电磁轨道发射状态下导轨的动态响应

当导轨通入电流时,电枢受到推力作用沿轨道移动;同时,电枢经过的导轨受到安培力和电枢压力的作用。由于导轨外部的外包层将对导轨起到弹性支撑的作用,因此,可将导轨简化为弹性地基梁。应用二维Fourier积分变换,导出了导轨在移动荷载作用下动态挠度的一般解。根据电磁场理论、传热学,以及弹性力学的基本方程,可以得到电枢受到的推力、导轨相互作用的斥力和电枢作用在导轨上的压力的表达式,从而得到了电磁轨道发射状态下导轨挠度解的具体形式,并且分析了通入电流、导轨尺寸、外包层刚度等参量对导轨动态响应的影响     

电磁轨道发射装置导轨动力学响应分析

为分析电磁轨道发射装置中导轨在发射过程的动力学响应,将分布式移动电磁载荷作用下的导轨简化为伯努利-欧拉梁,建立了悬臂支撑约束下的导轨振动控制方程。采用分离变量法求解高阶偏微分方程,通过模态叠加导出了给定初边界条件下的导轨振动解析解和临界速度表达式。分别计算分析了电枢匀速运动、典型电流驱动下变加速运动时导轨的动力学响应特征,讨论了导轨振动响应的临界速度效应。结合电枢在膛内的运动过程,分析了导轨的振动挠度、速度和横向加速度等参量的变化规律。研究结果可为发射器封装结构的设计提供一定的理论依据。     

裂尖具线性分布约束应力的运动裂纹模型及其解析解

以恒定速度运动的Griffith裂纹解析解为著名的Yoffe解。静止裂纹的条状屈服模型即Dugdale模型,将其推广到运动裂纹模型时发现,当裂纹运动速度跨越Rayliegh波速时,裂纹张开位移COD趋于(∞,且表现为间断。通过在裂尖引入一个约束应力区及两个速度效应函数,假设约束应力为线性分布,采用复变函数方法,求得动态应力强度因子SIF与裂纹张开位移COD的解析解。新的结果,在Rayleigh波速下裂纹张开位移连续且为有限值。给出裂纹张开位移的一些数值结果,获得了一些有意义的结论。     

基于POD降阶方法的复合材料曲壁板颤振响应特性研究

建立了三维复合材料曲壁板的气动弹性有限元方程,将本征正交分解方法(POD)应用于三维复合材料曲壁板的非线性颤振响应降阶分析中,通过POD方法构造三维复合材料曲壁板颤振响应的POD模态,然后将系统的运动方程变换到POD模态坐标下,通过数值积分方法计算三维复合材料曲壁板的颤振响应,与传统的模态缩减法计算结果相比,结果很好的吻合,且大大节省了计算时间。     

非轴对称移动载荷下有限长圆柱厚壳的动力响应

本文在介绍圆柱厚壳应力与位移理论分析发展的前提下,建立了有限长圆柱厚壳在非轴对称移动载荷作用下的三维力学模型,假设沿厚度方向径向剪切应变二次分布、径向正应变线性分布,且建立了为满足边界条件待定的位移表达式,采用Heaviside函数和Dirac函数表达移动和作用变化着的移动载荷的基础上,用最小势能原理建立了该圆柱厚壳的动力学微分方程组,应用Galerkin法和修正的Runge–Kutta–Fehlberg法,求得了非轴对称移动载荷作用下的圆柱厚壳的动力响应。通过具体算例,对有限长圆柱厚壳的位移响应和应力状态进行了分析,并将动态响应的理论解与ANSYS数值解进行了对比,从而相互印证了解的可靠性。     

机电集成超环面传动系统内共振研究

机电集成超环面传动系统为集机、电和控制于一体的新型广义复合机电耦合系统,工作中非线性电磁啮合力可能导致明显的内共振现象, 影响系统的正常运行。本文考虑系统中行星轮与蜗杆、定子间电磁啮合非线性,建立了系统强非线性运动微分方程组, 针对不存在与存在内共振两种情形,用多尺度法求出了系统时域响应的一次近似解析解,作出了系统振幅随时间的变化曲线和系统时域响应曲线;针对不存在与存在内共振两种情形,研究了系统各部件动态位移随时间的变化规律。研究结果表明：内共振使得系统能量在系统内不同零件间交互传递,导致各零件振动振幅增大,影响系统动态性能,设计时应该避免内共振的产生。     

电磁轨道发射过程中电枢运动特性参量的一种简捷算法

在介绍了电磁轨道发射装置发射过程模拟方法的基础上, 将电枢位移x(t) 、电枢速度v(t)等变量视为独立函数, 给出了发射过程中回路电流#em/em#(t) 的解析表达式。基于回路电流#em/em#(t) 、电枢位移x(t) 、电枢速度v(t)和电枢加速度a(t) 的基本方程, 提出了电磁轨道发射过程中电枢运动特性参量的一种简捷算法, 给出了该算法的流程图, 并指出了时间步长和收敛准则的确定方法。该算法可以移植到任何具备二次开发平台的有限元软件之中。通过电磁轨道发射装置的计算实例, 表明了该算法的有效性和可靠性。     

