Differential-game-based guidance law using target orientation observations

Modern 4th generation air-to-air missiles are quite capable of dealing with today's battlefield needs. Advanced aerodynamics, highly efficient warheads and smart target acquisition systems combine to yield higher missile lethality than ever. However, in order to intercept highly maneuverable targets, such as future unmanned combat air vehicles (UCAV), or to achieve higher tracking precision for missiles equipped with smaller warheads, further improvement in the missile guidance system is still needed. A new concept is presented here for deriving improved differential-game-based guidance laws that make use of information about the target orientation, which is acquired via an imaging seeker. The underlying idea is that of using measurements of the target attitude as a leading indicator of target acceleration. Knowledge of target attitude reduces the reachable set of target acceleration, facilitating the computation of an improved estimate of the zero-effort miss (ZEM) distance. In consequence, missile guidance accuracy is significantly improved. The new concept is applied in a horizontal interception scenario, where it is assumed that the target maneuver direction, constituting a partial attitude information, can be extracted via processing target images, acquired by an imaging sensor. The derivation results in a new guidance law that explicitly exploits the direction of the target acceleration. The performance of the new guidance law is studied via a computer simulation, which demonstrates its superiority over existing state-of-the-art differential-game-based guidance laws. It is demonstrated that a significant decrease in the miss distance can be expected via the use of partial target orientation information.     

基于广义多层次模糊模型的无人机路径规划

无人机自主飞行的路径规划涉及许多因素,为了使决策向量的获得过程尽可能多包含各个因素的信息,采用广义多层次Fuzzy综合评判是一种有效的方法.但是由于预先不知道权数分配,也无法知道评判结果,故无法用解决广义多层次Fuzzy综合评判或解决其逆问题的方法得到结果.为此引入遗传算法,利用其进化特性,求得合理的权数分配和广义多层次Fuzzy综合评判结果,可以达到控制飞机飞行过程的目的.这一过程提供了一种解决非正非逆问题的广义多层次Fuzzy综合评判问题的新思路和新方法.     

激光喷丸成形多尺度有限元模拟技术

激光喷丸技术是一种先进的金属塑性成形和表面强化技术,相比于弹丸喷丸,激光喷丸能量密度更大,因而成形能力更强,可以用于成形刚度更大的钣金件,如飞机整体壁板,在航空航天领域有广泛的应用前景。构建一种多尺度激光喷丸成形模拟方法,包括激光喷丸诱导应力场的计算方法和基于直接应力法的工件成形曲率的预测方法。预测结果通过2024–T351铝合金块状试件和典型截面单筋件激光喷丸试验得到了验证,试验结果与模拟结果吻合较好,表明此模拟方法有效可行。     

Comparison of ≳40 keV Electron Events at High and Low Heliolatitudes: Ulysses/HI-SCALE and ACE/EPAM

We have performed a joint survey of anisotropic ≳40 keV electron events from August 1997 to September 2000 using the matched detectors on the Ulysses (ULS)/HI-SCALE and the ACE/EPAM instruments. A computer algorithm selected events with strong, statistically significant pitch-angle anisotropies. Electron pitch-angle distributions at ACE (∼1 AU) are often ‘beams’ that are strongly collimated along the local interplanetary magnetic field (IMF). These flare-associated impulsive injections can display rapid rise times (∼15 min) and slower decays, or more irregular intensity histories. At ULS, the electron intensities are lower and the time histories smoother, but strong anisotropies are still observable, indicating direct, nearly field-aligned propagation outward from the Sun. We focus on four event periods, selected from the survey, during times when the angle between the footpoints of the IMF lines intersecting ACE and ULS is small. These events span three full years and cover a wide range of distances and heliographic latitudes. We found one reasonably good association between impulsive electron events at ACE and ULS, and two events with small field-aligned gradients. This revised version was published online in August 2006 with corrections to the Cover Date.     

Detection of chi-square fluctuating targets in arbitrary clutter

In a recent paper, general expressions were derived for the density and cumulative probability functions of the amplitude of a linear matched-filter output given a nonfluctuating target in a clutter-limited environment. These expressions were based on the clutter amplitude density function. The results are extended to calculate the cumulative probability function of the output of a linear matched filter used to detect a chi-square fluctuating target in a clutter-limited environment. The resulting method is applied to a common radar clutter model, and experimental sonar data.     

