Hall effect on magnetic reconnection at the Earth's magnetopause

We analyze in situ observations of magnetic reconnection at the Earth magnetopause to estimate the importance of the Hall current during the merging of interplanetary and magnetospheric magnetic field lines. The reconnection process is studied through numerical simulations, integrating the Hall MHD equations in 2.5 dimensions. A large influence of the Hall effect is found, which can be measured by a significant increase of the reconnection rate.     

潜器速升率的计算

本文提出了安装有槽道螺旋桨的潜器的速升率计算方法。因为航速对槽道桨发出的推力和力矩大小具有很大的影响，所以在速升率计算公式中应当引入对力臂的修正项。数值计算表明，计入该项修正能显著改善装有槽道桨潜器速升率的预报值。     

会善寺大雄宝殿结构动力性能分析

为更好保护会善寺大雄宝殿,对会善寺大雄宝殿进行了现场调研,结合点云技术建立并验证其数值分析模型,研究了大雄宝殿的动力特性及在多遇地震作用下的动力响应。结果表明:结构基本自振周期为1.82s,体现石木结构长周期特性;在纵向多遇地震作用下,前檐木柱变形大于后檐石柱,结构除平动外还存在扭转;在横向多遇地震作用下,明间与次间木屋架有较大横向位移差,连接明间与次间木屋架的檩条和枋等纵向构件可能出现较大滑移并导致屋盖错位;在双向地震作用下,结构纵向和横向最大位移是单向地震作用下的1.1~1.2倍,扭转效应比单向地震作用下大。研究结果可为会善寺大雄宝殿及同类建筑的维修加固提供理论支持。     

磁场梯度对Hall推力器放电特性影响的实验研究

为进一步探索Hall推力器通道内磁场优化设计理论,通过实验分析了强场区磁场梯度对推进剂的电离与加速等放电过程的影响. 研究发现,在本实验设计的磁场梯度范围内,磁场梯度大小对推进剂的电离过程影响较小,但是对离子流的加速特性会产生较为明显的影响.随着磁场梯度的增加,离子束的能量分布会趋于集中,推力器效率提高. 最后,对磁场轴向梯度进一步变大可能会引起的一系列物理问题如有限Larmor半径效应、电子传导机理转变规律和梯度漂移效应等进行了分析和思考.     

推力器失效形式对DP-2级动力定位系统最优作业方向影响

以3 000 m水深DP-2级动力定位半潜平台为算例,研究在风浪流同向作用下,平台在各个角度下所能抵抗的最大外界环境力,得到最优作业方向。在此角度下,着重分析当不同推力器失效时,对动力定位能力的影响。得到一般规律,并推广到一般平台。     

近地磁尾重联中哨声波和Hall磁场的Cluster观测

在2001～2003年Cluster飞船通过近地磁尾期间,共探测到14次重联事件,在这些事件中同时还观测到等离子体波活动.本文把14次事件分为三大类,其中：第I类包含了8次事件,它们是在等离子体片内先于重联事件观测到波活动,并且还同时观测到Hall磁场.经过分析判断,这类事件中观测到的波是右旋偏振的哨声波.第II类包含了2次事件,这类事件也观测到了Hall磁场和右旋偏振的哨声波.第Ⅲ类也包含了2次事件,这类事件只是普通的重联事件,没有观测到Hall磁场,但是波活动明显先于重联事件.在我们观测的14次事件中,比较强烈的哨声波和Hall 磁场是一一对应的,因此哨声波可能主要是在Hall磁场的四极结构区激发的.     

