特殊天气条件下的签派放行

恶劣气象条件对航空安全运行产生重要影响,如冬季的大雾(低能见度)、大风、低温等,尤其冰雪天气对航空安全运行危害最大。中国民用航空规章CCAR121.649款规定:当有霜、雪或冰附着在飞机机翼、操纵面、螺旋桨、发动机进气口或其他重要表面上,任何人不得使飞机起飞。但是2004年1月21日发生的一起空难再一次让我们震惊:东方航空公司一架CRJ-200飞机执行包头至上海航班,飞机起飞后不久     

Spatial fragmentation of solar flare plasma and beams

The observational and theoretical arguments for spatial fragmentation of the bulk of the thermal and non-thermal components of solar flare plasma are summarised. Observational aspects considered include XUV filling factors, EUV centre to limb variations, andH impact polarisation. Theoretical points addressed are the high flare inductance and beam/return current closure at the acceleration site.A high degree of beam/plasma filamentation implies strong transverse temperature gradients so that cross-field conduction must be included in energy transport modelling. Preliminary results are described for a simple two-component model.     

Lithium-ion cell performance under environmental extremes

High energy density, lithium secondary cells are very attractive for use in many future military applications. However, a number of technical challenges remain. Specifically, the development and qualification of a system capable of withstanding the harsh environmental conditions encountered during normal and abnormal zones of operation. This paper focuses on the environmental extremes that the Eagle-Picher lithium-ion system has tested to date. Emphasis is placed on low temperature performance, high temperature performance, power capability, and cycle life at these extremes. Other areas including safety and environmental issues have also been investigated     

The solar flare plasma: Observation and interpretation

In the past several years, X-ray observations of the Sun made from rockets and satellites have demonstrated the existence of high temperature (20 × 10⁶ – 100 × 10⁶ K), low density plasmas associated with solar flare phenomena. In the hard X-ray range ( < 1 ), spectra of the flaring plasma have been obtained using proportional and scintillation counter detectors. It is possible from these data to determine the evolution of the hard X-ray flare spectrum as the burst progresses; and by assuming either a non-thermal or thermal (Maxwellian) electron distribution function, characteristic plasma parameters such as emission measure and temperature (for a thermal interpretation) can be determined. Thermal interpretations of hard X-ray data require temperatures of 100 × 10⁶ K.In contrast, the soft X-ray flare spectrum (1 <<30 ) exhibits line emission from hydrogen-like and helium-like ions, e.g. Ne, Mg, Al, Si,... Fe, that indicates electron energies more characteristic of temperatures of 20 × 10⁶ K. Furthermore, line intensity ratios obtained during the course of an event show that the flare plasma can only be described satisfactorily by assuming a source composed of several different temperature regions; and that the emission measures and temperatures of these regions appear to change as the flare evolves. Temperatures are determined from line ratios of hydrogen-like to helium-like ions for a number of different elements, e.g., S, Si, and Mg, and from the slope of the X-ray continuum which is assumed to be due to free-free and free-bound emission. There is no obvious indication in soft X-ray flare spectra of non-thermal processes, although accurate continuum measurements are difficult with the data obtained to date because of higher order diffraction effects due to the use of crystal spectrometers.Soft X-ray flare spectra also show satellite lines of the hydrogen-like and helium-like ions, notably the 1s ²2s ² S-1s2s2p ² P transition of the lithium-like ion, and support the contention that in low density plasmas these lines are formed by dielectronic recombination to the helium-like ion. Also, series of allowed transitions of hydrogen-like and helium-like ions are strong, e.g., the Lyman series of S up to Lyman-, and ratios of the higher member lines to the Lyman- line can be compared with theoretical calculations of the relative line strengths obtained by assuming various processes of line formation.This review will discuss the X-ray spectrum of solar flares from 250 keV to 0.4 keV, but will be primarily concerned with the soft X-ray spectrum and the interpretation of emission lines and continuum features that lie in this spectral range.     

