Observations and predictions of secondary neutrons on Space Shuttle and aircraft.

The Cosmic Radiation Effects and Activation Monitor has flown on six Shuttle flights between September 1991 and February 1995 covering the full range of inclinations as well as altitudes between 220 and 570 km, while a version has flown at supersonic altitudes on Concorde between 1988 and 1992 and at subsonic altitudes on a SAS Boeing 767 between May and August 1993. The Shuttle flights have included passive packages in addition to the active cosmic ray monitor which comprises an array of pin diodes. These are positioned at a number of locations to investigate the influence of shielding and local materials. Use of both metal activation foils and scintillator crystals enables neutron fluences to be inferred from the induced radioactivity which is observed on return to Earth. Supporting radiation transport calculations are performed to predict secondary neutron spectra and the energy deposition due to nuclear reactions in silicon pin diodes and the induced radioactivity in the various scintillator crystals. The wide variety of orbital and atmospheric locations enables investigation of the influence of shielding on cosmic ray, trapped proton and solar flare proton spectra.     

Secondary radiation environments in heavy space vehicles and instruments.

Secondary radiations produced by the interactions of primary cosmic rays and trapped protons with spacecraft materials and detectors provides an important, and sometimes dominant, radiation environment for sensitive scientific instruments and biological systems. In this paper the success of a number of calculations in predicting a variety of effects will be examined. The calculation techniques include Monte Carlo transport codes and semi-empirical fragmentation calculations. Observations are based on flights of the Cosmic Radiation Environment and Activation Monitor at a number of inclinations and altitudes on Space Shuttle. The Shuttle experiments included an active cosmic-ray detector as well as metal activation foils and passive detector crystals of sodium iodide which were counted for induced radioactivity soon after return to earth. Results show that cosmic-ray secondaries increase the fluxes of particles of linear energy transfer less than 200 MeV/(gm cm-2), while the activation of the crystals is enhanced by about a factor of three due to secondary neutrons. Detailed spectra of induced radioactivity resulting from spallation products have been obtained. More than a hundred significant radioactive nuclides are included in the calculation and overall close agreement with the observations is obtained.     

Galactic cosmic ray gradients in the ecliptic plane and at high latitudes during two solar cycles (meteorite data)

Results of investigations of cosmogenic isotope radioactivity in chondrites fallen to earth during two solar cycles are presented. The data obtained on radial and latitudinal gradients cover the period 1955–1976, heliocentric distances from 1.03 AU to 3.33 AU, and heliographic latitudes from 23°S to 16°N. The dependence of radial and latitudinal gradients on the phase of solar activity is established, as well as a north-south asymmetry during a certain period after the inversion of the general solar magnetic field in 1969.     

Atmospheric electrical conductivity measurements and modeling for application to air pollution studies

The experimentally measured ground level atmospheric electrical conductivity is validated from a simplified ion–aerosol model for which the inputs are ionization rate from surface radioactivity, aerosol density and meteorological parameters. Also estimated from the model is the reduction in conductivity for assumed aerosol levels. It is seen that for an increase of ambient aerosols by threefold the percent reduction in conductivity is 7% and it is 10% for an increase by sixfold. Thus, the variations in the measured ground level conductivity can be used to examine the atmospheric pollution, if any.     

Comparison of model predictions with LDEF satellite radiation measurements.

Some early results are summarized from a program under way to utilize LDEF satellite data for evaluating and improving current models of the space radiation environment in low Earth orbit. Reported here are predictions and comparisons with some of the LDEF dose and induced radioactivity data, which are used to check the accuracy of current models describing the magnitude and directionality of the trapped proton environment. Preliminary findings are that the environment models underestimate both dose and activation from trapped protons by a factor of about two, and the observed anisotropy is higher than predicted.     

Experimental verification of particle distributions in proton-induced cascades.

Predictions of shielding requirements, levels of induced radioactivity and of radiation damage around high-energy accelerators require accurate simulation of the physics of proton-induced cascades from energies above the TeV to energies below the eV region. Experimental studies of cascades using activation detector, dosimeter and counter techniques provide valuable data for validating simulation procedures and for extrapolating the required accelerator design parameters directly. Such studies include the yields of low-energy secondary neutrons in proton-nucleus interactions, the spatial distribution of hadrons, low-energy neutrons and energy deposition close to the core of proton cascades and measurements at large lateral depths in shields. This paper describes some of these measurement and compares them with the predictions made by Monte-Carlo simulations.     

