戈登式辐射热流传感器动态特性测试技术

高速热流传感器广泛用于航空、航天、爆炸场等领域的热流密度测试,时间常数为传感器重要动态特性参数之一.传统测试方法仅能测试时间常数几百毫秒的热流传感器,无法满足未来高速热流传感器的测试需求.系统采用光纤输出半导体激光器作为辐射热流源,输出阶跃辐射信号通过微透镜光斑均匀化光学系统作用于高速Gardon计敏感面,利用信号调理电路和采集系统实现热流计输出信号的高速采集.系统响应时间为μs级,能够产生MW/m2级热流信号.完成了GD-B4-50K、GD-B4-200K和GD-D0-5M三种型号的辐射热流传感器动态测试,测得时间常数分别为0.199 s、0.521 s、0.052 s.可以有效解决航空飞行、航天再入等领域的辐射热流传感器测试难题.     

衍化的加速度再入制导律方案研究

传统的航天飞机再入制导采用的是标准轨道法,自适应能力较差,因此研究了其衍化算法.衍化算法通过对剩余航程的估算,周期性更新参考阻力加速度剖面.根据生成的参考剖面,侧向制导采用数字预测方法先后搜索了两次倾斜反向时刻;对参考阻力加速度剖向的跟踪采用反馈线性化方法.更新参考加速度剖面和搜索反向时刻的算法都是一维黄金分割法,因此衍化算法完全可由机载计算机完成.针对不同的再入飞行任务进行仿真,结果表明:制导方案都具有很好的稳定性和实时性.     

三维自主再入制导方法

基于阻力加速度-能量剖面设计,提出一种新的三维自主再入制导方法.该方法的阻力加速度-能量剖面由再入走廊上边界和下边界内插得到,倾侧角采用两次反转模式,轨迹规划同时考虑了飞行器的纵向和横向运动,并具有在线生成三维轨迹的能力.最后对制导方法的适应性进行了仿真分析,仿真结果表明给出的再入制导方法能适应不同情况的再入,使飞行器在具有较好轨迹特性的同时以较高的精度到达末端能量管理界面.     

气化炉与辐射废锅接口托架传热的数值分析

以通用的三维导热模型为基础,应用有限元法,计算了不同结构参数和操作条件下气化炉与辐射废锅接口内金属托架的传热特性.结果表明,托架长度、耐火纤维厚度、炉内温度是影响托架温度和热流密度分布的主要因素.托架最高温度和最大热流密度随着托架长度的增加而增大,随着炉内温度的提高而增大.托架外围包裹20 mm厚的耐火纤维,能有效降低托 .架的最高温度和最大热流密度.对于稳态操作的气化炉,其炉内温度变化范围约1 200℃～1 400℃,相应的金属托架最高温度变化范围约为420℃～480℃,最大热流密度约为(42.8～50.0)kW·m-2.     

我国推行电子政务的阻力研究

电子政务一直是近些年的热点问题,90年代后期,特别是进入21世纪后,伴随因特网的迅速发展和政府职能转变的力度加大,我国电子政务建设进入了全面规划、整体发展的新阶段.我国电子政务系统的建设取得了一些成绩,有了一定的效益,但和电子政务内在要求相比,还有不小的差距.差距产生的原因主要在于实施电子政务系统的过程中存在的一些阻力,本文提出并分析了电子政务系统过程中实施的主要阻力,并针对这些阻力,提出了一些建议.     

水下缆索环流阻力分析

研究水下缆索系统优化问题,非对称缆在流体中存在的环流,不仅产生侧向阻力,同时导致切向力和法向力之间呈现非线性关系,使速度投影法失效.为解决上述问题,提出一种根据坐标变换的算法,可将原始阻力直接获得三个阻力分量,适用于各种缆型的阻力计算;同时能避免缆流夹角的求解和符号处理问题,使算法得到了简化.在速度和缆体两种坐标系下,依据算法分别建立了相应的阻力计算模型.基于水下缆索有限段动力学模型,对典型非对称缆索水下运动过程进行了仿真,结果表明能正确反映缆索的水下运动规律,并证明了模型的正确性,解决了水下缆索存在的问题.     