High-resolution observations of Hα flare regions

This paper gives a review of the recent high-resolution H observations of solar flares and flare-productive active regions. From studies of the morphological and evolutional features of H flare emitting regions, two types of two-ribbon flares, which are termed separating two-ribbon flare and confined two-ribbon flare, are discussed. The former is characterized by conspicuous separating motions or expanding motions of the H two ribbons, whereas the latter shows only a short range of or no separating motions of the two ribbons. The explosive compact flares, which occur in some compact newly-emerging flux regions, are also discussed.Attention is paid to the successive and impulsive brightenings of H flare points which form the H flare kernels and the front lines of H two ribbons at the impulsive phases of flares. Temporal relationships between H line intensities or profiles and hard X-ray or microwave emissions are discussed to discriminate the energy transport mechanisms in the flare loops.H monochromatic image of high spatial resolution, at the present time, is the most sensitive detector for finding the first appearance of newly-emerging magnetic flux region and the developing features of sheared configuration of magnetic field, both of which are the key factors in flare energy build-up processes. It is suggested that the successive emergence of a twisted magnetic flux rope might be essential for the production of a major flare.Contributions from the Kwasan and Hida Observatories, Kyoto University, No. 292.     

Forming limit and failure behavior of fiber metal laminates under low-constraint conditions

Fiber Metal Laminates(FMLs), as high-performance composite materials, demonstrate exceptional potential in a wide range of applications, such as aeronautical and astronautical industries. However, the traditional cured FMLs possess complex interlayer stresses and low forming limits, restricting further promotion and application of FMLs. Low-constraint FMLs exhibit a lower forming resistance and better formability due to no curing during the forming process; however, the formation mechanism and response are not clear. This paper presents the Forming Limit Diagram(FLD) of low-constraint GLARE(glass fiber reinforced aluminum laminates) based on the forming limit test, and compares it with the conventionally cured laminates to evaluate the differences in the forming limit. In addition, combined with the analysis of failure mechanism and micro-deformation mechanism of specimens, the influence of different temperatures(20–80 °C)and forming states(width) on the deformation performance of laminates is further explored. The results reveal that the forming limit curve of low-constraint laminates shifts up with the increase of temperature, the forming limit initially increases with the increase of width, then followed by a gradual decrease, and the maximum principal strain of low-constraint laminates is increased by29% at 80 °C compared to 20 °C. The cured laminate has a principal strain range of 0–0.02, while the low-constraint laminates have a principal strain range of 0.03–0.14. Compared with cured laminates, low-constraint laminates possess a higher forming limit due to the improvement in deformable degree between layers by resin flow and fiber slippage, which enhances their formability.This study is expected to serve as a reference for establishing forming limit criteria and optimizing forming schemes for low-constraint laminates.     

Coordinated optical and Yohkoh observations of 26 June 1992 flare loops

Optical spectra of large flare loops were detected by the Ondejov Multichannel Flare Spectrograph (MFS) during coordinated observations with MSDP at Pic du Midi (H) and the soft X-ray telescope (SXT) on Yohkoh. The CCD video images taken by the MFS slit-jaw camera document the time-development of the flare loops as seen through the H filter. Preliminary analysis of the MSDP images shows the intensity structure of the cool flare loops and their velocity fields. From the spectra we can clearly see the intensity variations along the cool loops. SXT images show the structure of hot X-ray loops similar to that of cool loops. Special attention is devoted to the bright tops, simultaneously observed in X-rays, H and other optical lines. Based on a preliminary analysis of the optical spectra, we speculate about possible mechanisms leading to an observed bright emission at the tops of cool loops. We suggest that direct soft X-ray irradiation of cool loops at their tops could be, at least partly, responsible for such a strong brightening.     

Residual stresses and endurance strength under tension-compression in the conditions of stress concentration

Residual stresses and endurance strength of specimens with stress concentrators are considered. The results obtained make it possible to predict the fatigue limit of strengthened parts with concentrators in the case of tension-compression.     

Aircraft nonlinear stability analysis and multidimensional stability region estimation under icing conditions

Icing is one of the crucial factors that could pose great threat to flight safety,and thus research on stability and stability region of aircraft safety under icing conditions is significant for control and flight.Nonlinear dynamical equations and models of aerodynamic coefficients of an air craft are set up in this paper to study the stability and stability region of the aircraft under an icing condition.Firstly,the equilibrium points of the iced aircraft system are calculated and analyzed based on the theory of differential equation stability.Secondly,according to the correlation theory about equilibrium points and the stability region,this paper estimates the multidimensional stability region of the aircraft,based on which the stability regions before and after icing are compared.Finally,the results are confirmed by the time history analysis.The results can give a reference for stability analysis and envelope protection of the nonlinear system of an iced aircraft.     

