应用六西格玛方法提高TCAS系统可靠性

在大型民用飞机中,TCAS系统是保证飞机安全运行重要的航电系统之一。本文结合航空公司波音737NG机队运行中TCAS系统的故障情况,介绍了运用六西格玛方法的分析过程,有效地改进了TCAS系统的使用可靠性。     

Investigation on surface integrity of electron beam melted Ti-6Al-4 V by precision grinding and electropolishing

Electron beam melting (EBM), as an excellent Additive Manufacturing (AM) technology, enables the printing of Ti-6Al-4 V alloy for a wide range of applications such as aerospace and biomechanical industries. It improves functionality and integrity of components and negates complexities in assembly processes. However, due to the poor surface and sub-surface integrity represented by the rough surface finish and low dimensional accuracy, achieving a favorable surface condition is quite challenging. Therefore, post processing becomes essential for these electron beam melted (EBM-ed) Ti-6Al-4 V alloys. Being the most common technique to improve such parts, milling of Ti-6Al-4 V alloy is very challenging and resulting tool wear issues, due to its unique material properties. Thus, this paper presents a comprehensive study on the surface integrity of EBM-ed Ti-6Al-4 V parts processed by precision grinding and electropolishing, aiming to qualitatively and quantitatively clarify the interrelation between process parameters and processed surface quality. The surface and subsurface characteristics such as profile accuracy, surface roughness, microstructure, defective layer and residual stress before and after post processing were compared and evaluated. The results show that by precision grinding, the profile accuracy was improved from over 300 µm PV to 7 µm PV, while surface roughness (R_a) was reduced from 30 µm to about 2 µm. The layer with partially melt particles was removed, but introduced a deformed subsurface layer with more residual stress. Then by applying electropolishing, the residual stress was released and the deformed layer was removed. In addition, R_a was further reduced to 0.65 µm. The research can serve as a reference for the integration of post machining processes with AM.     

基于eN-数据库方法复杂构型飞机转捩预测

为探索边界层转捩对大型运输机在起降条件和有较大层流区的巡航条件下的气动力精确计算问题，通过在三维RANS求解器中引入eN-数据库方法来预测飞行器表面的转捩位置，并探索转捩对气动力的影响规律。方法与目前流行的基于间歇因子控制方程的转捩预测方法相比，具有计算效率高、易于工程应用、且考虑TS不稳定性转捩因素的特点。在此基础上，通过计算NASA梯形翼来分析起降构型条件下气动力受转捩影响的规律，并通过计算DLR－F6翼身组合体来探索三维构型在巡航条件下的气动力精度。使用eN-数据库转捩判断方法的计算结果与实验值吻合较好，验证了所构建的基于RANS求解器的eN-数据库转捩预测方法的有效性，并为大型运输机气动力精确计算提供了分析工具。     

Tribological evaluation of surface modified H13 tool steel in warm forming of Ti–6Al–4V titanium alloy sheet

The H13 hot-working tool steel is widely used as die material in the warm forming of Ti–6Al–4V titanium alloy sheet. However, under the heating condition, severe friction and lubricating conditions between the H13 tools and Ti–6Al–4V titanium alloy sheet would cause difficulty in guaranteeing forming quality. Surface modification may be used to control the level of friction force, reduce the friction wear and extend the service life of dies. In this paper, four surface modification methods(chromium plating, TiAlN coating, surface polishing and nitriding treatment)were applied to the H13 surfaces. Taking the coefficient of friction(CoF) and the wear degree as evaluation indicators, the high-temperature tribological behavior of the surface modified H13 steel was experimentally investigated under different tribological conditions. The results of this study indicate that the tribological properties of the TiAlN coating under dry friction condition are better than the others for a wide range of temperature(from room temperature to 500 C), while there is little difference of tribological properties between different surface modifications under graphite lubricated condition, and the variation law of CoF with temperature under graphite lubricated is opposite to that under the dry friction.     