基于CMAC网络的飞行器再入标准轨道制导

针对飞行器再入标准轨道制导方法中的参考阻力加速度跟踪问题,提出一种将CMAC网络与PID控制相结合的复合控制方案。该方案利用传统的PID控制器实现反馈控制,保证系统的稳定,并利用CMAC网络实现补偿控制,提高系统的抗干扰能力。三自由度仿真结果表明,在存在气动偏差和风场干扰等影响的情况下,该算法的跟踪精度与鲁棒性都有增强,终端精度和约束条件都得到了较好的满足。     

载重子午线轮胎滚动阻力有限元仿真分析

研究汽车轮胎低滚动阻力优化设计,针对轮胎滚动阻力引起的温度对材料性能影响难以测定的问题,根据车辆的轮胎温度与材料性能有关,建立了含热力学耦合的滚动阻力分析模型.要求模型包含三个部分:结构分析、传热分析和滚动阻力计算.与传统模型相比,增加了传热分析部分,利用传热分析计算结果更新材料参数,解决了以往在滚动阻力仿真时不考虑温度影响的问题.对模型进行仿真分析,通过滚动阻力试验验证改进的模型具有更高的精度,可以为低滚动阻力轮胎结构设计与优化提供指导.     

自由液面下增阻器水动力特性的数值仿真

水力增阻器是一个利用水的阻力来实现高速运动物体减速的装置.采用RANS方程和RNG湍流模型对增阻器特性进行了数值仿真计算,能得出了流场的自由液面变化情况、增阻器表面压力分布以及阻力系数随浸深和来流速度的变化规律等,从中缩短了增阻器阻力计算周期并节约了阻力试验成本.计算结果表明:增阻器压力主要集中在增阻器背面与流体接触面上,最大压力出现在增阻器拐角处下端;增阻器阻力系数受来流速度影响不大,但随着浸水深度的增加呈现总体减小的趋势.可为增阻器的结构设计以及阻力预报提供重要参考依据.     

基于拟连续高阶滑模的高超声速飞行器再入姿态控制

考虑模型参数不确定和外界干扰对再入制导控制性能的影响,基于拟连续高阶滑模控制策略对高超声速飞行器的再入制导控制问题进行了研究.首先,给出再入制导指令的设计过程.其次,基于再入飞行特性对模型进行简化,获得面向控制的姿态模型,在此基础上,通过引入新的控制变量,设计解耦滑模面,实现姿态间的解耦.再次,为了削弱控制抖振,通过引入虚拟控制,对系统进行增广,基于齐次性理论设计拟连续三阶滑模再入姿态控制器,确保系统在有限时间实现对制导指令的稳定跟踪.最后,六自由度再入飞行器的制导控制一体化仿真结果表明,本研究给出的控制策略在不影响系统鲁棒性的同时,能够实现对标称轨迹和再入姿态的综合控制.     

The interaction between membrane structure and wind based on the discontinuous boundary element

Small disturbance potential theory is widely used in solving aerodynamic problems with low Mach numbers, and it plays an important role in engineering design. Concerning structure wind engineering, the body of the structure is in a low velocity wind field, with a low viscosity of air and thin boundary layer, therefore, the tiny shear stress caused by the boundary layer can be ignored, only wind pressure being considered. In this paper, based on small disturbance potential theory, the fluid-structure interac...     

