声发射技术在试件疲劳试验中的预警作用

将声发射动态无损检测技术引入试件疲劳试验中,通过对试验过程中声发射信号的分析,获取试件的初始裂纹数据.证明声发射技术可以发现试验中试件的初始裂纹,并对其破坏具有预警作用.     

Effects of adiabaticity and non-adiabaticity of dust charge fluctuation on the propagation of the dust ion acoustic waves in inhomogeneous dusty plasma

A theoretical investigation has been made for adiabatic positive and negative dust charge fluctuations on the propagation of dust-ion acoustic waves (DIAWs) in a weakly inhomogeneous, collisionless, unmagnetized dusty plasmas consisting of cold positive ions, stationary positively and negatively charged dust particles and isothermal electrons. The reductive perturbation method is employed to reduce the basic set of fluid equations to the variable coefficients Korteweg–de Vries (KdV) equation. Either compressive or rarefactive solitons are shown to exist depending on the critical value of the ion density, which in turn, depends on the inhomogeneous distribution of the ion. The dissipative effects of non-adiabatic dust charge variation has been studied which cause generation of dust ion acoustic shock waves governed by KdV-Burger (KdVB) equation. The results of the present investigation may be applicable to some dusty plasma environments, such as dusty plasma existing in polar mesosphere region.     

Compensation of time-variable magnetic moments for a precise attitude control in nano- and micro-satellite missions

Theses days, many nano- and micro-satellites are applied to several astronomy and remote sensing missions. In order to achieve mission requirements, these satellites must control the attitude precisely. A magnetic disturbance is one of the dominant sources of attitude disturbances. Therefore, this disturbance should be canceled in-orbit or on the ground to achieve the attitude strict requirements. This paper presents the effect of the magnetic disturbance to the attitude in nano- and micro-satellite missions and the sources of the residual magnetic moment of the satellites, which causes the magnetic disturbance. Then, the paper proposes a method to compensate the residual magnetic moment both in-orbit and in the design phase of the satellites. The research also focused on a time-varying residual magnetic moment. Finally, the method is applied to a micro-astrometry satellite as an example.     

Study of the ionosphere during a magnetospheric storm using data on the ground and in space

For the magnetospheric storm of May 14–16, 1997 geophysical data of satellites DMSP and IMP-8 are compared with data of radio propagation on the high-latitude HF radio path of Heiss Island – St. Petersburg and data from European ionosondes. Peculiarities of variations of the operational frequencies range MOF–LOF (maximum and lowest observed frequencies) on the path were considered. The range has been determined by the method of oblique ionospheric sounding (OIS). The latter is more informative for observations during a magnetic storm compared to the vertical sounding method. Nevertheless, an analysis of variations of the critical frequency of the ionospheric F2 layer from the chain of European ionosondes was carried out. For interpretation of results, data of magnetospheric parameters, AE-indexes and riometer data were used. The variations of both frequency range on the path and critical frequencies of the F2 layer through the ionosondes chain during the disturbed period had certain regularities of behaviour. These regularities are being explained from the physical point of view. The analysis of the satellite DMSP data has showed that a magnetospheric disturbance causes displacement equatorward of precipitation and some growth of its width and energy.     

Study of TEC changes during geomagnetic storms occurred near the crest of the equatorial ionospheric ionization anomaly in the Indian sector

GPS satellites data obtained at Bhopal (23.16° N, 77.36° E, geomagnetic latitude 14.23° N) India were analyzed to study the TEC changes during several geomagnetic storms (−300 nT < Dst < −50 nT) occurred in 2005–2007. We had segregated the storms according to the Dst value, i.e. moderate storms (−100 nT < Dst ? −50 nT), strong storms (−150 nT < Dst < −100 nT), and severe storms (Dst less than −150 nT). Total of 21 geomagnetic storms (10 moderate, 9 strong, 2 severe) are considered for the present study. Deviation in vertical total electron content (VTEC) during the main phase of the storm was found to be associated with the prompt penetration of electric field originated due to the under-shielding and over-shielding conditions for almost all geomagnetic storms discussed in this paper. For most of the storms VTEC shows the positive percentage deviation during the main phase while it shows positive as well as the negative deviation during the recovery phase of the storms. The −80% deviation in VTEC was found for geomagnetic storm occurred on July 17, 2005 and the negative trend continued for recovery phase of the storm. This was mainly due to the thermospheric composition changes by Joule heating effect at auroral latitudes that generate electric field disturbance at low latitudes. Traveling ionospheric disturbances (TIDs) were responsible for the formation of wave like nature in VTEC for the storms occurred on May 15, 2005, whereas it was not observed for storm occurred on August 24, 2005.     

一种加速度干扰下的稳定被动定位跟踪算法

在研究一种具有误差自动解耦的观测域滤波的目标跟踪算法和自适应渐消EKF算法的基础上,提出一种匀速运动模型下,基于观测域的自适应目标跟踪算法。使用实测GPS导航数据进行数字仿真,结果表明：观测域的自适应目标跟踪算法在加速度扰动下,稳定性优于观测域滤波算法。     

弹上计算机自主抗干扰技术研究

分析了干扰作用机理 ,干扰对弹上计算机状态的影响 ,研究了计算机自主抗干扰技术 ,包括状态偏差的检测方法和正确状态的记录和恢复方法等 ,并给出了应用实例。     

一种小天体探测器绕飞轨道主动抗扰控制方法

针对小天体绕飞探测过程中,探测器受到的非球形引力摄动及太阳光压等多源扰动问题,结合绕飞探测的周期性特点,提出一种小天体探测器绕飞轨道主动抗扰控制方法。首先,通过迭代学习控制对小天体探测器受多源扰动影响产生的误差进行抑制,然后设计扰动观测器估计系统总扰动,构造自适应律实时估计扰动上界,进而设计控制律对总扰动进行主动补偿。最后以243Ida作为目标天体进行绕飞探测仿真分析,结果表明该控制方法能更加有效地提高小天体探测器的轨道跟踪控制精度。     

Superthermal electron’s effects on lump solitons structures in magnetized auroral plasma

Based on the considerations of the acknowledgements of the numerous space observations by satellites in the auroral plasma, astrophysics plasmas, spacecraft observations, various plasma models have been framed and revealed different interesting features, like electrostatic structures, solitary waves, double layers, supersolitons, etc. Soliton theory is a very efficient and competent way to describe nonlinear features. Using Viking satellite data in the auroral plasma, we have derived lump soliton solutions of the Kadomstev-Petviashvili (KP) equation by employing Hirota bilinear method. Due to its wide range of applications, the study of lump soliton is very attractive and important too. It has been shown that the lump solitons structures as well as in the one-dimensional form of lump soliton are varied with associated parameters in the auroral magnetized plasma. During the analysis of the features of the lump solitons, it is found that the system parameters play a pivotal role on the lump solitons structures.     

喷嘴式隔板与纵向肋式隔板阻尼效应分析

利用声学模型和单喷嘴声学模拟试验研究了喷嘴式隔板的耗散机理;用数值方法分析了纵向肋式隔板周围的涡流;用声学理论研究了纵向肋式隔板的声场。研究结果表明:选取合适的管间隙将会使喷嘴式隔板具有更好的稳定性作用;肋片周围是涡流产生的主要区域;肋高对燃烧室声学特性的影响远大于肋长。