极区Hall电流经度差异特征的统计学研究:CHAMP卫星观测

本文利用2001至2010年间CHAMP(CHallenging Minisatellite Payload)卫星标量磁力仪(Overhauser Magnetometer)观测的磁场数据,反演得到电离层霍尔(Hall)电流,并且对极区电离层Hall电流的特征进行了统计学研究.研究主要关注平静期,即重联电场小于2 mV·m~(-1)条件下,在磁纬60°至90°范围内的Hall电流在不同太阳活动、季节、磁经度、磁地方时等条件下的变化特征.研究发现:Hall电流具有明显的经度差异,在南北半球呈现显著一波经度结构,而且南北半球反相,即北半球电流密度呈现峰-谷-峰结构,而南半球呈现谷-峰-谷结构.Hall电流密度的经度结构与太阳活动紧密相关,太阳活动高年经度差异最大,太阳活动中年经度差异次之,太阳活动低年经度差异最小.研究发现,在磁地方时为10-14MLT的白天,影响Hall电流的因素主要是太阳辐射;而磁地方时为21-03MLT的夜晚,除了电导率的影响之外,可能存在其他的重要的物理过程影响着Hall电流的经度分布.本文还研究了与电流相关的焦耳热的经度分布情况,发现其在南北半球分别呈现单峰、单谷结构,经度差异亦十分明显.     

Full‐scale dynamic response of an RC building under weak seismic motions using earthquake recordings,ambient vibrations and modelling

In countries with a moderate seismic hazard, the classical methods developed for strong motion prone countries to estimate the seismic behaviour and subsequent vulnerability of existing buildings are often inadequate and not financially realistic. The main goals of this paper are to show how the modal analysis can contribute to the understanding of the seismic building response and the good relevancy of a modal model based on ambient vibrations for estimating the structural deformation under weak earthquakes. We describe the application of an enhanced modal analysis technique (frequency domain decomposition) to process ambient vibration recordings taken at the Grenoble City Hall building (France). The frequencies of ambient vibrations are compared with those of weak earthquakes recorded by the French permanent accelerometric network (RAP) that was installed to monitor the building. The frequency variations of the building under weak earthquakes are shown to be less (∼2%) and therefore ambient vibration frequencies are relevant over the elastic domain of the building. The modal parameters extracted from ambient vibrations are then used to determine the 1D lumped‐mass model in order to reproduce the inter‐storey drift under weak earthquakes and to fix a 3D numerical model that could be used for strong earthquakes. The correlation coefficients between data and synthetic motion are close to 80 and 90% in horizontal directions, for the 1D and 3D modelling, respectively. Copyright © 2009 John Wiley & Sons, Ltd.     

锚泊辅助动力定位系统艏向控制模式研究

锚泊辅助动力定位系统是一种将锚泊定位与动力定位结合起来的新型定位方式。对该系统的艏向控制模式进行了研究。在该模式下,控制系统将只对平台的艏向运动施加约束。同时对平台在该模式下的定位进行了时域模拟,并与锚泊定位和水平面三自由度均施加约束的全定位模式进行了对比。结果表明,在一般海况下,相比锚泊定位,该定位模式能显著提高平台的艏摇控制精度;相比全定位模式,该定位模式消耗的功率更小、更经济。艏向控制模式是锚泊辅助动力定位系统的一种工作模式,在相应海况条件下采取该定位模式,能够实现精确和经济的定位。     

On the use of the capability polar plots program for dynamic positioning systems for marine vessels

As the capability of polar plots becomes better understood, improved dynamic positioning (DP) systems are possible since the control algorithms greatly depend on the accuracy of the aerodynamic and hydrodynamic models. The measurements and estimation of the environmental disturbances have an important role in the optimal design and selection of a DP system for a marine vessel. The main objective of this work is to present a new software program capable of estimating the environmental forces, thrusters capability calculations, and capability polar plots for marine vessels. A flowchart illustrating the logic and data flow of a developed software program, the Capability Polar Plot Program (CPPP), and the estimated results for two case studies for a scientific drilling vessel and a survey vessel are presented. It is obvious from the obtained results that the developed program has a future potential for the estimation of the Capability Polar Plots for marine vessels. Moreover, the developed software program would be considered as a marine tool for the thrusters' selection and their configuration for marine vessels and floating production units for the Oil and Gas industries.