国内地面放射性测量模型标准装置的量值比对

核工业放射性勘查计量站于2015年组织西南、中南、华南和华东四家计量站实施了国内地面放射性测量模型标准装置的量值溯源比对,比对模型为核工业放射性勘查计量站的地面模型。从比对测量结果归一化偏差分析,仅有个别仪器在钾含量较低的YM1和钾含量存在争议的YM3模型的归一化偏差大于1,说明比对过程严谨、比对方法正确、结果可信。从比对测量结果与标称值比较分析,仍是YM1和YM3模型的钾含量相对偏差超过5%,其他均在8%不确定度之内,说明核工业放射性勘查计量站的地面模型量值稳定。     

Be-7 nuclei produced by galactic cosmic rays and solar energetic particles in the earth''s atmosphere

Be-7 radioactive nuclei with a half-life of 53.3 days result from spallation reactions of galactic cosmic rays(GCR) and solar energetic particles (SEP) with N and O nuclei in the Earth's atmosphere. We calculate the average global production of Be-7 in the atmosphere by GCR and SEP The result indicates that an intense SEP event produces a large amount of Be-7 in the polar stratosphere and part of them could be transported to the surface at lower latitudes. The ground-level measurement of Be-7 in Japan exhibits the possibility of enhancement in the Be-7 radioactivity associated with the intense SEP event on July 14, 2000. In addition, the present experiment shows seasonal variations in the surface Be-7 concentration which peaks in spring and autumn. We discuss the possible air mass mixing between the stratosphere and troposphere to explain the measured seasonal variations. The surface concentration of Pb-210 nuclei indicates a similar trend to that of Be-7 and we suggest two possible explanations.     

Simulations of an accelerator-based shielding experiment using the particle and heavy-ion transport code system PHITS.

In order to estimate the biological effects of HZE particles, an accurate knowledge of the physics of interaction of HZE particles is necessary. Since the heavy ion transport problem is a complex one, there is a need for both experimental and theoretical studies to develop accurate transport models. RIST and JAERI (Japan), GSI (Germany) and Chalmers (Sweden) are therefore currently developing and bench marking the General-Purpose Particle and Heavy-Ion Transport code System (PHITS), which is based on the NMTC and MCNP for nucleon/meson and neutron transport respectively, and the JAM hadron cascade model. PHITS uses JAERI Quantum Molecular Dynamics (JQMD) and the Generalized Evaporation Model (GEM) for calculations of fission and evaporation processes, a model developed at NASA Langley for calculation of total reaction cross sections, and the SPAR model for stopping power calculations. The future development of PHITS includes better parameterization in the JQMD model used for the nucleus-nucleus reactions, and improvement of the models used for calculating total reaction cross sections, and addition of routines for calculating elastic scattering of heavy ions, and inclusion of radioactivity and burn up processes. As a part of an extensive bench marking of PHITS, we have compared energy spectra of secondary neutrons created by reactions of HZE particles with different targets, with thicknesses ranging from <1 to 200 cm. We have also compared simulated and measured spatial, fluence and depth-dose distributions from different high energy heavy ion reactions. In this paper, we report simulations of an accelerator-based shielding experiment, in which a beam of 1 GeV/n Fe-ions has passed through thin slabs of polyethylene, Al, and Pb at an acceptance angle up to 4 degrees.     

航电设备故障诊断中的决策算法

设计了故障诊断专家系统中的多属性决策算法.分析了诊断决策算法对诊断效率的影响.根据各属性对诊断决策的影响,对属性值进行规范化.采用线性加权函数来评价各故障的优先级,利用对故障发生概率的偏好性求解各属性权值.设计修正向量对评价函数进行修正以满足它在属性边界点上跳变特性.通过实验分析了该多属性决策算法在不同情况下对诊断效率的提高程度.      

导弹中制导末段的最优搜索

研究超视距导弹中制导末段利用导弹的剩余动力,自动搜索活动目标,使目标捕捉概率达到最大的最优搜索问题.给出了活动目标的位置概率分布;提出了基于活动目标位置概率分布的导弹搜索航线的规划方法;拟订了搜索系统的组成方案并对系统进行了设计;对该系统进行了仿真,验证它的活动目标的捕捉概率.     

应用免疫遗传算法优化设计层合板铺层顺序

应用遗传算法对复合材料层合板的铺层顺序进行优化设计,并通过免疫机理解决基本遗传算法中存在的收敛效率低、"早熟"等问题.以层合板的面内几何因子和弯曲因子为优化对象,建立遗传算法的优化模型.通过交叉、变异等遗传操作,搜索问题的最优解.借助免疫系统对抗体的促进和抑制机制,调节种群中个体的多样性.数值算例中给定了层合板的面内几何因子和弯曲因子,应用免疫遗传算法求解层合板的最佳铺层顺序.并将应用免疫遗传算法与标准遗传算法得到的优化结果进行了比较,证明了免疫遗传算法的优越性和实用性.     

对地观测卫星有限推力快速轨道机动优化方法

研究了对地观测卫星在有限推力作用下,快速轨道机动到目标区域上空的优化算法.分析了任务需求并选取两次点火的变轨方法,使算法更具普适性.推导出考虑J2摄动的三维空间的有限推力动力学方程.使用Lambert方法确定有限推力时间变量的取值范围,并在此基础上使用遗传算法进行优化,最终得到时间最优意义的优化结果.通过一个算例对整个优化算法做了验证.结果表明该算法精度高、计算时间短,适用于快速轨道机动任务.      

