箭橇一体化设计方法研究

本文采用一种新型设计思路进行火箭橇设计,将助推用火箭发动机壳体设计为火箭橇主梁结构,并利用简单整流结构将火箭发动机壳体与火箭橇试验滑靴联结组成火箭橇试验橇体,大幅度降低了火箭橇体质量,减小了火箭橇滑行过程中的空气阻力,有效地提高了火箭橇推重比．此方法研究的火箭橇可以作为高Ma数火箭橇试验平台进行重复使用．     

箭橇一体化设计方法研究

本文采用一种新型设计思路进行火箭橇设计,将助推用火箭发动机壳体设计为火箭橇主梁结构,并利用简单整流结构将火箭发动机壳体与火箭橇试验滑靴联结组成火箭橇试验橇体,大幅度降低了火箭橇体质量,减小了火箭橇滑行过程中的空气阻力,有效地提高了火箭橇推重比.此方法研究的火箭橇可以作为高Ma数火箭橇试验平台进行重复使用.     

减振滑靴非线性动态特性数值分析

针对以降低火箭橇系统在轨振动为目的设计的减振滑靴，对其动态特性进行了数值分析。通过平面压缩试验及经验公式确定了减振滑靴减振层天然橡胶的本构参数，进而由有限元模型获得其非线性刚度，据此建立了减振滑靴非线性动力学模型对其求解并进行了试验验证。数值计算结果表明，减振滑靴相较于传统滑靴有着较好减振能力，其减振效率随其载荷提高而提高，但由于引入橡胶使得其在大载荷及高过载条件下易出现“跳跃”现象。根据“跳跃”现象确定了减振滑靴工作边界，典型工况下在1 Ma(350 m/s)速度下每枚减振滑靴载荷应小于311 kg,在2 Ma(700 m/s)载荷则应低于181 kg。     

高超声速二维滑靴热-固耦合仿真

本文采用FLUENT对某简易滑靴二维模型在5Ma条件下的气流场及结构域温度场进行耦合仿真,对滑靴在气动热作用下的熔化情况进行评估,为高超声速火箭橇滑靴气动及热防护设计方法提供有益参考.     

基于火箭橇试验的北斗接收机动态校准技术

提出一种基于火箭橇试验的北斗接收机动态校准技术,通过阐述动态校准过程,火箭橇试验标准弹道建立方法、接收机动态定位和速度误差评定方法、火箭橇试验外测参数的溯源及校准过程不确定度评定方法,建立了计量型可溯源的火箭橇试验系统,并对两款接收机校准结果进行了分析。结果表明火箭橇试验能够有效解决北斗接收机的高动态校准问题,具有一定的应用价值和扩展前景。     

火箭橇试验橇体时空位置全程测试——单台光电经纬仪法

本文针对火箭橇试验橇体时空位置的全程测试问题,提出了单台光电经纬仪时空位置测试法,该方法采用单台光电经纬仪对火箭橇试验橇体全程运动图像进行跟踪拍摄,通过跟踪图像判读获得的测角信息、光电经纬仪站址信息、火箭橇轨道直线方程3者之间的关系,事后处理出火箭橇全程时空位置．同时提出了采用同帧画幅处理与多点标定事后误差曲线拟合的方法对时空位置事后数据进行逐点修正,可大幅提高测试数据精度．     

“遥存结合”测试方法在火箭橇试验中的应用

针对火箭橇试验力学环境复杂难以测量以及侵彻类火箭橇试验橇上装置难以回收等问题,本文提出采用遥测和存储相结合的测试方法来解决此类试验的难题,并研制了火箭橇"遥存结合"发射装置,该装置已经成功应用在火箭橇试验测试中.     