Effects of slip on sheet-driven flow and heat transfer of a non-Newtonian fluid past a stretching sheet

The flow and heat transfer of an electrically conducting non-Newtonian fluid due to a stretching surface subject to partial slip is considered. The constitutive equation of the non-Newtonian fluid is modeled by that for a third grade fluid. The heat transfer analysis has been carried out for two heating processes, namely, (i) with prescribed surface temperature (PST-case) and (ii) prescribed surface heat flux (PHFcase) in presence of a uniform heat source or sink. Suitable similarity transformations are used to reduce the resulting highly nonlinear partial differential equations into ordinary differential equations. The issue of paucity of boundary conditions is addressed and an effective second order numerical scheme has been adopted to solve the obtained differential equations. The important finding in this communication is the combined effects of the partial slip, magnetic field, heat source (sink) parameter and the third grade fluid parameters on the velocity, skin friction coefficient and the temperature field. It is interesting to find that slip decreases the momentum boundary layer thickness and increases the thermal boundary layer thickness, whereas the third grade fluid parameter has an opposite effect on the thermal and velocity boundary layers.     

一维热传导问题时变边界上热通量重构问题

具有Neumann边界条件的抛物方程的初边值问题是偏微分方程研究领域的一类经典问题.正问题是由已知的边界条件和初始条件来求区域温度场的问题.如果边界条件不足,但给出了区域内部的一些额外信息,这样便构成了一类热通量重构的反问题.本文讨论了一维热传导问题时动边界上的热通量重构问题,借助于位势理论方法,引入密度函数,将反问题本质上转化为一类关于密度函数的具有弱奇性核的第一类Volterra积分方程,采用了Tikhonov正则化,在正则化参数的选取上采用了后验的模型函数方法,数值结果验证了反演方法的有效性.     

Modeling laser heated thin film media for heat assisted magnetic recording

In the present study, we concern laser induced heat generation and its effect on lubricant depletion on the multilayer disk structure. A mathematical model is applied to explore the local laser heating from the point of view of the interaction between the disk media and the electromagnetic wave. The absorption rate of optical energy in each layer of disk structure is derived from the Maxwell equations, which is incorporated into the energy equation by a source term. We simulate the unsteady heat transfer and lubricant depletion processes on a multilayer disk structure. The effect of multi-cycle heating on the lubricant depletion is investigated. Comparison between the present results and those obtained by applying a heat flux boundary condition is also made. The present simulations provide useful information on the media structure design of hard disk drives in heat assisted magnetic recording.     

超声速旋转火箭弹气动特性仿真和分析

采用CFD方法,基于剪切应力输运（Shear Stress Transport,SST）湍流模型,求解大长细比卷弧翼火箭弹在超声速情况下的气动力和气动热问题．对火箭弹流场进行数值计算,与实验数据进行对比．采用薄壁模型模拟结构耦合传热,计算在一定海拔和旋转情况下火箭弹的气动加热,并与不旋转的情况进行对比．计算结果表明该数值方法能较好地计算气动力因数和气动热分布．在特定的低转速和海拔情况下的火箭弹温度分布比不旋转的稍微大一点,在旋转情况下的火箭弹尾部截面压力分布不对称,尾部流线更加紊乱;弹头和尾翼前缘温度较高,应当在火箭弹设计中予以考虑．     

A mixed finite element method for boundary flux computation

Most finite element schemes for thermal problems estimate boundary heat flux directly from the derivative of the finite element solution. The boundary flux calculated by this approach is typically inaccurate and does not guarantee a global heat balance.In this paper we present a mixed finite element method for calculating the boundary flux and show the superiority of this method through numerical examples of both diffusion and advection-diffusion problems.     

基于光滑粒子流体动力学方法的交互式水流加热仿真

针对传统水流加热仿真中交互困难与效率低下的问题,提出一种基于光滑粒子流体动力学(SPH)的热运动仿真方法,旨在交互式控制水流加热变化过程。首先,基于SPH方法将连续水流粒子化,以粒子群模拟水流的运动,并通过碰撞检测方法将粒子运动限定在容器内;然后,采用第一类边界条件的热传导模型加热水粒子,并根据粒子的温度更新粒子的运动状态,以模拟加热过程中水流的热运动;最后,定义可编辑的系统参数与约束关系,通过人机交互仿真多种条件下水流加热及其运动过程。以太阳能热水器加热仿真为例,通过修改少量参数控制热水器的加热工作验证了SPH方法求解热传导问题时的交互性与高效性,为交互式水流加热在其他虚拟场景的应用提供了便利。     