气动式座舱压力调节系统稳定性的分析与优化

为了解决气动式座舱压力调节系统装配飞机时出现的座舱压力波动现象,分析了座舱压力控制系统的组成,根据余压段实际参与压力调制的组件,对控制系统进行了简化,以此为例分析系统的稳定性。首先对系统中的非线性环节进行了详细分析,得到其描述函数和负导描述函数曲线。比较了小孔-气容结构在常压、小幅充放气条件下的过渡过程,发现在该使用条件下的充放气时间基本相等,据此将小孔-气容结构的传递函数建模为一阶环节,指出了二者的相同及不同之处。使用描述函数的方法对系统的稳定性进行判断,提出了实现稳定的可行性方法。全物理仿真结果表明,使用该方法可使座舱压力调节系统的性能达到规范所要求的指标。      

区域覆盖特殊椭圆轨道星座优化设计

分析了椭圆轨道的优良特性,它可集中覆盖地面上某一指定纬度带或区域.阐述了临界倾角太阳同步回归轨道这种特殊椭圆轨道的设计方法,总结了其轨道要素的计算步骤.探讨了临界倾角太阳同步回归轨道星座的设计思路,指出了影响星座对目标覆盖性能的关键参数是各个卫星通过目标上空的时刻.介绍了用遗传算法进行星座优化设计的数学模型,利用遗传算法进行了优化设计.讨论了优化结果的统计规律,符合该规律的星座就是本文所研究的特殊椭圆轨道星座,星座性能分析结果表明这种星座适用于区域覆盖.      

一种复杂系统风险概率评估方法

对有限样本条件下的复杂系统风险发生概率评估问题,提出了小样本评估小概率事件的建模方法,通过非线性函数逼近累积概率与临界参数极值之间的映射关系.建立了风险概率评估数学模型,通过非线性回归方法得到了风险概率评估基本模型.对原始数据在评估模型中产生的误差作为目标函数,建立概率评估优化模型.并采用改进遗传算法对分布参数进行优化计算.以飞行安全为例,实现了有限样本情况下的飞行风险概率的计算,并通过最优逼近函数提高了计算精度.      

民用飞机驾驶舱构型快速设计方法

为在方案设计阶段提高民用飞机总体方案的设计质量和形成效率,研究了民用飞机驾驶舱构型的设计措施,并在一个开放式的飞机总体设计环境中实现了这一功能.定义了飞机机身坐标系,研究了确定驾驶员设计眼位、驾驶舱布置和风挡参数化设计与模型构建的方法.建立了交互式民机驾驶舱构型二、三维快速设计环境.在此基础上,实现了驾驶舱模型的自动化调整,为总体设计阶段进行多学科设计优化奠定了基础.通过设计实例证明了该方法的有效性.     

高可靠性航空电子设备热分析中的有限体积法

阐述了热对系统可靠性的影响,对比了数值法求解温度场分布的优缺点.针对航空电子设备热分析中同时要求满足高的分析精度和快的计算速度的问题,提出用有限体积法求解温度场分布的计算方法.根据典型航空电子设备的结构特点,建立了温度场的数学模型,给出了边界条件.在此基础上,用有限体积法对待求解方程离散化,给出了离散化过程中网格划分及边界的处理方法.结合实例进行了温度场求解,计算结果与热测量结果进行了对比,得到了较高的分析精度,验证了方法的有效性.最后对计算误差进行了分析,并提出了进一步热设计的合理化建议.      

某飞艇纵向气动估算及试验验证

针对某一具体的飞艇,在缺少风洞吹风数据的情况下,利用现有气动力手册中的工程估算公式,对飞艇作了气动力估算;采用飞艇的小扰动线化方程,进行本体特性分析.飞艇的小扰动线化方程从低速飞机的线化小扰动方程获得.在Matlab软件中的simulink工具箱中,进行了PID控制律的数字仿真;通过反复迭代循环,观察系统的时域响应,根据最后的响应结果,设计了其定高飞行的控制律;最后进行了真实的飞行试验.试验完成了飞艇自主远距离往返飞行,共飞行时间达20?min,指令飞行高度为300?m.将试验和理论结果进行比较,吻合较好,表明高度控制律设计合理,气动估算可行,有实用价值.     

矩形通道内气膜出流对内换热的影响规律

研究对象为矩形通道,包括2个直肋和9个气膜孔,主要研究气膜的出流比、开孔率对通道内换热的影响,温度场的测量采用了热色液晶测温技术.实验发现气膜出流对换热有强化作用,气膜孔对通道平均换热影响也与其在肋间的位置有关,其中肋后孔的影响最大.在不同的雷诺数下,开一个气膜孔时,出流比在6%~8%之间通道壁面内换热效果最好,低雷诺数下增强换热的效果显著;研究孔边的换热规律发现,在孔下游换热明显增强,从孔边到下游5倍孔直径处,强化换热比在1.1倍以上;此外还研究了开孔率对增强换热的影响规律.