直升机主桨叶的鸟撞有限元数值模拟

以某型直升机主桨叶为例,使用瞬态动力学分析软件(MSC.Dytran),采用先进的任意拉格朗日-欧拉(ALE)流固耦合算法,进行鸟撞过程的数值模拟.模拟结果表明:撞击过程中的最大应力达到199MPa,没有超出桨叶材料的屈服极限.研究结果为桨叶的抗鸟撞损伤设计提供了参考.      

对巡航导弹撞地有关因素的仿真研究

研究了巡航导弹低空地形跟踪飞行的撞地概率问题，针对地形随机输入和低空风随机干扰共同作用的情况，研究了撞地概率的仿真计算方法，在给定条件下求出了它们与撞地概率的关系曲线，分析了它们对撞地概率的影响，从中可以看出，协调参数，能有效降低撞地概率，提高巡航导弹的作战效能。     

Simulation of depth–dose distributions for various ions in polyethylene medium

Study of depth–dose distributions for intermediate energy ion beams in tissue-like media such as polyethylene (CH₂)_n provides a good platform for further improvements in the fields of hadrontherapy and space radiation shielding. The depth–dose distributions for ¹²C ions at various energies and for light and intermediate ion beams (³He, ¹⁶O, ²⁰Ne and ²⁸Si) as well as for heavy ions ⁵⁶Fe in polyethylene were estimated by using simulation toolkit: Geant4. Calculations were performed mainly by considering two different combinations of standard electromagnetic (EM), binary cascade (BIC), statistical multifragmentation (SMF) and Fermi breakup (FB) models. The energies of the ion beams were selected to achieve the Bragg peaks at predefined position (∼60 mm) and as per their availability. Variations of peak-to-entrance ratio (from 7.44 ± 0.05 to 8.87 ± 0.05), entrance dose (from 2.89 ± 0.01 to 203.71 ± 0.63 MeV/mm) and entrance stopping power (from 3.608 to 208.858 MeV/mm, calculated by SRIM) with atomic number (Z) were presented in a systematic manner. The better peak-to-entrance ratio and less entrance dose in the region Z = 2 to 8 (i.e. ³He to ¹⁶O) may provide the suitability of the ion beams for hadrontherapy.     

How Galactic Cosmic Ray models affect the estimation of radiation exposure in space

The radiation environment in space is a major concern for human spaceflight because of the adverse effects of high levels of radiation on astronauts’ health. Therefore, it is essential to perform radiation risk assessments already during the concept studies of a manned mission. Galactic Cosmic Rays (GCR) have been identified to be one of the primary sources of radiation exposure in space.     

The influence of in situ pitch-angle cosine coverage on the derivation of solar energetic particle injection and interplanetary transport conditions

Modelization of solar energetic particle (SEP) events aims at revealing the general scenario of SEP injection and interplanetary propagation and relies on in situ measurements of SEP distributions. In this paper, we study to what extent the LEFS60 and LEMS30 electron telescopes of the Electron Proton Alpha Monitor (EPAM) on board the Advanced Composition Explorer are able to scan pitch-angle distributions during near-relativistic electron events. We estimate the percentage of the pitch-angle cosine range scanned by both telescopes for a given magnetic field configuration. We obtain that the pitch-angle coverage is always higher for LEFS60 than for LEMS30. Therefore, LEFS60 provides more information of the directional distribution of the observed particles. The aim of the paper is to study the relevance of the coverage when fitting LEFS60 particle measurements in order to infer the solar injection and the interplanetary transport conditions. By studying synthetic electron events, we obtain that at least 70% of the pitch-angle cosine range needs to be scanned by the telescope. Otherwise, multiple scenarios can explain the data.     

Estimation of Galactic Cosmic Ray exposure inside and outside the Earth’s magnetosphere during the recent solar minimum between solar cycles 23 and 24

The evidently low solar activity observed between solar cycles 23 and 24 during the years 2008–2010 led to a substantial increase in the Galactic Cosmic Ray (GCR) intensity in comparison with preceding solar minima. As the GCRs consist of highly-ionizing charged particles having the potential to cause biological damage, they are a subject of concern for manned missions to space. With the enhanced particle fluxes observed between 2008 and 2010, it is reasonable to assume that the radiation exposure from GCR must have also increased to unusually high levels. In this paper, the GCR exposure outside and inside the Earth’s magnetosphere is numerically calculated for time periods starting from 1970 to the end of 2011 in order to investigate the increase in dose levels during the years 2008–2010 in comparison with the last three solar minima. The dose rates were calculated in a water sphere, used as a surrogate for the human body, either unshielded or surrounded by aluminium shielding of 0.3, 10 or 40 g/cm².     

二元矢量喷管流场及性能数值模拟

用有限差分法对二元矢量喷管的内流场及推力性能进行数值模拟。流场计算采用ＭａｃＣｏｒ－ｍａｃｋ两步格式，运用两层代数紊流模型，对初场、网格进行处理，采用加快收敛的当地时间步长，使计算精度和时间都能较好地满足工程应用的要求，得到了与实验数据较一致的喷管内特性。     

分子动力学及热分析方法研究CL-20与推进剂主要组分的相互作用

采用分子动力学模拟(MD)计算与差示扫描量热法(DSC)相结合,研究六硝基六氮杂异伍兹烷(CL-20)与推进剂主要组分间的相互作用,用理论键长变化趋势分析实验结果。分子动力学模拟计算键长变化趋势结果表明,CL-20与黑索今(RDX)、奥克托今(HMX)混合体系的引发键N—NO2键最大键长Lmax随温度升高显著的单调递增,且当CL-20与RDX、HMX共混后,键长普遍增大,更容易断裂分解;而CL-20与硝化棉(NC)、硝化甘油(NG)共混后各个键长均与单质状态下存在时的键长相比变化不大,一些键长均小于其单质状态下存在时的键长,推测CL-20与NG、NC键混合后稳定性较好,不易发生键的断裂分解。DSC结果表明,CL-20与RDX和HMX之间在大于156℃的较高温度条件下存在强烈的相互作用,CL-20与NG、NC之间没有明显的化学作用。     

双并联前向神经网络及其在飞行故障检测仿真研究中的应用

首次把飞行故障检测视为一个非线性数据分类问题,从而可望借助人工神经网络来处理。为了克服ＭＬＦＮＮ在数据分类中存在的学习慢与分类精度低,发展了由ＭＬＦＮＮ和ＳＬＦＮＮ并联并可接收编码输入的ＤＰＦＮＮ模型,还将训练ＭＬＰ的有关算法推广到ＤＰＦＮＮ情形。用计算机仿真了若干飞行故障模式并用于测试ＤＰＦＮＮ。     

乘波飞行器气动力、热特性的数值模拟研究

采用多块分区网格以及并行计算技术对给定乘波构形的高超声速飞行器进行了数值模 拟,分析了飞行器前缘小半径钝化对飞行器气动性能的影响,计算了前缘钝化后飞行器表面 的热流分布状况。结果表明,前缘钝化对飞行器的升力影响不大,对阻力和升阻比的影响较 大。对于曲率半径为1cm的钝化前缘,与原尖前缘飞行器相比,其升力降低了0.78％,阻 力增加6.96％,升阻比下降7.21％。前缘钝化后,乘波飞行器仍具有较好的气动性能, 飞行器前机身可为发动机提供比较均匀的气流,飞行器整体仍基本保持了乘波的状态,热流 主要集中在飞行器前缘上。为了有效防热,需要采用主动式冷却技术。