在核爆炸冲击波环境中飞行飞机的结构动力响应分析

着重分析在核爆炸冲击波环境中飞机结构动力响应有关问题,推导了动力学基本方程,介绍了飞机在核爆炸冲击波中非定常气动载荷计算方法,给出了结构动力响应分析的思路和计算过程,提出了飞行飞机在核爆炸冲击波作用下总体结构安全边界值的估算方法,并对存在的问题进行了讨论。     

一种TVD方法在三维非结构网格中的应用

以三维非结构网格的显式有限体积法为基础,采用了一种TVD方法求解三维Euler方程,使用Roe通量来计算网格单元边界处的守恒量通量.为了验证方法的可行性,用该方法模拟三维爆炸问题,得出的结论是我们的方法可行,稳定且有效.     

Supernova explosions — The role of a Rayleigh-Taylor instability

A two dimensional hydrodynamic study indicates that convectively unstable gradients which develop during core collapse and bounce give rise to large scale core overturn. It is also shown that the concomitant release of neutrini can deposit large amounts of energy and momentum in the infalling envelope and give rise to a powerful supernova explosion.     

The Origin of Mercury

Mercury’s unusually high mean density has always been attributed to special circumstances that occurred during the formation of the planet or shortly thereafter, and due to the planet’s close proximity to the Sun. The nature of these special circumstances is still being debated and several scenarios, all proposed more than 20 years ago, have been suggested. In all scenarios, the high mean density is the result of severe fractionation occurring between silicates and iron. It is the origin of this fractionation that is at the centre of the debate: is it due to differences in condensation temperature and/or in material characteristics (e.g. density, strength)? Is it because of mantle evaporation due to the close proximity to the Sun? Or is it due to the blasting off of the mantle during a giant impact? In this paper we investigate, in some detail, the fractionation induced by a giant impact on a proto-Mercury having roughly chondritic elemental abundances. We have extended the previous work on this hypothesis in two significant directions. First, we have considerably increased the resolution of the simulation of the collision itself. Second, we have addressed the fate of the ejecta following the impact by computing the expected reaccretion timescale and comparing it to the removal timescale from gravitational interactions with other planets (essentially Venus) and the Poynting–Robertson effect. To compute the latter, we have determined the expected size distribution of the condensates formed during the cooling of the expanding vapor cloud generated by the impact. We find that, even though some ejected material will be reaccreted, the removal of the mantle of proto-Mercury following a giant impact can indeed lead to the required long-term fractionation between silicates and iron and therefore account for the anomalously high mean density of the planet. Detailed coupled dynamical–chemical modeling of this formation mechanism should be carried out in such a way as to allow explicit testing of the giant impact hypothesis by forthcoming space missions (e.g. MESSENGER and BepiColombo).     

水下爆炸的数值模拟研究现状

阐明水下爆炸的深入研究对军事和民用工业都有着重要的意义,水下爆炸数值模拟可分为爆炸现象数值模拟和舰船及水下结构数值模拟两方面,文中分别从这两方面分析和总结了水下爆炸的数值模拟研究现状。     

High X-ray luminosity from dynamo stars

In the present work we intend to show that a stellar dynamo mechanism can produce high X-ray luminosities and also give account for modulation periods of the order thousand seconds or larger.We outline here that the model we propose does not require the presence of a very compact object in a binary system; indeed, we intend to show that faint late main sequence stars sufficiently fast rotating, can give rise by dynamo action to sufficiently high magnetic fields to give account for the strong X-ray emission of some galactic X-ray sources.We examine the possibility that also a fraction of those X-ray sources usually depicted as accreting binary systems may be interpreted as active stars supplied by the - dynamo mechanism.     

飞行器水载荷结构完整性数值模拟现状与展望-Part I:水上迫降和水上漂浮

现代飞行器面临水上迫降、水上漂浮、贮箱晃动和投汲水等复杂水载荷的结构完整性和乘员安全性分析问题日趋重要,随着科学技术的发展,数值模拟已经成为飞行器设计、分析和适航取证的重要手段。以固定翼飞机、水陆两栖飞机、直升机、火箭和卫星等现代航空航天飞行器为对象,围绕适用于飞行器水载荷分析的数值模拟方法进行综述,根据外流（水上迫降和水上漂浮）和内流（贮箱晃动和投汲水）的不同将综述内容分为Part I和Part II两部分。Part I的主要工作为：首先,归纳水上迫降和水上漂浮的事故和试验,总结水气两相流和流固耦合算法的发展现状和优缺点;随后,结合工程实际,介绍飞行器水上迫降和水上漂浮的范畴、水载荷分析要点、适用的数值模拟方法和软件的国内外发展情况,其中,水上迫降的总结包括飞行参数、波浪水面和弹性体对迫降性能的影响研究,水上漂浮的总结涵盖了飞行器构型参数、破舱和波浪对漂浮性能的影响研究;最后,指出复杂风浪情况下水上迫降和漂浮的水气固三相耦合工程应用难点和解决途径,并探讨飞行器水载荷数值分析的技术挑战和未来的发展方向。     

