灾害性雨雪天气之后的回顾与思考

(一)2008年春节前后,华东大部分地区发生数十年一遇的大面积连续雨雪天气。其中安徽、江苏中到大雪,上海小到中雪至大雪,南昌数日冻雨,杭州大到暴雪,宁波大雪,温州连续十多天降雨。受此影响,合肥、南京、南昌、上海浦东及虹桥机场几度关闭,杭州、宁波机场时开时闭。大面积航班受影响,空管保障受到严重挑战。     

应对极端灾害天气 加强春运气象服务

近期,我国部分地区受大范围的低温、降雪和冻雨的影响,交通运输出现阻滞,高速路关闭,铁路运输受阻,民航系统千余架次的航班被迫取消,数千架次的航班被迫延误,中南、西南、华东部分机场间歇性关闭。     

浅谈做好风沙天气下的气象观测工作

银川河东机场地处内陆,干旱少雨,多风沙天气是本场最突出的气候特征之一,也是对本场航班正常与飞行安全影响最大的天气现象之一。据2007年资料统计本场出现能见度低于10000米的天气现象共295天次,其中风沙天气占105天次,而沙尘暴天气占5天次,风沙天气占复杂天气总数的36％。因此如何做好风沙天气条件下的气象观测服务工作,一直是我们面对的重要课题。     

空间天气科学与有效和平利用空间

空间天气科学是一门新兴的前沿交叉科学。文章首先从发展历程、发展现状和发展态势角度对空间天气科学进行了系统介绍,并指出空间天气科学是经济社会发展的"助推器"、助力科技革命的"加速器"和关系空间安全的"倍增器";接着对空间天气科学与有效和平利用空间的关系进行了阐述;最后对我国空间天气科学的发展和对人类的服务前景进行了展望,并给出了制定和实施"国家空间天气十年计划"和"空间天气科学服务和平利用空间国家专项"建议的初步构想。     

临界天气告警及数值预报产品显示系统的设计与应用

天气条件始终是影响航空运行安全和效益的重要因素。据统计,近20年我国民航运输量约按13％的年平均增长率增长,到2006年,国内航班突破150万架次。随着航班量的持续增长,复杂天气对飞行正常的影响日益加剧,天气原因在航班延误事件中约占20％。如何最大限度地减少天气对飞行的影响,帮助航空公司向天气要效益,帮助管制部门应对复杂天气保安全,优质的航空气象服务越来越受到各航空运行单位的关注。     

CTL_88B天气雷达发射机“掉高压”故障分析

引言CTL_88(A、B、C)系列天气雷达是传统713天气雷达的改进型,该系列雷达是大量采用微波固体器件和集成电路为主的数字化天气雷达,具有高稳定性和可靠性。系统采用固定式5cm波段,主要用于探测     

奥运期间合肥机场重要天气背景分析

合肥机场是国家民航总局指定的北京2008奥运会航班的主要备降机场。合肥地处江淮之间,是冷暖空气的交汇之地,天气复杂,奥运时间,正值江淮盛夏,是雷雨、大风等恶劣天气的多发季节,这些天气会对航班的正常起降造成严重影响。因此,提前了解奥运期间内重要天气,及一些可能影响飞行的气象要素发生的背景与分布特点,对保证航班的安全正常,更好地服务奥运十分必要。     

浅析飞行危险天气影响航路飞行区域的划设方法

引言 飞行危险天气是影响航空安全,导致航班延误的首要原因。随着全球航空运输业务量的不断增加,研究在危险天气影响下如何安全、高效地飞行已迫在眉睫。飞行危险天气主要包括：雷暴、低空风切变、飞机颠簸、飞机积冰、大风和视程障碍,其中涉及航路飞行的危险天气主要为雷暴,及伴随其产生的其他天气现象。雷暴是由对流旺盛的积雨云引起的伴有闪电雷鸣的局地风暴,它是积雨云强烈发展的标志。     

大连机场夏季特殊复杂天气分析

引言影响大连机场航空飞行的复杂天气主要包括低云、低能见度、强降水、大风、雷暴和冰雹等强对流天气。当机场处在一定的天气形势和气象条件下时,这些复杂天气会在同一天甚至同一时段内同时出现,形成特殊的复杂天气,严重威胁飞机正常安全起降,影响航班运营正常。降水是指雨、雪、雹等从云中     