Bluntness impact on performance of waverider

Waverider serves as a good candidate for hypersonic vehicles, especially for high lift-to-drag ratio aircraft. Restricted by aerodynamic heat and manufacture techniques, the sharp leading edge of waverider needs to be blunted. In order to study the blunt leading edge’s influences on the waverider, computational fluid dynamics tools are used to study the aerodynamic and aero-thermodynamic property of waverider with different blunt radii. The numerical methods are validated by test case and empirical formula. Numerical simulations show that blunting the leading edge could reduce the maximum heat flux effectively, but it also degrades the aerodynamic performances. When the blunt radius increases, the aerodynamic performance degrades significantly, while the heat flux wears off. With a fixed blunt radius, the aerodynamic performance mainly depends on the angle of attack; while the heat flux is less affected by the angle of attack. When designing waverider, the influence of bluntness on aerodynamic force and heat flux should be considered synthetically and the optimal balance point needs to be determined.     

Interactive design of large end rings on stiffened conical shells using composites

Design study methods and results are presented of a composite reinforced base ring for the conical aeroshell structure of the planetary lander vehicle for Project Viking, an unmanned mission to Mars. The aeroshell is a ring and stringer-stiffened conical shell structure having a half angle of 70° with a large base ring mounted at the outer edge of the cone and a large pay-load ring in the interior with many smaller rings spaced along the inside shell surface. The purpose of the structure is to develop the aerodynamic drag required to decelerate the lander in the Mars atmosphere to facilitate a soft landing. The shell, therefore, must be designed to resist external pressure loads during Martian entry. Unlike conventional shell structures, the Viking aeroshell has no connecting supports at its large diameter edge and, therefore, it must resist the external pressure as an unsupported inertially loaded shell. Very little design information is available on large shell structures under these loading conditions. The structural weight of the aeroshell must be reduced to the minimum possible level while still retaining structural integrity. A currently proposed design for this structure is all metal, and the base ring accounts for 41 per cent of the total aeroshell structural weight. One possible method of reducing the weight of the proposed design is to selectively apply filamentary composites to reinforce a redesigned base ring. The filamentary reinforced base ring must be designed to take into account all possible modes of failure under the maximum design load conditions. The possible modes of failure are local or general buckling of the shell, ring buckling, and exceedence of the maximum permissible stress levels.The design of a shell structure of this complexity requires the use of the latest technology available in a large general purpose shell buckling program. A large general purpose non-linear shell buckling program developed by Lockheed (BOSOR 2) was used. Since the amount of computational effort is considerable for such a study, the turnaround time for using such a program as an aid in the design process was reduced by adapting the program to an interactive real time graphical system using the facilities of the Langley Research Center CDC computer complex.This paper describes the shell structure model and the stability results of a large Langley Research Center Viking aeroshell model, the BOSOR 2 computer program and its adaptation to an interactive system, and the design strategy used to re-design the base ring and the weight savings achieveable by composite reinforcements.     

基于有限元模拟的薄膜热流计结构设计及优化

精确的热流测量对航空航天领域发动机设计及使用过程至关重要.薄膜热流计以其体积小、热容量小、干扰小、不破坏部件表面气流等显著优势,成为发动机热端部件表面热流测量的新方法.针对传统工程经验设计薄膜热流计精确度不高且迭代耗时长的缺点,基于有限元仿真模拟方法,建立了一种薄膜热流计有限元分析模型,综合分析了热流密度、热阻层厚度、热电堆厚度等因素对热流计冷热结点温度梯度的影响,提出薄膜热流计优化思路.分析结果表明,优化后的薄膜热流计具有更出色的热学性能与电学性能.