Comprehensive modeling of ignition and combustion of multiscale aluminum particles under various pressure conditions

The ignition and combustion of aluminum particles are crucial to achieve optimal energy release in propulsion and power systems within a limited residence time.This study seeks to develop theoretical ignition and combustion models for aluminum particles ranging from 10 nm to 1000 μm under wide pressure ranges of normal to beyond 10 MPa.Firstly,a parametric analysis illustrates that the convective heat transfer and heterogeneous surface reaction are strongly influenced by pres-sure,which directly affects the ignition process.Accordingly,the ignition delay time can be corre-lated with pressure through the pb relationship,with b increasing from-1 to-0.1 as the system transitions from the free molecular regime to the continuum regime.Then,the circuit comparison analysis method was used to interpret an empirical formula capable of predicting the ignition delay time of aluminum particles over a wide range of pressures in N2,O2,H2O,and CO2 atmospheres.Secondly,an analysis of experimental data indicates that the exponents of pressure dependence in the combustion time of large micron-sized particles and nanoparticles are-0.15 and-0.65,respec-tively.Further,the dominant combustion mechanism of multiscale aluminum particles was quan-titatively demonstrated through the Damköhler number(Da)concept.Results have shown that aluminum combustion is mainly controlled by diffusion as Da＞10,by chemical kinetics when Da ≤ 0.1,and codetermined by both diffusion and chemical kinetics when 0.1＜Da ≤ 10.Finally,an empirical formula was proposed to predict the combustion time of multiscale aluminum particles under high pressure,which showed good agreement with available experimental data.     

考虑预设性能约束的运输机姿态容错控制

针对运输机舵面故障情况下的姿态容错控制问题,提出了一种考虑预设性能约束的自适应指令滤波增量反步(Adaptive Command-filtered Incremental Backstepping,ACFIBS)容错控制器。首先,构造运输机故障模型,在反步控制设计结构下,通过构造预设性能函数,保证外回路姿态角跟踪误差的动态性能。然后,考虑舵机偏转速率和幅值限制,引入受限指令滤波器和补偿信号,综合考虑气动参数不确定性,采用增量方法设计反步内环控制律。在此基础上,进一步考虑舵面故障情况,引入自适应方法及低通滤波器改进增量反步控制器。最后,通过理论推导和仿真试验验证了控制方法的有效性。仿真结果表明,所设计的控制器具有良好的容错性能,在不同舵面故障条件下均可实现对指令信号的预设性能跟踪,且在参数摄动情况下具有较强的鲁棒性。     

火场中电梯疏散失败的FTA分析与探讨

通过对火灾导致电梯疏散失败的故障树的建立与分析,计算了导致顶事件发生的最小割集与最小径集,以及影响顶事件发生的结构重要度和割集重要度。并由此提出了火灾情况下降低电梯运行风险,提高可靠性的相关措施。为火灾情况下利用电梯进行疏散的可靠性提供了参考依据。     

Synthesis of nonlinear nonstationary control systems by output under conditions of uncertainty

A problem of synthesizing the control laws for nonlinear nonstationary control systems by output being measured under uncertain external actions and nonlinearities that meet the sector constraints is considered.     

Dynamic temperature prediction of electronic equipment under high altitude long endurance conditions

Unmanned Aerial Vehicle (UAV) is developing towards the direction of High Altitude Long Endurance (HALE). This will have an important influence on the stability of its airborne electronic equipment using passive thermal management. In this paper, a multi-node transient thermal model for airborne electronic equipment is set up based on the thermal network method to predict their dynamic temperature responses under high altitude and long flight time conditions. Some relevant factors are considered into this temperature prediction model including flight environment, radiation, convection, heat conduction, etc. An experimental chamber simulating a high altitude flight environment was set up to survey the dynamic thermal responses of airborne electronic equipment in a UAV. According to the experimental measurement results, the multi-node transient thermal model is verified without consideration of the effects of flight speed. Then, a modified way about outside flight speed is added into the model to improve the temperature prediction performance. Finally, the corresponding simulation code is developed based on the proposed model. It can realize the dynamic temperature prediction of airborne electronic equipment under HALE conditions.     

