软体外物撞击叶栅时的切割模型

鸟、冰雹、冰块的撞击统称为软体撞击。随空气一起吸入发动机的软体外物首先要受到风扇或压气机叶栅的切割作用,故与叶片发生撞击的是经切割后的软体外物切片。为此,在着手分析撞击过程之前,首先要确定切片的几何形状及质量,即建立软体外物的切割模型。 本文推导了确定最大鸟切片与最大冰球、冰块切片的几何尺寸及质量的表达式。作为算例,针对某型号发动机的有关参数,计算了当受到不同质量的鸟及不同直径的冰球撞击时,最大切片的尺寸与质量。本文的工作为建立软体外物撞击叶栅时的载荷模型提供了前提条件。     

混杂化是改善CFRP韧性的有效途径

碳纤维复合材料(CFRP)虽然以模量高、强度高而作为受力构件材料越来越多地被应用。但CFRP性脆,韧性差,其应用在很大程度上受到了限制。若将玻璃纤维(G_纤)或Kevlar纤维(K_纤)代替部分碳纤维,即制成C/G,C/K混杂复合材料,在不太损失其它性能的前提下可以大大提高CFRP的冲击韧性[1][2]。实验证明,混杂化是改善CFRP韧性的一个切实可行的途径。     

某民用机场航空噪声影响计算分析

根据《机场周围飞机噪声环境标准（GB9660—88）》，以计权等效连续感觉噪声级￡删为评价量，同时参照ICAO（国际民航组织）和SAE（汽车工程师协会）的计算方法，借助FAA（美国联邦航空局）的INM（综合噪声模型）对某机场的航空噪声影响进行了详细分析，比较详细地考虑了机型组合、飞行架次、起降方向、时间分布和飞行程序等因素对机场噪声的强度、分布区域形状和分布区域面积的影响。提出一套先进的机场航空噪声影响计算与分析方法，可为今后机场作航空噪声环境影响评价提供借鉴。     

发动机叶片鸟撞击瞬态响应的数值模拟

 简介了叶片鸟撞击瞬态响应的计算方法, 并采用接触冲击算法计算模拟了不同质量的鸟撞击单个、多个及整级叶片的瞬态响应过程。结果表明: 接触冲击算法能较为真实反映叶片鸟撞击过程; 不同质量的鸟撞击叶片时, 叶片变形与应力有较大的差异; 大质量的鸟撞击时, 必须考虑撞击区附近的局部塑性变形、叶尖位移以及叶根的局部塑性变形。研究结果对于进行我国叶片抗鸟撞击损伤设计具有重要参考价值。     

起落架落震试验飞机机轮三向冲击位移的动态测量

为了研究飞机起落架受冲击载荷时的功量吸收状况，须在起落架落震试验中，对飞机着陆瞬间起落架机轮在空间三个方向上冲击位移的动态变化量进行测量。为此，本文设计了四自由度空间定位装置，并使其与计算机连接，实现了落震试验过程中，起落架在高速冲击状态下机轮三向位移的有效测量与记录。     

Expectations for Crater Size and Photometric Evolution from the Deep Impact Collision

The NASA Discovery Deep Impact mission involves a unique experiment designed to excavate pristine materials from below the surface of comet. In July 2005, the Deep Impact (DI) spacecraft, will release a 360 kg probe that will collide with comet 9P/Tempel 1. This collision will excavate pristine materials from depth and produce a crater whose size and appearance will provide fundamental insights into the nature and physical properties of the upper 20 to 40 m. Laboratory impact experiments performed at the NASA Ames Vertical Gun Range at NASA Ames Research Center were designed to assess the range of possible outcomes for a wide range of target types and impact angles. Although all experiments were performed under terrestrial gravity, key scaling relations and processes allow first-order extrapolations to Tempel 1. If gravity-scaling relations apply (weakly bonded particulate near-surface), the DI impact could create a crater 70 m to 140 m in diameter, depending on the scaling relation applied. Smaller than expected craters can be attributed either to the effect of strength limiting crater growth or to collapse of an unstable (deep) transient crater as a result of very high porosity and compressibility. Larger then expected craters could indicate unusually low density (< 0.3 g cm⁻³) or backpressures from expanding vapor. Consequently, final crater size or depth may not uniquely establish the physical nature of the upper 20 m of the comet. But the observed ejecta curtain angles and crater morphology will help resolve this ambiguity. Moreover, the intensity and decay of the impact “flash” as observed from Earth, space probes, or the accompanying DI flyby instruments should provide critical data that will further resolve ambiguities.     