直升机尾桨故障及其试飞研究

介绍了直升机尾桨故障类型及其处理方法和试飞方法。探讨了发动机功率、空速、飞行高度等因素对尾故障试飞的影响。在实际试飞的基础上，给出了正确处理尾桨故障的基本方法，为直升机飞行员在飞行时遇到类似故障后的处理及有关研究人员提供了重要的参考。     

高超声速三维碳—碳烧浊流场的数值研究

本文针对高超声速再体的烧蚀现象 ,利用简单隐式TVD差分格式和激波捕捉法 ,数值求解三维化学非平衡Navier Stokes方程 ,其中化学模型是碳 碳 (C C)空气化学模型 ,考虑 12个化学组分和 31个化学反应过程 ,研究了C C烧蚀对再入体头部区域的壁面温度和热流分布的影响。为了计算效率和稳定性提出壁面条件显式处理的方法。对再入高度为 6 5km和速度为 8km/s的再入体头部区域烧蚀流场进行了数值模拟 ,用飞行迎角α =0°的计算结果与国外文献进行了比较 ,符合得较好。同时给出了三维小迎角α =5°的计算结果     

MATLAB电力系统模块中频谱分析的实现

给出了利用电力系统模块(PSB)工具箱对仿真波形进行频谱分析的一种新方法.该方法以MATLAB提供的PSBFFT_SCOPE函数为基础,对其输入变量加以改造,克服了其不能应用于变步长算法模型频谱分析的缺陷,拓宽了在PSB工具箱中进行频谱分析的范围.实际仿真结果表明,该方法分析正确,使用简捷,在实际仿真过程中是切实可行的.     

The Genesis Solar-Wind Collector Materials

Genesis (NASA Discovery Mission #5) is a sample return mission. Collectors comprised of ultra-high purity materials will be exposed to the solar wind and then returned to Earth for laboratory analysis. There is a suite of fifteen types of ultra-pure materials distributed among several locations. Most of the materials are mounted on deployable panels (‘collector arrays’), with some as targets in the focal spot of an electrostatic mirror (the ‘concentrator’). Other materials are strategically placed on the spacecraft as additional targets of opportunity to maximize the area for solar-wind collection. Most of the collection area consists of hexagonal collectors in the arrays; approximately half are silicon, the rest are for solar-wind components not retained and/or not easily measured in silicon. There are a variety of materials both in collector arrays and elsewhere targeted for the analyses of specific solar-wind components. Engineering and science factors drove the selection process. Engineering required testing of physical properties such as the ability to withstand shaking on launch and thermal cycling during deployment. Science constraints included bulk purity, surface and interface cleanliness, retentiveness with respect to individual solar-wind components, and availability. A detailed report of material parameters planned as a resource for choosing materials for study will be published on a Genesis website, and will be updated as additional information is obtained. Some material is already linked to the Genesis plasma data website (genesis.lanl.gov). Genesis should provide a reservoir of materials for allocation to the scientific community throughout the 21st Century. This revised version was published online in August 2006 with corrections to the Cover Date.     

Huygens Probe Aerosol Collector Pyrolyser Experiment

ACP's main objective is the chemical analysis of the aerosols in Titan's atmosphere. For this purpose, it will sample the aerosols during descent and prepare the collected matter (by evaporation, pyrolysis and gas products transfer) for analysis by the Huygens Gas Chromatograph Mass Spectrometer (GCMS). A sampling system is required for sampling the aerosols in the 135'32 km and 22'17 km altitude regions of Titan's atmosphere. A pump unit is used to force the gas flow through a filter. In its sampling position, the filter front face extends a few mm beyond the inlet tube. The oven is a pyrolysis furnace where a heating element can heat the filter and hence the sampled aerosols to 250 °C or 600 °C. The oven contains the filter, which has a thimble-like shape (height 28 mm). For transferring effluent gas and pyrolysis products to GCMS, the carrier gas is a labeled nitrogen ¹⁵N₂, to avoid unwanted secondary reactions with Titan's atmospheric nitrogen. Aeraulic tests under cold temperature conditions were conducted by using a cold gas test system developed by ONERA. The objective of the test was to demonstrate the functional ability of the instrument during the descent of the probe and to understand its thermal behavior, that is to test the performance of all its components, pump unit and mechanisms. In order to validate ACP's scientific performance, pyrolysis tests were conducted at LISA on solid phase material synthesized from experimental simulation. The chromatogram obtained by GCMS analysis shows many organic compounds. Some GC peaks appear clearly from the total mass spectra, with specific ions well identified thanks to the very high sensitivity of the mass spectrometer. The program selected for calibrating the flight model is directly linked to the GCMS calibration plan. In order not to pollute the two flight models with products of solid samples such as tholins, we excluded any direct pyrolysis tests through the ACP oven during the first phase of the calibration. Post probe descent simulation of flight results are planned, using the much representative GCMS and ACP spare models. This revised version was published online in August 2006 with corrections to the Cover Date.