A two degrees of freedom model of two coupled suspension systems characterised by piecewise linear stiffness has been studied. The system, representing a pantograph current collector head, is shown to be sensitive to changes in excitation and system parameters, possessing chaotic, periodic and quasiperiodic behaviour. The coupled system has a more irregular behaviour with larger motions than the uncoupled suspension system, indicating that the response from the uncoupled suspension system cannot be used as a worst case measure. Since small changes in system parameters and excitation affect the results drastically then wear and mounting as well as actual operating conditions are crucial factors for the system behaviour.