基于LabVIEW的直升机发动机控制—机械扭振系统耦合稳定性分析

直升机发动机控制系统与传动系统所构成的耦合闭环系统在某些情况下可能会失稳,造成严重的后果,所以在设计时需要确保其为耦合稳定。本文首先分析了耦合系统失稳的原因,然后以LabVIEW为开发工具对实际直升机系统进行建模,输入各部分的传递函数,并对耦合系统的稳定性进行了分析,最后对提高系统稳定性提出了一些改进意见。     

基于拟压缩方法的叶片扩压器低速流场数值研究

摘要 发展了基于拟压缩方法的求解叶轮机械低马赫数流场的方法,研制了了时间推进方法对叶轮机械全流速范围流场的求解的计算程序,且对拟压缩因子的取值进行了讨论。通过对离心压缩机叶片扩压器的数值计算表明,本文发展的基于拟压缩方法能能够快速正确的预测叶轮机械内的低速流场;引入拟压缩方法是对时间推进方法的一个很好补充,使时间推进方法的应用范围得到了拓展。     

Autonomous mission reconstruction during the ascending flight of launch vehicles under typical propulsion system failures

In recent years, Chinese Long March(LM) launchers have experienced several launch failures, most of which occurred in their propulsion systems, and this paper studies Autonomous Mission Reconstruction(AMRC) technology to alleviate losses due to these failures. The status of the techniques related to AMRC, including trajectory and mission planning, guidance methods,and fault tolerant technologies, are reviewed, and their features are compared, which reflect the challenges faced by AMRC technology...     

基于摄动理论的爆高确定方法研究

分别讨论了两种通过飞行时间确定爆高的方法:解析计算修正法和时间偏导数法,这两种方法都是通过计算延迟时间来确定爆高,具有自主性强、可靠性高的特点。计算了两种方法在不同干扰条件下的结果,分析了造成计算偏差的原因。计算结果表明,两种方法的计算误差都非常小,均可应用于弹道导弹爆高确定。     

The cepheid luminosity scale

Conclusions The discrepancy between the luminosity scale for Cepheids derived from the intermediate band photometry and the presently accepted scale requires further investigation. We have discussed various factors which might affect the previous work and which might affect the present method but we are unable at this time to provide a definite explanation. However, since there is no obvious problem with the intermediate band photometry we should give serious consideration to the possibility that the Cepheid luminosity scale might require some revision.     

Particle Acceleration Mechanisms

In this paper we review the possible mechanisms for production of non-thermal electrons which are responsible for the observed non-thermal radiation in clusters of galaxies. Our primary focus is on non-thermal Bremsstrahlung and inverse Compton scattering, that produce hard X-ray emission. We first give a brief review of acceleration mechanisms and point out that in most astrophysical situations, and in particular for the intracluster medium, shocks, turbulence and plasma waves play a crucial role. We also outline how the effects of the turbulence can be accounted for. Using a generic model for turbulence and acceleration, we then consider two scenarios for production of non-thermal radiation. The first is motivated by the possibility that hard X-ray emission is due to non-thermal Bremsstrahlung by nonrelativistic particles and attempts to produce non-thermal tails by accelerating the electrons from the background plasma with an initial Maxwellian distribution. For acceleration rates smaller than the Coulomb energy loss rate, the effect of energising the plasma is to primarily heat the plasma with little sign of a distinct non-thermal tail. Such tails are discernible only for acceleration rates comparable or larger than the Coulomb loss rate. However, these tails are accompanied by significant heating and they are present for a short time of <10⁶ years, which is also the time that the tail will be thermalised. A longer period of acceleration at such rates will result in a runaway situation with most particles being accelerated to very high energies. These more exact treatments confirm the difficulty with this model, first pointed out by Petrosian (Astrophys. J. 557:560, 2001). Such non-thermal tails, even if possible, can only explain the hard X-ray but not the radio emission which needs GeV or higher energy electrons. For these and for production of hard X-rays by the inverse Compton model, we need the second scenario where there is injection and subsequent acceleration of relativistic electrons. It is shown that a steady state situation, for example arising from secondary electrons produced from cosmic ray proton scattering by background protons, will most likely lead to flatter than required electron spectra or it requires a short escape time of the electrons from the cluster. An episodic injection of relativistic electrons, presumably from galaxies or AGN, and/or episodic generation of turbulence and shocks by mergers can result in an electron spectrum consistent with observations but for only a short period of less than one billion years.     