基于ANSYS/LS-DYNA的停放制动滑橇螺栓跌落强度分析

中低速磁浮列车悬浮架各部件间主要通过螺栓进行联接，在列车悬浮失效跌落时，停放制动滑橇与托臂联接处的螺栓受到较大的剪切作用，存在结构安全风险。利用HyperMesh建立了悬浮架有限元模型，考虑了停放制动滑橇位置的螺栓联接及接触关系，基于ANSYS/LS-DYNA仿真了悬浮架不同速度下的跌落过程，计算了各接触对的接触力波动情况，分析了联接螺栓、滑橇键、滑橇安装座及托臂的应力变化及分布规律。结果表明：跌落碰撞瞬间各接触对的接触力达到峰值，然后在小幅波动过程中呈减小趋势；运动状态的悬浮架跌落时，各接触力远大于静悬落车工况，联接螺栓的应力显著增大，滑橇键、滑橇、滑橇安装座的最大等效应力超过了材料的屈服极限，存在结构安全风险，工程中需要注意及时检查。     

基于遥测的遮光板火箭橇时空位置测试方法

遮光板法是目前较为常用的靶场测试火箭橇时空位置信息的方法.针对遮光板法实时性差、存储记录仪需要回收等问题,本文采用了一种基于遥测的遮光板火箭橇时空位置测试方法.经试验验证,该方法能够实时地获取火箭橇时空位置测试数据.     

火箭橇试验推力测量方法研究

以典型火箭橇试验系统为对象,对系统运动的不同阶段进行力学分析。在建立推力测量系统基础上,对不同马赫数下火箭橇试验的推力数据进行分析处理。研究结果可为综合力学环境火箭橇试验平台的建立提供参考。     

基于线性互补问题的多体系统接触/碰撞动力学研究

多体系统往往包含大量的接触/碰撞行为,这些非光滑事件的存在造成了动力学方程的不连续或分段连续,给数值求解带来了很大的困难。为综合考虑平顺接触与碰撞,采用基于线性互补问题的非光滑动力学方法,首先在当前时刻为起点的短时间内对对缝隙函数进行均匀化,然后与法向接触力建立标准线性互补方程,最后将线性互补方程改造为一组非线性代数方程,通过非线性迭代可直接求解接触力。算例结果表明,采用该方法不需在接触状态发生改变时切换模型,且严格满足互补关系,保证了接触力的非负性。研究成果可成为求解多柔体系统接触/碰撞问题的新途径。     

Scaling numerical models for hypervelocity test sled slipper-rail impacts

Hypervelocity test sled slipper-rail impacts have been simulated numerically using the finite volume hydrocode, ChartD to the Three-Halves (CTH). This study addresses the difficulties of applying CTH model solutions to real test sled runs. Past CTH models using dimensions different than actual test sleds have been used to study phenomenological aspects of the problem. However, quantitative results from the CTH model solution do not apply directly to actual test sled runs due to strain rate effects and time scale differences. The Buckingham Pi Theorem is applied to two potential hypervelocity gouging models. Validity of the invariant products is tested using sample CTH hypervelocity gouging models that are scaled up to simulate dimensions of a real test sled. Real test sled dimensions are desired in order to more closely simulate actual test sled runs. Invariant products developed from application of the Buckingham Pi Theorem can be used as guidelines for determining whether a CTH model is applicable to a test sled with specific dimensions. Strain rate effects are investigated to study whether deviations between scaled CTH models may be reduced by modifying the constitutive model.     

Force propagation speed in a bed of particles due to an incident particle impact

The force propagation speed in granular matter is a very difficult property to be measured. A new technique has been developed to calculate the force propagation speed in granular matter based on measuring experimentally the contact time. The contact time for a particle hitting a bed of particles is estimated as the time taken for a particle to strike a bed of particles till the time of its ejection, and it is calculated using the discrete element method. The speed of force propagation in a bed of particles is estimated by plotting the dependence of the path length of the contact force on the contact time and finding the gradient of such dependence. Such approach leads to accurate results if the impact speed is below the yield velocity, i.e. no plastic deformations. It is found that the force propagation speed in spherical granular matter is proportional to the impact speed of the incident particle, which is different from force propagation in continuum matter. It is also found that the propagation speed is dependent on the material and diameters ratio of the interacting particles, but it is not dependent on the number of bed layers. The propagation speed in granular matter is normalized by dividing it by a reference propagation speed, i.e. the propagation speed at an impact speed of 1 m/s. It is found that the normalized propagation speed is independent of the material and diameter of the interacting particles, but it is logarithmically proportional to the impact speed. The proportionality constant is equal to 0.16, which can be taken as a universal constant for force propagation in spherical granular matter.     