一次罕见的冰雪天气过程的分析

冰冻是湖南冬季主要灾害性天气之一．中低层逆温层和地面冷空气是冰冻天气产生的必要条件。2008年1月12日至2月2日是湖南省50年以来遭受最严重的冰冻灾害天气。近年来有一些北方的预报员利用多普勒雷达资料对冰雪天气过程进行了分析研究．但是南方近几年降雪量偏少．预报员缺少用多普勒雷达资料对降雪临近预报的方法和经验。     

一次雨、雪、霰天气的观测

一、充分了解天气背景和发展趋势(一)降雪前首都机场天气背景从2010年3月12日05时(UTC)时开始,首都机场一直维持东南风,风向在110°～140°之间,风速在3～5米/秒之间。同时,云量也在逐步增加,云层不断下沉增厚,到了13日的19:40时以后,首都机场已经是漫天层积云,云底高1200米,且相对湿度也在明显上升。由于云层的夜间保温效应,降雪前,本场地面气温较前几日明显偏高(在2℃以上)。     

Influence of freezing rate oscillations and convection on eutectic microstructure

As discussed in our review paper (Wilcox, W. R. and Regel, L. L., Microgravity Quarterly, 1994, 4, 147–156), the influence of microgravity on eutectic microstructure has been rather erratic and largely unexplained. Directional solidification in microgravity sometimes coarsened the structure, sometimes made it finer, and sometimes, even on the same system, had no measurable effect. Theoretical models predicted no influence of the weak buoyancy-driven convection that occurs in the vertical Bridgman technique on earth. Thus, we hypothesized that freezing rate fluctuations due to irregular convection might be responsible. For example, with a fibrous microstructure an increase in freezing rate must cause new fibers to form, either by branching or by nucleation. A decrease in freezing rate would cause fibers to terminate by overgrowth of the matrix phase. If the kinetics of fiber formation differs from that for fiber termination, an oscillatory freezing rate would cause the average fiber spacing to deviate from that at a steady freezing rate. We have been investigating this hypothesis both experimentally and theoretically. Vertical Bridgman experiments were performed on the MnBi–Bi eutectic with freezing rate oscillations caused by periodic electric current pulses passed through the material. With increased current amplitude, more and more grains exhibited irregular microstructures. Of the grains with continued quasi-regular rod structure, the microstructure became finer. This result was contrary to that expected from our hypothesis for this system. Numerical modeling also predicted that an oscillatory freezing rate should yield a finer microstructure. It was also predicted that freezing interface oscillations should cause the average melt composition at the freezing rate to deviate from the eutectic. This results in the formation of a composition boundary layer of sufficient thickness that it would become sensitive to convection. Hence we have arrived at a revised hypothesis. On earth, irregular convection causes freezing rate fluctuations that change the interfacial melt composition, leading to a thick composition boundary layer. Convection interacts with this boundary layer to change the interfacial melt composition, thereby altering the response of the system to freezing rate fluctuations.     

低冰点推进剂1N单组元发动机技术研究

单组元发动机采用低冰点推进剂具有良好的低温冷起动和工作性能,对于实现航天器的长期在轨驻留、轨道控制和姿态调整具有十分重要的意义。对-30℃低冰点四体系推进剂的特性进行了分析,对低冰点推进剂小推力量级发动机催化分解技术进行了试验研究。试验结果表明,发动机冷起动、关机正常,稳态、脉冲工作稳定,性能可靠。     

On laboratory simulation and the effect of small temperature oscillations about the freezing point and ice formation on the evaporation rate of water on Mars

We report measurements of the evaporation rate of water under Mars-like conditions (CO2 atmosphere at 7 mbar and approximately 0 degrees C) in which small temperature oscillations about the freezing point repeatedly formed and removed a thin layer of ice. We found that the average evaporation at 2.7 +/- 0.5 degrees C without an ice layer (corrected for the difference in gravity on Earth and on Mars) was 1.24 +/- 0.12 mm/h, while at -2.1 +/- 0.3 degrees C with an ice layer the average evaporation rate was 0.84 +/- 0.08 mm/h. These values are in good agreement with those calculated for the evaporation of liquid water and ice when it is assumed that evaporation only depends on diffusion and buoyancy. Our findings suggest that such differences in evaporation rates are entirely due to the temperature difference and that the ice layer has little effect on evaporation rate. We infer that the formation of thin layers of ice on pools of water on Mars does not significantly increase the stability of water on the surface of Mars.     