爆炸载荷作用下单向加筋方板的大挠度塑性动力响应分析

从分别列出加筋板面板以及加强筋的运动方程出发,详细分析了爆炸载荷作用下单向加筋固支方板的大挠度塑性动力响应.分析表明:取决于加强筋的相对刚度以及载荷峰值的大小,加筋板的运动将呈现三种不同的模式.限于讨论加筋板的总体变形模式.首先讨论了同时计及弯矩和面力(轴力)作用的解析解,在此基础上进一步讨论了忽略弯矩影响的薄膜解以及能量解.理论结果与已有的试验结果在多数情况下符合良好,表明提出的简化理论分析方法能对爆炸载荷下单向加筋固支方板的永久变形做出较为合理的预报.     

飞机加筋壁板紧固件松脱损伤检测的自相关分析方法

提出了一种基于自相关函数的损伤检测方法。首先证明归一化后的结构各测点加速度响应自相关函数零点值仅与结构的模态参数有关,然后利用其构造损伤指标用于结构损伤的定位。飞机加筋壁板紧固件松脱损伤的损伤检测实验表明,该方法只需要利用结构在一定带宽白噪声激励下的加速度响应就能准确定位加筋壁板紧固件的松脱损伤,适用于紧固件松脱损伤的实时检测。     

三维粘弹壁板颤振分析

基于Kelvin粘弹模型,根据Von Karman大变形应变-位移关系和一阶活塞气动力理论,运用伽辽金方法建立了三维粘弹壁板颤振方程,并采用Rouge-Kutta法进行数值积分,分析粘弹阻尼,面内压力及壁板几何尺寸对粘弹壁板颤振的影响,进而取动压为分叉参数,研究粘弹壁板颤振时的分叉及混沌等特性。结果表明：随着粘弹性阻尼的增大, 系统的静态稳定区域先减小后增大,而静态屈曲解几乎不受影响,同时发现混沌运动区域随着粘弹阻尼的增大而快速减小。当取动压为分叉参数时发现粘弹壁板分叉特性很复杂,系统由屈曲状态进入混沌振动,再经历一系列的分叉进入简谐极限环振动状态;而较大面内压力和较小的长宽比不利于粘弹壁板的稳定。     

Stress analysis of the rails of a new high velocity armature design in an electromagnetic launcher

In an electromagnetic launcher, the magnetic field creates a dynamic force that moves the armature forward. In an electromagnetic launcher, the armature reaches a critical velocity during the launch which causes high amplitude stress and strain. In addition, high stress and strain damage the rails and reduces its life span. The purpose of this paper is to investigate the effect of armature velocity as well as the rails physical and geometrical properties on the dynamic response of the rails in an electromagnetic launcher. In this study the second moment of inertia of the rails cross-section, Young modulus, foundation stiffness and density of the rails are constant in location and time. In our formulation of governing non-linear differential equations, Maxwell equations and deflection equation are applied to the rails under dynamic loading. To solve the non-linear governing differential equations a finite difference method is utilized.     

Elastic waves and solid armature contact pressure in electromagnetic launchers

Electromagnetic launchers suffer a phenomenon referred to as armature transitioning: when the armature and rails suddenly lose contact with each other, damage can occur to the armature and the rails of the launcher. In this paper, we explore transient elastic waves as a possible explanation for the transitioning of solid armatures in electromagnetic launchers. We use a finite-element code to model the transient dynamics of a typical electromagnetic launcher guide rail. We found that dynamic rail deflections caused by the movement of the armature are similar in magnitude to those caused by the magnetic field, and that the contact pressure between the armature and the rails changes dramatically when the speed of the armature reaches the critical velocity of the rails.     

Critical velocity for rails in hypervelocity launchers

This paper is related to the dynamic and strength analysis and optimized design of hypervelocity electromagnetic launchers. Projectile motion along the rails at critical velocity is associated with damaging resonant regimes. These regimes reveal increased displacements and stress that can lead to failure of a launcher. To calculate critical velocity and to visualize dynamic deformations of the launcher we have developed two alternative approaches utilizing analytical and finite element models. The first approach employs a closed form analytical solution for critical velocity that is based on the Bernoulli–Euler model of a beam resting on an elastic foundation and subjected to a moving load. The critical velocity is expressed as a function of geometric and material parameters of the rail and equivalent stiffness of the supporting structure. The stiffness of the supporting structure is found from a 2D finite element model. In the second approach, we employed beam finite element and 3D solid finite element models to visualize and measure the “natural” and “forced” bending waves traveling along the rails. These approaches helped to better understand the transient resonant dynamic processes and offered insight on how to alter the launching device materials and geometry to reduce the critical-velocity effects.     

Interactive electromagnetic launcher simulation

The mathematical model, usage, and documentation of an interactive computer simulation for an electromagnetic launcher is presented. The launcher is modeled as an electrical circuit. Three slight variations of the program permit studies of a launcher with (1) rail skin effects, (2) rail skin effects and approximated storage coil skin effects, or (3) neither of these effects. Usage of the program as currently implemented on the Westinghouse R&D Univac 1106 is described, with a sample session shown. The implementation of the program permits rapid scoping of the effects of parameter changes.     