流冰撞击力作用下列车–简支梁桥耦合振动分析

建立撞击荷载作用下列车‐桥梁系统动力分析模型,将现场实测的流冰撞击力时程作为系统的撞击荷载。通过计算机仿真分析,对流冰撞击作用下高速铁路桥梁的动力响应及其对桥上列车运行安全的影响进行研究。采用自编程序模拟列车过桥的全过程,计算分析7 m×24 m简支箱梁桥在流冰撞击力作用下动力响应及桥上高速列车的动力响应。计算结果表明,在实测流冰撞击力作用下,桥梁横向加速度以及车辆脱轨系数和轮重减载率等行车安全指标在列车速度250 km/h以上时超过容许值,说明流冰撞击作用对车桥系统耦合振动响应具有较大的影响。     

Moderately high speed impact of two identical spheres

This paper deals with impacts between two identical spheres in moderately high speed range. Impact of spheres is one of basic problems in mechanical dynamics. Severity of impact is generally characterized by the coefficient of restitution. However, influence of material property on the coefficient of restitution has not been clarified yet. The authors previously investigated direct central impacts of two identical spheres in low speed range and revealed that strain rate sensitivity of material properties could not be ignored even in the low speed impacts. Therefore, this paper investigates the direct central impact of two identical spheres in higher speed range. The impact experiments were performed in range of impact speed 10 m/s–20 m/s by using air-gun setup. It was confirmed that the expressions for the coefficient of restitution and the contact time derived from the low speed impact remained effective in the moderately high speed range. Then numerical simulations by using Finite Element Method (F.E.M) have been carried out, in which the material properties and the strain rate effect were taken into account. The coefficient of restitution, contact time, sphere’s compression and contact circle diameter obtained by experiments and F.E.M. were compared and they matched well. Contact pressure distributions at maximum contact force were investigated. The contact pressure at sphere center varied little with impact speed but the contact pressure increased with impact speed near contact edge. Theoretical expression for prediction of the coefficient of restitution proposed by C. Thornton was examined to the experimental results of this study. To provide an accurate prediction, it is necessary to estimate the contact pressure depending on material properties. Finally, the Meyer analysis was applied to the case of this study and it was found that the Meyer’s law holds in the moderately high speed impact between two identical spheres.     

Gouge initiation in high-velocity rocket sled testing

A model is presented which describes the formation of surface damage “gouging” on the rails that guide rocket sleds. An unbalanced sled can randomly cause a very shallow-angle, oblique impact between the sled shoe and the rail. This damage phenomenon has also been observed in high-velocity guns where the projectile is analogous to the moving sled shoe and the gun barrel is analogous to the stationary rail. At sufficiently high velocity, the oblique impact will produce a thin hot layer of soft material on the contact surfaces. Under the action of a normal moving load, the soft layer lends itself to an anti-symmetric deformation and the formation of a “hump” in front of the moving load. A gouge is formed when this hump is overrun by the sled shoe. The phenomenon is simulated numerically using the CTH strong shock physics code, and the results are in good agreement with experimental observation.     

地震碰撞分析中接触单元模型的精细积分解法

地震碰撞数值分析是结构抗震研究的重要内容,本文将精细积分法引入到地震碰撞数值分析中。结合5种常用接触单元模型的特点,将碰撞力计算式表达成统一的形式,推导了碰撞阶段的精细积分公式。将地震碰撞过程划分为碰撞阶段和非碰撞阶段,对不同的阶段采用不同的积分步长,并且提出一种基于线性加速度假定的碰撞时刻搜索法。用两小球自由弹性碰撞模型对精细积分法程序进行验证。并采用本文方法对Chau振动台碰撞试验进行了数值仿真。结论为：本文数值分析方法既保证了模拟地震碰撞的精度又具有较高的计算效率;在地震碰撞分析中应合理选择接触单元模型和模型参数;对于近似弹性碰撞情况Hertz模型和Hertz-damp模型数值仿真结果与试验结果吻合较好。