基于刚体转动四元数模型的航天器再定向方案

介绍了一种新的刚体转动的四元数模型。这些模型可以提高再定向控制的对边界条件的适应能力，在此基础上还介绍了这些模型的一些实际应用。     

Determination of parameters of attitude motion of a small communication satellite using the data of measurements of current of solar panels

A communication satellite (small spacecraft) injected into a geosynchronous orbit is considered. Flywheel engines are used to control the rotational spacecraft motion. The spacecraft after the emergency situation has passed into a state of uncontrolled rotation. In this case, no direct telemetric information about parameters of its rotational motion was accessible. As a result, the problem arose to determine the rotational satellite motion according to the available indirect information: current taken from the solar panels. Telemetric measurements of solar panel current obtained on the time interval of a few hours were simultaneously processed by the least squares method integrating the equations of rotational satellite motion. We present the results of processing 10 intervals of the measurement data allowing one to determine the real rotational spacecraft motion and to estimate the total angular momentum of flywheel engines.     

攻角变化对超音速进气道再起动特性的影响

以二维非定常可压缩流的N-S方程为控制方程,采用SST k-ω湍流模型对攻角变化引起的超音速进气道再起动过程进行了数值模拟,研究了攻角变化对超音速进气道再起动特性的影响.结果表明,当超音速进气道不起动时,可通过合理改变攻角实现进气道的再起动工作;超音速进气道的再起动攻角随攻角变化速率的增大近似呈线性增加;攻角变化速率较...     

多自由度微振动环境时域波形复现的数值仿真

为满足航天器微振动环境模拟的需要,开展了多自由度微振动时域波形复现控制方法研究。首先,介绍了基于时域波形复现的多自由度微振动环境模拟控制理论方法。其次,针对六自由度微振动激励系统,应用MATLAB软件建立了基于实测传递函数矩阵的多输入多输出微振动激励仿真系统,针对微振动时域波形复现闭环控制过程进行了算法编程,并给出了仿真的闭环控制流程图。最后,通过算例对多自由度微振动时域波形复现进行了数值仿真,以给定的白噪声为输入,模拟对实际存在的系统非线性、测量误差等影响因素的控制效果。仿真结果验证了多自由度微振动时域波形复现控制方法的可行性及有效性,所得结论可以为研究多自由度微振动时域波形复现控制系统提供参考。     

On solving the problems of optimization of trajectories of many-revolution orbit transfers of spacecraft

The problem of optimal control over many-revolution spacecraft orbit transfers between circular coplanar orbits of satellites is considered. The spacecraft flight is controlled by a thrust vector of a jet engine with restricted thrust (JERT). The mass expenditure is minimized at a limited time of flight. The optimal control problem is solved based on the maximum principle. The boundary value problem of the maximum principle is solved numerically using the shooting method. A modified computation scheme of the shooting method is suggested (multi-point shooting), as well as a method (correlated with the scheme) of choosing the initial approximation with the use of a solution to the optimization problem in the impulse formulation. The scheme and method allow one to construct many-revolution spacecraft orbit transfers.     

热变形对一种天线指向机构指向精度的影响分析

热变形对天线指向机构的指向精度具有重要影响,但利用传统的设计方法很难实现对指向精度的准确计算,尤其是热变形对指向精度影响的研究工作更是少见。为此建立了机构的三维实体热-结构耦合有限元分析模型,根据有限元分析结果并结合机构的运动链关系,构建了各关键运动副运动误差的计算方法;在此基础上实现了机构指向误差的计算,研究了运动副名义、最大以及最小配合间隙条件下,温度载荷对各关键运动副运动误差和指向精度的影响。研究结果表明,温度载荷对关键运动副的运动误差以及机构的指向精度具有重要影响,随着温度载荷偏离常温数值的增加,指向误差不断增大,名义配合间隙条件下的指向误差最大。