基于变步长CFD/RBD方法的旋转弹轨迹仿真

采用变步长方法实现非定常Navier-Stokes方程和刚体六自由度运动方程的耦合求解,并对美国ARL旋转弹试验模型的飞行轨迹进行了仿真。旋转弹自由飞行过程中受到空气阻力作用,转速下降,气动力变化趋缓。因此轨迹仿真时先选取较小的时间步长,随着转速的下降逐渐增大步长,这样可以减少计算时间。刚体六自由度运动方程的数值求解采用变步长Adams预估校正法。将定步长和变步长两种方法应用于旋转弹实验模型轨迹仿真,并将计算得到的旋转弹空间位置、姿态角与试验结果进行了对比,结果显示:方法能较精确地仿真旋转弹飞行轨迹。在相同初始步长条件下,变步长方法较定步长方法计算时间减半;在相同计算时间条件下,变步长方法较定步长方法精度更高。     

应用6Sigma改进方法提高TCAS系统可靠性

在大型民用飞机中TCAS系统是重要的飞行安全运行的航电系统之一,其故障会对飞机正常营运造成很大的影响。应用6Sigma原理进行维修管理可以有效地改进TCAS系统的可靠性。结合航空公司波音737NG机队的运行中TCAS系统故障情况,介绍运用6Sienna方法的分析过程达到的实际改进效果。     

The AWIATOR airborne LIDAR turbulence sensor

The development and first flight tests are described of a short pulse direct measuring UV LIDAR for the measurement of gusts, turbulence and potentially wake vortices. The results of these stage 1 tests confirm that relative wind velocities can be measured with a standard deviation of below 10 m/s even at high altitudes with no appreciable aerosol concentrations. Operating the system under various flight conditions including rain, dense clouds, and clear air up to 24,000 ft was highly successful. Means to push the standard deviation below 1.6 m/s, foremost by increasing the laser output power and the efficiency of the light collecting system, are identified and quantified. Questions of instrument stability are addressed.     

Comparison of ground reflectance measurement with satellite derived atmospherically corrected reflectance: A case study over semi-arid landscape

Atmospheric corrections to satellite data are important for comparing multitemporal data sets over tropical regions with variable aerosol loading. In this study, we evaluated the potential of 6S radiative transfer model for atmospheric corrections of IRS-P6 AWiFS satellite data sets, in a semi-arid landscape. Ground measurements of surface reflectance representing different land use/land cover categories were conducted to relate IRS-P6 AWiFS top of atmospheric reflectance. The 6S radiative transfer model was calibrated for local conditions using ground measurements for aerosol optical depth, water vapor and ozone with a sun photometer. Surface reflectance retrieved from 6S code was compared with top of atmosphere (TOA) reflectance and ground based spectroradiometer measurements. Accurate parameterization of the 6S model using measurements of aerosol optical depth, water vapor and ozone plays an important role while comparing ground and satellite derived reflectance measurements.     

An inversion approach for lunar regolith layer thickness using optical albedo data and microwave emission simulation

An approach to inversion of the lunar regolith layer thickness by using multi-channel brightness temperature observation in passive microwave remote sensing is developed. To first make simulation of brightness temperature from the lunar layered media, the lunar regolith layer thickness (d) is proposed being constructed by available lunar DEM (digital elevation mapping) and on site measurements. The physical temperature distribution (T) over the lunar surface is also empirically assumed as a monotonic function of the latitude. Optical albedo of the lunar nearside from the telescopic observation is employed to construct the spatial distribution of the FeO+TiO₂ content (S) in the lunar regolith layer. A statistic relationship between the DEM and S of the lunar nearside is further extended to construction of S of the lunar farside. Thus, the dielectric permittivity (ε) of global lunar regolith layer can then be determined. Based on all these conditions (d,T,ε), brightness temperature of the lunar regolith layer in passive microwave remote sensing, which is planned for China's Chang-E lunar project, is numerically simulated by a parallel layering model using the strong fluctuation theory of random media.Then, taking these simulations with random noise as observations, an inversion method of the lunar regolith layer thickness is developed by using three- or two-channels brightness temperatures. When the S is low, and the four channels brightness temperatures in China's Chang-E project are well distinguishable, the regolith layer thickness and physical temperature of the underlying lunar rock media can be inverted by the three-channels approach. When the S becomes high that the brightness temperature at high frequency channels such as 19.35, 37 GHz are saturated, the regolith layer thickness is alternatively inverted only by the two-channels approach.Numerical simulation and inversion approach in this paper make an evaluation of the performance for lunar passive microwave remote sensing, and for future data calibration and validation.