电磁轨道炮发射过程的轨道变形研究

电磁轨道炮发射电枢过程中,移动载荷对轨道的作用会引发轨道挠度变形。本文依据试验电流波形数据确定电枢速度和滑动距离,根据弹性梁的动力学响应方程,考虑电枢的作用力及磨损,求解了轨道的挠度幅值。对比了电枢作用力和轨道斥力对轨道变形幅值的影响,获得了轨道的挠度变化随轨道位置和发射时间的变化曲线,为进一步分析轨道炮寿命和绝缘支撑体结构设计提供参考依据。     

Stress intensity factors evaluation for through-transverse crack in slab track system under vehicle dynamic load

The stress intensity factors (SIFs) for through-transverse crack in the China Railway Track System (CRTS II) slab track system under vehicle dynamic load are evaluated in this paper. A coupled dynamic model of a half-vehicle and the slab track is presented in which the half-vehicle is treated as a 18-degree-of-freedom multi-body system. The slab track is modeled as two continuous Bernoulli–Euler beams supported by a series of elastic rectangle plates on a viscoelastic foundation. The model is applied to calculate the vertical and lateral dynamic wheel–rail forces. A three-dimensional finite element model of the slab track system is then established in which the through-transverse crack at the bottom of concrete base is created by using extended finite element method (XFEM). The wheel–rail forces obtained by the vehicle-track dynamics calculation are utilized as the inputs to finite element model, and then the values of dynamic SIFs at the crack-tip are extracted from the XFEM solution by domain based interaction integral approach. The influences of subgrade modulus, crack length, crack angle, friction coefficient between cracked surfaces, and friction coefficient between faces of concrete base and subgrade on dynamic SIFs are investigated in detail. The analysis indicates that the subgrade modulus, crack length and crack angle have great effects on dynamic SIFs at the crack-tip, while both of the friction coefficients have negligible influences on variations of dynamic SIFs. Also the statistical characteristics of varying SIFs due to random wheel–rail forces are studied and results reveal that the distributions of dynamic SIFs follow an approximately Gaussian distribution with different mean values and standard deviations. The numerical results obtained are very useful in the maintenance of the slab track system.     

车站结构型式对地铁诱发环境振动的影响分析

地铁诱发环境振动是城市轨道交通工程设计中重点关注的课题。本文系统研究了地铁车站考虑地铁运行诱发环境振动的数值建模问题,给出了计算模型建立的思路及相关计算参数的取值方法。以某拟建地铁车站为例,建立了车站结构-土的准三维有限元模型,分析车站结构型式对地铁诱发环境振动的影响,从振动加速度时程反应、1/3倍频程谱和峰值衰减规律等方面对叠合墙式、复合墙式和离壁墙式三种不同型式车站方案进行了详细的对比分析。研究结果表明：分离车站结构内衬墙和地下连续墙可减小地铁诱发的环境振动。对于环境振动水平需要严格控制的地区,地铁车站可选用离壁墙式结构方案。     

Electromagnetic coaxial railgun

Key design parameters of railguns are examined, namely, the inductance gradient, current distribution, electromagnetic pulses distribution and rail separation forces. A comparison of coaxial and parallel railguns indicates that the coaxial system has some advantages and should be considered during system design tradeoffs for an orbiting space probe launcher. It is suggested that an orbiting launcher could be used to send small and relatively inexpensive probes towards the planets and asteroid belt. A small, low-energy capacitor-powered coaxial railgun designed and built to demonstrate the armature acceleration and absence of the electromagnetic pulse forward of the armature is described     

考虑有限深度土体运动的Winkler地基梁1/2次谐波共振响应分析

土-结构相互作用系统动力响应的基本特征之一是有限范围内弹性地基与其支承结构共同运动,将土体运动引入系统的动力学方程可体现其对系统动力学特性的影响。基于考虑有限深度土体运动影响的Winkler地基上有限长梁的非线性运动方程,利用Galerkin法和多尺度法,求得弹性地基梁1/2次谐波共振的幅频响应方程和位移的二阶近似解。进而通过数值计算,得到了梁1/2次谐波共振的幅频响应曲线,研究了地基深度、质量、弹性模量、Winkler参数和阻尼等对弹性地基梁1/2次谐波共振响应的影响。研究结果表明:有限深度土体运动对Winkler地基梁1/2次谐波共振响应影响显著。运动方程中引入土体运动的影响后,梁1/2次谐波共振区间明显减小。随地基深度、质量和弹性模量改变,弹性地基梁1/2次谐波共振的幅频响应曲线偏转程度、共振区间和响应幅值等均发生定量改变。当弹性地基刚度增大到一定程度,Winkler地基参数变化对系统1/2次谐波共振响应的影响明显减弱。阻尼对系统动力响应起抑制作用,当参数η增大到一定值后将不会出现1/2次谐波共振响应的非平凡解。