A formal approach using SysML for capturing functional requirements in avionics domain

In this work, a Model-Based Systems Engineering approach based on SysML is proposed. This approach is used for the capture and the definition of functional requirements in avionics domain. The motivation of this work is triple: guide the capture of functional requirements, validate these functional requirements through functional simulation, and verify efficiently the consistency of these functional requirements. The proposed approach is decomposed into several steps that are detailed to go from conceptual model of avionics domain to a formal functional model that can be simulated in its operating context. To achieve this work, a subset of SysML has been used as an intermediate modelling language to ensure progressive transformation that can be understood and agreed by system stakeholders. Formal concepts are introduced to ensure theoretical consistency of the approach. In addition, transformation rules are defined and the mappings between concepts of ARP4754A civil aircraft guidelines and SysML are formalized through meta-model. The resulting formalization enables engineers to perform functional simulation of the top-level functional architecture extracted from operational scenarios. Finally, the approach has been tested on an industrial avionics system called the Onboard Maintenance System.     

C_(nβ.dyn)作为大迎角稳定性判据的分析

 本文通过具体算便分析了C_(n β.d y x)迎角稳定性判据的可靠性,对使用这一判据可能造成失误的原因作了归纳,得出了一些便于使用这一判据的结论。     

Wolf–Rayet star nucleosynthesis and the isotopic composition of the Galactic Cosmic Rays

There is now strong observational evidence that the composition of the Galactic Cosmic Rays (GCRs) exhibits some significant deviations with respect to the abundances measured in the local (solar neighbourhood) interstellar medium (ISM). Two main scenarios have been proposed in order to account for these differences (`anomalies). The first one, referred to as the `two-component scenario, invokes two distinct components to be accelerated to GCR energies by supernova blast waves. One of these components is just made of ISM material of `normal solar composition, while the other one emerges from the wind of massive mass-losing stars of the Wolf–Rayet (WR) type. The second model, referred to as the `metallicity-gradient scenario, envisions the acceleration of ISM material whose bulk composition is different from the local one as a result of the fact that it originates from inner regions of the Galaxy, where the metallicity has not the local value. In both scenarios, massive stars, particularly of the WR type, play an important role in shaping the GCR composition. After briefly reviewing some basic observations and predictions concerning WR stars (including s-process yields), this paper revisits the two proposed scenarios in the light of recent non-rotating or rotating WR models.     

某实际发动机篦齿封严装置振动特性和稳定性分析

篦齿式封严装置是一种非常有效的非接触密封装置,在航空燃气涡轮发动机等叶轮机械中得到广泛应用。随着航空发动机性能的提高,篦齿封严装置的振动故障问题愈发突出,颤振、声固耦合及振型协调等振动故障发生的可能性越来越大。本文针对某实际航空发动机的篦齿封严装置,对其进行了振动特性和气弹稳定性分析,有较强的工程实际意义。      

The development of a digital video motion detection test set

This paper describes the current effort to develop a standardized data set, or suite of digital video sequences, that can be used for test and evaluation of digital video motion detectors (VMDs) for exterior applications. We have drawn from an extensive video database of typical application scenarios to assemble a comprehensive data set. These data, some existing for many years on analog videotape, have been converted to a reproducible digital format and edited to generate test sequences several minutes long for many scenarios. Sequences include non-alarm video, intrusions and nuisance alarm sources, taken with a variety of imaging sensors including monochrome CCD cameras and infrared (thermal) imaging cameras, under a variety of daytime and nighttime conditions. The paper presents an analysis of the variables and estimates the complexity of a thorough data set. Some of this video data test has been digitized for CD-ROM storage and playback. We are considering developing a DVD disk for possible use in screening and testing VMDs prior to government testing and deployment. In addition, this digital video data may be used by VMD developers for further refinement or customization of their product to meet specific requirements. These application scenarios may also be used to define the testing parameters for future procurement qualification. A personal computer may be used to play back either the CD-ROM or the DVD video data. A consumer electronics-style DVD player may be used to replay the DVD disk. This paper also discusses various aspects of digital video storage including formats, resolution, CD-ROM and DVD storage capacity, formats, editing and playback     

Multiple model PMHT and its application to the benchmark radar tracking problem

The probabilistic multiple hypothesis tracker (PMHT) uses the expectation-maximization (EM) algorithm to solve the measurement-origin uncertainty problem. Here, we explore some of its variants for maneuvering targets and in particular discuss the multiple model PMHT. We apply this PMHT to the six "typical" tracking scenarios given in the second benchmark problem from W. D. Blair and G. A. Watson (1998). The manner in which the PMHT is used to track the targets and to manage radar allocation is discussed, and the results compared with those of the interacting multiple model probabilistic data association filter (IMM/PDAF) and IMM/MHT (multiple hypothesis tracker). The PMHT works well: its performance lies between those of the IMM/PDAF and IMM/MHT both in terms of tracking performance and computational load.