Impact Cratering Theory and Modeling for the Deep Impact Mission: From Mission Planning to Data Analysis

The cratering event produced by the Deep Impact mission is a unique experimental opportunity, beyond the capability of Earth-based laboratories with regard to the impacting energy, target material, space environment, and extremely low-gravity field. Consequently, impact cratering theory and modeling play an important role in this mission, from initial inception to final data analysis. Experimentally derived impact cratering scaling laws provide us with our best estimates for the crater diameter, depth, and formation time: critical in the mission planning stage for producing the flight plan and instrument specifications. Cratering theory has strongly influenced the impactor design, producing a probe that should produce the largest possible crater on the surface of Tempel 1 under a wide range of scenarios. Numerical hydrocode modeling allows us to estimate the volume and thermodynamic characteristics of the material vaporized in the early stages of the impact. Hydrocode modeling will also aid us in understanding the observed crater excavation process, especially in the area of impacts into porous materials. Finally, experimentally derived ejecta scaling laws and modeling provide us with a means to predict and analyze the observed behavior of the material launched from the comet during crater excavation, and may provide us with a unique means of estimating the magnitude of the comet’s gravity field and by extension the mass and density of comet Tempel 1.     

球形弹丸高速撞击航天器防护结构的数值模拟分析

给出了空间碎片超高速撞击航天器双层防护结构模型，采用非线性有限元方法中的光滑粒子流体动力算法，计算了球形弹丸对航天器双层防护墙结构超高速撞击过程，获得了弹丸穿过第一层防护墙后，碎裂形成颗粒云团及其对第二层防护墙的损伤效应。计算结果表明多层防护墙结构能够有效地缓减高速空间碎片对航天器的破坏作用。     

Assessing the Impact Risk of Orbital Debris on Space Tethers

Tethers are being proposed for a growing number of space applications. However, they may be particularly vulnerable to orbital debris and meteoroid impacts. In order to provide useful reference data for tether systems design, detailed analytical and numerical computations were carried out to assess the average impact rate of artificial debris and meteoroids. The specific geometric properties of tethers as debris targets, when compared to typical satellites, are discussed, and the results obtained are presented in tabular form, as a function of debris size and tether diameter.The computations were carried out for six circular orbits, spanning three altitudes (600, 800 and 1000km) and two inclinations (30° and 50°). Tether diameters in between 1mm and 2cm and debris larger than 0.1mm were considered in the analysis. The collision risk of tethers with spacecraft and upper stages in orbit was estimated as well.In the debris interval and orbital regimes considered, artificial debris represent the dominant contributor to the impact rate. At 600km and in the 0.1–10mm size range, the meteoroid and orbital debris impact rates are still comparable; however, at higher altitudes and in the 1–10cm size range, meteoroids contribute 20–30 times less to the collision probability.The results obtained confirm that for single-strand tethers in low Earth orbit the probability to be severed by orbital debris and meteoroid impacts is quite significant, making necessary the adoption of innovative designs for long duration missions.     

基于MCMC方法的运输类飞机鸟撞冲击能量研究

鸟撞冲击能量是运输类飞机结构安全设计和鸟撞适航条款制定的重要基础,目前我国运输类飞机鸟撞相关研究都是参照FAA中的鸟撞冲击能量标准要求,并没有考虑我国的自然环境等特点.针对这一问题,运用马尔科夫链蒙特卡洛(Markov Chain Monte Carlo,MCMC)估计方法,采用Gibbs抽样原理,在贝叶斯理论的框架下,对我国运输类飞机鸟撞冲击能量开展了研究,在小样本条件下对鸟撞冲击能量概率分布进行估算,为后续鸟撞安全性分析提供了重要基础.