Simulation of heat and mass transfer in composite heat protective materials under high temperature conditions

We present a mathematical model, worked out on the basis of the law of binder composite material (CM) decomposition suggested by authors for numerical solution of the heat and mass transfer problems in the heat protective CM under conditions of aero-gas-dynamic heating. The model makes it possible not to consider hard-realizable chemical kinetics of the binder decomposition and can practically be applied to any CM under high temperature conditions. Numerical examples are given.     

Experimental and numerical study of chaff cloud kinetic performance under impact of high speed airflow

To solve the kinetic and diffusion problem of surface-type infrared decoy, multi-chaff kinetic models are established and chaff cloud holistic kinetic performance are analyzed under the impact of high speed airflow in this work. Chaffs rotate rapidly during the motion under the impact of high speed airflow. The rotation speed is correlated with lift, position of pressure center and aerodynamic damping. Computational Fluid Dynamics (CFD) is used to compute the aerodynamic coefficients of chaff. It is found that there exists serious aerodynamic interference which mainly relates to the overlapping area and distance among chaffs during the diffusion of chaff cloud. The chaff wind tunnel test and rocket sled experiment are carried out to verify the credibility of the models in this work. Then, the variation of chaff cloud expectation and extremum are analyzed to achieve the holistic kinetic and diffusing performance of chaff cloud. Simulation results demonstrate that the chaffs diffuse rapidly under the impact of high speed airflow and chaff cloud can be formed rapidly within 0.5?s. The shape of the chaff cloud is similar to cone that forms a certain angle with the horizontal plane and most chaffs focus on the second half.     

Experiments on unsteady vortex flowfield of typical rotor airfoils under dynamic stall conditions

A new experiment for airfoil dynamic stall is conducted by employing the advanced particle image velocimetry(PIV) technology in an open-return wind tunnel. The aim of this experimental investigation is to demonstrate the influences of different motion parameters on the convection velocity, position and strength of leading edge vortex(LEV) of airfoil under different dynamic stall conditions. Two different typical rotor airfoils, OA209 and SC1095, are measured at different free stream velocities, oscillation frequencies, and angles of attack. It is demonstrated by the measured data that the airfoil with larger leading edge radius could notably decrease the strength of LEV. The angle of attack(Ao A) of airfoil can obviously influence the dynamic stall characteristics of airfoil,and the LEV would be effectively inhibited by decreasing the mean pitch angle. In addition, the convection velocity of LEV is estimated in this measurement, and the results demonstrate that the influence of airfoil shape on convection velocity of LEV is limited, but the convection velocity of LEV would be increased by enlarging the oscillation frequency. Meanwhile, the convection velocity of LEV is a time variant value, and this value would increase as the LEV convects to the trailing edge of airfoil.     

Surface protection by shielding from a hot source under conditions of free convection

In this paper, one way of heat protection from hot elements of the ground-based power-driven high-temperature gas turbine plant case have been experimentally studied by using shields placed between the case and outer skin under free convection in air gaps. Using the experimental model setup, experiments aimed at studying the temperature state of all its elements, namely, hot and cold walls, shield, and air gaps under free convection have been conducted. In the course of these experiments, the temperature of hot wall and air gap thicknesses were varied. The plots obtained by thermometering all walls are presented. As a result, generalization of the data obtained makes it possible to augment the data base and use it in choosing an optimal version of heat protection.     

激光冲击中应力状态和显微组织变化对金属疲劳性能影响

从应力状态与显微组织的变化两个方面分析了激光冲击强化改善金属疲劳性能的机理.首先研究了残余应力的作用,认为激光冲击强化产生的残余压应力降低了零部件承受的平均应力水平.然后利用位错理论分析了金属经激光冲击强化引起的显微组织变化,认为激光冲击强化在材料表层产生了大量位错、晶界以及亚晶界等缺陷,这些缺陷阻碍了位错的移动,使金属得到强化.